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DRIP Entity Tag Authentication Formats & Protocols for Broadcast Remote ID
draft-ietf-drip-auth-22

Document Type Active Internet-Draft (drip WG)
Authors Adam Wiethuechter , Stuart W. Card , Robert Moskowitz
Last updated 2022-09-29
Replaces draft-wiethuechter-drip-auth
Stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Formats
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OPSDIR Early Review Incomplete, due 2022-09-22
GENART Early Review Incomplete, due 2022-09-22
Stream WG state In WG Last Call
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Sep 2020
Solution space documents adopted by the WG
Jun 2022
Submit DRIP Authentication Formats to the IESG
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draft-ietf-drip-auth-22
DRIP Working Group                              A. Wiethuechter (Editor)
Internet-Draft                                                   S. Card
Intended status: Standards Track                      AX Enterprize, LLC
Expires: 2 April 2023                                       R. Moskowitz
                                                          HTT Consulting
                                                       29 September 2022

DRIP Entity Tag Authentication Formats & Protocols for Broadcast Remote
                                   ID
                        draft-ietf-drip-auth-22

Abstract

   This document describes how to add trust into the Broadcast Remote ID
   (RID) specification discussed in the DRIP Architecture; first trust
   in the RID ownership and second in the source of the RID messages.
   It defines message types and associated formats (sent within the
   Authentication Message) that can be used to authenticate past
   messages sent by an unmanned aircraft (UA) and provide proof of UA
   trustworthiness even in the absence of Internet connectivity at the
   receiving node.

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 2 April 2023.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   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.

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   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
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Required Terminology  . . . . . . . . . . . . . . . . . .   4
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Reasoning for IETF DRIP Authentication  . . . . . . . . .   6
       3.1.1.  UA Signed Evidence  . . . . . . . . . . . . . . . . .   6
       3.1.2.  DIME Endorsement of UA DET/HI . . . . . . . . . . . .   7
       3.1.3.  DIME Hierarchy Endorsements . . . . . . . . . . . . .   7
       3.1.4.  UAS RID Trust . . . . . . . . . . . . . . . . . . . .   7
     3.2.  ASTM Authentication Message . . . . . . . . . . . . . . .   7
       3.2.1.  Authentication Page . . . . . . . . . . . . . . . . .   7
       3.2.2.  Authentication Payload Field  . . . . . . . . . . . .   8
       3.2.3.  ASTM Broadcast RID Constraints  . . . . . . . . . . .   9
   4.  DRIP Authentication Formats . . . . . . . . . . . . . . . . .  10
     4.1.  DRIP Authentication Field Definitions . . . . . . . . . .  11
       4.1.1.  SAM Data Format . . . . . . . . . . . . . . . . . . .  12
       4.1.2.  UA Signed Evidence  . . . . . . . . . . . . . . . . .  13
     4.2.  DRIP Link . . . . . . . . . . . . . . . . . . . . . . . .  15
     4.3.  DRIP Wrapper  . . . . . . . . . . . . . . . . . . . . . .  16
       4.3.1.  Message Count . . . . . . . . . . . . . . . . . . . .  16
       4.3.2.  Wrapper over Extended Transports  . . . . . . . . . .  16
       4.3.3.  Wrapper Limitations . . . . . . . . . . . . . . . . .  18
     4.4.  DRIP Manifest . . . . . . . . . . . . . . . . . . . . . .  18
       4.4.1.  Hash Count  . . . . . . . . . . . . . . . . . . . . .  19
       4.4.2.  Pseudo-Blockchain Hashes  . . . . . . . . . . . . . .  19
       4.4.3.  Hash Algorithms and Operation . . . . . . . . . . . .  19
     4.5.  DRIP Frame  . . . . . . . . . . . . . . . . . . . . . . .  20
       4.5.1.  Frame Type  . . . . . . . . . . . . . . . . . . . . .  21
   5.  Forward Error Correction  . . . . . . . . . . . . . . . . . .  21
     5.1.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . .  21
     5.2.  Decoding  . . . . . . . . . . . . . . . . . . . . . . . .  23
     5.3.  FEC Limitations . . . . . . . . . . . . . . . . . . . . .  26
   6.  Requirements & Recommendations  . . . . . . . . . . . . . . .  26
     6.1.  Legacy Transports . . . . . . . . . . . . . . . . . . . .  26
     6.2.  Extended Transports . . . . . . . . . . . . . . . . . . .  26
     6.3.  Authentication  . . . . . . . . . . . . . . . . . . . . .  26
     6.4.  Operational . . . . . . . . . . . . . . . . . . . . . . .  27
       6.4.1.  DRIP Wrapper  . . . . . . . . . . . . . . . . . . . .  28
       6.4.2.  UAS RID Trust Assessment  . . . . . . . . . . . . . .  28

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   7.  Summary of Addressed DRIP Requirements  . . . . . . . . . . .  29
   8.  ICAO Considerations . . . . . . . . . . . . . . . . . . . . .  29
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  29
     9.1.  IANA DRIP Registry  . . . . . . . . . . . . . . . . . . .  29
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  30
     10.1.  Replay Attacks . . . . . . . . . . . . . . . . . . . . .  30
     10.2.  VNA Timestamp Offsets for DRIP Authentication Formats  .  30
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  31
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  31
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  31
     12.2.  Informative References . . . . . . . . . . . . . . . . .  32
   Appendix A.  Authentication State Diagrams & Color Scheme . . . .  32
     A.1.  State Colors  . . . . . . . . . . . . . . . . . . . . . .  33
     A.2.  State Diagrams  . . . . . . . . . . . . . . . . . . . . .  33
       A.2.1.  Notations . . . . . . . . . . . . . . . . . . . . . .  34
       A.2.2.  General . . . . . . . . . . . . . . . . . . . . . . .  34
       A.2.3.  DRIP SAM  . . . . . . . . . . . . . . . . . . . . . .  35
       A.2.4.  DRIP Link . . . . . . . . . . . . . . . . . . . . . .  36
       A.2.5.  DRIP Wrapper/Manifest/Frame . . . . . . . . . . . . .  37
   Appendix B.  Broadcast Endorsement: DIME, UA  . . . . . . . . . .  39
   Appendix C.  Example TX/RX Flow . . . . . . . . . . . . . . . . .  41
   Appendix D.  Additional FEC Decoding Heuristic  . . . . . . . . .  41
   Appendix E.  Operational Recommendation Analysis  . . . . . . . .  43
     E.1.  Definitions . . . . . . . . . . . . . . . . . . . . . . .  43
     E.2.  Methodology . . . . . . . . . . . . . . . . . . . . . . .  43
     E.3.  ASTM Maximum Schedule Example . . . . . . . . . . . . . .  45
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  47

1.  Introduction

   The initial regulations (e.g.  [FAA-14CFR]) and standards (e.g.
   [F3411]) for Unmanned Aircraft (UA) Systems (UAS) Remote
   Identification and tracking (RID) do not address trust.  This is a
   requirement that will need to be addressed for various different
   parties that have a stake in the safe operation of National Airspace
   Systems (NAS).  DRIP's goal as stated in the charter 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.

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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]).

   Without authentication, an Observer has no basis for trust.  As the
   messages are sent via wireless broadcast, they may be transmitted
   anywhere within wireless range and making any claims desired by the
   sender.

