<?xml version='1.0' encoding='utf-8'?>
<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent" [
<!ENTITY SigSection "9.1">
<!ENTITY MacSection "9.2">
<!ENTITY ContentSection "9.3">
<!ENTITY KDFSection "9.4">
<!ENTITY CKeyDistributeSection "9.5">
<!ENTITY DirectDistribute "9.5.1">
<!ENTITY KeyWrap "9.5.2">
]>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<?rfc toc="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?> version="1.0" encoding="UTF-8"?>

<rfc xmlns:xi="http://www.w3.org/2001/XInclude" ipr="trust200902" category="info" docName="draft-ietf-cose-rfc8152bis-algs-11"
     docName="draft-ietf-cose-rfc8152bis-algs-12" number="9053"
     obsoletes="8152" submissionType="IETF" version="3" consensus="true"> category="info" consensus="true"
     tocInclude="true" sortRefs="true" symRefs="true" xml:lang="en"
     version="3">

  <!-- xml2rfc v2v3 conversion 2.24.0 -->
  <front>

    <title abbrev="COSE Algorithms">
      CBOR Object Signing&nbsp;and&nbsp;Encryption&nbsp;(COSE): Signing and Encryption (COSE): Initial Algorithms
    </title>
    <seriesInfo name="Internet-Draft" value="draft-ietf-cose-rfc8152bis-algs-11"/> name="RFC" value="9053"/>
    <author initials="J." surname="Schaad" fullname="Jim Schaad">
      <organization>August Cellars</organization>
      <address>
        <email>ietf@augustcellars.com</email>
      </address>
    </author>
    <date/>
    <date year="2021" month="July" />
    <area>Security</area>
    <workgroup>COSE Working Group</workgroup>

<!-- [rfced] Please insert any keywords (beyond those that appear in the title) for use on https://www.rfc-editor.org/search. -->

<keyword>example</keyword>

    <abstract>
      <t>
        Concise Binary Object Representation (CBOR) is a data format designed for small code size and small message size.
        There is a need for the ability to have be able to define basic security services defined for this data format.
        THis
        This document defines a set of algorithms that can be used with the
	CBOR Object Signing and Encryption (COSE) protocol RFC XXXX. <!-- <xref target="I-D.ietf-cose-rfc8152bis-struct"/>.--> (RFC 9052).
      </t>
    </abstract>
    <note removeInRFC="true">

      <name>Contributing to this document</name>
<!-- [rfced] Should the abstract include mention that it obsoletes RFC EDITOR - Please remove this note before publishing 8152? -->
      <t>
        The source for this draft is being maintained in GitHub.
        Suggested changes should be submitted as pull requests  at <eref target="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.
      </t>
    </note>

    </abstract>
  </front>
  <middle>
    <section anchor="introduction">

      <name>Introduction</name>
      <t>
        There has been an increased focus on small, constrained devices that make up the Internet of Things (IoT).
        One of the standards that has come out of this process is "Concise
	Binary Object Representation (CBOR)" <xref target="RFC7049"/>. target="RFC8949"/>.
        CBOR extended the data model of JavaScript Object Notation (JSON)
	<xref target="STD90"/> by allowing for binary data, among other
	changes.
        CBOR is being adopted by several of the IETF working groups dealing
	with the IoT world as their encoding method of encoding data structures.
        CBOR was designed specifically to be both small in terms of both messages
	transported and implementation size and be a schema-free decoder.
        A need exists to provide message security services for IoT, and using
	CBOR as the message-encoding format makes sense.
      </t>
      <t>
        The core COSE specification consists of two documents.
        <xref target="I-D.ietf-cose-rfc8152bis-struct"/> target="RFC9052"/> contains the serialization structures and the procedures for using the different cryptographic algorithms.
        This document provides an initial set of algorithms for use with those structures.
      </t>
      <section anchor="requirements-terminology">

        <name>Requirements Terminology</name>
        <t>
          The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
          NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED",
          "MAY", "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL
          NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>",
          "<bcp14>MAY</bcp14>", and "OPTIONAL" "<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as
          described in BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they
          appear in all capitals, as shown here.
        </t>
      </section>
      <section>

        <name>Changes from RFC8152</name> RFC 8152</name>

        <ul>

          <li>
              Extract
              Extracted the sections dealing with specific algorithms and place
	      them into this document.
              The sections dealing with structure and general processing rules
	      are placed in <xref target="I-D.ietf-cose-rfc8152bis-struct"/>. target="RFC9052"/>.
            </li>
          <li>Text
          <li>Made text clarifications and changes in terminology.</li>
        </ul>
      </section>
      <section>

        <name>Document Terminology</name>
        <t>In this document, we use the following terminology: </t>
        <t>Byte is a
<dl>
        <dt>Byte:</dt><dd>A synonym for octet.</t>
        <t>Constrained octet.</dd>
        <dt>Constrained Application Protocol (CoAP) is a (CoAP):</dt><dd>A specialized
	web transfer protocol for use in constrained systems.  It is defined
	in <xref target="RFC7252"/>.  </t>
        <t>
          Authenticated target="RFC7252"/>.</dd>
        <dt>Authenticated Encryption (AE) <xref target="RFC5116"/> algorithms are encryption <xref target="RFC5116"/>:
	</dt><dd>Encryption algorithms that provide an
	authentication check of the contents with the encryption service.
          An example of an AE algorithm used in COSE is AES Key Wrap <xref target="RFC3394"/>.
          These algorithms are used for key encryption algorithms, but AEAD algorithms would be preferred.
        </t>
        <t>
	  Authenticated Encryption with Associated Data (AEAD) <xref target="RFC5116"/>
	  algorithms provide would be preferred.
        </dd>
        <dt>AEAD algorithms <xref
	target="RFC5116"/>:</dt><dd>Provide the same authentication service of
	the content as AE algorithms do. They also allow for
	associated data to be included in the authentication service, but which that is not part of the encrypted body. body to be included
	in the authentication service. An example of an AEAD
	algorithm used in COSE is AES-GCM <xref target="RFC5116"/>. These
	algorithms are used for content encryption and can be used for key
	encryption as well.
        </t>
        </dd>
</dl>
        <t>The term 'byte string' "byte string" is used for sequences of bytes, while the term 'text string' "text string" is used for sequences of characters.</t>

        <t>
          The tables for algorithms contain the following columns:
        </t>
        <ul>
          <li>A name for the algorithms for use in documents for the algorithms.</li> documents.</li>
          <li>
            The value used on the wire for the algorithm.
            One place this is used is the algorithm header parameter of a message.
          </li>
          <li>A short description so that the algorithm can be easily identified when scanning the IANA registry.</li>
        </ul>
        <t>
          Additional columns may be present in the a table depending on the
	  algorithms.
        </t>
      </section>
      <section>

        <name>CBOR Grammar</name>
        <t>
<!--[rfced] According to RFC 8610 (cited below), the correct expansion for
CDDL is "Concise Data Definition Language"; we have updated the text accordingly.

Original:
At the time that [RFC8152] was initially published, the CBOR Data
Definition Language (CDDL) [RFC8610] had not yet been published.
-->
          At the time that <xref target="RFC8152"/> was initially published,
	  the CBOR Data Definition Language (CDDL) <xref target="RFC8610"/>
	  had not yet been published.
          This document uses a variant of CDDL which that is described in <xref target="I-D.ietf-cose-rfc8152bis-struct"/>. target="RFC9052"/>.
        </t>
      </section>
      <section anchor="examples">

        <name>Examples</name>
        <t>
          A GitHub project has been created at <xref
	  target="GitHub-Examples"/> that contains a set of testing examples
	  as well.
          Each 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 for debugging, and the output of the example.
          The results are encoded using both hexadecimal and
	  CBOR diagnostic notation format.
        </t>
        <t>
          Some of the examples are designed to test the failure case; these
	  are clearly marked as such in the JSON file.
          If errors in the examples in this document are found, the examples
	  on GitHub will be updated, and a note to that effect will be placed
	  in the JSON file.
        </t>
      </section>
    </section>

    <section anchor="SigAlgs">

      <name>Signature Algorithms</name>
      <t>
        <relref section="&SigSection;" target="I-D.ietf-cose-rfc8152bis-struct"/>
<!--[rfced] 1) The first sentence below cites a section that does not exist in
the cited document.  We have updated the text to refer to Section 8.1.  Please let us know if this is incorrect.

2) In the second sentence, does "the document" refer to
ietf-cose-rfc8152bis-struct or this document?

Original:
Section 9.1 of [I-D.ietf-cose-rfc8152bis-struct] contains a generic
description of signature algorithms.  The document defines signature
algorithm identifiers for two signature algorithms.
-->
        <xref section="8.1" target="RFC9052"/> contains a generic description of signature algorithms.
        The document defines signature algorithm identifiers for two signature algorithms.
      </t>
      <section anchor="ECDSA">

        <name>ECDSA</name>
        <t>ECDSA

        <t>The Elliptic Curve Digital Signature Algorithm (ECDSA) <xref
	target="DSS"/> defines a signature algorithm using ECC. Elliptic Curve Cryptography (ECC).
	Implementations <bcp14>SHOULD</bcp14> use a deterministic version of
	ECDSA such as the one defined in <xref target="RFC6979"/>.  The use of
	a deterministic signature algorithm allows for systems to avoid relying on
	random number generators in order to avoid generating the same value
	of 'k' "k" (the per-message random value). Biased generation of the value 'k'
	"k" can be attacked, and collisions of this value leads lead to leaked
	keys.  It additionally allows for doing performing deterministic tests for the
	signature algorithm.  The use of deterministic ECDSA does not lessen
	the need to have good random number generation when creating the
	private key.  </t>
        <t>The ECDSA signature algorithm is parameterized with a hash function
	(h).  In the event that the length of the hash function output is
	greater than the group of the key, the leftmost bytes of the hash
	output are used.  </t>

        <t>The algorithms defined in this document can be found in <xref target="x-table_ecdsa"/>.  </t>
        <table anchor="x-table_ecdsa" align="center">

          <name>ECDSA Algorithm Values</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th align="center">Value</th>
              <th>Hash</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>ES256</td>
              <td>-7</td>
              <td  align="center">-7</td>
              <td>SHA-256</td>
              <td>ECDSA w/ SHA-256</td>
            </tr>
            <tr>
              <td>ES384</td>
              <td>-35</td>
              <td  align="center">-35</td>
              <td>SHA-384</td>
              <td>ECDSA w/ SHA-384</td>
            </tr>
            <tr>
              <td>ES512</td>
              <td>-36</td>
              <td align="center">-36</td>
              <td>SHA-512</td>
              <td>ECDSA w/ SHA-512</td>
            </tr>
          </tbody>
        </table>
        <t>This document defines ECDSA
<!--[rfced] In the following sentence, should another "only" be inserted to work
match the first two statements?

Original:
In order to promote interoperability, it is suggested that SHA-256 be
used only with curve P-256, SHA-384 be used only with curve P-384,
and SHA-512 be used with curve P-521.

Perhaps:
... and SHA-512 be used only with curve P-521.
-->
        <t>This document defines ECDSA as working only with the curves P-256,
	P-384, and P-521.  This document requires that the curves be encoded
	using the 'EC2' "EC2" (two coordinate elliptic curve) key type.
	Implementations need to check that the key type and curve are correct
	when creating and verifying a signature.  Future documents may define
	it to work with other curves and points in the future.  </t>
        <t>In order to promote interoperability, it is suggested that SHA-256 be used only with curve P-256, SHA-384 be used only with curve P-384, and SHA-512 be used with curve P-521.  This is aligned with the recommendation in Section 4 of <xref target="RFC5480"/>. target="RFC5480" section="4" sectionFormat="of"/>.  </t>
        <t>
          The signature algorithm results in a pair of integers (R, S).
          These integers will be the same length as the length of the key used for the signature process.
          The signature is encoded by converting the integers into byte strings of the same length as the key size.
          The length is rounded up to the nearest byte and is left padded with zero bits to get to the correct length.
          The two integers are then concatenated together to form a byte string that is the resulting signature.
        </t>
        <t>
          Using the function defined in <xref target="RFC8017"/>, the signature is:
        </t>
        <t>
          Signature = I2OSP(R, n) | I2OSP(S, n)
        </t>
        <t>
          where n = ceiling(key_length / 8)
        </t>
        <t>When using a COSE key for this algorithm, the following checks are made:
        </t>

        <ul>

          <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'EC2'.</li> "EC2".</li>

          <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match the ECDSA signature algorithm being used.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'sign' "sign" when creating an ECDSA signature.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'verify' "verify" when verifying an ECDSA signature.</li>
        </ul>
        <section>

          <name>Security Considerations for ECDSA</name>
          <t>The security strength of the signature is no greater than the minimum of the security strength associated with the bit length of the key and the security strength of the hash function.  </t>

          <t>
            Note: Use of a deterministic signature technique is a good idea
	    even when good random number generation exists.
            Doing so both reduces the possibility of having the same value of 'k'
	    "k" in two signature operations and allows for reproducible
	    signature values, which helps testing.
            There have been recent attacks involving faulting the device in
	    order to extract the key.
            This can be addressed by combining both randomness and determinism
	    <xref target="I-D.mattsson-cfrg-det-sigs-with-noise"/>.
          </t>

          <t>There are two substitution attacks that can theoretically be mounted against the ECDSA signature algorithm.
          </t>

          <ul>

            <li>Changing the curve used to validate the signature: If one
	    changes the curve used to validate the signature, then potentially
	    one could have two messages with the same signature, each computed
	    under a different curve.  The only requirement requirements on the new curve is are
	    that its order be the same as the old one and that it be acceptable to
	    the client.  An example would be to change from using the curve
	    secp256r1 (aka P-256) to using secp256k1.  (Both are 256-bit
	    curves.) We currently do not have any way to deal with this
	    version of the attack except to restrict the overall set of curves
	    that can be used.  </li>

            <li>Change

            <li>Changing the hash function used to validate the signature: If
	    one either has two different hash functions of the same length or
	    can truncate a hash function, then one could potentially find
	    collisions between the hash functions rather than within a single
	    hash function (for function. For example, truncating SHA-512 to 256 bits might
	    collide with a SHA-256 bit hash value). value. As the hash algorithm is
	    part of the signature algorithm identifier, this attack is
	    mitigated by including a signature algorithm identifier in the protected header
	    protected-header bucket.  </li>
          </ul>
        </section>
      </section>
      <section>

       <name>Edwards-Curve Digital Signature Algorithms (EdDSAs)</name>
        <t><xref target="RFC8032"/> describes the elliptic curve signature
	scheme Edwards-curve Digital Signature Algorithm (EdDSA).  In that
	document, the signature algorithm is instantiated using parameters for
	edwards25519 and edwards448 curves.  The document additionally
	describes two variants of the EdDSA algorithm: Pure EdDSA, where no
	hash function is applied to the content before signing, and HashEdDSA,
	where a hash function is applied to the content before signing and the
	result of that hash function is signed.  For EdDSA, the content to be
	signed (either the message or the pre-hash prehash value) is processed twice
	inside of the signature algorithm.  For use with COSE, only the pure
	EdDSA version is used.  This is because it is not expected that
	extremely large contents are going to be needed and, based on the
	arrangement of the message structure, the entire message is going to
	need to be held in memory in order to create or verify a signature.  This means that
	Therefore, there does not appear to be a need to be able to do
	block updates of the hash, followed by eliminating the message from
	memory.  Applications can provide the same features by defining the
	content of the message as a hash value and transporting the COSE
	object (with the hash value) and the content as separate items.  </t>
        <t>The algorithms algorithm defined in this document can be found in <xref target="x-table-eddsa-algs"/>.  A single signature algorithm is defined, which can be used for multiple curves.  </t>
        <table anchor="x-table-eddsa-algs" align="center">

          <name>EdDSA Algorithm Values</name> Value</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th align="center">Value</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>EdDSA</td>
              <td>-8</td>
              <td align="center">-8</td>
              <td>EdDSA</td>
            </tr>
          </tbody>
        </table>
        <t><xref target="RFC8032"/> describes the method of encoding the signature value.  </t>
        <t>When using a COSE key for this algorithm, the following checks are made:
        </t>

        <ul>

          <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'OKP' "OKP" (Octet Key Pair).  </li>

          <li>The 'crv' "crv" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be a curve defined for this signature algorithm.</li>

          <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match 'EdDSA'.</li> "EdDSA".</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'sign' "sign" when creating an EdDSA signature.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'verify' "verify" when verifying an EdDSA signature.</li>
        </ul>
        <section>

          <name>Security Considerations for EdDSA</name>
          <t>How
<!--[rfced] What is "the other algorithm" mentioned in the following sentence?

