[Search] [txt|html|xml|pdf|bibtex] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]

Versions: (draft-wiethuechter-drip-auth)   00 01         Standards Track
DRIP Working Group                                       A. Wiethuechter
Internet-Draft                                                   S. Card
Intended status: Standards Track                      AX Enterprize, LLC
Expires: 20 December 2021                                   R. Moskowitz
                                                          HTT Consulting
                                                            18 June 2021


                      DRIP Authentication Formats
                        draft-ietf-drip-auth-01

Abstract

   This document describes how to include trust into the ASTM Remote ID
   specification defined in ASTM F3411-19 under a Broadcast Remote ID
   (RID) scenario.  It defines a few different message schemes (based on
   the Authentication Message) that can be used to assure past messages
   sent by a UA and also act as an assurance for UA trustworthiness 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 20 December 2021.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.










Wiethuechter, et al.    Expires 20 December 2021                [Page 1]


Internet-Draft                auth-formats                     June 2021


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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  DRIP Requirements Addressed . . . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Required Terminology  . . . . . . . . . . . . . . . . . .   4
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Problem Space and Focus . . . . . . . . . . . . . . . . .   4
     3.2.  Reasoning for IETF DRIP Authentication  . . . . . . . . .   4
     3.3.  ASTM Authentication Message . . . . . . . . . . . . . . .   5
   4.  DRIP Authentication Formats . . . . . . . . . . . . . . . . .   6
     4.1.  UAS ID Signature  . . . . . . . . . . . . . . . . . . . .   6
     4.2.  Operator ID Signature . . . . . . . . . . . . . . . . . .   7
     4.3.  Message Set Signature . . . . . . . . . . . . . . . . . .   8
     4.4.  Specific Method . . . . . . . . . . . . . . . . . . . . .   9
       4.4.1.  DRIP Frame Format . . . . . . . . . . . . . . . . . .   9
       4.4.2.  DRIP Wrapper Format . . . . . . . . . . . . . . . . .  11
       4.4.3.  DRIP Manifest Format  . . . . . . . . . . . . . . . .  11
       4.4.4.  DRIP Link Format  . . . . . . . . . . . . . . . . . .  13
   5.  Transport Methods & Recommendations . . . . . . . . . . . . .  13
     5.1.  Legacy Advertisements (Bluetooth 4.X) . . . . . . . . . .  13
     5.2.  Extended Advertisements (Bluetooth 5.X, WiFi NaN, WiFi
           Beacon) . . . . . . . . . . . . . . . . . . . . . . . . .  14
     5.3.  DRIP Recommendations  . . . . . . . . . . . . . . . . . .  14
   6.  ICAO Considerations . . . . . . . . . . . . . . . . . . . . .  14
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  14
     8.1.  Manifest Hash Length  . . . . . . . . . . . . . . . . . .  15
     8.2.  Replay Attacks  . . . . . . . . . . . . . . . . . . . . .  15
     8.3.  Trust Timestamp Offsets . . . . . . . . . . . . . . . . .  16
   9.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  16
   10. Appendix A: Thoughts on ASTM Authentication Message . . . . .  16
   11. Appendix B: DRIP Attestations . . . . . . . . . . . . . . . .  17
     11.1.  Self-Attestation (Axx) . . . . . . . . . . . . . . . . .  17
     11.2.  Attestation (Axy)  . . . . . . . . . . . . . . . . . . .  18
     11.3.  Concise Attestation (C-Axy)  . . . . . . . . . . . . . .  19
     11.4.  Mutual Attestation (M-Axy) . . . . . . . . . . . . . . .  20
     11.5.  Link Attestation (L-Axy) . . . . . . . . . . . . . . . .  21



Wiethuechter, et al.    Expires 20 December 2021                [Page 2]


