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DRIP Entity Tag Authentication Formats & Protocols for Broadcast Remote ID
draft-ietf-drip-auth-46

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 9575.
Authors Adam Wiethuechter , Stuart W. Card , Robert Moskowitz
Last updated 2024-02-01 (Latest revision 2024-01-25)
Replaces draft-wiethuechter-drip-auth
RFC stream Internet Engineering Task Force (IETF)
Formats
Reviews
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Associated WG milestones
Sep 2020
Solution space documents adopted by the WG
Oct 2023
Submit DRIP Authentication Formats to the IESG
Document shepherd Mohamed Boucadair
Shepherd write-up Show Last changed 2023-12-14
IESG IESG state Became RFC 9575 (Proposed Standard)
Consensus boilerplate Yes
Telechat date (None)
Has enough positions to pass.
Responsible AD Éric Vyncke
Send notices to mohamed.boucadair@orange.com
IANA IANA review state IANA OK - Actions Needed
draft-ietf-drip-auth-46
DRIP Working Group                                  A. Wiethuechter, Ed.
Internet-Draft                                                   S. Card
Intended status: Standards Track                      AX Enterprize, LLC
Expires: 28 July 2024                                       R. Moskowitz
                                                          HTT Consulting
                                                         25 January 2024

DRIP Entity Tag Authentication Formats & Protocols for Broadcast Remote
                                   ID
                        draft-ietf-drip-auth-46

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
   assessment of trustworthiness of received RID messages and observed
   UAS, even by Observers then 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 detached
   messages were signed by the registered owner of the DRIP Entity Tag
   (DET) claimed.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on 28 July 2024.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents (https://trustee.ietf.org/
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

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 & Procedures  . . . . . . .   5
     3.1.  DRIP Authentication Protocol Description  . . . . . . . .   5
       3.1.1.  UA Signed Evidence  . . . . . . . . . . . . . . . . .   6
       3.1.2.  DIME Endorsements of Subordinate DET  . . . . . . . .   7
       3.1.3.  DIME Hierarchy Endorsements . . . . . . . . . . . . .   7
       3.1.4.  UAS RID Trust . . . . . . . . . . . . . . . . . . . .   7
     3.2.  ASTM Authentication Message Framing . . . . . . . . . . .   7
       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 . . . . . . . . . . . . . . . . .  12
     4.1.  Endorsement Structure for UA Signed Evidence  . . . . . .  12
     4.2.  DRIP Link . . . . . . . . . . . . . . . . . . . . . . . .  14
     4.3.  DRIP Wrapper  . . . . . . . . . . . . . . . . . . . . . .  16
       4.3.1.  Wrapped Count & Sanity Check  . . . . . . . . . . . .  17
       4.3.2.  Wrapper over Extended Transports  . . . . . . . . . .  17
       4.3.3.  Wrapper Limitations . . . . . . . . . . . . . . . . .  19
     4.4.  DRIP Manifest . . . . . . . . . . . . . . . . . . . . . .  19
       4.4.1.  Hash Count & Sanity Check . . . . . . . . . . . . . .  20
       4.4.2.  Manifest Ledger Hashes  . . . . . . . . . . . . . . .  21
       4.4.3.  Hash Algorithms and Operation . . . . . . . . . . . .  21
     4.5.  DRIP Frame  . . . . . . . . . . . . . . . . . . . . . . .  22
   5.  Forward Error Correction  . . . . . . . . . . . . . . . . . .  23
     5.1.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . .  23
     5.2.  Decoding  . . . . . . . . . . . . . . . . . . . . . . . .  24
     5.3.  FEC Limitations . . . . . . . . . . . . . . . . . . . . .  27
   6.  Requirements & Recommendations  . . . . . . . . . . . . . . .  27
     6.1.  Legacy Transports . . . . . . . . . . . . . . . . . . . .  27
     6.2.  Extended Transports . . . . . . . . . . . . . . . . . . .  27
     6.3.  Authentication  . . . . . . . . . . . . . . . . . . . . .  27