Original:
How public values are computed is not the same when looking at EdDSA
and Elliptic Curve Diffie-Hellman (ECDH); for this reason, the public
key should not be used with the other algorithm.
-->
          <name>Security Considerations for EdDSA</name>
          <t>Public values are computed differently in EdDSA and Elliptic Curve
	  Diffie-Hellman (ECDH); for this reason, the public key should not be
	  used with the other algorithm.  </t>
          <t>If batch signature verification is performed, a well-seeded
	  cryptographic random number generator is <bcp14>REQUIRED</bcp14> (<relref
	  (<xref target="RFC8032" section="8.2"/>).  Signing and non-batch nonbatch
	  signature verification are deterministic operations and do not need
	  random numbers of any kind.  </t>
        </section>
      </section>
    </section>
    <section>

      <name>Message Authentication Code (MAC) Algorithms</name>
      <t>
        <relref section="&MacSection;" target="I-D.ietf-cose-rfc8152bis-struct"/>
<!--[rfced] The following sentence cites a section that does not exist in the
cited document. We have updated the text to refer to Section 8.2.  Please let us know if this is incorrect.

Original:
Section 9.2 of [I-D.ietf-cose-rfc8152bis-struct] contains a generic
description of MAC algorithms.
-->
        <xref section="9.2" target="RFC9052"/> contains a generic description
	of MAC algorithms.
        This section defines the conventions for two MAC algorithms.
      </t>
      <section>

        <name>Hash-Based Message Authentication Codes (HMACs)</name>
        <t>HMAC <xref target="RFC2104"/> <xref target="RFC4231"/> was designed
	to deal with length extension attacks.  The algorithm was also
	designed to allow for new hash algorithms to be directly plugged in
	without changes to the hash function.  The HMAC design process has
	been shown as solid since, while to be solid; although the security of hash algorithms such
	as MD5 has decreased over time; time, the security of HMAC combined with MD5
	has not yet been shown to be compromised <xref target="RFC6151"/>.
	</t>
        <t>The HMAC algorithm is parameterized by an inner and outer padding,
	a hash function (h), and an authentication tag value length.  For this
	specification, the inner and outer padding are fixed to the values set
	in <xref target="RFC2104"/>.  The length of the authentication tag
	corresponds to the difficulty of producing a forgery.  For use in
	constrained environments, we define one HMAC algorithm that is
	truncated.  There are currently no known issues with truncation;
	however, the security strength of the message tag is correspondingly
	reduced in strength.  When truncating, the leftmost tag length tag-length bits
	are kept and transmitted.  </t>
        <t>The algorithms defined in this document can be found in <xref target="x-table-hmac"/>.  </t>
        <table anchor="x-table-hmac" align="center">

          <name>HMAC Algorithm Values</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th align="center">Value</th>
              <th>Hash</th>
              <th>Tag
              <th align="center">Tag Length</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>HMAC 256/64</td>
              <td>4</td>
              <td align="center">4</td>
              <td>SHA-256</td>
              <td>64</td>
              <td align="center">64</td>
              <td>HMAC w/ SHA-256 truncated to 64 bits</td>
            </tr>
            <tr>
              <td>HMAC 256/256</td>
              <td>5</td>
              <td align="center">5</td>
              <td>SHA-256</td>
              <td>256</td>
              <td align="center">256</td>
              <td>HMAC w/ SHA-256</td>
            </tr>
            <tr>
              <td>HMAC 384/384</td>
              <td>6</td>
              <td align="center">6</td>
              <td>SHA-384</td>
              <td>384</td>
              <td align="center">384</td>
              <td>HMAC w/ SHA-384</td>
            </tr>
            <tr>
              <td>HMAC 512/512</td>
              <td>7</td>
              <td align="center">7</td>
              <td>SHA-512</td>
              <td>512</td>
              <td align="center">512</td>
              <td>HMAC w/ SHA-512</td>
            </tr>
          </tbody>
        </table>
        <t>Some recipient algorithms transport the key, while others derive a key from secret data.  For those algorithms that transport the key (such as AES Key Wrap), the size of the HMAC key <bcp14>SHOULD</bcp14> be the same size as the output of the  underlying hash function.  For those algorithms that derive the key (such as ECDH), the derived key <bcp14>MUST</bcp14> be the same size as the underlying hash function.  </t>
        <t>When using a COSE key for this algorithm, the following checks are made:
        </t>

        <ul>

          <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'Symmetric'.</li> "Symmetric".</li>

          <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match the HMAC algorithm being used.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'MAC create' "MAC create" when creating an HMAC authentication tag.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'MAC verify' "MAC verify" when verifying an HMAC authentication tag.</li>
        </ul>
        <t>Implementations creating and validating MAC values <bcp14>MUST</bcp14> validate that the key type, key length, and algorithm are correct and appropriate for the entities involved.  </t>
        <section>

          <name>Security Considerations for HMAC</name>
          <t>HMAC has proved to be resistant to attack even when used with weakened hash algorithms.  The current best known attack is to brute force the key.  This means that key size is going to be directly related to the security of an HMAC operation.  </t>
        </section>
      </section>
      <section>

        <name>AES Message Authentication Code (AES-CBC-MAC)</name>
<!-- [rfced] Sections 3.2 and subsequent:  Are "AES-CBC-MAC" and "AES-MAC"
interchangeable terms?  (We also see "CBC-MAC" as defined in RFC 3610; is
this also interchangeable with the other terms?)  Please let us know if any
clarifications are needed for readers; if yes, maybe an update to the first
paragraph of Section 3.2?

Original (Section 3.2):
AES-CBC-MAC is defined in [MAC].  (Note that this is not the same
algorithm as AES Cipher-Based Message Authentication Code (AES-CMAC)
[RFC4493].)

Possibly (assuming that the three terms are interchangeable):
AES-CBC-MAC (also referred to here as "AES-MAC" or CBC-MAC (Section 3.2.1))
is defined in [MAC].  (Note that this is not the same algorithm
as AES Cipher-Based Message Authentication Code (AES-CMAC)
[RFC4493].) -->
        <t>AES-CBC-MAC is defined in <xref target="MAC"/>.  (Note that this is
	not the same algorithm as AES Cipher-Based Message Authentication Code
	(AES-CMAC) <xref target="RFC4493"/>.) </t>
        <t>AES-CBC-MAC is parameterized by the key length, the
	authentication tag length, and the Initialization Vector (IV) used.
	For all of these algorithms, the IV is fixed to all zeros.  We provide
	an array of algorithms for various key lengths and tag lengths.  The
	algorithms defined in this document are found in <xref
	target="x-table-aes-mac"/>.  </t>
        <table anchor="x-table-aes-mac" align="center">

          <name>AES-MAC Algorithm Values</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th>Key
              <th align="center">Value</th>
              <th align="center">Key Length</th>
              <th>Tag
              <th align="center">Tag Length</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>AES-MAC 128/64</td>
              <td>14</td>
              <td>128</td>
              <td>64</td>
              <td align="center">14</td>
              <td align="center">128</td>
              <td align="center">64</td>
              <td>AES-MAC 128-bit key, 64-bit tag</td>
            </tr>
            <tr>
              <td>AES-MAC 256/64</td>
              <td>15</td>
              <td>256</td>
              <td>64</td>
              <td align="center">15</td>
              <td align="center">256</td>
              <td align="center">64</td>
              <td>AES-MAC 256-bit key, 64-bit tag</td>
            </tr>
            <tr>
              <td>AES-MAC 128/128</td>
              <td>25</td>
              <td>128</td>
              <td>128</td>
              <td align="center">25</td>
              <td align="center">128</td>
              <td align="center">128</td>
              <td>AES-MAC 128-bit key, 128-bit tag</td>
            </tr>
            <tr>
              <td>AES-MAC 256/128</td>
              <td>26</td>
              <td>256</td>
              <td>128</td>
              <td align="center">26</td>
              <td align="center">256</td>
              <td align="center">128</td>
              <td>AES-MAC 256-bit key, 128-bit tag</td>
            </tr>
          </tbody>
        </table>
        <t>Keys may be obtained either from either a key structure or from a
	recipient structure.  Implementations creating and validating MAC
	values <bcp14>MUST</bcp14> validate that the key type, key length, and
	algorithm are correct and appropriate for the entities involved.  </t>
        <t>When using a COSE key for this algorithm, the following checks are made:
        </t>

        <ul>

          <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'Symmetric'.</li> "Symmetric".</li>

          <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match the AES-MAC algorithm being used.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'MAC create' "MAC create" when creating an AES-MAC authentication tag.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'MAC verify' "MAC verify" when verifying an AES-MAC authentication tag.</li>
        </ul>
        <section>

          <name>Security Considerations AES-CBC_MAC for AES-CBC-MAC </name>
<!-- [rfced] We have updated the section title for 3.2.1 as shown below.  Please let us know if any corrections are needed.

Original (note the underscore):
   3.2.1.  Security Considerations AES-CBC_MAC

Current:
   3.2.1.  Security Considerations for AES-CBC-MAC
-->

          <t>A number of attacks exist against Cipher Block Chaining Message Authentication Code (CBC-MAC) that need to be considered.

          </t>

          <ul>

            <li>A single key must only be used for messages of a fixed or
	    known length.  If this is not the case, an attacker will be able
	    to generate a message with a valid tag given two
	    message and tag pairs.  This can be addressed by using different
	    keys for
	    messages of different lengths. The current structure mitigates
	    this problem, as a specific encoding structure that includes
	    lengths is built and signed.  (CMAC also addresses this issue.)
	    </li>

            <li>In cipher Cipher Block Chaining (CBC) mode, if the same key is used
	    for both encryption and authentication operations, an attacker can
	    produce messages with a valid authentication code.   </li>

            <li>If the IV can be modified, then messages can be forged.  This is addressed by fixing the IV to all zeros.  </li>
          </ul>
        </section>
      </section>
    </section>
    <section>

      <name>Content Encryption Algorithms</name>
      <t>
        <relref section="&ContentSection;" target="I-D.ietf-cose-rfc8152bis-struct"/>

<!--[rfced] The following sentence cites a section that does not exist in the
cited document. updated to refer to 8.3

Original:
Section 9.3 of [I-D.ietf-cose-rfc8152bis-struct] contains a generic
description of Content Encryption algorithms.
-->
        <xref section="9.3" target="RFC9052"/> contains a generic description
	of content encryption algorithms.
        This document defines the identifier and usages for three
	content encryption algorithms.
      </t>
      <section>

        <name>AES GCM</name>

        <name>AES-GCM</name>
<!-- [rfced] Note that we have removed "mode" when it appeared after GCM because M stands for mode (i.e., it reads as "Galois/Counter Mode mode").  Please let us know any objections.
-->

        <t>The Galois/Counter Mode (GCM) mode is a generic AEAD block cipher
	mode defined in <xref target="AES-GCM"/>.  The GCM mode is combined
	with the AES block encryption algorithm to define an AEAD cipher.
	</t>
        <t>The GCM mode is parameterized by the size of the authentication tag
	and the size of the nonce.  This document fixes the size of the nonce
	at 96 bits.  The size of the authentication tag is limited to a small
	set of values.  For this document document, however, the size of the
	authentication tag is fixed at 128 bits.  </t>
        <t>The set of algorithms defined in this document are is in <xref
	target="x-table-AES-GCM"/>.  </t>
        <table anchor="x-table-AES-GCM" align="center">

          <name>Algorithm Value Values for AES-GCM</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th align="center">Value</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>A128GCM</td>
              <td>1</td>
              <td align="center">1</td>
              <td>AES-GCM mode w/ 128-bit key, 128-bit tag</td>
            </tr>
            <tr>
              <td>A192GCM</td>
              <td>2</td>
              <td align="center">2</td>
              <td>AES-GCM mode w/ 192-bit key, 128-bit tag</td>
            </tr>
            <tr>
              <td>A256GCM</td>
              <td>3</td>
              <td align="center">3</td>
              <td>AES-GCM mode w/ 256-bit key, 128-bit tag</td>
            </tr>
          </tbody>
        </table>
        <t>Keys may be obtained either from either a key structure or from a recipient
	structure.  Implementations that are encrypting and decrypting
	<bcp14>MUST</bcp14> validate that the key type, key length, and
	algorithm are correct and appropriate for the entities involved.  </t>
        <t>When using a COSE key for this algorithm, the following checks are made:
        </t>

        <ul>

          <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'Symmetric'.</li> "Symmetric".</li>

          <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match the AES-GCM algorithm being used.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'encrypt' "encrypt" or 'wrap key' "wrap key" when encrypting.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'decrypt' "decrypt" or 'unwrap key' "unwrap key"  when decrypting.</li>
        </ul>
        <section>

          <name>Security Considerations for AES-GCM</name>
          <t>When using AES-GCM, the following restrictions <bcp14>MUST</bcp14> be enforced:
          </t>

          <ul>

            <li>The key and nonce pair <bcp14>MUST</bcp14> be unique for every
	    message encrypted.  </li>

<!-- [rfced] For clarity, we suggest the following updates:

Original from Section 4.1.1:
   *  The total number of messages encrypted for a single key MUST NOT
      exceed 2^32 [SP800-38d].  An explicit check is required only in
      environments where it is expected that it might be exceeded.

Original from Section 4.2.1:
     This limitation is the sum of times the
     block cipher is used in computing the MAC value and in performing
     stream encryption operations.  An explicit check is required only
     in environments where it is expected that it might be exceeded.

Perhaps:
      ... An explicit check is required only in
      environments where this limitation might be exceeded.
-->

            <li>The total number of messages encrypted for a single key
	    <bcp14>MUST NOT</bcp14> exceed 2^32 2<sup>32</sup> <xref target="SP800-38d"/>. target="SP800-38D"/>.
	    An explicit check is required only in environments where it is expected that it might be exceeded. </li>

            <li>
              A more recent analysis in <xref target="ROBUST"/> indicates that
	      the the number of failed decryptions needs to be taken into account
	      as part of determining when a key roll-over rollover is to be done.
<!--[rfced] There seems to be a word missing in the sentence below. Whose
recommendation is being followed; should a reference be added?  Note that this text appears more than once.

Original:
Following the recommendation of for DTLS, the number of failed message
decryptions should be limited to 2^36.