Internet-Draft                auth-formats                     June 2021


     11.6.  Broadcast Attestation (B-Axy)  . . . . . . . . . . . . .  22
     11.7.  Link Certificate (L-Cxy) . . . . . . . . . . . . . . . .  24
     11.8.  Mutual Certificate (M-Cxy) . . . . . . . . . . . . . . .  24
     11.9.  Example Registration with Attestation  . . . . . . . . .  25
   12. Appendix C: DRIP Broadcast Attestation Structure  . . . . . .  26
     12.1.  Attestor Hierarchical Host Identity Tag  . . . . . . . .  27
     12.2.  Attestation Data . . . . . . . . . . . . . . . . . . . .  27
     12.3.  Trust Timestamp  . . . . . . . . . . . . . . . . . . . .  27
     12.4.  Signing Timestamp  . . . . . . . . . . . . . . . . . . .  27
     12.5.  Attestor Signature . . . . . . . . . . . . . . . . . . .  28
   13. Appendix D: Forward Error Correction  . . . . . . . . . . . .  28
     13.1.  Encoding . . . . . . . . . . . . . . . . . . . . . . . .  28
       13.1.1.  Single Page FEC  . . . . . . . . . . . . . . . . . .  28
       13.1.2.  Multi Page FEC . . . . . . . . . . . . . . . . . . .  29
     13.2.  Decoding . . . . . . . . . . . . . . . . . . . . . . . .  29
       13.2.1.  Single Page FEC  . . . . . . . . . . . . . . . . . .  29
       13.2.2.  Multi Page FEC . . . . . . . . . . . . . . . . . . .  29
     13.3.  FEC Limitations  . . . . . . . . . . . . . . . . . . . .  29
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  29
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  29
     14.2.  Informative References . . . . . . . . . . . . . . . . .  30
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  30

1.  Introduction

   UA Systems (UAS) are usually in a volatile environment when it comes
   to communication.  UA are generally small with little computational
   (or flying) horsepower to carry standard communication equipment.
   This limits the mediums of communication to few viable options.

   Observer systems (e.g. smartphones and tablets) place further
   constraints on the communication options.  The Remote ID Broadcast
   messages MUST be available to applications on these platforms without
   modifying the devices.

   The ASTM standard [F3411-19] focuses on two ways of communicating to
   a UAS for RID: Broadcast and Network.

   This document will focus on adding trust to Broadcast RID in the
   current (and an expanded) Authentication Message format.

1.1.  DRIP Requirements Addressed

   The following [drip-requirements] will be addressed:

   GEN 1: Provable Ownership  This will be addressed using the DRIP
      Link.




Wiethuechter, et al.    Expires 20 December 2021                [Page 3]


Internet-Draft                auth-formats                     June 2021


   GEN 2: Provable Binding  This requirement is addressed using the DRIP
      Link, Manifest.

   GEN 3: Provable Registration  This requirement is addressed using the
      DRIP Link.

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

   See [drip-requirements] for common DRIP terms.

   Aircraft:  In this document whenever the word Aircraft is used it is
      referring to an Unmanned Aircraft (UA) not a Manned Aircraft.

3.  Background

3.1.  Problem Space and Focus

   The current standard for Remote ID (RID) does not, in any meaningful
   capacity, address the concerns of trust in the UA space with
   communication in the Broadcast RID environment.  This is a
   requirement that will need to be addressed eventually for various
   different parties that have a stake in the UA industry.

   The following subsections will provide a high level reference to the
   ASTM standard for Authentication Messages and how their current
   limitations effect trust in the Broadcast RID environment.

3.2.  Reasoning for IETF DRIP Authentication

   The ASTM Authentication Message has provisions in [F3411-19] to allow
   for other organizations to define (and standardize) Authentication
   formats.  The standardization of special 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.  No
   existing formats (defined by ASTM or others) was flexible enough to
   satisfy this goal resulting in the work reflected in this document.





Wiethuechter, et al.    Expires 20 December 2021                [Page 4]


Internet-Draft                auth-formats                     June 2021


3.3.  ASTM Authentication Message

     Page 0:
      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
     +---------------+-----------------------------------------------+
     |  Auth Header  |                                               |
     +---------------+  ASTM Authentication Headers  +---------------+
     |                                               |               |
     +-----------------------------------------------+               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                Authentication Data / Signature                |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------------------------------------------------------+

     Page 1 - 15:
      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
     +---------------+-----------------------------------------------+
     |  Auth Header  |                                               |
     +---------------+                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                Authentication Data / Signature                |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------------------------------------------------------+

     Auth Header (1 byte):
         Contains Authentication Type (AuthType) and Page Number.

     ASTM Authentication Headers: (6 bytes)
         Contains other header information for the Authentication
         Message from ASTM UAS RID Standard.

     Authentication Data / Signature: (0 to 255 bytes)
         Opaque authentication data.

           Figure 1: Standard ASTM Authentication Message format




Wiethuechter, et al.    Expires 20 December 2021                [Page 5]


Internet-Draft                auth-formats                     June 2021


   The above diagram is the format defined by ASTM [F3411-19] that is
   the frame which everything this document fits into.  The specific
   details of the ASTM headers are abstracted away as they are not
   necessarily required for this document.

   There is a 25th byte exclude in the diagrams that comes before the
   Auth Header.  This is the ASTM Header and consists of the Protocol
   Version and Message Type of the given message frame/page.

