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Versions: (draft-wiethuechter-tmrid-auth) 00

DRIP                                                     A. Wiethuechter
Internet-Draft                                                   S. Card
Intended status: Standards Track                           AX Enterprize
Expires: 24 September 2020                                  R. Moskowitz
                                                          HTT Consulting
                                                           23 March 2020


                      DRIP Authentication Formats
                    draft-wiethuechter-drip-auth-00

Abstract

   This document describes how to include trust into the ASTM Remote ID
   specification defined in ASTM3411 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 24 September 2020.

Copyright Notice

   Copyright (c) 2020 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.
   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



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   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terms and Definitions . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Terminology  . . . . . . . . . . . . . . . .   3
     2.2.  Definitions . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Problem Space And Document Focus  . . . . . . . . . . . .   4
     3.2.  ASTM Authentication Message . . . . . . . . . . . . . . .   4
     3.3.  Thoughts on ASTM Authentication Message . . . . . . . . .   6
   4.  HIP Based Extensions to the ASTM Authentication Message . . .   7
     4.1.  Message Wrapper . . . . . . . . . . . . . . . . . . . . .   7
       4.1.1.  Inner Header  . . . . . . . . . . . . . . . . . . . .   9
       4.1.2.  Trust Timestamp . . . . . . . . . . . . . . . . . . .  10
       4.1.3.  Payload . . . . . . . . . . . . . . . . . . . . . . .  10
       4.1.4.  Forward Error Correction  . . . . . . . . . . . . . .  10
     4.2.  Signed Hash Lists . . . . . . . . . . . . . . . . . . . .  12
       4.2.1.  Hash Operation  . . . . . . . . . . . . . . . . . . .  15
       4.2.2.  Pseudo-blockchain Hashes  . . . . . . . . . . . . . .  15
       4.2.3.  Limitations . . . . . . . . . . . . . . . . . . . . .  16
     4.3.  Offline Claim . . . . . . . . . . . . . . . . . . . . . .  16
       4.3.1.  Claim: Registry on Aircraft . . . . . . . . . . . . .  17
       4.3.2.  Foward Error Correction . . . . . . . . . . . . . . .  22
   5.  Example Use Cases . . . . . . . . . . . . . . . . . . . . . .  22
     5.1.  Trusted Messages  . . . . . . . . . . . . . . . . . . . .  22
     5.2.  Wrapped Signed Hashes . . . . . . . . . . . . . . . . . .  24
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  26
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  27
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  27
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  28

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.



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   The ASTM standard 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 authentication message format, using the Host Identity
   Protocol Version 2 (HIPv2) [RFC7401] Hierarchical HIT (HHIT)
   [I-D.moskowitz-hip-hierarchical-hit].

2.  Terms and Definitions

2.1.  Requirements 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

   HI
      Host Identity.  The public key portion of an assymetric keypair
      from HIP.  In this document it is assumed that the HI is based on
      a EdDSA25519 keypair.  This is supported by new crypto defined in
      [I-D.moskowitz-hip-new-crypto].

   HIT
      Host Identity Tag. A 128 bit handle on the HI.  Defined in HIPv2
      [RFC7401].

   HHIT
      Hierarchical Host Identity Tag. A 128 bit handle on the HI contain
      extra information not found in a standard HIT.  Defined in
      [I-D.moskowitz-hip-hierarchical-hit].

   UA
      Unmanned Aircraft.  In this document UA's are typically though of
      as drones of commerical or military variety.  This is a very
      strict definition which can be relaxed to include any and all
      aircraft that are unmanned.

   UAS
      Unmanned Aircraft System.  Composed of Unmanned Aircraft and all
      required on-board subsystems, payload, control station, other
      required off-board subsystems, any required launch and recovery
      equipment, all required crew members, and C2 links between UA and
      the control station.




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   RID
      Remote ID.  A unique identifier found on all UA to be used in
      communication and in regulation of UA operation.

   Observer
      Referred to in other UAS documents as a "user", but there are also
      other classes of RID users, so we prefer "observer" to denote an
      individual who has observed an UA and wishes to know something
      about it, starting with its RID.