-->
              Following the recommendation of for DTLS, the number of failed
	      message decryptions should be limited to 2<sup>36</sup>.
            </li>

          </ul>
          <t>Consideration was given to supporting smaller tag values; the
	  constrained community would desire tag sizes in the 64-bit
	  range. Doing so Such use drastically changes both the maximum messages message size
	  (generally not an issue) and the number of times that a key can be
	  used.  Given that Counter with CBC-MAC (CCM) is the usual mode for
	  constrained environments, restricted modes are not supported.  </t>
        </section>
      </section>
      <section>

        <name>AES CCM</name>

        <name>AES-CCM</name>
        <t>CCM is a generic authentication encryption block cipher mode
	defined in <xref target="RFC3610"/>.  The CCM mode is combined with
	the AES block encryption algorithm to define a commonly used
	content encryption algorithm used in constrained devices.  </t>
        <t>The CCM
        <t>CCM mode has two parameter choices.  The first choice is M, the
	size of the authentication field.  The choice of the value for M
	involves a trade-off between message growth (from the tag) and the
	probability that an attacker can undetectably modify a message.  The
	second choice is L, the size of the length field.  This value requires
	a trade-off between the maximum message size and the size of the Nonce.
	nonce.  </t>
        <t>It is unfortunate that the specification for CCM specified L and M as a count of bytes rather than a count of bits.  This leads to possible misunderstandings where AES-CCM-8 is frequently used to refer to a version of CCM mode where the size of the authentication is 64 bits and not 8 bits.  These values have traditionally been specified as bit counts rather than byte counts.  This document will follow the convention of using bit counts so that it is easier to compare the different algorithms presented in this document.  </t>
        <t>We define a matrix of algorithms in this document over the values of L and M.  Constrained devices are usually operating in situations where they use short messages and want to avoid doing recipient-specific cryptographic operations.  This favors smaller values of both L and M.  Less-constrained devices will want to be able to use larger messages and are more willing to generate new keys for every operation.  This favors larger values of L and M.  </t>
        <t>The following values are used for L:
        </t>

        <dl newline="false">
          <dt>16 bits (2):</dt>
          <dd>This limits messages to 2^16 2<sup>16</sup> bytes (64 KiB) in length.
	  This is sufficiently long for messages in the constrained world.
	  The nonce length is 13 bytes allowing for 2^104 2<sup>104</sup> possible values of
	  the nonce without repeating.  </dd>

          <dt>64 bits (8):</dt>
          <dd>This limits messages to 2^64 2<sup>64</sup> bytes in length.  The
	  nonce length is 7 bytes bytes, allowing for 2^56 2<sup>56</sup> possible values of the nonce without repeating.  </dd>
        </dl>
        <t>The following values are used for M:
        </t>

        <dl newline="false">
          <dt>64 bits (8):</dt>
          <dd>This produces a 64-bit authentication tag.  This implies that
	  there is a 1 in 2^64 2<sup>64</sup> chance that a modified message will authenticate.  </dd>
	  authenticate.</dd>

          <dt>128 bits (16):</dt>
          <dd>This produces a 128-bit authentication tag.  This implies that
	  there is a 1 in 2^128 2<sup>128</sup> chance that a modified message will authenticate.  </dd>
	  authenticate.</dd>
        </dl>
        <table anchor="x-table-AES-CCM" align="center">

          <name>Algorithm Values for AES-CCM</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th align="center">Value</th>
              <th>L</th>
              <th>M</th>
              <th>Key
              <th align="center">Key Length</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>AES-CCM-16-64-128</td>
              <td>10</td>
              <td align="center">10</td>
              <td>16</td>
              <td>64</td>
              <td>128</td>
              <td align="center">128</td>
              <td>AES-CCM mode 128-bit key, 64-bit tag, 13-byte nonce</td>
            </tr>
            <tr>
              <td>AES-CCM-16-64-256</td>
              <td>11</td>
              <td align="center">11</td>
              <td>16</td>
              <td>64</td>
              <td>256</td>
              <td align="center">256</td>
              <td>AES-CCM mode 256-bit key, 64-bit tag, 13-byte nonce</td>
            </tr>
            <tr>
              <td>AES-CCM-64-64-128</td>
              <td>12</td>
              <td align="center">12</td>
              <td>64</td>
              <td>64</td>
              <td>128</td>
              <td align="center">128</td>
              <td>AES-CCM mode 128-bit key, 64-bit tag, 7-byte nonce</td>
            </tr>
            <tr>
              <td>AES-CCM-64-64-256</td>
              <td>13</td>
              <td align="center">13</td>
              <td>64</td>
              <td>64</td>
              <td>256</td>
              <td align="center">256</td>
              <td>AES-CCM mode 256-bit key, 64-bit tag, 7-byte nonce</td>
            </tr>
            <tr>
              <td>AES-CCM-16-128-128</td>
              <td>30</td>
              <td align="center">30</td>
              <td>16</td>
              <td>128</td>
              <td>128</td>
              <td align="center">128</td>
              <td>AES-CCM mode 128-bit key, 128-bit tag, 13-byte nonce</td>
            </tr>
            <tr>
              <td>AES-CCM-16-128-256</td>
              <td>31</td>
              <td align="center">31</td>
              <td>16</td>
              <td>128</td>
              <td>256</td>
              <td align="center">256</td>
              <td>AES-CCM mode 256-bit key, 128-bit tag, 13-byte nonce</td>
            </tr>
            <tr>
              <td>AES-CCM-64-128-128</td>
              <td>32</td>
              <td align="center">32</td>
              <td>64</td>
              <td>128</td>
              <td>128</td>
              <td align="center">128</td>
              <td>AES-CCM mode 128-bit key, 128-bit tag, 7-byte nonce</td>
            </tr>
            <tr>
              <td>AES-CCM-64-128-256</td>
              <td>33</td>
              <td align="center">33</td>
              <td>64</td>
              <td>128</td>
              <td>256</td>
              <td align="center">256</td>
              <td>AES-CCM mode 256-bit key, 128-bit tag, 7-byte nonce</td>
            </tr>
          </tbody>
        </table>
        <t>Keys may be obtained either from either a key structure or from a recipient
	structure.  Implementations that are encrypting and decrypting
	<bcp14>MUST</bcp14> validate that the key type, key length, and
	algorithm are correct and appropriate for the entities involved.  </t>
        <t>When using a COSE key for this algorithm, the following checks are made:
        </t>

        <ul>

          <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'Symmetric'.</li> "Symmetric".</li>

          <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match the AES-CCM algorithm being used.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'encrypt' "encrypt" or 'wrap key' "wrap key" when encrypting.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'decrypt' "decrypt" or 'unwrap key' "unwrap key"  when decrypting.</li>
        </ul>
        <section>

          <name>Security Considerations for AES-CCM</name>
          <t>When using AES-CCM, the following restrictions <bcp14>MUST</bcp14> be enforced:
          </t>

          <ul>

            <li>The key and nonce pair <bcp14>MUST</bcp14> be unique for every message encrypted. Note that the value of L influences the number of unique nonces.  </li>

            <li>The total number of times the AES block cipher is used
	    <bcp14>MUST NOT</bcp14> exceed 2^61 2<sup>61</sup> operations.  This
	    limitation is the sum of times the block cipher is used in
	    computing the MAC value and in performing stream encryption
	    operations.  An explicit check is required only in environments
	    where it is expected that it this number might be exceeded.  </li>
            <li>
              <xref target="I-D.ietf-quic-tls"/> target="RFC9001"/> contains an analysis on the
	      use of AES-CCM in that environment.
              Based on that reommendation, recommendation, one should restrict the number of
	      messages encrypted to 2^23. 2<sup>23</sup>.
              If one is using the 64-bit tag, then the limits are signficantly significantly smaller if one wants to keep the same integrity limits.
              A protocol recommending this needs to analysis analyze what level of integrity is acceptable for the smaller tag size.
              It may be that that, to keep the desired integrity integrity, one needs to re-key rekey as often as every 2^7 2<sup>7</sup> messages.
            </li>
            <li>
              In addition to the number of messages successfully decrypted, the number of failed decryptions needs to be kept as well.
              If the number of failed decryptions exceeds 2^23 2<sup>23</sup>, then
	      a rekeying operation should occur.
            </li>
          </ul>
          <t><xref target="RFC3610"/> additionally calls out one other
	  consideration of note.  It is possible to do a pre-computation precomputation
	  attack against the algorithm in cases where portions of the
	  plaintext are  highly predictable.  This reduces the security of the
	  key size by half.  Ways to deal with this attack include adding a
	  random portion to the nonce value and/or increasing the key size
	  used.  Using a portion of the nonce for a random value will decrease
	  the number of messages that a single key can be used for.
	  Increasing the key size may require more resources in the
	  constrained device.  See Sections 5 <xref target="RFC3610" section="5"
	  sectionFormat="bare"/> and 10 <xref target="RFC3610" section="10"
	  sectionFormat="bare"/> of <xref target="RFC3610"/> for more
	  information.  </t>
        </section>
      </section>
      <section>

        <name>ChaCha20 and Poly1305</name>
        <t>ChaCha20 and Poly1305 combined together is an AEAD mode that is defined in <xref target="RFC8439"/>.  This is an algorithm defined to be a cipher that is not AES and thus would not suffer from any future weaknesses found in AES.  These cryptographic functions are designed to be fast in software-only implementations.  </t>
        <t>The ChaCha20/Poly1305 AEAD construction defined in <xref
	target="RFC8439"/> has no parameterization.  It takes as inputs a
	256-bit key and a 96-bit nonce, as well as the plaintext and
	additional data as inputs data, and produces the ciphertext as an option.  We define
	one algorithm identifier for this algorithm in <xref
	target="x-table-CHACHA"/>.  </t>
        <table anchor="x-table-CHACHA" align="center">

          <name>Algorithm Value for ChaCha20/Poly1305</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th align="center">Value</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>ChaCha20/Poly1305</td>
              <td>24</td>
              <td align="center">24</td>
              <td>ChaCha20/Poly1305 w/ 256-bit key, 128-bit tag</td>
            </tr>
          </tbody>
        </table>
        <t>Keys may be obtained either from either a key structure or from a recipient
	structure.  Implementations that are encrypting and decrypting
	<bcp14>MUST</bcp14> validate that the key type, key length, and
	algorithm are correct and appropriate for the entities involved.  </t>
        <t>When using a COSE key for this algorithm, the following checks are made:
        </t>

        <ul>

          <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'Symmetric'.</li> "Symmetric".</li>

          <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match the ChaCha20/Poly1305 algorithm being used.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'encrypt' "encrypt" or 'wrap key' "wrap key" when encrypting.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'decrypt' "decrypt" or 'unwrap key' "unwrap key"  when decrypting.</li>
        </ul>
        <section>

          <name>Security Considerations for ChaCha20/Poly1305</name>
          <t>The key and nonce values <bcp14>MUST</bcp14> be a unique pair for every invocation of the algorithm.  Nonce counters are considered to be an acceptable way of ensuring that they are unique.  </t>
<t>
              A

	  <t>A more recent analysis in <xref target="ROBUST"/> indicates that
	  the the number of failed decryptions needs to be taken into account as
	  part of determining when a key roll-over rollover is to be done. Following the
	  recommendation of for DTLS, the number of failed message decryptions
	  should be limited to 2^36. 2<sup>36</sup>.
</t>
<t>
              <xref target="I-D.ietf-quic-tls"/> target="RFC9001"/> recommends that no more than 2^24.5
	      2<sup>24.5</sup> messages be encrypted under a single key.
</t>
        </section>
      </section>
    </section>
    <section>
      <name>Key Derivation Functions (KDFs)</name>
      <t>
        <relref section="&KDFSection;" target="I-D.ietf-cose-rfc8152bis-struct"/>
<!--[rfced] The following sentence cites a section that does not exist in the
cited document. We have updated this section to point to 8.4.  Please let us know if this is incorrect.

Original:
Section 9.4 of [I-D.ietf-cose-rfc8152bis-struct] contains a generic
description of Key Derivation Functions.
-->
        <xref section="9.4" target="RFC9052"/> contains a generic description
	of key derivation functions.
        This document defines a single context structure and a single KDF.
        These elements are used for all of the recipient algorithms defined in
	this document that require a KDF process.
        These algorithms are defined in Sections <xref target="direct-kdf"
	format="counter"/>, <xref target="ECDH" format="counter"/>, and <xref
	target="ECDH-wrap" format="counter"/>.
      </t>
      <section anchor="HKDF-section">

        <name>HMAC-Based Extract-and-Expand Key Derivation Function (HKDF)</name>

        <t>The HKDF key derivation algorithm is defined in <xref target="RFC5869"/><xref
	target="RFC5869"/> and <xref target="HKDF"/>.  </t>

	<t>The HKDF algorithm takes these inputs:
        </t>

        <ul empty="true">

          <li>secret -- a inputs:</t>

	<dl>
          <dt>secret:</dt><dd> A shared value that is secret.  Secrets may be
	  either previously shared or derived from operations like a
	  Diffie-Hellman (DH) key agreement.  </li>

          <li>salt -- an  </dd>

          <dt>salt:</dt><dd> An optional value that is used to change the
	  generation process.  The salt value can be either public or private.
	  If the salt is public and carried in the message, then the 'salt' "salt"
	  algorithm header parameter defined in <xref
	  target="HKDF_Alg_Params"/> is used.  While <xref target="RFC5869"/>
	  suggests that the length of the salt be the same as the length of
	  the underlying hash value, any positive salt length will improve the security
	  security, as different key values will be generated.  This parameter
	  is protected by being included in the key computation and does not
	  need to be separately authenticated.  The salt value does not need
	  to be unique for every message sent.  </li>

          <li>length -- the  </dd>

          <dt>length:</dt><dd>The number of bytes of output that need to be generated.  </li>

          <li>context information -- Information  </dd>

          <dt>context information:</dt><dd>Information that describes the
	  context in which the resulting value will be used.  Making this
	  information specific to the context in which the material is going
	  to be used ensures that the resulting material will always be tied
	  to that usage.  The context structure defined in <xref
	  target="context"/> is used by the KDFs in this document.  </li>

          <li>PRF --  </dd>

          <dt>PRF:</dt><dd> The underlying pseudorandom function to be used in
	  the HKDF algorithm.  The PRF is encoded into the HKDF algorithm
	  selection.  </li>
        </ul>  </dd>
 </dl>

        <t>HKDF is defined to use HMAC as the underlying PRF.  However, it is
	possible to use other functions in the same construct to provide a
	different KDF that is more appropriate in the constrained world.
	Specifically, one can use AES-CBC-MAC as the PRF for the expand step,
	but not for the extract step.  When using a good random shared secret
	of the correct length, the extract step can be skipped.  For the AES
	algorithm versions, the extract step is always skipped.  </t>

        <t>The extract step cannot be skipped if the secret is not uniformly random,
	random -- for example, if it is the result of an ECDH key agreement
	step. This implies that the AES HKDF version cannot be used with
	ECDH. If the extract step is skipped, the 'salt' "salt" value is not used as
	part of the HKDF functionality.  </t>
        <t>The algorithms defined in this document are found in <xref target="x-table-hkdf"/>.  </t>
        <table anchor="x-table-hkdf" align="center">

          <name>HKDF Algorithms</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>PRF</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>HKDF SHA-256</td>
              <td>HMAC with SHA-256</td>
              <td>HKDF using HMAC SHA-256 as the PRF</td>
            </tr>
            <tr>
              <td>HKDF SHA-512</td>
              <td>HMAC with SHA-512</td>
              <td>HKDF using HMAC SHA-512 as the PRF</td>
            </tr>
            <tr>
              <td>HKDF AES-MAC-128</td>
              <td>AES-CBC-MAC-128</td>
              <td>HKDF using AES-MAC as the PRF w/ 128-bit key</td>
            </tr>
            <tr>
              <td>HKDF AES-MAC-256</td>
              <td>AES-CBC-MAC-256</td>
              <td>HKDF using AES-MAC as the PRF w/ 256-bit key</td>
            </tr>
          </tbody>
        </table>
        <table anchor="HKDF_Alg_Params" align="center">

<!-- [rfced]  Table 9:  Because this table deals with one algorithm
parameter - the "salt" parameter - we have updated the title so that
it does not indicate more than one parameter.

Original:
Table 9: HKDF Algorithm Parameters

Current:
Table 9: HKDF Algorithm Header Parameter -->

          <name>HKDF Algorithm Parameters</name> Parameter</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Label</th>
              <th>Type</th>
              <th>Algorithm</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>salt</td>
              <td>-20</td>
              <td>bstr</td>
              <td>direct+HKDF-SHA-256, direct+HKDF-SHA-512, direct+HKDF-AES-128, direct+HKDF-AES-256, ECDH-ES+HKDF-256, ECDH-ES+HKDF-512, ECDH-SS+HKDF-256, ECDH-SS+HKDF-512, ECDH-ES+A128KW, ECDH-ES+A192KW, ECDH-ES+A256KW, ECDH-SS+A128KW, ECDH-SS+A192KW, ECDH-SS+A256KW </td>
              <td>Random salt</td>
            </tr>
          </tbody>
        </table>
      </section>
      <section anchor="context">

        <name>Context Information Structure</name>
        <t>The context information structure is used to ensure that the
	derived keying material is "bound" to the context of the transaction.
	The context information structure used here is based on that defined
	in <xref target="SP800-56A"/>.  By using CBOR for the encoding of the
	context information structure, we automatically get the same type and
	length separation of fields that is obtained by the use of ASN.1.
<!--[rfced] JOSE doesn't seem to be discussed in the cited section. Please
review the citation for accuracy.