4.  DRIP Authentication Formats

   To keep consistent formatting across the different mediums (Bluetooth
   4, Bluetooth 5 and WiFi NaN) and their independent restrictions the
   authentication data being sent is REQUIRED to fit within the first 9
   pages (Page 0 through Page 8) of the Authentication Message (giving a
   max of 201 bytes).  The rest of the pages of the message is reserved
   exclusively for Forward Error Correction bytes and is only present on
   Bluetooth 4.

4.1.  UAS ID Signature

   The existing ASTM [F3411-19] Authentication Type 0x1 can be used to
   send a fresh Self-Attestation of the UA over 7 pages.




























Wiethuechter, et al.    Expires 20 December 2021                [Page 6]


Internet-Draft                auth-formats                     June 2021


      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 Hierarchical                        |
     |                       Host Identity Tag                       |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                        UA Host Identity                       |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                         Trust Timestamp                       |
     +---------------+---------------+---------------+---------------+
     |                        Signing Timestamp                      |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                          UA Signature                         |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

                      Figure 2: DRIP UAS ID Signature

4.2.  Operator ID Signature

   The existing ASTM [F3411-19] Authentication Type 0x2 can be used to
   send a static Self-Attestation of the Operator over 7 pages.






Wiethuechter, et al.    Expires 20 December 2021                [Page 7]


Internet-Draft                auth-formats                     June 2021


      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                     Operator Hierarchical                     |
     |                       Host Identity Tag                       |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                     Operator Host Identity                    |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                         Trust Timestamp                       |
     +---------------+---------------+---------------+---------------+
     |                        Signing Timestamp                      |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                       Operator Signature                      |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

                    Figure 3: DRIP Operator ID Signature

4.3.  Message Set Signature

   When running under Extended Advertisements, the existing ASTM
   [F3411-19] Authentication Type 0x3 can be used to sign over the
   adjacent ASTM Messages in the Message Pack (0xF).





Wiethuechter, et al.    Expires 20 December 2021                [Page 8]


Internet-Draft                auth-formats                     June 2021


   The concatenation of all messages in the Message Pack (excluding
   Authentication) before signing MUST be in Message Type order and be
   placed between the UA HHIT and Signing Timestamp field.

      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 Hierarchical                        |
     |                       Host Identity Tag                       |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                         Trust Timestamp                       |
     +---------------+---------------+---------------+---------------+
     |                        Signing Timestamp                      |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                          UA Signature                         |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

                    Figure 4: DRIP Message Set Signature

4.4.  Specific Method

   Under Specific Method (Authentication Type 0x5) is where the main set
   of DRIP Authentication Formats are defined.  These formats unlike the
   previous ones are more well defined and can include Forward Error
   Correction data.

4.4.1.  DRIP Frame Format

   This is specified when the SAM ID is DRIP Frame.  It is encapsulated
   by the ASTM Authentication Message (Section 3.3) and fills the
   Authentication Data / Signature field in Figure 1.



Wiethuechter, et al.    Expires 20 December 2021                [Page 9]


Internet-Draft                auth-formats                     June 2021


      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 ID     |                                               |
     +---------------+                                               |
     .                                                               .
     .                    DRIP Authentication Data                   .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                     Forward Error Correction                  .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+

     SAM ID (1 byte):
         The SAM ID (Specific Authentication Method ID) is
         defined by ASTM under AuthType 0x5 and values allocated
         by ICAO.

         For DRIP there are four SAM IDs allocated:

             SAM ID                       | Value
             -----------------------------+-------
             DRIP Frame                   | 0
             DRIP Wrapper                 | 1
             DRIP Manifest                | 2
             DRIP Link                    | 3

     DRIP Authentication Data (0 to 200 bytes):
         DRIP Authentication data.

     Forward Error Correction (0 to 161 bytes):
         Forward Error Correction data.

                        Figure 5: DRIP Frame Format

4.4.1.1.  Specific Authentication Method ID (SAM ID)

   Defined by ASTM (only under AuthType 0x5), values are allocated by
   ICAO.  For DRIP there are four SAM IDs: DRIP Frame, DRIP Wrapper,
   DRIP Manifest and DRIP Link.







Wiethuechter, et al.    Expires 20 December 2021               [Page 10]


Internet-Draft                auth-formats                     June 2021


4.4.1.2.  DRIP Authentication Data

   This field has a maximum size of 200 bytes.  If the data is less than
   the max and a page is only partially filled then the rest of the
   partially filled page must be null padded.  Note that the Length
   field in the Authentication Message is set to the length of the DRIP
   Authentication Data and MUST NOT include the Forward Error
   Correction.

   When possible the DRIP Broadcast Attestation Structure (Section 12)
   should be used in this space.