   DRIP Specific Authentication Methods, carried in ASTM Authentication
   Messages (Message Type 0x2) are defined herein.  These methods, when
   properly used, enable a high level of trust in that the content of
   other ASTM Messages was generated by their claimed registered source.
   These messages are designed to provide the Observers with immediately
   actionable information.

   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 [F3411] further support the important use
   case of Observers who are sometimes offline at the time of
   observation.

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

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 defined in [RFC9153].  In
   addition, the following terms are defined:

   DRIP Entity Tag (DET):

      An HHIT that is used as an identifier in DRIP as specified in
      [drip-rid].

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   DRIP Identity Management Entity:

      Registry service for DETs and other information in DRIP as
      specified in [drip-registries].

   Legacy Transports:

      use of broadcast frames (Bluetooth 4.x) as specified in [F3411].

   Extended Transports:

      use of extended advertisements (Bluetooth 5.x), service info (Wi-
      Fi NaN) or vendor specific element information (Wi-Fi BEACON) in
      broadcast frames as specified in [F3411].  Must use ASTM Message
      Pack (Message Type 0xF).

   Hierarchial Host Identity Tag (HHIT):

      A special-use, non-routable, IPv6 address constructed as specified
      in [drip-rid].

   HHIT Domain Authority (HDA):

      A class of DIME usually associated with a USS in UTM.

   Hierarchial ID (HID):

      Encoding of the RAA and HDA into the HHIT structure as defined in
      [drip-rid].

   Host Identity (HI):

      Public key have of an asymmetric keypair used in generating a HHIT
      as specified in [drip-rid].

   Registered Assigning Authority (RAA):

      A class of DIME usually associated with a CAA such as the US FAA.

3.  Background

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3.1.  Reasoning for IETF DRIP Authentication

   [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 even those.
   [F3411] Annex A1 defines a Broadcast Authentication Verifier Service,
   which has a heavy reliance on Observer real-time connectivity to the
   Internet (specifically into UTM) that is not always guaranteed.
   Fortunately, [F3411] also allows third party standard Authentication
   Types, several of which DRIP defines herein.

   The standardization of specific formats to support the DRIP
   requirements in UAS RID for trustworthy communications over Broadcast
   RID is an important part of the chain of trust for a UAS ID.  Per
   [drip-arch] in Section 5, there is a need to have Authentication
   formats 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.

3.1.1.  UA Signed Evidence

   When an Observer receives a DRIP-based Authentication Message
   (Section 4.3, Section 4.4, Section 4.5) containing UA signed Evidence
   it SHOULD validate the signature using the HI corresponding to the
   UA's DET.

   The UA's HI, SHOULD be retrieved from DNS (Section 5,
   [drip-registries]).  If not available it may have been revoked.  Note
   that accurate revocation status is a DIME inquiry; DNS non-response
   is a hint to the DET being expired or revoked.  It MAY be retrieved
   from a local cache, if present.  The local cache SHOULD be 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 further (or
   cached previous) 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.

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3.1.2.  DIME Endorsement of UA DET/HI

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

   The DIME's HI, SHOULD be retrieved from from DNS (Section 5,
   [drip-registries]), when available.  It MAY be cached from a prior
   DNS lookup or it may 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 SHOULD be validated.

3.1.4.  UAS RID Trust

   Section 3.1.1, Section 3.1.2 and Section 3.1.3 above complete the
   trust chain but the chain cannot yet be trusted as having any
   relevance to the observed UA because reply 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 in the form of DRIP Wrapper or Manifest
   (Section 4.3, Section 4.4) containing at least one ASTM Vector/
   Location Message and/or System Message (which contains a timestamp).
   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

   The ASTM Authentication Message (Message Type 0x2) is a unique
   message in the Broadcast [F3411] standard as it is the only one that
   is larger than the Bluetooth 4.x frame size.  To address this, it is
   defined as a set of "pages" that each fits into a single Bluetooth
   4.x broadcast frame.  For other media these pages are still used but
   all in a single frame.

3.2.1.  Authentication Page

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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
     +---------------+---------------+---------------+---------------+
     |  Page Header  |                                               |
     +---------------+                                               |
     |                                                               |
     |                                                               |
     |                     Authentication Payload                    |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Page Header: (1 byte)
         Authentication Type (4 bits)
         Page Number (4 bits)

     Authentication Payload: (23 bytes per page)
         Authentication Payload, including headers. Null padded.

            Figure 1: Standard ASTM Authentication Message 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.  This is denoted
   in every Authentication Page in the Page Header.  The SAM Type is
   denoted as a field in the Authentication Payload (see Section 4.1.1).

   The Authentication Message is structured as a set of pages.  There is
   a technical maximum of 16 pages (indexed 0 to 15 in the Page Header)
   that can be sent for a single Authentication Message, with each page
   carrying a maximum 23-byte Authentication Payload.  See Section 3.2.3
   for more details.  Over Bluetooth 4.x, these messages are
   "fragmented", with each page sent in a separate Bluetooth 4.x
   broadcast 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 (Bluetooth or Wi-
   Fi).

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 pages.

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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
     +---------------+---------------+---------------+---------------+
     |                     Authentication Headers                    |
     |                               +---------------+---------------+
     |                               |                               |
     +---------------+---------------+                               |
     .                                                               .
     .                Authentication Data / Signature                .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |      ADL      |                                               |
     +---------------+                                               |
     .                                                               .
     .                       Additional Data                         .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Authentication Headers: (6-bytes)
         As defined in F3411.

     Authentication Data / Signature: (255-bytes max)
         Opaque authentication data.

     Additional Data Length (ADL): (1-byte - unsigned)
         Length in bytes of Additional Data.

     Additional Data: (255-bytes max):
         Data that follows the Authentication Data / Signature but
         is not considered part of the Authentication Data.

                Figure 2: ASTM Authentication Message Fields

   When Additional Data is being sent, a single unsigned byte
   (Additional Data Length) directly follows the Authentication Data /
   Signature and has the length, in bytes, of the following Additional
   Data.  For DRIP, this field is used to carry Forward Error Correction
   as defined in Section 5.

3.2.3.  ASTM Broadcast RID Constraints

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3.2.3.1.  Wireless Frame Constraints

   A UA has the option of broadcasting using Bluetooth (4.x and 5.x) or
   Wi-Fi (BEACON or NAN), see Section 6.  With Bluetooth, FAA and other
   Civil Aviation Authorities (CAA) mandate transmitting simultaneously
   over both 4.x and 5.x.  With Wi-Fi, use of BEACON is recommended.
   Wi-Fi NAN is another option, depending on the CAA.  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-bytes of payload per frame where the others all can
   support larger payloads per frame.  However, the [F3411] messaging
   framing dictated by Bluetooth 4.x constraints is inherited by [F3411]
   over other media.

3.2.3.2.  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 denotes the
       length in bytes of Authentication Data / Signature only) MUST NOT
       exceed the value of 201.  This includes the SAM Type but excludes
       Additional Data such as FEC.

4.  DRIP Authentication Formats

   All formats defined in this section are the content for the
   Authentication Data / Signature field in Figure 2 and use the
   Specific Authentication Method (SAM, Authentication Type 0x5).  The
   first byte of the Authentication Data / Signature of Figure 2, is
   used to multiplex between these various formats.