Original:
This means that there is no need to encode the lengths for the base
elements, as it is done by the encoding used in JOSE (Section 4.6.2
of <xref target="RFC7518"/>).   </t> [RFC7518]).
-->
	This means that there is no need to encode the lengths for the base
	elements, as it is done by the encoding used in JSON Object Signing
	and Encryption (JOSE) (<xref target="RFC7518" section="4.6.2"
	sectionFormat="of"/>).</t>
<!-- [rfced] Please consider whether instances of "Party U" and "Party V" should be "PartyU" and "PartyV" thoughout.  If the intent is to use "Party V" and "Party U" (with spaces) in general text, some updates may be needed.
-->

        <t>The context information structure refers to PartyU and PartyV as
	the two parties that are doing the key derivation.  Unless the
	application protocol defines differently, we assign PartyU to the
	entity that is creating the message and PartyV to the entity that is
	receiving the message.  By doing defining this association, different keys
	will be derived for each direction direction, as the context information is
	different in each direction.  </t> direction.</t>
        <t>The context structure is built from information that is known to both entities.  This information can be obtained from a variety of sources:
        </t>

        <ul>

          <li>Fields can be defined by the application.  This is commonly used to assign fixed names to parties, but it can be used for other items such as nonces.  </li>

          <li>Fields can be defined by usage of the output.  Examples of this are the algorithm and key size that are being generated.  </li>

          <li>Fields can be defined by parameters from the message.  We define
	  a set of header parameters in <xref
	  target="KDF_Context_Alg_Params"/> that can be used to carry the
	  values associated with the context structure.  Examples of this are
	  identities and nonce values.  These header parameters are designed
	  to be placed in the unprotected bucket of the recipient structure;
	  they do not need to be in the protected bucket bucket, since they already are already
	  included in the cryptographic computation by virtue of being
	  included in the context structure. </li>
        </ul>
        <table anchor="KDF_Context_Alg_Params" align="center">

          <name>Context Algorithm Parameters</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Label</th>
              <th>Type</th>
              <th>Algorithm</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>PartyU identity</td>
              <td>-21</td>
              <td>bstr</td>
              <td>direct+HKDF-SHA-256, direct+HKDF-SHA-512, direct+HKDF-AES-128, direct+HKDF-AES-256, ECDH-ES+HKDF-256, ECDH-ES+HKDF-512, ECDH-SS+HKDF-256, ECDH-SS+HKDF-512, ECDH-ES+A128KW, ECDH-ES+A192KW, ECDH-ES+A256KW, ECDH-SS+A128KW, ECDH-SS+A192KW, ECDH-SS+A256KW </td>
              <td>Party U identity information</td>
            </tr>
            <tr>
              <td>PartyU nonce</td>
              <td>-22</td>
              <td>bstr / int</td>
              <td>direct+HKDF-SHA-256, direct+HKDF-SHA-512, direct+HKDF-AES-128, direct+HKDF-AES-256, ECDH-ES+HKDF-256, ECDH-ES+HKDF-512, ECDH-SS+HKDF-256, ECDH-SS+HKDF-512, ECDH-ES+A128KW, ECDH-ES+A192KW, ECDH-ES+A256KW, ECDH-SS+A128KW, ECDH-SS+A192KW, ECDH-SS+A256KW </td>
              <td>Party U provided nonce</td>
            </tr>
            <tr>
              <td>PartyU other</td>
              <td>-23</td>
              <td>bstr</td>
              <td>direct+HKDF-SHA-256, direct+HKDF-SHA-512, direct+HKDF-AES-128, direct+HKDF-AES-256, ECDH-ES+HKDF-256, ECDH-ES+HKDF-512, ECDH-SS+HKDF-256, ECDH-SS+HKDF-512, ECDH-ES+A128KW, ECDH-ES+A192KW, ECDH-ES+A256KW, ECDH-SS+A128KW, ECDH-SS+A192KW, ECDH-SS+A256KW </td>
              <td>Party U other provided information</td>
            </tr>
            <tr>
              <td>PartyV identity</td>
              <td>-24</td>
              <td>bstr</td>
              <td>direct+HKDF-SHA-256, direct+HKDF-SHA-512, direct+HKDF-AES-128, direct+HKDF-AES-256, ECDH-ES+HKDF-256, ECDH-ES+HKDF-512, ECDH-SS+HKDF-256, ECDH-SS+HKDF-512, ECDH-ES+A128KW, ECDH-ES+A192KW, ECDH-ES+A256KW, ECDH-SS+A128KW, ECDH-SS+A192KW, ECDH-SS+A256KW </td>
              <td>Party V identity information</td>
            </tr>
            <tr>
              <td>PartyV nonce</td>
              <td>-25</td>
              <td>bstr / int</td>
              <td>direct+HKDF-SHA-256, direct+HKDF-SHA-512, direct+HKDF-AES-128, direct+HKDF-AES-256, ECDH-ES+HKDF-256, ECDH-ES+HKDF-512, ECDH-SS+HKDF-256, ECDH-SS+HKDF-512, ECDH-ES+A128KW, ECDH-ES+A192KW, ECDH-ES+A256KW, ECDH-SS+A128KW, ECDH-SS+A192KW, ECDH-SS+A256KW </td>
              <td>Party V provided nonce</td>
            </tr>
            <tr>
              <td>PartyV other</td>
              <td>-26</td>
              <td>bstr</td>
              <td>direct+HKDF-SHA-256, direct+HKDF-SHA-512, direct+HKDF-AES-128, direct+HKDF-AES-256, ECDH-ES+HKDF-256, ECDH-ES+HKDF-512, ECDH-SS+HKDF-256, ECDH-SS+HKDF-512, ECDH-ES+A128KW, ECDH-ES+A192KW, ECDH-ES+A256KW, ECDH-SS+A128KW, ECDH-SS+A192KW, ECDH-SS+A256KW </td>
              <td>Party V other provided information</td>
            </tr>
          </tbody>
        </table>
        <t>We define a CBOR object to hold the context information.  This object is referred to as COSE_KDF_Context.  The object is based on a CBOR array type.  The fields in the array are:
        </t>

        <dl newline="false">
          <dt>AlgorithmID:</dt>
          <dd>
            This field indicates the algorithm for which the key material will be used.
            This normally is either a key wrap algorithm identifier or a
	    content encryption algorithm identifier.
            The values are from the "COSE Algorithms" registry.
            This field is required to be present.
            The field exists in the context information so that a different key is generated for each algorithm even of if all of the other context information is the same.
            In practice, this means if algorithm A is broken and thus finding the key is relatively easy, the key derived for algorithm B will not be the same as the key derived for algorithm A.
          </dd>

          <dt>PartyUInfo:</dt>

          <dd>
            <t>This field holds information about party U. PartyU.  The PartyUInfo is
	    encoded as a CBOR array.  The elements of PartyUInfo are encoded
	    in the order presented below.  The elements of the PartyUInfo
	    array are:

            </t>

            <dl newline="false">
              <dt>identity:</dt>

              <dd>
                <t>This contains the identity information for party U. PartyU.  The
		identities can be assigned in one of two manners.  First, a
		protocol can assign identities based on roles.  For example,
		the roles of "client" and "server" may be assigned to
		different entities in the protocol.  Each entity would then
		use the correct label for the data they send it sends or receive. receives.  The
		second way for a protocol to assign identities is to use a
		name based on a naming system (i.e., DNS, DNS or X.509 names).
                </t>
                <t> We define an algorithm parameter 'PartyU identity' parameter, "PartyU identity", that
		can be used to carry identity information in the message.
		However, identity information is often known as to be part of the
		protocol and can thus be inferred rather than made explicit.
		If identity information is carried in the message,
		applications <bcp14>SHOULD</bcp14> have a way of validating
		the supplied identity information.  The identity information
		does not need to be specified and is set to nil in that case.
		</t>
              </dd>
              <dt>nonce:</dt>

              <dd>
                <t>This contains a nonce value.  The nonce can either be either
		implicit from the protocol or be carried as a value in the
		unprotected header bucket.

                </t>
                <t>
<!-- [rfced] Assuming that "the nonce value" and "the value" mean the same thing, should "and" be "or" here (i.e., the nonce value could be determined by the application or the value determined from elsewhere)?

Original:
         We define an algorithm parameter 'PartyU nonce' that can be
         used to carry this value in the message; however, the nonce
         value could be determined by the application and the value
         determined from elsewhere.

                </t>
-->

                <t> This option does not need to be specified and is set to nil in We define an algorithm parameter, "PartyU nonce", that case. can be used to carry this value in the message; however, the nonce value could be determined by the application and the value determined from elsewhere.

                </t>
                <t> This option does not need to be specified; if not
		needed, it is set to nil. </t>
              </dd>
              <dt>other:</dt>

              <dd>This contains other information that is defined by the protocol. This option does not need to be specified and specified; if not needed, it is set to nil in that case. nil. </dd>
            </dl>
          </dd>
          <dt>PartyVInfo:</dt>

          <dd>This field holds information about party V.  The content of the structure is the same as for the PartyUInfo but for party V.  </dd>
          <dt>SuppPubInfo:</dt>

          <dd>
            <t>This field contains public information that is mutually known to both parties.

            </t>

            <dl newline="false">
              <dt>keyDataLength:</dt>

              <dd>This is set to the number of bits of the desired output
	      value.  This practice means if algorithm A can use two different
	      key lengths, the key derived for the longer key size will not
	      contain the key for the shorter key size as a prefix. </dd>
              <dt>protected:</dt>

              <dd>This field contains the protected parameter field.  If there
	      are no elements in the protected "protected" field, then use a zero-length
	      bstr.  </dd>
              <dt>other:</dt>

              <dd>This field is for free form free-form data defined by the application.  An example is that
	      For example, an application could define two different
	      byte strings to be placed here to generate different keys for a
	      data stream versus a control stream.  This field is optional and
	      will only be present if the application defines a structure for
	      this information.  Applications that define this
	      <bcp14>SHOULD</bcp14> use CBOR to encode the data so that types
	      and lengths are correctly included.  </dd>
            </dl>
          </dd>
          <dt>SuppPrivInfo:</dt>

          <dd>This field contains private information that is mutually known private information.  An example of this information would be a preexisting pre-existing shared secret.  (This could, for example, be used in combination with an ECDH key agreement to provide a secondary proof of identity.) The field is optional and will only be present if the application defines a structure for this information.  Applications that define this <bcp14>SHOULD</bcp14> use CBOR to encode the data so that types and lengths are correctly included.  </dd>
        </dl>
        <t>The following CDDL fragment corresponds to the text above.  </t>
        <artwork type="CDDL" name="" alt=""><![CDATA[

        <sourcecode type="CDDL"><![CDATA[
PartyInfo = (
    identity : bstr / nil,
    nonce : bstr / int / nil,
    other : bstr / nil
)

COSE_KDF_Context = [
    AlgorithmID : int / tstr,
    PartyUInfo : [ PartyInfo ],
    PartyVInfo : [ PartyInfo ],
    SuppPubInfo : [
        keyDataLength : uint,
        protected : empty_or_serialized_map,
        ? other : bstr
    ],
    ? SuppPrivInfo : bstr
]
]]></artwork>
]]></sourcecode>
      </section>
    </section>
    <section anchor="key-management-algs">

      <name>Content Key Distribution Methods</name>
      <t>
        <relref section="&CKeyDistributeSection;" target="I-D.ietf-cose-rfc8152bis-struct"/>
<!--[rfced] The following sentence cites a section that does not exist in the
cited document. We have updated this to point to Section 8.5 of RFC 9052.  Please review.

Original:
Section 9.5 of [I-D.ietf-cose-rfc8152bis-struct] contains a generic
description of content key distribution methods.
-->
        <xref section="8.5" target="RFC9052"/> contains a generic description of content key distribution methods.
        This document defines the identifiers and usage for a number of content key distribution methods.
      </t>
      <section>
        <name>Direct Encryption</name>
        <t>
<!--[rfced] The following sentence cites a section that does not exist in the
cited document. We have updated the text to refer to Section 9.5.1.  Please let us know if any corrections are needed.

Original:
Direct encryption algorithm is defined in <relref section="&DirectDistribute;" target="I-D.ietf-cose-rfc8152bis-struct"/>. Section 9.5.1 of
[I-D.ietf-cose-rfc8152bis-struct].
-->
          A direct encryption algorithm is defined in <xref section="8.5.1"
	  target="RFC9052"/>.
          Information about how to fill in the COSE_Recipient structure are is detailed there.
        </t>
        <section>

          <name>Direct Key</name>
          <t>
          This recipient algorithm is the simplest; the identified key is directly used as the key for the next layer down in the message.
          There are no algorithm parameters defined for this algorithm.
          The algorithm identifier value is assigned  in <xref target="x-table-direct"/>.
          </t>
          <t>
          When this algorithm is used, the protected "protected" field
	  <bcp14>MUST</bcp14> be have zero length.
          The key type <bcp14>MUST</bcp14> be 'Symmetric'. "Symmetric".

          </t>
          <table anchor="x-table-direct" align="center">

            <name>Direct Key</name>
            <thead>
              <tr>
                <th>Name</th>
                <th>Value</th>
                <th align="center">Value</th>
                <th>Description</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td>direct</td>
                <td>-6</td>
                <td align="center">-6</td>

                <td>Direct use of CEK</td> content encryption key (CEK)</td>
              </tr>
            </tbody>
          </table>
          <section>

            <name>Security Considerations for Direct Key</name>
            <t>This recipient algorithm has several potential problems that need to be considered:
            </t>

            <ul>

              <li>These keys need to have some method to be of being regularly updated over time.  All of the content encryption algorithms specified in this document have limits on how many times a key can be used without significant loss of security.  </li>

              <li>These keys need to be dedicated to a single algorithm.  There have been a number of attacks developed over time when a single key is used for multiple different algorithms.  One example of this is the use of a single key for both the CBC encryption mode and the CBC-MAC authentication mode.  </li>

              <li>Breaking one message means all messages are broken.  If an adversary succeeds in determining the key for a single message, then the key for all messages is also determined.  </li>
            </ul>
          </section>
        </section>
        <section anchor="direct-kdf">

          <name>Direct Key with KDF</name>
          <t>These recipient algorithms take a common shared secret between
	  the two parties and applies the apply HKDF function (<xref
	  target="HKDF-section"/>), using the context structure defined in
	  <xref target="context"/> to transform the shared secret into the
	  CEK.  The 'protected' "protected" field can be of non-zero nonzero length.  Either the 'salt' "salt"
	  parameter of HKDF or the 'PartyU nonce' "PartyU nonce" parameter of the context
	  structure <bcp14>MUST</bcp14> be present.  The salt/nonce "salt"/"nonce" parameter
	  can be generated either randomly or deterministically.  The
	  requirement is that it be a unique value for the shared secret in
	  question.  </t>
          <t>If the salt/nonce value is generated randomly, then it is suggested that the length of the random value be the same length as the output of the hash function underlying HKDF.  While there is no way to guarantee that it will be unique, there is a high probability that it will be unique.  If the salt/nonce value is generated deterministically, it can be guaranteed to be unique, and thus there is no length requirement.  </t>
          <t>A new IV must be used for each message if the same key is used.  The IV can be modified in a predictable manner, a random manner, or an unpredictable manner (i.e., encrypting a counter).  </t>
          <t>The IV used for a key can also be generated from using the same HKDF
	  functionality as used to generate the key is generated. key.  If HKDF is used for
	  generating the IV, the algorithm identifier is set to
	  "IV-GENERATION".  </t>

          <t>The set of algorithms defined in this document can be found in <xref target="x-table-direct-kdf"/>.  </t>

          <table anchor="x-table-direct-kdf" align="center">

            <name>Direct Key with KDF</name>
            <thead>
              <tr>
                <th>Name</th>
                <th>Value</th>
                <th align="center">Value</th>
                <th>KDF</th>
                <th>Description</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td>direct+HKDF-SHA-256</td>
                <td>-10</td>
                <td align="center">-10</td>
                <td>HKDF SHA-256</td>
                <td>Shared secret w/ HKDF and SHA-256</td>
              </tr>
              <tr>
                <td>direct+HKDF-SHA-512</td>
                <td>-11</td>
                <td align="center">-11</td>
                <td>HKDF SHA-512</td>
                <td>Shared secret w/ HKDF and SHA-512</td>
              </tr>
              <tr>
                <td>direct+HKDF-AES-128</td>
                <td>-12</td>
                <td align="center">-12</td>
                <td>HKDF AES-MAC-128</td>
                <td>Shared secret w/ AES-MAC 128-bit key</td>
              </tr>
              <tr>
                <td>direct+HKDF-AES-256</td>
                <td>-13</td>
                <td align="center">-13</td>
                <td>HKDF AES-MAC-256</td>
                <td>Shared secret w/ AES-MAC 256-bit key</td>
              </tr>
            </tbody>
          </table>
          <t>When using a COSE key for this algorithm, the following checks are made:
          </t>

          <ul>

            <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'Symmetric'.</li> "Symmetric".</li>

            <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match the algorithm being used.</li>

            <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'deriveKey' "deriveKey" or 'deriveBits'.</li> "deriveBits".</li>
          </ul>
          <section>

            <name>Security Considerations for Direct Key with KDF</name>
            <t>The shared secret needs to have some method to be of being regularly
	    updated over time.  The shared secret forms the basis of trust.
	    Although not used directly, it should still be subject to
	    scheduled rotation.  </t>
            <t>While these
            <t>These methods do not provide for perfect forward secrecy, as
	    the same shared secret is used for all of the keys generated, generated;
	    however, if the key for any single message is discovered, only the
	    message (or or series of messages) messages using that derived key are
	    compromised.  A new key derivation step will generate a new key that requires the same
	    amount of work to get the key.  </t>
          </section>
        </section>
      </section>
      <section anchor="key_wrap_algs">
        <name>Key Wrap</name>
        <t>
<!--[rfced] The following sentence cites a section that does not exist in the
cited document. We have updated the text to refer to Section 8.5.2.  Please let us know if any correctiosn are needed.