3.  Background

3.1.  Problem Space And Document 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 envirorment.

3.2.  ASTM Authentication Message


























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   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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+  ASTM Authentication Headers  +---------------+
   |                                               |               |
   +-----------------------------------------------+               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                Authentication Data / Signature                |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 1 - 4:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                Authentication Data / Signature                |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   ASTM Header (1 byte):
           Contains basic ASTM information such as message type and
           protocol version.

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

   Authentication Data / Signature: (109 bytes: 17+23*4)
       Opaque authentication data.

   The above diagram is the format defined by ASTM that is the frame
   which everything this document fits into.  The specific details of




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   the ASTM headers are abstracted away as they are not necessarily
   required for this document.

3.3.  Thoughts on ASTM Authentication Message

   The format standardized by the ASTM is designed with a few major
   considerations in mind, which the authors 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".

   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 seperately
   which can result in lose of pages on the reciever.  This is
   disasterous 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 Authentation
   message pages so loss of pages can be mitigated.

   All these problems are further amplified by the speed at which UA fly
   and the Oberserver's position to recieve transmissions.  There is no
   guarentee that the Observer will recieve 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 congestes 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.





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4.  HIP Based Extensions to the ASTM Authentication Message

   The following section describes various methods that HIP can help
   enable more trustworthy communication using the Authentication
   Message as the base.  Each diagram will show all pages of the format
   filled out.

   In the future it is probably necessary to have a AuthType assigned by
   ASTM for DRIP related authentication message formats.  How this is
   accomplished and how it extends if more formats are proposed is still
   TBD.

4.1.  Message Wrapper

   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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+  ASTM Authentication Headers  +---------------+
   |                                               |  Inner Header |
   +-----------------------------------------------+---------------+
   |                                                               |
   |                                                               |
   |                                                               |
   |                             HHIT                              |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                 Trust Timestamp               /
   +---------------+-----------------------------------------------+
   /               |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                      Payload (Bytes 1-19)                     |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+




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   Page 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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |            Payload (Bytes 20-24)              /
   +---------------+               +-------------------------------+
   /                               |                               |
   +-------------------------------+                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                   HHIT Signature (Bytes 1-18)                 |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 3:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                   HHIT Signature (Bytes 19-41)                |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 4:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                   HHIT Signature (Bytes 42-64)                |
   |                                                               |
   |                                                               |
   |                                                               |



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   |                                                               |
   +---------------------------------------------------------------+

   Inner Header (1 byte):
           See Inner Header section.

   HHIT: (16 bytes)
       HHIT using the EdDSA25519 HI.

   Trust Timestamp: (4 bytes)
       Timestamp denoting current time plus an offset to trust
       message to.

   Payload: (24 bytes)
       Opaque payload data.

   HHIT Signature: (64 bytes)
       Signature over precedding fields using the EdDSA25519 keypair.

   When this authentication format is recieved the HHIT is first looked
   up in DNS by standard mechanisms to retrieve the HIP RR.  From this
   the HI can be used to perform signature verifiction.  The data signed
   is all the data preceding the 64 byte signature (excluding the ASTM
   Headers and ASTM Authentication Headers).

   When there is no Internet connectivity on the Observers device the HI
   of the UA can be obtained by referencing the claim sent in the
   Offline Based Authentication format, if sent by the UA.

4.1.1.  Inner Header

   When the payload is another ASTM message then the first byte of the
   full message should be used to fill in the Inner Header field.  This
   byte can be signed but is primarily for identitying the inner message
   type (for unpacking purposes if desired by the Observer device).

   Another use of the Inner Header byte is holding the H-Alg and H-Len
   fields if this format is used for Hashed Messages.  See Section 5.2
   for a detailed example of this.  When this format is used all 24
   bytes of the payload MUST be filled with hash values.  This
   requirement means that only even numbered hash lengths can be used.

   Any other wrapped messages that are not 24 bytes long and require
   padding on the payload MUST use the Inner Header to inform the
   reciever the length of payload in octets.

   To accomadate payload differences the use of AuthType in the ASTM
   Authentication Headers section SHOULD be set in the range of 0xA-F



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   (which is availible for Private Use).  Only recommended values are
   defined here, as the allocation in the reserved space of this header
   is controlled by ASTM.

       AuthType                            Values
       --------                            ------
       Wrapped ASTM Message                A
       Wrapped Hashes                      B
       Wrapped Message Length (octets)     C

4.1.2.  Trust Timestamp

   Trust Timestamp MUST be current UNIX time plus an offset into the
   future.

