rfc9052.original   rfc9052.txt 
COSE Working Group J. Schaad Internet Engineering Task Force (IETF) J. Schaad
Internet-Draft August Cellars Request for Comments: 9052 August Cellars
Obsoletes: 8152 (if approved) 1 February 2021 STD: 96 July 2021
Intended status: Standards Track Obsoletes: 8152
Expires: 5 August 2021 Category: Standards Track
ISSN: 2070-1721
CBOR Object Signing and Encryption (COSE): Structures and Process CBOR Object Signing and Encryption (COSE): Structures and Process
draft-ietf-cose-rfc8152bis-struct-15
Abstract Abstract
Concise Binary Object Representation (CBOR) is a data format designed Concise Binary Object Representation (CBOR) is a data format designed
for small code size and small message size. There is a need for the for small code size and small message size. There is a need for the
ability to have basic security services defined for this data format. ability to have basic security services defined for this data format.
This document defines the CBOR Object Signing and Encryption (COSE) This document defines the CBOR Object Signing and Encryption (COSE)
protocol. This specification describes how to create and process protocol. This specification describes how to create and process
signatures, message authentication codes, and encryption using CBOR signatures, message authentication codes, and encryption using CBOR
for serialization. This specification additionally describes how to for serialization. This specification additionally describes how to
represent cryptographic keys using CBOR. represent cryptographic keys using CBOR.
This document along with [I-D.ietf-cose-rfc8152bis-algs] obsoletes This document, along with RFC 9053, obsoletes RFC 8152.
RFC8152.
Contributing to this document
This note is to be removed before publishing as an RFC.
The source for this draft is being maintained in GitHub. Suggested
changes should be submitted as pull requests at https://github.com/
cose-wg/cose-rfc8152bis. Instructions are on that page as well.
Editorial changes can be managed in GitHub, but any substantial
issues need to be discussed on the COSE mailing list.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This document is a product of the Internet Engineering Task Force
Task Force (IETF). Note that other groups may also distribute (IETF). It represents the consensus of the IETF community. It has
working documents as Internet-Drafts. The list of current Internet- received public review and has been approved for publication by the
Drafts is at https://datatracker.ietf.org/drafts/current/. Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Internet-Drafts are draft documents valid for a maximum of six months Information about the current status of this document, any errata,
and may be updated, replaced, or obsoleted by other documents at any and how to provide feedback on it may be obtained at
time. It is inappropriate to use Internet-Drafts as reference https://www.rfc-editor.org/info/rfc9052.
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 August 2021.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights publication of this document. Please review these documents
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described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction
1.1. Requirements Terminology . . . . . . . . . . . . . . . . 6 1.1. Requirements Terminology
1.2. Changes from RFC8152 . . . . . . . . . . . . . . . . . . 6 1.2. Changes from RFC 8152
1.3. Design Changes from JOSE . . . . . . . . . . . . . . . . 6 1.3. Design Changes from JOSE
1.4. CBOR Grammar . . . . . . . . . . . . . . . . . . . . . . 7 1.4. CBOR Grammar
1.5. CBOR-Related Terminology . . . . . . . . . . . . . . . . 8 1.5. CBOR-Related Terminology
1.6. Document Terminology . . . . . . . . . . . . . . . . . . 9 1.6. Document Terminology
2. Basic COSE Structure . . . . . . . . . . . . . . . . . . . . 10 2. Basic COSE Structure
3. Header Parameters . . . . . . . . . . . . . . . . . . . . . . 13 3. Header Parameters
3.1. Common COSE Header Parameters . . . . . . . . . . . . . . 15 3.1. Common COSE Header Parameters
4. Signing Objects . . . . . . . . . . . . . . . . . . . . . . . 18 4. Signing Objects
4.1. Signing with One or More Signers . . . . . . . . . . . . 18 4.1. Signing with One or More Signers
4.2. Signing with One Signer . . . . . . . . . . . . . . . . . 20 4.2. Signing with One Signer
4.3. Externally Supplied Data . . . . . . . . . . . . . . . . 21 4.3. Externally Supplied Data
4.4. Signing and Verification Process . . . . . . . . . . . . 22 4.4. Signing and Verification Process
5. Encryption Objects . . . . . . . . . . . . . . . . . . . . . 24 5. Encryption Objects
5.1. Enveloped COSE Structure . . . . . . . . . . . . . . . . 24 5.1. Enveloped COSE Structure
5.1.1. Content Key Distribution Methods . . . . . . . . . . 26 5.1.1. Content Key Distribution Methods
5.2. Single Recipient Encrypted . . . . . . . . . . . . . . . 26 5.2. Single Recipient Encrypted
5.3. How to Encrypt and Decrypt for AEAD Algorithms . . . . . 27 5.3. How to Encrypt and Decrypt for AEAD Algorithms
5.4. How to Encrypt and Decrypt for AE Algorithms . . . . . . 29 5.4. How to Encrypt and Decrypt for AE Algorithms
6. MAC Objects . . . . . . . . . . . . . . . . . . . . . . . . . 30 6. MAC Objects
6.1. MACed Message with Recipients . . . . . . . . . . . . . . 31 6.1. MACed Message with Recipients
6.2. MACed Messages with Implicit Key . . . . . . . . . . . . 32 6.2. MACed Messages with Implicit Key
6.3. How to Compute and Verify a MAC . . . . . . . . . . . . . 33 6.3. How to Compute and Verify a MAC
7. Key Objects . . . . . . . . . . . . . . . . . . . . . . . . . 34 7. Key Objects
7.1. COSE Key Common Parameters . . . . . . . . . . . . . . . 35 7.1. COSE Key Common Parameters
8. Taxonomy of Algorithms used by COSE . . . . . . . . . . . . . 37 8. Taxonomy of Algorithms Used by COSE
8.1. Signature Algorithms . . . . . . . . . . . . . . . . . . 38 8.1. Signature Algorithms
8.2. Message Authentication Code (MAC) Algorithms . . . . . . 40 8.2. Message Authentication Code (MAC) Algorithms
8.3. Content Encryption Algorithms . . . . . . . . . . . . . . 40 8.3. Content Encryption Algorithms
8.4. Key Derivation Functions (KDFs) . . . . . . . . . . . . . 41 8.4. Key Derivation Functions (KDFs)
8.5. Content Key Distribution Methods . . . . . . . . . . . . 41 8.5. Content Key Distribution Methods
8.5.1. Direct Encryption . . . . . . . . . . . . . . . . . . 42 8.5.1. Direct Encryption
8.5.2. Key Wrap . . . . . . . . . . . . . . . . . . . . . . 42 8.5.2. Key Wrap
8.5.3. Key Transport . . . . . . . . . . . . . . . . . . . . 43 8.5.3. Key Transport
8.5.4. Direct Key Agreement . . . . . . . . . . . . . . . . 43 8.5.4. Direct Key Agreement
8.5.5. Key Agreement with Key Wrap . . . . . . . . . . . . . 44 8.5.5. Key Agreement with Key Wrap
9. CBOR Encoding Restrictions . . . . . . . . . . . . . . . . . 45 9. CBOR Encoding Restrictions
10. Application Profiling Considerations . . . . . . . . . . . . 45 10. Application Profiling Considerations
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 46 11. IANA Considerations
11.1. COSE Header Parameters Registry . . . . . . . . . . . . 47 11.1. COSE Header Parameters Registry
11.2. COSE Key Common Parameters Registry . . . . . . . . . . 47 11.2. COSE Key Common Parameters Registry
11.3. Media Type Registrations . . . . . . . . . . . . . . . . 47 11.3. Media Type Registrations
11.3.1. COSE Security Message . . . . . . . . . . . . . . . 47 11.3.1. COSE Security Message
11.3.2. COSE Key Media Type . . . . . . . . . . . . . . . . 48 11.3.2. COSE Key Media Type
11.4. CoAP Content-Formats Registry . . . . . . . . . . . . . 50 11.4. CoAP Content-Formats Registry
11.5. CBOR Tags Registry . . . . . . . . . . . . . . . . . . . 50 11.5. CBOR Tags Registry
11.6. Expert Review Instructions . . . . . . . . . . . . . . . 51 11.6. Expert Review Instructions
12. Security Considerations . . . . . . . . . . . . . . . . . . . 52 12. Security Considerations
13. Implementation Status . . . . . . . . . . . . . . . . . . . . 53 13. References
13.1. Author's Versions . . . . . . . . . . . . . . . . . . . 54 13.1. Normative References
13.2. JavaScript Version . . . . . . . . . . . . . . . . . . . 55 13.2. Informative References
13.3. Python Version . . . . . . . . . . . . . . . . . . . . . 55
13.4. COSE Testing Library . . . . . . . . . . . . . . . . . . 55
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 56
14.1. Normative References . . . . . . . . . . . . . . . . . . 56
14.2. Informative References . . . . . . . . . . . . . . . . . 56
Appendix A. Guidelines for External Data Authentication of Appendix A. Guidelines for External Data Authentication of
Algorithms . . . . . . . . . . . . . . . . . . . . . . . 60 Algorithms
Appendix B. Two Layers of Recipient Information . . . . . . . . 63 Appendix B. Two Layers of Recipient Information
Appendix C. Examples . . . . . . . . . . . . . . . . . . . . . . 65 Appendix C. Examples
C.1. Examples of Signed Messages . . . . . . . . . . . . . . . 66 C.1. Examples of Signed Messages
C.1.1. Single Signature . . . . . . . . . . . . . . . . . . 66 C.1.1. Single Signature
C.1.2. Multiple Signers . . . . . . . . . . . . . . . . . . 67 C.1.2. Multiple Signers
C.1.3. Signature with Criticality . . . . . . . . . . . . . 68 C.1.3. Signature with Criticality
C.2. Single Signer Examples . . . . . . . . . . . . . . . . . 69 C.2. Single Signer Examples
C.2.1. Single ECDSA Signature . . . . . . . . . . . . . . . 69 C.2.1. Single ECDSA Signature
C.3. Examples of Enveloped Messages . . . . . . . . . . . . . 70 C.3. Examples of Enveloped Messages
C.3.1. Direct ECDH . . . . . . . . . . . . . . . . . . . . . 70 C.3.1. Direct ECDH
C.3.2. Direct Plus Key Derivation . . . . . . . . . . . . . 71 C.3.2. Direct Plus Key Derivation
C.3.3. Encrypted Content with External Data . . . . . . . . 72 C.3.3. Encrypted Content with External Data
C.4. Examples of Encrypted Messages . . . . . . . . . . . . . 73 C.4. Examples of Encrypted Messages
C.4.1. Simple Encrypted Message . . . . . . . . . . . . . . 73 C.4.1. Simple Encrypted Message
C.4.2. Encrypted Message with a Partial IV . . . . . . . . . 74 C.4.2. Encrypted Message with a Partial IV
C.5. Examples of MACed Messages . . . . . . . . . . . . . . . 74 C.5. Examples of MACed Messages
C.5.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 74 C.5.1. Shared Secret Direct MAC
C.5.2. ECDH Direct MAC . . . . . . . . . . . . . . . . . . . 75 C.5.2. ECDH Direct MAC
C.5.3. Wrapped MAC . . . . . . . . . . . . . . . . . . . . . 76 C.5.3. Wrapped MAC
C.5.4. Multi-Recipient MACed Message . . . . . . . . . . . . 77 C.5.4. Multi-Recipient MACed Message
C.6. Examples of MAC0 Messages . . . . . . . . . . . . . . . . 78 C.6. Examples of MAC0 Messages
C.6.1. Shared Secret Direct MAC . . . . . . . . . . . . . . 78 C.6.1. Shared-Secret Direct MAC
C.7. COSE Keys . . . . . . . . . . . . . . . . . . . . . . . . 79 C.7. COSE Keys
C.7.1. Public Keys . . . . . . . . . . . . . . . . . . . . . 79 C.7.1. Public Keys
C.7.2. Private Keys . . . . . . . . . . . . . . . . . . . . 80 C.7.2. Private Keys
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 82 Acknowledgments
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 83 Author's Address
1. Introduction 1. Introduction
There has been an increased focus on small, constrained devices that There has been an increased focus on small, constrained devices that
make up the Internet of Things (IoT). One of the standards that has make up the Internet of Things (IoT). One of the standards that has
come out of this process is "Concise Binary Object Representation come out of this process is "Concise Binary Object Representation
(CBOR)" [I-D.ietf-cbor-7049bis]. CBOR extended the data model of the (CBOR)" [RFC8949]. CBOR extended the data model of the JavaScript
JavaScript Object Notation (JSON) [STD90] by allowing for binary Object Notation (JSON) [STD90] by allowing for binary data, among
data, among other changes. CBOR has been adopted by several of the other changes. CBOR has been adopted by several of the IETF working
IETF working groups dealing with the IoT world as their encoding of groups dealing with the IoT world as their encoding of data
data structures. CBOR was designed specifically both to be small in structures. CBOR was designed specifically to be small in terms of
terms of messages transported and implementation size and to be a both messages transported and implementation size and to be a schema-
schema-free decoder. A need exists to provide message security free decoder. A need exists to provide message security services for
services for IoT, and using CBOR as the message-encoding format makes IoT, and using CBOR as the message-encoding format makes sense.
sense.
The JOSE working group produced a set of documents [RFC7515] The JOSE Working Group produced a set of documents [RFC7515]
[RFC7516] [RFC7517] [RFC7518] that specified how to process [RFC7516] [RFC7517] [RFC7518] that specified how to process
encryption, signatures, and Message Authentication Code (MAC) encryption, signatures, and Message Authentication Code (MAC)
operations and how to encode keys using JSON. This document defines operations and how to encode keys using JSON. This document defines
the CBOR Object Signing and Encryption (COSE) standard, which does the CBOR Object Signing and Encryption (COSE) standard, which does
the same thing for the CBOR encoding format. This document is the same thing for the CBOR encoding format. This document is
combined with [I-D.ietf-cose-rfc8152bis-algs] which provides an combined with [RFC9053], which provides an initial set of algorithms.
initial set of algorithms. While there is a strong attempt to keep While there is a strong attempt to keep the flavor of the original
the flavor of the original JSON Object Signing and Encryption (JOSE) JSON Object Signing and Encryption (JOSE) documents, two
documents, two considerations are taken into account: considerations are taken into account:
* CBOR has capabilities that are not present in JSON and are * CBOR has capabilities that are not present in JSON and are
appropriate to use. One example of this is the fact that CBOR has appropriate to use. One example of this is the fact that CBOR has
a method of encoding binary directly without first converting it a method of encoding binary directly without first converting it
into a base64-encoded text string. into a base64-encoded text string.
* COSE is not a direct copy of the JOSE specification. In the * COSE is not a direct copy of the JOSE specification. In the
process of creating COSE, decisions that were made for JOSE were process of creating COSE, decisions that were made for JOSE were
re-examined. In many cases, different results were decided on as re-examined. In many cases, different results were decided on, as
the criteria were not always the same. the criteria were not always the same.
This document contains: This document contains:
* The description of the structure for the CBOR objects which are * The description of the structure for the CBOR objects that are
transmitted over the wire. Two objects are defined for each of transmitted over the wire. Two objects each are defined for
encryption, signing and message authentication. One object is encryption, signing, and message authentication. One object is
defined for transporting keys and one for transporting groups of defined for transporting keys and one for transporting groups of
keys. keys.
* The procedures used to build the inputs to the cryptographic * The procedures used to build the inputs to the cryptographic
functions required for each of the structures. functions required for each of the structures.
* A set of attributes that apply to the different security objects. * A set of attributes that apply to the different security objects.
This document does not contain the rules and procedures for using This document does not contain the rules and procedures for using
specific cryptographic algorithms. Details on specific algorithms specific cryptographic algorithms. Details on specific algorithms
can be found in [I-D.ietf-cose-rfc8152bis-algs] and [RFC8230]. can be found in [RFC9053] and [RFC8230]. Details for additional
Details for additional algorithms are expected to be defined in algorithms are expected to be defined in future documents.
future documents.
COSE was initially designed as part of a solution to provide security COSE was initially designed as part of a solution to provide security
to Constrained RESTful Environments (CoRE), and this is done using to Constrained RESTful Environments (CoRE), and this is done using
[RFC8613] and [I-D.ietf-core-groupcomm-bis]. However, COSE is not [RFC8613] and [CORE-GROUPCOMM]. However, COSE is not restricted to
restricted to just these cases and can be used in any place where one just these cases and can be used in any place where one would
would consider either JOSE or CMS [RFC5652] for the purpose of consider either JOSE or Cryptographic Message Syntax (CMS) [RFC5652]
providing security services. COSE, like JOSE and CMS, is only for for the purpose of providing security services. COSE, like JOSE and
use in store and forward or offline protocols. The use of COSE in CMS, is only for use in store-and-forward or offline protocols. The
online protocols needing encryption, require that an online key use of COSE in online protocols needing encryption requires that an
establishment process be done before sending objects back and forth. online key establishment process be done before sending objects back
Any application which uses COSE for security services first needs to and forth. Any application that uses COSE for security services
determine what security services are required and then select the first needs to determine what security services are required and then
appropriate COSE structures and cryptographic algorithms based on select the appropriate COSE structures and cryptographic algorithms
those needs. Section 10 provides additional information on what based on those needs. Section 10 provides additional information on
applications need to specify when using COSE. what applications need to specify when using COSE.
One feature that is present in CMS that is not present in this One feature that is present in CMS that is not present in this
standard is a digest structure. This omission is deliberate. It is standard is a digest structure. This omission is deliberate. It is
better for the structure to be defined in each protocol as different better for the structure to be defined in each protocol as different
protocols will want to include a different set of fields as part of protocols will want to include a different set of fields as part of
the structure. While an algorithm identifier and the digest value the structure. While an algorithm identifier and the digest value
are going to be common to all applications, the two values may not are going to be common to all applications, the two values may not
always be adjacent as the algorithm could be defined once with always be adjacent, as the algorithm could be defined once with
multiple values. Applications may additionally want to define multiple values. Applications may additionally want to define
additional data fields as part of the structure. One such additional data fields as part of the structure. One such
application-specific element would be to include a URI or other application-specific element would be to include a URI or other
pointer to where the data that is being hashed can be obtained. pointer to where the data that is being hashed can be obtained.
[I-D.ietf-cose-hash-algs] contains one such possible structure along [RFC9054] contains one such possible structure and defines a set of
with defining a set of digest algorithms. digest algorithms.
During the process of advancing COSE to Internet Standard, it was During the process of advancing COSE to Internet Standard, it was
noticed the description of the security properties of noticed that the description of the security properties of
countersignatures was incorrect for the COSE_Sign1 structure. Since countersignatures was incorrect for the COSE_Sign1 structure. Since
the security properties that were described, those of a true the security properties that were described -- those of a true
countersignature, were those that the working group desired, the countersignature -- were those that the working group desired, the
decision was made to remove all of the countersignature text from decision was made to remove all of the countersignature text from
this document and create a new document [I-D.ietf-cose-countersign] this document and create a new document [COSE-COUNTERSIGN] to both
to both deprecate the old countersignature algorithm and header deprecate the old countersignature algorithm and header parameters
parameters and to define a new algorithm and header parameters with and define a new algorithm and header parameters with the desired
the desired security properties. security properties.
1.1. Requirements Terminology 1.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
1.2. Changes from RFC8152 1.2. Changes from RFC 8152
* Split the original document into this document and * Split the original document into this document and [RFC9053].
[I-D.ietf-cose-rfc8152bis-algs].
* Add some text describing why there is no digest structure defined * Added some text describing why there is no digest structure
by COSE. defined by COSE.
* Text clarifications and changes in terminology. * Made text clarifications and changes in terminology.
* All of the details relating to countersignatures have been removed * Removed all of the details relating to countersignatures and
and placed in [I-D.ietf-cose-countersign]. placed in [COSE-COUNTERSIGN].
1.3. Design Changes from JOSE 1.3. Design Changes from JOSE
* Define a single overall message structure so that encrypted, * A single overall message structure has been defined so that
signed, and MACed messages can easily be identified and still have encrypted, signed, and MACed messages can easily be identified and
a consistent view. still have a consistent view.
* Signed messages distinguish between the protected and unprotected * Signed messages distinguish between the protected and unprotected
header parameters that relate to the content and those that relate header parameters that relate to the content and those that relate
to the signature. to the signature.
* MACed messages are separated from signed messages. * MACed messages are separated from signed messages.
* MACed messages have the ability to use the same set of recipient * MACed messages have the ability to use the same set of recipient
algorithms as enveloped messages for obtaining the MAC algorithms as enveloped messages for obtaining the MAC
authentication key. authentication key.
* Use binary encodings, rather than base64url encodings, to encode * Binary encodings are used, rather than base64url encodings, to
binary data. encode binary data.
* Combine the authentication tag for encryption algorithms with the * The authentication tag for encryption algorithms has been combined
ciphertext. with the ciphertext.
* The set of cryptographic algorithms has been expanded in some * The set of cryptographic algorithms has been expanded in some
directions and trimmed in others. directions and trimmed in others.
1.4. CBOR Grammar 1.4. CBOR Grammar
There was not a standard CBOR grammar available when COSE was There was not a standard CBOR grammar available when COSE was
originally written. For that reason the CBOR data objects defined originally written. For that reason, the CBOR data objects defined
here are described in prose. Since that time CBOR Data Definition here are described in prose. Since that time, Concise Data
Language (CDDL) [RFC8610] has been published as an RFC. The CBOR Definition Language (CDDL) [RFC8610] has been published as an RFC.
grammar presented in this document is compatible with CDDL. The CBOR grammar presented in this document is compatible with CDDL.
The document was developed by first working on the grammar and then This document was developed by first working on the grammar and then
developing the prose to go with it. An artifact of this is that the developing the prose to go with it. An artifact of this is that the
prose was written using the primitive type strings defined by CBOR prose was written using the primitive-type strings defined by Concise
Data Definition Language (CDDL) [RFC8610]. In this specification, Data Definition Language (CDDL) [RFC8610]. In this specification,
the following primitive types are used: the following primitive types are used:
any -- non-specific value that permits all CBOR values to be any: A nonspecific value that permits all CBOR values to be placed
placed here. here.
bool -- a boolean value (true: major type 7, value 21; false: bool: A boolean value (true: major type 7, value 21; false: major
major type 7, value 20). type 7, value 20).
bstr -- byte string (major type 2). bstr: Byte string (major type 2).
int -- an unsigned integer or a negative integer. int: An unsigned integer or a negative integer.
nil -- a null value (major type 7, value 22). nil: A null value (major type 7, value 22).
nint -- a negative integer (major type 1). nint: A negative integer (major type 1).
tstr -- a UTF-8 text string (major type 3). tstr: A UTF-8 text string (major type 3).
uint -- an unsigned integer (major type 0). uint: An unsigned integer (major type 0).
Two syntaxes from CDDL appear in this document as shorthand. These Two syntaxes from CDDL appear in this document as shorthand. These
are: are:
FOO / BAR -- indicates that either FOO or BAR can appear here. FOO / BAR: Indicates that either FOO or BAR can appear here.
[+ FOO] -- indicates that the type FOO appears one or more times [+ FOO]: Indicates that the type FOO appears one or more times in an
in an array. array.
* FOO -- indicates that the type FOO appears zero or more times. * FOO: Indicates that the type FOO appears zero or more times.
Two of the constraints defined by CDDL are also used in this Two of the constraints defined by CDDL are also used in this
document. These are: document. These are:
type1 .cbor type2 -- indicates that the contents of type1, usually type1 .cbor type2: Indicates that the contents of type1, usually
bstr, contains a value of type2. bstr, contains a value of type2.
type1 .size integer -- indicates that the contents of type1 is type1 .size integer: Indicates that the contents of type1 is integer
integer bytes long bytes long.