Original:
Key wrap is defined in Section 9.5.1 of [I-D.ietf-cose-rfc8152bis-struct].
-->
          Key wrap  is defined in <relref section="&DirectDistribute;" target="I-D.ietf-cose-rfc8152bis-struct"/>. <xref section="8.5.2" target="RFC9052"/>.
          Information about how to fill in the COSE_Recipient structure is detailed there.
        </t>

        <section>
        <name>AES Key Wrap</name>
        <t>The AES Key Wrap algorithm is defined in <xref target="RFC3394"/>.
	This algorithm uses an AES key to wrap a value that is a multiple of
	64 bits.  As such, it can be used to wrap a key for any of the
	content encryption algorithms defined in this document. The algorithm
	requires a single fixed parameter, the initial value.  This is fixed
	to the value specified in Section 2.2.3.1 of <xref target="RFC3394"/>. target="RFC3394" section="2.2.3.1"
	sectionFormat="of"/>.  There are no public key parameters that vary on
	a per-invocation basis.  The protected header bucket
	<bcp14>MUST</bcp14> be empty.  </t>
        <t>Keys may be obtained either from either a key structure or from a recipient
	structure.  Implementations that are encrypting and decrypting
	<bcp14>MUST</bcp14> validate that the key type, key length, and
	algorithm are correct and appropriate for the entities involved.  </t>
        <t>When using a COSE key for this algorithm, the following checks are made:
        </t>

        <ul>

          <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'Symmetric'.</li> "Symmetric".</li>

          <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match the AES Key Wrap algorithm being used.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'encrypt' "encrypt" or 'wrap key' "wrap key" when encrypting.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'decrypt' "decrypt" or 'unwrap key' "unwrap key"  when decrypting.</li>
        </ul>
        <table anchor="x-table_aes_keywrap" align="center">

          <name>AES Key Wrap Algorithm Values</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th>Key
              <th align="center">Value</th>
              <th align="center">Key Size</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>A128KW</td>
              <td>-3</td>
              <td>128</td>
              <td align="center">-3</td>
              <td align="center">128</td>
              <td>AES Key Wrap w/ 128-bit key</td>
            </tr>
            <tr>
              <td>A192KW</td>
              <td>-4</td>
              <td>192</td>
              <td align="center">-4</td>
              <td align="center">192</td>
              <td>AES Key Wrap w/ 192-bit key</td>
            </tr>
            <tr>
              <td>A256KW</td>
              <td>-5</td>
              <td>256</td>
              <td align="center">-5</td>
              <td align="center">256</td>
              <td>AES Key Wrap w/ 256-bit key</td>
            </tr>
          </tbody>
        </table>
        <section>

          <name>Security Considerations for AES-KW</name> AES Key Wrap</name>
          <t>The shared secret needs to have some method to be of being regularly updated over time.  The shared secret is the basis of trust.  </t>
        </section>
        </section>
      </section>

      <section>
        <name>Direct Key Agreement</name>

        <t>
<!--[rfced] The following sentence cites a section that does not exist in the
cited document.  We have updated the document to refer to Section 8.5.3.  Please let us know if any corretions are needed.

Original:
Key Transport is defined in <relref section="9.5.4" target="I-D.ietf-cose-rfc8152bis-struct"/>.
          Information Section 9.5.4 of [I-D.ietf-cose-rfc8152bis-struct].
-->
          Key transport is defined in <xref section="8.5.3" target="RFC9052"/>.
          Information about how to fill in the COSE_Recipient structure is detailed there.
        </t>

      <section anchor="ECDH">

        <name>Direct ECDH</name>
        <t>The mathematics for ECDH can be found in <xref target="RFC6090"/>.  In this document, the algorithm is extended to be used with the two curves defined in <xref target="RFC7748"/>.  </t>
        <t>ECDH is parameterized by the following:
        </t>

        <ul>

          <li>
            <t>Curve Type/Curve: The

        <dl>

         <dt>Curve Type/Curve:</dt><dd> <t>The curve selected controls not only the size of the shared secret, but the mathematics for computing the shared secret.  The curve selected also controls how a point in the curve is represented and what happens for the identity points on the curve.  In this specification, we allow for a number of different curves to be used.  A set of curves are is defined in <xref target="x-table-ec-curves"/>.

            </t> target="x-table-ec-curves"/>.</t>

 <t> The math used to obtain the computed secret is based on the curve selected and not on the ECDH algorithm.  For this reason, a new algorithm does not need to be defined for each of the curves. </t>
          </li>

          <li>Computed
          </dd>

          <dt>Computed Secret to Shared Secret: Secret:</dt><dd> Once the computed
	  secret is known, the resulting value needs to be converted to a byte
	  string to run the KDF.  The x-coordinate is used for all of the
	  curves defined in this document.  For curves X25519 and X448, the
	  resulting value is used directly directly, as it is a byte string of a known
	  length.  For the P-256, P-384, and P-521 curves, the x-coordinate is
	  run through the I2OSP Integer-to-Octet-String primitive (I2OSP) function
	  defined in <xref target="RFC8017"/>,
	  using the same computation for n as is defined in <xref
	  target="ECDSA"/>.  </li>

          <li>Ephemeral-Static  </dd>

<!-- [rfced] We asked this terminology question in RFC 9052.  We will align the documents as needed.

RFC-to-be 9052 mostly uses "static-static" (there is one instance of "static-Static"); "Ephemeral-Static" is consistently capped.  In addition, this document (RFC-to-be 9053) mostly uses "Ephemeral-Static" (there is one instance of ephemeral-static); "static-static" is consistent.

Please review and let us know how/if these may be made consistent.
-->

          <dt>Ephemeral-Static or Static-Static: Static-Static:</dt><dd> The key agreement
          process may be done using either a static or an ephemeral
          key for the sender's side.  When using ephemeral keys, the
          sender <bcp14>MUST</bcp14> generate a new ephemeral key for
          every key agreement operation.  The ephemeral key is placed
          in the 'ephemeral key' "ephemeral key" parameter and <bcp14>MUST</bcp14> be
          present for all algorithm identifiers that use ephemeral
          keys.  When using static keys, the sender
          <bcp14>MUST</bcp14> either generate a new random value or
          create a unique value.  For the KDFs used, this means that either
          the 'salt' "salt" parameter for HKDF (<xref
          target="HKDF_Alg_Params"/>) or the 'PartyU nonce' "PartyU nonce" parameter
          for the context structure (<xref
          target="KDF_Context_Alg_Params"/>) <bcp14>MUST</bcp14> be
          present (both can be present if desired). The value in the
          parameter <bcp14>MUST</bcp14> be unique for the pair of keys
          being used.  It is acceptable to use a global counter that
          is incremented for every static-static operation and use the
          resulting value.  Care must be taken that the counter is
          saved to permanent storage in a way to avoid that avoids reuse of that
          counter value. When using static keys, the static key should
          be identified to the recipient.  The static key can be
          identified either by providing either the key ('static key') ("static key") or by providing
          a key identifier for the static key ('static ("static key id').
          id").  Both of these header parameters are defined in <xref
          target="x-table-ecdh-es-parameter-table"/>.
        </li>

          <li>Key
        </dd>

          <dt>Key Derivation Algorithm: The Algorithm:</dt><dd>The result of an ECDH
	  key agreement process does not provide a uniformly random secret.
	  As such, it needs to be run through a KDF in order to produce a usable
	  key.  Processing the secret through a KDF also allows for the
	  introduction of context material: how the key is going to be used
	  and one-time material for static-static key agreement.  All of the
	  algorithms defined in this document use one of the HKDF algorithms
	  defined in <xref target="HKDF-section"/> with the context structure
	  defined in <xref target="context"/>.  </li>

          <li>Key  </dd>

          <dt>Key Wrap Algorithm: Algorithm:</dt><dd> No key wrap algorithm is used.
	  This is represented in <xref target="x-table-ecdh-es-table"/> as 'none'.
	  "none".  The key size for the context structure is the
	  content layer encryption algorithm size.  </li>
        </ul>  </dd>
        </dl>

        <t>
          COSE does not have an Ephemeral-Ephemeral version defined.
          The reason for this is that COSE is not an online protocol by itself and thus does not have a method to establish of establishing ephemeral secrets on both sides.
          The expectation is that a protocol would establish the secrets for both sides, and then they would be used as static-static for the purposes of COSE, or that the protocol would generate a shared secret and a direct encryption would be used.
        </t>
        <t>The set of direct ECDH algorithms defined in this document are is found
	in <xref target="x-table-ecdh-es-table"/>.  </t>
        <table anchor="x-table-ecdh-es-table" align="center">

          <name>ECDH Algorithm Values</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th>KDF</th>
              <th>Ephemeral- Static</th>
              <th>Ephemeral-Static</th>
              <th>Key Wrap</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>ECDH-ES + HKDF-256</td>
              <td>-25</td>
              <td>HKDF - -- SHA-256</td>
              <td>yes</td>
              <td>none</td>
              <td>ECDH ES w/ HKDF - -- generate key directly</td>
            </tr>
            <tr>
              <td>ECDH-ES + HKDF-512</td>
              <td>-26</td>
              <td>HKDF - -- SHA-512</td>
              <td>yes</td>
              <td>none</td>
              <td>ECDH ES w/ HKDF - -- generate key directly</td>
            </tr>
            <tr>
              <td>ECDH-SS + HKDF-256</td>
              <td>-27</td>
              <td>HKDF - -- SHA-256</td>
              <td>no</td>
              <td>none</td>
              <td>ECDH SS w/ HKDF - -- generate key directly</td>
            </tr>
            <tr>
              <td>ECDH-SS + HKDF-512</td>
              <td>-28</td>
              <td>HKDF - -- SHA-512</td>
              <td>no</td>
              <td>none</td>
              <td>ECDH SS w/ HKDF - -- generate key directly</td>
            </tr>
          </tbody>
        </table>
        <table anchor="x-table-ecdh-es-parameter-table" align="center">

          <name>ECDH Algorithm Parameters</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Label</th>
              <th>Type</th>
              <th>Algorithm</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>ephemeral key</td>
              <td>-1</td>
              <td>COSE_Key</td>
              <td>ECDH-ES+HKDF-256, ECDH-ES+HKDF-512, ECDH-ES+A128KW, ECDH-ES+A192KW, ECDH-ES+A256KW</td>
              <td>Ephemeral public key for the sender</td>
            </tr>
            <tr>
              <td>static key</td>
              <td>-2</td>
              <td>COSE_Key</td>
              <td>ECDH-SS+HKDF-256, ECDH-SS+HKDF-512, ECDH-SS+A128KW, ECDH-SS+A192KW, ECDH-SS+A256KW </td>
              <td>Static public key for the sender</td>
            </tr>
            <tr>
              <td>static key id </td>
              <td>-3</td>
              <td>bstr</td>
              <td>ECDH-SS+HKDF-256, ECDH-SS+HKDF-512, ECDH-SS+A128KW, ECDH-SS+A192KW, ECDH-SS+A256KW </td>
              <td>Static public key identifier for the sender</td>
            </tr>
          </tbody>
        </table>
        <t>This document defines these algorithms to be used with the curves P-256, P-384, P-521, X25519, and X448.  Implementations <bcp14>MUST</bcp14> verify that the key type and curve are correct.  Different curves are restricted to different key types.  Implementations <bcp14>MUST</bcp14> verify that the curve and algorithm are appropriate for the entities involved.  </t>
        <t>When using a COSE key for this algorithm, the following checks are made:
        </t>

        <ul>

          <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'EC2' "EC2" or 'OKP'.</li> "OKP".</li>

          <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match the
	  key agreement algorithm being used.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'derive key' "derive key" or 'derive bits' "derive bits" for the private key.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> be empty for the public key.</li>
        </ul>
        <section>

          <name>Security Considerations for ECDH</name>
          <t>
            There is a method of checking that points provided from external entities are valid.
            For the 'EC2' "EC2" key format, this can be done by checking that the x and y values form a point on the curve.
            For the 'OKP' "OKP" format, there is no simple way to do perform point validation.
          </t>
          <t>
<!--[rfced] The following sentence cites a section that does not exist in the
cited document. Please review.

Original:
Consideration was given to requiring that the public keys of both
entities be provided as part of the key derivation process (as
recommended in Section 6.4 of [RFC7748]).
-->
            Consideration was given to requiring that the public keys of both
	    entities be provided as part of the key derivation process (as
	    recommended in <relref <xref target="RFC7748" section="6.4"/>).  This was
	    not done as done, because COSE is used in a store and forward store-and-forward
	    format rather than in online key exchange.
            In order for this to be a problem, either the receiver public key has to be chosen maliciously or the sender has to be malicious.
            In either case, all security evaporates anyway.
          </t>
          <t>A proof of possession of the private key associated with the public key is recommended when a key is moved from untrusted to trusted (either by the end user or by the entity that is responsible for making trust statements on keys). </t>
        </section>
      </section>
      </section>
    <section>
      <name>Key Agreement with Key Wrap</name>
        <t>
<!--[rfced] The following sentence cites a section that does not exist in the
cited document.  We have updated the text to refer to Section 8.5.5.  Please let us know if corrections are needed.

Original:
Key Agreement with Key Wrap is defined in Section 9.5.5 of
[I-D.ietf-cose-rfc8152bis-struct].
-->
          Key Agreement with Key Wrap is defined in <relref section="9.5.5" target="I-D.ietf-cose-rfc8152bis-struct"/>. <xref section="8.5.5" target="RFC9052"/>.
          Information about how to fill in the COSE_Recipient structure are is detailed there.
        </t>

      <section anchor="ECDH-wrap">

        <name>ECDH with Key Wrap</name>
        <t>These algorithms are defined in <xref target="x-table-ecdh-es-table-wrap"/>.  </t>
        <t>ECDH with Key Agreement is parameterized by the same header parameters as for ECDH; see <xref target="ECDH"/>, with the following modifications:
        </t>

        <ul>

          <li>Key

        <dl>

          <dt>Key Wrap Algorithm: Algorithm:</dt><dd> Any of the key wrap algorithms
	  defined in <xref target="key_wrap_algs"/> are supported.  The size
	  of the key used for the key wrap algorithm is fed into the KDF.  The
	  set of identifiers are is found in <xref
	  target="x-table-ecdh-es-table-wrap"/>.  </li>
        </ul>  </dd>
        </dl>

        <table anchor="x-table-ecdh-es-table-wrap" align="center">

          <name>ECDH Algorithm Values with Key Wrap</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th>KDF</th>
              <th>Ephemeral- Static</th>
              <th>Ephemeral-Static</th>
              <th>Key Wrap</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>ECDH-ES + A128KW</td>
              <td>-29</td>
              <td>HKDF - -- SHA-256</td>
              <td>yes</td>
              <td>A128KW</td>
              <td>ECDH ES w/ Concat KDF and AES Key Wrap w/ 128-bit key</td>
            </tr>
            <tr>
              <td>ECDH-ES + A192KW</td>
              <td>-30</td>
              <td>HKDF - -- SHA-256</td>
              <td>yes</td>
              <td>A192KW</td>
              <td>ECDH ES w/ Concat KDF and AES Key Wrap w/ 192-bit key</td>
            </tr>
            <tr>
              <td>ECDH-ES + A256KW</td>
              <td>-31</td>
              <td>HKDF - -- SHA-256</td>
              <td>yes</td>
              <td>A256KW</td>
              <td>ECDH ES w/ Concat KDF and AES Key Wrap w/ 256-bit key</td>
            </tr>
            <tr>
              <td>ECDH-SS + A128KW</td>
              <td>-32</td>
              <td>HKDF - -- SHA-256</td>
              <td>no</td>
              <td>A128KW</td>
              <td>ECDH SS w/ Concat KDF and AES Key Wrap w/ 128-bit key</td>
            </tr>
            <tr>
              <td>ECDH-SS + A192KW</td>
              <td>-33</td>
              <td>HKDF - -- SHA-256</td>
              <td>no</td>
              <td>A192KW</td>
              <td>ECDH SS w/ Concat KDF and AES Key Wrap w/ 192-bit key</td>
            </tr>
            <tr>
              <td>ECDH-SS + A256KW</td>
              <td>-34</td>
              <td>HKDF - -- SHA-256</td>
              <td>no</td>
              <td>A256KW</td>
              <td>ECDH SS w/ Concat KDF and AES Key Wrap w/ 256-bit key</td>
            </tr>
          </tbody>
        </table>