   When sending data over a medium that does not have underlying Forward
   Error Correction (FEC), for example Bluetooth 4.x, then Section 5
   MUST be used.  Appendix A gives a high-level overview of a state

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   machine for decoding and determining a trustworthiness state.
   Appendix C shows an example of using the formats defined in this
   section.

4.1.  DRIP Authentication Field Definitions

   ASTM Message (25-bytes):

      Full ASTM Message as defined in [F3411]; specifically Message
      Types 0x0, 0x1, 0x3, 0x4, and 0x5

   ASTM Message Hash (8-bytes):

      Hash of a single full ASTM Message using hash operations described
      in (Section 4.4.3).  Multiple hashes MUST be in Message Type
      order.

   Broadcast Endorsement (136-bytes):

      DIME HI over UA DET/HI.  Generated by a DIME during a UA DET,
      being used as a Session ID, registration.  Used in Section 4.2.

   Current Manifest Hash (12-bytes):

      Hash of the current Manifest Message (Section 4.4).  See
      Section 4.4.2.

   Evidence (0 to 112 bytes):

      Opaque evidence data that the UA is endorsing during its flight in
      Figure 4.

   Frame Type (1-byte):

      Sub-type for future different DRIP Frame formats.  See
      Section 4.5.1.

   Previous Manifest Hash (12-bytes):

      Hash of the previously sent Manifest Message (Section 4.4).  See
      Section 4.4.2.

   UA DRIP Entity Tag (DET) (16-bytes):

      The UA DET [drip-rid] in byte form (network byte order) and is
      part of Figure 4.

   UA Signature (64-bytes):

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      Signature over all 4 preceding fields of Figure 4 using the HI of
      the UA.

   Valid Not After (VNA) Timestamp by UA (4-bytes):

      Timestamp denoting recommended time to stop trusting data in
      Figure 4.  MUST follow the format defined in [F3411].  That is a
      Unix-style timestamp but with an epoch of 01/01/2019 00:00:00 with
      an additional offset is then added to push a short time into the
      future (relative to Not Before Timestamp) to avoid replay attacks.
      The offset used against the Unix-style timestamp 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 Not After Timestamp 2 minutes after Not Before
      Timestamp.

   Valid Not Before (VNB) Timestamp by UA (4-bytes):

      Timestamp denoting recommended time to start trusting data in
      Figure 4.  MUST follow the format defined in [F3411].  That is a
      Unix-style timestamp but with an epoch of 01/01/2019 00:00:00.
      MUST be set no earlier than the time the signature is generated.

4.1.1.  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                   .
  .                                                               .
  |                                                               |
  +---------------+---------------+---------------+---------------+

  SAM Type (1 byte):
      Byte defined by F3411 to multiplex SAMs

  SAM Authentication Data (0 to 200 bytes):
      Authentication data (opaque to baseline F3411 but parsed by DRIP).

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                        Figure 3: SAM Data Format

4.1.1.1.  SAM Type

   The SAM Type field is maintained by the International Civil Aviation
   Organization (ICAO) and for DRIP four are planned to be allocated:

                +==========+=============================+
                | 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

4.1.1.2.  SAM Authentication Data

   This field has a maximum size of 200-bytes, as defined by
   Section 3.2.3.  The Broadcast Attestation Structure (Section 4.1.2)
   MUST be used in this space.

4.1.2.  UA Signed Evidence

   The DRIP Endorsement Structure (DES) [drip-registries] is used to
   created Signed Evidence by the UA during flight.  It is encapsulated
   by the SAM Authentication Data field of Figure 3.

   The DES MUST be used by DRIP Wrapper (Section 4.3), Manifest
   Section 4.4 and Frame (Section 4.5).  DRIP Link (Section 4.2) MUST
   NOT use the DES as it will not fit in the ASTM Authentication
   Message.

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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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                              UA                               |
     |                        DRIP Entity Tag                        |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                            Evidence                           .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                      VNA Timestamp by UA                      |
     +---------------+---------------+---------------+---------------+
     |                      VNB Timestamp by UA                      |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                          UA Signature                         |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

            Figure 4: Binary Encoded DRIP Endorsement Structure

   UA DRIP Entity Tag:

      This is the identity section of the DES and MUST be set to the UA
      DET (hhit).

   Evidence:

      The evidence section MUST be filled in with data in the form of an
      opaque object specified in the DRIP Wrapper, Manifest or Frame
      sections.

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   UA Signature:

      The UA private key MUST be used to generate the signature
      (sig_b16) found in the signature section.

   The DES MUST be encoded in the binary form (as defined in
   [drip-registries]) to create the UA Signed Evidence.  The general
   structure of the binary form can be seen in Figure 4.

   When using the DES, 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

   The DRIP Link SAM Type is used to transmit Broadcast Endorsements.
   For example, the Broadcast Endorsement: DIME, UA is sent (see
   Section 6.3) as a DRIP Link message.  The structure is defined in
   [drip-registries] and an example of it can be found in Appendix B.

   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
   validations of the contents when the DIME DET/HI is in the receiver's
   cache.  It also provides the UA HI so that connectivity is not
   required when performing validation of other DRIP Authentication
   Messages.

      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                      Broadcast Endorsement                    .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+

                            Figure 5: DRIP Link

   This DRIP Authentication Message is used in conjunction with other
   DRIP SAM Types (such as Manifest or 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.  The hash of such a message SHOULD merely be
   included in a DRIP Manifest, but an entire such message MAY be
   encapsulated in a DRIP Wrapper periodically for stronger security.

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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 DES (Section 4.1.2) is populated with
   full (25-byte) [F3411] Broadcast RID messages.  The ASTM Messages can
   be concatenated together into a single byte object (like in Figure 6)
   or be set in the evidence section as individual Claims.

   The minimum number of messages support is 1 and the maximum supported
   is 4.  The messages MUST be in Message Type order as defined by
   [F3411].  All message types except Authentication (Message Type 0x2)
   and Message Pack (Message Type 0xF) are allowed.  Thus it may be
   preferred in some operation modes to use DRIP Manifest Section 4.4
   instead.

      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                         ASTM Message(s)                       .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+

                      Figure 6: DRIP Wrapper Evidence

4.3.1.  Message Count

   When decoding a DRIP Wrapper on a receiver, the number of messages
   wrapped can be determined by checking the length between the UA DET
   and the VNB Timestamp by UA is a multiple of 25-bytes.

4.3.2.  Wrapper over Extended Transports

   To send the DRIP Wrapper over Extended Transports the messages being
   wrapped are co-located with the Authentication Message in a ATM
   Message Pack (Message Type 0xF).  The evidence section of the DES is
   cleared after signing leaving the following binary structure that is
   placed into the SAM Authentication Data of Figure 3 and sent in the
   same Message Pack.

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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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                              UA                               |
     |                        DRIP Entity Tag                        |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                   Not Before Timestamp by UA                  |
     +---------------+---------------+---------------+---------------+
     |                    Not After Timestamp by UA                  |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                          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 Message Type order and set the DES
   evidence section before performing signature verification.