As well as the prose description, a version of a CBOR grammar is As well as the prose description, a version of a CBOR grammar is
presented in CDDL. The CDDL grammar is informational; the prose presented in CDDL. The CDDL grammar is informational; the prose
description is normative. description is normative.
The collected CDDL can be extracted from the XML version of this The collected CDDL can be extracted from the XML version of this
document via the following XPath expression below. (Depending on the document via the XPath expression below. (Depending on the XPath
XPath evaluator one is using, it may be necessary to deal with > evaluator one is using, it may be necessary to deal with > as an
as an entity.) entity.)
//sourcecode[@type='CDDL']/text() //sourcecode[@type='CDDL']/text()
CDDL expects the initial non-terminal symbol to be the first symbol CDDL expects the initial nonterminal symbol to be the first symbol in
in the file. For this reason, the first fragment of CDDL is the file. For this reason, the first fragment of CDDL is presented
presented here. here.
start = COSE_Messages / COSE_Key / COSE_KeySet / Internal_Types start = COSE_Messages / COSE_Key / COSE_KeySet / Internal_Types
; This is defined to make the tool quieter: ; This is defined to make the tool quieter:
Internal_Types = Sig_structure / Enc_structure / MAC_structure Internal_Types = Sig_structure / Enc_structure / MAC_structure
The non-terminal Internal_Types is defined for dealing with the The nonterminal Internal_Types is defined for dealing with the
automated validation tools used during the writing of this document. automated validation tools used during the writing of this document.
It references those non-terminals that are used for security It references those nonterminals that are used for security
computations but are not emitted for transport. computations but are not emitted for transport.
1.5. CBOR-Related Terminology 1.5. CBOR-Related Terminology
In JSON, maps are called objects and only have one kind of map key: a In JSON, maps are called objects and only have one kind of map key: a
text string. In COSE, we use text strings, negative integers, and text string. In COSE, we use text strings, negative integers, and
unsigned integers as map keys. The integers are used for compactness unsigned integers as map keys. The integers are used for compactness
of encoding and easy comparison. The inclusion of text strings of encoding and easy comparison. The inclusion of text strings
allows for an additional range of short encoded values to be used as allows for an additional range of short encoded values to be used as
well. Since the word "key" is mainly used in its other meaning, as a well. Since the word "key" is mainly used in its other meaning, as a
cryptographic key, we use the term "label" for this usage as a map cryptographic key, we use the term "label" for this usage as a map
key. key.
The presence a label that is neither a text string or an integer, in In a CBOR map, the presence a label that is neither a text string nor
a CBOR map, is an error. Applications can either fail processing or an integer is an error. Applications can either fail processing or
process messages by ignoring incorrect labels; however, they MUST NOT process messages by ignoring incorrect labels; however, they MUST NOT
create messages with incorrect labels. create messages with incorrect labels.
A CDDL grammar fragment defines the non-terminal 'label', as in the A CDDL grammar fragment defines the nonterminal "label", as in the
previous paragraph, and 'values', which permits any value to be used. previous paragraph, and "values", which permits any value to be used.
label = int / tstr label = int / tstr
values = any values = any
1.6. Document Terminology 1.6. Document Terminology
In this document, we use the following terminology: In this document, we use the following terminology:
Byte is a synonym for octet. Byte is a synonym for octet.
Constrained Application Protocol (CoAP) is a specialized web transfer Constrained Application Protocol (CoAP) is a specialized web transfer
protocol for use in constrained systems. It is defined in [RFC7252]. protocol for use in constrained systems. It is defined in [RFC7252].
Authenticated Encryption (AE) [RFC5116] algorithms are encryption Authenticated Encryption (AE) [RFC5116] algorithms are encryption
algorithms that provide an authentication check of the contents with algorithms that provide an authentication check of the contents with
the encryption service. An example of an AE algorithm used in COSE the encryption service. An example of an AE algorithm used in COSE
is AES Key Wrap [RFC3394]. These algorithms are used for key is Advanced Encryption Standard (AES) Key Wrap [RFC3394]. These
encryption algorithms, but AEAD algorithms would be preferred. algorithms are used for key encryption algorithms, but Authenticated
Encryption with Associated Data (AEAD) algorithms would be preferred.
Authenticated Encryption with Associated Data (AEAD) [RFC5116] AEAD [RFC5116] algorithms provide the same authentication service of
algorithms provide the same authentication service of the content as the content as AE algorithms do. They also allow associated data
AE algorithms do. They also allow for associated data to be included that is not part of the encrypted body to be included in the
in the authentication service, but which is not part of the encrypted authentication service. An example of an AEAD algorithm used in COSE
body. An example of an AEAD algorithm used in COSE is AES-GCM is AES in Galois/Counter Mode (GCM) [RFC5116]. These algorithms are
[RFC5116]. These algorithms are used for content encryption and can used for content encryption and can be used for key encryption as
be used for key encryption as well. well.
Context is used throughout the document to represent information that "Context" is used throughout the document to represent information
is not part of the COSE message. Information which is part of the that is not part of the COSE message. Information that is part of
context can come from several different sources including: Protocol the context can come from several different sources, including
interactions, associated key structures, and program configuration. protocol interactions, associated key structures, and program
The context to use can be implicit, identified using the 'kid configuration. The context to use can be implicit, identified using
context' header parameter defined in [RFC8613], or identified by a the "kid context" header parameter defined in [RFC8613], or
protocol-specific identifier. Context should generally be included identified by a protocol-specific identifier. Context should
in the cryptographic construction; for more details see Section 4.3. generally be included in the cryptographic construction; for more
details, see Section 4.3.
The term 'byte string' is used for sequences of bytes, while the term The term "byte string" is used for sequences of bytes, while the term
'text string' is used for sequences of characters. "text string" is used for sequences of characters.
2. Basic COSE Structure 2. Basic COSE Structure
The COSE object structure is designed so that there can be a large The COSE object structure is designed so that there can be a large
amount of common code when parsing and processing the different types amount of common code when parsing and processing the different types
of security messages. All of the message structures are built on the of security messages. All of the message structures are built on the
CBOR array type. The first three elements of the array always CBOR array type. The first three elements of the array always
contain the same information: contain the same information:
1. The protected header parameters, encoded and wrapped in a bstr. 1. The protected header parameters, encoded and wrapped in a bstr.
2. The unprotected header parameters as a map. 2. The unprotected header parameters as a map.
3. The content of the message. The content is either the plaintext 3. The content of the message. The content is either the plaintext
or the ciphertext as appropriate. The content may be detached or the ciphertext, as appropriate. The content may be detached
(i.e. transported separately from the COSE structure), but the (i.e., transported separately from the COSE structure), but the
location is still used. The content is wrapped in a bstr when location is still used. The content is wrapped in a bstr when
present and is a nil value when detached. present and is a nil value when detached.
Elements after this point are dependent on the specific message type. Elements after this point are dependent on the specific message type.
COSE messages are built using the concept of layers to separate COSE messages are built using the concept of layers to separate
different types of cryptographic concepts. As an example of how this different types of cryptographic concepts. As an example of how this
works, consider the COSE_Encrypt message (Section 5.1). This message works, consider the COSE_Encrypt message (Section 5.1). This message
type is broken into two layers: the content layer and the recipient type is broken into two layers: the content layer and the recipient
layer. The content layer contains the encrypted plaintext and layer. The content layer contains the encrypted plaintext and
information about the encrypted message. The recipient layer information about the encrypted message. The recipient layer
contains the encrypted content encryption key (CEK) and information contains the encrypted content encryption key (CEK) and information
about how it is encrypted for each recipient. A single layer version about how it is encrypted for each recipient. A single-layer version
of the encryption message COSE_Encrypt0 (Section 5.2) is provided for of the encryption message COSE_Encrypt0 (Section 5.2) is provided for
cases where the CEK is pre-shared. cases where the CEK is preshared.
Identification of which type of message has been presented is done by Identification of which type of message has been presented is done by
the following methods: the following methods:
1. The specific message type is known from the context. This may be 1. The specific message type is known from the context. This may be
defined by a marker in the containing structure or by defined by a marker in the containing structure or by
restrictions specified by the application protocol. restrictions specified by the application protocol.
2. The message type is identified by a CBOR tag. Messages with a 2. The message type is identified by a CBOR tag. Messages with a
CBOR tag are known in this specification as tagged messages, CBOR tag are known in this specification as tagged messages,
while those without the CBOR tag are known as untagged messages. while those without the CBOR tag are known as untagged messages.
This document defines a CBOR tag for each of the message This document defines a CBOR tag for each of the message
structures. These tags can be found in Table 1. structures. These tags can be found in Table 1.
3. When a COSE object is carried in a media type of 'application/ 3. When a COSE object is carried in a media type of "application/
cose', the optional parameter 'cose-type' can be used to identify cose", the optional parameter "cose-type" can be used to identify
the embedded object. The parameter is OPTIONAL if the tagged the embedded object. The parameter is OPTIONAL if the tagged
version of the structure is used. The parameter is REQUIRED if version of the structure is used. The parameter is REQUIRED if
the untagged version of the structure is used. The value to use the untagged version of the structure is used. The value to use
with the parameter for each of the structures can be found in with the parameter for each of the structures can be found in
Table 1. Table 1.
4. When a COSE object is carried as a CoAP payload, the CoAP 4. When a COSE object is carried as a CoAP payload, the CoAP
Content-Format Option can be used to identify the message Content-Format Option can be used to identify the message
content. The CoAP Content-Format values can be found in Table 2. content. The CoAP Content-Format values can be found in Table 2.
The CBOR tag for the message structure is not required as each The CBOR tag for the message structure is not required, as each
security message is uniquely identified. security message is uniquely identified.
+==========+===============+===============+=======================+ +==========+===============+===============+=======================+
| CBOR Tag | cose-type | Data Item | Semantics | | CBOR Tag | cose-type | Data Item | Semantics |
+==========+===============+===============+=======================+ +==========+===============+===============+=======================+
| 98 | cose-sign | COSE_Sign | COSE Signed Data | | 98 | cose-sign | COSE_Sign | COSE Signed Data |
| | | | Object | | | | | Object |
+----------+---------------+---------------+-----------------------+ +----------+---------------+---------------+-----------------------+
| 18 | cose-sign1 | COSE_Sign1 | COSE Single Signer | | 18 | cose-sign1 | COSE_Sign1 | COSE Single Signer |
| | | | Data Object | | | | | Data Object |
skipping to change at page 12, line 5 skipping to change at line 493
+----------+---------------+---------------+-----------------------+ +----------+---------------+---------------+-----------------------+
| 97 | cose-mac | COSE_Mac | COSE MACed Data | | 97 | cose-mac | COSE_Mac | COSE MACed Data |
| | | | Object | | | | | Object |
+----------+---------------+---------------+-----------------------+ +----------+---------------+---------------+-----------------------+
| 17 | cose-mac0 | COSE_Mac0 | COSE Mac w/o | | 17 | cose-mac0 | COSE_Mac0 | COSE Mac w/o |
| | | | Recipients Object | | | | | Recipients Object |
+----------+---------------+---------------+-----------------------+ +----------+---------------+---------------+-----------------------+
Table 1: COSE Message Identification Table 1: COSE Message Identification
+===========================+==========+=====+============+ +===========================+==========+=====+===========+
| Media Type | Encoding | ID | Reference | | Media Type | Encoding | ID | Reference |
+===========================+==========+=====+============+ +===========================+==========+=====+===========+
| application/cose; cose- | | 98 | [[THIS | | application/cose; cose- | | 98 | RFC 9052 |
| type="cose-sign" | | | DOCUMENT]] | | type="cose-sign" | | | |
+---------------------------+----------+-----+------------+ +---------------------------+----------+-----+-----------+
| application/cose; cose- | | 18 | [[THIS | | application/cose; cose- | | 18 | RFC 9052 |
| type="cose-sign1" | | | DOCUMENT]] | | type="cose-sign1" | | | |
+---------------------------+----------+-----+------------+ +---------------------------+----------+-----+-----------+
| application/cose; cose- | | 96 | [[THIS | | application/cose; cose- | | 96 | RFC 9052 |
| type="cose-encrypt" | | | DOCUMENT]] | | type="cose-encrypt" | | | |
+---------------------------+----------+-----+------------+ +---------------------------+----------+-----+-----------+
| application/cose; cose- | | 16 | [[THIS | | application/cose; cose- | | 16 | RFC 9052 |
| type="cose-encrypt0" | | | DOCUMENT]] | | type="cose-encrypt0" | | | |
+---------------------------+----------+-----+------------+ +---------------------------+----------+-----+-----------+
| application/cose; cose- | | 97 | [[THIS | | application/cose; cose- | | 97 | RFC 9052 |
| type="cose-mac" | | | DOCUMENT]] | | type="cose-mac" | | | |
+---------------------------+----------+-----+------------+ +---------------------------+----------+-----+-----------+
| application/cose; cose- | | 17 | [[THIS | | application/cose; cose- | | 17 | RFC 9052 |
| type="cose-mac0" | | | DOCUMENT]] | | type="cose-mac0" | | | |
+---------------------------+----------+-----+------------+ +---------------------------+----------+-----+-----------+
| application/cose-key | | 101 | [[THIS | | application/cose-key | | 101 | RFC 9052 |
| | | | DOCUMENT]] | +---------------------------+----------+-----+-----------+
+---------------------------+----------+-----+------------+ | application/cose-key-set | | 102 | RFC 9052 |
| application/cose-key-set | | 102 | [[THIS | +---------------------------+----------+-----+-----------+
| | | | DOCUMENT]] |
+---------------------------+----------+-----+------------+
Table 2: CoAP Content-Formats for COSE Table 2: CoAP Content-Formats for COSE
The following CDDL fragment identifies all of the top messages The following CDDL fragment identifies all of the top messages
defined in this document. Separate non-terminals are defined for the defined in this document. Separate nonterminals are defined for the
tagged and the untagged versions of the messages. tagged and untagged versions of the messages.
COSE_Messages = COSE_Untagged_Message / COSE_Tagged_Message COSE_Messages = COSE_Untagged_Message / COSE_Tagged_Message
COSE_Untagged_Message = COSE_Sign / COSE_Sign1 / COSE_Untagged_Message = COSE_Sign / COSE_Sign1 /
COSE_Encrypt / COSE_Encrypt0 / COSE_Encrypt / COSE_Encrypt0 /
COSE_Mac / COSE_Mac0 COSE_Mac / COSE_Mac0
COSE_Tagged_Message = COSE_Sign_Tagged / COSE_Sign1_Tagged / COSE_Tagged_Message = COSE_Sign_Tagged / COSE_Sign1_Tagged /
COSE_Encrypt_Tagged / COSE_Encrypt0_Tagged / COSE_Encrypt_Tagged / COSE_Encrypt0_Tagged /
COSE_Mac_Tagged / COSE_Mac0_Tagged COSE_Mac_Tagged / COSE_Mac0_Tagged
skipping to change at page 13, line 18 skipping to change at line 548
information that are not considered to be part of the payload itself, information that are not considered to be part of the payload itself,
but are used for holding information about content, algorithms, keys, but are used for holding information about content, algorithms, keys,
or evaluation hints for the processing of the layer. These two or evaluation hints for the processing of the layer. These two
buckets are available for use in all of the structures except for buckets are available for use in all of the structures except for
keys. While these buckets are present, they may not always be usable keys. While these buckets are present, they may not always be usable
in all instances. For example, while the protected bucket is defined in all instances. For example, while the protected bucket is defined
as part of the recipient structure, some of the algorithms used for as part of the recipient structure, some of the algorithms used for
recipient structures do not provide for authenticated data. If this recipient structures do not provide for authenticated data. If this
is the case, the protected bucket is left empty. is the case, the protected bucket is left empty.
Both buckets are implemented as CBOR maps. The map key is a 'label' Both buckets are implemented as CBOR maps. The map key is a "label"
(Section 1.5). The value portion is dependent on the definition for (Section 1.5). The value portion is dependent on the definition for
the label. Both maps use the same set of label/value pairs. The the label. Both maps use the same set of label/value pairs. The
integer and text string values for labels have been divided into integer and text-string values for labels have been divided into
several sections including a standard range, a private range, and a several sections, including a standard range, a private range, and a
range that is dependent on the algorithm selected. The defined range that is dependent on the algorithm selected. The defined
labels can be found in the "COSE Header Parameters" IANA registry labels can be found in the "COSE Header Parameters" IANA registry
(Section 11.1). (Section 11.1).
The two buckets are: The two buckets are:
protected: Contains parameters about the current layer that are protected: Contains parameters about the current layer that are
cryptographically protected. This bucket MUST be empty if it is cryptographically protected. This bucket MUST be empty if it is
not going to be included in a cryptographic computation. This not going to be included in a cryptographic computation. This
bucket is encoded in the message as a binary object. This value bucket is encoded in the message as a binary object. This value
is obtained by CBOR encoding the protected map and wrapping it in is obtained by CBOR encoding the protected map and wrapping it in
a bstr object. Senders SHOULD encode a zero-length map as a zero- a bstr object. Senders SHOULD encode a zero-length map as a zero-
length byte string rather than as a zero-length map (encoded as length byte string rather than as a zero-length map (encoded as
h'a0'). The zero-length binary encoding is preferred because it h'a0'). The zero-length binary encoding is preferred, because it
is both shorter and the version used in the serialization is both shorter and the version used in the serialization
structures for cryptographic computation. Recipients MUST accept structures for cryptographic computation. Recipients MUST accept
both a zero-length byte string and a zero-length map encoded in a both a zero-length byte string and a zero-length map encoded in a
byte string. byte string.
Wrapping the encoding with a byte string allows for the protected Wrapping the encoding with a byte string allows the protected map
map to be transported with a greater chance that it will not be to be transported with a greater chance that it will not be
altered accidentally in transit. (Badly behaved intermediates altered accidentally in transit. (Badly behaved intermediates
could decode and re-encode, but this will result in a failure to could decode and re-encode, but this will result in a failure to
verify unless the re-encoded byte string is identical to the verify unless the re-encoded byte string is identical to the
decoded byte string.) This avoids the problem of all parties decoded byte string.) This avoids the problem of all parties
needing to be able to do a common canonical encoding of the map needing to be able to do a common canonical encoding of the map
for input to cyprtographic operations. for input to crytographic operations.
unprotected: Contains parameters about the current layer that are unprotected: Contains parameters about the current layer that are
not cryptographically protected. not cryptographically protected.
Only header parameters that deal with the current layer are to be Only header parameters that deal with the current layer are to be
placed at that layer. As an example of this, the header parameter placed at that layer. As an example of this, the header parameter
'content type' describes the content of the message being carried in "content type" describes the content of the message being carried in
the message. As such, this header parameter is placed only in the the message. As such, this header parameter is placed only in the
content layer and is not placed in the recipient or signature layers. content layer and is not placed in the recipient or signature layers.
In principle, one should be able to process any given layer without In principle, one should be able to process any given layer without
reference to any other layer. With the exception of the COSE_Sign reference to any other layer. With the exception of the COSE_Sign
structure, the only data that needs to cross layers is the structure, the only data that needs to cross layers is the
cryptographic key. cryptographic key.
The buckets are present in all of the security objects defined in The buckets are present in all of the security objects defined in
this document. The fields in order are the 'protected' bucket (as a this document. The fields, in order, are the "protected" bucket (as
CBOR 'bstr' type) and then the 'unprotected' bucket (as a CBOR 'map' a CBOR "bstr" type) and then the "unprotected" bucket (as a CBOR
type). The presence of both buckets is required. The header "map" type). The presence of both buckets is required. The header
parameters that go into the buckets come from the IANA "COSE Header parameters that go into the buckets come from the IANA "COSE Header
Parameters" registry (Section 11.1). Some header parameters are Parameters" registry (Section 11.1). Some header parameters are
defined in the next section. defined in the next section.
Labels in each of the maps MUST be unique. When processing messages, Labels in each of the maps MUST be unique. When processing messages,
if a label appears multiple times, the message MUST be rejected as if a label appears multiple times, the message MUST be rejected as
malformed. Applications SHOULD verify that the same label does not malformed. Applications SHOULD verify that the same label does not
occur in both the protected and unprotected header parameters. If occur in both the protected and unprotected header parameters. If
the message is not rejected as malformed, attributes MUST be obtained the message is not rejected as malformed, attributes MUST be obtained
from the protected bucket, and only if not found are attributes from the protected bucket, and only if not found are attributes
obtained from the unprotected bucket. obtained from the unprotected bucket.
The following CDDL fragment represents the two header parameter The following CDDL fragment represents the two header-parameter
buckets. A group "Headers" is defined in CDDL that represents the buckets. A group "Headers" is defined in CDDL that represents the
two buckets in which attributes are placed. This group is used to two buckets in which attributes are placed. This group is used to
provide these two fields consistently in all locations. A type is provide these two fields consistently in all locations. A type is
also defined that represents the map of common header parameters. also defined that represents the map of common header parameters.
Headers = ( Headers = (
protected : empty_or_serialized_map, protected : empty_or_serialized_map,
unprotected : header_map unprotected : header_map
) )
skipping to change at page 15, line 9 skipping to change at line 632
Generic_Headers, Generic_Headers,
* label => values * label => values
} }
empty_or_serialized_map = bstr .cbor header_map / bstr .size 0 empty_or_serialized_map = bstr .cbor header_map / bstr .size 0
3.1. Common COSE Header Parameters 3.1. Common COSE Header Parameters
This section defines a set of common header parameters. A summary of This section defines a set of common header parameters. A summary of
these header parameters can be found in Table 3. This table should these header parameters can be found in Table 3. This table should
be consulted to determine the value of label and the type of the be consulted to determine the value of the label and the type of the
value. value.
The set of header parameters defined in this section are: The set of header parameters defined in this section is as follows:
alg: This header parameter is used to indicate the algorithm used alg: This header parameter is used to indicate the algorithm used
for the security processing. This header parameter MUST be for the security processing. This header parameter MUST be
authenticated where the ability to do so exists. This support is authenticated where the ability to do so exists. This support is
provided by AEAD algorithms or construction (e.g. COSE_Sign and provided by AEAD algorithms or construction (e.g., COSE_Sign and
COSE_Mac0). This authentication can be done either by placing the COSE_Mac0). This authentication can be done either by placing the
header parameter in the protected header parameter bucket or as header parameter in the protected-header-parameter bucket or as
part of the externally supplied data Section 4.3). The value is part of the externally supplied data (Section 4.3). The value is
taken from the "COSE Algorithms" registry (see [COSE.Algorithms]). taken from the "COSE Algorithms" registry (see [COSE.Algorithms]).
crit: This header parameter is used to indicate which protected crit: This header parameter is used to indicate which protected
header parameters an application that is processing a message is header parameters an application that is processing a message is
required to understand. Header parameters defined in this required to understand. Header parameters defined in this
document do not need to be included as they should be understood document do not need to be included, as they should be understood
by all implementations. When present, this the 'crit' header by all implementations. When present, the "crit" header parameter
parameter MUST be placed in the protected header parameter bucket. MUST be placed in the protected-header-parameter bucket. The
The array MUST have at least one value in it. array MUST have at least one value in it.
Not all header parameter labels need to be included in the 'crit' Not all header-parameter labels need to be included in the "crit"
header parameter. The rules for deciding which header parameters header parameter. The rules for deciding which header parameters
are placed in the array are: are placed in the array are:
* Integer labels in the range of 0 to 7 SHOULD be omitted. * Integer labels in the range of 0 to 7 SHOULD be omitted.
