DRIP Working Group
Internet Engineering Task Force (IETF) A. Wiethuechter, Ed.
Internet-Draft
Request for Comments: 9575 S. Card
Intended status:
Category: Standards Track AX Enterprize, LLC
Expires: 24 August 2024
ISSN: 2070-1721 R. Moskowitz
HTT Consulting
21 February
April 2024
DRIP Entity Tag Authentication Formats & and Protocols for Broadcast
Remote
ID
draft-ietf-drip-auth-49 Identification
Abstract
The Drone Remote Identification Protocol (DRIP), plus trust policies
and periodic access to registries, augments Unmanned Aircraft System
(UAS) Remote Identification (RID), enabling local real time real-time
assessment of trustworthiness of received RID messages and observed
UAS, even by Observers lacking Internet access. This document
defines DRIP message types and formats to be sent in Broadcast RID
Authentication Messages to verify that attached and recent recently detached
messages were signed by the registered owner of the DRIP Entity Tag
(DET) claimed.
Status of This Memo
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This Internet-Draft will expire on 24 August 2024.
https://www.rfc-editor.org/info/rfc9575.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. DRIP Entity Tag (DET) Authentication Goals for Broadcast
RID . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Required Terminology . . . . . . . . . . . . . . . . . . 5
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
3. UAS RID Authentication Background & and Procedures . . . . . . . 5
3.1. DRIP Authentication Protocol Description . . . . . . . . 6
3.1.1. Usage of DNS . . . . . . . . . . . . . . . . . . . . 6
3.1.2. Providing UAS RID Trust . . . . . . . . . . . . . . . 7
3.2. ASTM Authentication Message Framing . . . . . . . . . . . 8
3.2.1. Authentication Page . . . . . . . . . . . . . . . . . 8
3.2.2. Authentication Payload Field . . . . . . . . . . . . 9
3.2.3. Specific Authentication Method (SAM) . . . . . . . . 10
3.2.4. ASTM Broadcast RID Constraints . . . . . . . . . . . 11
4. DRIP Authentication Formats . . . . . . . . . . . . . . . . . 13
4.1. UA Signed Evidence Structure . . . . . . . . . . . . . . 13
4.2. DRIP Link . . . . . . . . . . . . . . . . . . . . . . . . 15
4.3. DRIP Wrapper . . . . . . . . . . . . . . . . . . . . . . 17
4.3.1. Wrapped Count & and Format Validation . . . . . . . . . . 18
4.3.2. Wrapper over Extended Transports . . . . . . . . . . 18
4.3.3. Wrapper Limitations . . . . . . . . . . . . . . . . . 20
4.4. DRIP Manifest . . . . . . . . . . . . . . . . . . . . . . 20
4.4.1. Hash Count & and Format Validation . . . . . . . . . . . 21
4.4.2. Manifest Ledger Hashes . . . . . . . . . . . . . . . 22
4.4.3. Hash Algorithms and Operation . . . . . . . . . . . . 22
4.5. DRIP Frame . . . . . . . . . . . . . . . . . . . . . . . 23
5. Forward Error Correction . . . . . . . . . . . . . . . . . . 24
5.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . . 25
5.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . . 26
5.3. FEC Limitations . . . . . . . . . . . . . . . . . . . . . 29
6. Requirements & and Recommendations . . . . . . . . . . . . . . . 29
6.1. Legacy Transports . . . . . . . . . . . . . . . . . . . . 29
6.2. Extended Transports . . . . . . . . . . . . . . . . . . . 29
6.3. Authentication . . . . . . . . . . . . . . . . . . . . . 29
6.4. Operational . . . . . . . . . . . . . . . . . . . . . . . 30
6.4.1. DRIP Wrapper . . . . . . . . . . . . . . . . . . . . 31
6.4.2. UAS RID Trust Assessment . . . . . . . . . . . . . . 31
7. Summary of Addressed DRIP Requirements . . . . . . . . . . . 31
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32
8.1. IANA DRIP Registry . . . . . . . . . . . . . . . . . . . 32
9. Security Considerations . . . . . . . . . . . . . . . . . . . 33
9.1. Replay Attacks . . . . . . . . . . . . . . . . . . . . . 33
9.2. Wrapper vs Manifest . . . . . . . . . . . . . . . . . . . 34
9.3. VNA Timestamp Offsets for DRIP Authentication Formats . . 35
9.4. DNS Security in DRIP . . . . . . . . . . . . . . . . . . 36
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 37
11.1. Normative References . . . . . . . . . . . . . . . . . . 37
11.2. Informative References . . . . . . . . . . . . . . . . . 38
Appendix A. Authentication States . . . . . . . . . . . . . . . 38
A.1. None: Black . . . . . . . . . . . . . . . . . . . . . . . 40
A.2. Partial: Gray . . . . . . . . . . . . . . . . . . . . . . 40
A.3. Unsupported: Brown . . . . . . . . . . . . . . . . . . . 41
A.4. Unverifiable: Yellow . . . . . . . . . . . . . . . . . . 41
A.5. Verified: Green . . . . . . . . . . . . . . . . . . . . . 41
A.6. Trusted: Blue . . . . . . . . . . . . . . . . . . . . . . 41
A.7. Questionable: Orange . . . . . . . . . . . . . . . . . . 41
A.8. Unverified: Red . . . . . . . . . . . . . . . . . . . . . 42
A.9. Conflicting: Purple . . . . . . . . . . . . . . . . . . . 42
Appendix B. Operational Recommendation Analysis . . . . . . . . 42
B.1. Page Counts vs Frame Counts . . . . . . . . . . . . . . . 42
B.1.1. Special Cases . . . . . . . . . . . . . . . . . . . . 44
B.2. Full Authentication Example . . . . . . . . . . . . . . . 44
B.2.1. Raw Example . . . . . . . . . . . . . . . . . . . . . 46
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47
1. Introduction
The initial regulations (e.g., [FAA-14CFR]) and standards (e.g.,
[F3411]) for Unmanned Aircraft (UA) Systems (UAS) Remote Identification
(RID) and tracking (RID) do not address trust. However, this is a
requirement that needs to be addressed for various different parties
that have a stake in the safe operation of National Airspace Systems
(NAS). Drone Remote ID Protocol's (DRIP's) goal is to specify how
RID can be made trustworthy and available in both Internet and local-only local-
only connected scenarios, especially in emergency situations.
UAS often operate in a volatile environment. Small UA offer A small Unmanned
Aircraft (UA) offers little capacity for computation and
communication. UAS RID must also be accessible with ubiquitous and
inexpensive devices without modification. This limits options. Most
current small UAS are IoT Internet of Things (IoT) devices even if they
are not typically thought of as such. Thus many IoT considerations
apply here. Some DRIP work, currently strongly scoped to UAS RID, is
likely to be applicable to some other IoT use-cases. use cases.
Generally, two communication schemes for UAS RID are considered:
Broadcast and Network. This document focuses on adding trust to
Broadcast RID (Section 3.2 of [RFC9153] and Section 1.2.2 of
[RFC9434]). As defined in [F3411] and outlined in [RFC9153] and
[RFC9434], Broadcast RID is a one-way RF Radio Frequency (RF)
transmission of MAC Media Access Control (MAC) layer messages over
Bluetooth or Wi-Fi.
Senders can make any claims the RID message formats allow. Observers
have no standardized means to assess the trustworthiness of message
content, nor verify whether the messages were sent by the UA
identified therein, nor confirm that the UA identified therein is the
one they are visually observing. Indeed, Observers have no way to
detect whether the messages were sent by a UA, UA or spoofed by some
other transmitter (e.g., a laptop or smartphone) anywhere in direct
wireless broadcast range. Authentication is the primary strategy for
mitigating this issue.
1.1. DRIP Entity Tag (DET) Authentication Goals for Broadcast RID
ASTM [F3411] Authentication Messages (Message Type 0x2), when used
with DRIP Entity Tag (DET) [RFC9374] based formats, DET-based formats [RFC9374], enable a high level of trust that
the content of other ASTM Messages was generated by their claimed
registered source. These messages are designed to provide the
Observers with trustworthy and immediately actionable information.
Appendix A provides a high-level overview of the various states of
trustworthiness that may be used along with these formats.
This authentication approach also provides some error correction
(Section 5) as mandated by the United States (US) Federal Aviation
Administration (FAA) [FAA-14CFR], which is missing from [F3411] over
Legacy Transports (Bluetooth 4.x).
These DRIP enhancements to ASTM's specification for RID and tracking
[F3411] further support the important use case of Observers who may
be offline at the time of observation.
A summary of
Section 7 summarizes the DRIP requirements [RFC9153] addressed herein is provided
in Section 7.
herein.
Note: The Endorsement (used in Section 4.2) that proves that a DET is
registered MUST come from its immediate parent in the registration
hierarchy, e.g., a DRIP Identity Management Entity (DIME) [drip-registries]. [DRIP-REG].
In the definitive hierarchy, the parent of the UA is its HHIT Domain
Authority (HDA), the parent of an HDA is its Registered Assigning
Authority (RAA), etc. It is also assumed that all DRIP-aware
entities use a DET as their identifier during interactions with other
DRIP-aware entities.
2. Terminology
2.1. Required Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Definitions
This document makes use of the terms (CAA, Observer, USS, UTM, etc.)
defined in [RFC9153]. Other terms (such as DIME) are from [RFC9434],
while others (HI, DET, RAA, HDA, etc.) are from [RFC9374].
In addition, the following terms are defined for this document:
Extended Transports: Use of extended advertisements (Bluetooth 5.x),
service info (Wi-
Fi (Wi-Fi Neighbor Awareness Networking (NAN)), or IEEE
802.11 Beacons with vendor specific the vendor-specific information element as
specified in [F3411]. Must use ASTM Message Pack (Message Type
0xF).
Legacy Transports: Use of broadcast frames (Bluetooth 4.x) as
specified in [F3411].