4.4.1.3.  Forward Error Correction

   This field has a maximum size of 161 bytes and SHOULD be page aligned
   at start.  The number of pages present after the data indicate the
   FEC scheme.  When a single page of FEC is present an XOR operation
   MUST be used.  When there are multiple pages of FEC (2 or more) a
   Reed Solomon method MUST be used.

   See Section 13 for more.

4.4.2.  DRIP Wrapper Format

   This is specified when the SAM ID is DRIP Wrapper.  It is
   encapsulated by the DRIP Frame (Section 4.4.1) and Broadcast
   Attestation Structure (Section 12); filling the Attestation Data
   (Section 12.2) field with full (25-byte) ASTM Messages.  The minimum
   number of ASTM Messages being 1 (Editors Note: Is this minimum 1 or
   0?) and the max being 4.  The encapsulated ASTM Messages MUST be in
   Message Type order as defined by ASTM.  All message types except
   Authentication (0x2) and Message Pack (0xF) are allowed.

   To determine the number of messages wrapped the receiver can check
   that the length of the Attestation Data (Section 12.2) field of the
   DRIP Broadcast Attestation (Section 12) is a multiple of 25-bytes.

4.4.2.1.  Wrapper Limitations

   TODO

4.4.3.  DRIP Manifest Format

   This format is specified when SAM ID is set to DRIP Manifest.  It is
   encapsulated by the DRIP Frame (Section 4.4.1) and Broadcast
   Attestation Structure (Section 12); filling the Attestation Data
   (Section 12.2) field with 8-byte hashes of previous ASTM Messages.




Wiethuechter, et al.    Expires 20 December 2021               [Page 11]


Internet-Draft                auth-formats                     June 2021


   By hashing previously sent messages and signing them we gain trust in
   UAs previous reports.  An observer who has been listening for any
   considerable length of time can hash received messages and cross
   check against listed hashes.  This is a way to evade the limitation
   of a maximum of 4 messages in the Wrapper Format and reduce overhead.

   (Editors Note: Manifests MUST NOT be of a length multiple of 25-bytes
   or 48-bytes.)

4.4.3.1.  Hash Algorithms and Operation

   The hash algorithm used for the Manifest Message is the same hash
   algorithm used in creation of the HHIT that is signing the Manifest.

   A standard HHIT would be using cSHAKE128 from [NIST.SP.800-185].
   With cSHAKE128, the hash is computed as follows:

   cSHAKE128(Message, 128, "", "Remote ID Auth Hash")

4.4.3.2.  Pseudo-Blockchain Hashes

   Two special hashes are included in all Manifest messages; a previous
   manifest hash, which links to the previous manifest message, as well
   as a 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.

   Creation:  During creation and signing of this message format this
      field MUST be set to 0.  So the signature will be based on this
      field being 0, as well as its own hash.  It is an open question of
      if we compute the hash, then sign or sign then compute.

   Cycling:  There a few different ways to cycle this message.  We can
      "roll up" the hash of 'current' to 'previous' when needed or to
      completely recompute the hash.  This mostly depends on the
      previous note.

4.4.3.3.  Manifest Limitations

   A potential limitation to this format is dwell time of the UA.  If
   the UA is not sticking to a general area then most likely the
   Observer will not obtain many (if not all) of the messages in the
   manifest.  Without the original messages received no verification can
   be done.  Examples of such scenarios include delivery or survey UA.

   Another limitation is the length of hash, which is discussed in
   Section 8.




Wiethuechter, et al.    Expires 20 December 2021               [Page 12]


Internet-Draft                auth-formats                     June 2021


4.4.4.  DRIP Link Format

   This format is specified when SAM ID is set to DRIP Link.  It is
   encapsulated by the DRIP Frame (Section 4.4.1) and Broadcast
   Attestation Structure (Section 12) but the attestation has already
   taken place, thus the UA need not dynamically sign the structure.

   See Broadcast Attestation as defined in [drip-rid] and Section 11.6.

4.4.4.1.  Link Limitations

   TODO

5.  Transport Methods & Recommendations

5.1.  Legacy Advertisements (Bluetooth 4.X)

   With Legacy Advertisements the goal is to attempt to bring reliable
   receipt of the paged Authentication Message.  Forward Error
   Correction (Section 4.4.1.3) MUST be enabled when using Legacy
   Advertising methods (such as Bluetooth 4.X).

   Under ASTM Bluetooth 4.X rules, transmission of dynamic messages are
   at least every 1 second while static messages (which is what
   Authentication is classified under) are sent at least every 3
   seconds.

   Under DRIP the Certificate Message MUST be transmitted to properly
   meet the GEN 1 and GEN 3 requirement.