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     6.4.  Operational . . . . . . . . . . . . . . . . . . . . . . .  28
       6.4.1.  DRIP Wrapper  . . . . . . . . . . . . . . . . . . . .  29
       6.4.2.  UAS RID Trust Assessment  . . . . . . . . . . . . . .  29
   7.  Summary of Addressed DRIP Requirements  . . . . . . . . . . .  29
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  30
     8.1.  IANA DRIP Registry  . . . . . . . . . . . . . . . . . . .  30
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  31
     9.1.  Replay Attacks  . . . . . . . . . . . . . . . . . . . . .  31
     9.2.  VNA Timestamp Offsets for DRIP Authentication Formats . .  32
   10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  32
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  33
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  33
     11.2.  Informative References . . . . . . . . . . . . . . . . .  33
   Appendix A.  Authentication States  . . . . . . . . . . . . . . .  34
     A.1.  None: Black . . . . . . . . . . . . . . . . . . . . . . .  36
     A.2.  Partial: Gray . . . . . . . . . . . . . . . . . . . . . .  36
     A.3.  Unsupported: Brown  . . . . . . . . . . . . . . . . . . .  36
     A.4.  Unverifiable: Yellow  . . . . . . . . . . . . . . . . . .  36
     A.5.  Verified: Green . . . . . . . . . . . . . . . . . . . . .  36
     A.6.  Trusted: Blue . . . . . . . . . . . . . . . . . . . . . .  36
     A.7.  Questionable: Orange  . . . . . . . . . . . . . . . . . .  36
     A.8.  Unverified: Red . . . . . . . . . . . . . . . . . . . . .  37
     A.9.  Conflicting: Purple . . . . . . . . . . . . . . . . . . .  37
   Appendix B.  Operational Recommendation Analysis  . . . . . . . .  37
     B.1.  Page Counts vs Frame Counts . . . . . . . . . . . . . . .  38
       B.1.1.  Special Cases . . . . . . . . . . . . . . . . . . . .  39
     B.2.  Full Authentication Example . . . . . . . . . . . . . . .  40
       B.2.1.  Raw Example . . . . . . . . . . . . . . . . . . . . .  42
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  43

1.  Introduction

   The initial regulations (e.g., [FAA-14CFR]) and standards (e.g.,
   [F3411]) for Unmanned Aircraft (UA) Systems (UAS) Remote
   Identification 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).  DRIP's goal is to specify how RID can be
   made trustworthy and available in both Internet and local-only
   connected scenarios, especially in emergency situations.

   UAS often operate in a volatile environment.  Small UA offer 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
   devices even if 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.

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   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]).

   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, 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, 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 [F3411] further support the
   important use case of Observers who may be offline at the time of
   observation.

   A summary of DRIP requirements [RFC9153] addressed herein is provided
   in Section 7.

      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].  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.

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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 Neighbor Awareness Networking (NAN)), or IEEE 802.11 Beacons
      with 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 immutable list of items being transported (in this specific
      case over wireless communication).

3.  UAS RID Authentication Background & 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 standard
   Authentication Types using Type 5 Specific Authentication Method
   (SAM), several of which DRIP defines herein.

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   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 resulting in the work
   reflected in this document.

   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 in line
   with best security practices.  Many participating nodes will have
   limited local processing power and/or poor, low bandwidth QoS paths.
   Appropriate and feasible security techniques will be highly UAS and
   Observer situation dependent.  Therefore specification of particular
   DNS security options, transports, etc. is outside the scope of this
   document.

3.1.1.  UA Signed Evidence

   When an Observer receives a DRIP-based Authentication Message
   (Section 4.3, Section 4.4, or Section 4.5) containing UA-signed
   Evidence (in an Endorsement structure Section 4.1) it MUST validate
   the signature using the Host Identity (HI) corresponding to the UA's
   DET [RFC9374].