   To avoid replay attacks the Trust Timestamp field must be well
   founded.  When wrapping a vector (position) message the payload WILL
   contain (by ASTM rules) constantly changing data, this includes its
   own timestamp.  In this case the Trust Timestamp could be argued as
   superfoulous.

   Other message types, such as Basic ID and Self-ID are static messages
   with no changing data.  To protect a replay of these signed messages
   the Trust Timestamp is the field during signing to be guarenteed to
   change.

   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 envirorment, and propgation
   characteristics of the messages being sent.

4.1.3.  Payload

   The payload can be anything that fits within the 24 byte limit.  An
   example of what could be done with this format is found in
   Section 5.1.  If the payload is less than 24 bytes, null padding MUST
   be used to fill up to 24 bytes and the AuthType of 0xC MUST be used
   to identity message size.

4.1.4.  Forward Error Correction

   Due to the nature of the wireless link a FEC method is suggested.
   Under DRIP the Message Wrapper format has two forms of FEC that can
   be used.







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   Page 5:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                     Foward Error Correction                   |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

4.1.4.1.  Reed Solomon

   The prefered form of FEC is using Reed Solomon.  With this the entire
   authentication message (all pages, including headers) are used to
   generate 23 bytes of parity.  This parity is appended in one page
   allowing for recovery when any single page is lost in transmission.

4.1.4.2.  Exclusive Or

   This method of FEC is experimental and created by one of the authors
   during initial prototyping.  Note that this format of FEC requires a
   10-page authentication message, currently unsupported by ASTM.






















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   +--------------+                     +-----------------------------+
   | Page 0: Data |-------------------->| Page 1: XOR(Page 0, Page 2) |
   +--------------+----+    +---------->+-----------------------------+
                       |    |
                       |    |
   +--------------+----|----+           +-----------------------------+
   | Page 2: Data |----|--------------->| Page 3: XOR(Page 2, Page 4) |
   +--------------+    |     +--------->+-----------------------------+
                       |     |
                       |     |
   +--------------+----|-----+          +-----------------------------+
   | Page 4: Data |----|--------------->| Page 5: XOR(Page 4, Page 6) |
   +--------------+    |     +--------->+-----------------------------+
                       |     |
                       |     |
   +--------------+----|-----+          +-----------------------------+
   | Page 6: Data |----|--------------->| Page 7: XOR(Page 6, Page 8) |
   +--------------+    |     +--------->+-----------------------------+
                       |     |
                       +-----|-----+
   +--------------+----------+     |    +-----------------------------+
   | Page 8: Data |                +--->| Page 9: XOR(Page 8, Page 0) |
   +--------------+-------------------->+-----------------------------+

   The above illustration shows the relationship between the 10 page
   authentication message and the XOR operation performed.

   The advantage of this format is that a large percentage of the pages
   can be lost in transmission cand recovered using other pages
   recieved.

   The authors are well aware that this has a high overhead (100%) that
   might be avoided using other methods.  In some cases where wireless
   links are highly congested or weak this could potentionally prove
   useful.

4.2.  Signed Hash Lists

   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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+  ASTM Authentication Headers  +---------------+
   |                                               | H-Alg | H-Len |
   +---------------------------------------------------------------+
   |                Hash of Previous Auth. Message                 |
   +---------------------------------------------------------------+



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   |                Hash of Current Auth. Message                  |
   +---------------------------------------------------------------+
   |                          Message Hash                         |
   +---------------------------------------------------------------+
   |                          Message Hash                         |
   +---------------------------------------------------------------+

   Page 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
   +---------------+---------------+-------------------------------+
   |  ASTM Header  | H-Alg | H-Len |            PADDING            |
   +---------------+---------------+-------------------------------+
   |                          Message Hash                         |
   +---------------------------------------------------------------+
   |                          Message Hash                         |
   +---------------------------------------------------------------+
   |                          Message Hash                         |
   +---------------------------------------------------------------+
   |                          Message Hash                         |
   +---------------------------------------------------------------+
   |                          Message Hash                         |
   +---------------------------------------------------------------+

   Page 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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                    PADDING                    |
   +---------------+               +-------------------------------+
   |                               |                               |
   +-------------------------------+                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                         HHIT Signature                        |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 3:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |



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   |                                                               |
   |                                                               |
   |                                                               |
   |                         HHIT Signature                        |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 4:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                         HHIT Signature                        |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   H-Alg, H-Len: (4 bits), (4 bits)
       These are fields for relaying information of the Hash
       algorithm used for the messages and the Hash length (in octets).
       For this example of the format a length of 4 bytes is
       used.