        <t>When using a COSE key for this algorithm, the following checks are made:
        </t>

        <ul>

          <li>The 'kty' "kty" field <bcp14>MUST</bcp14> be present, and it <bcp14>MUST</bcp14> be 'EC2' "EC2" or 'OKP'.</li> "OKP".</li>

          <li>If the 'alg' "alg" field is present, it <bcp14>MUST</bcp14> match the key agreement algorithm being used.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> include 'derive key' "derive key" or 'derive bits' "derive bits" for the private key.</li>

          <li>If the 'key_ops' "key_ops" field is present, it <bcp14>MUST</bcp14> be empty for the public key.</li>
        </ul>
      </section>
    </section>
    </section>
    <section anchor="Key-specific-labels">

      <name>Key Object Parameters</name>
      <t>The COSE_Key object defines a way to hold a single key object.  It is still required that the members of individual key types be defined.  This section of the document is where we define an initial set of members for specific key types.  </t>
      <t>For each of the key types, we define both public and private members.
      The public members are what is transmitted to others for their usage.
      Private members allow for the archival of keys by individuals. individuals to archive keys.  However,
      there are some circumstances in which private keys may be distributed to
      entities in a protocol.  Examples include:  entities that have poor
      random number generation, centralized key creation for multi-cast type multicast-type
      operations, and protocols in which a shared secret is used as a bearer
      token for authorization purposes.  </t>
      <t>Key types are identified by the 'kty' "kty" member of the COSE_Key object.  In this document, we define four values for the member: </t>
      <table anchor="x-table_key_types" align="center">

        <name>Key Type Values</name>
        <thead>
          <tr>
            <th>Name</th>
            <th>Value</th>
            <th align="center">Value</th>
            <th>Description</th>
          </tr>
        </thead>
        <tbody>
          <tr>
            <td>OKP</td>
            <td>1</td>
            <td align="center">1</td>
            <td>Octet Key Pair</td>
          </tr>
          <tr>
            <td>EC2</td>
            <td>2</td>
            <td align="center">2</td>
            <td>Elliptic Curve Keys w/ x- and y-coordinate pair</td>
          </tr>
          <tr>
            <td>Symmetric</td>
            <td>4</td>
            <td align="center">4</td>
            <td>Symmetric Keys</td>
          </tr>
          <tr>
            <td>Reserved</td>
            <td>0</td>
            <td align="center">0</td>
            <td>This value is reserved</td>
          </tr>
        </tbody>
      </table>
      <section>

        <name>Elliptic Curve Keys</name>
        <t>Two different key structures are defined for elliptic curve keys.
	One version uses both an x-coordinate and a y-coordinate, potentially
	with point compression ('EC2'). ("EC2").  This is the traditional EC
	elliptic curve (EC) point
	representation that is used in <xref target="RFC5480"/>.  The other
	version uses only the x-coordinate x-coordinate, as the y-coordinate is either to
	be recomputed or not needed for the key agreement operation ('OKP'). ("OKP").
	</t>
        <t>Applications <bcp14>MUST</bcp14> check that the curve and the key type are consistent and reject a key if they are not.  </t>
        <table anchor="x-table-ec-curves" align="center">

          <name>Elliptic Curves</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Value</th>
              <th>Key
              <th align="center">Value</th>
              <th align="center">Key Type</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>P-256</td>
              <td>1</td>
              <td>EC2</td>
              <td align="center">1</td>
              <td align="center">EC2</td>
              <td>NIST P-256 P-256, also known as secp256r1</td>
            </tr>
            <tr>
              <td>P-384</td>
              <td>2</td>
              <td>EC2</td>
              <td align="center">2</td>
              <td align="center">EC2</td>
              <td>NIST P-384 P-384, also known as secp384r1</td>
            </tr>
            <tr>
              <td>P-521</td>
              <td>3</td>
              <td>EC2</td>
              <td align="center">3</td>
              <td align="center">EC2</td>
              <td>NIST P-521 P-521, also known as secp521r1</td>
            </tr>
            <tr>
              <td>X25519</td>
              <td>4</td>
              <td>OKP</td>
              <td align="center">4</td>
              <td align="center">OKP</td>
              <td>X25519 for use w/ ECDH only</td>
            </tr>
            <tr>
              <td>X448</td>
              <td>5</td>
              <td>OKP</td>
              <td align="center">5</td>
              <td align="center">OKP</td>
              <td>X448 for use w/ ECDH only</td>
            </tr>
            <tr>
              <td>Ed25519</td>
              <td>6</td>
              <td>OKP</td>
              <td align="center">6</td>
              <td align="center">OKP</td>
              <td>Ed25519 for use w/ EdDSA only</td>
            </tr>
            <tr>
              <td>Ed448</td>
              <td>7</td>
              <td>OKP</td>
              <td align="center">7</td>
              <td align="center">OKP</td>
              <td>Ed448 for use w/ EdDSA only</td>
            </tr>
          </tbody>
        </table>
        <section anchor="EC2-Keys">

          <name>Double Coordinate Curves</name>
          <t>The traditional way of sending ECs has been to send either both
	  the x-coordinate and y-coordinate or the x-coordinate and a sign bit
	  for the y-coordinate.  The latter encoding has not been recommended in
	  by the IETF due to potential IPR
	  issues.  However, for operations in constrained environments, the
	  ability to shrink a message by not sending the y-coordinate is
	  potentially useful.  </t>
          <t>For EC keys with both coordinates, the 'kty' "kty" member is set to 2 (EC2).  The key parameters defined in this section are summarized in <xref target="x-table-ec2-keys"/>.  The members that are defined for this key type are:
          </t>

          <dl newline="false" indent="5">
            <dt>crv:</dt>

            <dd>This contains an identifier of the curve to be used with the key. The curves defined in this document for this key type can be found in <xref target="x-table-ec-curves"/>.  Other curves may be registered in the future, and private curves can be used as well.  </dd>
            <dt>x:</dt>

            <dd>This contains the x-coordinate for the EC point.
<!--[rfced] The integer is converted to a byte cited document mentions bit strings, not byte strings. Please
review which term should be used here.

Original:
The integer is converted to a byte string as defined in [SEC1].
-->
            <dd>This contains the x-coordinate for the EC point.  The integer
	    is converted to a byte string as defined in <xref target="SEC1"/>.  Leading zero
	    Leading-zero octets <bcp14>MUST</bcp14> be preserved.
 </dd>
            <dt>y:</dt>

            <dd>This contains either the sign bit or the value of the y-coordinate for the EC point.  When encoding the value y, the integer is converted to an a byte string (as defined in <xref target="SEC1"/>) and encoded as a CBOR bstr.  Leading zero  Leading-zero octets <bcp14>MUST</bcp14> be preserved.  The compressed  Compressed point encoding is also supported.  Compute the sign bit as laid out in the Elliptic-Curve-Point-to-Octet-String Conversion function of <xref target="SEC1"/>.  If the sign bit is zero, then encode y as a CBOR false value; otherwise, encode y as a CBOR true value.  The encoding of the infinity point is not supported.  </dd>
            <dt>d:</dt>

            <dd>This contains the private key.  </dd>
          </dl>
          <t>For public keys, it is <bcp14>REQUIRED</bcp14> that 'crv', 'x', "crv", "x", and 'y' "y" be present in the structure.  For private keys, it is <bcp14>REQUIRED</bcp14> that 'crv' "crv" and 'd' "d" be present in the structure.  For private keys, it is <bcp14>RECOMMENDED</bcp14> that 'x' "x" and 'y' "y" also be present, but they can be recomputed from the required elements elements, and omitting them saves on space.  </t>
          <table anchor="x-table-ec2-keys" align="center">

            <name>EC Key Parameters</name>
            <thead>
              <tr>
                <th>Key
                <th align="center">Key Type</th>
                <th>Name</th>
                <th>Label</th>
                <th align="center">Name</th>
                <th align="center">Label</th>
                <th>CBOR Type</th>
                <th>Description</th>
              </tr>
            </thead>
            <tbody>
              <tr>
                <td>2</td>
                <td>crv</td>
                <td>-1</td>
                <td align="center">2</td>
                <td align="center">crv</td>
                <td align="center">-1</td>
                <td>int / tstr</td>
                <td>EC identifier - -- Taken from the "COSE Elliptic Curves" registry</td>
              </tr>
              <tr>
                <td>2</td>
                <td>x</td>
                <td>-2</td>
                <td align="center">2</td>
                <td align="center">x</td>
                <td align="center">-2</td>
                <td>bstr</td>
                <td>x-coordinate</td>
              </tr>
              <tr>
                <td>2</td>
                <td>y</td>
                <td>-3</td>
                <td align="center">2</td>
                <td align="center">y</td>
                <td align="center">-3</td>
                <td>bstr / bool</td>
                <td>y-coordinate</td>
              </tr>
              <tr>
                <td>2</td>
                <td>d</td>
                <td>-4</td>
                <td align="center">2</td>
                <td align="center">d</td>
                <td align="center">-4</td>
                <td>bstr</td>
                <td>Private key</td>
              </tr>
            </tbody>
          </table>
        </section>
      </section>
      <section>

        <name>Octet Key Pair</name>
        <t>A new key type is defined for Octet Key Pairs (OKP). (OKPs).  Do not assume that keys using this type are elliptic curves.  This key type could be used for other curve types (for example, mathematics based on hyper-elliptic surfaces).  </t>
        <t>The key parameters defined in this section are summarized in <xref target="x-table-ec1-keys"/>.  The members that are defined for this key type are:
        </t>

        <dl newline="false" indent="5">
          <dt>crv:</dt>

          <dd>This contains an identifier of the curve to be used with the key. The curves defined in this document for this key type can be found in <xref target="x-table-ec-curves"/>.  Other curves may be registered in the future future, and private curves can be used as well.  </dd>
          <dt>x:</dt>

          <dd>This contains the public key.  The byte string contains the public key as defined by the algorithm. (For X25519, internally it is a little-endian integer.) </dd>
          <dt>d:</dt>

          <dd>This contains the private key.  </dd>
        </dl>
        <t>For public keys, it is <bcp14>REQUIRED</bcp14> that 'crv' "crv" and  'x'  "x" be present in the structure.  For private keys, it is <bcp14>REQUIRED</bcp14> that 'crv' "crv" and 'd' "d" be present in the structure.  For private keys, it is <bcp14>RECOMMENDED</bcp14> that 'x' "x" also be present, but it can be recomputed from the required elements elements, and omitting it saves on space.  </t>
        <table anchor="x-table-ec1-keys" align="center">

         <name>Octet Key Pair Parameters</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Key
              <th align="center">Key Type</th>
              <th>Label</th>
              <th align="center">Label</th>
              <th>Type</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>crv</td>
              <td>1</td>
              <td>-1</td>
              <td align="center">1</td>
              <td align="center">-1</td>
              <td>int / tstr</td>
              <td>EC identifier - -- Taken from the "COSE Elliptic Curves" registry</td>
            </tr>
            <tr>
              <td>x</td>
              <td>1</td>
              <td>-2</td>
              <td align="center">1</td>
              <td align="center">-2</td>
              <td>bstr</td>
              <td>Public Key</td>
            </tr>
            <tr>
              <td>d</td>
              <td>1</td>
              <td>-4</td>
              <td align="center">1</td>
              <td align="center">-4</td>
              <td>bstr</td>
              <td>Private key</td>
            </tr>
          </tbody>
        </table>
      </section>
      <section>

        <name>Symmetric Keys</name>
        <t>Occasionally
        <t>Occasionally, it is required that a symmetric key be transported between entities.  This key structure allows for that to happen.  </t>
        <t>For symmetric keys, the 'kty' "kty" member is set to 4 ('Symmetric'). ("Symmetric").  The member that is defined for this key type is:

        </t>

        <dl newline="false">
          <dt>k:</dt>

          <dd>This contains the value of the key.  </dd>
        </dl>
        <t>This key structure does not have a form that contains only public members.  As it is expected that this key structure is going to be transmitted, care must be taken that it is never transmitted accidentally or insecurely.  For symmetric keys, it is <bcp14>REQUIRED</bcp14> that 'k' "k" be present in the structure.  </t>
        <table anchor="x-table-symmetric-keys" align="center">

          <name>Symmetric Key Parameters</name> Parameter</name>
          <thead>
            <tr>
              <th>Name</th>
              <th>Key
              <th align="center">Name</th>
              <th align="center">Key Type</th>
              <th>Label</th>
              <th>Type</th>
              <th align="center">Label</th>
              <th align="center">Type</th>
              <th>Description</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>k</td>
              <td>4</td>
              <td>-1</td>
              <td>bstr</td>
              <td align="center">k</td>
              <td align="center">4</td>
              <td align="center">-1</td>
              <td align="center">bstr</td>
              <td>Key Value</td>
            </tr>
          </tbody>
        </table>
      </section>
    </section>

    <section anchor="COSE-Capabilities">
      <name>COSE Capabilities</name>
      <t>
        There are some
        Some situations that have been identified where identification of capabilities of an algorithm or a key type need needs to be specified.
        One example of this is in <xref target="I-D.ietf-core-oscore-groupcomm"/>
	target="I-D.ietf-core-oscore-groupcomm"/>, where the capabilities of
	the counter signature algorithm are mixed into the traffic key derivation process. process of traffic-key
	derivation.
        This has a counterpart in the S/MIME specifications specifications, where SMIMECapabilities is defined in <xref target="RFC8551" section="2.5a.2"/>. section="2.5.2"/>.
        This document defines the same concept for COSE.
      </t>

      <t>
        The algorithm identifier is not included in the capabilities data data, as
	it should be encoded elsewhere in the message. The key type identifier
	is included in the capabilities data data, as it is not expected to be
	encoded elsewhere.
      </t>

      <t>
        Two different types of capabilities are defined: capabilities for algorithms and capabilities for key type.
        Once defined by registration with IANA, the list of capabilities for an algorithm or key type is immutable.
        If it is later found that a new capability is needed for a key type or an algorithm, it will require that a new code point be assigned to deal with that.
        As a general rule, the capabilities are going to map to algorithm-specific header parameters or key parameters, but they do not need to do so.
        An example of this is the HSS-LMS key capabilities defined below below, where the hash algorithm used is included.
      </t>

      <t>
        The capability structure is an array of values, values; the values included in the structure are dependent on a specific algorithm or key type.
        For algorithm capabilities, the first element should always be a
	key type value if applicable, but the items that are specific to a key
	(for example example, a curve) should not be included in the algorithm
	capabilities.
        This means that if one wishes to enumerate all of the capabilities for
	a device which that implements ECDH, it requires that all of the
	combinations of algorithms and key pairs to be specified.
        The last example of <xref target="cap-examples"/> provides a case
	where this is done by allowing for a cross product to be specified
	between an array of algorithm capabilities and key type capabilities
	(see the ECDH-ES+A25KW element).
        For a key, the first element should be the key type value.
        While this means that the key type value will be duplicated if both an algorithm and key capability are used, the key type is needed in order to understand the rest of the values.
      </t>

      <section>
        <name>Assignments for Existing Algorithms</name>
<!-- [rfced]  Section 8.1:  We had trouble parsing this sentence.
If the suggested text is not correct, please clarify how many items
are listed here.

Original:
For the current set of algorithms in the registry, those in this
document as well as those in [RFC8230] and [I-D.ietf-cose-hash-sig],
the capabilities list is an array with one element, the key type
(from the "COSE Key Types" Registry).