   The ASTM Message Wrapper and Manifest both satisfy the GEN 2
   requirement.  At least one MUST be implemented to comply with the GEN
   2 requirement.

   A single Manifest can carry at most (using the full 10 page limit and
   8 byte hashes) 12 unique hashes of previously sent messages (of any
   type).  This results in a total of 22 (12 + 10) frames of Bluetooth
   data being transmitted over Bluetooth.

   In comparison the Message Wrapper sends 6 pages (each a single frame)
   for each wrapped message.  For backwards compatibility the
   implementation should also send the standard ASTM message that was
   wrapped for non-DRIP compliant receivers to obtain.  This method
   results in 84 total Bluetooth frames (12 + (12 * 6)) sent.

   The question of which is better suited is up to the implementation.





Wiethuechter, et al.    Expires 20 December 2021               [Page 13]


Internet-Draft                auth-formats                     June 2021


5.2.  Extended Advertisements (Bluetooth 5.X, WiFi NaN, WiFi Beacon)

   Under the ASTM specification, Bluetooth 5 or WiFi NaN transport of
   Remote ID is to use the Message Pack (Type 0xF) format for all
   transmissions.  Under Message Pack all messages are sent together (in
   Message Type order) in a single Bluetooth frame (up to 9 single frame
   equivalent messages).  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 Forward
   Error Correction (Section 4.4.1.3) MUST NOT be used as it is
   impractical.

5.3.  DRIP Recommendations

   For DRIP it is RECOMMENDED the following Authentication Formats are
   sent:

   1.  DRIP Link using the Broadcast Attestation of HID Root and the CAA

   2.  DRIP Link using the Broadcast Attestation of CAA and the USS

   3.  DRIP Link using the Broadcast Attestation of USS and the UA

   4.  Any other DRIP Authentication Format where the UA is dynamically
       signing data

6.  ICAO Considerations

   DRIP requests the following SAM IDs to be allocated:

   1.  DRIP Frame

   2.  DRIP Wrapper

   3.  DRIP Manifest

   4.  DRIP Link

7.  IANA Considerations

   This document does not require any actions by IANA.

8.  Security Considerations







Wiethuechter, et al.    Expires 20 December 2021               [Page 14]


Internet-Draft                auth-formats                     June 2021


8.1.  Manifest Hash Length

   For DRIP Manifest an 8-byte hash length has been selected by the
   authors for a number of reasons.

   1.  Hash lengths smaller than 8-bytes (for example 4-bytes) were
       originally contemplated but ruled out by comments by various
       cryptographers.  The main concern raised in this forum was that
       the length of hash would not provide strong resistance against
       collision rate.  The authors also after further review agreed
       with this and also realized operationally it was not necessarily
       viable.  While 4-byte hashes would allow more messages to be
       filled into a single DRIP Manifest payload (up to 22 individual
       hashes) the length of time for the UA to stay in a single place
       where the Observer would receive all the originally messages to
       rehash to verify such a message was impractical.

   2.  Hash lengths larger than 8-bytes (for example 16-bytes) were also
       considered by the authors.  These got the approval of the
       cryptographers but the number of hashes to send became much lower
       (only 5 individual hashes).  While this lower number is a more
       reasonable number of original messages the Observer would have to
       capture it would also mean that potentially more DRIP Manifests
       would need to be sent.  Overall the increase length of the hash
       did not operationally justify the cost.

   3.  Simplifying the current design and locking it into using the same
       hash as the HHIT instead of allowing for agility in either hash
       algorithm or length seemed more realistic to the authors today.

8.2.  Replay Attacks

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

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

   2.  Under DRIP it is RECOMMENDED to send more than just DRIP Link
       messages, specifically those that sign over changing data using
       the current session keypair, and those messages are sent more
       frequently.  An aircraft beaconing these messages then actually
       signing other messages using the keypair validates the data



Wiethuechter, et al.    Expires 20 December 2021               [Page 15]


Internet-Draft                auth-formats                     June 2021


       receiver by an Observer.  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.

8.3.  Trust Timestamp Offsets

   Note the discussion of Trust Timestamp Offsets here is in context of
   the DRIP Wrapper (Section 4.4.2) and DRIP Manifest (Section 4.4.3)
   messages.  For DRIP Link (Section 4.4.4) messages these offsets are
   set by the Attestor (typically a registry) and have their own set of
   considerations as seen in (TODO: link to registry draft security
   considerations here).

   The offset of the Trust Timestamp (defined as a very short Expiration
   Timestamp) 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.

9.  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 WiFi protocols would not 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) - this drove the requirement for max page
   length of Authentication Data itself.