Manifest:
an An immutable list of items being transported (in this
specific case over wireless communication).
3. UAS RID Authentication Background & and Procedures
3.1. DRIP Authentication Protocol Description
[F3411] defines Authentication Message framing only. It does not
define authentication formats or methods. It explicitly anticipates
several signature options but does not fully define those. Annex A1
of [F3411] defines a Broadcast Authentication Verifier Service, which
has a heavy reliance on Observer real-time connectivity to the
Internet. Fortunately, [F3411] also allows third party third-party standard
Authentication Types using the Type 5 Specific Authentication Method
(SAM), several of which DRIP defines herein.
The standardization of specific formats to support the DRIP
requirements in UAS RID for trustworthy communications over Broadcast
RID is an important part of the chain of trust for a UAS ID. Per
Section 5 of [RFC9434], Authentication formats are needed to relay
information for Observers to determine trust. No existing formats
(defined in [F3411] or other organizations leveraging this feature)
provide the functionality to satisfy this goal goal, resulting in the work
reflected in this document.
3.1.1. Usage of DNS
Like most aviation matters, the overall objectives here are security
and ultimately safety oriented. Since DRIP depends on DNS for some
of its functions, DRIP usage of DNS needs to be protected as per best
security practices. Many participating nodes will have limited local
processing power and/or poor, low bandwidth low-bandwidth QoS paths. Appropriate
and feasible security techniques will be highly dependent on the UAS
and Observer
situation dependent. Therefore situation. Therefore, specification of particular DNS
security options, transports, etc. is outside the scope of this
document (see also Section 9.4).
In DRIP DRIP, Observers MUST validate all signatures received. This
requires that the Host Identity (HI) corresponding correspond to a DET [RFC9374].
HI's MAY be retrieved from a local cache, if present. The local
cache is pre-configured with well knowns well-known HIs (such as those of CAA
DIMEs) and is further populated by received Broadcast Endorsements
(BEs) (Section 3.1.2.1) and DNS lookups (when available).
The Observer MUST perform a DNS query, when connectivity allows, to
obtain an HI not a previously known. unknown HI. If a query can not cannot be performed, the
message SHOULD be cached by the Observer to be validated once the HI
is obtained.
A more comprehensive specification of DRIP's use of DNS is out of
scope for this document and can be found in [drip-registries]. [DRIP-REG].
3.1.2. Providing UAS RID Trust
For DRIP, two actions together provide a mechanism for an Observer to
trust in UAS RID using Authentication Messages.
First is the transmission of an entire trust chain via Broadcast
Endorsements (Section 3.1.2.1). This provides a hierarchy of DIMEs
down to and including an individual UA's registration of a claimed
DET and corresponding HI (public key). This alone cannot be trusted
as having any relevance to the observed UA because replay attacks are
trivial.
After an Observer has gathered such a complete key trust chain (from
pre-configured cache entries, Broadcast Endorsements received over
the air and/or DNS lookups) and verified all of its links, that
device can trust that the claimed DET and corresponding public key
are properly registered, but the UA has not yet been proven to
possess the corresponding private key.
It is necessary for the UA to prove possession by dynamically signing
data that is unique and unpredictable but easily verified by the
Observer (Section 3.1.2.2). Verification of this signed data MUST be
performed by the Observer as part of the received UAS RID information
trust assessment (Section 6.4.2).
3.1.2.1. DIME Endorsements of Subordinate DETs
Observers receive DRIP Link Authentication Messages (Section 4.2)
containing Broadcast Endorsements by DIMEs of child DET
registrations. A series of these Endorsements confirms a path
through the hierarchy, defined in [drip-registries], [DRIP-REG], from the DET Prefix
Owner all the way to an individual UA DET registration.
Note: For the remainder of this document document, Broadcast Endorsement:
Parent, Child will be abbreviated to as BE: Parent, Child. For
example example,
Broadcast Endorsement: RAA, HDA will be abbreviated to as BE: RAA, HDA.
3.1.2.2. UA Signed Evidence
To prove possession of the private key associated to with the DET, the
UA MUST send data that is unique and unpredictable but easily
validated by the Observer, that is signed over. The data can be an
ASTM Message that fulfills the requirements to be unpredictable but
easily validated. An Observer receives this UA-signed UA signed Evidence from DRIP-
based
DRIP-based Authentication Messages (Section (Sections 4.3 or Section 4.4).
Whether the content is true is a separate question which that DRIP cannot
address, but validation performed using observable and/or out of band out-of-band
data (Section 6) are is possible and encouraged.
3.2. ASTM Authentication Message Framing
The Authentication Message (Message Type 0x2) is unique in the ASTM
[F3411] Broadcast standard standard, as it is the only message that can be
larger than the Legacy Transport size. To address this limitation
around transport size, it is defined as a set of "pages", each of
which fits into a single Legacy Transport frame. For Extended
Transports, pages are still used but all they are all in a single frame.
Informational Note: Message Pack (Message Type 0xF) is also larger
than the Legacy Transport size but is limited for use only on
Extended Transports where is can be supported.
The following sub-sections subsections are a brief overview of the Authentication
Message format defined in [F3411] for better context on how DRIP
Authentication fills and uses various fields already defined by ASTM
[F3411].
3.2.1. Authentication Page
This document leverages Authentication Type 0x5, Specific 0x5 (Specific
Authentication Method (SAM), (SAM)) as the principal authentication
container, defining a set of SAM Types in Section 4. Authentication
Type is encoded in every Authentication Page in the Page Header. The
SAM Type is defined as a field in the Authentication Payload (see
Section 3.2.3.1).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Page Header | |
+---------------+ |
| |
| |
| Authentication Payload |
| |
| |
+---------------+---------------+---------------+---------------+
Figure 1: Standard ASTM Authentication Message Page
Page Header: (1 octet)
Authentication Type (4 bits) and Page Number (4 bits)
Authentication Payload: (23 octets per page)
Authentication Payload, including headers. Null padded. See
Section 3.2.2.
The Authentication Message is structured as a set of pages per
Figure 1. There is a technical maximum of 16 pages (indexed 0 to 15)
that can be sent for a single Authentication Message, with each page
carrying a maximum 23 octet 23-octet Authentication Payload. See
Section 3.2.4 for more details. Over Legacy Transports, these
messages are "fragmented", with each page sent in a separate Legacy
Transport frame.
Either as a single Authentication Message or a set of fragmented
Authentication Message Pages, the structure is further wrapped by
outer ASTM framing and the specific link framing.
3.2.2. Authentication Payload Field
Figure 2 is the source data view of the data fields found in the
Authentication Message as defined by [F3411]. This data is placed
into Figure 1's the Authentication Payload, spanning Payload shown in Figure 1, which spans
multiple Authentication Pages.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Authentication Headers |
| +---------------+---------------+
| | |
+---------------+---------------+ |
. .
. Authentication Data / Signature .
. .
| |
+---------------+---------------+---------------+---------------+
| ADL | |
+---------------+ |
. .
. Additional Data .
. .
| |
+---------------+---------------+---------------+---------------+
Figure 2: ASTM Authentication Message Fields
Authentication Headers: (6 octets)
As defined in [F3411].
Authentication Data / Signature: (0 to 255 octets)
Opaque authentication data. The length of this payload is known
through a field in the Authentication Headers (defined in
[F3411]).
Additional Data Length (ADL): (1 octet - unsigned)
Length in octets of Additional Data. The value of ADL is
calculated as the minimum of 361 - Authentication Data / Signature
Length and 255. Only present with Additional Data.
Additional Data: (ADL octets)
Data that follows the Authentication Data / Signature but is not
considered part of the Authentication Data Data, and thus is not
covered by a signature. For DRIP, this field is used to carry
Forward Error Correction (FEC) generated by transmitters and
parsed by receivers as defined in Section 5.
3.2.3. Specific Authentication Method (SAM)
3.2.3.1. SAM Data Format
Figure 3 is the general format to hold authentication data when using
SAM and is placed inside the Authentication Data/Signature Data / Signature field in
Figure 2.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| SAM Type | |
+---------------+ |
. .
. SAM Authentication Data .
. .
| |
+---------------+---------------+---------------+---------------+
Figure 3: SAM Data Format
SAM Type: (1 octet)
The following SAM Types are allocated to DRIP:
+==========+=============================+
| SAM Type | Description |
+==========+=============================+
| 0x01 | DRIP Link (Section 4.2) |
+----------+-----------------------------+
| 0x02 | DRIP Wrapper (Section 4.3) |
+----------+-----------------------------+
| 0x03 | DRIP Manifest (Section 4.4) |
+----------+-----------------------------+
| 0x04 | DRIP Frame (Section 4.5) |
+----------+-----------------------------+
Table 1: DRIP SAM Types
Note: ASTM International is the owner of these code points as they
are defined in [F3411]. In accordance with Annex 5 of the ASTM's [F3411], the
International Civil Aviation Organization (ICAO) has been selected by
ASTM as the registrar to manage allocations of these code points.
The list of which can be found is available at [ASTM-Remote-ID].
SAM Authentication Data: (0 to 200 octets)
Contains opaque authentication data formatted as defined by the
preceding SAM Type.
3.2.4. ASTM Broadcast RID Constraints
3.2.4.1. Wireless Frame Constraints
A UA has the option of broadcasting to broadcast using Bluetooth (4.x and 5.x), Wi-Fi
NAN, or IEEE 802.11 Beacon, Beacon; see Section 6. With Bluetooth, FAA and
other Civil Aviation Authorities (CAA) mandate transmitting
simultaneously over both 4.x and 5.x. The same application layer application-layer
information defined in [F3411] MUST be transmitted over all the
physical layer
physical-layer interfaces performing the function of RID. This is RID, because Observer transports
may be limited. If an Observer can support multiple transports transports, it
should be assumed to use the latest data regardless of the transport
received over.