Suggested (noting that the "COSE Key Types" registry also cites RFC 9021,
 which we assume does not apply to this document because it defines
 kty(6)):
For the current set of algorithms in the "COSE Key Types"
registry - including those in this document as well as those in
[RFC8230] and [RFC8778] - the capabilities list is an array with
one element: the key type. -->
        <t>
          For the current set of algorithms in the registry, those in this document as well as those in <xref target="RFC8230"/> and <xref target="I-D.ietf-cose-hash-sig"/>, target="RFC8778"/>, the capabilities list is an array with one element, the key type (from the "COSE Key Types" Registry). registry).
          It is expected that future registered algorithms could have zero, one, or multiple elements.
        </t>

      </section>

      <section>
        <name>Assignments for Existing Key Types</name>
        <t>
          There are a number of pre-existing key types, types; the following deals with creating the capability definition for those structures:
</t>

<!-- FYI tried this as a dl but went with keeping the bullets to match the original-->

<ul>

<li>
  <t>OKP, EC2: The list of capabilities is:</t>
<ul>
<li>The key type value.  (1 for OKP or 2 for EC2.)</li>
<li>One curve for that key type from the "COSE Elliptic Curve" Curves" registry.</li>
</ul>
</li>

<li>
<t>RSA: The list of capabilities is:</t>
<ul>
<li>The key type value (3).</li>
</ul>
</li>

  <li>
<t>Symmetric: The list of capabilities is:</t>
<ul>
<li>The key type value (4).</li>
</ul>
</li>

  <li>
<t>HSS-LMS: The list of capabilities is:</t>
<ul>
<li>The key type value (5),</li> (5).</li>
<li>Algorithm identifier for the underlying hash function from the "COSE
Algorithms" registry.</li>
</ul>
</li>
</ul>

      </section>

      <section anchor="cap-examples">
        <name>Examples</name>
        <t>
          Capabilities can be use used in a key derivation process to make sure
	  that both sides are using the same parameters.
          This is the approach that is being used by the group communication
	  KDF in <xref target="I-D.ietf-core-oscore-groupcomm"/>.
          The three examples below show different ways that one might include things:
        </t>
        <ul>
          <li>
          Just an algorithm
<!--[rfced] Can you clarify what is meant by "include things" in the last
sentence below?  What are "things"?

Original:
Capabilities can be use in a key derivation process to make sure that
both sides are using the same parameters. ... The three examples below show
different ways that one might include things:
-->
          The three examples below show different ways that one might include things:
        </t>
        <ul>
          <li>
          Only an algorithm capability: This is useful if the protocol wants to require a specific algorithm algorithm, such as ECDSA, but it is agnostic about which curve is being used.
          This does require requires that the algorithm identifier be specified in the protocol. See the first example.
          </li>
          <li>
            Just
            Only a key type capability: This is useful if the protccol protocol wants
	    to require a specific a specific key type and curve, such as
	    P-256, but will accept any algorithm using that curve (e.g. (e.g., both
	    ECDSA and ECDH).
            See the second example.
          </li>
          <li>
            Both an algorithm and a key type capability: capabilities: This is used if the
	    protocol needs to nail down all of the options surrounding an
	    algorithm  E.g. -- e.g., EdDSA with the curve X25519.
            As with the first example, the algorithm identifier needs to be specified in the protocol. See the third example example, which just concatenates the two capabilities together.
          </li>
        </ul>

        <artwork>

        <sourcecode type="CDDL">
Algorithm ECDSA

0x8102                 / [2 \ EC2 \ ] /

Key type EC2 with P-256 curve:

0x820201               / [2 \ EC2 \, 1 \ P-256 \] /

ECDH-ES + A256KW with an X25519 curve:

0x8101820104           / [1 \ OKP \],[1 \ OKP \, 4 \ X25519 \] /
        </artwork>
        </sourcecode>

        <t>
          The capabilities can also be used by and an entity to advertise what it is capabable capable of doing.
          The decoded example below is one of many encoding encodings that could be used for that purpose.
          Each array element includes three fields: the algorithm identifier, one or more algorithm capabilities, and one or more key type capabilities.
        </t>

        <artwork>

        <sourcecode type="CDDL">
[
 [-8 / EdDSA /,
   [1 / OKP key type /],
   [
     [1 / OKP /, 6 / Ed25519 / ],
     [1 /OKP/, 7 /Ed448 /]
   ]
 ],
 [-7 / ECDSA with SHA-256/,
   [2 /EC2 key type/],
   [
     [2 /EC2/, 1 /P-256/],
     [2 /EC2/, 3 /P-521/]
   ]
 ],
 [ -31 / ECDH-ES+A256KW/,
   [
     [ 2 /EC2/],
     [1 /OKP/ ]
   ],
   [
     [2 /EC2/, 1 /P-256/],
     [1 /OKP/, 4 / X25519/ ]
   ]
 ],
 [ 1 / A128GCM /,
   [ 4 / Symmetric / ],
   [ 4 / Symmetric /]
 ]
]
        </artwork>
        </sourcecode>
        <t>
          Examining the above:
        </t>
        <ul>
          <li>The first element indicates that the entity supports EdDSA with curves Ed25519 and Ed448.</li>
          <li>The second element indicates that the entity supports ECDSA with curves P-256 and P-521.</li>
          <li>
            The third element indicates that the entity support supports ephemeral-static ECDH using AES256 key wrap.
            The entity can support the P-256 curve with an EC2 key type and the X25519 curve with an OKP key type.
          </li>
          <li>The last element indicates that the entity supports AES-GCM of 128 bits for content encryption.</li>
        </ul>
        <t>
          The entity does not advertise that it supports any MAC algorithms.
        </t>

      </section>

    </section>

    <section anchor="CBOR-Canonical">

      <name>CBOR Encoding Restrictions</name>
      <t>This document limits the restrictions it imposes on how the CBOR Encoder
      encoder needs to work. It has been narrowed down to the following
      restrictions: </t>

<!--[rfced] Please check that erratum 5066 <https://www.rfc-editor.org/errata/eid5066> does not impact the
following sentence.

Current sentence:
The restriction applies to the encoding of the COSE_KDF_Context.

RFC 8152 erratum correction:
The restriction applies to the encoding of the COSE_KDF_Context,
Sig_structure, the Enc_structure, and the MAC_structure.
-->
      <ul>
        <li>
          The restriction applies to the encoding of the COSE_KDF_Context.
        </li>

<!--[rfced] There seems to be a word missing in the following sentence. The
length of what must be the minimum?

Original:
Encoding MUST be done using definite lengths and the length of the
MUST be the minimum possible length.
-->
        <li>
          Encoding <bcp14>MUST</bcp14> be done using definite lengths lengths, and the
	  length of the <bcp14>MUST</bcp14> be the minimum possible length.
          This means that the integer 1 is encoded as "0x01" and not "0x1801".
        </li>

        <li>
          Applications <bcp14>MUST NOT</bcp14> generate messages with the same label used twice as a key in a single map.
          Applications <bcp14>MUST NOT</bcp14> parse and process messages with
	  the same label used twice as a key in a single map.
          Applications can enforce the parse and process parse-and-process requirement by using
	  parsers that will either fail the parse step or by using parsers that will pass all keys to the
	  application, and the application can perform
	  the check for duplicate keys.
        </li>
      </ul>
    </section>

    <section anchor="iana-considerations">
      <name>IANA Considerations</name>
<!--[rfced] Please check whether RFC 8152 erratum 5545 <https://www.rfc-editor.org/errata/eid5545> affects the following statement:

IANA is requested to update all COSE registeries except for "COSE
Header Parmeters" and "COSE Key Common Parameters" [RFC8152] to [[This
Document]].

The erratum changes Table 3: Key Map Labels. The note states:
The value registry for kty should be COSE Key Types, as indicated in the text
following Table 3. This change affects the IANA registry:
https://www.iana.org/assignments/cose/cose.xhtml#key-common-parameters
-->
      <t>IANA has updated all COSE registries except for "COSE
      Header Parameters" and "COSE Key Common Parameters" to point to this document instead of <xref target="RFC8152"/>.</t>
      <section>
        <name>Changes to the "COSE Key Types" registry.</name> Registry</name>
      <t>
        IANA is requested to create has added a new column in the "COSE Key Types" registry.
        The new column is to be labeled "Capabilities".
        The new column is to be "Capabilities" and has been populated according to the entries in <xref target="initial-kty-caps"/>.
      </t>

        <table anchor="initial-kty-caps">
          <name>Key Type Capabilities</name>
          <thead>
            <tr>
              <th>Value</th>
              <th>Name</th>
              <th>Capabilities</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>1</td>
              <td>OKP</td>
              <td>[kty(1), crv]</td>
            </tr>
            <tr>
              <td>2</td>
              <td>EC2</td>
              <td>[kty(2), crv]</td>
            </tr>
            <tr>
              <td>3</td>
              <td>RSA</td>
              <td>[kty(3)]</td>
            </tr>
            <tr>
              <td>4</td>
              <td>Symmetric</td>
              <td>[kty(4)]</td>
            </tr>
            <tr>
              <td>5</td>
              <td>HSS-LMS</td>
              <td>[kty(5), hash algorithm]</td>
            </tr>
          </tbody>
        </table>
        <t>
          IANA is requested to update the pointer for expert review to [[this document]].
        </t>
      </section>

      <section>
        <name>Changes to the "COSE Algorithms" registry</name> Registry</name>
        <t>
          IANA is requested to create has added a new column in the "COSE Algorithms" registry.
          The new column is to be labeled "Capabilities".
          The new column is "Capabilities" and has been populated with "[kty]" for all current, non-provisional,
	  nonprovisional registrations.
          It is expected that the documents which that define those algorithms will
	  be expanded to include this registration.
          If this is not done done, then the Designated Expert designated expert should be consulted
	  before final registration for this document is done.
        </t>

        <t>
          IANA is requested to update all references from RFC 8152 to [[This Document]].
        </t>

        <t>
          IANA is requested to update the pointer for expert rview to [[this document]].
        </t>
        <t>
          IANA is requested to update has updated the reference Reference column in the "COSE Algorithms" registry to include [[This Document]] this document as a reference for all rows where it is was not already present.
        </t>

        <t>
          IANA is requested to add has added a new row to the "COSE Algorithms" registry.
        </t>

<!-- [rfced] Table 23 is the only table that doesn't have a title.  Would you like to give it a title?

Original:
Table 23

Possibly:
Table 23: IV-GENERATION Algorithm Identifier -->

        <table>
          <thead>
            <tr>
            <th>Name</th>
            <th>Value</th>
            <th>Description</th>
            <th>Reference</th>
            <th>Recommended</th>
            </tr>
          </thead>
          <tbody>
            <tr>
              <td>IV Generation</td>
              <td>IV-GENERATION</td>
              <td>For doing IV generation for symmetric algorithms.</td>
              <td>[[THIS DOCUMENT]]</td>
              <td>RFC 9053</td>
              <td>No</td>
            </tr>
          </tbody>
        </table>

        <t>
          The capabilities Capabilities column for this registration is to be empty.
        </t>
      </section>

      <section>
        <name>Changes to the "COSE Key Type Parameters" registry</name> Registry</name>
        <t>
<!--[rfced] Table 20 does not have a line with "Key Type" of
2.  Please review the instructions and the table.

Original:
IANA is requested to modify the description to "Public Key" for the
line with "Key Type" of 2 and the "Name" of "x". See <xref target="x-table-ec1-keys"/> Table 20 which
has been modified with this change.
        </t>
        <t>
          IANA is requested to update the references

Perhaps this row in the table from RFC8152 to [[This Document]].
        </t>
        <t> Table should be updated as follows:

Original:
| x    |    1     |   -2  | bstr  | Public Key                      |

Perhaps:
| x    |    2     |   -2  | bstr  | Public Key                      |

-->
          IANA is requested to update modify the pointer for expert rview description to [[this document]].
        </t>
      </section>

      <section anchor="IANA-Alg-Registry">
        <name>COSE Header Algorithm Parameters Registry</name>
        <t>
          IANA created a registry titled  "COSE Header Algorithm Parameters" as part "Public Key" for the
	  line with "Key Type" of processing 2 and the "Name" of "x".
          See <xref target="RFC8152"/>.
          The registry target="x-table-ec1-keys"/>, which has been created to use the "Expert Review Required" registration procedure <xref target="RFC8126"/>.
        </t>
        <t>
          IANA is requested to update the references from <xref target="RFC8152"/> to modified with
	  this document.
        </t>
        <t>
          IANA is requested to update the pointer for expert rview to [[this document]]. change.
        </t>
      </section>

      <section title="Expert Review Instructions" anchor="review"  >
        <t>
          All of the IANA registries established by <xref target="RFC8152"/> are, at least in part, defined as expert review. Expert Review.  This section gives some general guidelines for what the experts should be looking for, but they are being designated as experts for a reason, so they should be given substantial latitude.
        </t>
        <t>Expert reviewers should take into consideration the following points:
        </t>
        <ul>

<li>Point squatting should be discouraged.  Reviewers are encouraged to get sufficient information for registration requests to ensure that the usage is not going to duplicate one that is already registered, and that the point is likely to be used in deployments.  The zones tagged as private use are intended for testing purposes and closed environments; code points in other ranges should not be assigned for testing.  </li>

<li>Specifications

<!-- [rfced] Same question as in RFC-to-be 9052: RFC 8126 indicates that Standards Track or BCP RFCs are  required to register something via Standards Action.  Using "specifications" to refer to Standards Track documents could be confusing.  For clarity, we suggest an update.  Also, we suggest updating "before a
specification is available" to "before an RFC is available".

Original:
   *  Specifications are required for the standards track range of point
      assignment.  Specifications should exist for specification
      required ranges, but early assignment before a specification is
      available is considered to be permissible.  Specifications are
      needed for the first-come, first-serve range if they are expected
      to be used outside of closed environments in an interoperable way.
      When specifications are not provided, the description provided
      needs to have sufficient information to identify what the point is
      being used for.  </li>

<li>Experts should take into account the expected usage of fields when

Perhaps:
   *  Standards Track or BCP RFCs are required to register a code point in
      the Standards Action range.  Specifications should exist for Specification
      Required ranges, but early assignment before an RFC is
      available is permissible.  Specifications are
      needed for the first-come, first-serve range if the points are
      expected to be used outside of closed environments in an
      interoperable way.  When specifications are not provided, the
      description provided needs to have sufficient information to
      identify what the point is being used for.
-->

<li>Specifications are required for the Standards Track range of point
assignments.  Specifications should exist for Specification Required ranges,
but early assignment before a specification is available is considered to be
permissible.  Specifications are needed for the first-come, first-serve range
if the points are expected to be used outside of closed environments in an
interoperable way.  When specifications are not provided, the description
provided needs to have sufficient information to identify what the point is
being used for.  </li>

<li>Experts should take into account the expected usage of fields when
approving point assignment.

<!-- [rfced] Same question as for RFC-to-be 9052: Should "range for standards track documents" be "Standards Action range"?

Original:
      The fact that there is a range for
      standards track documents does not mean that a standards track
      document cannot have points assigned outside of that range.
-->

The fact that there is a range for Standards
Track documents does not mean that a Standards Track document cannot have
points assigned outside of that range.  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 used on, and the number of code points left that encode to
that size. </li>

<li>When algorithms are registered, vanity registrations should be discouraged.  One way to do this is to require registrations to provide additional documentation on security analysis of the algorithm.  Another thing that should be considered is requesting an opinion on the algorithm from the Crypto Forum Research Group (CFRG).

<!-- [rfced] Same question as for RFC-to-be 9052: What does "community and the message structures" refer to?