10.  Appendix A: Thoughts on ASTM Authentication Message

   (Editor Note: is this valid anymore to keep?)

   The format standardized by the ASTM is designed with a few major
   considerations in mind, which the authors of this document feel put
   significant limitations on the expansion of the standard.

   The primary consideration (in this context) is the use of the
   Bluetooth 5.X Extended Frame format.  This method allows for a 255
   byte payload to be sent in what the ASTM refers to as a "Message
   Pack".






Wiethuechter, et al.    Expires 20 December 2021               [Page 16]


Internet-Draft                auth-formats                     June 2021


   The idea is to include up to five standard ASTM Broadcast RID
   messages (each of which are 25 bytes) plus a single authentication
   message (5 pages of 25 bytes each) in the Message Pack.  The
   reasoning is then the Authentication Message is for the entire
   Message Pack.

   The authors have no issues with this proposed approach; this is a
   valid format to use for the Authentication Message provided by the
   ASTM.  However, by limiting the Authentication Message to ONLY five
   pages in the standard it ignores the possibility of other formatting
   options to be created and used.

   Another issue with this format, not fully addressed in this document
   is fragmentation.  Under Bluetooth 4.X, each page is sent separately
   which can result in lose of pages on the receiver.  This is
   disastrous as the loss of even a single page means any signature is
   incomplete.

   With the current limitation of 5 pages, Forward Error Correction
   (FEC) is nearly impossible without sacrificing the amount of data
   sent.  More pages would allow FEC to be performed on the
   Authentication Message pages so loss of pages can be mitigated.

   All these problems are further amplified by the speed at which UA fly
   and the Observer's position to receive transmissions.  There is no
   guarantee that the Observer will receive all the pages of even a 5
   page Authentication Message in the time it takes a UA to traverse
   across their line of sight.  Worse still is that is not including
   other UA in the area, which congests the spectrum and could cause
   further confusion attempting to collate messages from various UA.
   This specific problem is out of scope for this document and our
   solutions in general, but should be noted as a design consideration.

11.  Appendix B: DRIP Attestations

11.1.  Self-Attestation (Axx)















Wiethuechter, et al.    Expires 20 December 2021               [Page 17]


Internet-Draft                auth-formats                     June 2021


      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                          Hierarchical                         |
     |                       Host Identity Tag                       |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                          Host Identity                        |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                         Trust Timestamp                       |
     +---------------+---------------+---------------+---------------+
     |                        Signing Timestamp                      |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                            Signature                          |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Length = 120-bytes

                      Figure 6: DRIP Self-Attestation

11.2.  Attestation (Axy)







Wiethuechter, et al.    Expires 20 December 2021               [Page 18]


Internet-Draft                auth-formats                     June 2021


      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                              Axx                              .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                              Ayy                              .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                      Trust Timestamp by X                     |
     +---------------+---------------+---------------+---------------+
     |                     Signing Timestamp by X                    |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                         Signature by X                        |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Length = 312-bytes

                         Figure 7: DRIP Attestation

11.3.  Concise Attestation (C-Axy)









Wiethuechter, et al.    Expires 20 December 2021               [Page 19]


Internet-Draft                auth-formats                     June 2021


      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                          Hierarchical                         |
     |                    Host Identity Tag of X                     |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                          Hierarchical                         |
     |                    Host Identity Tag of Y                     |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                      Trust Timestamp by X                     |
     +---------------+---------------+---------------+---------------+
     |                     Signing Timestamp by X                    |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                         Signature by X                        |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Length = 104-bytes

                     Figure 8: DRIP Concise Attestation

11.4.  Mutual Attestation (M-Axy)











Wiethuechter, et al.    Expires 20 December 2021               [Page 20]


Internet-Draft                auth-formats                     June 2021


      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                              Axy                              .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                      Trust Timestamp by Y                     |
     +---------------+---------------+---------------+---------------+
     |                     Signing Timestamp by Y                    |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                         Signature by Y                        |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Length = 384-bytes

                     Figure 9: DRIP Mutual Attestation

11.5.  Link Attestation (L-Axy)















Wiethuechter, et al.    Expires 20 December 2021               [Page 21]


Internet-Draft                auth-formats                     June 2021


      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                             C-Axy                             .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                      Trust Timestamp by Y                     |
     +---------------+---------------+---------------+---------------+
     |                     Signing Timestamp by Y                    |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                         Signature by Y                        |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Length = 176-bytes

                      Figure 10: DRIP Link Attestation

11.6.  Broadcast Attestation (B-Axy)















Wiethuechter, et al.    Expires 20 December 2021               [Page 22]