   The functionality of Wrapper in this form is identical to Message Set
   Signature (Authentication Type 0x3) when running over Extended
   Transports.  What 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 relies on Internet connectivity for verification
   which the receiver may not have at the time of receipt of an
   Authentication Message.  This is something 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 format is the bounding of up to
   4 ASTM Messages that can be sent within it.  Another limitation is
   that the format can not be used as a surrogate for messages it is
   wrapping.  This is due to high potential a receiver on the ground
   does not support DRIP.  Thus, when Wrapper is being used the wrapper
   data must effectively be sent twice, once as a single framed message
   (as specified in [F3411]) and then again wrapped within the Wrapper
   format.

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 retransmitting them.  An Observer who
   has been listening for any length of time SHOULD hash received
   messages and cross-check them against the manifest hashes.  This is a
   way to evade the limitation of a maximum of 4 messages in the Wrapper
   Format (Section 4.3.3) and greatly reduce overhead.

   Judicious use of 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 E).

   The evidence section of the DES (Section 4.1.2) is populated with
   8-byte hashes of [F3411] Broadcast RID messages and two special
   hashes (Section 4.4.2).  All these hashes can be concatenated
   together into a single byte object or be set in the evidence section
   individually.  The Previous Manifest Hash and Current Manifest 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 E.

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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                             |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                      ASTM Message Hashes                      .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+

                 Figure 8: DRIP Manifest Evidence Structure

4.4.1.  Hash Count

   The number of hashes in the Manifest can be variable (2-12).  An easy
   way to determine the number of hashes is to take the length of the
   data between the end of the UA DET and VNB Timestamp by UA and divide
   it by the hash length (8).  If this value is not an integer, the
   message is invalid.

4.4.2.  Pseudo-Blockchain Hashes

   Two special hashes are included in all Manifest messages; the
   Previous Manifest Hash, which links to the previous manifest message,
   as well as the Current Manifest Hash.  This gives a pseudo-blockchain
   provenance to the manifest message that could be traced back if the
   Observer was present for extended periods of time.

4.4.3.  Hash Algorithms and Operation

   The hash algorithm used for the Manifest Message is the same hash
   algorithm used in creation of a DET [drip-rid] that is signing the
   Manifest.

   An DET using cSHAKE128 [NIST.SP.800-185] computes the hash as
   follows:

   cSHAKE128(ASTM Message, 8, "", "Remote ID Auth Hash")

      Informative Note: [drip-rid] specifies cSHAKE128 but is open for
      the expansion of other OGAs.

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   When building the manifest of hashes the Previous Manifest Hash is
   known from the previous Manifest message.  For the first built
   manifest this value is null filled.  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.

4.4.3.1.  Legacy Transport Hashing

   Under this transport DRIP hashes the full ASTM Message being sent
   over the Bluetooth Advertising frame.  For paged ASTM Messages
   (currently only Authentication Messages) all the pages are
   concatenated together and hashed as one object.  For all other
   Message Types each individual 25-byte message is hashed.

4.4.3.2.  Extended Transport Hashing

   Under this transport DRIP hashes the full ASTM Message Pack (Message
   Type 0xF) - regardless of its content.

4.5.  DRIP Frame

   This SAM Type is for when the authentication data does not fit in
   other defined formats under DRIP and is reserved for future expansion
   under DRIP if required.

   The population of the evidence section of the DES (Section 4.1.2) is
   not defined in this document and MUST be openly specified by the
   implementation (or specification) using it.

      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 9: DRIP Frame

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4.5.1.  Frame Type

   Byte to sub-type for future different DRIP Frame formats.  It takes
   the first byte in Figure 9 leaving 111-bytes available for Frame
   Evidence Data.

             +============+==============+==================+
             | Frame Type | Name         | Description      |
             +============+==============+==================+
             | 0x00       | Reserved     | Reserved         |
             +------------+--------------+------------------+
             | 0xC0-0xFF  | Experimental | Experimental Use |
             +------------+--------------+------------------+

                                 Table 2

5.  Forward Error Correction

   For Broadcast RID, Forward Error Correction (FEC) is provided by the
   lower layers in Extended Transports (Bluetooth 5.x, Wi-Fi NaN, and
   Wi-Fi BEACON).  The Bluetooth 4.x Legacy Transport does not have
   supporting FEC so with DRIP Authentication the following application
   level FEC scheme is used to add 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.  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:

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   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 bytes + number of parity bytes.

   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.

   To generate the parity a simple XOR operation using the previous
   parity page and current page is used.  Only the 23-byte
   Authentication Payload field of Figure 1 is used in the XOR
   operations.  For Page 0, a 23-byte null pad is used for the previous
   parity page.

   Figure 10 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-bytes of FEC data and
   in this example 10-bytes of padding to line it up into Page N.

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     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 10: Example Single Page FEC Encoding

5.2.  Decoding

   To determine if FEC has been used a simple check of the Last Page
   Index can be used.  In general if the Last Page Index field is one
   greater than that necessary to hold Length bytes of Authentication
   Data then FEC has been used.  Note however that if Length bytes was
   exhausted exactly at the end of an Authentication Page then the
   Additional Data Length will occupy the first byte of the following
   page the remainder of which under DRIP will be null padded: in this
   case the Last Page Index will have been incremented by one more for
   FEC.

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   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 1-byte in length, so it
   will roll over (to 0x00) after reaching its maximum value (0xFF).  If
   only 1-page is missing in the Authentication Message the resulting
   parity bytes 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 are REQUIRED to be sanity checked by DRIP.  The pseudo-code in
   Figure 11 can be used for both checks.

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   function decode_check(auth_pages[], decoded_lpi, decoded_length) {
     // check decoded Last Page Index (LPI) does not exceed maximum LPI
     if (decoded_lpi >= 16) {
       return DECODE_FAILURE
     }

     // check that decoded length does not exceed DRIP maximum
     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
   }

                  Figure 11: Pseudo-code for Decode Checks

   Implementations MAY also implement an heuristic extension
   (Appendix D) to decode if both the first page (Page 0) and last page
   (Last Page Index) are missing.

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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-bytes 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.  This should be avoided
   where possible in an effort to maintain efficiency.

6.  Requirements & Recommendations

6.1.  Legacy Transports

   With Legacy Advertisements the goal is to attempt to bring reliable
   receipt of the paged Authentication Message.  FEC (Section 5) MUST be
   used, per mandated RID rules (for example the US FAA RID Rule
   [FAA-14CFR]), when using Legacy Advertising methods (such as
   Bluetooth 4.x).

   Under ASTM Bluetooth 4.x rules, transmission of dynamic messages is
   at least every 1 second.  DRIP Authentication Messages typically
   contain dynamic data (such as the DRIP Manifest or DRIP Wrapper) and
   should be sent at the dynamic rate of 1 per second.

6.2.  Extended Transports

   Under the ASTM specification, Bluetooth 5.x, Wi-Fi NaN, and Wi-Fi
   BEACON transport of RID is to use the Message Pack (Message Type 0xF)
   format for all transmissions.  Under Message Pack messages are sent
   together (in Message Type order) in a single Bluetooth 5.x extended
   frame (up to 9 single frame equivalent messages under Bluetooth 4).
   Message Packs are required by ASTM to be sent at a rate of 1 per
   second (like dynamic messages).