Bluetooth 4.x presents a payload size payload-size challenge in that it can only
transmit 25 octets of payload per frame frame, while other transports can
support larger payloads per frame. However, the [F3411] messaging message
framing dictated by Bluetooth 4.x constraints is inherited by [F3411]
over other media.
It should be noted that Extended Transports by definition have Error
Correction built in, unlike Legacy Transports. For Authentication
Messages
Messages, this means that over Legacy Transport pages could be may not
received by Observers resulting in incomplete messages during
operation, although the use of DRIP FEC (Section 5) reduces the
likelihood of this. its
likelihood. Authentication Messages sent using Extended Transports
do not suffer this issue issue, as the full message (all pages)
are is sent
using a single Message Pack. Furthermore Furthermore, the use of one-way RF
broadcasts prohibits the use of any congestion control congestion-control or loss loss-
recovery schemes that require ACKs or NACKs.
3.2.4.2. Paged Authentication Message Constraints
To keep consistent formatting across the different transports (Legacy
and Extended) and their independent restrictions, the authentication
data being sent is REQUIRED to fit within the page limit that the
most constrained existing transport can support. Under Broadcast
RID, the Extended Transport that can hold the least amount of
authentication data is Bluetooth 5.x at 9 pages.
As such such, DRIP transmitters are REQUIRED to adhere to the following
when using the Authentication Message:
1. Authentication Data / Signature data MUST fit in the first 9
pages (Page Numbers 0 through 8).
2. The Length field in the Authentication Headers (which encodes the
length in octets of Authentication Data / Signature only) MUST
NOT exceed the value of 201. This includes the SAM Type but
excludes Additional Data.
3.2.4.3. Timestamps
In ASTM [F3411] [F3411], timestamps are a Unix-style timestamp with an epoch
of 2019-01-01 00:00:00 UTC. For DRIP DRIP, this format is adopted for
Authentication to keep a common time format in Broadcast payloads.
Under DRIP DRIP, there are two timestamps defined defined: Valid Not Before (VNB)
and Valid Not After (VNA).
Valid Not Before (VNB) Timestamp: (4 octets)
Timestamp denoting the recommended time at which to start trusting data in.
data. MUST follow the format defined in [F3411] as described
above. MUST be set no earlier than the time the signature (across
a given structure) is generated.
Valid Not After (VNA) Timestamp: (4 octets)
Timestamp denoting the recommended time at which to stop trusting
data. MUST follow the format defined in [F3411] as described
above. Has an additional offset to push a short time into the
future (relative to VNB) to avoid replay attacks. The exact
offset is not defined in this document. Best practice for
identifying an acceptable offset should be used taking and should take
into consideration the UA environment, and propagation characteristics
of the messages being sent, and clock differences between the UA
and Observers. A reasonable time would be to set VNA 2 minutes
after VNB.
4. DRIP Authentication Formats
All formats defined in this section are the content of contained in the
Authentication Data / Signature field in Figure 2 and use the
Specific Authentication Method (SAM, Authentication Type 0x5). The
first octet of the Authentication Data / Signature of Figure 2 is
used to multiplex among these various formats.
When sending data over a medium that does not have underlying FEC,
for example Legacy Transports, then Section 5 MUST be used.
Examples of Link, Wrapper Wrapper, and Manifest are shown as part of an
operational schedule in Appendix B.2.1.
4.1. UA Signed Evidence Structure
The UA Signed Evidence Structure (Figure 4) is used by the UA during
flight to sign over information elements using the private key
associated with the current UA DET. It is encapsulated by the SAM
Authentication Data field of Figure 3.
This structure is used by the DRIP Wrapper (Section 4.3), Manifest
Section 4.4, 4.4), and Frame (Section 4.5). DRIP Link (Section 4.2) MUST
NOT use it it, as it will not fit in the ASTM Authentication Message
with its intended content (i.e., a Broadcast Endorsement).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| VNB Timestamp by UA |
+---------------+---------------+---------------+---------------+
| VNA Timestamp by UA |
+---------------+---------------+---------------+---------------+
| |
. .
. Evidence .
. .
| |
+---------------+---------------+---------------+---------------+
| |
| UA |
| DRIP Entity Tag |
| |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| UA Signature |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
Figure 4: Endorsement Structure for UA Signed Evidence
Valid Not Before (VNB) Timestamp by UA: (4 octets)
See Section 3.2.4.3. Set by the UA.
Valid Not After (VNA) Timestamp by UA: (4 octets)
See Section 3.2.4.3. Set by the UA.
Evidence: (0 to 112 octets)
The evidence section MUST be filled in with data in the form of an
opaque object specified in the DRIP Wrapper (Section 4.3),
Manifest (Section 4.4), or Frame (Section 4.5).
UA DRIP Entity Tag: (16 octets)
This is the current DET [RFC9374] being used by the UA assumed to
be a Specific Session ID (a type of UAS ID).
UA Signature: (64 octets)
Signature over concatenation of preceding fields (VNB, VNA,
Evidence, and UA DET) using the keypair of the UA DET. The
signature algorithm is specified by the HHIT Hierarchical Host Identity
Tags (HHIT) Suite ID of the DET.
When using this structure, the UA is minimally self-endorsing its
DET. The HI of the UA DET can be looked up by mechanisms described
in [drip-registries] [DRIP-REG] or by extracting it from a Broadcast Endorsement (see Section
Sections 4.2 and Section 6.3).
4.2. DRIP Link
This SAM Type is used to transmit Broadcast Endorsements. For
example, the BE: HDA, UA is sent (see Section 6.3) as a DRIP Link
message.
DRIP Link is important as its contents are used to provide trust in
the DET/HI pair that the UA is currently broadcasting. This message
does not require Internet connectivity to perform signature
verification of the contents when the DIME DET/HI is in the
Observer's cache. It also provides the UA HI, when it is filled with
a BE: HDA, UA, so that connectivity is not required when performing
signature verification of other DRIP Authentication Messages.
Various Broadcast Endorsements are sent during operation to ensure
that the full Broadcast Endorsement chain is available offline. See
Section 6.3 for further details.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| VNB Timestamp by Parent |
+---------------+---------------+---------------+---------------+
| VNA Timestamp by Parent |
+---------------+---------------+---------------+---------------+
| |
| DET |
| of Child |
| |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| HI of Child |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
| |
| DET |
| of Parent |
| |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| Signature by Parent |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
Figure 5: Broadcast Endorsement / DRIP Link
VNB Timestamp by Parent: (4 octets)
See Section 3.2.4.3. Set by Parent Entity.
VNA Timestamp by Parent: (4 octets)
See Section 3.2.4.3. Set by Parent Entity.
DET of Child: (16 octets)
DRIP Entity Tag of Child Entity.
HI of Child: (32 octets)
Host Identity of Child Entity.
DET of Parent: (16 octets)
DRIP Entity Tag of Parent Entity in DIME Hierarchy.
Signature by Parent: (64 octets)
Signature over concatenation of preceding fields (VNB, VNA, DET of
Child, HI of Child, and DET of Parent) using the keypair of the
Parent DET.
This DRIP Authentication Message is used in conjunction with other
DRIP SAM Types (such as the Manifest or the Wrapper) that contain
data (e.g., the ASTM Location/Vector Message, Message Type 0x2) that
is guaranteed to be unique, unpredictable, and easily cross-checked
by the receiving device.
A hash of the final link (BE: HDA on UA) in the Broadcast Endorsement
chain MUST be included in each DRIP Manifest Section 4.4. (Section 4.4).
4.3. DRIP Wrapper
This SAM Type is used to wrap and sign over a list of other [F3411]
Broadcast RID messages.
The evidence section of the UA Signed Evidence Structure
(Section 4.1) is populated with up to four ASTM [F3411] Messages [F3411] in a
contiguous octet sequence. Only ASTM Message Types 0x0, 0x1, 0x3,
0x4, and 0x5 are allowed and must be in Message Type order as defined
by [F3411]. These messages MUST include the Message Type and
Protocol Version octet and MUST NOT include the Message Counter octet
(thus are fixed at 25 octets in length).
4.3.1. Wrapped Count & and Format Validation
When decoding a DRIP Wrapper on a receiver, a calculation of the
number of messages wrapped and a validation MUST be performed by
using the number of octets (defined as wrapperLength) between the VNA
Timestamp by UA and the UA DET as shown in Figure 6.
<CODE BEGINS>
if (wrapperLength MOD 25) != 0 {
return DECODE_FAILURE;
}
wrappedCount = wrapperLength / 25;
if (wrappedCount == 0) {
// DECODE_SUCCESS; treat as DRIP Wrapper over extended transport
}
else if (wrappedCount > 4) {
return DECODE_FAILURE;
} else {
// DECODE_SUCCESS; treat as standard DRIP Wrapper
}
<CODE ENDS>
Figure 6: Pseudo-code Pseudocode for Wrapper validation Validation and number Number of
messages
Messages calculation
4.3.2. Wrapper over Extended Transports
When using Extended Transports Transports, an optimization can be made to DRIP Wrapper can
be made to sign over co-located data in an ASTM Message Pack (Message
Type 0xF).
To perform this optimization optimization, the UA Signed Evidence Structure is
filled with the ASTM Messages to be in the ASTM Message Pack, the
signature is generated, and then the evidence field is cleared cleared,
leaving the encoded form shown in Figure 7.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| VNB Timestamp by UA |
+---------------+---------------+---------------+---------------+
| VNA Timestamp by UA |
+---------------+---------------+---------------+---------------+
| |
| UA |
| DRIP Entity Tag |
| |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| UA Signature |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
Figure 7: DRIP Wrapper over Extended Transports
To verify the signature, the receiver MUST concatenate all the
messages in the Message Pack (excluding the Authentication Message
found in the same Message Pack) in ASTM Message Type order and set
the evidence section of the UA Signed Evidence Structure before
performing signature verification.