* Integer labels in the range -1 to -128 can be omitted. * Integer labels in the range -1 to -128 can be omitted.
Algorithms can assign labels in this range where the ability to Algorithms can assign labels in this range where the ability to
process the content of the label is considered to be core to process the content of the label is considered to be core to
implementing the algorithm. Algorithms can assign labels implementing the algorithm. Algorithms can assign labels
outside of this range where the ability to process the content outside of this range where the ability to process the content
of the label is not considered to be core, but needs to be of the label is not considered to be core but needs to be
understood to correctly process this instance. Integer labels understood to correctly process this instance. Integer labels
in the range -129 to -65536 SHOULD be included as these would in the range -129 to -65536 SHOULD be included, as these would
be less common header parameters that might not be generally be less common header parameters that might not be generally
supported. supported.
* Labels for header parameters required for an application MAY be * Labels for header parameters required for an application MAY be
omitted. Applications should have a statement if the label can omitted. Applications should have a statement if the label can
be omitted. be omitted.
The header parameters indicated by 'crit' can be processed by The header parameters indicated by "crit" can be processed by
either the security library code or an application using a either the security-library code or an application using a
security library; the only requirement is that the header security library; the only requirement is that the header
parameter is processed. If the 'crit' value list includes a label parameter is processed. If the "crit" value list includes a label
for which the header parameter is not in the protected header for which the header parameter is not in the protected-header-
parameters bucket, this is a fatal error in processing the parameters bucket, this is a fatal error in processing the
message. message.
content type: This header parameter is used to indicate the content content type: This header parameter is used to indicate the content
type of the data in the payload or ciphertext fields. Integers type of the data in the "payload" or "ciphertext" fields.
are from the "CoAP Content-Formats" IANA registry table Integers are from the "CoAP Content-Formats" IANA registry table
[COAP.Formats]. Text values following the syntax of "<type- [COAP.Formats]. Text values follow the syntax of "<type-
name>/<subtype-name>" where <type-name> and <subtype-name> are name>/<subtype-name>", where <type-name> and <subtype-name> are
defined in Section 4.2 of [RFC6838]. Leading and trailing defined in Section 4.2 of [RFC6838]. Leading and trailing
whitespace is also omitted. Textual content values along with whitespace is also omitted. Textual content values, along with
parameters and subparameters can be located using the IANA "Media parameters and subparameters, can be located using the IANA "Media
Types" registry. Applications SHOULD provide this header Types" registry. Applications SHOULD provide this header
parameter if the content structure is potentially ambiguous. parameter if the content structure is potentially ambiguous.
kid: This header parameter identifies one piece of data that can be kid: This header parameter identifies one piece of data that can be
used as input to find the needed cryptographic key. The value of used as input to find the needed cryptographic key. The value of
this header parameter can be matched against the 'kid' member in a this header parameter can be matched against the "kid" member in a
COSE_Key structure. Other methods of key distribution can define COSE_Key structure. Other methods of key distribution can define
an equivalent field to be matched. Applications MUST NOT assume an equivalent field to be matched. Applications MUST NOT assume
that 'kid' values are unique. There may be more than one key with that "kid" values are unique. There may be more than one key with
the same 'kid' value, so all of the keys associated with this the same "kid" value, so all of the keys associated with this
'kid' may need to be checked. The internal structure of 'kid' "kid" may need to be checked. The internal structure of "kid"
values is not defined and cannot be relied on by applications. values is not defined and cannot be relied on by applications.
Key identifier values are hints about which key to use. This is Key identifier values are hints about which key to use. This is
not a security-critical field. For this reason, it can be placed not a security-critical field. For this reason, it can be placed
in the unprotected header parameters bucket. in the unprotected-header-parameters bucket.
IV: This header parameter holds the Initialization Vector (IV) IV: This header parameter holds the Initialization Vector (IV)
value. For some symmetric encryption algorithms, this may be value. For some symmetric encryption algorithms, this may be
referred to as a nonce. The IV can be placed in the unprotected referred to as a nonce. The IV can be placed in the unprotected
bucket as modifying the IV will cause the decryption to yield bucket, as modifying the IV will cause the decryption to yield
plaintext that is readily detectable as garbled. plaintext that is readily detectable as garbled.
Partial IV: This header parameter holds a part of the IV value. Partial IV: This header parameter holds a part of the IV value.
When using the COSE_Encrypt0 structure, a portion of the IV can be When using the COSE_Encrypt0 structure, a portion of the IV can be
part of the context associated with the key (Context IV) while a part of the context associated with the key (Context IV), while a
portion can be changed with each message (Partial IV). This field portion can be changed with each message (Partial IV). This field
is used to carry a value that causes the IV to be changed for each is used to carry a value that causes the IV to be changed for each
message. The Partial IV can be placed in the unprotected bucket message. The Partial IV can be placed in the unprotected bucket,
as modifying the value will cause the decryption to yield as modifying the value will cause the decryption to yield
plaintext that is readily detectable as garbled. The plaintext that is readily detectable as garbled. The
'Initialization Vector' and 'Partial Initialization Vector' header "Initialization Vector" and "Partial Initialization Vector" header
parameters MUST NOT both be present in the same security layer. parameters MUST NOT both be present in the same security layer.
The message IV is generated by the following steps: The message IV is generated by the following steps:
1. Left-pad the Partial IV with zeros to the length of IV 1. Left-pad the Partial IV with zeros to the length of IV
(determined by the algorithm). (determined by the algorithm).
2. XOR the padded Partial IV with the context IV. 2. XOR the padded Partial IV with the Context IV.
+=========+=======+========+=====================+==================+ +=========+=======+========+=====================+==================+
| Name | Label | Value | Value Registry | Description | | Name | Label | Value | Value Registry | Description |
| | | Type | | | | | | Type | | |
+=========+=======+========+=====================+==================+ +=========+=======+========+=====================+==================+
| alg | 1 | int / | COSE Algorithms | Cryptographic | | alg | 1 | int / | COSE Algorithms | Cryptographic |
| | | tstr | registry | algorithm to use | | | | tstr | registry | algorithm to use |
+---------+-------+--------+---------------------+------------------+ +---------+-------+--------+---------------------+------------------+
| crit | 2 | [+ | COSE Header | Critical header | | crit | 2 | [+ | COSE Header | Critical header |
| | | label] | Parameters | parameters to be | | | | label] | Parameters | parameters to be |
skipping to change at page 17, line 42 skipping to change at line 761
+---------+-------+--------+---------------------+------------------+ +---------+-------+--------+---------------------+------------------+
| Partial | 6 | bstr | | Partial | | Partial | 6 | bstr | | Partial |
| IV | | | | Initialization | | IV | | | | Initialization |
| | | | | Vector | | | | | | Vector |
+---------+-------+--------+---------------------+------------------+ +---------+-------+--------+---------------------+------------------+
Table 3: Common Header Parameters Table 3: Common Header Parameters
The CDDL fragment that represents the set of header parameters The CDDL fragment that represents the set of header parameters
defined in this section is given below. Each of the header defined in this section is given below. Each of the header
parameters is tagged as optional because they do not need to be in parameters is tagged as optional, because they do not need to be in
every map; header parameters required in specific maps are discussed every map; header parameters required in specific maps are discussed
above. above.
Generic_Headers = ( Generic_Headers = (
? 1 => int / tstr, ; algorithm identifier ? 1 => int / tstr, ; algorithm identifier
? 2 => [+label], ; criticality ? 2 => [+label], ; criticality
? 3 => tstr / int, ; content type ? 3 => tstr / int, ; content type
? 4 => bstr, ; key identifier ? 4 => bstr, ; key identifier
? 5 => bstr, ; IV ? 5 => bstr, ; IV
? 6 => bstr ; Partial IV ? 6 => bstr ; Partial IV
skipping to change at page 18, line 29 skipping to change at line 789
be converted between each other; as the signature computation be converted between each other; as the signature computation
includes a parameter identifying which structure is being used, the includes a parameter identifying which structure is being used, the
converted structure will fail signature validation. converted structure will fail signature validation.
4.1. Signing with One or More Signers 4.1. Signing with One or More Signers
The COSE_Sign structure allows for one or more signatures to be The COSE_Sign structure allows for one or more signatures to be
applied to a message payload. Header parameters relating to the applied to a message payload. Header parameters relating to the
content and header parameters relating to the signature are carried content and header parameters relating to the signature are carried
along with the signature itself. These header parameters may be along with the signature itself. These header parameters may be
authenticated by the signature, or just present. An example of a authenticated by the signature, or just be present. An example of a
header parameter about the content is the content type header header parameter about the content is the content type header
parameter. An example of a header parameter about the signature parameter. An example of a header parameter about the signature
would be the algorithm and key used to create the signature. would be the algorithm and key used to create the signature.
RFC 5652 indicates that: RFC 5652 indicates that:
| When more than one signature is present, the successful validation | When more than one signature is present, the successful validation
| of one signature associated with a given signer is usually treated | of one signature associated with a given signer is usually treated
| as a successful signature by that signer. However, there are some | as a successful signature by that signer. However, there are some
| application environments where other rules are needed. An | application environments where other rules are needed. An
| application that employs a rule other than one valid signature for | application that employs a rule other than one valid signature for
| each signer must specify those rules. Also, where simple matching | each signer must specify those rules. Also, where simple matching
| of the signer identifier is not sufficient to determine whether | of the signer identifier is not sufficient to determine whether
| the signatures were generated by the same signer, the application | the signatures were generated by the same signer, the application
| specification must describe how to determine which signatures were | specification must describe how to determine which signatures were
| generated by the same signer. Support for different communities | generated by the same signer. Support of different communities of
| of recipients is the primary reason that signers choose to include | recipients is the primary reason that signers choose to include
| more than one signature. | more than one signature.
For example, the COSE_Sign structure might include signatures For example, the COSE_Sign structure might include signatures
generated with the Edwards-curve Digital Signature Algorithm (EdDSA) generated with the Edwards-curve Digital Signature Algorithm (EdDSA)
[RFC8032] and with the Elliptic Curve Digital Signature Algorithm [RFC8032] and the Elliptic Curve Digital Signature Algorithm (ECDSA)
(ECDSA) [DSS]. This allows recipients to verify the signature [DSS]. This allows recipients to verify the signature associated
associated with one algorithm or the other. More-detailed with one algorithm or the other. More detailed information on
information on multiple signature evaluations can be found in multiple signature evaluations can be found in [RFC5752].
[RFC5752].
The signature structure can be encoded as either tagged or untagged The signature structure can be encoded as either tagged or untagged,
depending on the context it will be used in. A tagged COSE_Sign depending on the context it will be used in. A tagged COSE_Sign
structure is identified by the CBOR tag 98. The CDDL fragment that structure is identified by the CBOR tag 98. The CDDL fragment that
represents this is: represents this is:
COSE_Sign_Tagged = #6.98(COSE_Sign) COSE_Sign_Tagged = #6.98(COSE_Sign)
A COSE Signed Message is defined in two parts. The CBOR object that A COSE Signed Message is defined in two parts. The CBOR object that
carries the body and information about the body is called the carries the body and information about the body is called the
COSE_Sign structure. The CBOR object that carries the signature and COSE_Sign structure. The CBOR object that carries the signature and
information about the signature is called the COSE_Signature information about the signature is called the COSE_Signature
structure. Examples of COSE Signed Messages can be found in structure. Examples of COSE Signed Messages can be found in
Appendix C.1. Appendix C.1.
The COSE_Sign structure is a CBOR array. The fields of the array in The COSE_Sign structure is a CBOR array. The fields of the array, in
order are: order, are:
protected: This is as described in Section 3. protected: This is as described in Section 3.
unprotected: This is as described in Section 3. unprotected: This is as described in Section 3.
payload: This field contains the serialized content to be signed. payload: This field contains the serialized content to be signed.
If the payload is not present in the message, the application is If the payload is not present in the message, the application is
required to supply the payload separately. The payload is wrapped required to supply the payload separately. The payload is wrapped
in a bstr to ensure that it is transported without changes. If in a bstr to ensure that it is transported without changes. If
the payload is transported separately ("detached content"), then a the payload is transported separately ("detached content"), then a
skipping to change at page 20, line 12 skipping to change at line 867
The CDDL fragment that represents the above text for COSE_Sign The CDDL fragment that represents the above text for COSE_Sign
follows. follows.
COSE_Sign = [ COSE_Sign = [
Headers, Headers,
payload : bstr / nil, payload : bstr / nil,
signatures : [+ COSE_Signature] signatures : [+ COSE_Signature]
] ]
The COSE_Signature structure is a CBOR array. The fields of the The COSE_Signature structure is a CBOR array. The fields of the
array in order are: array, in order, are:
protected: This is as described in Section 3. protected: This is as described in Section 3.
unprotected: This is as described in Section 3. unprotected: This is as described in Section 3.
signature: This field contains the computed signature value. The signature: This field contains the computed signature value. The
type of the field is a bstr. Algorithms MUST specify padding if type of the field is a bstr. Algorithms MUST specify padding if
the signature value is not a multiple of 8 bits. the signature value is not a multiple of 8 bits.
The CDDL fragment that represents the above text for COSE_Signature The CDDL fragment that represents the above text for COSE_Signature
skipping to change at page 20, line 34 skipping to change at line 889
COSE_Signature = [ COSE_Signature = [
Headers, Headers,
signature : bstr signature : bstr
] ]
4.2. Signing with One Signer 4.2. Signing with One Signer
The COSE_Sign1 signature structure is used when only one signature is The COSE_Sign1 signature structure is used when only one signature is
going to be placed on a message. The header parameters dealing with going to be placed on a message. The header parameters dealing with
the content and the signature are placed in the same pair of buckets the content and the signature are placed in the same pair of buckets,
rather than having the separation of COSE_Sign. rather than having the separation of COSE_Sign.
The structure can be encoded as either tagged or untagged depending The structure can be encoded as either tagged or untagged depending
on the context it will be used in. A tagged COSE_Sign1 structure is on the context it will be used in. A tagged COSE_Sign1 structure is
identified by the CBOR tag 18. The CDDL fragment that represents identified by the CBOR tag 18. The CDDL fragment that represents
this is: this is:
COSE_Sign1_Tagged = #6.18(COSE_Sign1) COSE_Sign1_Tagged = #6.18(COSE_Sign1)
The CBOR object that carries the body, the signature, and the The CBOR object that carries the body, the signature, and the
information about the body and signature is called the COSE_Sign1 information about the body and signature is called the COSE_Sign1
structure. Examples of COSE_Sign1 messages can be found in structure. Examples of COSE_Sign1 messages can be found in
Appendix C.2. Appendix C.2.
The COSE_Sign1 structure is a CBOR array. The fields of the array in The COSE_Sign1 structure is a CBOR array. The fields of the array,
order are: in order, are:
protected: This is as described in Section 3. protected: This is as described in Section 3.
unprotected: This is as described in Section 3. unprotected: This is as described in Section 3.
payload: This is as described in Section 4.1. payload: This is as described in Section 4.1.
signature: This field contains the computed signature value. The signature: This field contains the computed signature value. The
type of the field is a bstr. type of the field is a bstr.
skipping to change at page 21, line 24 skipping to change at line 928
COSE_Sign1 = [ COSE_Sign1 = [
Headers, Headers,
payload : bstr / nil, payload : bstr / nil,
signature : bstr signature : bstr
] ]
4.3. Externally Supplied Data 4.3. Externally Supplied Data
One of the features offered in the COSE document is the ability for One of the features offered in the COSE document is the ability for
applications to provide additional data to be authenticated, but that applications to provide additional data that is to be authenticated
is not carried as part of the COSE object. The primary reason for but is not carried as part of the COSE object. The primary reason
supporting this can be seen by looking at the CoAP message structure for supporting this can be seen by looking at the CoAP message
[RFC7252], where the facility exists for options to be carried before structure [RFC7252], where the facility exists for options to be
the payload. Examples of data that can be placed in this location carried before the payload. Examples of data that can be placed in
would be the CoAP code or CoAP options. If the data is in the this location would be the CoAP code or CoAP options. If the data is
headers of the CoAP message, then it is available for proxies to help in the headers of the CoAP message, then it is available for proxies
in performing its operations. For example, the Accept Option can be to help in performing its operations. For example, the Accept option
used by a proxy to determine if an appropriate value is in the can be used by a proxy to determine if an appropriate value is in the
proxy's cache. But the sender can cause a failure at the server if a proxy's cache. But the sender can cause a failure at the server if a
proxy, or an attacker, changes the set of accept values by including proxy, or an attacker, changes the set of Accept values by including
the field in the externally supplied data. the field in the externally supplied data.
This document describes the process for using a byte array of This document describes the process for using a byte array of
externally supplied authenticated data; the method of constructing externally supplied authenticated data; the method of constructing
the byte array is a function of the application. Applications that the byte array is a function of the application. Applications that
use this feature need to define how the externally supplied use this feature need to define how the externally supplied
authenticated data is to be constructed. Such a construction needs authenticated data is to be constructed. Such a construction needs
to take into account the following issues: to take into account the following issues:
* If multiple items are included, applications need to ensure that * If multiple items are included, applications need to ensure that
the same byte string cannot be produced if there are different the same byte string cannot be produced if there are different
inputs. This would occur by concatenating the text strings 'AB' inputs. This would occur by concatenating the text strings "AB"
and 'CDE' or by concatenating the text strings 'ABC' and 'DE'. and "CDE" or by concatenating the text strings "ABC" and "DE".
This is usually addressed by making fields a fixed width and/or This is usually addressed by making fields a fixed width and/or
encoding the length of the field as part of the output. Using encoding the length of the field as part of the output. Using
options from CoAP [RFC7252] as an example, these fields use a TLV options from CoAP [RFC7252] as an example, these fields use a TLV
structure so they can be concatenated without any problems. structure so they can be concatenated without any problems.
* If multiple items are included, an order for the items needs to be * If multiple items are included, an order for the items needs to be
defined. Using options from CoAP as an example, an application defined. Using options from CoAP as an example, an application
could state that the fields are to be ordered by the option could state that the fields are to be ordered by the option
number. number.
* Applications need to ensure that the byte string is going to be * Applications need to ensure that the byte string is going to be
the same on both sides. Using options from CoAP might give a the same on both sides. Using options from CoAP might give a
problem if the same relative numbering is kept. An intermediate problem if the same relative numbering is kept. An intermediate
node could insert or remove an option, changing how the relative node could insert or remove an option, changing how the relative
number is done. An application would need to specify that the numbering is done. An application would need to specify that the
relative number must be re-encoded to be relative only to the relative number must be re-encoded to be relative only to the
options that are in the external data. options that are in the external data.
4.4. Signing and Verification Process 4.4. Signing and Verification Process
In order to create a signature, a well-defined byte string is needed. In order to create a signature, a well-defined byte string is needed.
The Sig_structure is used to create the canonical form. This signing The Sig_structure is used to create the canonical form. This signing
and verification process takes in the body information (COSE_Sign or and verification process takes in the body information (COSE_Sign or
COSE_Sign1), the signer information (COSE_Signature), and the COSE_Sign1), the signer information (COSE_Signature), and the
application data (external source). A Sig_structure is a CBOR array. application data (external source). A Sig_structure is a CBOR array.
The fields of the Sig_structure in order are: The fields of the Sig_structure, in order, are:
1. A context text string identifying the context of the signature. 1. A context text string identifying the context of the signature.
The context text string is: The context text string is:
"Signature" for signatures using the COSE_Signature structure. "Signature" for signatures using the COSE_Signature structure.
"Signature1" for signatures using the COSE_Sign1 structure. "Signature1" for signatures using the COSE_Sign1 structure.
2. The protected attributes from the body structure encoded in a 2. The protected attributes from the body structure, encoded in a
bstr type. If there are no protected attributes, a zero-length bstr type. If there are no protected attributes, a zero-length
byte string is used. byte string is used.
3. The protected attributes from the signer structure encoded in a 3. The protected attributes from the signer structure, encoded in a
bstr type. If there are no protected attributes, a zero-length bstr type. If there are no protected attributes, a zero-length
byte string is used. This field is omitted for the COSE_Sign1 byte string is used. This field is omitted for the COSE_Sign1
signature structure. signature structure.
4. The externally supplied data from the application encoded in a 4. The externally supplied data from the application, encoded in a
bstr type. If this field is not supplied, it defaults to a zero- bstr type. If this field is not supplied, it defaults to a zero-
length byte string. (See Section 4.3 for application guidance on length byte string. (See Section 4.3 for application guidance on
constructing this field.) constructing this field.)
5. The payload to be signed encoded in a bstr type. The payload is 5. The payload to be signed, encoded in a bstr type. The payload is
placed here independent of how it is transported. placed here, independent of how it is transported.
The CDDL fragment that describes the above text is: The CDDL fragment that describes the above text is:
Sig_structure = [ Sig_structure = [
context : "Signature" / "Signature1", context : "Signature" / "Signature1",
body_protected : empty_or_serialized_map, body_protected : empty_or_serialized_map,
? sign_protected : empty_or_serialized_map, ? sign_protected : empty_or_serialized_map,
external_aad : bstr, external_aad : bstr,
payload : bstr payload : bstr
] ]
How to compute a signature: How to compute a signature:
1. Create a Sig_structure and populate it with the appropriate 1. Create a Sig_structure and populate it with the appropriate
fields. fields.
2. Create the value ToBeSigned by encoding the Sig_structure to a 2. Create the value ToBeSigned by encoding the Sig_structure to a
byte string, using the encoding described in Section 9. byte string, using the encoding described in Section 9.
3. Call the signature creation algorithm passing in K (the key to 3. Call the signature creation algorithm, passing in K (the key to
sign with), alg (the algorithm to sign with), and ToBeSigned (the sign with), alg (the algorithm to sign with), and ToBeSigned (the
value to sign). value to sign).
4. Place the resulting signature value in the correct location. 4. Place the resulting signature value in the correct location.
This is the 'signature' field of the COSE_Signature or COSE_Sign1 This is the "signature" field of the COSE_Signature or COSE_Sign1
structure. structure.
The steps for verifying a signature are: The steps for verifying a signature are:
1. Create a Sig_structure and populate it with the appropriate 1. Create a Sig_structure and populate it with the appropriate
fields. fields.
2. Create the value ToBeSigned by encoding the Sig_structure to a 2. Create the value ToBeSigned by encoding the Sig_structure to a
byte string, using the encoding described in Section 9. byte string, using the encoding described in Section 9.
3. Call the signature verification algorithm passing in K (the key 3. Call the signature verification algorithm, passing in K (the key
to verify with), alg (the algorithm used sign with), ToBeSigned to verify with), alg (the algorithm used to sign with),
(the value to sign), and sig (the signature to be verified). ToBeSigned (the value to sign), and sig (the signature to be
verified).
In addition to performing the signature verification, the application In addition to performing the signature verification, the application
performs the appropriate checks to ensure that the key is correctly performs the appropriate checks to ensure that the key is correctly
paired with the signing identity and that the signing identity is paired with the signing identity and that the signing identity is
authorized before performing actions. authorized before performing actions.
5. Encryption Objects 5. Encryption Objects
COSE supports two different encryption structures. COSE_Encrypt0 is COSE supports two different encryption structures. COSE_Encrypt0 is
used when a recipient structure is not needed because the key to be used when a recipient structure is not needed because the key to be
used is known implicitly. COSE_Encrypt is used the rest of the time. used is known implicitly. COSE_Encrypt is used the rest of the time.
This includes cases where there are multiple recipients or a This includes cases where there are multiple recipients or a
recipient algorithm other than direct (i.e. pre-shared secret) is recipient algorithm other than direct (i.e., preshared secret) is
used. used.