   Without any fragmentation or loss of pages with transmission FEC
   (Section 5) MUST NOT be used as it is impractical.

6.3.  Authentication

   It is REQUIRED that a UA send the following DRIP Authentication
   Formats to fulfill the requirements in [RFC9153]:

   1.  SHOULD: send DRIP Link (Section 4.2) using the Broadcast
       Endorsement: DIME:Apex, DIME:RAA (satisfying GEN-3); at least
       once per 5 minutes

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

   3.  MUST: send DRIP Link (Section 4.2) using the Broadcast
       Endorsement: DIME: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.  Where a UA is dwelling in one location, and the channel is
   heavily used by other devices, "occasional" message authentication
   may be sufficient for an Observer.  Contrast this with a UA
   traversing an area, and then every message should be authenticated as
   soon as possible for greatest success as viewed by the receiver.

   Thus how/when these DRIP Authentication Messages are sent is up to
   each implementation.  Further complication comes in contrasting
   Legacy and Extended Transports.  In Legacy, each message is a
   separate hash within the Manifest.  So, again in dwelling, may lean
   toward occasional message authentication.  In Extended Transports,
   the hash is over the Message Pack so only few hashes need to be in a
   Manifest.  A single Manifest can handle a potential two Message Packs
   (for a full set of messages) and a DRIP Link Authentication Message
   for the Broadcast Endorsement: DIME, UA.

   A separate issue is the frequency of transmitting the DRIP Link
   Authentication Message for the Broadcast Endorsement: DIME, UA when
   using a Manifest Message.  This message content is static; its hash
   never changes radically.  The only change is the 4-byte timestamp in
   the Authentication Message headers.  Thus, potentially, in a dwelling
   operation it can be sent once per minute, where its hash is in every
   Manifest.  A receiver can cache all DRIP Link Authentication Message
   for the Broadcast Endorsement: DIME, UA to mitigate potential packet
   loss.

   The following operational configuration is RECOMMENDED (in alignment
   with Section 6.3):

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   1.  Per CAA requirements, generate and transmit a set of ASTM
       Messages (example; Basic ID, Location and System).

   2.  Under Extended Transports, generate and include in the same
       Message Pack as the CAA required ASTM Messages a DRIP Wrapper as
       specified in Section 4.3.2.

   3.  Under Legacy Transports, generate and transmit every 5 seconds a
       DRIP Manifest (Section 4.4) hashing as many sets of recent CAA
       required ASTM Messages.  The system MAY periodically replace the
       DRIP Manifest with a DRIP Wrapper (Section 4.3) containing at
       least a Location Message (Message Type 0x2).

   4.  Under both Legacy or Extended Transports, generate and transmit a
       DRIP Link's (Section 4.2) containing; Broadcast Endorsement:
       DIME:HDA, UA every minute, Broadcast Endorsement: DIME:RAA,
       DIME:HDA every 5 minutes, Broadcast Endorsement: DIME:Apex,
       DIME:RAA every 5 minutes.

   The reasoning and math behind this recommendation can be found in
   Appendix E.

6.4.1.  DRIP Wrapper

   The DRIP Wrapper MUST NOT be used in place of sending the ASTM
   messages as is.  All receivers MUST be able to process all the
   messages specified in [F3411].  Sending them within the DRIP Wrapper
   makes them opaque to receivers lacking support for DRIP
   Authentication Messages.  Thus, messages within a Wrapper are sent
   twice: in the clear and authenticated within the Wrapper.  The DRIP
   Manifest format would seem to be a more efficient use of the
   transport channel.

   The DRIP Wrapper has a specific use case for DRIP aware receivers.
   For 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 verification
   of the data being received in Broadcast RID.

   After signature validation 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 verification.  An example of another
   source of information is a visual confirmation of the UA position.

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   When correlation of these different data streams do 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] are addressed in this document:

   ID-5: Non-spoofability

      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.  ICAO Considerations

   DRIP requests the following SAM Types to be allocated:

   1.  DRIP Link

   2.  DRIP Wrapper

   3.  DRIP Manifest

   4.  DRIP Frame

9.  IANA Considerations

9.1.  IANA DRIP Registry

   This document requests a new subregistry for Frame Type under the
   DRIP registry (https://datatracker.ietf.org/doc/html/draft-ietf-drip-
   rid-28#section-8.2).

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   DRIP Frame Type:  This 8-bit valued subregistry is for Frame Types in
      DRIP Frame Authentication Messages.  Future additions to this
      subregistry are to be made through Expert Review (Section 4.5 of
      [RFC8126]).  The following values are defined:

   | Frame Type | Name         | Description      |
   | ---------- | ------------ | ---------------- |
   | 0x00       | Reserved     | Reserved         |
   | 0xC0-0xFF  | Experimental | Experimental Use |

10.  Security Considerations

10.1.  Replay Attacks

   The astute reader may note that the DRIP Link messages, which are
   recommended to be sent, are static in nature and contain various
   timestamps.  These DRIP Link messages can easily be replayed by an
   attacker who has copied them from previous broadcasts.

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

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

10.2.  VNA Timestamp Offsets for DRIP Authentication Formats

   Note the discussion of VNA Timestamp offsets here is in 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 as seen 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 recommended that 3-5 minutes should be sufficient
   to serve this purpose in any scenario, but is not limited by design.

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11.  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).

   *  Many thanks to Rick Salz for the secdir review.

12.  References

12.1.  Normative References

   [drip-arch]
              Card, S. W., Wiethuechter, A., Moskowitz, R., Zhao, S.,
              and A. Gurtov, "Drone Remote Identification Protocol
              (DRIP) Architecture", Work in Progress, Internet-Draft,
              draft-ietf-drip-arch-29, 16 August 2022,
              <https://www.ietf.org/archive/id/draft-ietf-drip-arch-
              29.txt>.

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

   [NIST.SP.800-185]
              Kelsey, J., Change, S., and R. Perlner, "SHA-3 Derived
              Functions: cSHAKE, KMAC, TupleHash and ParallelHash", NIST
              Special Publication SP 800-185,
              DOI 10.6028/nist.sp.800-185, December 2016,
              <http://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>.

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   [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>.

12.2.  Informative References

   [drip-registries]
              Wiethuechter, A., Card, S. W., Moskowitz, R., and J. Reid,
              "DRIP Entity Tag (DET) Registration & Lookup", Work in
              Progress, Internet-Draft, draft-ietf-drip-registries-05,
              11 July 2022, <https://www.ietf.org/archive/id/draft-ietf-
              drip-registries-05.txt>.

   [drip-rid] Moskowitz, R., Card, S. W., Wiethuechter, A., and A.
              Gurtov, "UAS Remote ID", Work in Progress, Internet-Draft,
              draft-ietf-drip-uas-rid-01, 9 September 2020,
              <https://www.ietf.org/archive/id/draft-ietf-drip-uas-rid-
              01.txt>.

   [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 State Diagrams & Color Scheme

   ASTM Authentication has only 3 states: None, Invalid or Valid.  This
   is because under ASTM the idea is that Authentication is done by an
   external service hosted somewhere on the Internet so it is assumed
   you will always get some sort of answer back.  With DRIP this
   classification becomes more complex with the support of "offline"
   scenarios where the receiver does not have Internet connectivity.
   With the use of asymmetric keys this means the public key (PK) must
   somehow be obtained - [drip-registries] gets more into detail how
   these keys are stored on DNS and one reason for DRIP Authentication
   is to send PK's over Broadcast RID.