   An Observer SHOULD query DNS for the UA's HI.  If not available it
   may have been revoked.  Note that accurate revocation status is a
   DIME inquiry; DNS non-response is a hint that a DET is expired or
   revoked.  It MAY be retrieved from a local cache, if present.  The
   local cache is typically populated by DNS lookups and/or by received
   Broadcast Endorsements (Section 3.1.2).

   Once the Observer has the registered UA's DET and HI, all subsequent
   y received (or previously cached) DRIP-based Authentication Messages
   using the UA DET can be validated.  Signed content, tied to the DET,
   can now be trusted to have been signed by the holder of the private
   key corresponding to the DET.

   Whether the content is true is a separate question which DRIP cannot
   address, but sanity checks (Section 6) are possible and encouraged.

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3.1.2.  DIME Endorsements of Subordinate DET

   When an Observer receives a DRIP Link Authentication Message
   (Section 4.2) containing an Endorsement by the DIME of a child DET
   registration, it MUST validate the signature using the HI
   corresponding to the DIME's DET.

   An Observer SHOULD query DNS for the DIME's HI (e.g., Section 5 of
   [drip-registries]), when able.  It MAY be cached from a prior DNS
   lookup or be stored in a distinct local store.

3.1.3.  DIME Hierarchy Endorsements

   An Observer can receive a series of DRIP Link Authentication Messages
   (Section 4.2), each one pertaining to a DIME's registration in the
   DIME above it in the hierarchy.  Similar to Section 3.1.2, each link
   in this chain MUST be validated.

3.1.4.  UAS RID Trust

   Section 3.1.1, Section 3.1.2, and Section 3.1.3 complete the trust
   chain for the claimed DET and associated HI (public key), but the
   chain cannot yet be trusted as having any relevance to the observed
   UA because replay attacks are trivial.  At this point, the key
   nominally possessed by the UA is trusted but the UA has not yet been
   proven to possess that 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.  This can be a DRIP Wrapper or Manifest (Section 4.3,
   Section 4.4) containing an ASTM Message that fulfills the
   requirements.  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).

3.2.  ASTM Authentication Message Framing

   The Authentication Message (Message Type 0x2) is unique in the ASTM
   [F3411] Broadcast 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 are 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.

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   The following sub-sections 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
   Authentication Method (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 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.

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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 Authentication Payload, spanning 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.

   Additional Data: (255 octets max)

      Data that follows the Authentication Data / Signature but is not
      considered part of the Authentication Data thus is not covered by
      a signature.  When Additional Data is being sent, a single

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      unsigned octet (Additional Data Length (ADL)) directly follows the
      Authentication Data / Signature and has the length, in octets, of
      the following Additional Data.  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 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

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      been selected by ASTM as the registrar to manage allocations of
      these code points.  The list of which can be found 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 using Bluetooth (4.x and 5.x),
   Wi-Fi NAN, or IEEE 802.11 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
   information defined in [F3411] MUST be transmitted over all the
   physical layer interfaces performing the function of RID.

   Bluetooth 4.x presents a payload size challenge in that it can only
   transmit 25 octets of payload per frame while other transports can
   support larger payloads per frame.  However, the [F3411] messaging
   framing dictated by Bluetooth 4.x constraints is inherited by [F3411]
   over other media.

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 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.

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3.2.4.3.  Timestamps

   In ASTM [F3411] timestamps are a Unix-style timestamp with an epoch
   of 2019-01-01 00:00:00 UTC.  For DRIP this format is adopted for
   Authentication to keep a common time format in Broadcast payloads.

   Under DRIP there are two timestamps defined Valid Not Before (VNB)
   and Valid Not After (VNA).

   Valid Not Before (VNB) Timestamp: (4 octets)

      Timestamp denoting recommended time to start trusting data in.
      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 recommended time 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 identifying an acceptable offset
      should be used taking 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 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 and Manifest are shown as part of an
   operational schedule in Appendix B.2.1.

4.1.  Endorsement Structure for UA Signed Evidence

   The Endorsement Structure for UA Signed Evidence (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.

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   This structure is used by the DRIP Wrapper (Section 4.3), Manifest
   Section 4.4, and Frame (Section 4.5).  DRIP Link (Section 4.2) MUST
   NOT use 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)

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      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.