5.1. Enveloped COSE Structure 5.1. Enveloped COSE Structure
The enveloped structure allows for one or more recipients of a The enveloped structure allows for one or more recipients of a
message. There are provisions for header parameters about the message. There are provisions for header parameters about the
content and header parameters about the recipient information to be content and header parameters about the recipient information to be
carried in the message. The protected header parameters associated carried in the message. The protected header parameters associated
with the content are authenticated by the content encryption with the content are authenticated by the content encryption
algorithm. The protected header parameters associated with the algorithm. The protected header parameters associated with the
recipient are authenticated by the recipient algorithm (when the recipient are authenticated by the recipient algorithm (when the
algorithm supports it). Examples of header parameters about the algorithm supports it). Examples of header parameters about the
content are the type of the content and the content encryption content are the type of the content and the content encryption
algorithm. Examples of header parameters about the recipient are the algorithm. Examples of header parameters about the recipient are the
recipient's key identifier and the recipient's encryption algorithm. recipient's key identifier and the recipient's encryption algorithm.
The same techniques and nearly the same structure are used for The same techniques and nearly the same structure are used for
encrypting both the plaintext and the keys. This is different from encrypting both the plaintext and the keys. This is different from
the approach used by both "Cryptographic Message Syntax (CMS)" the approach used by both "Cryptographic Message Syntax (CMS)"
[RFC5652] and "JSON Web Encryption (JWE)" [RFC7516] where different [RFC5652] and "JSON Web Encryption (JWE)" [RFC7516], where different
structures are used for the content layer and for the recipient structures are used for the content layer and the recipient layer.
layer. Two structures are defined: COSE_Encrypt to hold the Two structures are defined: COSE_Encrypt to hold the encrypted
encrypted content and COSE_recipient to hold the encrypted keys for content and COSE_recipient to hold the encrypted keys for recipients.
recipients. Examples of encrypted messages can be found in Examples of encrypted messages can be found in Appendix C.3.
Appendix C.3.
The COSE_Encrypt structure can be encoded as either tagged or The COSE_Encrypt structure can be encoded as either tagged or
untagged depending on the context it will be used in. A tagged untagged, depending on the context it will be used in. A tagged
COSE_Encrypt structure is identified by the CBOR tag 96. The CDDL COSE_Encrypt structure is identified by the CBOR tag 96. The CDDL
fragment that represents this is: fragment that represents this is:
COSE_Encrypt_Tagged = #6.96(COSE_Encrypt) COSE_Encrypt_Tagged = #6.96(COSE_Encrypt)
The COSE_Encrypt structure is a CBOR array. The fields of the array The COSE_Encrypt structure is a CBOR array. The fields of the array,
in order are: in order, are:
protected: This is as described in Section 3. protected: This is as described in Section 3.
unprotected: This is as described in Section 3. unprotected: This is as described in Section 3.
ciphertext: This field contains the ciphertext encoded as a bstr. ciphertext: This field contains the ciphertext, encoded as a bstr.
If the ciphertext is to be transported independently of the If the ciphertext is to be transported independently of the
control information about the encryption process (i.e., detached control information about the encryption process (i.e., detached
content), then the field is encoded as a nil value. content), then the field is encoded as a nil value.
recipients: This field contains an array of recipient information recipients: This field contains an array of recipient information
structures. The type for the recipient information structure is a structures. The type for the recipient information structure is a
COSE_recipient. COSE_recipient.
The CDDL fragment that corresponds to the above text is: The CDDL fragment that corresponds to the above text is:
COSE_Encrypt = [ COSE_Encrypt = [
Headers, Headers,
ciphertext : bstr / nil, ciphertext : bstr / nil,
recipients : [+COSE_recipient] recipients : [+COSE_recipient]
] ]
The COSE_recipient structure is a CBOR array. The fields of the The COSE_recipient structure is a CBOR array. The fields of the
array in order are: array, in order, are:
protected: This is as described in Section 3. protected: This is as described in Section 3.
unprotected: This is as described in Section 3. unprotected: This is as described in Section 3.
ciphertext: This field contains the encrypted key encoded as a bstr. ciphertext: This field contains the encrypted key, encoded as a
All encoded keys are symmetric keys; the binary value of the key bstr. All encoded keys are symmetric keys; the binary value of
is the content. If there is not an encrypted key, then this field the key is the content. If there is not an encrypted key, then
is encoded as a nil value. this field is encoded as a nil value.
recipients: This field contains an array of recipient information recipients: This field contains an array of recipient information
structures. The type for the recipient information structure is a structures. The type for the recipient information structure is a
COSE_recipient (an example of this can be found in Appendix B). COSE_recipient (an example of this can be found in Appendix B).
If there are no recipient information structures, this element is If there are no recipient information structures, this element is
absent. absent.
The CDDL fragment that corresponds to the above text for The CDDL fragment that corresponds to the above text for
COSE_recipient is: COSE_recipient is:
skipping to change at page 26, line 19 skipping to change at line 1151
each recipient, using a key specific to that recipient. The details each recipient, using a key specific to that recipient. The details
of this encryption depend on which class the recipient algorithm of this encryption depend on which class the recipient algorithm
falls into. Specific details on each of the classes can be found in falls into. Specific details on each of the classes can be found in
Section 8.5. A short summary of the five content key distribution Section 8.5. A short summary of the five content key distribution
methods is: methods is:
direct: The CEK is the same as the identified previously distributed direct: The CEK is the same as the identified previously distributed
symmetric key or is derived from a previously distributed secret. symmetric key or is derived from a previously distributed secret.
No CEK is transported in the message. No CEK is transported in the message.
symmetric key-encryption keys (KEK): The CEK is encrypted using a symmetric key-encryption keys (KEKs): The CEK is encrypted using a
previously distributed symmetric KEK. Also known as key wrap. previously distributed symmetric KEK. Also known as key wrap.
key agreement: The recipient's public key and a sender's private key key agreement: The recipient's public key and a sender's private key
are used to generate a pairwise secret, a Key Derivation Function are used to generate a pairwise secret, a Key Derivation Function
(KDF) is applied to derive a key, and then the CEK is either the (KDF) is applied to derive a key, and then the CEK is either the
derived key or encrypted by the derived key. derived key or encrypted by the derived key.
key transport: The CEK is encrypted with the recipient's public key. key transport: The CEK is encrypted with the recipient's public key.
passwords: The CEK is encrypted in a KEK that is derived from a passwords: The CEK is encrypted in a KEK that is derived from a
skipping to change at page 26, line 45 skipping to change at line 1177
The COSE_Encrypt0 encrypted structure does not have the ability to The COSE_Encrypt0 encrypted structure does not have the ability to
specify recipients of the message. The structure assumes that the specify recipients of the message. The structure assumes that the
recipient of the object will already know the identity of the key to recipient of the object will already know the identity of the key to
be used in order to decrypt the message. If a key needs to be be used in order to decrypt the message. If a key needs to be
identified to the recipient, the enveloped structure ought to be identified to the recipient, the enveloped structure ought to be
used. used.
Examples of encrypted messages can be found in Appendix C.3. Examples of encrypted messages can be found in Appendix C.3.
The COSE_Encrypt0 structure can be encoded as either tagged or The COSE_Encrypt0 structure can be encoded as either tagged or
untagged depending on the context it will be used in. A tagged untagged, depending on the context it will be used in. A tagged
COSE_Encrypt0 structure is identified by the CBOR tag 16. The CDDL COSE_Encrypt0 structure is identified by the CBOR tag 16. The CDDL
fragment that represents this is: fragment that represents this is:
COSE_Encrypt0_Tagged = #6.16(COSE_Encrypt0) COSE_Encrypt0_Tagged = #6.16(COSE_Encrypt0)
The COSE_Encrypt0 structure is a CBOR array. The fields of the array The COSE_Encrypt0 structure is a CBOR array. The fields of the
in order are: array, in order, are:
protected: This is as described in Section 3. protected: This is as described in Section 3.
unprotected: This is as described in Section 3. unprotected: This is as described in Section 3.
ciphertext: This is as described in Section 5.1. ciphertext: This is as described in Section 5.1.
The CDDL fragment for COSE_Encrypt0 that corresponds to the above The CDDL fragment for COSE_Encrypt0 that corresponds to the above
text is: text is:
skipping to change at page 27, line 25 skipping to change at line 1206
Headers, Headers,
ciphertext : bstr / nil, ciphertext : bstr / nil,
] ]
5.3. How to Encrypt and Decrypt for AEAD Algorithms 5.3. How to Encrypt and Decrypt for AEAD Algorithms
The encryption algorithm for AEAD algorithms is fairly simple. The The encryption algorithm for AEAD algorithms is fairly simple. The
first step is to create a consistent byte string for the first step is to create a consistent byte string for the
authenticated data structure. For this purpose, we use an authenticated data structure. For this purpose, we use an
Enc_structure. The Enc_structure is a CBOR array. The fields of the Enc_structure. The Enc_structure is a CBOR array. The fields of the
Enc_structure in order are: Enc_structure, in order, are:
1. A context text string identifying the context of the 1. A context text string identifying the context of the
authenticated data structure. The context text string is: authenticated data structure. The context text string is:
"Encrypt0" for the content encryption of a COSE_Encrypt0 data "Encrypt0" for the content encryption of a COSE_Encrypt0 data
structure. structure.
"Encrypt" for the first layer of a COSE_Encrypt data structure "Encrypt" for the first layer of a COSE_Encrypt data structure
(i.e., for content encryption). (i.e., for content encryption).
"Enc_Recipient" for a recipient encoding to be placed in an "Enc_Recipient" for a recipient encoding to be placed in a
COSE_Encrypt data structure. COSE_Encrypt data structure.
"Mac_Recipient" for a recipient encoding to be placed in a "Mac_Recipient" for a recipient encoding to be placed in a
MACed message structure. MACed message structure.
"Rec_Recipient" for a recipient encoding to be placed in a "Rec_Recipient" for a recipient encoding to be placed in a
recipient structure. recipient structure.
2. The protected attributes from the body structure encoded in a 2. The protected attributes from the body structure, encoded in a
bstr type. If there are no protected attributes, a zero-length bstr type. If there are no protected attributes, a zero-length
byte string is used. byte string is used.
3. The externally supplied data from the application encoded in a 3. The externally supplied data from the application encoded in a
bstr type. If this field is not supplied, it defaults to a zero- bstr type. If this field is not supplied, it defaults to a zero-
length byte string. (See Section 4.3 for application guidance on length byte string. (See Section 4.3 for application guidance on
constructing this field.) constructing this field.)
The CDDL fragment that describes the above text is: The CDDL fragment that describes the above text is:
skipping to change at page 28, line 28 skipping to change at line 1258
2. Encode the Enc_structure to a byte string (Additional 2. Encode the Enc_structure to a byte string (Additional
Authenticated Data (AAD)), using the encoding described in Authenticated Data (AAD)), using the encoding described in
Section 9. Section 9.
3. Determine the encryption key (K). This step is dependent on the 3. Determine the encryption key (K). This step is dependent on the
class of recipient algorithm being used. For: class of recipient algorithm being used. For:
No Recipients: The key to be used is determined by the algorithm No Recipients: The key to be used is determined by the algorithm
and key at the current layer. Examples are key transport keys and key at the current layer. Examples are key transport keys
(Section 8.5.3), key wrap keys (Section 8.5.2), or pre-shared (Section 8.5.3), key wrap keys (Section 8.5.2), and preshared
secrets. secrets.
Direct Encryption and Direct Key Agreement: The key is Direct Encryption and Direct Key Agreement: The key is
determined by the key and algorithm in the recipient determined by the key and algorithm in the recipient
structure. The encryption algorithm and size of the key to be structure. The encryption algorithm and size of the key to be
used are inputs into the KDF used for the recipient. (For used are inputs into the KDF used for the recipient. (For
direct, the KDF can be thought of as the identity operation.) direct, the KDF can be thought of as the identity operation.)
Examples of these algorithms are found in Sections 6.1.2 and Examples of these algorithms are found in Sections 6.1.2 and
6.3 of [I-D.ietf-cose-rfc8152bis-algs]. 6.3 of [RFC9053].
Other: The key is randomly or pseudo-randomly generated. Other: The key is randomly or pseudorandomly generated.
4. Call the encryption algorithm with K (the encryption key), P (the 4. Call the encryption algorithm with K (the encryption key), P (the
plaintext), and AAD. Place the returned ciphertext into the plaintext), and AAD. Place the returned ciphertext into the
'ciphertext' field of the structure. "ciphertext" field of the structure.
5. For recipients of the message, recursively perform the encryption 5. For recipients of the message, recursively perform the encryption
algorithm for that recipient, using K (the encryption key) as the algorithm for that recipient, using K (the encryption key) as the
plaintext. plaintext.
How to decrypt a message: How to decrypt a message:
1. Create an Enc_structure and populate it with the appropriate 1. Create an Enc_structure and populate it with the appropriate
fields. fields.
2. Encode the Enc_structure to a byte string (AAD), using the 2. Encode the Enc_structure to a byte string (AAD), using the
encoding described in Section 9. encoding described in Section 9.
3. Determine the decryption key. This step is dependent on the 3. Determine the decryption key. This step is dependent on the
class of recipient algorithm being used. For: class of recipient algorithm being used. For:
No Recipients: The key to be used is determined by the algorithm No Recipients: The key to be used is determined by the algorithm
and key at the current layer. Examples are key transport keys and key at the current layer. Examples are key transport keys
(Section 8.5.3), key wrap keys (Section 8.5.2), or pre-shared (Section 8.5.3), key wrap keys (Section 8.5.2), and preshared
secrets. secrets.
Direct Encryption and Direct Key Agreement: The key is Direct Encryption and Direct Key Agreement: The key is
determined by the key and algorithm in the recipient determined by the key and algorithm in the recipient
structure. The encryption algorithm and size of the key to be structure. The encryption algorithm and size of the key to be
used are inputs into the KDF used for the recipient. (For used are inputs into the KDF used for the recipient. (For
direct, the KDF can be thought of as the identity operation.) direct, the KDF can be thought of as the identity operation.)
Other: The key is determined by decoding and decrypting one of Other: The key is determined by decoding and decrypting one of
the recipient structures. the recipient structures.
4. Call the decryption algorithm with K (the decryption key to use), 4. Call the decryption algorithm with K (the decryption key to use),
C (the ciphertext), and AAD. C (the ciphertext), and AAD.
5.4. How to Encrypt and Decrypt for AE Algorithms 5.4. How to Encrypt and Decrypt for AE Algorithms
How to encrypt a message: How to encrypt a message:
1. Verify that the 'protected' field is empty. 1. Verify that the "protected" field is empty.
2. Verify that there was no external additional authenticated data 2. Verify that there was no external additional authenticated data
supplied for this operation. supplied for this operation.
3. Determine the encryption key. This step is dependent on the 3. Determine the encryption key. This step is dependent on the
class of recipient algorithm being used. For: class of recipient algorithm being used. For:
No Recipients: The key to be used is determined by the algorithm No Recipients: The key to be used is determined by the algorithm
and key at the current layer. Examples are key transport keys and key at the current layer. Examples are key transport keys
(Section 8.5.3), key wrap keys (Section 8.5.2), or pre-shared (Section 8.5.3), key wrap keys (Section 8.5.2), and preshared
secrets. secrets.
Direct Encryption and Direct Key Agreement: The key is Direct Encryption and Direct Key Agreement: The key is
determined by the key and algorithm in the recipient determined by the key and algorithm in the recipient
structure. The encryption algorithm and size of the key to be structure. The encryption algorithm and size of the key to be
used are inputs into the KDF used for the recipient. (For used are inputs into the KDF used for the recipient. (For
direct, the KDF can be thought of as the identity operation.) direct, the KDF can be thought of as the identity operation.)
Examples of these algorithms are found in Sections 6.1.2 and Examples of these algorithms are found in Sections 6.1.2 and
6.3 of [I-D.ietf-cose-rfc8152bis-algs]. 6.3 of [RFC9053].
Other: The key is randomly generated. Other: The key is randomly generated.
4. Call the encryption algorithm with K (the encryption key to use) 4. Call the encryption algorithm with K (the encryption key to use)
and P (the plaintext). Place the returned ciphertext into the and P (the plaintext). Place the returned ciphertext into the
'ciphertext' field of the structure. "ciphertext" field of the structure.
5. For recipients of the message, recursively perform the encryption 5. For recipients of the message, recursively perform the encryption
algorithm for that recipient, using K (the encryption key) as the algorithm for that recipient, using K (the encryption key) as the
plaintext. plaintext.
How to decrypt a message: How to decrypt a message:
1. Verify that the 'protected' field is empty. 1. Verify that the "protected" field is empty.
2. Verify that there was no external additional authenticated data 2. Verify that there was no external additional authenticated data
supplied for this operation. supplied for this operation.
3. Determine the decryption key. This step is dependent on the 3. Determine the decryption key. This step is dependent on the
class of recipient algorithm being used. For: class of recipient algorithm being used. For:
No Recipients: The key to be used is determined by the algorithm No Recipients: The key to be used is determined by the algorithm
and key at the current layer. Examples are key transport keys and key at the current layer. Examples are key transport keys
(Section 8.5.3), key wrap keys (Section 8.5.2), or pre-shared (Section 8.5.3), key wrap keys (Section 8.5.2), and preshared
secrets. secrets.
Direct Encryption and Direct Key Agreement: The key is Direct Encryption and Direct Key Agreement: The key is
determined by the key and algorithm in the recipient determined by the key and algorithm in the recipient
structure. The encryption algorithm and size of the key to be structure. The encryption algorithm and size of the key to be
used are inputs into the KDF used for the recipient. (For used are inputs into the KDF used for the recipient. (For
direct, the KDF can be thought of as the identity operation.) direct, the KDF can be thought of as the identity operation.)
Examples of these algorithms are found in Sections 6.1.2 and Examples of these algorithms are found in Sections 6.1.2 and
6.3 of [I-D.ietf-cose-rfc8152bis-algs]. 6.3 of [RFC9053].
Other: The key is determined by decoding and decrypting one of Other: The key is determined by decoding and decrypting one of
the recipient structures. the recipient structures.
4. Call the decryption algorithm with K (the decryption key to use) 4. Call the decryption algorithm with K (the decryption key to use)
and C (the ciphertext). and C (the ciphertext).
6. MAC Objects 6. MAC Objects
COSE supports two different MAC structures. COSE_MAC0 is used when a COSE supports two different MAC structures. COSE_MAC0 is used when a
recipient structure is not needed because the key to be used is recipient structure is not needed because the key to be used is
implicitly known. COSE_MAC is used for all other cases. These implicitly known. COSE_MAC is used for all other cases. These
include a requirement for multiple recipients, the key being unknown, include a requirement for multiple recipients, the key being unknown,
or a recipient algorithm of other than direct. or a recipient algorithm other than direct.
In this section, we describe the structure and methods to be used In this section, we describe the structure and methods to be used
when doing MAC authentication in COSE. This document allows for the when doing MAC authentication in COSE. This document allows for the
use of all of the same classes of recipient algorithms as are allowed use of all of the same classes of recipient algorithms as are allowed
for encryption. for encryption.
When using MAC operations, there are two modes in which they can be There are two modes in which MAC operations can be used. The first
used. The first is just a check that the content has not been is just a check that the content has not been changed since the MAC
changed since the MAC was computed. Any class of recipient algorithm was computed. Any class of recipient algorithm can be used for this
can be used for this purpose. The second mode is to both check that purpose. The second mode is to both check that the content has not
the content has not been changed since the MAC was computed and to been changed since the MAC was computed and use the recipient
use the recipient algorithm to verify who sent it. The classes of algorithm to verify who sent it. The classes of recipient algorithms
recipient algorithms that support this are those that use a pre- that support this are those that use a preshared secret or do static-
shared secret or do static-static (SS) key agreement (without the key static (SS) key agreement (without the key wrap step). In both of
wrap step). In both of these cases, the entity that created and sent these cases, the entity that created and sent the message MAC can be
the message MAC can be validated. (This knowledge of the sender validated. (This knowledge of the sender assumes that there are only
assumes that there are only two parties involved and that you did not two parties involved and that you did not send the message to
send the message to yourself.) The origination property can be yourself.) The origination property can be obtained with both of the
obtained with both of the MAC message structures. MAC message structures.
6.1. MACed Message with Recipients 6.1. MACed Message with Recipients
The multiple recipient MACed message uses two structures: the A multiple-recipient MACed message uses two structures: the COSE_Mac
COSE_Mac structure defined in this section for carrying the body and structure defined in this section for carrying the body and the
the COSE_recipient structure (Section 5.1) to hold the key used for COSE_recipient structure (Section 5.1) to hold the key used for the
the MAC computation. Examples of MACed messages can be found in MAC computation. Examples of MACed messages can be found in
Appendix C.5. Appendix C.5.
The MAC structure can be encoded as either tagged or untagged The MAC structure can be encoded as either tagged or untagged
depending on the context it will be used in. A tagged COSE_Mac depending on the context it will be used in. A tagged COSE_Mac
structure is identified by the CBOR tag 97. The CDDL fragment that structure is identified by the CBOR tag 97. The CDDL fragment that
represents this is: represents this is:
COSE_Mac_Tagged = #6.97(COSE_Mac) COSE_Mac_Tagged = #6.97(COSE_Mac)
The COSE_Mac structure is a CBOR array. The fields of the array in The COSE_Mac structure is a CBOR array. The fields of the array, in
order are: order, are:
protected: This is as described in Section 3. protected: This is as described in Section 3.
unprotected: This is as described in Section 3. unprotected: This is as described in Section 3.
payload: This field contains the serialized content to be MACed. If payload: This field contains the serialized content to be MACed. If
the payload is not present in the message, the application is the payload is not present in the message, the application is
required to supply the payload separately. The payload is wrapped required to supply the payload separately. The payload is wrapped
in a bstr to ensure that it is transported without changes. If in a bstr to ensure that it is transported without changes. If
the payload is transported separately (i.e., detached content), the payload is transported separately (i.e., detached content),
skipping to change at page 32, line 36 skipping to change at line 1453
6.2. MACed Messages with Implicit Key 6.2. MACed Messages with Implicit Key
In this section, we describe the structure and methods to be used In this section, we describe the structure and methods to be used
when doing MAC authentication for those cases where the recipient is when doing MAC authentication for those cases where the recipient is
implicitly known. implicitly known.
The MACed message uses the COSE_Mac0 structure defined in this The MACed message uses the COSE_Mac0 structure defined in this
section for carrying the body. Examples of MACed messages with an section for carrying the body. Examples of MACed messages with an
implicit key can be found in Appendix C.6. implicit key can be found in Appendix C.6.
The MAC structure can be encoded as either tagged or untagged The MAC structure can be encoded as either tagged or untagged,
depending on the context it will be used in. A tagged COSE_Mac0 depending on the context it will be used in. A tagged COSE_Mac0
structure is identified by the CBOR tag 17. The CDDL fragment that structure is identified by the CBOR tag 17. The CDDL fragment that
represents this is: represents this is:
COSE_Mac0_Tagged = #6.17(COSE_Mac0) COSE_Mac0_Tagged = #6.17(COSE_Mac0)
The COSE_Mac0 structure is a CBOR array. The fields of the array in The COSE_Mac0 structure is a CBOR array. The fields of the array, in
order are: order, are:
protected: This is as described in Section 3. protected: This is as described in Section 3.
unprotected: This is as described in Section 3. unprotected: This is as described in Section 3.
payload: This is as described in Section 6.1. payload: This is as described in Section 6.1.
tag: This field contains the MAC value. tag: This field contains the MAC value.