Original:
      Algorithms that do not meet the security requirements of
      the community and the messages structures should not be
      registered.
-->
Algorithms that do not meet the security requirements of the community and the message structures should not be registered.  </li>
</ul>
</section>
    </section>

    <section anchor="security-considerations">

      <name>Security Considerations</name>
      <t>There are a number of security considerations that need to be taken into account by implementers of this specification.  The security considerations that are specific to an individual algorithm are placed next to the description of the algorithm.  While some considerations have been highlighted here, additional considerations may be found in the documents listed in the references.  </t>
      <t>Implementations need to protect the private key material for any
      individuals.  There are some  Some cases in this document that need to be highlighted on with
      regard to this issue.
      </t>

      <ul>

        <li>Using

        <li>Use of the same key for two different algorithms can leak information about the key.  It is therefore recommended that keys be restricted to a single algorithm.  </li>

        <li>Use of 'direct' "direct" as a recipient algorithm combined with a second recipient algorithm exposes the direct key to the second recipient.  </li>

        <li>Several of the algorithms in this document have limits on the number of times that a key can be used without leaking information about the key.  </li>
      </ul>
      <t>The use of ECDH and direct plus KDF (with no key wrap) will not
      directly lead to the private key being leaked; the one way one-way function of
      the KDF will prevent that.  There is, however, a different issue that
      needs to be addressed.  Having two recipients requires that the CEK be
      shared between two recipients.  The second recipient therefore has a CEK
      that was derived from material that can be used for the weak proof of
      origin.  The second recipient could create a message using the same CEK
      and send it to the first recipient; the first recipient would, for
      either static-static ECDH or direct plus KDF, make an assumption that
      the CEK could be used for proof of origin even though it is from the
      wrong entity.  If the key wrap step is added, then no proof of origin is
      implied and this is not an issue.  </t>
      <t>Although it has been mentioned before, the use of a single key for
      multiple algorithms has been demonstrated in some cases to leak
      information about a key, provide providing the opportunity for attackers to forge
      integrity tags, tags or gain information about encrypted content.  Binding a
      key to a single algorithm prevents these problems.  Key creators and key
      consumers are strongly encouraged to not only to create new keys for each
      different algorithm, but to include that selection of algorithm in any
      distribution of key material and strictly enforce the matching of
      algorithms in the key structure to algorithms in the message structure.
      In addition to checking that algorithms are correct, the key form needs
      to be checked as well.  Do not use an 'EC2' key where an 'OKP' key is expected.  </t>
      <t>Before using a key
<!--[rfced] Same question as for RFC-to-be 9052: Would it be helpful to include expansions for EC2 and OKP?
RFC 8152 included the following in the body of the docment:
    - (2 coordinate elliptic curve)
    - (Octet Key Pair)

Original:
   Do not use an 'EC2' key where an 'OKP' key is expected.
-->
Do not use an "EC2" key where an "OKP" key is
      expected.  </t>
      <t>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
      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 with this
      trust decision.  Some of the ones that are highlighted here are:
      </t>

      <ul>

        <li>What are the permissions associated with the key owner?</li>

        <li>Is the cryptographic algorithm acceptable in the current context?</li>

        <li>Have the restrictions associated with the key, such as algorithm
	or freshness, been checked checked, and are they correct?</li>

        <li>Is the request something that is reasonable, given the current state of the application?</li>

        <li>Have any security considerations that are part of the message been enforced (as specified by the application or 'crit' "crit" parameter)?</li>
      </ul>
      <t>There are a large number of algorithms presented in this
      document that use nonce values.  For all of the nonces defined
      in this document, there is some type of restriction on the nonce
      being a unique value either for either a key or for some other
      conditions.  In all of these cases, there is no known
      requirement on the nonce being both unique and unpredictable;
      under these circumstances, it's reasonable to use a counter for
      creation of the nonce.  In cases where one wants the pattern of
      the nonce to be unpredictable as well as unique, one can use a
      key created for that purpose and encrypt the counter to produce
      the nonce value.  </t> <t>One area that has been getting
      exposure is traffic analysis of encrypted messages based on the
      length of the message.  This specification does not provide for
      a uniform method of providing padding as part of the message
      structure.  An observer can distinguish between two different
      messages (for example, 'YES' "YES" and 'NO') "NO") based on the length for
      all of the content encryption algorithms that are defined in
      this document.  This means that it is up to the applications to
      document how content padding is to be done done, in order to prevent
      or discourage such analysis.  (For example, the text strings
      could be defined as 'YES' "YES" and 'NO '.) "NO".) </t> <t> The analsys analysis done
      in <xref target="I-D.ietf-quic-tls"/> target="RFC9001"/> is based on the number of
      records/packets that are sent.  This should map well to the
      number of messages sent when use COSE using COSE, so that analysis should
      hold here as well.  It needs to be noted that the limits are
      based on the number of messages, but QUIC and DTLS are always pair-wise based endpoints,
      pairwise-based endpoints <xref
      target="I-D.ietf-core-oscore-groupcomm"/> and use COSE in a group
      communication.  Under these circumstances circumstances, it may be that no one
      single entity will see all of the messages that are encrypted an encrypted, and
      therefore no single entity can trigger the rekey operation.
      </t> </section> </middle>
<back>

<displayreference target="I-D.ietf-core-oscore-groupcomm"
		  to="OSCORE-GROUPCOMM"/>
<displayreference target="I-D.mattsson-cfrg-det-sigs-with-noise"
		  to="CFRG-DET-SIGS"/>

<references>
      <name>References</name>
<references> <name>Normative References</name>
<!-- draft-ietf-cose-rfc8152bis-struct-13; RFC 9052 -->

<reference anchor="RFC9052" target="https://www.rfc-editor.org/info/rfc9052">
<front>
<title>CBOR Object Signing and Encryption (COSE): Structures and Process</title>
<author initials='J' surname='Schaad' >
  <organization/>
</author>
<date month='July' year='2021'/>
</front>
<seriesInfo name="STD" value="96"/>
<seriesInfo name="RFC" value="9052"/>
<seriesInfo name="DOI" value="10.17487/RFC9052"/>
</reference>

<xi:include href="reference.I-D.ietf-cose-rfc8152bis-struct.xml"/>
        <xi:include href="reference.RFC.2104.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2104.xml"/>
<xi:include href="reference.RFC.2119.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/>
<xi:include href="reference.RFC.3394.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3394.xml"/>
<xi:include href="reference.RFC.3610.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3610.xml"/>
<xi:include href="reference.RFC.5869.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5869.xml"/>
<xi:include href="reference.RFC.6090.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6090.xml"/>
<xi:include href="reference.RFC.6979.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6979.xml"/>
<xi:include href="reference.RFC.7049.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8949.xml"/>
<xi:include href="reference.RFC.8439.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8439.xml"/>
<xi:include href="reference.RFC.7748.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7748.xml"/>
<xi:include href="reference.RFC.8174.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/>

<reference anchor="AES-GCM"
      target="https://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf">
      <front> <title>Recommendation for Block Cipher Modes of
      Operation: Galois/Counter Mode (GCM) and GMAC</title>
      <seriesInfo name="DOI" value="10.6028/NIST.SP.800-38D"/>
            <seriesInfo name="NIST Special Publication" value="800-38D"/>
            <author>
              <organization>National Institute of Standards and Technology</organization>
            </author>
      <author initials="M" surname="Dworkin" />
<date year="2007" month="November"/>
</front>
      <seriesInfo name="DOI" value="10.6028/NIST.SP.800-38D"/>
</reference>

<reference anchor="DSS" target="http://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf">
      target="https://nvlpubs.nist.gov/nistpubs/FIPS/NIST.FIPS.186-4.pdf">
      <front>
<title>Digital Signature Standard (DSS)</title>
      <seriesInfo name="DOI" value="10.6028/NIST.FIPS.186-4"/>
            <seriesInfo name="FIPS PUB" value="186-4"/>
<author>
      <organization>National Institute of Standards and
Technology</organization> </author>
<date year="2013" month="July"/> </front>
      <seriesInfo name="DOI" value="10.6028/NIST.FIPS.186-4"/>
</reference>

<reference anchor="MAC">
          <!--
              RFC Editor - help

              A.  Menezes,  P.  van Oorschot,  S.  Vanstone,
              Handbook  of  Applied  Cryptography,  CRC  Press, Inc., Boca Raton (1996).
          --> anchor="MAC" target="https://cacr.uwaterloo.ca/hac/">
<front> <title>Handbook of Applied Cryptography</title>
<author initials="A." surname="Menees"/> surname="Menezes"/>
<author initials="P." surname="van Oorschot"/>
<author initials="S." surname="Vanstone"/>
<date year="1996"/> </front>
<refcontent>CRC Press, Boca Raton</refcontent>
      </reference>

      <reference anchor="SEC1" target="http://www.secg.org/sec1-v2.pdf"> target="https://www.secg.org/sec1-v2.pdf">
	<front>
	  <title>SEC 1: Elliptic Curve Cryptography</title>
	  <author>
	    <organization>Certicom Research</organization> </author>
	    <date year="2009" month="May"/>
      </front>
      <refcontent>Standards for Efficient Cryptography</refcontent>
      </reference>
<xi:include href="reference.RFC.8032.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8032.xml"/>
<xi:include href="reference.RFC.8017.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8017.xml"/>
      </references>

<references> <name>Informative References</name>
<!--[rfced] RFC 8126 is provided as an informative reference, but there are
no citations for it in the document.  Please let us know it should be cited.
-->
<xi:include href="reference.RFC.8126.xml"/>
        <xi:include href="reference.RFC.8610.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8126.xml"/>
<xi:include href="reference.RFC.4231.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8610.xml"/>
<xi:include href="reference.RFC.4493.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4231.xml"/>
<xi:include href="reference.RFC.5116.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.4493.xml"/>
<xi:include href="reference.RFC.5480.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5116.xml"/>
<xi:include href="reference.RFC.6151.xml"/>
<!-- href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5480.xml"/>
<xi:include href="bibxml9/reference.STD.0090.xml"/> -->
<referencegroup href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.6151.xml"/>

   <reference anchor="STD90" target="https://www.rfc-editor.org/info/std90">
<!-- reference.RFC.8259.xml -->
<reference anchor="RFC8259" target="https://www.rfc-editor.org/info/rfc8259">

     <front>
<title>
The
       <title>The JavaScript Object Notation (JSON) Data Interchange Format
</title> Format</title>

       <author initials="T." surname="Bray" fullname="T. fullname="Tim Bray" role="editor">
<organization/>
         <organization />
       </author>

       <date month="December" year="2017" month="December"/>
<abstract>
<t>
JavaScript Object Notation (JSON) is a lightweight, text-based, language-independent data interchange format. It was derived from the ECMAScript Programming Language Standard. JSON defines a small set of formatting rules for the portable representation of structured data.
</t>
<t>
This document removes inconsistencies with other specifications of JSON, repairs specification errors, and offers experience-based interoperability guidance.
</t>
</abstract> />
     </front>
     <seriesInfo name="STD" value="90"/> value="90" />
     <seriesInfo name="RFC" value="8259"/>
<seriesInfo name="DOI" value="10.17487/RFC8259"/> value="8259" />
   </reference>
</referencegroup>

<xi:include href="reference.RFC.7252.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7252.xml"/>
<xi:include href="reference.RFC.7518.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7518.xml"/>
<xi:include href="reference.RFC.8152.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8152.xml"/>
<xi:include href="reference.RFC.8551.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8551.xml"/>
<xi:include href="reference.RFC.8230.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8230.xml"/>

      <!-- [I-D.ietf-core-oscore-groupcomm] IESG state I-D Exists -->
      <xi:include href="reference.I-D.ietf-core-oscore-groupcomm.xml"/>
      href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.ietf-core-oscore-groupcomm.xml"/>

      <!-- [I-D.ietf-cose-hash-sig] Published as RFC 8778 -->

<xi:include href="reference.I-D.ietf-cose-hash-sig.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8778.xml"/>

      <reference anchor="SP800-38d" anchor="SP800-38D"
      target="https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf">
      <front>
	<title>Recommendation for Block Cipher Modes of Operation:
	Galois/Counter Mode (GCM) and GMAC</title>
      <seriesInfo name="NIST Special Publication 800-38D" value=""/> Publication" value="800-38D"/>
      <author initials="M." surname="Dworkin"/>
      <date year="2007" month="Nov"/> month="November"/> </front> </reference>

<!-- [rfced]  References:  Per
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-56Ar2.pdf>,
the May 2013 version of [SP800-56A] has been superseded.  Please let us know
if we may make the following update, per the NIST page.

Original:
[SP800-56A]
           Barker, E., Chen, L., Roginsky, A., and M. Smid,
           "Recommendation for Pair-Wise Key Establishment Schemes
           Using Discrete Logarithm Cryptography",
           DOI 10.6028/NIST.SP.800-56Ar2, NIST Special Publication
           800-56A, Revision 2, May 2013,
           <http://nvlpubs.nist.gov/nistpubs/SpecialPublications/
           NIST.SP.800-56Ar2.pdf>.

Suggested:
[SP800-56A]
           Barker, E., Chen, L., Roginsky, A., Vassilev, A., and R.
           Davis, "Recommendation for Pair-Wise Key-Establishment
           Schemes Using Discrete Logarithm Cryptography",
           DOI 10.6028/NIST.SP.800-56Ar3, NIST Special Publication
           800-56A, Revision 3, April 2018,
           <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
           NIST.SP.800-56Ar3.pdf>. -->

<reference anchor="SP800-56A" target="http://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-56Ar2.pdf">
      target="https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-56Ar2.pdf">
      <front>
	<title>Recommendation for Pair-Wise Key Establishment
      Schemes Using Discrete Logarithm Cryptography</title>
            <seriesInfo name="DOI" value="10.6028/NIST.SP.800-56Ar2"/>
            <seriesInfo name="NIST Special Publication 800-56A," value="Revision 2"/>
      <author initials="E." surname="Barker">
              <organization>U.S. National Institute of Standards and Technology</organization>
      <organization/> </author>
      <author initials="L." surname="Chen">
              <organization>U.S. National Institute of Standards and Technology</organization>
	<organization/> </author>
      <author initials="A." surname="Roginsky">
              <organization>U.S. National Institute of Standards and Technology</organization>
	<organization/> </author>
      <author initials="M." surname="Smid">
              <organization>Orion Security Solutions, Inc.</organization>
            </author>
	<organization/></author>
	<date year="2013" month="May"/>
      </front>
      <seriesInfo name="DOI" value="10.6028/NIST.SP.800-56Ar2"/>
<refcontent>NIST Special Publication 800-56A, Revision 2</refcontent>
    </reference>

<reference anchor="GitHub-Examples"
	   target="https://github.com/cose-wg/Examples">
  <front>
  <title>GitHub Examples of COSE</title> <author/>
<date month="June" day="3" year="2020"/>
</front>
<refcontent>commit 3221310</refcontent>
      </reference>

<!-- [I-D.mattsson-cfrg-det-sigs-with-noise] IESG state Expired -->
      <xi:include href="reference.I-D.mattsson-cfrg-det-sigs-with-noise.xml"/>
      href="https://datatracker.ietf.org/doc/bibxml3/reference.I-D.mattsson-cfrg-det-sigs-with-noise.xml"/>

<reference anchor="HKDF" target="https://eprint.iacr.org/2010/264.pdf">
  <front>
    <title>Cryptographic Extraction and Key Derivation: The HKDF
    Scheme</title>
    <author initials="H." surname="Krawczyk">
      <organization>IBM T.J. Watson Research Center</organization>
      </author>
      <date year="2010"/>
    </front>
  </reference>

<!-- [ROBUST] The URL below returns a "File Not Found" error.  Please provide a working and stable URL - perhaps <https://eprint.iacr.org/2020/718.pdf>?

Original:
[ROBUST]   Fischlin, M., Günther, F., and C. Janson, "Robust
              Channels: Handling Unreliable Networks in the Record
              Layers of QUIC and DTLS", February 2020,
              <https://www.felixguenther.info/docs/
              QUIP2020_RobustChannels.pdf>.
-->
<reference anchor="ROBUST" target="https://www.felixguenther.info/docs/QUIP2020_RobustChannels.pdf">
	   target="https://eprint.iacr.org/2020/718.pdf">
  <front>
    <title>Robust Channels: Handling Unreliable Networks in
      the Record Layers of QUIC and DTLS</title>
      <author initials="M." surname="Fischlin"/>
      <author initials="F." surname="Günther"/>
      <author initials="C." surname="Janson"/>
      <date year="2020" month="Feb"/>
    </front>
  </reference>

<xi:include href="reference.I-D.ietf-quic-tls.xml"/> href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.9001.xml"/>

</references>
</references>

<section numbered="false">
      <name>Acknowledgments</name>
      <t>This document is a product of the COSE working group Working Group of the IETF.  </t>
      <t>The following individuals are to blame for getting me started on this
      project in the first place: Richard Barnes, Matt Miller, and Martin Thomson. <contact fullname="Richard Barnes"/>,
      <contact fullname="Matt Miller"/>, and <contact fullname="Martin
      Thomson"/>.  </t>
      <t>The initial draft version of the specification was based to some degree on
      the outputs of the JOSE and S/MIME working groups. Working Groups.  </t>
      <t>The following individuals provided input into the final form of the
      document: Carsten Bormann, John Bradley, Brain Campbell, Michael <contact fullname="Carsten Bormann"/>, <contact fullname="John
      Bradley"/>, <contact fullname="Brian Campbell"/>, <contact
      fullname="Michael B. Jones, Ilari Liusvaara, Francesca Palombini, Ludwig Seitz, and Göran Selander. Jones"/>, <contact fullname="Ilari Liusvaara"/>,
      <contact fullname="Francesca Palombini"/>, <contact fullname="Ludwig
      Seitz"/>, and <contact fullname="Göran Selander"/>.  </t>
    </section>
<!-- [rfced] Please review the "Inclusive Language" portion of the online
Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
and let us know if any changes are needed.

In particular, please review the use of "tradition" and "traditionally" in this document.
<https://www.nist.gov/nist-research-library/nist-technical-series-publications-author-instructions#table1> includes the following:

   Note: This term may (1) create an inequitable relationship; and
   (2) introduce ambiguity (“traditional” is a subjective term). When possible,
   precise language is preferred.

We agree that tradition* may be ambiguous and suggest updating for clarity (where possible).
-->

  </back>
</rfc>