Internet-Draft                auth-formats                     June 2021


      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                          Hierarchical                         |
     |                    Host Identity Tag of X                     |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                          Hierarchical                         |
     |                    Host Identity Tag of Y                     |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                       Host Identity of Y                      |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                      Trust Timestamp by X                     |
     +---------------+---------------+---------------+---------------+
     |                     Signing Timestamp by X                    |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                         Signature by X                        |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Length = 136-bytes

                   Figure 11: DRIP Broadcast Attestation




Wiethuechter, et al.    Expires 20 December 2021               [Page 23]


Internet-Draft                auth-formats                     June 2021


11.7.  Link Certificate (L-Cxy)

      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                          Hierarchical                         |
     |                    Host Identity Tag of Z                     |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                             L-Axy                             .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                      Trust Timestamp by Z                     |
     +---------------+---------------+---------------+---------------+
     |                     Signing Timestamp by Z                    |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                         Signature by Z                        |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Length = 264-bytes

                      Figure 12: DRIP Link Certificate

11.8.  Mutual Certificate (M-Cxy)








Wiethuechter, et al.    Expires 20 December 2021               [Page 24]


Internet-Draft                auth-formats                     June 2021


      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                              Azz                              .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                             M-Axy                             .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                      Trust Timestamp by Z                     |
     +---------------+---------------+---------------+---------------+
     |                     Signing Timestamp by Z                    |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                         Signature by Z                        |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+

     Length = 264-bytes

                     Figure 13: DRIP Mutual Certificate

11.9.  Example Registration with Attestation

   1.  X generates Axx and Y generates Ayy

   2.  Y sends Ayy to X





Wiethuechter, et al.    Expires 20 December 2021               [Page 25]


Internet-Draft                auth-formats                     June 2021


   3.  X verified Ayy; composes Axy, C-Axy, B-Axy; sends Axy, C-Axy,
       B-Axy and B-Axy's from parents

   4.  Y composes M-Axy and L-Axy

   5.  Y broadcasts B-Axy's

12.  Appendix C: DRIP Broadcast Attestation Structure

   When possible the following format should be used in the DRIP
   Authentication Data (Section 4.4.1.2) field.

      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
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                      Attestor Hierarchical                    |
     |                       Host Identity Tag                       |
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     .                                                               .
     .                        Attestation Data                       .
     .                                                               .
     |                                                               |
     +---------------+---------------+---------------+---------------+
     |                         Trust Timestamp                       |
     +---------------+---------------+---------------+---------------+
     |                        Signing Timestamp                      |
     +---------------+---------------+---------------+---------------+
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                        Attestor Signature                     |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     |                                                               |
     +---------------+---------------+---------------+---------------+




Wiethuechter, et al.    Expires 20 December 2021               [Page 26]


Internet-Draft                auth-formats                     June 2021


     Attestor Hierarchial Host Identity Tag (16 bytes):
         The Attestors HHIT in byte form (network byte order).

     Attestation Data (0 to 112 bytes):
         Opaque attestation data.

     Trust Timestamp (4 bytes):
         Timestamp denoting recommended time to trust data to.

     Signing Timestamp (4 bytes):
         Current time at signing.

     Attestor Signature (64 bytes):
         Signature over preceding fields using the keypair of
         the Attestor.

            Figure 14: DRIP Broadcast Attestation Data Structure

12.1.  Attestor Hierarchical Host Identity Tag

   The HHIT is an enhancement of the Host Identity Tag (HIT) [RFC7401]
   introducing hierarchy and how they are used in UAS RID as defined in
   [drip-rid].

12.2.  Attestation Data

   This field has a maximum of 112 bytes in length.  It is nominally
   filled with data as defined by the SAM ID being set or other sub-
   multiplexer in the authentication payload.

12.3.  Trust Timestamp

   The Trust Timestamp is of the format defined in [F3411-19].  That is
   a UNIX timestamp offset by 01/01/2019 00:00:00.  An additional offset
   is then added to push the timestamp a short time into the future to
   avoid replay attacks.

   The offset used against the UNIX timestamp is not defined in this
   document.  Best practices to identify a acceptable offset should be
   used taking into consideration the UA environment, and propagation
   characteristics of the messages being sent.

12.4.  Signing Timestamp

   Follows the format defined in [F3411-19].  That is a UNIX timestamp
   offset by 01/01/2019 00:00:00.





Wiethuechter, et al.    Expires 20 December 2021               [Page 27]


Internet-Draft                auth-formats                     June 2021


12.5.  Attestor Signature

   The signature is generated over all the preceding data.  ASTM/DRIP
   Headers are exclude from this operation only information within the
   Broadcast Attestation Structure (Section 12) is signed.