The CDDL fragment that corresponds to the above text is: The CDDL fragment that corresponds to the above text is:
skipping to change at page 33, line 19 skipping to change at line 1483
COSE_Mac0 = [ COSE_Mac0 = [
Headers, Headers,
payload : bstr / nil, payload : bstr / nil,
tag : bstr, tag : bstr,
] ]
6.3. How to Compute and Verify a MAC 6.3. How to Compute and Verify a MAC
In order to get a consistent encoding of the data to be In order to get a consistent encoding of the data to be
authenticated, the MAC_structure is used to have a canonical form. authenticated, the MAC_structure is used to have a canonical form.
The MAC_structure is a CBOR array. The fields of the MAC_structure The MAC_structure is a CBOR array. The fields of the MAC_structure,
in order are: in order, are:
1. A context text string that identifies the structure that is being 1. A context text string that identifies the structure that is being
encoded. This context text string is "MAC" for the COSE_Mac encoded. This context text string is "MAC" for the COSE_Mac
structure. This context text string is "MAC0" for the COSE_Mac0 structure. This context text string is "MAC0" for the COSE_Mac0
structure. structure.
2. The protected attributes from the COSE_MAC structure. If there 2. The protected attributes from the COSE_MAC structure. If there
are no protected attributes, a zero-length bstr is used. are no protected attributes, a zero-length bstr is used.
3. The externally supplied data from the application encoded as a 3. The externally supplied data from the application, encoded as a
bstr type. If this field is not supplied, it defaults to a zero- bstr type. If this field is not supplied, it defaults to a zero-
length byte string. (See Section 4.3 for application guidance on length byte string. (See Section 4.3 for application guidance on
constructing this field.) constructing this field.)
4. The payload to be MACed encoded in a bstr type. The payload is 4. The payload to be MACed, encoded in a bstr type. The payload is
placed here independent of how it is transported. placed here, independent of how it is transported.
The CDDL fragment that corresponds to the above text is: The CDDL fragment that corresponds to the above text is:
MAC_structure = [ MAC_structure = [
context : "MAC" / "MAC0", context : "MAC" / "MAC0",
protected : empty_or_serialized_map, protected : empty_or_serialized_map,
external_aad : bstr, external_aad : bstr,
payload : bstr payload : bstr
] ]
The steps to compute a MAC are: The steps to compute a MAC are:
1. Create a MAC_structure and populate it with the appropriate 1. Create a MAC_structure and populate it with the appropriate
fields. fields.
2. Create the value ToBeMaced by encoding the MAC_structure to a 2. Create the value ToBeMaced by encoding the MAC_structure to a
byte string, using the encoding described in Section 9. byte string, using the encoding described in Section 9.
3. Call the MAC creation algorithm passing in K (the key to use), 3. Call the MAC creation algorithm, passing in K (the key to use),
alg (the algorithm to MAC with), and ToBeMaced (the value to alg (the algorithm to MAC with), and ToBeMaced (the value to
compute the MAC on). compute the MAC on).
4. Place the resulting MAC in the 'tag' field of the COSE_Mac or 4. Place the resulting MAC in the "tag" field of the COSE_Mac or
COSE_Mac0 structure. COSE_Mac0 structure.
5. For COSE_Mac structures, encrypt and encode the MAC key for each 5. For COSE_Mac structures, encrypt and encode the MAC key for each
recipient of the message. recipient of the message.
The steps to verify a MAC are: The steps to verify a MAC are:
1. Create a MAC_structure and populate it with the appropriate 1. Create a MAC_structure and populate it with the appropriate
fields. fields.
2. Create the value ToBeMaced by encoding the MAC_structure to a 2. Create the value ToBeMaced by encoding the MAC_structure to a
byte string, using the encoding described in Section 9. byte string, using the encoding described in Section 9.
3. For COSE_Mac structures, obtain the cryptographic key from one of 3. For COSE_Mac structures, obtain the cryptographic key from one of
the recipients of the message. the recipients of the message.
4. Call the MAC creation algorithm passing in K (the key to use), 4. Call the MAC creation algorithm, passing in K (the key to use),
alg (the algorithm to MAC with), and ToBeMaced (the value to alg (the algorithm to MAC with), and ToBeMaced (the value to
compute the MAC on). compute the MAC on).
5. Compare the MAC value to the 'tag' field of the COSE_Mac or 5. Compare the MAC value to the "tag" field of the COSE_Mac or
COSE_Mac0 structure. COSE_Mac0 structure.
7. Key Objects 7. Key Objects
A COSE Key structure is built on a CBOR map. The set of common A COSE Key structure is built on a CBOR map. The set of common
parameters that can appear in a COSE Key can be found in the IANA parameters that can appear in a COSE Key can be found in the IANA
"COSE Key Common Parameters" registry (Section 11.2). Additional "COSE Key Common Parameters" registry (Section 11.2). Additional
parameters defined for specific key types can be found in the IANA parameters defined for specific key types can be found in the IANA
"COSE Key Type Parameters" registry ([COSE.KeyParameters]). "COSE Key Type Parameters" registry [COSE.KeyTypes].
A COSE Key Set uses a CBOR array object as its underlying type. The A COSE Key Set uses a CBOR array object as its underlying type. The
values of the array elements are COSE Keys. A COSE Key Set MUST have values of the array elements are COSE Keys. A COSE Key Set MUST have
at least one element in the array. Examples of COSE Key Sets can be at least one element in the array. Examples of COSE Key Sets can be
found in Appendix C.7. found in Appendix C.7.
Each element in a COSE Key Set MUST be processed independently. If Each element in a COSE Key Set MUST be processed independently. If
one element in a COSE Key Set is either malformed or uses a key that one element in a COSE Key Set is either malformed or uses a key that
is not understood by an application, that key is ignored and the is not understood by an application, that key is ignored, and the
other keys are processed normally. other keys are processed normally.
The element "kty" is a required element in a COSE_Key map. The element "kty" is a required element in a COSE_Key map.
The CDDL grammar describing COSE_Key and COSE_KeySet is: The CDDL grammar describing COSE_Key and COSE_KeySet is:
COSE_Key = { COSE_Key = {
1 => tstr / int, ; kty 1 => tstr / int, ; kty
? 2 => bstr, ; kid ? 2 => bstr, ; kid
? 3 => tstr / int, ; alg ? 3 => tstr / int, ; alg
skipping to change at page 35, line 25 skipping to change at line 1585
* label => values * label => values
} }
COSE_KeySet = [+COSE_Key] COSE_KeySet = [+COSE_Key]
7.1. COSE Key Common Parameters 7.1. COSE Key Common Parameters
This document defines a set of common parameters for a COSE Key This document defines a set of common parameters for a COSE Key
object. Table 4 provides a summary of the parameters defined in this object. Table 4 provides a summary of the parameters defined in this
section. There are also parameters that are defined for specific key section. There are also parameters that are defined for specific key
types. Key-type-specific parameters can be found in types. Key-type-specific parameters can be found in [RFC9053].
[I-D.ietf-cose-rfc8152bis-algs].
+=========+=======+========+============+====================+ +=========+=======+========+============+====================+
| Name | Label | CBOR | Value | Description | | Name | Label | CBOR | Value | Description |
| | | Type | Registry | | | | | Type | Registry | |
+=========+=======+========+============+====================+ +=========+=======+========+============+====================+
| kty | 1 | tstr / | COSE Key | Identification of | | kty | 1 | tstr / | COSE Key | Identification of |
| | | int | Types | the key type | | | | int | Types | the key type |
+---------+-------+--------+------------+--------------------+ +---------+-------+--------+------------+--------------------+
| kid | 2 | bstr | | Key identification | | kid | 2 | bstr | | Key identification |
| | | | | value -- match to | | | | | | value -- match to |
| | | | | kid in message | | | | | | "kid" in message |
+---------+-------+--------+------------+--------------------+ +---------+-------+--------+------------+--------------------+
| alg | 3 | tstr / | COSE | Key usage | | alg | 3 | tstr / | COSE | Key usage |
| | | int | Algorithms | restriction to | | | | int | Algorithms | restriction to |
| | | | | this algorithm | | | | | | this algorithm |
+---------+-------+--------+------------+--------------------+ +---------+-------+--------+------------+--------------------+
| key_ops | 4 | [+ | | Restrict set of | | key_ops | 4 | [+ | | Restrict set of |
| | | (tstr/ | | permissible | | | | (tstr/ | | permissible |
| | | int)] | | operations | | | | int)] | | operations |
+---------+-------+--------+------------+--------------------+ +---------+-------+--------+------------+--------------------+
| Base IV | 5 | bstr | | Base IV to be xor- | | Base IV | 5 | bstr | | Base IV to be xor- |
skipping to change at page 36, line 11 skipping to change at line 1619
+---------+-------+--------+------------+--------------------+ +---------+-------+--------+------------+--------------------+
Table 4: Key Map Labels Table 4: Key Map Labels
kty: This parameter is used to identify the family of keys for this kty: This parameter is used to identify the family of keys for this
structure and, thus, the set of key-type-specific parameters to be structure and, thus, the set of key-type-specific parameters to be
found. The set of values defined in this document can be found in found. The set of values defined in this document can be found in
[COSE.KeyTypes]. This parameter MUST be present in a key object. [COSE.KeyTypes]. This parameter MUST be present in a key object.
Implementations MUST verify that the key type is appropriate for Implementations MUST verify that the key type is appropriate for
the algorithm being processed. The key type MUST be included as the algorithm being processed. The key type MUST be included as
part of the trust decision process. part of the trust-decision process.
alg: This parameter is used to restrict the algorithm that is used alg: This parameter is used to restrict the algorithm that is used
with the key. If this parameter is present in the key structure, with the key. If this parameter is present in the key structure,
the application MUST verify that this algorithm matches the the application MUST verify that this algorithm matches the
algorithm for which the key is being used. If the algorithms do algorithm for which the key is being used. If the algorithms do
not match, then this key object MUST NOT be used to perform the not match, then this key object MUST NOT be used to perform the
cryptographic operation. Note that the same key can be in a cryptographic operation. Note that the same key can be in a
different key structure with a different or no algorithm different key structure with a different or no algorithm
specified; however, this is considered to be a poor security specified; however, this is considered to be a poor security
practice. practice.
kid: This parameter is used to give an identifier for a key. The kid: This parameter is used to give an identifier for a key. The
identifier is not structured and can be anything from a user- identifier is not structured and can be anything from a user-
provided byte string to a value computed on the public portion of provided byte string to a value computed on the public portion of
the key. This field is intended for matching against a 'kid' the key. This field is intended for matching against a "kid"
parameter in a message in order to filter down the set of keys parameter in a message in order to filter down the set of keys
that need to be checked. The value of the identifier is not a that need to be checked. The value of the identifier is not a
unique value and can occur in other key objects, even for unique value and can occur in other key objects, even for
different keys. different keys.
key_ops: This parameter is defined to restrict the set of operations key_ops: This parameter is defined to restrict the set of operations
that a key is to be used for. The value of the field is an array that a key is to be used for. The value of the field is an array
of values from Table 5. Algorithms define the values of key ops of values from Table 5. Algorithms define the values of key ops
that are permitted to appear and are required for specific that are permitted to appear and are required for specific
operations. The set of values matches that in [RFC7517] and operations. The set of values matches that in [RFC7517] and
[W3C.WebCrypto]. [W3C.WebCrypto].
Base IV: This parameter is defined to carry the base portion of an Base IV: This parameter is defined to carry the base portion of an
IV. It is designed to be used with the Partial IV header IV. It is designed to be used with the Partial IV header
parameter defined in Section 3.1. This field provides the ability parameter defined in Section 3.1. This field provides the ability
to associate a Base IV with a key that is then modified on a per to associate a Base IV with a key that is then modified on a per-
message basis with the Partial IV. message basis with the Partial IV.
Extreme care needs to be taken when using a Base IV in an Extreme care needs to be taken when using a Base IV in an
application. Many encryption algorithms lose security if the same application. Many encryption algorithms lose security if the same
IV is used twice. IV is used twice.
If different keys are derived for each sender, starting at the If different keys are derived for each sender, starting at the
same Base IV is likely to satisfy this condition. If the same key same Base IV is likely to satisfy this condition. If the same key
is used for multiple senders, then the application needs to is used for multiple senders, then the application needs to
provide for a method of dividing the IV space up between the provide for a method of dividing the IV space up between the
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+---------+-------+----------------------------------------------+ +---------+-------+----------------------------------------------+
| MAC | 9 | The key is used for creating MACs. | | MAC | 9 | The key is used for creating MACs. |
| create | | | | create | | |
+---------+-------+----------------------------------------------+ +---------+-------+----------------------------------------------+
| MAC | 10 | The key is used for validating MACs. | | MAC | 10 | The key is used for validating MACs. |
| verify | | | | verify | | |
+---------+-------+----------------------------------------------+ +---------+-------+----------------------------------------------+
Table 5: Key Operation Values Table 5: Key Operation Values
8. Taxonomy of Algorithms used by COSE 8. Taxonomy of Algorithms Used by COSE
In this section, a taxonomy of the different algorithm types that can In this section, a taxonomy of the different algorithm types that can
be used in COSE is laid out. This taxonomy should not be considered be used in COSE is laid out. This taxonomy should not be considered
to be exhaustive. New algorithms will be created which will not fit to be exhaustive. New algorithms will be created that will not fit
into this taxonomy. into this taxonomy.
8.1. Signature Algorithms 8.1. Signature Algorithms
Signature algorithms provide data origination and data integrity Signature algorithms provide data-origination and data-integrity
services. Data origination provides the ability to infer who services. Data origination provides the ability to infer who
originated the data based on who signed the data. Data integrity originated the data based on who signed the data. Data integrity
provides the ability to verify that the data has not been modified provides the ability to verify that the data has not been modified
since it was signed. since it was signed.
There are two general signature algorithm schemes. The first is There are two general signature algorithm schemes. The first is
signature with appendix. In this scheme, the message content is signature with appendix. In this scheme, the message content is
processed and a signature is produced; the signature is called the processed and a signature is produced; the signature is called the
appendix. This is the scheme used by algorithms such as ECDSA and appendix. This is the scheme used by algorithms such as ECDSA and
the RSA Probabilistic Signature Scheme (RSASSA-PSS). (In fact, the the RSA Probabilistic Signature Scheme (RSASSA-PSS). (In fact, the
SSA in RSASSA-PSS stands for Signature Scheme with Appendix.) SSA in RSASSA-PSS stands for Signature Scheme with Appendix.)
The signature functions for this scheme are: The signature functions for this scheme are:
signature = Sign(message content, key) signature = Sign(message content, key)
valid = Verification(message content, key, signature) valid = Verification(message content, key, signature)
The second scheme is signature with message recovery (an example of The second scheme is signature with message recovery; an example of
such an algorithm is [PVSig]). In this scheme, the message content such an algorithm is [PVSig]. In this scheme, the message content is
is processed, but part of it is included in the signature. Moving processed, but part of it is included in the signature. Moving bytes
bytes of the message content into the signature allows for smaller of the message content into the signature allows for smaller
signatures; the signature size is still potentially large, but the signatures; the signature size is still potentially large, but the
message content has shrunk. This has implications for systems message content has shrunk. This has implications for systems
implementing these algorithms and for applications that use them. implementing these algorithms and applications that use them. The
The first is that the message content is not fully available until first is that the message content is not fully available until after
after a signature has been validated. Until that point, the part of a signature has been validated. Until that point, the part of the
the message contained inside of the signature is unrecoverable. The message contained inside of the signature is unrecoverable. The
second is that the security analysis of the strength of the signature second implication is that the security analysis of the strength of
can be very much dependent on the structure of the message content. the signature can be very much dependent on the structure of the
Finally, in the event that multiple signatures are applied to a message content. Finally, in the event that multiple signatures are
message, all of the signature algorithms are going to be required to applied to a message, all of the signature algorithms are going to be
consume the same bytes of message content. This means that the required to consume the same bytes of message content. This means
mixing of the signature with message recovery and signature with that the mixing of the signature-with-message-recovery and signature-
appendix schemes in a single message is not supported. with-appendix schemes in a single message is not supported.
The signature functions for this scheme are: The signature functions for this scheme are:
signature, message sent = Sign(message content, key) signature, message sent = Sign(message content, key)
valid, message content = Verification(message sent, key, signature) valid, message content = Verification(message sent, key, signature)
No message recovery signature algorithms have been formally defined No message recovery signature algorithms have been formally defined
for COSE yet, and given the new constraints arising from this for COSE yet. Given the new constraints arising from this scheme,
schemes, while some of these issues have already been identified while some of these issues have already been identified, there is a
there is a high probability that additional issues will arise when high probability that additional issues will arise when integrating
integrating message recovery signature algorithms. The first message recovery signature algorithms. The first algorithm defined
algorithm defined is going to need to make decisions about these is going to need to make decisions about these issues, and those
issues and those decisions are likely to be binding on any further decisions are likely to be binding on any further algorithms defined.
algorithms defined.
We use the following terms below: We use the following terms below:
message content bytes: The byte provided by the application to be message content bytes: The byte provided by the application to be
signed. signed.
to-be-signed bytes: The byte string passed into the signature to-be-signed bytes: The byte string passed into the signature
algorithm. algorithm.
recovered bytes: The bytes recovered during the signature recovered bytes: The bytes recovered during the signature
verification process. verification process.
Some of the issues that have already been identified are: Some of the issues that have already been identified are:
* The to-be-signed bytes are not the same as the message content * The to-be-signed bytes are not the same as the message content
bytes. This is because we build a larger to-be-signed message bytes. This is because we build a larger to-be-signed message
during the signature processing. The recovered bytes length may during the signature processing. The length of the recovered
exceed the message content length, but not the length of the to- bytes may exceed the length of the message content, but not the
be-signed bytes. This may lead to privacy considerations if, for length of the to-be-signed bytes. This may lead to privacy
example, the externally supplied data contains confidential considerations if, for example, the externally supplied data
information. contains confidential information.
* There may be difficulties in determining where the recovered bytes * There may be difficulties in determining where the recovered bytes
match up with the to-be-signed bytes, because the recovered bytes match up with the to-be-signed bytes, because the recovered bytes
contains data not in the message content bytes. One possible contain data not in the message content bytes. One possible
option would be to create a padding scheme to prevent that. option would be to create a padding scheme to prevent that.
* Not all message recovery signature algorithms take the recovered * Not all message recovery signature algorithms take the recovered
bytes from the end of the to-be-signed bytes. This is a problem bytes from the end of the to-be-signed bytes. This is a problem,
because the message content bytes are at the end of the to-be- because the message content bytes are at the end of the to-be-
signed bytes. If the bytes to be recovered are taken from the signed bytes. If the bytes to be recovered are taken from the
start of the to-be-signed bytes then, by default, none of the start of the to-be-signed bytes, then, by default, none of the
message content bytes may be included in the recovered bytes. One message content bytes may be included in the recovered bytes. One
possible option to deal with this is to reverse the to-be-signed possible option to deal with this is to reverse the to-be-signed
data in the event that recovered bytes are taken from the start data in the event that recovered bytes are taken from the start
rather than end of the to-be-signed bytes. rather than the end of the to-be-signed bytes.
Signature algorithms are used with the COSE_Signature and COSE_Sign1 Signature algorithms are used with the COSE_Signature and COSE_Sign1
structures. At the time of this writing, only signatures with structures. At the time of this writing, only signatures with
appendixes are defined for use with COSE; however, considerable appendices are defined for use with COSE; however, considerable
interest has been expressed in using a signature with message interest has been expressed in using a signature-with-message-
recovery algorithm due to the effective size reduction that is recovery algorithm, due to the effective size reduction that is
possible. possible.
8.2. Message Authentication Code (MAC) Algorithms 8.2. Message Authentication Code (MAC) Algorithms
Message Authentication Codes (MACs) provide data authentication and Message Authentication Codes (MACs) provide data authentication and
integrity protection. They provide either no or very limited data integrity protection. They provide either no or very limited data
origination. A MAC, for example, cannot be used to prove the origination. A MAC, for example, cannot be used to prove the
identity of the sender to a third party. identity of the sender to a third party.
MACs use the same scheme as signature with appendix algorithms. The MACs use the same scheme as signature-with-appendix algorithms. The
message content is processed and an authentication code is produced. message content is processed, and an authentication code is produced.
The authentication code is frequently called a tag. The authentication code is frequently called a tag.
The MAC functions are: The MAC functions are:
tag = MAC_Create(message content, key) tag = MAC_Create(message content, key)
valid = MAC_Verify(message content, key, tag) valid = MAC_Verify(message content, key, tag)
MAC algorithms can be based on either a block cipher algorithm (i.e., MAC algorithms can be based on either a block cipher algorithm (i.e.,
AES-MAC) or a hash algorithm (i.e., a Hash-based Message AES-MAC) or a hash algorithm (i.e., a Hash-based Message
Authentication Code (HMAC)). [I-D.ietf-cose-rfc8152bis-algs] defines Authentication Code (HMAC)). [RFC9053] defines a MAC algorithm using
a MAC algorithm using each of these constructions. each of these constructions.
MAC algorithms are used in the COSE_Mac and COSE_Mac0 structures. MAC algorithms are used in the COSE_Mac and COSE_Mac0 structures.
8.3. Content Encryption Algorithms 8.3. Content Encryption Algorithms
Content encryption algorithms provide data confidentiality for Content encryption algorithms provide data confidentiality for
potentially large blocks of data using a symmetric key. They provide potentially large blocks of data using a symmetric key. They provide
integrity on the data that was encrypted; however, they provide integrity on the data that was encrypted; however, they provide
either no or very limited data origination. (One cannot, for either no or very limited data origination. (One cannot, for
example, be used to prove the identity of the sender to a third example, be used to prove the identity of the sender to a third
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those that support authentication both of the content and additional those that support authentication both of the content and additional
data. The encryption process will generate some type of data. The encryption process will generate some type of
authentication value, but that value may be either explicit or authentication value, but that value may be either explicit or
implicit in terms of the algorithm definition. For simplicity's implicit in terms of the algorithm definition. For simplicity's
sake, the authentication code will normally be defined as being sake, the authentication code will normally be defined as being
appended to the ciphertext stream. The encryption functions are: appended to the ciphertext stream. The encryption functions are:
ciphertext = Encrypt(message content, key, additional data) ciphertext = Encrypt(message content, key, additional data)
valid, message content = Decrypt(ciphertext, key, additional data) valid, message content = Decrypt(ciphertext, key, additional data)
Most AEAD algorithms are logically defined as returning the message Most AEAD algorithms are logically defined as returning the message
content only if the decryption is valid. Many but not all content only if the decryption is valid. Many, but not all,
implementations will follow this convention. The message content implementations will follow this convention. The message content
MUST NOT be used if the decryption does not validate. MUST NOT be used if the decryption does not validate.
These algorithms are used in COSE_Encrypt and COSE_Encrypt0. These algorithms are used in COSE_Encrypt and COSE_Encrypt0.
8.4. Key Derivation Functions (KDFs) 8.4. Key Derivation Functions (KDFs)
KDFs are used to take some secret value and generate a different one. KDFs are used to take some secret value and generate a different one.
The secret value comes in three flavors: The secret value comes in three flavors:
* Secrets that are uniformly random: This is the type of secret that * Secrets that are uniformly random. This is the type of secret
is created by a good random number generator. that is created by a good random number generator.
* Secrets that are not uniformly random: This is type of secret that * Secrets that are not uniformly random. This is the type of secret
is created by operations like key agreement. that is created by operations like key agreement.