   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] or by extracting it from a Broadcast Endorsement
   (see Section 4.2 and Section 6.3).

4.2.  DRIP Link

   This SAM Type is used to transmit Broadcast Endorsements.  For
   example, the Broadcast Endorsement: HDA, UA is sent (see Section 6.3)
   as a DRIP Link message.

      Note: For the remainder of this document Broadcast Endorsement:
      Parent, Child will be abbreviated to BE: Parent, Child.

   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
   receiver'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.

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      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)

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      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.

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 Endorsement Structure for UA Signed
   Evidence (Section 4.1) is populated with up to four ASTM [F3411]
   Messages 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).

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4.3.1.  Wrapped Count & Sanity Check

   When decoding a DRIP Wrapper on a receiver, a calculation of the
   number of messages wrapped and a sanity check 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) {
     // DRIP Wrapper over extended transport
   }
   else if (wrappedCount > 4) {
     return DECODE_FAILURE;
   } else {
     // standard DRIP Wrapper
   }
   <CODE ENDS>

   Figure 6: Pseudo-code for Wrapper sanity check and number of messages
                                calculation

4.3.2.  Wrapper over Extended Transports

   When using Extended Transports an optimization can be made to DRIP
   Wrapper to sign over co-located data in an ASTM Message Pack (Message
   Type 0xF).

   To perform this optimization the Endorsement Structure for UA Signed
   Evidence is filled with the ASTM Messages to be in the ASTM Message
   Pack, the signature is generated, then the evidence field is cleared
   leaving the encoded form shown in Figure 7.

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      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 Authentication Message found
   in the same Message Pack) in ASTM Message Type order and set the
   evidence section of the Endorsement Structure for UA Signed Evidence
   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 Wrapper provides is the same format but over
   both Extended and Legacy Transports allowing the transports to be
   similar.  Message Set Signature also implies using the ASTM validator
   system architecture which depends on Internet connectivity for
   verification which the receiver may not have at the time of receipt
   of an Authentication Message.  This is something the Wrapper, and all
   DRIP Authentication Formats, avoid when the UA key is obtained via a
   DRIP Link Authentication Message.

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4.3.3.  Wrapper Limitations

   The primary limitation of the Wrapper is the bounding of up to 4 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 a receiver 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 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 them.  This is a
   way to evade the limitation of a maximum of 4 messages in the Wrapper
   (Section 4.3.3) and greatly reduce overhead.

   An Observer who has been listening for any length of time MUST hash
   received messages and cross-check them against the Manifest hashes.

   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
   Appendix B).

   The evidence section of the Endorsement Structure for UA Signed
   Evidence (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 these hashes MUST be concatenated to form a
   contiguous octet sequence in the evidence section.  It is RECOMMENDED
   the max number of ASTM Message Hashes be used is 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.

   A receiver SHOULD 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, see Section 6.4 and
   Appendix B.

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      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 & Sanity Check

   When decoding a DRIP Manifest on a receiver, a calculation of the
   number of hashes and a sanity check can be performed by using the
   number of octets (defined as manifestLength) between the UA DET and
   the VNB Timestamp by UA such as shown in Figure 9.

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   <CODE BEGINS>
   if (manifestLength MOD 8) != 0 {
     return DECODE_FAILURE
   }
   hashCount = (manifestLength / 8) - 3;
   <CODE ENDS>

    Figure 9: Pseudo-code 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 which is the currently filled Manifest.  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).

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.

   DET's using cSHAKE128 [NIST.SP.800-185] compute the hash as follows:

   cSHAKE128(ASTM Message, 64, "", "Remote ID Auth Hash")

   For OGAs other than "5" [RFC9374], use the construct appropriate for
   the associated hash.  For example, for "2" which is ECDSA/SHA-384:

   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 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
   Hashes section.  When all messages are hashed, the Current Manifest
   Hash is computed over the Previous Manifest Hash, Current Manifest
   Hash (null filled) and ASTM Messages Hashes.  This hash value
   replaces the null filled Current Manifest Hash and becomes the
   Previous Manifest Hash for the next Manifest.