The functionality of a Wrapper in this form is equivalent to Message
Set Signature (Authentication Type 0x3) when running over Extended
Transports. What the The Wrapper provides is the same format but over both
Extended and Legacy Transports allowing Transports, which allows the transports to be
similar. Message Set Signature also implies using the ASTM validator
system architecture architecture, which depends on Internet connectivity for
verification which that the receiver may not have at the time of receipt
of an
Authentication Message. Message is received. This is something the Wrapper,
and all DRIP Authentication Formats, avoid when the UA key is
obtained via a DRIP Link Authentication Message.
4.3.3. Wrapper Limitations
The primary limitation of the Wrapper is the bounding of up to 4 four
ASTM Messages that can be sent within it. Another limitation is that
the format cannot be used as a surrogate for messages it is wrapping
due to the potential that an Observer on the ground does not support
DRIP. Thus, when a Wrapper is being used, the wrapped data must
effectively be sent twice, once as a single framed single-framed message (as
specified in [F3411]) and then again within the Wrapper.
4.4. DRIP Manifest
This SAM Type is used to create message manifests that contain hashes
of previously sent ASTM Messages.
By hashing previously sent messages and signing them, we gain trust
in a UA's previous reports without re-transmitting retransmitting them. This is a
way to evade the limitation of a maximum of 4 four messages in the
Wrapper (Section 4.3.3) and greatly reduce overhead.
Observers MUST hash all received ASTM Messages and cross-check them
against hashes in received Manifests.
Judicious use of a Manifest enables an entire Broadcast RID message
stream to be strongly authenticated with less than 100% overhead
relative to a completely unauthenticated message stream (see
Section 6.3 and Appendix B).
The evidence section of the UA Signed Evidence Structure
(Section 4.1) is populated with 8-octet hashes of [F3411] Broadcast
RID messages (up to 11) and three special hashes (Section 4.4.2).
All of these hashes MUST be concatenated to form a contiguous octet
sequence in the evidence section. It is RECOMMENDED that the max maximum
number of ASTM Message Hashes be used is be 10 (see Appendix B.1.1.2).
The Previous Manifest Hash, Current Manifest Hash, and DRIP Link (BE:
HDA, UA) Hash MUST always come before the ASTM Message Hashes as seen
in Figure 8.
An Observer MUST use the Manifest to verify each ASTM Message hashed
therein that it has previously received. It can do this without
having received them all. A Manifest SHOULD typically encompass a
single transmission cycle of messages being sent, sent; see Section 6.4 and
Appendix B.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Previous Manifest |
| Hash |
+---------------+---------------+---------------+---------------+
| Current Manifest |
| Hash |
+---------------+---------------+---------------+---------------+
| DRIP Link (BE: HDA, UA) |
| Hash |
+---------------+---------------+---------------+---------------+
| |
. .
. ASTM Message Hashes .
. .
| |
+---------------+---------------+---------------+---------------+
Figure 8: DRIP Manifest Evidence Structure
Previous Manifest Hash: (8 octets)
Hash of the previously sent Manifest Message.
Current Manifest Hash: (8 octets)
Hash of the current Manifest Message.
DRIP Link (BE: HDA, UA): (8 octets)
Hash of the DRIP Link Authentication Message carrying BE: HDA, UA
(see Section 4.2).
ASTM Message Hash: (8 octets)
Hash of a single full ASTM Message using hash operations described
in Section 4.4.3.
4.4.1. Hash Count & and Format Validation
When decoding a DRIP Manifest on a receiver, a calculation of the
number of hashes and a validation can be performed by using the
number of octets (defined as manifestLength) between the UA DET and the VNB Timestamp by UA
(defined as manifestLength) such as shown in Figure 9.
<CODE BEGINS>
if (manifestLength MOD 8) != 0 {
return DECODE_FAILURE
}
hashCount = (manifestLength / 8) - 3;
<CODE ENDS>
Figure 9: Pseudo-code Pseudocode for Manifest Sanity Check and Number of
Hashes Calculation
4.4.2. Manifest Ledger Hashes
Three special hashes are included in all Manifests. The Previous
Manifest Hash, links to the previous Manifest, and the Current
Manifest Hash is of the Manifest in which it appears. These two
hashes act as a ledger of provenance to the Manifest that could be
traced back if the Observer was present for extended periods of time.
The DRIP Link (BE: HDA, UA) is included so there is a direct
signature by the UA over the Broadcast Endorsement (see Section 4.2).
Typical operation would expect that the list of ASTM Message Hash's Hashes
contain nonce-link nonce-like data. To enforce a binding between the BE: HDA,
UA and avoid trivial replay attack vectors (see Section 9.1) 9.1), at
least
1 one ASTM Message Hash MUST be from an [F3411] message that
satisfies the 4th fourth requirement in Section 6.3.
4.4.3. Hash Algorithms and Operation
The hash algorithm used for the Manifest is the same hash algorithm
used in creation of the DET [RFC9374] that is signing the Manifest.
This is encoded as part of the DET using the HHIT Suite ID.
DET's using
DETs that use cSHAKE128 [NIST.SP.800-185] compute the hash as
follows:
cSHAKE128(ASTM Message, 64, "", "Remote ID Auth Hash")
For OGAs ORCHID Generation Algorithms (OGAs) other than "5" (EdDSA/
cSHAKE128) [RFC9374], use the construct appropriate for the
associated hash. For example, the hash for "2" which (ECDSA/SHA-384) is ECDSA/SHA-384:
computed as follows:
Ltrunc( SHA-384( ASTM Message | "Remote ID Auth Hash" ), 8 )
When building the list of hashes, the Previous Manifest Hash is known
from the previous Manifest. For the first built Manifest Manifest, this value
is filled with a random nonce. The Current Manifest Hash is null
filled while ASTM Messages are hashed and fill the ASTM Messages Messaged
Hashes section. When all messages are hashed, the Current Manifest
Hash is computed over the Previous Manifest Hash, Current Manifest
Hash (null filled) filled), and ASTM Messages Message Hashes. This hash value
replaces the null filled null-filled Current Manifest Hash and becomes the
Previous Manifest Hash for the next Manifest.
4.4.3.1. Legacy Transport Hashing
Under this transport transport, DRIP hashes the full ASTM Message being sent
over the Bluetooth Advertising frame. This is the 25-octet object
start
that starts with the Message Type and Protocol Version octet along
with the 24 octets of message data. The hash MUST NOT included include the
Message Counter octet.
For paged ASTM Messages (currently only Authentication Messages) Messages), all
of the pages are concatenated together in Page Number order and
hashed as one object.
4.4.3.2. Extended Transport Hashing
Under this transport transport, DRIP hashes the full ASTM Message Pack (Message
Type 0xF) regardless of its content. The hash MUST NOT included include the
Message Counter octet.
4.5. DRIP Frame
This SAM Type is defined to enable the use of Section 4.1 in the
future beyond the previously defined formats (Wrapper and Manifest)
by the inclusion of a single octet to signal the format of evidence
data (up to 111 octets).
The content format of Frame Evidence Data is not defined in this
document. Other specifications MUST define the contents and register
for a Frame Type. At the time of publication publication, there are no defined
Frame Types other than an Experimental range.
Observers MUST check the signature of the structure (Section 4.1) per
Section 3.1.2.2 and MAY, if the specification of Frame Type is known,
parse the content in Frame Evidence Data.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Frame Type | |
+---------------+ .
. Frame Evidence Data .
. .
| |
+---------------+---------------+---------------+---------------+
Figure 10: DRIP Frame
Frame Type: (1 octet)
Byte to sub-type subtype for future different DRIP Frame formats. It takes
the first octet in Figure 10, leaving 111 octets available for
Frame Evidence Data. See Section 8.1 for Frame Type allocations.
5. Forward Error Correction
For Broadcast RID, FEC is provided by the lower layers in Extended
Transports. The Bluetooth 4.x Legacy Transport does not have
supporting support FEC,
so with DRIP Authentication the following application
level application-level scheme is used with DRIP
Authentication to add some FEC. When sending data over a medium that
does not have underlying FEC, for example Bluetooth 4.x,
then this section
MUST be used.
The Bluetooth 4.x lower layers have error detection but not
correction. Any frame in which Bluetooth detects an error is dropped
and not delivered to higher layers (in our case, DRIP). Thus it can
be treated as an erasure.
DRIP standardizes a single page FEC scheme using XOR parity across
all page data of an Authentication Message. This allows the
correction of a single erased page in an Authentication Message. If
more than a single page is missing missing, then handling of an incomplete
Authentication Message is determined by higher layers.
Other FEC schemes, to protect more than a single page of an
Authentication Message or multiple [F3411] Messages, is are left for
future standardization if operational experience proves it necessary
and/or practical.
The data added during FEC is not included in the Authentication Data
/ Signature, but instead in the Additional Data field of Figure 2.
This may cause the Authentication Message to exceed 9-pages, 9 pages, up to a
maximum of 16-pages. 16 pages.
5.1. Encoding
When encoding encoding, two things are REQUIRED:
1. The FEC data MUST start on a new Authentication Page. To do
this, the results of parity encoding MUST be placed in the
Additional Data field of Figure 2 with null padding before it to
line up with the next page. The Additional Data Length field
MUST be set to number of padding octets + number of parity
octets.
2. The Last Page Index field (in Page 0) MUST be incremented from
what it would have been without FEC by the number of pages
required for the Additional Data Length field, null padding padding, and
FEC.
To generate the parity, a simple XOR operation using the previous
parity page and current page is used. Only the 23-octet
Authentication Payload field of Figure 1 is used in the XOR
operations. For Page 0, a 23-octet null pad is used for the previous
parity page.
Figure 11 shows an example of the last two pages (out of N) of an
Authentication Message using DRIP Single Page FEC. The Additional
Data Length is set to 33 33, as there are always 23 octets of FEC data
and in this example there are 10 octets of padding in this example to line it up into
Page N.