* Secrets that are not random: This is the type of secret that * Secrets that are not random. This is the type of secret that
people generate for things like passwords. people generate for things like passwords.
General KDFs work well with the first type of secret, can do General KDFs work well with the first type of secret, can do
reasonably well with the second type of secret, and generally do reasonably well with the second type of secret, and generally do
poorly with the last type of secret. Functions like Argon2 poorly with the last type of secret. Functions like Argon2
[I-D.irtf-cfrg-argon2] need to be used for non-random secrets. [CFRG-ARGON2] need to be used for nonrandom secrets.
The same KDF can be set up to deal with the first two types of The same KDF can be set up to deal with the first two types of
secrets in a different way. The KDF defined in section 5.1 of secrets in different ways. The KDF defined in Section 5.1 of
[I-D.ietf-cose-rfc8152bis-algs] is such a function. This is [RFC9053] is such a function. This is reflected in the set of
reflected in the set of algorithms defined around the HMAC-based algorithms defined around the HMAC-based Extract-and-Expand Key
Extract-and-Expand Key Derivation Function (HKDF). Derivation Function (HKDF).
When using KDFs, one component that is included is context When using KDFs, one component that is included is context
information. Context information is used to allow for different information. Context information is used to allow for different
keying information to be derived from the same secret. The use of keying information to be derived from the same secret. The use of
context-based keying material is considered to be a good security context-based keying material is considered to be a good security
practice. practice.
8.5. Content Key Distribution Methods 8.5. Content Key Distribution Methods
Content key distribution methods (recipient algorithms) can be Content key distribution methods (recipient algorithms) can be
defined into a number of different classes. COSE has the ability to defined into a number of different classes. COSE has the ability to
support many classes of recipient algorithms. In this section, a support many classes of recipient algorithms. In this section, a
number of classes are listed. The names of the recipient algorithm number of classes are listed. The names of the recipient algorithm
classes used here are the same as those defined in [RFC7516]. Other classes used here are the same as those defined in [RFC7516]. Other
specifications use different terms for the recipient algorithm specifications use different terms for the recipient algorithm
classes or do not support some of the recipient algorithm classes. classes or do not support some of the recipient algorithm classes.
8.5.1. Direct Encryption 8.5.1. Direct Encryption
The direct encryption class algorithms share a secret between the The Direct Encryption class of algorithms share a secret between the
sender and the recipient that is used either directly or after sender and the recipient that is used either directly or after
manipulation as the CEK. When direct encryption mode is used, it manipulation as the CEK. When direct-encryption mode is used, it
MUST be the only mode used on the message. MUST be the only mode used on the message.
The COSE_Recipient structure for the recipient is organized as The COSE_Recipient structure for the recipient is organized as
follows: follows:
* The 'protected' field MUST be a zero-length byte string unless it * The "protected" field MUST be a zero-length byte string unless it
is used in the computation of the content key. is used in the computation of the content key.
* The 'alg' header parameter MUST be present. * The "alg" header parameter MUST be present.
* A header parameter identifying the shared secret SHOULD be * A header parameter identifying the shared secret SHOULD be
present. present.
* The 'ciphertext' field MUST be a zero-length byte string. * The "ciphertext" field MUST be a zero-length byte string.
* The 'recipients' field MUST be absent. * The "recipients" field MUST be absent.
8.5.2. Key Wrap 8.5.2. Key Wrap
In key wrap mode, the CEK is randomly generated and that key is then In key wrap mode, the CEK is randomly generated, and that key is then
encrypted by a shared secret between the sender and the recipient. encrypted by a shared secret between the sender and the recipient.
All of the currently defined key wrap algorithms for COSE are AE All of the currently defined key wrap algorithms for COSE are AE
algorithms. Key wrap mode is considered to be superior to direct algorithms. Key wrap mode is considered to be superior to Direct
encryption if the system has any capability for doing random key Encryption if the system has any capability for doing random-key
generation. This is because the shared key is used to wrap random generation. This is because the shared key is used to wrap random
data rather than data that has some degree of organization and may in data rather than data that has some degree of organization and may in
fact be repeating the same content. The use of key wrap loses the fact be repeating the same content. The use of key wrap loses the
weak data origination that is provided by the direct encryption weak data origination that is provided by the direct-encryption
algorithms. algorithms.
The COSE_Recipient structure for the recipient is organized as The COSE_Recipient structure for the recipient is organized as
follows: follows:
* The 'protected' field MUST be absent if the key wrap algorithm is * The "protected" field MUST be absent if the key wrap algorithm is
an AE algorithm. an AE algorithm.
* The 'recipients' field is normally absent, but can be used. * The "recipients" field is normally absent but can be used.
Applications MUST deal with a recipient field being present that Applications MUST deal with a recipient field being present that
has an unsupported algorithm. Failing to decrypt that specific has an unsupported algorithm. Failing to decrypt that specific
recipient is an acceptable way of dealing with it. Failing to recipient is an acceptable way of dealing with it. Failing to
process the message is not an acceptable way of dealing with it. process the message is not an acceptable way of dealing with it.
* The plaintext to be encrypted is the key from next layer down * The plaintext to be encrypted is the key from the next layer down
(usually the content layer). (usually the content layer).
* At a minimum, the 'unprotected' field MUST contain the 'alg' * At a minimum, the "unprotected" field MUST contain the "alg"
header parameter and SHOULD contain a header parameter identifying header parameter and SHOULD contain a header parameter identifying
the shared secret. the shared secret.
8.5.3. Key Transport 8.5.3. Key Transport
Key transport mode is also called key encryption mode in some Key transport mode is also called key encryption mode in some
standards. Key transport mode differs from key wrap mode in that it standards. Key transport mode differs from key wrap mode in that it
uses an asymmetric encryption algorithm rather than a symmetric uses an asymmetric encryption algorithm rather than a symmetric
encryption algorithm to protect the key. A set of key transport encryption algorithm to protect the key. A set of key transport
algorithms are defined in [RFC8230]. algorithms is defined in [RFC8230].
When using a key transport algorithm, the COSE_Recipient structure When using a key transport algorithm, the COSE_Recipient structure
for the recipient is organized as follows: for the recipient is organized as follows:
* The 'protected' field MUST be absent. * The "protected" field MUST be absent.
* The plaintext to be encrypted is the key from the next layer down * The plaintext to be encrypted is the key from the next layer down
(usually the content layer). (usually the content layer).
* At a minimum, the 'unprotected' field MUST contain the 'alg' * At a minimum, the "unprotected" field MUST contain the "alg"
header parameter and SHOULD contain a parameter identifying the header parameter and SHOULD contain a parameter identifying the
asymmetric key. asymmetric key.
8.5.4. Direct Key Agreement 8.5.4. Direct Key Agreement
The 'direct key agreement' class of recipient algorithms uses a key The Direct Key Agreement class of recipient algorithms uses a key
agreement method to create a shared secret. A KDF is then applied to agreement method to create a shared secret. A KDF is then applied to
the shared secret to derive a key to be used in protecting the data. the shared secret to derive a key to be used in protecting the data.
This key is normally used as a CEK or MAC key, but could be used for This key is normally used as a CEK or MAC key but could be used for
other purposes if more than two layers are in use (see Appendix B). other purposes if more than two layers are in use (see Appendix B).
The most commonly used key agreement algorithm is Diffie-Hellman, but The most commonly used key agreement algorithm is Diffie-Hellman, but
other variants exist. Since COSE is designed for a store and forward other variants exist. Since COSE is designed for a store-and-forward
environment rather than an online environment, many of the DH environment rather than an online environment, many of the DH
variants cannot be used as the receiver of the message cannot provide variants cannot be used, as the receiver of the message cannot
any dynamic key material. One side effect of this is that forward provide any dynamic key material. One side effect of this is that
secrecy (see [RFC4949]) is not achievable. A static key will always forward secrecy (see [RFC4949]) is not achievable. A static key will
be used for the receiver of the COSE object. always be used for the receiver of the COSE object.
Two variants of DH that are supported are: Two variants of DH that are supported are:
Ephemeral-Static (ES) DH: where the sender of the message creates Ephemeral-Static (ES) DH: The sender of the message creates a one-
a one-time DH key and uses a static key for the recipient. The time DH key and uses a static key for the recipient. The use of
use of the ephemeral sender key means that no additional random the ephemeral sender key means that no additional random input is
input is needed as this is randomly generated for each message. needed, as this is randomly generated for each message.
Static-Static (SS) DH: where a static key is used for both the Static-Static (SS) DH: A static key is used for both the sender and
sender and the recipient. The use of static keys allows for the the recipient. The use of static keys allows for the recipient to
recipient to get a weak version of data origination for the get a weak version of data origination for the message. When
message. When static-static key agreement is used, then some static-static key agreement is used, then some piece of unique
piece of unique data for the KDF is required to ensure that a data for the KDF is required to ensure that a different key is
different key is created for each message. created for each message.
When direct key agreement mode is used, there MUST be only one When direct key agreement mode is used, there MUST be only one
recipient in the message. This method creates the key directly, and recipient in the message. This method creates the key directly, and
that makes it difficult to mix with additional recipients. If that makes it difficult to mix with additional recipients. If
multiple recipients are needed, then the version with key wrap needs multiple recipients are needed, then the version with key wrap needs
to be used. to be used.
The COSE_Recipient structure for the recipient is organized as The COSE_Recipient structure for the recipient is organized as
follows: follows:
* At a minimum, headers MUST contain the 'alg' header parameter and * At a minimum, headers MUST contain the "alg" header parameter and
SHOULD contain a header parameter identifying the recipient's SHOULD contain a header parameter identifying the recipient's
asymmetric key. asymmetric key.
* The headers SHOULD identify the sender's key for the static-static * The headers SHOULD identify the sender's key for the static-static
versions and MUST contain the sender's ephemeral key for the versions and MUST contain the sender's ephemeral key for the
ephemeral-static versions. ephemeral-static versions.
8.5.5. Key Agreement with Key Wrap 8.5.5. Key Agreement with Key Wrap
Key Agreement with Key Wrap uses a randomly generated CEK. The CEK Key Agreement with Key Wrap uses a randomly generated CEK. The CEK
is then encrypted using a key wrap algorithm and a key derived from is then encrypted using a key wrap algorithm and a key derived from
the shared secret computed by the key agreement algorithm. The the shared secret computed by the key agreement algorithm. The
function for this would be: function for this would be:
encryptedKey = KeyWrap(KDF(DH-Shared, context), CEK) encryptedKey = KeyWrap(KDF(DH-Shared, context), CEK)
The COSE_Recipient structure for the recipient is organized as The COSE_Recipient structure for the recipient is organized as
follows: follows:
* The 'protected' field is fed into the KDF context structure. * The "protected" field is fed into the KDF context structure.
* The plaintext to be encrypted is the key from the next layer down * The plaintext to be encrypted is the key from the next layer down
(usually the content layer). (usually the content layer).
* The 'alg' header parameter MUST be present in the layer. * The "alg" header parameter MUST be present in the layer.
* A header parameter identifying the recipient's key SHOULD be * A header parameter identifying the recipient's key SHOULD be
present. A header parameter identifying the sender's key SHOULD present. A header parameter identifying the sender's key SHOULD
be present. be present.
9. CBOR Encoding Restrictions 9. CBOR Encoding Restrictions
This document limits the restrictions it imposes on how the CBOR This document limits the restrictions it imposes on how the CBOR
Encoder needs to work. It has been narrowed down to the following encoder needs to work. It has been narrowed down to the following
restrictions: restrictions:
* The restriction applies to the encoding of the Sig_structure, the * The restriction applies to the encoding of the COSE_KDF_Context,
Enc_structure, and the MAC_structure. the Sig_structure, the Enc_structure, and the MAC_structure.
* Encoding MUST be done using definite lengths and the value's * Encoding MUST be done using definite lengths, and the value's
length MUST be the minimum possible length. This means that the length MUST be the minimum possible length. This means that the
integer 1 is encoded as "0x01" and not "0x1801". integer 1 is encoded as "0x01" and not "0x1801".
* Applications MUST NOT generate messages with the same label used * Applications MUST NOT generate messages with the same label used
twice as a key in a single map. Applications MUST NOT parse and twice as a key in a single map. Applications MUST NOT parse and
process messages with the same label used twice as a key in a process messages with the same label used twice as a key in a
single map. Applications can enforce the parse and process single map. Applications can enforce the parse and process
requirement by using parsers that will fail the parse step or by requirement by using parsers that will fail the parse step or by
using parsers that will pass all keys to the application, and the using parsers that will pass all keys to the application, and the
application can perform the check for duplicate keys. application can perform the check for duplicate keys.
10. Application Profiling Considerations 10. Application Profiling Considerations
This document is designed to provide a set of security services, but This document is designed to provide a set of security services but
not impose algorithm implementation requirements for specific usage. not impose algorithm implementation requirements for specific usage.
The interoperability requirements are provided for how each of the The interoperability requirements are provided for how each of the
individual services are used and how the algorithms are to be used individual services are used and how the algorithms are to be used
for interoperability. The requirements about which algorithms and for interoperability. The requirements about which algorithms and
which services are needed are deferred to each application. which services are needed are deferred to each application.
An example of a profile can be found in [RFC8613] where one was An example of a profile can be found in [RFC8613], where one was
developed for carrying content in combination with CoAP headers. developed for carrying content in combination with CoAP headers.
It is intended that a profile of this document be created that It is intended that a profile of this document be created that
defines the interoperability requirements for that specific defines the interoperability requirements for that specific
application. This section provides a set of guidelines and topics application. This section provides a set of guidelines and topics
that need to be considered when profiling this document. that need to be considered when profiling this document.
* Applications need to determine the set of messages defined in this * Applications need to determine the set of messages defined in this
document that they will be using. The set of messages corresponds document that they will be using. The set of messages corresponds
fairly directly to the set of security services that are needed fairly directly to the needed set of security services security
and to the security levels needed. levels.
* Applications may define new header parameters for a specific * Applications may define new header parameters for a specific
purpose. Applications will often times select specific header purpose. Applications will oftentimes select specific header
parameters to use or not to use. For example, an application parameters to use or not to use. For example, an application
would normally state a preference for using either the IV or the would normally state a preference for using either the IV or the
Partial IV header parameter. If the Partial IV header parameter Partial IV header parameter. If the Partial IV header parameter
is specified, then the application also needs to define how the is specified, then the application also needs to define how the
fixed portion of the IV is determined. fixed portion of the IV is determined.
* When applications use externally defined authenticated data, they * When applications use externally defined authenticated data, they
need to define how that data is encoded. This document assumes need to define how that data is encoded. This document assumes
that the data will be provided as a byte string. More information that the data will be provided as a byte string. More information
can be found in Section 4.3. can be found in Section 4.3.
* Applications need to determine the set of security algorithms that * Applications need to determine the set of security algorithms that
are to be used. When selecting the algorithms to be used as the is to be used. When selecting the algorithms to be used as the
mandatory-to-implement set, consideration should be given to mandatory-to-implement set, consideration should be given to
choosing different types of algorithms when two are chosen for a choosing different types of algorithms when two are chosen for a
specific purpose. An example of this would be choosing HMAC- specific purpose. An example of this would be choosing HMAC-
SHA512 and AES-CMAC as different MAC algorithms; the construction SHA512 and AES-CMAC (Cipher-Based Message Authentication Code) as
is vastly different between these two algorithms. This means that different MAC algorithms; the construction is vastly different
a weakening of one algorithm would be unlikely to lead to a between these two algorithms. This means that a weakening of one
weakening of the other algorithms. Of course, these algorithms do algorithm would be unlikely to lead to a weakening of the other
not provide the same level of security and thus may not be algorithms. Of course, these algorithms do not provide the same
comparable for the desired security functionality. Additional level of security and thus may not be comparable for the desired
guidance can be found in [BCP201]. security functionality. Additional guidance can be found in
[BCP201].
* Applications may need to provide some type of negotiation or * Applications may need to provide some type of negotiation or
discovery method if multiple algorithms or message structures are discovery method if multiple algorithms or message structures are
permitted. The method can be as simple as requiring pre- permitted. The method can be as simple as requiring
configuration of the set of algorithms to providing a discovery preconfiguration of the set of algorithms to providing a discovery
method built into the protocol. S/MIME provided a number of method built into the protocol. S/MIME provided a number of
different ways to approach the problem that applications could different ways to approach the problem that applications could
follow: follow:
- Advertising in the message (S/MIME capabilities) [RFC5751]. - Advertising in the message (S/MIME capabilities) [RFC8551].
- Advertising in the certificate (capabilities extension) - Advertising in the certificate (capabilities extension)
[RFC4262]. [RFC4262].
- Minimum requirements for the S/MIME, which have been updated - Minimum requirements for the S/MIME, which have been updated
over time [RFC2633] [RFC5751] (note that [RFC2633] has been over time [RFC2633] [RFC5751] [RFC8551]. (Note that [RFC2633]
obsoleted by [RFC5751]). was obsoleted by [RFC3851], which was obsoleted by [RFC5751],
which was obsoleted by [RFC8551].)
11. IANA Considerations 11. IANA Considerations
The registries and registrations listed below were created during The registries and registrations listed below were defined by RFC
processing of RFC 8152 [RFC8152]. The majority of the following 8152 [RFC8152]. The majority of the following actions are to update
actions are to update the references to point to this document. the references to point to this document.
Note that while [I-D.ietf-cose-rfc8152bis-algs] also updates the Note that while [RFC9053] also updates the registries and
registries and registrations originally established by [RFC8152], the registrations originally established by [RFC8152], the requested
requested updates are mutually exclusive. The updates requested in updates are mutually exclusive. The updates requested in this
this document do not conflict or overlap with the updates requested document do not conflict or overlap with the updates requested in
in [I-D.ietf-cose-rfc8152bis-algs], and vice versa. [RFC9053], and vice versa.
11.1. COSE Header Parameters Registry 11.1. COSE Header Parameters Registry
IANA created a registry titled "COSE Header Parameters" as part of The "COSE Header Parameters" registry was defined by [RFC8152]. IANA
processing [RFC8152]. IANA is requested to update the reference for has updated the reference for this registry to point to this document
this registry from [RFC8152] to this document. IANA is also instead of [RFC8152]. IANA has also updated all entries that
requested to update the reference for all entries, except "counter referenced [RFC8152], except "counter signature" and
signature" and "CounterSignature0", in the table from [RFC8152] to "CounterSignature0", to refer to this document. The references for
this document. The reference for "counter signature" and "counter signature" and "CounterSignature0" continue to reference
"CounterSignature0" are to be left as-is. [RFC8152].
11.2. COSE Key Common Parameters Registry 11.2. COSE Key Common Parameters Registry
IANA created a registry titled "COSE Key Common Parameters" as part The "COSE Key Common Parameters" registry was defined [RFC8152].
of the processing of [RFC8152]. IANA is requested to update the IANA has updated the reference for this registry to point to this
reference for this registry from [RFC8152] to this document. IANA is document instead of [RFC8152]. IANA has also updated the entries
also requested to update the reference for entries in the table from that referenced [RFC8152] to refer to this document.
[RFC8152] to this document.
11.3. Media Type Registrations 11.3. Media Type Registrations
11.3.1. COSE Security Message 11.3.1. COSE Security Message
This section registers the 'application/cose' media type in the IANA has registered the "application/cose" media type in the "Media
"Media Types" registry. These media types are used to indicate that Types" registry. These media types are used to indicate that the
the content is a COSE message. content is a COSE message.
Type name: application Type name: application
Subtype name: cose Subtype name: cose
Required parameters: N/A Required parameters: N/A
Optional parameters: cose-type Optional parameters: cose-type
Encoding considerations: binary Encoding considerations: binary
Security considerations: See the Security Considerations section Security considerations: See the Security Considerations section of
of [[This Document]]. RFC 9052.
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: [[this document]] Published specification: RFC 9052
Applications that use this media type: IoT applications sending
security content over HTTP(S) transports.
Fragment identifier considerations: N/A Applications that use this media type: IoT applications sending
security content over HTTP(S) transports.
Additional information: Fragment identifier considerations: N/A
- Deprecated alias names for this type: N/A Additional information:
* Deprecated alias names for this type: N/A
- Magic number(s): N/A * Magic number(s): N/A
- File extension(s): cbor * File extension(s): cbor
- Macintosh file type code(s): N/A * Macintosh file type code(s): N/A
Person & email address to contact for further information: Person & email address to contact for further information: iesg@ietf
iesg@ietf.org .org
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: N/A Restrictions on usage: N/A
Author: Jim Schaad, ietf@augustcellars.com Author: Jim Schaad, ietf@augustcellars.com
Change Controller: IESG Change Controller: IESG
Provisional registration? No Provisional registration? No
11.3.2. COSE Key Media Type 11.3.2. COSE Key Media Type
This section registers the 'application/cose-key' and 'application/ IANA has registered the "application/cose-key" and "application/cose-
cose-key-set' media types in the "Media Types" registry. These media key-set" media types in the "Media Types" registry. These media
types are used to indicate, respectively, that content is a COSE_Key types are used to indicate, respectively, that content is a COSE_Key
or COSE_KeySet object. or COSE_KeySet object.
The template for registering 'application/cose-key' is: The template for "application/cose-key" is as follows:
Type name: application Type name: application
Subtype name: cose-key Subtype name: cose-key
Required parameters: N/A Required parameters: N/A
Optional parameters: N/A Optional parameters: N/A
Encoding considerations: binary Encoding considerations: binary
Security considerations: See the Security Considerations section
of [[This Document]].
Interoperability considerations: N/A Security considerations: See the Security Considerations section of
RFC 9052.
Published specification: [[this document]] Interoperability considerations: N/A
Applications that use this media type: Distribution of COSE based Published specification: RFC 9052
Applications that use this media type: Distribution of COSE-based
keys for IoT applications. keys for IoT applications.
Fragment identifier considerations: N/A Fragment identifier considerations: N/A
Additional information: Additional information:
* Deprecated alias names for this type: N/A
- Deprecated alias names for this type: N/A * Magic number(s): N/A
- Magic number(s): N/A * File extension(s): cbor
- File extension(s): cbor * Macintosh file type code(s): N/A
- Macintosh file type code(s): N/A Person & email address to contact for further information: iesg@ietf
.org
Person & email address to contact for further information: Intended usage: COMMON
iesg@ietf.org
Intended usage: COMMON Restrictions on usage: N/A
Restrictions on usage: N/A Author: Jim Schaad, ietf@augustcellars.com
Author: Jim Schaad, ietf@augustcellars.com Change Controller: IESG
Change Controller: IESG Provisional registration? No
Provisional registration? No The template for registering "application/cose-key-set" is:
The template for registering 'application/cose-key-set' is: Type name: application
Type name: application Subtype name: cose-key-set
Subtype name: cose-key-set Required parameters: N/A
Required parameters: N/A Optional parameters: N/A
Optional parameters: N/A Encoding considerations: binary
Encoding considerations: binary Security considerations: See the Security Considerations section of
Security considerations: See the Security Considerations section RFC 9052.
of [[This Document]].
Interoperability considerations: N/A Interoperability considerations: N/A
Published specification: [[this document]] Published specification: RFC 9052
Applications that use this media type: Distribution of COSE based Applications that use this media type: Distribution of COSE-based
keys for IoT applications. keys for IoT applications.