       H-Alg       Values
       -----       ------
       RESERVED    0
       cSHAKE128   1 [SP800-185] (RECOMMENDED)

   Hash of Previous Auth. Message: (4 bytes)
       A hash of the previously sent Authentication message.

   Hash of Current Auth. Message: (4 bytes)
       A hash of the current Authentication message.

   Message Hash: (4 bytes)
       A hash of a previously sent message.

   HHIT Signature: (64 bytes)



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       EdDSA25519 signature using an EdDSA25519-based HI from HIP.

   This format is designed to provide provenance to Broadcast RID
   messages sent by a given UAS.  It should be noted that the HHIT is
   not provided in the format like others specified here - instead it
   must be obtained via the Basic ID Message in a detached fashion.

   By hashing previously sent messages and signing them we gain trust in
   UAS previous reports.  An observer who has been listening for any
   length of time can hash received messages and cross check against
   listed hashes.  The signature is signed across the list of hashes.

4.2.1.  Hash Operation

   With cSHAKE128 NIST SP 800-185 [NIST.SP.800-185], the hash is
   computed as follows:

        cSHAKE128(MAC|Message, 8*H-Len, "", "RemoteID Auth Hash")

   The message MAC is prepended to the message, as the MAC is the only
   information that links a UA's messages from a specific UA.

4.2.2.  Pseudo-blockchain Hashes

   Two special hashes are included; a previous authentication hash,
   which links to the previous signed hash list message, as well as a
   current hash.  This gives a pseudo-blockchain provenance to the
   authentication message that could be traced back if the observer was
   present for extended periods of time.

   In regards to the creation and use of the current authentication hash
   field:

      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.

      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.









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4.2.3.  Limitations

   With the current format proposed by ASTM only 7 messages can be
   hashed reasonably in the above format.  PADDING and redundant H-Alg,
   H-Len fields could be removed.  This would increase the total list of
   hashes to 9 while losing word alignment of the hashes in each page.

   To address this problem properly the authors feel that the
   Authentication Messages needs to have a max bound of 10 pages,
   instead of 5.

4.3.  Offline Claim

   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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+  ASTM Authentication Headers  +---------------+
   |                                               |               |
   +-----------------------------------------------+               |
   |                                                               |
   |                                                               |
   |                                                               |
   |           Claim: Registry on Aircraft (Bytes 1-17)            |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 1-8:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |           Claim: Registry on Aircraft (Bytes 18-200)          |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 9:



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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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                     Foward Error Correction                   |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Certificate: Registry on Aircraft (200 bytes):
           A certificate granted by the Registry that asserts the
           binding of UA to the given Registry. Note that Page 8's final
           byte is actually padding.

   Foward Error Correction (FEC) (23 bytes):
           FEC on the previous 9 pages.

   This specific format does not currently fit within the ASTM
   specification.  Requiring a minimum of 200 bytes, this would require
   the Authentication Message to have 10 pages, instead of the current 5
   page limit.  The rest of this section assumes 10 pages to demonstrate
   how this message is laid out and works.

   What this grants is the ability to authenticate UA information when
   the receiving device of the observer (e.g. a smartphone with a
   dedicated RID application) has no Internet service (e.g.  LTE
   signal).

   By including the device HI along with a signature from the registry
   the UA is under, we can assert trust of a given UA without requiring
   the need for immediate reverse lookups online.

4.3.1.  Claim: Registry on Aircraft

   The bulk of this message is made up with the 200 byte claim titled
   "Registry on Aircraft" (henceforth refered to as "Cra").  Below is
   Cra fully marked out inside the ASTM Authentication Message.