   There are two keys of interest: the PK of the UA and the PK of the
   DIME.  This document gives a clear way to send the PK of the UA over
   the Broadcast RID messages.  The key of the DIME can be sent over
   Broadcast RID using the same mechanisms (see Section 4.2 and

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   Section 6.3) but is not required due to potential operational
   constraints of sending multiple DRIP Link messages.  As such there
   are scenarios where you may have part of the key-chain but not all of
   it.

   The intent of this appendix is to give some kind of recommended way
   to classify these various states and convey it to the user through
   colors and state names/text.

A.1.  State Colors

   The table below lays out the RECOMMENDED colors to associate with
   state.

       +==============+========+===================================+
       | State        | Color  | Details                           |
       +==============+========+===================================+
       | None         | Black  | No Authentication being received  |
       +--------------+--------+-----------------------------------+
       | Partial      | Gray   | Authentication being received but |
       |              |        | missing pages                     |
       +--------------+--------+-----------------------------------+
       | Unsupported  | Brown  | Authentication Type/SAM Type of   |
       |              |        | received message not supported    |
       +--------------+--------+-----------------------------------+
       | Unverifiable | Yellow | Data needed for verification      |
       |              |        | missing                           |
       +--------------+--------+-----------------------------------+
       | Verified     | Green  | Valid verification results        |
       +--------------+--------+-----------------------------------+
       | Trusted      | Blue   | Valid verification results and    |
       |              |        | DIME is marked as trusted         |
       +--------------+--------+-----------------------------------+
       | Questionable | Orange | Inconsistent verification results |
       +--------------+--------+-----------------------------------+
       | Unverified   | Red    | Invalid verification results      |
       +--------------+--------+-----------------------------------+
       | Conflicting  | Purple | Inconsistent verification results |
       |              |        | and DIME is marked as trusted     |
       +--------------+--------+-----------------------------------+

                                  Table 3

A.2.  State Diagrams

   This section gives some RECOMMENDED state flows that DRIP should
   follow.  Note that the state diagrams do not have all error
   conditions mapped.

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A.2.1.  Notations

                   o--------------o
                   |   PROCESS    |
                   o--------------o

                   +--------------+
                   |    STATE     |
                   +--------------+

                    ooooo
                   o  N  o    Transition N
                    ooooo

                   +----->    Transition Option False/No

                   ----->     Transition Option True/Yes

                        Figure 12: Diagram Notations

A.2.2.  General

 o---------------------o      ooooo        +------+
 |        Start        |---->o  1  o+----->| None |
 o---------------------o      ooooo        +------+
                                |
                                v
                              ooooo        +-------------+
                             o  2  o+----->| Unsupported |
                              ooooo        +-------------+
                                |             ^
                                v             |
           +---------+        ooooo           |
           | Partial |<-----+o  3  o          |
           +---------+        ooooo           |
                                |             |
                                v             +
                              ooooo         ooooo        o-------------o
                             o  4  o------>o  5  o------>| SAM Decoder |
                              ooooo         ooooo        o-------------o
                                +
                                |
                                v
                         o------------------o
                         | AuthType Decoder |
                         o------------------o

            Figure 13: Standard Authentication Colors/State

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    +============+=============================+======================+
    | Transition | Transition Query            | Next State/Process/  |
    |            |                             | Transition (Yes, No) |
    +============+=============================+======================+
    | 1          | Receiving Authentication    | 2, None              |
    |            | Pages?                      |                      |
    +------------+-----------------------------+----------------------+
    | 2          | Authentication Type         | 3, Unsupported       |
    |            | Supported?                  |                      |
    +------------+-----------------------------+----------------------+
    | 3          | All Pages of Authentication | 4, Partial           |
    |            | Message Received?           |                      |
    +------------+-----------------------------+----------------------+
    | 4          | Is Authentication Type      | 5, AuthType Decoder  |
    |            | received 5?                 |                      |
    +------------+-----------------------------+----------------------+
    | 5          | Is SAM Type Supported?      | SAM Decoder,         |
    |            |                             | Unsupported          |
    +------------+-----------------------------+----------------------+

                                  Table 4

A.2.3.  DRIP SAM

   o-------------o      ooooo        o-----------------------------o
   | SAM Decoder |---->o  6  o------>| DRIP Wrapper/Manifest/Frame |
   o-------------o      ooooo        o-----------------------------o
                          +                 |              ^
                          |                 |              |
                          v                 v              |
                   o-----------o    o--------------------o |
                   | DRIP Link |--->| Update State Cache | |
                   o-----------o    o--------------------o |
                                      |                    |
                                      v                    |
           o--------------o         ooooo       o----------------------o
           | NOP / Return |<------+o  7  o----->| Extract Message from |
           o--------------o         ooooo       | Verification Queue   |
                                                o----------------------o

                        Figure 14: DRIP SAM Decoder

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       +============+=====================+========================+
       | Transition | Transition Query    | Next State/Process/    |
       |            |                     | Transition (Yes, No)   |
       +============+=====================+========================+
       | 6          | Is SAM Type DRIP    | DRIP Link, DRIP        |
       |            | Link?               | Wrapper/Manifest/Frame |
       +------------+---------------------+------------------------+
       | 7          | Messages in         | Extract Message from   |
       |            | Verification Queue? | Verification Queue,    |
       |            |                     | NOP / Return           |
       +------------+---------------------+------------------------+

                                  Table 5

A.2.4.  DRIP Link

      o-----------o       ooooo         ooooo        +--------------+
      | DRIP Link |----->o  8  o+----->o  9  o+----->| Unverifiable |
      o-----------o       ooooo         ooooo        +--------------+
                            |             |
                            |-------------'
                            v
                          ooooo        +------------+
                         o  10 o+----->| Unverified |
                          ooooo        +------------+
                            |
                            v
                      o---------------------o
                      | Add UA DET/PK       |
                      | to Key Cache        |
                      o---------------------o
                            |
                            v
                          ooooo         +----------+
                         o  11 o+------>| Verified |
                          ooooo         +----------+
                            |              ^
                            v              |
                      o-------------------------o
                      | Mark UA DET/PK          |
                      | as Trusted in Key Cache |
                      o-------------------------o

                     Figure 15: DRIP Link State Decoder

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    +============+=======================+===========================+
    | Transition | Transition Query      | Next State/Process/       |
    |            |                       | Transition (Yes, No)      |
    +============+=======================+===========================+
    | 8          | DIME DET/PK in Key    | 10, 9                     |
    |            | Cache?                |                           |
    +------------+-----------------------+---------------------------+
    | 9          | DIME PK found Online? | 10, Unverifiable          |
    +------------+-----------------------+---------------------------+
    | 10         | DIME Signature        | Add UA DET/PK to Key      |
    |            | Verified?             | Cache, Unverified         |
    +------------+-----------------------+---------------------------+
    | 11         | DIME DET/PK marked as | Mark UA DET/PK as Trusted |
    |            | Trusted in Key Cache? | in Key Cache, Verified    |
    +------------+-----------------------+---------------------------+