Page N-1:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Page Header | |
+---------------+ |
| Authentication Data / Signature |
| |
| +---------------+---------------+---------------+
| | ADL=33 | |
+---------------+---------------+ |
| Null Padding |
| |
+---------------+---------------+---------------+---------------+
Page N:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| Page Header | |
+---------------+ |
| |
| Forward Error Correction |
| |
| |
| |
+---------------+---------------+---------------+---------------+
Figure 11: Example Single Page FEC Encoding
5.2. Decoding
Frame decoding is independent of the transmit media. However However, the
decoding process can determine from the first Authentication page
that there may be a Bluetooth 4.x FEC page at the end. The decoding
process MUST test for the presence of FEC and apply it as follows.
To determine if FEC has been used, a check of the Last Page Index is
performed. In general general, if the Last Page Index field is one greater
than that necessary to hold Length octets of Authentication Data Data,
then FEC has been used. Note that if Length octets are exhausted
exactly at the end of an Authentication Page, the Additional Data
Length field will occupy the first octet of the following page. The
remainder of this page will be null padded under DRIP to align the
FEC to its own page. In this case case, the Last Page Index will have
been incremented once for initializing the Additional Data Length
field and once for the FEC page, for a total of two additional pages,
as in the last row of Table 5.
To decode FEC in DRIP, a rolling XOR is used on each Authentication
Page received in the current Authentication Message. A Message
Counter, outside of the ASTM Message but specified in [F3411], is
used to signal a different Authentication Message and to correlate
pages to messages. This Message Counter is only a single octet in
length, so it will roll over (to 0x00) after reaching its maximum
value (0xFF). If only a single page is missing in the Authentication
Message the resulting parity octets should be the data of the erased
page.
Authentication Page 0 contains various important fields, only located
on that page, that help decode the full ASTM Authentication Message.
If Page 0 has been reconstructed, the Last Page Index and Length
fields MUST be validated by DRIP. The pseudo-code pseudocode in Figure 12 can be
used for both checks.
<CODE BEGINS>
function decode_check(auth_pages[], decoded_lpi, decoded_length) {
// check decoded_lpi does not exceed maximum value
if (decoded_lpi >= 16) {
return DECODE_FAILURE
}
// check that decoded length does not exceed DRIP maximum value
if (decoded_length > 201) {
return DECODE_FAILURE
}
// grab the page at index where length ends and extract its data
auth_data = auth_pages[(decoded_length - 17) / 23].data
// find the index of last auth byte
last_auth_byte = (17 + (23 * last_auth_page)) - decoded_length
// look for non-nulls after the last auth byte
if (auth_data[(last_auth_byte + 2):] has non-nulls) {
return DECODE_FAILURE
}
// check that byte directly after last auth byte is null
if (auth_data[last_auth_byte + 1] equals null) {
return DECODE_FAILURE
}
// we set our presumed Additional Data Length (ADL)
presumed_adl = auth_data[last_auth_byte + 1]
// use the presumed ADL to calculate a presumed LPI
presumed_lpi = (presumed_adl + decoded_length - 17) / 23
// check that presumed LPI and decoded LPI match
if (presumed_lpi not equal decoded_lpi) {
return DECODE_FAILURE
}
return DECODE_SUCCESS
}
<CODE ENDS>
Figure 12: Pseudo-code Pseudocode for Decode Checks
5.3. FEC Limitations
The worst-case scenario is when the Authentication Data / Signature
ends perfectly on a page boundary (Page N-1). This means the
Additional Data Length would start the next page (Page N) and have 22
octets worth of null padding to align the FEC to begin at the start
of the next page (Page N+1). In this scenario, an entire page (Page
N) is being wasted just to carry the Additional Data Length.
6. Requirements & and Recommendations
6.1. Legacy Transports
Under DRIP, the goal is to attempt to bring reliable receipt of the paged
Authentication Message using Legacy Transports. FEC (Section 5) MUST
be used, per mandated RID rules (for example example, the US FAA RID Rule Rules
[FAA-14CFR]), when using Legacy Transports (such as Bluetooth 4.x).
Under [F3411], Authentication Messages are transmitted at the static
rate (at least every 3 seconds). Any DRIP Authentication Messages
containing dynamic data (such as the DRIP Wrapper) MAY be sent at the
dynamic rate (at least every 1 second).
6.2. Extended Transports
Under the ASTM specification, Extended Transports of RID must use the
Message Pack (Message Type 0xF) format for all transmissions. Under
Message Pack, ASTM Messages are sent together (in Message Type order)
in a single frame (up to 9 single frame single-frame equivalent messages under
Legacy Transports). Message Packs are required by [F3411] to be sent
at a rate of 1 per second (like dynamic messages).
Message Packs are sent only over Extended Transports that provide
FEC. Thus, the DRIP decoders will never be presented with a Message
Pack from which a constituent Authentication Page has been dropped;
DRIP FEC could never provide a benefit to a Message Pack, only consume
its precious payload space. Therefore, DRIP FEC (Section 5) MUST NOT
be used in Message Packs.
6.3. Authentication
To fulfill the requirements in [RFC9153], a UA:
1. MUST: send DRIP Link (Section 4.2) using the BE: Apex, RAA
(partially satisfying GEN-3); at least once per 5 minutes. Apex
in this context is the DET prefix owner owner.
2. MUST: send DRIP Link (Section 4.2) using the BE: RAA, HDA
(partially satisfying GEN-3); at least once per 5 minutes minutes.
3. MUST: send DRIP Link (Section 4.2) using the BE: HDA, UA
(satisfying ID-5, GEN-1 and partially satisfying GEN-3); at least
once per minute minute.
4. MUST: send any other DRIP Authentication Format (non-DRIP Link)
where the UA is dynamically signing data that is guaranteed to be
unique, unpredictable unpredictable, and easily cross checked by the receiving
device (satisfying ID-5, GEN-1 and GEN-2); at least once per 5
seconds
seconds.
These four transmission requirements collectively satisfy GEN-3.
6.4. Operational
UAS operation may impact the frequency of sending DRIP Authentication
messages. When a UA dwells at an approximate location, and the
channel is heavily used by other devices, less frequent message
authentication may be effective (to minimize RF packet collisions)
for an Observer. Contrast this with a UA transiting an area, where
authenticated messages SHOULD be sufficiently frequent for an
Observer to have a high probability of receiving an adequate number
for validation during the transit.
A RECOMMENDED operational configuration (in alignment with
Section 6.3) with reasoning rationale can be found in Appendix B. It consists
of the following recommendations for every second:
* Under Legacy Transport:
- Two sets of those ASTM Messages required by a CAA in its
jurisdiction (example: Basic ID, Location and System) and one
set of other ASTM Messages (example: Self ID, Operator ID)
- An FEC protected FEC-protected DRIP Manifest enabling authentication of those
ASTM Messages sent
- A single page of an FEC protected FEC-protected DRIP Link
* Under Extended Transport:
- A Message Pack of ASTM Messages (up to 4) and a DRIP Wrapper
(per Section 4.3.2)
- A Message Pack of a DRIP Link
6.4.1. DRIP Wrapper
If DRIP Wrappers are sent, they MUST be sent in addition to any
required ASTM Messages in a given jurisdiction. An implementation
MUST NOT send DRIP Wrappers in place of any required ASTM Messages it
may encapsulate. Thus, messages within a Wrapper are sent twice:
once in the clear and once authenticated within the Wrapper.
The DRIP Wrapper has a specific use case for DRIP aware DRIP-aware Observers.
For an Observer plotting Location Messages (Message Type 0x2) on a
map, display of an embedded Location Message in a DRIP Wrapper can be
marked differently (e.g., via color) to signify trust in the Location
data.
6.4.2. UAS RID Trust Assessment
As described in Section 3.1.2, the Observer MUST perform validation
of the data being received in Broadcast RID. This is because trust
in a key is different from trust that an observed UA possesses that
key.
A chain of DRIP Links provides trust in a key. A message containing
rapidly changing, not predictable far in advance (relative to typical
operational flight times) that can be validated by Observers, signed
by that key, provides trust that some agent with access to that data
also possesses that key. If the validation involves correlating
physical world observations of the UA with claims in that data, then
the probability is high that the observed UA is (or is collaborating
with or observed in real time by) the agent with the key.
After signature verification of any DRIP Authentication Message
containing UAS RID information elements (e.g., DRIP Wrapper
Section 4.3) the Observer MUST use other sources of information to
correlate against and perform validation. An example of another
source of information is a visual confirmation of the UA position.
When correlation of these different data streams does not match in
acceptable thresholds, the data MUST be rejected as if the signature
failed to validate. Acceptable thresholds threshold limits and what happens
after such a rejection are out of scope for this document.
7. Summary of Addressed DRIP Requirements
The following [RFC9153] requirements as defined in [RFC9153] are addressed in
this document:
ID-5: Non-spoofability
Addressed using the DRIP Wrapper (Section 4.3), DRIP Manifest
(Section 4.4) 4.4), or DRIP Frame (Section 4.5).
GEN-1: Provable Ownership
Addressed using the DRIP Link (Section 4.2) and DRIP Wrapper
(Section 4.3), DRIP Manifest (Section 4.4) 4.4), or DRIP Frame
(Section 4.5).
GEN-2: Provable Binding
Addressed using the DRIP Wrapper (Section 4.3), DRIP Manifest
(Section 4.4) or DRIP Frame (Section 4.5).
GEN-3: Provable Registration
Addressed using the DRIP Link (Section 4.2).
8. IANA Considerations
8.1. IANA DRIP Registry
This document requests two new registries, for DRIP
IANA has created the "DRIP SAM Type Types" and DRIP "DRIP Frame Type, under Types"
registries within the DRIP "Drone Remote ID Protocol" registry group
(https://www.iana.org/assignments/drip/drip.xhtml).
(https://www.iana.org/assignments/drip).