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   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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+  ASTM Authentication Headers  +---------------+
   |                                               |               |
   +-----------------------------------------------+               |
   |                                                               |
   |                                                               |
   |                          Registry HHIT                        |
   |                                                               |
   |                                                               |
   |                                               +---------------+
   |                                               |  UA HHIT (1)  |
   +-----------------------------------------------+---------------+

   Page 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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                         UA HHIT (2-16)                        |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+
   |                                                               |
   |                           UA HI (1-8)                         |
   |                                                               |
   +---------------------------------------------------------------+

   Page 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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                           UA HI (9-31)                        |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |



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   |                                                               |
   +---------------------------------------------------------------+

   Page 3:
    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 Header  |   UA HI (32)  |          UA Expiration        /
   +---------------+---------------+-------------------------------+
   /           Timestamp           |                               |
   +-------------------------------+                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                        UA Signature (1-18)                    |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 4:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                        UA Signature (19-41)                   |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 5:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                        UA Signature (42-64)                   |



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   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 6:
    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 Header  |         Registry Expiration Timestamp         /
   +---------------+-----------------------------------------------+
   /               |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                      Registry Signature (1-19)                |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 7:
    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                     Registry Signature (20-42)                |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 8:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |



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   |                                                               |
   |                                                               |
   |                     Registry Signature (43-64)                |
   |                                                               |
   |                                                               |
   |                                               +---------------+
   |                                               |    PADDING    |
   +-----------------------------------------------+---------------+

   Registry HHIT (16 bytes):
           Registry HHIT that UA is registered under and handle
           for the HI used in the signing of full certificate.

   Claim: Aircraft on Aircraft [Cra] (116 bytes):
           UA HHIT (16 bytes):
                   Nominally the Aircraft HHIT (specificed here as UA)

           UA HI (32 bytes):
                   Public half of EdDSA-25519 asymmetric keypair used
                   to sign Caa.

           UA Expiration Timestamp (4 bytes):
                   UNIX current time (at time of signing) + offset

           UA Signature (64 bytes):
                   Signature with UA keypair using the data of UA HHIT,
                   UA HI and UA Expiration Timestamp.

   Registry Expiration Timestamp (4 bytes):
           UNIX current time (at time of signing) + offset

   Registry Signature (64 bytes):
           Signature with Registry keypair using the data of
           Registry HHIT, Caa and Registry Expiration Timestamp.

   Cra is in practice a binding claim between the Registry and the
   Aircraft, asserting the relationship between the two entities.  Cra
   signs another claim, Caa (Claim: Aircraft on Aircraft), that is
   created during UA provisioning.

   Importantly this claim allows offline signature verification from the
   UA.  This is as the UA HI is included in the claim.  Also included is
   the HHIT of the Registry to check the local shortlist of Registries
   that the Observer device trusts (mapping HHITs to HIs).

   More details about Caa, Cra, other claims and the provisioning
   process can be found in [I-D.wiethuechter-tmrid-identity-claims].




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4.3.2.  Foward Error Correction

   Page 9:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                     Foward Error Correction                   |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   The prefered form of FEC is using Reed Solomon.  With this the entire
   authentication message (all pages, including headers) are used to
   generate 23 bytes of parity.  This parity is inserted into the final
   page of the Claim format for recovery when any single page is lost in
   transmission.

5.  Example Use Cases

   This section introduces potentional use cases of the HIP based
   extensions to the proposed ASTM standard authentication message.

5.1.  Trusted Messages

   Using the HIP Based Authentication Wrapper any single Broadcast RID
   message defined by ASTM can become what the authors refer to as a
   "Trusted Message".

   One specific use case that is useful in the UAS RID space is the
   creation of a "Trusted Vector Message".  By placing a previous [or
   new] vector message into the payload section of this format a
   verifiable broadcast can be created.

   Due to being signed this creates an authentic vector that is hard to
   spoof, which can confirm flight paths in near real time.

   The figure below is a example of a "Trusted Vector Message".






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   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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+  ASTM Authentication Headers  +---------------+
   |                                               | Vector Header |
   +-----------------------------------------------+---------------+
   |                                                               |
   |                                                               |
   |                                                               |
   |                             HHIT                              |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                 Trust Timestamp               /
   +---------------+-----------------------------------------------+
   /               |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                    Vector Message (Bytes 1-19)                |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |         Vector Message (Bytes 20-24)          /
   +---------------+               +-------------------------------+
   /                               |                               |
   +-------------------------------+                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                   HHIT Signature (Bytes 1-18)                 |
   |                                                               |
   |                                                               |



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   |                                                               |
   +---------------------------------------------------------------+

   Page 3:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                   HHIT Signature (Bytes 19-41)                |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 4:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                   HHIT Signature (Bytes 42-64)                |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

5.2.  Wrapped Signed Hashes

   Using the Message Wrapper a [short] list of hashes can be signed.
   These hashes are of previous individual RID messages.