                                 Table 6

A.2.5.  DRIP Wrapper/Manifest/Frame

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     o-----------------------------o         +--------------+
     | DRIP Wrapper/Manifest/Frame |         | Unverifiable |
     o-----------------------------o         +--------------+
                |                                   ^
                v                                   |
              ooooo         ooooo        o--------------------o
             o  12 o+----->o  13 o+----->| Add Message to     |
              ooooo         ooooo        | Verification Queue |
                |             |          o--------------------o
                |             |
                |-------------'
                v
              ooooo         ooooo         ooooo        +------------+
             o  14 o+----->o  15 o+----->o  16 o+----->| Unverified |
              ooooo         ooooo         ooooo        +------------+
                |             |             |
                v             v             |
              ooooo        +-------------+  |
             o  17 o+----->| Conflicting |  |
              ooooo        +-------------+  |
                |                           |
                v                           v
              ooooo                  +--------------+
             o  18 o---------------->| Questionable |
              ooooo                  +--------------+
                +
                |
                v
              ooooo        +----------+
             o  19 o+----->| Verified |
              ooooo        +----------+
                |
                v
             +---------+
             | Trusted |
             +---------+

            Figure 16: DRIP Wrapper/Manifest/Frame State Decoder

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   +============+==============================+======================+
   | Transition | Transition Query             | Next State/Process/  |
   |            |                              | Transition (Yes, No) |
   +============+==============================+======================+
   | 12         | UA DET/PK in Key Cache?      | 14, 13               |
   +------------+------------------------------+----------------------+
   | 13         | UA PK found Online?          | 14, Add Message to   |
   |            |                              | Verification Queue   |
   +------------+------------------------------+----------------------+
   | 14         | UA Signature Verified?       | 17, 15               |
   +------------+------------------------------+----------------------+
   | 15         | Has past Messages of this    | Conflicting, 16      |
   |            | type been marked as Trusted? |                      |
   +------------+------------------------------+----------------------+
   | 16         | Has past Messages of this    | Questionable,        |
   |            | type been marked as          | Unverified           |
   |            | Questionable or Verified?    |                      |
   +------------+------------------------------+----------------------+
   | 17         | Has past Messages of this    | Conflicting, 18      |
   |            | type been marked as          |                      |
   |            | Conflicting?                 |                      |
   +------------+------------------------------+----------------------+
   | 18         | Has past Messages of this    | Questionable, 19     |
   |            | type been marked as          |                      |
   |            | Questionable or Unverified?  |                      |
   +------------+------------------------------+----------------------+
   | 19         | Is UA DET/PK marked as       | Trusted, Verified    |
   |            | Trusted in Key Cache?        |                      |
   +------------+------------------------------+----------------------+

                                 Table 7

Appendix B.  Broadcast Endorsement: DIME, UA

      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                             DRIP                              |
     |                      Entity Tag of DIME                       |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                             DRIP                              |
     |                       Entity Tag of UA                        |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |

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     |                                                               |
     |                                                               |
     |                      Host Identity of UA                      |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                     VNB Timestamp by DIME                     |
     +---------------+---------------+---------------+---------------+
     |                     VNA Timestamp by DIME                     |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                      Signature by DIME                        |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     DRIP Entity Tag of DIME: (16-bytes)
         DET of DIME.

     DRIP Entity Tag of UA: (16-bytes)
         DET of UA.

     Host Identity of UA: (32-bytes)
         HI of UA.

     VNB Timestamp by DIME (4-bytes):
         Current time at signing.

     VNA Timestamp by DIME (4-bytes):
         Timestamp denoting recommended time to trust DIME Endorsement
         of UA DET and HI (may be minutes to months in the future).

     DIME Signature (64-bytes):
         Signature over preceding fields using the keypair of

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         the DIME.

          Figure 17: Example DRIP Broadcast Endorsement: DIME, UA

Appendix C.  Example TX/RX Flow

   In this example the UA is sending all DRIP Authentication Message
   formats (DRIP Link, DRIP Wrapper and DRIP Manifest) during flight,
   along with standard ASTM Messages.  The objective is to show the
   combinations of messages that must be received to properly validate a
   DRIP equipped UA and examples of their various states (as described
   in Appendix A).

           +-------------------+
     .-----| Unmanned Aircraft |-----.
     |     +-------------------+     |
     | 0             | 1             | 2
     |               |               |

     O               O               O
   --|--           --|--           --|--
    / \             / \             / \
     A               B               C

   Broadcast Paths: Messages Received
   0: None
   1: DRIP Link or DRIP Wrapper or DRIP Manifest
   2: DRIP Link and DRIP Wrapper or DRIP Manifest

   Observers: Authentication State
   A: None
   B: Unverifiable
   C: Verified, Trusted, Unverified, Questionable, or Conflicting

   As the above example shows to properly authenticate both a DRIP Link
   and a DRIP Wrapper or DRIP Manifest are required.

Appendix D.  Additional FEC Decoding Heuristic

   With Section 5, if Page 0 and the FEC page are missing from the
   Authentication Message there is a heuristic that can be applied
   instead of FEC decoding to obtain the Authentication Data.  This is
   based on the structure of the DRIP Authentication Messages and
   additional information sent over the broadcast or via lookup in DNS.

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   Looking at Page 0 (Figure 18) of any DRIP Authentication Format the
   payload data is always a DET.  For DRIP Link (Section 4.2) this DET
   is of the DIME while for DRIP Wrapper (Section 4.3), Manifest
   (Section 4.4) and Frame (Section 4.5) it is the DET of the UA.

      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 Headers    +---------------+
     |                                               |   SAM Type    |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                              DRIP                             |
     |                           Entity Tag                          |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Page Header: (1-byte)
         Authentication Type (4-bits)
         Page Number (4 bits)

     Authentication Headers: (6-bytes)
         As defined in F3411

     SAM Type (1-byte):
         Byte defined by F3411 to multiplex SAMs

     DRIP Entity Tag: (16-bytes)
       DET of an entity in network byte order

         Figure 18: Example Page 0 from DRIP Authentication Message

   Under DRIP, the Basic ID Message (Message Type 0x1) SHOULD be using
   Specific Session ID (ID Type 4) subtype IETF DRIP Entity ID (Type 1).
   This DET of the UA can be used in place of the missing DET in DRIP
   Wrapper, Manifest and Frame.  For DRIP Link, which is missing the DET
   of the DIME, the lookup properties of the DET enables the discovery,
   via DNS, the DIME's DET.

   These DETs obtained via other means can replace the missing payload
   of Authentication Page 0 and enable the full decoding and
   verification of the DRIP Authentication Message.

   When the missing DET is supposed to be of the UA the DET MAY be
   sourced from the Basic ID Message (Message Type 0x1).  Under DRIP,
   this SHOULD be set to the DET missing in the Authentication Data.

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Appendix E.  Operational Recommendation Analysis

   The recommendations found in (Section 6.4) may seem heavy handed and
   specific.  This appendix lays out the math and assumptions made to
   come to the recommendations listed there.  This section is solely
   based on operations using Bluetooth 4.x; as such all calculations of
   frame counts for DRIP included FEC using (Section 5).

E.1.  Definitions

   Frame:

      A single Bluetooth 4.x frame containing an ASTM Message or ASTM
      Authentication Page.