DRIP SAM Type: Types:
This registry is a mirror for SAM Types containing the subset of
allocations used by DRIP Authentication Messages. Future
additions MUST be done through ASTM's designated registrar registrar, which
is ICAO [ASTM-Remote-ID] at the time of publication of this RFC is ICAO
[ASTM-Remote-ID]. RFC.
Additions for DRIP will be coordinated by IANA and the ASTM
designated registrar before final publication as Standards Track
RFCs. The following values have been allocated to the IETF and are defined here:
+==========+===============+=======================================+ IETF:
+==========+===========+=======================================+
| SAM Type | Name | Description |
+==========+===============+=======================================+
+==========+===========+=======================================+
| 0x01 | DRIP Link | Format to hold Broadcast Endorsements |
+----------+---------------+---------------------------------------+
+----------+-----------+---------------------------------------+
| 0x02 | DRIP Wrapper | Authenticate full ASTM Messages |
+----------+---------------+---------------------------------------+
| | Wrapper | |
+----------+-----------+---------------------------------------+
| 0x03 | DRIP Manifest | Authenticate hashes of ASTM Messages |
+----------+---------------+---------------------------------------+
| | Manifest | |
+----------+-----------+---------------------------------------+
| 0x04 | DRIP Frame | Format for future DRIP authentication |
+----------+---------------+---------------------------------------+
| | Frame | |
+----------+-----------+---------------------------------------+
Table 2: DRIP SAM Types
DRIP Frame Type: Types:
This 8-bit valued value registry is for Frame Types in DRIP Frame
Authentication Messages. Future additions to this registry are to
be made through Expert Review (Section 4.5 of [RFC8126]) for the
values of 0x01 to 0x9F and First Come, Come First Served (Section 4.4 of
[RFC8126]) for values 0xA0 to 0xEF. The following values are
defined:
+=============+==============+====================================+
+=============+==============+===============================+
| Frame Type | Name | Description |
+=============+==============+====================================+
+=============+==============+===============================+
| 0x00 | Reserved | Reserved |
+-------------+--------------+------------------------------------+
+-------------+--------------+-------------------------------+
| 0x01 - 0x9F | Reserved | Reserved: Expert Review |
+-------------+--------------+------------------------------------+
| 0xA0 - 0xEF | Reserved Unassigned | Reserved: First Come, First Served |
+-------------+--------------+------------------------------------+
+-------------+--------------+-------------------------------+
| 0xF0 - 0xFF 0xF0-0xFF | Experimental | Reserved for Experimental Use |
+-------------+--------------+------------------------------------+
+-------------+--------------+-------------------------------+
Table 3: DRIP Frame Types
Criteria that should be applied by the designated experts includes
determining whether the proposed registration duplicates existing
functionality and whether the registration description is clear and
fits the purpose of this registry.
Registration requests MUST be sent to drip-reg-review@ietf.org
(mailto:drip-reg-review@ietf.org) and be evaluated within a three-
week review period on the advice of by one or more
designated experts. experts within a three-week review period. Within that
review period, the designated experts will either approve or deny the
registration request, and communicate their decision to the review
list and IANA. Denials should include an explanation and, if
applicable, suggestions to successfully register the DRIP Frame Type.
Registration requests that are undetermined for a period longer than
28 days can be brought to the IESG's attention for resolution.
9. Security Considerations
9.1. Replay Attacks
[F3411] (regardless of transport) lacks replay protection, as it more
fundamentally lacks fully specified authentication. An attacker can
spoof the UA sender MAC address and UAS ID, replaying (with or
without modification) previous genuine messages, and/or crafting
entirely new messages. Using DRIP in [F3411] Authentication message
framing enables verification that messages were signed with
registered keys, but when naively used may be vulnerable to replay
attacks. Technologies such as Single Emitter Identification can
detect such attacks, but they are not readily available and can be
prohibitively expensive, especially for typical Observer devices such
as smartphones.
Replay attack detection using DRIP requires Observer devices to
combine information from multiple messages and sources other than
Broadcast RID. A complete chain of Link messages (Section 4.2), 4.2) from
an Endorsement root of trust to the claimed sender, sender must be collected
and verified by the Observer device to provide trust in a key.
Successful signature verification, using that key, of a Wrapper
(Section 4.3) or Manifest (Section 4.4) message, authenticating
content that is nonce-like, provides trust that the sender actually
possesses that key.
By
The term "nonce-like" is meant data means the that data is unique, not accurately
predictable long in advance, and readily validated by the Observer.
This is described in Section 6.3 (requirement 4) and Section 3.1.2.2.
The [F3411] Location message [F3411] reporting precise UA position and
velocity at a precise and very recent time, time is to be checked by the
Observer against visual observations of the UA within RF and thus typically
visual RF. Thus,
Visual Line Of of Sight is typically the recommended form of this data.
For specification of the foregoing, see Section Sections 3.1.2 and Section 6.4.2.
Messages that pass signature verification with trusted keys could
still be replays if they contain only static information (e.g.,
Broadcast Endorsements (Section 4.2), [F3411] Basic ID or [F3411]
Operator ID) ID), or information that cannot be readily validated (e.g.,
[F3411] Self-ID). Replay of Link messages is harmless (unless sent
so frequently as to cause RF data link congestion) and indeed can
increase the likelihood of an Observer device collecting an entire
trust chain in a short time window. Replay of other messages
([F3411] Basic ID, [F3411] Operator ID, or [F3411] Self-ID) remains a
vulnerability, unless they are combined with messages containing
nonce-like data ([F3411] Location or [F3411] System) in a Wrapper or
Manifest. For specification of this last requirement, see
Section 4.4.2.
9.2. Wrapper vs Manifest
Implementations have a choice on of using Wrapper (Section 4.3),
Manifest (Section 4.4), or a combination to satisfy the 4th fourth
requirement in Section 6.3.
Wrapper is an attached signature of the full content of one or more
[F3411] messages, providing strong authentication. However, the size
limitation means it can not cannot support such signatures over other
Authentication Messages, thus Messages; thus, it can not cannot provide a direct binding to
any part of the trust chain (Section (Sections 3.1.2 and Section 6.4.2).
Manifest explicitly provides the binding of the last link in the
trust chain (with the inclusion of the hash of the Link containing
BE: HDA, UA). The use of hashes and their length also allows for a
larger number (11 vs 4) number of any [F3411] messages to be authenticated,
making it more efficient compared to the Wrapper. However, the
detached signature requires additional Observer overhead in storing
and comparing hashes of received messages (some that of which may not be
received) of with those in a Manifest.
Appendix B contains a breakdown of frame counts and an example of a
schedule using both Manifest and Wrapper. Typical operation may see
(as an example) 2x Basic ID, 2x Location, 2x System, 1x Operator ID
and 1x Self ID broadcast per second to comply with jurisdiction
mandates. Each of these messages are is a single frame in size. A Link
message is 8 frames long (including FEC). This is a base frame count
of *16 frames*.
When Wrapper is used, up to 4 four of the previous messages (except the
Link) can be authenticated. For this comparison, we will sign all
the messages we can in two Wrappers. This results in _20 frames_
(with FEC). Due to not being able to fit, size constraints, the Link message is left
unauthenticated. The total frame count using Wrappers is *36 frames*
(wrapper frame count + base frame count).
When Manifest is used, up to 10 previous messages can be
authenticated. For this example example, all messages (8) are hashed
(including the Link) resulting in a single Manifest that is _9
frames_ (with FEC). The total frame count using Manifest is *25
frames* (manifest frame count + base frame count).
9.3. VNA Timestamp Offsets for DRIP Authentication Formats
Note the discussion of VNA Timestamp offsets here is in the context
of the DRIP Wrapper (Section 4.3), DRIP Manifest (Section 4.4), and
DRIP Frame (Section 4.5). For DRIP Link (Section 4.2) 4.2), these offsets
are set by the DIME and have their own set of considerations in
[drip-registries].
[DRIP-REG].
The offset of the VNA Timestamp by UA is one that needs careful
consideration for any implementation. The offset should be shorter
than any given flight duration (typically less than an hour) but be
long enough to be received and processed by Observers (larger than a
few seconds). It is recommended that 3-5 minutes should be
sufficient to serve this purpose in any scenario, but it is not
limited by design.
9.4. DNS Security in DRIP
As stated in Section 3.1 specification of particular DNS security
options, transports, etc. is outside the scope of this document.
[drip-registries]
[DRIP-REG] is the main specification for DNS operations in DRIP and
as such will specify DRIP usage of best common practices for security
(such as [RFC9364]).
10. Acknowledgments
* Ryan Quigley, James Mussi Mussi, and Joseph Stanton of AX Enterprize,
LLC for early prototyping to find holes in the draft specifications earlier drafts of this
specification
* Carsten Bormann for the simple approach of using bit-column-wise
parity for erasure (dropped frame) FEC
* Soren Friis for pointing out that Wi-Fi implementations would not
always give access to the MAC Address, as was originally used in
calculation of the hashes for DRIP Manifest. Also, for confirming
that Message Packs (0xF) can only carry up to 9 ASTM frames worth
of data (9 Authentication pages)
* Gabriel Cox (chair of the working group that produced [F3411]) in for
reviewing the specification for the SAM Type request as the ASTM
Designated Expert
* Mohamed Boucadair (Document Shepherd) for his many patches and
comments
* Eric Vyncke (DRIP AD) for his guidance through regarding the documents document's
path to publication
* Thanks to the following reviewers:
- Rick Salz (secdir)
- Matt Joras (genart)
- Di Ma (dnsdir)
- Gorry Fairhurst (tsvart)
- Carlos Bernardos (intdir)
- Behcet Sarikaya (iotdir)
- Martin Duke (IESG)
- Roman Danyliw (IESG)
- Murray Kucherawy (IESG)
- Erik Kline (IESG)
- Warren Kumari (IESG)
- Paul Wouters (IESG)
11. References
11.1. Normative References
[F3411] ASTM International, "Standard Specification for Remote ID
and Tracking", ASTM F3411-22A, DOI 10.1520/F3411-22A, July
2022, <https://www.astm.org/f3411-22a.html>.
