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
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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.
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Please review these documents carefully, as they describe your rights
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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
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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.
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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.
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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
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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.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| |
| UA 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.
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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
+---------------+---------------+---------------+---------------+
| |
| 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).
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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.
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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
+---------------+---------------+---------------+---------------+
| 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.
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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.
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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.
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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.
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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
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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
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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".
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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)
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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
+---------------+---------------+---------------+---------------+
| |
| Hierarchical |
| Host Identity Tag |
| |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| Host Identity |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
| Trust Timestamp |
+---------------+---------------+---------------+---------------+
| Signing Timestamp |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| Signature |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
Length = 120-bytes
Figure 6: DRIP Self-Attestation
11.2. Attestation (Axy)
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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
+---------------+---------------+---------------+---------------+
| |
. .
. 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)
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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
+---------------+---------------+---------------+---------------+
| |
| 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)
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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
+---------------+---------------+---------------+---------------+
| |
. .
. 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)
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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
+---------------+---------------+---------------+---------------+
| |
. .
. 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)
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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
+---------------+---------------+---------------+---------------+
| |
| 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
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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)
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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
+---------------+---------------+---------------+---------------+
| |
. .
. 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
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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 |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
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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.
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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.
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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.
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[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
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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
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