   Cycle:

      A set of frames containing all required information elements
      within the maximum allowable time as per applicable regulation.
      In the us this a 1 second window with basic, location, system. in
      eu this is a 1 second window with basic, location, system and
      operator id as of the publication of this document (2022).

   Schedule:

      Broadcast RID messages

E.2.  Methodology

   In the US, 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.

      Information Note: in Europe the Operator ID Message (0x5) is also
      included; pushing the frame count to 8 per cycle.

   To calculate the frame count of a given DRIP Authentication Message
   the following formula is used:

      1 + ceiling((((16 + 8 + 64) + (Item Size * Item Count) + 2) - 16)
      / 23) + 1

   The leading 1 is counting for the Page 0 which is always present.
   The DET (16-bytes), timestamps (8-bytes) and signature (64-bytes) all
   make up the required fields for DRIP.  Item Size (in bytes) is size
   of each item in a given format; for Wrapper it is 25 (a full ASTM
   Message), while for Manifest it is 8 (a single hash). 2 more is added

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   to account for the SAM Type and the ADL byte.  The value 16 is the
   number of bytes not counted (as they are part of Page 0 which is
   already counted for). 23 is the number of bytes per Authentication
   Page (pages 1 - 15).  After dividing by 23 the value is raised to the
   nearest whole value as we can only send full frames, not partial.
   The final 1 is counting for a single page of FEC applied in DRIP
   under Bluetooth 4.x.

      Informational Note: for DRIP Link the Item Size is 48 and Item
      Count is 1; resulting in a frame count of 8

   Comparing DRIP Wrapper and Manifest Authentication Message frame
   counts we have the following:

     +===============+=========+==========+===============+==========+
     | Authenticated | Wrapper | Manifest | Total Wrapper | Total    |
     | Frames        | Frames  | Frames   | Frames        | Manifest |
     |               |         |          |               | Frames   |
     +===============+=========+==========+===============+==========+
     | 1             | 7       | 7        | 8             | 8        |
     +---------------+---------+----------+---------------+----------+
     | 2             | 8       | 7        | 10            | 9        |
     +---------------+---------+----------+---------------+----------+
     | 3             | 9       | 7        | 12            | 10       |
     +---------------+---------+----------+---------------+----------+
     | 4             | 10      | 8        | 14            | 12       |
     +---------------+---------+----------+---------------+----------+
     | 5             | N/A     | 8        | N/A           | 13       |
     +---------------+---------+----------+---------------+----------+
     | 6             | N/A     | 8        | N/A           | 14       |
     +---------------+---------+----------+---------------+----------+
     | 7             | N/A     | 9        | N/A           | 16       |
     +---------------+---------+----------+---------------+----------+
     | 8             | N/A     | 9        | N/A           | 17       |
     +---------------+---------+----------+---------------+----------+
     | 9             | N/A     | 10       | N/A           | 19       |
     +---------------+---------+----------+---------------+----------+
     | 10            | N/A     | 10       | N/A           | 20       |
     +---------------+---------+----------+---------------+----------+
     | 11            | N/A     | 10       | N/A           | 21       |
     +---------------+---------+----------+---------------+----------+

                           Table 8: Frame Counts

   Note that for Manifest Frames the calculations use an Item Count that
   is 2 + Authentication Frames.  This is to account for the two special
   hashes.

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   The values in Total Frames is calculated by adding in the Item Count
   (to either the Wrapper Frames or Manifest Frames column) to account
   for the ASTM Messages being sent outside the Authentication Message.

E.3.  ASTM Maximum Schedule Example

   For this example we will assume the following ASTM Messages are in
   play:

   *  1x Basic ID (0x0) set as ID Type for Serial Number (0x1)

   *  1x Basic ID (0x0) set as ID Type for CAA Assigned ID (0x2)

   *  1x Basic ID (0x0) set as ID Type for UTM Assigned ID (0x3)

   *  1x Basic ID (0x0) set as ID Type for Specific Session ID (0x4)

   *  2x Location (0x1)

   *  1x Self ID (0x3)

   *  2x System (0x4)

   *  2x Operator ID (0x5)

   This message set is uses all single frame ASTM Messages, sending a
   set of them (Location, System and Operator ID) at a rate of 2 per
   second.  Two Basic ID's are sent in a single second and rotate
   between the 4 defined (1x per type).  A single Self ID is sent every
   second.  All messages in a given second if appear more than once are
   exact duplicates.

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   +-----------------------------------------------------------+
   |                        Frame Slots                        |
   | 00 | 01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10 | 11 |
   +----+----+----+----+----+----+----+----+----+----+----+----+
   | A* | V* | S  | O  | B  | V  | S* | O  | I  |   L/W[0,2]   |
   +----+----+----+----+----+----+----+----+----+----+----+----+
   | C* | V  | S* | O  | D* | V* | S  | O  | I* |   L/W[3,5]   |
   +----+----+----+----+----+----+----+----+----+----+----+----+
   | A  | V* | S  | O* | B* | V  | S  | O  | I  |L/W[6,7] | ## |
   +----+----+----+----+----+----+----+----+----+----+----+----+
   | C  | V  | S  | O  | D  | V  | S  | O  | I  |    M[0,2]    |
   +----+----+----+----+----+----+----+----+----+----+----+----+
   | A  | V  | S  | O  | B  | V  | S  | O  | I  |    M[3,5]    |
   +----+----+----+----+----+----+----+----+----+----+----+----+
   | C  | V  | S  | O  | D  | V  | S  | O  | I  |    M[6,8]    |
   +----+----+----+----+----+----+----+----+----+----+----+----+
   | A  | V  | S  | O  | B  | V  | S  | O  | I  |M[9]| ## | ## |
   +----+----+----+----+----+----+----+----+----+----+----+----+

   # = Empty Frame Slot
   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 = DRIP Link Authentication Message (0x2)
   W[y,z] = DRIP Wrapper Authentication Message (0x2)
     Wrapping Location (0x1) and System (0x4)
   M(x)[y,z] = DRIP Manifest Authentication Message (0x2)
     x = Number Hashes
     y = Start Page
     z = End Page
   * = Message in DRIP Manifest Authentication Message

   This scheme of repeated multiple times changing between Link and
   Wrapper messages (and their contents) in the following schedule
   order:

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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: ??? on Apex

   Any messages not required for a local jurisdiction can be removed
   from the schedule.  It is RECOMMENDED this empty frame slot is left
   empty to help with timing due to RF constraints/concerns.  For
   example in the US the Location (0x1), Self ID(0x3) and Operator ID
   (0x5) are not required and can be ignored in the above figures.  In
   the US only one Basic ID (0x0) is selected at any given time, opening
   up 3 more slots.

Authors' Addresses

   Adam Wiethuechter
   AX Enterprize, LLC
   4947 Commercial Drive
   Yorkville, NY 13495
   United States of America
   Email: adam.wiethuechter@axenterprize.com

   Stuart Card
   AX Enterprize, LLC
   4947 Commercial Drive
   Yorkville, NY 13495
   United States of America
   Email: stu.card@axenterprize.com

   Robert Moskowitz
   HTT Consulting
   Oak Park, MI 48237
   United States of America

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   Email: rgm@labs.htt-consult.com

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