Fragment identifier considerations: N/A Fragment identifier considerations: N/A
Additional information:
- Deprecated alias names for this type: N/A Additional information:
* Deprecated alias names for this type: N/A
- Magic number(s): N/A * Magic number(s): N/A
- File extension(s): cbor * File extension(s): cbor
- Macintosh file type code(s): N/A * Macintosh file type code(s): N/A
Person & email address to contact for further information: Person & email address to contact for further information: iesg@ietf
iesg@ietf.org .org
Intended usage: COMMON Intended usage: COMMON
Restrictions on usage: N/A Restrictions on usage: N/A
Author: Jim Schaad, ietf@augustcellars.com Author: Jim Schaad, ietf@augustcellars.com
Change Controller: IESG Change Controller: IESG
Provisional registration? No Provisional registration? No
11.4. CoAP Content-Formats Registry 11.4. CoAP Content-Formats Registry
IANA added entries to the "CoAP Content-Formats" registry while IANA added entries to the "CoAP Content-Formats" registry as defined
processing [RFC8152]. IANA is requested to update the reference in [RFC8152]. IANA has updated the reference to point to this
value from [RFC8152] to [[This Document]]. document instead of [RFC8152].
11.5. CBOR Tags Registry 11.5. CBOR Tags Registry
IANA is requested to update the references from [RFC8152] to [[This IANA has updated the references to point to this document instead of
Document]]. [RFC8152].
11.6. Expert Review Instructions 11.6. Expert Review Instructions
All of the IANA registries established by [RFC8152] are, at least in All of the IANA registries established by [RFC8152] are, at least in
part, defined as expert review. This section gives some general part, defined as expert review. This section gives some general
guidelines for what the experts should be looking for, but they are guidelines for what the experts should be looking for, but they are
being designated as experts for a reason, so they should be given being designated as experts for a reason, so they should be given
substantial latitude. substantial latitude.
Expert reviewers should take into consideration the following points: Expert reviewers should take the following into consideration:
* Point squatting should be discouraged. Reviewers are encouraged * Point squatting should be discouraged. Reviewers are encouraged
to get sufficient information for registration requests to ensure to get sufficient information for registration requests to ensure
that the usage is not going to duplicate one that is already that the usage is not going to duplicate an existing registration
registered, and that the point is likely to be used in and that the code point is likely to be used in deployments. The
deployments. The zones tagged as private use are intended for zones tagged as private use are intended for testing purposes and
testing purposes and closed environments; code points in other closed environments; code points in other ranges should not be
ranges should not be assigned for testing. assigned for testing.
* Specifications are required for the standards track range of point * Specifications are required for the Standards Track range of code
assignment. Specifications should exist for specification point assignment. Specifications should exist for specification
required ranges, but early assignment before a specification is required ranges, but early assignment before a specification is
available is considered to be permissible. Specifications are available is considered to be permissible. Specifications are
needed for the first-come, first-serve range if they are expected needed for the first-come, first-serve range if the points are
to be used outside of closed environments in an interoperable way. expected to be used outside of closed environments in an
When specifications are not provided, the description provided interoperable way. When specifications are not provided, the
needs to have sufficient information to identify what the point is description provided needs to have sufficient information to
being used for. identify what the point is being used for.
* Experts should take into account the expected usage of fields when * Experts should take into account the expected usage of fields when
approving point assignment. The fact that there is a range for approving code point assignment. The fact that there is a range
standards track documents does not mean that a standards track for Standards Track documents does not mean that a Standards Track
document cannot have points assigned outside of that range. The document cannot have code points assigned outside of that range.
length of the encoded value should be weighed against how many The length of the encoded value should be weighed against how many
code points of that length are left, the size of device it will be code points of that length are left, the size of device it will be
used on, and the number of code points left that encode to that used on, and the number of code points left that encode to that
size. size.
* When algorithms are registered, vanity registrations should be * When algorithms are registered, vanity registrations should be
discouraged. One way to do this is to require registrations to discouraged. One way to do this is to require registrations to
provide additional documentation on security analysis of the provide additional documentation on security analysis of the
algorithm. Another thing that should be considered is requesting algorithm. Another thing that should be considered is requesting
an opinion on the algorithm from the Crypto Forum Research Group an opinion on the algorithm from the Crypto Forum Research Group
(CFRG). Algorithms that do not meet the security requirements of (CFRG). Algorithms that do not meet the security requirements of
the community and the messages structures should not be the community and the message structures should not be registered.
registered.
12. Security Considerations 12. Security Considerations
There are a number of security considerations that need to be taken There are a number of security considerations that need to be taken
into account by implementers of this specification. While some into account by implementers of this specification. While some
considerations have been highlighted here, additional considerations considerations have been highlighted here, additional considerations
may be found in the documents listed in the references. may be found in the documents listed in the references.
Implementations need to protect the private key material for any Implementations need to protect the private key material for all
individuals. There are some cases that need to be highlighted on individuals. There are some cases that need to be highlighted on
this issue. this issue.
* Using the same key for two different algorithms can leak * Use of the same key for two different algorithms can leak
information about the key. It is therefore recommended that keys information about the key. It is therefore recommended that keys
be restricted to a single algorithm. be restricted to a single algorithm.
* Use of 'direct' as a recipient algorithm combined with a second * Use of "direct" as a recipient algorithm combined with a second
recipient algorithm exposes the direct key to the second recipient algorithm exposes the direct key to the second
recipient. recipient.
* Several of the algorithms in [I-D.ietf-cose-rfc8152bis-algs] have * Several of the algorithms in [RFC9053] have limits on the number
limits on the number of times that a key can be used without of times that a key can be used without leaking information about
leaking information about the key. the key.
The use of ECDH and direct plus KDF (with no key wrap) will not The use of Elliptic Curve Diffie-Hellman (ECDH) and direct plus KDF
directly lead to the private key being leaked; the one way function (with no key wrap) will not directly lead to the private key being
of the KDF will prevent that. There is, however, a different issue leaked; the one-way function of the KDF will prevent that. There is,
that needs to be addressed. Having two recipients requires that the however, a different issue that needs to be addressed. Having two
CEK be shared between two recipients. The second recipient therefore recipients requires that the CEK be shared between two recipients.
has a CEK that was derived from material that can be used for the The second recipient therefore has a CEK that was derived from
weak proof of origin. The second recipient could create a message material that can be used for the weak proof of origin. The second
using the same CEK and send it to the first recipient; the first recipient could create a message using the same CEK and send it to
recipient would, for either static-static ECDH or direct plus KDF, the first recipient; the first recipient would, for either static-
make an assumption that the CEK could be used for proof of origin static ECDH or direct plus KDF, make an assumption that the CEK could
even though it is from the wrong entity. If the key wrap step is be used for proof of origin, even though it is from the wrong entity.
added, then no proof of origin is implied and this is not an issue. If the key wrap step is added, then no proof of origin is implied and
this is not an issue.
Although it has been mentioned before, the use of a single key for Although it has been mentioned before, the use of a single key for
multiple algorithms has been demonstrated in some cases to leak multiple algorithms has been demonstrated in some cases to leak
information about that key, provide the opportunity for attackers to information about that key, providing the opportunity for attackers
forge integrity tags, or gain information about encrypted content. to forge integrity tags or gain information about encrypted content.
Binding a key to a single algorithm prevents these problems. Key Binding a key to a single algorithm prevents these problems. Key
creators and key consumers are strongly encouraged not only to create creators and key consumers are strongly encouraged not only to create
new keys for each different algorithm, but to include that selection new keys for each different algorithm, but to include that selection
of algorithm in any distribution of key material and strictly enforce of algorithm in any distribution of key material and strictly enforce
the matching of algorithms in the key structure to algorithms in the the matching of algorithms in the key structure to algorithms in the
message structure. In addition to checking that algorithms are message structure. In addition to checking that algorithms are
correct, the key form needs to be checked as well. Do not use an correct, the key form needs to be checked as well. Do not use an
'EC2' key where an 'OKP' key is expected. "EC2" key where an "OKP" key is expected.
Before using a key for transmission, or before acting on information Before using a key for transmission, or before acting on information
received, a trust decision on a key needs to be made. Is the data or received, a trust decision on a key needs to be made. Is the data or
action something that the entity associated with the key has a right action something that the entity associated with the key has a right
to see or a right to request? A number of factors are associated to see or a right to request? A number of factors are associated
with this trust decision. Some of the ones that are highlighted here with this trust decision. Some of the ones that are highlighted here
are: are:
* What are the permissions associated with the key owner? * What are the permissions associated with the key owner?
* Is the cryptographic algorithm acceptable in the current context? * Is the cryptographic algorithm acceptable in the current context?
* Have the restrictions associated with the key, such as algorithm * Have the restrictions associated with the key, such as algorithm
or freshness, been checked and are they correct? or freshness, been checked, and are they correct?
* Is the request something that is reasonable, given the current * Is the request something that is reasonable, given the current
state of the application? state of the application?
* Have any security considerations that are part of the message been * Have any security considerations that are part of the message been
enforced (as specified by the application or 'crit' header enforced (as specified by the application or "crit" header
parameter)? parameter)?
One area that has been getting exposure is traffic analysis of One area that has been getting exposure is traffic analysis of
encrypted messages based on the length of the message. This encrypted messages based on the length of the message. This
specification does not provide for a uniform method of providing specification does not provide for a uniform method of providing
padding as part of the message structure. An observer can padding as part of the message structure. An observer can
distinguish between two different messages (for example, 'YES' and distinguish between two different messages (for example, "YES" and
'NO') based on the length for all of the content encryption "NO") based on the length for all of the content encryption
algorithms that are defined in [I-D.ietf-cose-rfc8152bis-algs] algorithms that are defined in [RFC9053]. This means that it is up
document. This means that it is up to the applications to document to the applications to document how content padding is to be done in
how content padding is to be done in order to prevent or discourage order to prevent or discourage such analysis. (For example, the text
such analysis. (For example, the text strings could be defined as strings could be defined as "YES" and "NO".)
'YES' and 'NO '.)
13. Implementation Status
This section is to be removed before publishing as an RFC.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
13.1. Author's Versions
There are three different implementations that have been created by
the author of the document both to create the examples that are
included in the document and to validate the structures and
methodology used in the design of COSE.
* Implementation Location: https://github.com/cose-wg
* Primary Maintainer: Jim Schaad
* Languages: There are three different languages that are currently
supported: Java, C# and C.
* Cryptography: The Java and C# libraries use Bouncy Castle to
provide the required cryptography. The C version uses OPENSSL
Version 1.1 for the cryptography.
* Coverage: All versions have support to allow for implicit
algorithm support as they allow for the application to set
attributes that are not to be sent in the message.
* Testing: All of the examples in the example library are generated
by the C# library and then validated using the Java and C
libraries. All three libraries have tests to allow for the
creating of the same messages that are in the example library
followed by validating them. These are not compared against the
example library. The Java and C# libraries have unit testing
included. Not all of the MUST statements in the document have
been implemented as part of the libraries. One such statement is
the requirement that unique labels be present.
* Licensing: Revised BSD License
13.2. JavaScript Version
* Implementation Location: https://github.com/erdtman/cose-js
* Primary Maintainer: Samuel Erdtman
* Languages: JavaScript
* Cryptography: TBD
* Coverage: Full Encrypt, Signature and MAC objects are supported.
* Testing: Basic testing against the common example library.
* Licensing: Apache License 2.0
13.3. Python Version
* Implementation Location: https://github.com/TimothyClaeys/COSE-
PYTHON
* Primary Maintainer: Timothy Claeys
* Languages: Python
* Cryptography: pyecdsak, crypto python libraries
* Coverage: TBD 13. References
* Testing: Basic testing plus running against the common example 13.1. Normative References
library.
* Licensing: BSD 3-Clause License [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
13.4. COSE Testing Library [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
* Implementation Location: https://github.com/cose-wg/Examples [RFC8949] Bormann, C. and P. Hoffman, "Concise Binary Object
Representation (CBOR)", STD 94, RFC 8949,
DOI 10.17487/RFC8949, December 2020,
<https://www.rfc-editor.org/info/rfc8949>.
* Primary Maintainer: Jim Schaad [RFC9053] Schaad, J., "CBOR Object Signing and Encryption (COSE):
* Description: A set of tests for the COSE library is provided as Initial Algorithms", RFC 9053, DOI 10.17487/RFC9053, July
part of the implementation effort. Both success and fail tests 2021, <https://www.rfc-editor.org/info/rfc9053>.
have been provided. All of the examples in this document are part
of this example set.
* Coverage: An attempt has been made to have test cases for every 13.2. Informative References
message type and algorithm in the document. Currently examples
dealing with ECDH with Goldilocks are missing.
* Licensing: Public Domain [BCP201] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, November 2015,
<https://www.rfc-editor.org/info/bcp201>.
14. References [CFRG-ARGON2]
Biryukov, A., Dinu, D., Khovratovich, D., and S.
Josefsson, "The memory-hard Argon2 password hash and
proof-of-work function", Work in Progress, Internet-Draft,
draft-irtf-cfrg-argon2-13, 11 March 2021,
<https://datatracker.ietf.org/doc/html/draft-irtf-cfrg-
argon2-13>.
14.1. Normative References [COAP.Formats]
IANA, "CoAP Content-Formats",
<https://www.iana.org/assignments/core-parameters/>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [CORE-GROUPCOMM]
Requirement Levels", BCP 14, RFC 2119, Dijk, E., Wang, C., and M. Tiloca, "Group Communication
DOI 10.17487/RFC2119, March 1997, for the Constrained Application Protocol (CoAP)", Work in
<https://www.rfc-editor.org/info/rfc2119>. Progress, Internet-Draft, draft-ietf-core-groupcomm-bis-
03, 22 February 2021,
<https://datatracker.ietf.org/doc/html/draft-ietf-core-
groupcomm-bis-03>.
[I-D.ietf-cbor-7049bis] [COSE-COUNTERSIGN]
Bormann, C. and P. Hoffman, "Concise Binary Object Schaad, J. and R. Housley, "CBOR Object Signing and
Representation (CBOR)", Work in Progress, Internet-Draft, Encryption (COSE): Countersignatures", Work in Progress,
draft-ietf-cbor-7049bis-16, 30 September 2020, Internet-Draft, draft-ietf-cose-countersign-05, 23 June
<https://tools.ietf.org/html/draft-ietf-cbor-7049bis-16>. 2021, <https://datatracker.ietf.org/doc/html/draft-ietf-
cose-countersign-05>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [COSE.Algorithms]
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, IANA, "COSE Algorithms",
May 2017, <https://www.rfc-editor.org/info/rfc8174>. <https://www.iana.org/assignments/cose/>.
[I-D.ietf-cose-rfc8152bis-algs] [COSE.KeyParameters]
Schaad, J., "CBOR Object Signing and Encryption (COSE): IANA, "COSE Key Common Parameters",
Initial Algorithms", Work in Progress, Internet-Draft, <https://www.iana.org/assignments/cose/>.
draft-ietf-cose-rfc8152bis-algs-12, 24 September 2020,
<https://tools.ietf.org/html/draft-ietf-cose-rfc8152bis-
algs-12>.
14.2. Informative References [COSE.KeyTypes]
IANA, "COSE Key Types",
<https://www.iana.org/assignments/cose/>.
[RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)", [DSS] National Institute of Standards and Technology, "Digital
RFC 8152, DOI 10.17487/RFC8152, July 2017, Signature Standard (DSS)", FIPS 186-4,
<https://www.rfc-editor.org/info/rfc8152>. DOI 10.6028/NIST.FIPS.186-4, July 2013,
<https://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.186-4.pdf>.
[RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data [PVSig] Brown, D.R.L. and D.B. Johnson, "Formal Security Proofs
Definition Language (CDDL): A Notational Convention to for a Signature Scheme with Partial Message Recovery",
Express Concise Binary Object Representation (CBOR) and LNCS Volume 2020, DOI 10.1007/3-540-45353-9_11, June 2000,
JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, <https://www.certicom.com/content/dam/certicom/images/
June 2019, <https://www.rfc-editor.org/info/rfc8610>. pdfs/CerticomWP-PVSigSec_login.pdf>.
[RFC2633] Ramsdell, B., Ed., "S/MIME Version 3 Message [RFC2633] Ramsdell, B., Ed., "S/MIME Version 3 Message
Specification", RFC 2633, DOI 10.17487/RFC2633, June 1999, Specification", RFC 2633, DOI 10.17487/RFC2633, June 1999,
<https://www.rfc-editor.org/info/rfc2633>. <https://www.rfc-editor.org/info/rfc2633>.
[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394,
September 2002, <https://www.rfc-editor.org/info/rfc3394>.
[RFC3851] Ramsdell, B., Ed., "Secure/Multipurpose Internet Mail
Extensions (S/MIME) Version 3.1 Message Specification",
RFC 3851, DOI 10.17487/RFC3851, July 2004,
<https://www.rfc-editor.org/info/rfc3851>.
[RFC4262] Santesson, S., "X.509 Certificate Extension for Secure/ [RFC4262] Santesson, S., "X.509 Certificate Extension for Secure/
Multipurpose Internet Mail Extensions (S/MIME) Multipurpose Internet Mail Extensions (S/MIME)
Capabilities", RFC 4262, DOI 10.17487/RFC4262, December Capabilities", RFC 4262, DOI 10.17487/RFC4262, December
2005, <https://www.rfc-editor.org/info/rfc4262>. 2005, <https://www.rfc-editor.org/info/rfc4262>.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", [RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007, FYI 36, RFC 4949, DOI 10.17487/RFC4949, August 2007,
<https://www.rfc-editor.org/info/rfc4949>. <https://www.rfc-editor.org/info/rfc4949>.
[RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated [RFC5116] McGrew, D., "An Interface and Algorithms for Authenticated
skipping to change at page 57, line 47 skipping to change at line 2579
"Use of the RSA-KEM Key Transport Algorithm in the "Use of the RSA-KEM Key Transport Algorithm in the
Cryptographic Message Syntax (CMS)", RFC 5990, Cryptographic Message Syntax (CMS)", RFC 5990,
DOI 10.17487/RFC5990, September 2010, DOI 10.17487/RFC5990, September 2010,
<https://www.rfc-editor.org/info/rfc5990>. <https://www.rfc-editor.org/info/rfc5990>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13, Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013, RFC 6838, DOI 10.17487/RFC6838, January 2013,
<https://www.rfc-editor.org/info/rfc6838>. <https://www.rfc-editor.org/info/rfc6838>.
[STD90] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", STD 90, RFC 8259, December 2017.
<https://www.rfc-editor.org/info/std90>
[BCP201] Housley, R., "Guidelines for Cryptographic Algorithm
Agility and Selecting Mandatory-to-Implement Algorithms",
BCP 201, RFC 7696, November 2015.
<https://www.rfc-editor.org/info/bcp201>
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252, Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014, DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>. <https://www.rfc-editor.org/info/rfc7252>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web [RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>. 2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)", [RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
skipping to change at page 58, line 37 skipping to change at line 2605
[RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518, [RFC7518] Jones, M., "JSON Web Algorithms (JWA)", RFC 7518,
DOI 10.17487/RFC7518, May 2015, DOI 10.17487/RFC7518, May 2015,
<https://www.rfc-editor.org/info/rfc7518>. <https://www.rfc-editor.org/info/rfc7518>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital [RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032, Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017, DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>. <https://www.rfc-editor.org/info/rfc8032>.
[DSS] National Institute of Standards and Technology, "Digital [RFC8152] Schaad, J., "CBOR Object Signing and Encryption (COSE)",
Signature Standard (DSS)", DOI 10.6028/NIST.FIPS.186-4, RFC 8152, DOI 10.17487/RFC8152, July 2017,
FIPS PUB 186-4, July 2013, <https://www.rfc-editor.org/info/rfc8152>.
<http://nvlpubs.nist.gov/nistpubs/FIPS/
NIST.FIPS.186-4.pdf>.
[PVSig] Brown, D. and D. Johnson, "Formal Security Proofs for a
Signature Scheme with Partial Message Recovery",
DOI 10.1007/3-540-45353-9_11, LNCS Volume 2020, June 2000,
<https://doi.org/10.1007/3-540-45353-9_11>.
[W3C.WebCrypto]
Watson, M., "Web Cryptography API", W3C Recommendation,
January 2017, <https://www.w3.org/TR/WebCryptoAPI/>.
[RFC8230] Jones, M., "Using RSA Algorithms with CBOR Object Signing [RFC8230] Jones, M., "Using RSA Algorithms with CBOR Object Signing
and Encryption (COSE) Messages", RFC 8230, and Encryption (COSE) Messages", RFC 8230,
DOI 10.17487/RFC8230, September 2017, DOI 10.17487/RFC8230, September 2017,
<https://www.rfc-editor.org/info/rfc8230>. <https://www.rfc-editor.org/info/rfc8230>.
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running [RFC8551] Schaad, J., Ramsdell, B., and S. Turner, "Secure/
Code: The Implementation Status Section", BCP 205, Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
RFC 7942, DOI 10.17487/RFC7942, July 2016, Message Specification", RFC 8551, DOI 10.17487/RFC8551,
<https://www.rfc-editor.org/info/rfc7942>. April 2019, <https://www.rfc-editor.org/info/rfc8551>.
[RFC3394] Schaad, J. and R. Housley, "Advanced Encryption Standard
(AES) Key Wrap Algorithm", RFC 3394, DOI 10.17487/RFC3394,
September 2002, <https://www.rfc-editor.org/info/rfc3394>.
[I-D.ietf-cose-hash-algs]
Schaad, J., "CBOR Object Signing and Encryption (COSE):
Hash Algorithms", Work in Progress, Internet-Draft, draft-
ietf-cose-hash-algs-09, 14 September 2020,
<https://tools.ietf.org/html/draft-ietf-cose-hash-algs-
09>.
[I-D.ietf-core-groupcomm-bis] [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data
Dijk, E., Wang, C., and M. Tiloca, "Group Communication Definition Language (CDDL): A Notational Convention to
for the Constrained Application Protocol (CoAP)", Work in Express Concise Binary Object Representation (CBOR) and
Progress, Internet-Draft, draft-ietf-core-groupcomm-bis- JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610,
02, 2 November 2020, <https://tools.ietf.org/html/draft- June 2019, <https://www.rfc-editor.org/info/rfc8610>.
ietf-core-groupcomm-bis-02>.
[RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz, [RFC8613] Selander, G., Mattsson, J., Palombini, F., and L. Seitz,
"Object Security for Constrained RESTful Environments "Object Security for Constrained RESTful Environments
(OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019, (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, July 2019,
<https://www.rfc-editor.org/info/rfc8613>. <https://www.rfc-editor.org/info/rfc8613>.
[I-D.irtf-cfrg-argon2] [RFC9054] Schaad, J., "CBOR Object Signing and Encryption (COSE):
Biryukov, A., Dinu, D., Khovratovich, D., and S. Hash Algorithms", RFC 9054, DOI 10.17487/RFC9054, July
Josefsson, "The memory-hard Argon2 password hash and 2021, <https://www.rfc-editor.org/info/rfc9054>.
proof-of-work function", Work in Progress, Internet-Draft,
draft-irtf-cfrg-argon2-12, 8 September 2020,
<https://tools.ietf.org/html/draft-irtf-cfrg-argon2-12>.
[COAP.Formats]
IANA, "CoAP Content-Formats",
<https://www.iana.org/assignments/core-parameters/core-
parameters.xhtml#content-formats>.
[COSE.Algorithms]
IANA, "COSE Algorithms",
<https://www.iana.org/assignments/cose/
cose.xhtml#algorithms>.
[COSE.KeyParameters]
IANA, "COSE Key Parameters",
<https://www.iana.org/assignments/cose/cose.xhtml#key-
common-parameters>.
[COSE.KeyTypes] [STD90] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
IANA, "COSE Key Types", Interchange Format", STD 90, RFC 8259, December 2017,
<https://www.iana.org/assignments/cose/cose.xhtml#key- <https://www.rfc-editor.org/info/std90>.
type>.