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4.4.3.1.  Legacy Transport Hashing

   Under this transport DRIP hashes the full ASTM Message being sent
   over the Bluetooth Advertising frame.  This is the 25-octet object
   start with the Message Type and Protocol Version octet along with the
   24 octets of message data.  The hash MUST NOT included the Message
   Counter octet.

   For paged ASTM Messages (currently only Authentication Messages) all
   the pages are concatenated together in Page Number order and hashed
   as one object.

4.4.3.2.  Extended Transport Hashing

   Under this transport DRIP hashes the full ASTM Message Pack (Message
   Type 0xF) regardless of its content.  The hash MUST NOT included 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 evidence formats.

   The content of Frame Evidence Data is not defined in this document.
   Other specifications MUST define the contents and register for a
   Frame Type.

      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 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.

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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 FEC, so with DRIP Authentication the following application
   level scheme is used 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 single erased page in an Authentication Message.  If
   more than a single page is 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 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, up to a
   maximum of 16-pages.

5.1.  Encoding

   When 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 and
       FEC.

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   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 as there are always 23 octets of FEC data
   and in this example 10 octets of padding 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 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.

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   To determine if FEC has been used, a check of the Last Page Index is
   performed.  In general if the Last Page Index field is one greater
   than that necessary to hold Length octets of Authentication 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 the Last Page Index will have been
   incremented once for initializing the Additional Data Length field
   and once for 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 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 sanity checked by DRIP.  The pseudo-code in Figure 12
   can be used for both checks.

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   <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 for Decode Checks

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5.3.  FEC Limitations

   The worst-case scenario is when the Authentication Data / Signature
   ends perfectly on a page (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 & 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 the US
   FAA RID Rule [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 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
       (satisfying GEN-3); at least once per 5 minutes.  Apex in this
       context is the DET prefix owner

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   2.  MUST: send DRIP Link (Section 4.2) using the BE: RAA, HDA
       (satisfying GEN-3); at least once per 5 minutes

   3.  MUST: send DRIP Link (Section 4.2) using the BE: HDA, UA
       (satisfying ID-5, GEN-1 and GEN-3); at least once per minute

   4.  MUST: send any other DRIP Authentication Format (RECOMMENDED:
       DRIP Manifest (Section 4.4) or DRIP Wrapper (Section 4.3)) where
       the UA is dynamically signing data that is guaranteed to be
       unique, unpredictable and easily cross checked by the receiving
       device (satisfying ID-5, GEN-1 and GEN-2); at least once per 5
       seconds

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 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 DRIP Manifest enabling authentication of those
         ASTM Messages sent

      -  A single page of an 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

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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 receivers.
   For a receiver plotting Location Messages (Message Type 0x2) on a
   map, display 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 3.1.4, the receiver 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) but sanity-checkable data, signed by that
   key, provides trust that some agent with access to that data also
   possesses that key.  If the sanity check 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 SHOULD be rejected as if the
   signature failed to validate.  Acceptable thresholds 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 are addressed in this document:

   ID-5: Non-spoofability

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      Addressed using the DRIP Wrapper (Section 4.3), DRIP Manifest
      (Section 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) 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 SAM Type and DRIP
   Frame Type, under the DRIP registry group
   (https://www.iana.org/assignments/drip/drip.xhtml).