[NIST.SP.800-185]
Kelsey, J., Change, Chang, S., Perlner, R., and NIST, R. Perlner, "SHA-3
derived functions: Derived
Functions: cSHAKE, KMAC, TupleHash and ParallelHash", NIST
Special Publications
(General) Publication 800-185, DOI 10.6028/NIST.SP.800-185,
December 2016,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-185.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC9153] Card, S., Ed., Wiethuechter, A., Moskowitz, R., and A.
Gurtov, "Drone Remote Identification Protocol (DRIP)
Requirements and Terminology", RFC 9153,
DOI 10.17487/RFC9153, February 2022,
<https://www.rfc-editor.org/info/rfc9153>.
[RFC9374] Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
"DRIP Entity Tag (DET) for Unmanned Aircraft System Remote
ID (UAS RID)", RFC 9374, DOI 10.17487/RFC9374, March 2023,
<https://www.rfc-editor.org/info/rfc9374>.
[RFC9434] Card, S., Wiethuechter, A., Moskowitz, R., Zhao, S., Ed.,
and A. Gurtov, "Drone Remote Identification Protocol
(DRIP) Architecture", RFC 9434, DOI 10.17487/RFC9434, July
2023, <https://www.rfc-editor.org/info/rfc9434>.
11.2. Informative References
[ASTM-Remote-ID]
"ICAO Remote
International Civil Aviation Organization (ICAO), "Remote
ID Number Registration", December 2023,
<https://www.icao.int/airnavigation/IATF/Pages/ASTM-
Remote-ID.aspx>.
[drip-registries]
[DRIP-REG] Wiethuechter, A. and J. Reid, "DRIP Entity Tag (DET)
Identity Management Architecture", Work in Progress,
Internet-Draft, draft-ietf-drip-registries-14, 4 December
2023, draft-ietf-drip-registries-15, 1 April
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
drip-registries-14>.
drip-registries-15>.
[FAA-14CFR]
Federal Aviation Administration (FAA), "Remote
Identification of Unmanned Aircraft", January 2021,
<https://www.govinfo.gov/content/pkg/FR-2021-01-15/
pdf/2020-28948.pdf>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC9364] Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237,
RFC 9364, DOI 10.17487/RFC9364, February 2023,
<https://www.rfc-editor.org/info/rfc9364>.
Appendix A. Authentication States
ASTM Authentication has only three states: None, Invalid, and Valid.
This is because, under ASTM, the authentication is done by an
external service hosted somewhere on the Internet so it is assumed an
authoritative response will always be returned. This classification
becomes more complex in DRIP with the support of "offline" scenarios
where a an Observer does not have Internet connectivity. With the use
of asymmetric cryptography cryptography, this means that the public key (PK) must
somehow be obtained. [drip-registries] gets [DRIP-REG] provides more into detail on how these
keys are stored on the DNS and one use of how DRIP Authentication messages is can
be used to send PK's over Broadcast RID.
There are a few keys of interest: the PK of the UA and the PK's PKs of
relevant DIMEs. This document describes how to send the PK of the UA
over the Broadcast RID messages. The key keys of DIMEs are sent over
Broadcast RID using the same mechanisms (see Section Sections 4.2 and
Section 6.3)
but MAY be sent at a far lower rate due to potential operational
constraints (such as saturation of limited bandwidth). As such,
there are scenarios where part of the key-chain may be unavailable at
the moment a full Authentication Message is received and processed.
The intent of this informative appendix is to give recommend a recommended way to
classify these various states and convey it to the user through
colors and state names/text. These states can apply to either a
single authentication message, a DET (and its associated public key),
and/or a sender.
The table below lays out the recommended colors to associate with
state and a brief description of each.
+==============+========+=================================+
+==============+========+===================================+
| State | Color | Details |
+==============+========+=================================+
+==============+========+===================================+
| None | Black | No Authentication being received |
| | | received (as yet) |
+--------------+--------+---------------------------------+
+--------------+--------+-----------------------------------+
| Partial | Gray | Authentication being received but |
| | | but missing pages |
+--------------+--------+---------------------------------+
+--------------+--------+-----------------------------------+
| Unsupported | Brown | Authentication Type/SAM Type / SAM Type of |
| | | received message not supported |
+--------------+--------+---------------------------------+
+--------------+--------+-----------------------------------+
| Unverifiable | Yellow | Data needed for signature |
| | | verification is missing |
+--------------+--------+---------------------------------+
+--------------+--------+-----------------------------------+
| Verified | Green | Valid signature verification and |
| | | and content validation |
+--------------+--------+---------------------------------+
+--------------+--------+-----------------------------------+
| Trusted | Blue | evidence Evidence of Verified and DIME is |
| | | is marked as only registering DETs |
| | | DETs for trusted entities |
+--------------+--------+---------------------------------+
+--------------+--------+-----------------------------------+
| Unverified | Red | Invalid signature verification or |
| | | or content validation |
+--------------+--------+---------------------------------+
+--------------+--------+-----------------------------------+
| Questionable | Orange | evidence Evidence of both Verified & both"Verified and |
| | | Unverified for the same claimed |
| | | sender |
+--------------+--------+---------------------------------+
+--------------+--------+-----------------------------------+
| Conflicting | Purple | evidence Evidence of both Trusted & and |
| | | Unverified for the same claimed |
| | | sender |
+--------------+--------+---------------------------------+
+--------------+--------+-----------------------------------+
Table 4: Authentication State Names, Colors & Colors, and Descriptions
A.1. None: Black
The default state where no authentication information has yet to be been
received.
A.2. Partial: Gray
A pending state where authentication pages are being received received, but a
full authentication message has yet to be compiled.
A.3. Unsupported: Brown
A state wherein authentication data is being or has been received, received but
cannot be used, as the Authentication Type or SAM Type is not
supported by the Observer.
A.4. Unverifiable: Yellow
A pending state where a full authentication message has been received
but other information, such as public keys to verify signatures, is
missing.
A.5. Verified: Green
A state where all authentication messages that have been received, received
from that claimed sender up to that point from that claimed sender, pass signature verification
and the requirement of Section 6.4.2 has been met.
A.6. Trusted: Blue
A state where all authentication messages that have been received, up
to that point, received
from that claimed sender, sender up to that point have passed signature
verification, the requirement of Section 6.4.2 has been met, and the
public key of the sending UA is has been marked as trusted.
The sending UA key will have been marked as trusted if the relevant
DIMEs only register DETs (of subordinate DIMEs, UAS operators, and
UA) that have been vetted as per their published registration
policies, and those DIMEs have been marked, by the owner (individual
or organizational) of the Observer, as per that owner's policy, as
trusted to register DETs only for trusted parties.
A.7. Questionable: Orange
A state where there is a mix of authentication messages received that
are Verified (Appendix A.5) and Unverified (Appendix A.8).
Transition to this state is
State transitions from Verified to Questionable if a subsequent
message fails verification verification, so it would have otherwise been marked Unverified, or
Unverified. State transitions from Unverified to Questionable if a
subsequent message passes verification or
validation validation, so it would
otherwise have been marked Verified, or Verified. It may transition from either
of those state states upon mixed results on the requirement of
Section 6.4.2.
A.8. Unverified: Red
A state where all authentication messages that have been received, up
to that point, received
from that claimed sender, sender up to that point failed signature
verification or the requirement of Section 6.4.2.
A.9. Conflicting: Purple
A state where there is a mix of authentication messages received that
are Trusted (Appendix A.6) and Unverified (Appendix A.8) and the
public key of the aircraft is marked as trusted.
Transition to this state is
State transitions from Trusted to Conflicting if a subsequent message
fails verification verification, so it would have otherwise been marked Unverified, or
Unverified. State transitions from Unverified to Conflicting if a
subsequent message passes verification or validation and policy checks
checks, so it would otherwise have been marked
Trusted, or Trusted. It may
transition from either of those state states upon mixed results on the
requirement of Section 6.4.2.
Appendix B. Operational Recommendation Analysis
The recommendations found in Section 6.4 may seem heavy handed heavy-handed and
specific. This informative appendix lays out the math and
assumptions made to come to the that resulted in those recommendations listed there as well
as and provides
an example.
In many jurisdictions, the required ASTM Messages to be transmitted
every second are: Basic ID (0x1), Location (0x2), and System (0x4).
Typical implementations will most likely send at a higher rate (2x
sets per cycle) resulting in 6 frames sent per cycle. Transmitting
this set of message messages more than once a second is not discouraged discouraged, but
awareness is needed to avoid congesting the RF spectrum, causing
further issues.
Informational Note: In Europe, the Operator ID Message (0x5) is also
required. In Japan, two Basic ID (0x0), Location (0x1), and
Authentication (0x2) are required. Self ID (0x3) is optional but can
carry Emergency Status information.