[I-D.ietf-cose-countersign] [W3C.WebCrypto]
Schaad, J., "CBOR Object Signing and Encryption (COSE): Watson, M., Ed., "Web Cryptography API", W3C
Countersignatures". Recommendation, 26 January 2017,
<https://www.w3.org/TR/WebCryptoAPI/>.
Appendix A. Guidelines for External Data Authentication of Algorithms Appendix A. Guidelines for External Data Authentication of Algorithms
During development of COSE, the requirement that the algorithm During development of COSE, the requirement that the algorithm
identifier be located in the protected attributes was relaxed from a identifier be located in the protected attributes was relaxed from a
must to a should. There were two basic reasons that have been must to a should. Two basic reasons have been advanced to support
advanced to support this position. First, the resulting message will this position. First, the resulting message will be smaller if the
be smaller if the algorithm identifier is omitted from the most algorithm identifier is omitted from the most common messages in a
common messages in a CoAP environment. Second, there is a potential CoAP environment. Second, there is a potential bug that will arise
bug that will arise if full checking is not done correctly between if full checking is not done correctly between the different places
the different places that an algorithm identifier could be placed that an algorithm identifier could be placed (the message itself, an
(the message itself, an application statement, the key structure that application statement, the key structure that the sender possesses,
the sender possesses, and the key structure the recipient possesses). and the key structure the recipient possesses).
This appendix lays out how such a change can be made and the details This appendix lays out how such a change can be made and the details
that an application needs to specify in order to use this option. that an application needs to specify in order to use this option.
Two different sets of details are specified: those needed to omit an Two different sets of details are specified: those needed to omit an
algorithm identifier and those needed to use the variant on the algorithm identifier and those needed to use the variant on the
countersignature attribute that contains no attributes about itself. countersignature attribute that contains no attributes about itself.
Three sets of recommendations are laid out. The first set of Three sets of recommendations are laid out. The first set of
recommendations applies to having an implicit algorithm identified recommendations applies to having an implicit algorithm identified
for a single layer of a COSE object. The second set of for a single layer of a COSE object. The second set of
skipping to change at page 61, line 12 skipping to change at line 2677
recommendations applies to having implicit algorithms for multiple recommendations applies to having implicit algorithms for multiple
COSE object constructs. COSE object constructs.
The key words from [RFC2119] are deliberately not used here. This The key words from [RFC2119] are deliberately not used here. This
specification can provide recommendations, but it cannot enforce specification can provide recommendations, but it cannot enforce
them. them.
This set of recommendations applies to the case where an application This set of recommendations applies to the case where an application
is distributing a fixed algorithm along with the key information for is distributing a fixed algorithm along with the key information for
use in a single COSE object. This normally applies to the smallest use in a single COSE object. This normally applies to the smallest
of the COSE objects, specifically COSE_Sign1, COSE_Mac0, and of the COSE objects -- specifically, COSE_Sign1, COSE_Mac0, and
COSE_Encrypt0, but could apply to the other structures as well. COSE_Encrypt0 -- but could apply to the other structures as well.
The following items should be taken into account: The following items should be taken into account:
* Applications need to list the set of COSE structures that implicit * Applications need to list the set of COSE structures that implicit
algorithms are to be used in. Applications need to require that algorithms are to be used in. Applications need to require that
the receipt of an explicit algorithm identifier in one of these the receipt of an explicit algorithm identifier in one of these
structures will lead to the message being rejected. This structures will lead to the message being rejected. This
requirement is stated so that there will never be a case where requirement is stated so that there will never be a case where
there is any ambiguity about the question of which algorithm there is any ambiguity about the question of which algorithm
should be used, the implicit or the explicit one. This applies should be used, the implicit or the explicit one. This applies
even if the transported algorithm identifier is a protected even if the transported algorithm identifier is a protected
attribute. This applies even if the transported algorithm is the attribute. This applies even if the transported algorithm is the
same as the implicit algorithm. same as the implicit algorithm.
* Applications need to define the set of information that is to be * Applications need to define the set of information that is to be
considered to be part of a context when omitting algorithm considered to be part of a context when omitting algorithm
identifiers. At a minimum, this would be the key identifier (if identifiers. At a minimum, this would be the key identifier (if
needed), the key, the algorithm, and the COSE structure it is used needed), the key, the algorithm, and the COSE structure it is used
with. Applications should restrict the use of a single key to a with. Applications should restrict the use of a single key to a
single algorithm. As noted for some of the algorithms in single algorithm. As noted for some of the algorithms in
[I-D.ietf-cose-rfc8152bis-algs], the use of the same key in [RFC9053], the use of the same key in different, related
different related algorithms can lead to leakage of information algorithms can lead to leakage of information about the key,
about the key, leakage about the data or the ability to perform leakage about the data, or the ability to perform forgeries.
forgeries.
* In many cases, applications that make the algorithm identifier * In many cases, applications that make the algorithm identifier
implicit will also want to make the context identifier implicit implicit will also want to make the context identifier implicit
for the same reason. That is, omitting the context identifier for the same reason. That is, omitting the context identifier
will decrease the message size (potentially significantly will decrease the message size (potentially significantly,
depending on the length of the identifier). Applications that do depending on the length of the identifier). Applications that do
this will need to describe the circumstances where the context this will need to describe the circumstances where the context
identifier is to be omitted and how the context identifier is to identifier is to be omitted and how the context identifier is to
be inferred in these cases. (An exhaustive search over all of the be inferred in these cases. (An exhaustive search over all of the
keys would normally not be considered to be acceptable.) An keys would normally not be considered to be acceptable.) An
example of how this can be done is to tie the context to a example of how this can be done is to tie the context to a
transaction identifier. Both would be sent on the original transaction identifier. Both would be sent on the original
message, but only the transaction identifier would need to be sent message, but only the transaction identifier would need to be sent
after that point as the context is tied into the transaction after that point, as the context is tied into the transaction
identifier. Another way would be to associate a context with a identifier. Another way would be to associate a context with a
network address. All messages coming from a single network network address. All messages coming from a single network
address can be assumed to be associated with a specific context. address can be assumed to be associated with a specific context.
(In this case, the address would normally be distributed as part (In this case, the address would normally be distributed as part
of the context.) of the context.)
* Applications cannot rely on key identifiers being unique unless * Applications cannot rely on key identifiers being unique unless
they take significant efforts to ensure that they are computed in they take significant efforts to ensure that they are computed in
such a way as to create this guarantee. Even when an application such a way as to create this guarantee. Even when an application
does this, the uniqueness might be violated if the application is does this, the uniqueness might be violated if the application is
skipping to change at page 62, line 32 skipping to change at line 2745
encryption, MAC, and signature algorithms. It can be used in the encryption, MAC, and signature algorithms. It can be used in the
SuppPrivInfo field for those algorithms that use a KDF to derive a SuppPrivInfo field for those algorithms that use a KDF to derive a
key value. Applications may also want to protect other key value. Applications may also want to protect other
information that is part of the context structure as well. It information that is part of the context structure as well. It
should be noted that those fields, such as the key or a Base IV, should be noted that those fields, such as the key or a Base IV,
are protected by virtue of being used in the cryptographic are protected by virtue of being used in the cryptographic
computation and do not need to be included in the external data computation and do not need to be included in the external data
field. field.
The second case is having multiple implicit algorithm identifiers The second case is having multiple implicit algorithm identifiers
specified for a multiple layer COSE object. An example of how this specified for a multiple-layer COSE object. An example of how this
would work is the encryption context that an application specifies, would work is the encryption context that an application specifies,
which contains a content encryption algorithm, a key wrap algorithm, which contains a content encryption algorithm, a key wrap algorithm,
a key identifier, and a shared secret. The sender omits sending the a key identifier, and a shared secret. The sender omits sending the
algorithm identifier for both the content layer and the recipient algorithm identifier for both the content layer and the recipient
layer leaving only the key identifier. The receiver then uses the layer, leaving only the key identifier. The receiver then uses the
key identifier to get the implicit algorithm identifiers. key identifier to get the implicit algorithm identifiers.
The following additional items need to be taken into consideration: The following additional items need to be taken into consideration:
* Applications that want to support this will need to define a * Applications that want to support this will need to define a
structure that allows for, and clearly identifies, both the COSE structure that allows for, and clearly identifies, both the COSE
structure to be used with a given key and the structure and structure to be used with a given key and the structure and
algorithm to be used for the secondary layer. The key for the algorithm to be used for the secondary layer. The key for the
secondary layer is computed as normal from the recipient layer. secondary layer is computed as normal from the recipient layer.
skipping to change at page 63, line 11 skipping to change at line 2772
targeted at potentially unrelated layers or different COSE objects. targeted at potentially unrelated layers or different COSE objects.
There are a number of different scenarios where this might be There are a number of different scenarios where this might be
applicable. Some of these scenarios are: applicable. Some of these scenarios are:
* Two contexts are distributed as a pair. Each of the contexts is * Two contexts are distributed as a pair. Each of the contexts is
for use with a COSE_Encrypt message. Each context will consist of for use with a COSE_Encrypt message. Each context will consist of
distinct secret keys and IVs and potentially even different distinct secret keys and IVs and potentially even different
algorithms. One context is for sending messages from party A to algorithms. One context is for sending messages from party A to
party B, and the second context is for sending messages from party party B, and the second context is for sending messages from party
B to party A. This means that there is no chance for a reflection B to party A. This means that there is no chance for a reflection
attack to occur as each party uses different secret keys to send attack to occur, as each party uses different secret keys to send
its messages; a message that is reflected back to it would fail to its messages; a message that is reflected back to it would fail to
decrypt. decrypt.
* Two contexts are distributed as a pair. The first context is used * Two contexts are distributed as a pair. The first context is used
for encryption of the message, and the second context is used to for encryption of the message, and the second context is used to
place a countersignature on the message. The intention is that place a countersignature on the message. The intention is that
the second context can be distributed to other entities the second context can be distributed to other entities
independently of the first context. This allows these entities to independently of the first context. This allows these entities to
validate that the message came from an individual without being validate that the message came from an individual without being
able to decrypt the message and see the content. able to decrypt the message and see the content.
skipping to change at page 63, line 41 skipping to change at line 2802
considered: considered:
* Applications need to ensure that the multiple contexts stay * Applications need to ensure that the multiple contexts stay
associated. If one of the contexts is invalidated for any reason, associated. If one of the contexts is invalidated for any reason,
all of the contexts associated with it should also be invalidated. all of the contexts associated with it should also be invalidated.
Appendix B. Two Layers of Recipient Information Appendix B. Two Layers of Recipient Information
All of the currently defined recipient algorithm classes only use two All of the currently defined recipient algorithm classes only use two
layers of the COSE structure. The first layer (COSE_Encrypt) is the layers of the COSE structure. The first layer (COSE_Encrypt) is the
message content, and the second layer (COSE_Recipint) is the content message content, and the second layer (COSE_Recipient) is the content
key encryption. However, if one uses a recipient algorithm such as key encryption. However, if one uses a recipient algorithm such as
the RSA Key Encapsulation Mechanism (RSA-KEM) (see Appendix A of RSA- the RSA Key Encapsulation Mechanism (RSA-KEM) (see Appendix A of RSA-
KEM [RFC5990]), then it makes sense to have two layers of the KEM [RFC5990]), then it makes sense to have two layers of the
COSE_Recipient structure. COSE_Recipient structure.
These layers would be: These layers would be:
* Layer 0: The content encryption layer. This layer contains the * Layer 0: The content encryption layer. This layer contains the
payload of the message. payload of the message.
* Layer 1: The encryption of the CEK by a KEK. * Layer 1: The encryption of the CEK by a KEK.
* Layer 2: The encryption of a long random secret using an RSA key * Layer 2: The encryption of a long random secret using an RSA key
and a key derivation function to convert that secret into the KEK. and a key derivation function to convert that secret into the KEK.
This is an example of what a triple layer message would look like. This is an example of what a triple-layer message would look like.
The message has the following layers: The message has the following layers:
* Layer 0: Has a content encrypted with AES-GCM using a 128-bit key. * Layer 0: Has content encrypted with AES-GCM using a 128-bit key.
* Layer 1: Uses the AES Key Wrap algorithm with a 128-bit key. * Layer 1: Uses the AES Key Wrap algorithm with a 128-bit key.
* Layer 2: Uses ECDH Ephemeral-Static direct to generate the layer 1 * Layer 2: Uses ECDH Ephemeral-Static direct to generate the Layer 1
key. key.
In effect, this example is a decomposed version of using the In effect, this example is a decomposed version of using the ECDH-
ECDH-ES+A128KW algorithm. ES+A128KW algorithm.
Size of binary file is 183 bytes Size of binary file is 183 bytes
96( 96(
[ / COSE_Encrypt / [ / COSE_Encrypt /
/ protected h'a10101' / << { / protected h'a10101' / << {
/ alg / 1:1 / AES-GCM 128 / / alg / 1:1 / AES-GCM 128 /
} >>, } >>,
/ unprotected / { / unprotected / {
/ iv / 5:h'02d1f7e6f26c43d4868d87ce' / iv / 5:h'02d1f7e6f26c43d4868d87ce'
}, },
/ ciphertext / h'64f84d913ba60a76070a9a48f26e97e863e2852948658f0 / ciphertext / h'64f84d913ba60a76070a9a48f26e97e863e2852948658f0
811139868826e89218a75715b', 811139868826e89218a75715b',
skipping to change at page 66, line 10 skipping to change at line 2887
features and message types that have been defined in this document. features and message types that have been defined in this document.
To make the examples easier to read, they are presented using the To make the examples easier to read, they are presented using the
extended CBOR diagnostic notation (defined in [RFC8610]) rather than extended CBOR diagnostic notation (defined in [RFC8610]) rather than
as a binary dump. as a binary dump.
A GitHub project has been created at <https://github.com/cose-wg/ A GitHub project has been created at <https://github.com/cose-wg/
Examples> that contains not only the examples presented in this Examples> that contains not only the examples presented in this
document, but a more complete set of testing examples as well. Each document, but a more complete set of testing examples as well. Each
example is found in a JSON file that contains the inputs used to example is found in a JSON file that contains the inputs used to
create the example, some of the intermediate values that can be used create the example, some of the intermediate values that can be used
in debugging the example and the output of the example presented both in debugging the example, and the output of the example presented
as a hex dump and in CBOR diagnostic notation format. Some of the both as a hex dump and in CBOR diagnostic notation format. Some of
examples at the site are designed failure testing cases; these are the examples at the site are designed failure-testing cases; these
clearly marked as such in the JSON file. If errors in the examples are clearly marked as such in the JSON file. If errors in the
in this document are found, the examples on GitHub will be updated, examples in this document are found, the examples on GitHub will be
and a note to that effect will be placed in the JSON file. updated, and a note to that effect will be placed in the JSON file.
As noted, the examples are presented using the CBOR's diagnostic As noted, the examples are presented using CBOR's diagnostic
notation. A Ruby-based tool exists that can convert between the notation. A Ruby-based tool exists that can convert between the
diagnostic notation and binary. This tool can be installed with the diagnostic notation and binary. This tool can be installed with the
command line: command line:
gem install cbor-diag gem install cbor-diag
The diagnostic notation can be converted into binary files using the The diagnostic notation can be converted into binary files using the
following command line: following command line:
diag2cbor.rb < inputfile > outputfile diag2cbor.rb < inputfile > outputfile
The examples can be extracted from the XML version of this document The examples can be extracted from the XML version of this document
via an XPath expression as all of the sourcecode is tagged with the via an XPath expression, as all of the source code is tagged with the
attribute type='CBORdiag'. (Depending on the XPath evaluator one is attribute type='cbor-diag'. (Depending on the XPath evaluator one is
using, it may be necessary to deal with &gt; as an entity.) using, it may be necessary to deal with &gt; as an entity.)
//sourcecode[@type='CDDL']/text() //sourcecode[@type='CDDL']/text()
C.1. Examples of Signed Messages C.1. Examples of Signed Messages
C.1.1. Single Signature C.1.1. Single Signature
This example uses the following: This example uses the following:
skipping to change at page 68, line 44 skipping to change at line 2994
] ]
] ]
) )
C.1.3. Signature with Criticality C.1.3. Signature with Criticality
This example uses the following: This example uses the following:
* Signature Algorithm: ECDSA w/ SHA-256, Curve P-256 * Signature Algorithm: ECDSA w/ SHA-256, Curve P-256
* There is a criticality marker on the "reserved" header parameter * There is a criticality marker on the "reserved" header parameter.
Size of binary file is 125 bytes Size of binary file is 125 bytes
98( 98(
[ [
/ protected h'a2687265736572766564f40281687265736572766564' / / protected h'a2687265736572766564f40281687265736572766564' /
<< { << {
"reserved":false, "reserved":false,
/ crit / 2:[ / crit / 2:[
"reserved" "reserved"
] ]
} >>, } >>,
/ unprotected / {}, / unprotected / {},
skipping to change at page 76, line 37 skipping to change at line 3299
] ]
] ]
) )
C.5.3. Wrapped MAC C.5.3. Wrapped MAC
This example uses the following: This example uses the following:
* MAC: AES-MAC, 128-bit key, truncated to 64 bits * MAC: AES-MAC, 128-bit key, truncated to 64 bits
* Recipient class: AES Key Wrap w/ a pre-shared 256-bit key * Recipient class: AES Key Wrap w/ a preshared 256-bit key
Size of binary file is 109 bytes Size of binary file is 109 bytes
97( 97(
[ [
/ protected h'a1010e' / << { / protected h'a1010e' / << {
/ alg / 1:14 / AES-CBC-MAC-128//64 / / alg / 1:14 / AES-CBC-MAC-128//64 /
} >> , } >> ,
/ unprotected / {}, / unprotected / {},
/ payload / 'This is the content.', / payload / 'This is the content.',
/ tag / h'36f5afaf0bab5d43', / tag / h'36f5afaf0bab5d43',
/ recipients / [ / recipients / [
[ [
skipping to change at page 77, line 32 skipping to change at line 3331
] ]
] ]
) )
C.5.4. Multi-Recipient MACed Message C.5.4. Multi-Recipient MACed Message
This example uses the following: This example uses the following:
* MAC: HMAC w/ SHA-256, 128-bit key * MAC: HMAC w/ SHA-256, 128-bit key
* Recipient class: Uses three different methods * Recipient class: Uses three different methods.
1. ECDH Ephemeral-Static, Curve P-521, AES Key Wrap w/ 128-bit 1. ECDH Ephemeral-Static, Curve P-521, AES Key Wrap w/ 128-bit
key key
2. AES Key Wrap w/ 256-bit key 2. AES Key Wrap w/ 256-bit key
Size of binary file is 309 bytes Size of binary file is 309 bytes
97( 97(
[ [
/ protected h'a10105' / << { / protected h'a10105' / << {
/ alg / 1:5 / HMAC 256//256 / / alg / 1:5 / HMAC 256//256 /
} >> , } >> ,
/ unprotected / {}, / unprotected / {},
/ payload / 'This is the content.', / payload / 'This is the content.',
/ tag / h'bf48235e809b5c42e995f2b7d5fa13620e7ed834e337f6aa43df16 / tag / h'bf48235e809b5c42e995f2b7d5fa13620e7ed834e337f6aa43df16
1e49e9323e', 1e49e9323e',
/ recipients / [ / recipients / [
skipping to change at page 78, line 47 skipping to change at line 3383
}, },
/ ciphertext / h'0b2c7cfce04e98276342d6476a7723c090dfdd15f9a / ciphertext / h'0b2c7cfce04e98276342d6476a7723c090dfdd15f9a
518e7736549e998370695e6d6a83b4ae507bb' 518e7736549e998370695e6d6a83b4ae507bb'
] ]
] ]
] ]
) )
C.6. Examples of MAC0 Messages C.6. Examples of MAC0 Messages
C.6.1. Shared Secret Direct MAC C.6.1. Shared-Secret Direct MAC
This example uses the following: This example uses the following:
* MAC: AES-CMAC, 256-bit key, truncated to 64 bits * MAC: AES-CMAC, 256-bit key, truncated to 64 bits
* Recipient class: direct shared secret * Recipient class: direct shared secret
Size of binary file is 37 bytes Size of binary file is 37 bytes
17( 17(
[ [
/ protected h'a1010f' / << { / protected h'a1010f' / << {
/ alg / 1:15 / AES-CBC-MAC-256//64 / / alg / 1:15 / AES-CBC-MAC-256//64 /
} >> , } >> ,
/ unprotected / {}, / unprotected / {},
skipping to change at page 79, line 28 skipping to change at line 3413
Note that this example uses the same inputs as Appendix C.5.1. Note that this example uses the same inputs as Appendix C.5.1.
C.7. COSE Keys C.7. COSE Keys
C.7.1. Public Keys C.7.1. Public Keys
This is an example of a COSE Key Set. This example includes the This is an example of a COSE Key Set. This example includes the
public keys for all of the previous examples. public keys for all of the previous examples.
In order the keys are: In order, the keys are:
* An EC key with a kid of "meriadoc.brandybuck@buckland.example" * An EC key with a kid of "meriadoc.brandybuck@buckland.example"
* An EC key with a kid of "peregrin.took@tuckborough.example" * An EC key with a kid of "11"
* An EC key with a kid of "bilbo.baggins@hobbiton.example" * An EC key with a kid of "bilbo.baggins@hobbiton.example"
* An EC key with a kid of "11" * An EC key with a kid of "peregrin.took@tuckborough.example"
Size of binary file is 481 bytes Size of binary file is 481 bytes
[ [
{ {
-1:1, -1:1,
-2:h'65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de439c0 -2:h'65eda5a12577c2bae829437fe338701a10aaa375e1bb5b5de108de439c0
8551d', 8551d',
-3:h'1e52ed75701163f7f9e40ddf9f341b3dc9ba860af7e0ca7ca7e9eecd008 -3:h'1e52ed75701163f7f9e40ddf9f341b3dc9ba860af7e0ca7ca7e9eecd008
4d19c', 4d19c',
skipping to change at page 82, line 40 skipping to change at line 3557
{ {
1:4, 1:4,
2:'018c0ae5-4d9b-471b-bfd6-eef314bc7037', 2:'018c0ae5-4d9b-471b-bfd6-eef314bc7037',
-1:h'849b57219dae48de646d07dbb533566e976686457c1491be3a76dcea6c4 -1:h'849b57219dae48de646d07dbb533566e976686457c1491be3a76dcea6c4
27188' 27188'
} }
] ]
Acknowledgments Acknowledgments
This document is a product of the COSE working group of the IETF. This document is a product of the COSE Working Group of the IETF.
The following individuals are to blame for getting me started on this The following individuals are to blame for getting me started on this
project in the first place: Richard Barnes, Matt Miller, and Martin project in the first place: Richard Barnes, Matt Miller, and Martin
Thomson. Thomson.
The initial version of the specification was based to some degree on The initial draft version of the specification was based to some
the outputs of the JOSE and S/MIME working groups. degree on the outputs of the JOSE and S/MIME Working Groups.
The following individuals provided input into the final form of the The following individuals provided input into the final form of the
document: Carsten Bormann, John Bradley, Brain Campbell, Michael B. document: Carsten Bormann, John Bradley, Brian Campbell, Michael
Jones, Ilari Liusvaara, Francesca Palombini, Ludwig Seitz, and B. Jones, Ilari Liusvaara, Francesca Palombini, Ludwig Seitz, and
G&#246;ran Selander. Göran Selander.
Author's Address Author's Address
Jim Schaad Jim Schaad
August Cellars August Cellars
Email: ietf@augustcellars.com Email: ietf@augustcellars.com
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