   DRIP SAM Type:  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
      which at the time of publication of this RFC is ICAO.  Additions
      for DRIP will be coordinated by IETF and the ASTM designated
      registrar by circulation of Internet Drafts intended for
      subsequent publication as Standards Track RFCs.  The following
      values have been allocated to the IETF and are defined here:

   +==========+===============+=======================================+
   | SAM Type | Name          | Description                           |
   +==========+===============+=======================================+
   | 0x01     | DRIP Link     | Format to hold Broadcast Endorsements |
   +----------+---------------+---------------------------------------+
   | 0x02     | DRIP Wrapper  | Authenticate full ASTM Messages       |
   +----------+---------------+---------------------------------------+
   | 0x03     | DRIP Manifest | Authenticate hashes of ASTM Messages  |
   +----------+---------------+---------------------------------------+
   | 0x04     | DRIP Frame    | Format for future DRIP authentication |
   +----------+---------------+---------------------------------------+

                         Table 2: DRIP SAM Types

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   DRIP Frame Type:  This 8-bit valued 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, 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     | Reserved: First Come, First Served |
    +-------------+--------------+------------------------------------+
    | 0xF0 - 0xFF | Experimental | 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 one or more designated experts.
   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

   DRIP Link messages are static in nature.  These DRIP Link messages
   can easily be replayed by an attacker who has copied them from
   previous broadcasts.

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   If an attacker (who is smart and spoofs more than just the UAS ID/
   data payloads) willingly replays a DRIP Link message, they have in
   principle actually helped by ensuring the DRIP Link is sent more
   frequently and be received by potential Observers.

   The primary mitigation is that the UA is REQUIRED to send more than
   DRIP Link messages, specifically the Manifest and/or Wrapper messages
   that sign over changing data ASTM Messages (e.g., Location/Vector
   Messages) using the DET private key.  A UA sending these messages
   then actually signing these and other messages using the DET key
   provides the Observer with data that proves real-time signing.  A UA
   that does not either run DRIP themselves or does not have possession
   of the same private key, would be clearly exposed upon signature
   verification.

9.2.  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) these offsets
   are set by the DIME and have their own set of considerations in
   [drip-registries].

   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 is not limited
   by design.

10.  Acknowledgments

   *  Ryan Quigley and James Mussi of AX Enterprize, LLC for early
      prototyping to find holes in the draft specifications.

   *  Soren Friis for pointing out that Wi-Fi implementations would not
      always give access to the MAC Address, 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).

   *  Thanks to the following reviewers:

      -  Rick Salz (secdir)

      -  Matt Joras (genart)

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      -  Di Ma (dnsdir)

      -  Gorry Fairhurst (tsvart)

11.  References

11.1.  Normative References

   [F3411]    "F3411-22a: Standard Specification for Remote ID and
              Tracking", July 2022.

   [NIST.SP.800-185]
              Kelsey, J., Change, S., Perlner, R., and NIST, "SHA-3
              derived functions: cSHAKE, KMAC, TupleHash and
              ParallelHash", NIST Special Publications
              (General) 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

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   [ASTM-Remote-ID]
              "ICAO Remote ID Number Registration", December 2023,
              <https://www.icao.int/airnavigation/IATF/Pages/ASTM-
              Remote-ID.aspx>.

   [drip-registries]
              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, <https://datatracker.ietf.org/doc/html/draft-ietf-
              drip-registries-14>.

   [FAA-14CFR]
              "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>.

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 receiver does not have Internet connectivity.  With the use
   of asymmetric cryptography this means that the public key (PK) must
   somehow be obtained. [drip-registries] gets more into detail how
   these keys are stored on DNS and one use of DRIP Authentication
   messages is to send PK's over Broadcast RID.

   There are a few keys of interest: the PK of the UA and the PK's of
   relevant DIMEs.  This document describes how to send the PK of the UA
   over the Broadcast RID messages.  The key of DIMEs are sent over
   Broadcast RID using the same mechanisms (see Section 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.