B.1. Page Counts vs Frame Counts
There are two formulas to determine the number of Authentication
Pages required, one required. The following formula is for Wrapper:
<CODE BEGINS>
wrapper_struct_size = 89 + (25 * num_astm_messages)
wrapper_page_count = ceiling((wrapper_struct_size - 17) / 23) + 1
<CODE ENDS>
and one
The following formula is for Manifest:
<CODE BEGINS>
manifest_struct_size = 89 + (8 * (num_astm_hashes + 3))
manifest_page_count = ceiling((manifest_struct_size - 17) / 23) + 1
<CODE ENDS>
A similar formula can be applied to Link Links, as they are of fixed size:
<CODE BEGINS>
link_page_count = ceiling((137 - 17) / 23) + 1 = 7
<CODE ENDS>
Comparing Wrapper and Manifest Authentication Message page counts
against total frame counts counts, we have the following:
+==========+=========+==========+=================+===============+
| ASTM | Wrapper | Manifest | ASTM Messages + | ASTM Messages |
| Messages | (w/FEC) | (w/FEC) | Wrapper (w/FEC) | + Manifest |
| | | | | (w/FEC) |
+==========+=========+==========+=================+===============+
| 0 | 5 (6) | 6 (7) | 5 (6) | 6 (7) |
+----------+---------+----------+-----------------+---------------+
| 1 | 6 (7) | 6 (7) | 7 (8) | 7 (8) |
+----------+---------+----------+-----------------+---------------+
| 2 | 7 (8) | 6 (7) | 9 (10) | 8 (9) |
+----------+---------+----------+-----------------+---------------+
| 3 | 8 (9) | 7 (8) | 11 (12) | 10 (11) |
+----------+---------+----------+-----------------+---------------+
| 4 | 9 (10) | 7 (8) | 13 (14) | 11 (12) |
+----------+---------+----------+-----------------+---------------+
| 5 | N/A | 7 (8) | N/A | 12 (13) |
+----------+---------+----------+-----------------+---------------+
| 6 | N/A | 8 (9) | N/A | 14 (15) |
+----------+---------+----------+-----------------+---------------+
| 7 | N/A | 8 (9) | N/A | 15 (16) |
+----------+---------+----------+-----------------+---------------+
| 8 | N/A | 8 (9) | N/A | 16 (17) |
+----------+---------+----------+-----------------+---------------+
| 9 | N/A | 9 (10) | N/A | 18 (19) |
+----------+---------+----------+-----------------+---------------+
| 10 | N/A | 9 (10) | N/A | 19 (20) |
+----------+---------+----------+-----------------+---------------+
| 11 | N/A | 9 (11) | N/A | 20 (22) |
+----------+---------+----------+-----------------+---------------+
Table 5: Page & and Frame Counts
Link shares the same page counts as Manifest with 5 ASTM Messages.
B.1.1. Special Cases
B.1.1.1. Zero ASTM Messages
Zero ASTM Messages in (see Table 5 5) is where Extended Wrapper
(Section 4.3.2) without FEC is used in Message Packs. With a max maximum
of
9 nine "message slots" in a Message Pack Pack, an Extended Wrapper fills 5
slots,
five slots; thus it can authenticate up to 4 four ASTM Messages co-located co-
located in the same Message Pack.
B.1.1.2. Eleven ASTM Messages
Eleven ASTM Messages in (see Table 5 5) is where a Manifest with FEC
invokes the situation mentioned in Section 5.3.
Eleven is the max maximum number of ASTM Messages Message Hashes that can be
supported resulting in 14 total hashes. This completely fills the
evidence section of the structure making its total size 200 octets.
This fits on exactly 9 Authentication Pages ((201 - 17) / 23 == 8) 8),
so when the ADL is added added, it is placed on the next page (Page 10).
Per rule 1 in Section 5.1 5.1, this means that all of Page 10 is null
padded (expect the ADL octet) and FEC data fills Page 11, resulting
in a
plus two plus-two page count when FEC is applied.
This drives the recommendation is Section 4.4 to only use up to 10
ASTM Message Hashes and Hashes, not 11.
B.2. Full Authentication Example
This example is focused on showing that 100% of ASTM Messages can be
authenticated over Legacy Transports with up to 125% overhead in
Authentication Pages. Extended Transports Transport is not shown as
Authentication with DRIP in that case is covered using Extended
Wrapper (Section 4.3.2). Two ASTM Message Packs are sent in a given
cycle: one containing up to 4 four ASTM Messages and an Extended
Wrapper (authenticating the pack) pack), and one containing a Link message
with a Broadcast Endorsement and up to two other ASTM Messages.
This example transmit scheme covers and meets every known regulatory
case enabling manufacturers to use the same firmware worldwide.
+------------------------------------------------------+
| Frame Slots |
| 00 - 04 | 05 - 07 | 08 - 16 | 17 |
+-------------------+---------------+---------+--------+
| {A|B|C|D},V,S,I,O | {A|B|C|D},V,S | M[0,8] | L/W[0] |
+-------------------+---------------+---------+--------+
| {A|B|C|D},V,S,I,O | {A|B|C|D},V,S | M[0,8] | L/W[1] |
+-------------------+---------------+---------+--------+
| {A|B|C|D},V,S,I,O | {A|B|C|D},V,S | M[0,8] | L/W[2] |
+-------------------+---------------+---------+--------+
| {A|B|C|D},V,S,I,O | {A|B|C|D},V,S | M[0,8] | L/W[3] |
+-------------------+---------------+---------+--------+
| {A|B|C|D},V,S,I,O | {A|B|C|D},V,S | M[0,8] | L/W[4] |
+-------------------+---------------+---------+--------+
| {A|B|C|D},V,S,I,O | {A|B|C|D},V,S | M[0,8] | L/W[5] |
+-------------------+---------------+---------+--------+
| {A|B|C|D},V,S,I,O | {A|B|C|D},V,S | M[0,8] | L/W[6] |
+-------------------+---------------+---------+--------+
| {A|B|C|D},V,S,I,O | {A|B|C|D},V,S | M[0,8] | L/W[7] |
+-------------------+---------------+---------+--------+
A = Basic ID Message (0x0) ID Type 1
B = Basic ID Message (0x0) ID Type 2
C = Basic ID Message (0x0) ID Type 3
D = Basic ID Message (0x0) ID Type 4
V = Location/Vector Message (0x1)
I = Self ID Message (0x3)
S = System Message (0x4)
O = Operator ID Message (0x5)
L[y,z] = DRIP Link Authentication Message (0x2)
W[y,z] = DRIP Wrapper Authentication Message (0x2)
M[y,z] = DRIP Manifest Authentication Message (0x2)
y = Start Page
z = End Page
# = Empty Frame Slot
* = Message in DRIP Manifest Authentication Message
Figure 13: Full Example of a Fully Authenticated Legacy Transport
Transmit Schedule
Example
Every common required message (Basic ID, Location Location, and System) is
sent twice plus along with Operator ID and Self ID in a single second.
The Manifest is over all messages (8) in slots 00 - 04 and 05 - 07.
In two seconds seconds, either a Link or Wrapper are sent. The content and
order of Links and Wrappers runs as follows:
Link: HDA on UA
Link: RAA on HDA
Link: HDA on UA
Link: Apex on RAA
Link: HDA on UA
Link: RAA on HDA
Link: HDA on UA
Wrapper: Location (0x1), System (0x4)
Link: HDA on UA
Link: RAA on HDA
Link: HDA on UA
Link: Apex on RAA
Link: HDA on UA
Link: RAA on HDA
Link: HDA on UA
Wrapper: Location (0x1), System (0x4)
Link: IANA on UAS RID Apex
With perfect receipt of all messages, in 8 seconds all messages (up to that point
then all in future) are authenticated within 8 seconds using the
Manifest. Within 136 seconds seconds, the entire Broadcast Endorsement chain
is received and can be validated; interspersed with 4 four messages
directly signed over via Wrapper.
B.2.1. Raw Example
Assuming the following DET and HI:
2001:3f:fe00:105:a29b:3ff4:2226:c04e
b5fef530d450dedb59ebafa18b00d7f5ed0ac08a81975034297bea2b00041813
The following ASTM Messages are to be sent in a single second:
0240012001003ffe000105a29b3ff42226c04e000000000000
12000000000000000000000000000000000000000060220000
32004578616d706c652053656c662049440000000000000000
420000000000000000000100000000000000000010ea510900
52004578616d706c65204f70657261746f7220494400000000
0240012001003ffe000105a29b3ff42226c04e000000000000
12000000000000000000000000000000000000000060220000
420000000000000000000100000000000000000010ea510900
This is a Link with FEC that would be spread out over 8 seconds:
2250078910ea510904314b8564b17e66662001003ffe000105
2251a29b3ff42226c04eb5fef530d450dedb59ebafa18b00d7
2252f5ed0ac08a81975034297bea2b000418132001003ffe00
22530105b82bf1c99d87273103fc83f6ecd9b91842f205c222
2254dd71d8e165ad18ca91daf9299a73eec850c756a7e9be46
2255f51dddfa0f09db7bfdde14eec07c7a6dd1061c1d5ace94
2256d9ad97940d280000000000000000000000000000000000
2257a03b0f7a6feb0d198167045058cfc49f73129917024d22
This is a Wrapper with FEC that would be spread out over 8 seconds:
2250078b10ea510902e0dd7c6560115e671200000000000000
22510000000000000000000000000060220000420000000000
2252000000000100000000000000000010ea5109002001003f
2253fe000105a29b3ff42226c04ef0ecad581a030ca790152a
22542f08df5762a463e24a742d1c530ec977bbe0d113697e2b
2255b909d6c7557bdaf1227ce86154b030daadda4a6b8474de
22569a62f6c375020826000000000000000000000000000000
2257f5e8eebcb04f8c2197526053e66c010d5d7297ff7c1fe0
This is the Manifest with FEC sent in the same second as the original
messages:
225008b110ea510903e0dd7c6560115e670000000000000000
2251d57594875f8608b4d61dc9224ecf8b842bd4862734ed01
22522ca2e5f2b8a3e61547b81704766ba3eeb651be7eafc928
22538884e3e28a24fd5529bc2bd4862734ed012ca2e5f2b8a3
2254e61547b81704766ba3eeb62001003ffe000105a29b3ff4
22552226c04efb729846e7d110903797066fd96f49a77c5a48
2256c4c3b330be05bc4a958e9641718aaa31aeabad368386a2
22579ed2dce2769120da83edbcdc0858dd1e357755e7860317
2258e7c06a5918ea62a937391cbfe0983539de1b2e688b7c83
Authors' Addresses
Adam Wiethuechter (editor)
AX Enterprize, LLC
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: adam.wiethuechter@axenterprize.com
Stuart Card
AX Enterprize, LLC
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: stu.card@axenterprize.com
Robert Moskowitz
HTT Consulting
Oak Park, MI 48237
United States of America
Email: rgm@labs.htt-consult.com