13.  Appendix D: Forward Error Correction

   (Editors Note: move specifics of FEC (everything below) into its own
   draft for titled Integrity Protection)

   Remote ID data can be sent across many different broadcast link
   media, all with different characteristics.  To enable robustness in
   Remote ID transmission media that has Forward Error Correction
   capability SHOULD be used.

   In cases where FEC is not available below the equivalent of the
   transport layer (known as Legacy Advertisements) DRIP Authentication
   REQUIRES that an application level FEC scheme is used.  In cases
   where FEC is available below the equivalent of the transport layer
   (known as Extended Advertisements) DRIP MUST NOT use any application
   level FEC and instead SHALL rely on the lower layers FEC
   functionality.

   For current Remote ID the media options are the following:

   Legacy Advertisements:  Bluetooth 4.X

   Extended Advertisements:  WiFi NAN, WiFi Beacon, Bluetooth 5.X

   (Editors Note: add in self-protecting and more-than-self-protecting
   options, with their justifications)

13.1.  Encoding

13.1.1.  Single Page FEC

   When generating the parity the first byte of every Authentication
   Page MUST be exclude from the XOR operation.  For pages 1 through N
   this leaves the data portion of the page while page 0 will include a
   number of headers along with 17 bytes of data.

   To generate the parity a simple XOR operation using the previous and
   current page is used.  For page 0, a 23 byte null pad is used for the
   previous page.  The resulting 23 bytes of parity is appended in one
   full page (always the last) allowing for recovery when any single
   page is lost in transmission.




Wiethuechter, et al.    Expires 20 December 2021               [Page 28]


Internet-Draft                auth-formats                     June 2021


13.1.2.  Multi Page FEC

   TODO (Reed Solomon)

13.2.  Decoding

   Due to the nature of Bluetooth 4 and the existing ASTM paging
   structure an optimization can be used.  If a Bluetooth frame fails
   its CRC check, then the frame is dropped without notification to the
   upper protocol layers.  From the Remote ID perspective this means the
   loss of a complete frame/message/page.  In Authentication Messages,
   each page is already numbered so the loss of a page allows the
   receiving application to build a "dummy" page filling the
   Authentication Data field (and ASTM Authentication Headers fields if
   page 0) with nulls.

   If page 0 is being reconstructed an additional check of the Page
   Count, to check against how many pages are actually present, MUST be
   performed for sanity.  An additional check on the Data Length field
   SHOULD also be performed.

13.2.1.  Single Page FEC

   Using the same methods as encoding, an XOR operation is used between
   the previous and current page (a 23 byte null pad is used when page 0
   is the current page).  The resulting 23 bytes is the data of the
   missing page.

13.2.2.  Multi Page FEC

   TODO (Reed Solomon)

13.3.  FEC Limitations

   If more than one page is lost (>1/5 for 5 page messages, >1/10 for 10
   page messages) than the error rate of the link is already beyond
   saving and the application has more issues to deal with.

   (Editors Note: Is this valid anymore, for XOR yes but for multi-page
   FEC?)

14.  References

14.1.  Normative References

   [F3411-19] "Standard Specification for Remote ID and Tracking",
              February 2020.




Wiethuechter, et al.    Expires 20 December 2021               [Page 29]


Internet-Draft                auth-formats                     June 2021


   [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>.

14.2.  Informative References

   [drip-requirements]
              Card, S. W., Wiethuechter, A., Moskowitz, R., and A.
              Gurtov, "Drone Remote Identification Protocol (DRIP)
              Requirements", Work in Progress, Internet-Draft, draft-
              ietf-drip-reqs-13, 14 June 2021,
              <https://www.ietf.org/archive/id/draft-ietf-drip-reqs-
              13.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>.

   [identity-claims]
              Wiethuechter, A., Card, S., and R. Moskowitz, "DRIP
              Identity Claims", Work in Progress, Internet-Draft, draft-
              wiethuechter-drip-identity-claims-03, 2 November 2020,
              <https://www.ietf.org/archive/id/draft-wiethuechter-drip-
              identity-claims-03.txt>.

   [RFC7401]  Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
              Henderson, "Host Identity Protocol Version 2 (HIPv2)",
              RFC 7401, DOI 10.17487/RFC7401, April 2015,
              <https://www.rfc-editor.org/info/rfc7401>.

Authors' Addresses





Wiethuechter, et al.    Expires 20 December 2021               [Page 30]


Internet-Draft                auth-formats                     June 2021


   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

   Email: rgm@labs.htt-consult.com



























Wiethuechter, et al.    Expires 20 December 2021               [Page 31]