   This follows the format of the Signed Hash List, excluding the
   psuedo-blockchain hashes found in the Signed Hash List.

   To the authors, this format has limited use due to numerous concerns
   of replay attacks.  It is suggested to instead use the full Signed
   Hash List format.



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   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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                                               |
   +---------------+  ASTM Authentication Headers  +---------------+
   |                                               | H-Alg | H-Len |
   +-----------------------------------------------+---------------+
   |                                                               |
   |                                                               |
   |                                                               |
   |                             HHIT                              |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 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
   +---------------+-----------------------------------------------+
   |  ASTM Header  |                 Trust Timestamp               /
   +---------------+-----------------------------------------------+
   /               |                  Message Hash                 /
   +---------------+-----------------------------------------------+
   /               |                  Message Hash                 /
   +---------------+-----------------------------------------------+
   /               |                  Message Hash                 /
   +---------------+-----------------------------------------------+
   /               |                  Message Hash                 /
   +---------------+-----------------------------------------------+
   /               |                  Message Hash                 /
   +---------------------------------------------------------------+

   Page 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
   +---------------+-----------------------------------------------+
   |  ASTM Header  /               |         Message Hash          /
   +---------------+---------------+-------------------------------+
   /                               |                               |
   +-------------------------------+                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                   HHIT Signature (Bytes 1-18)                 |
   |                                                               |
   |                                                               |



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   |                                                               |
   +---------------------------------------------------------------+

   Page 3:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                   HHIT Signature (Bytes 19-41)                |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

   Page 4:
    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 Header  |                                               |
   +---------------+                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   |                   HHIT Signature (Bytes 42-64)                |
   |                                                               |
   |                                                               |
   |                                                               |
   |                                                               |
   +---------------------------------------------------------------+

6.  IANA Considerations

   TBD

7.  Security Considerations

   TBD







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8.  Acknowledgments

   Ryan Quigley and James Mussi at AX Enterprize for early prototyping
   to find holes in the draft specifications.

9.  References

9.1.  Normative References

   [NIST.SP.800-185]
              Kelsey, J., Change, S., and R. Perlner, "SHA-3 derived
              functions: cSHAKE, KMAC, TupleHash and ParallelHash",
              National Institute of Standards and Technology report,
              DOI 10.6028/nist.sp.800-185, December 2016,
              <https://doi.org/10.6028/nist.sp.800-185>.

   [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>.

9.2.  Informative References

   [I-D.moskowitz-hip-hierarchical-hit]
              Moskowitz, R., Card, S., and A. Wiethuechter,
              "Hierarchical HITs for HIPv2", Work in Progress, Internet-
              Draft, draft-moskowitz-hip-hierarchical-hit-04, 3 March
              2020, <https://tools.ietf.org/html/draft-moskowitz-hip-
              hierarchical-hit-04>.

   [I-D.moskowitz-hip-new-crypto]
              Moskowitz, R., Card, S., and A. Wiethuechter, "New
              Cryptographic Algorithms for HIP", Work in Progress,
              Internet-Draft, draft-moskowitz-hip-new-crypto-04, 23
              January 2020, <https://tools.ietf.org/html/draft-
              moskowitz-hip-new-crypto-04>.

   [I-D.wiethuechter-tmrid-identity-claims]
              Wiethuechter, A., Card, S., and R. Moskowitz, "TMRID
              Identity Claims", Work in Progress, Internet-Draft, draft-
              wiethuechter-tmrid-identity-claims-01, 9 March 2020,
              <https://tools.ietf.org/html/draft-wiethuechter-tmrid-
              identity-claims-01>.




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   [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

   Adam Wiethuechter
   AX Enterprize
   4947 Commercial Drive
   Yorkville, NY 13495
   United States of America

   Email: adam.wiethuechter@axenterprize.com


   Stuart W. Card
   AX Enterprize
   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




















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