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   The intent of this informative appendix is to give 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 (as yet)               |
        +--------------+--------+---------------------------------+
        | Partial      | Gray   | Authentication being received   |
        |              |        | but missing pages               |
        +--------------+--------+---------------------------------+
        | Unsupported  | Brown  | Authentication Type/SAM Type of |
        |              |        | received message not supported  |
        +--------------+--------+---------------------------------+
        | Unverifiable | Yellow | Data needed for signature       |
        |              |        | verification is missing         |
        +--------------+--------+---------------------------------+
        | Verified     | Green  | Valid signature verification    |
        |              |        | and content validation          |
        +--------------+--------+---------------------------------+
        | Trusted      | Blue   | evidence of Verified and DIME   |
        |              |        | is marked as only registering   |
        |              |        | DETs for trusted entities       |
        +--------------+--------+---------------------------------+
        | Unverified   | Red    | Invalid signature verification  |
        |              |        | or content validation           |
        +--------------+--------+---------------------------------+
        | Questionable | Orange | evidence of both Verified &     |
        |              |        | Unverified for the same claimed |
        |              |        | sender                          |
        +--------------+--------+---------------------------------+
        | Conflicting  | Purple | evidence of both Trusted &      |
        |              |        | Unverified for the same claimed |
        |              |        | sender                          |
        +--------------+--------+---------------------------------+

         Table 4: Authentication State Names, Colors & Descriptions

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A.1.  None: Black

   The default state where no authentication information has yet to be
   received.

A.2.  Partial: Gray

   A pending state where authentication pages are being 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,
   but cannot be used, as the Authentication Type or SAM Type is not
   supported by the receiver.

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, 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, from that claimed sender, have passed signature
   verification, the requirement of Section 6.4.2 has been met, and the
   public key of the sending UA is 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 receiver, 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).

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   Transition to this state is from Verified if a subsequent message
   fails verification so would have otherwise been marked Unverified, or
   from Unverified if a subsequent message passes verification or
   validation so would otherwise have been marked Verified, or from
   either of those state 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, from that claimed sender, 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 from Trusted if a subsequent message
   fails verification so would have otherwise been marked Unverified, or
   from Unverified if a subsequent message passes verification or
   validation and policy checks so would otherwise have been marked
   Trusted, or from either of those state 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 and
   specific.  This informative appendix lays out the math and
   assumptions made to come to the recommendations listed there as well
   as 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 more than once a second is not 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.

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B.1.  Page Counts vs Frame Counts

   There are two formulas to determine the number of Authentication
   Pages required, one 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 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 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 we have the following:

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    +==========+=========+==========+=================+===============+
    | 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 & 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 Table 5 is where Extended Wrapper
   (Section 4.3.2) without FEC is used in Message Packs.  With a max of
   9 "message slots" in a Message Pack an Extended Wrapper fills 5
   slots, thus can authenticate up to 4 ASTM Messages co-located in the
   same Message Pack.

B.1.1.2.  Eleven ASTM Messages

   Eleven ASTM Messages in Table 5 is where a Manifest with FEC invokes
   the situation mentioned in Section 5.3.

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   Eleven is the max number of ASTM Messages 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) so
   when the ADL is added it is placed on the next page (Page 10).  Per
   rule 1 in Section 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 page count when FEC is applied.

   This drives the recommendation is Section 4.4 to only use up to 10
   ASTM Message Hashes and 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 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 ASTM Messages and an Extended Wrapper
   (authenticating the 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.

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         +------------------------------------------------------+
         |                      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 Authenticated Legacy Transport Transmit Schedule
                                  Example

   Every common required message (Basic ID, Location and System) is sent
   twice plus 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 either a Link or Wrapper are sent.  The content and
   order of Links and Wrappers runs as follows:

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   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 using the
   Manifest.  Within 136 seconds the entire Broadcast Endorsement chain
   is received and can be validated; interspersed with 4 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 to be sent in a single second:

   0240012001003ffe000105a29b3ff42226c04e000000000000
   12000000000000000000000000000000000000000060220000
   32004578616d706c652053656c662049440000000000000000
   420000000000000000000100000000000000000010ea510900
   52004578616d706c65204f70657261746f7220494400000000
   0240012001003ffe000105a29b3ff42226c04e000000000000
   12000000000000000000000000000000000000000060220000
   420000000000000000000100000000000000000010ea510900

   This is Link with FEC that would be spread out over 8 seconds:

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   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

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   Email: stu.card@axenterprize.com

   Robert Moskowitz
   HTT Consulting
   Oak Park, MI 48237
   United States of America
   Email: rgm@labs.htt-consult.com

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