rfc9575.original   rfc9575.txt 
DRIP Working Group A. Wiethuechter, Ed. Internet Engineering Task Force (IETF) A. Wiethuechter, Ed.
Internet-Draft S. Card Request for Comments: 9575 S. Card
Intended status: Standards Track AX Enterprize, LLC Category: Standards Track AX Enterprize, LLC
Expires: 24 August 2024 R. Moskowitz ISSN: 2070-1721 R. Moskowitz
HTT Consulting HTT Consulting
21 February 2024 June 2024
DRIP Entity Tag Authentication Formats & Protocols for Broadcast Remote DRIP Entity Tag (DET) Authentication Formats and Protocols for Broadcast
ID Remote Identification (RID)
draft-ietf-drip-auth-49
Abstract Abstract
The Drone Remote Identification Protocol (DRIP), plus trust policies The Drone Remote Identification Protocol (DRIP), plus trust policies
and periodic access to registries, augments Unmanned Aircraft System and periodic access to registries, augments Unmanned Aircraft System
(UAS) Remote Identification (RID), enabling local real time (UAS) Remote Identification (RID), enabling local real-time
assessment of trustworthiness of received RID messages and observed assessment of trustworthiness of received RID messages and observed
UAS, even by Observers lacking Internet access. This document UAS, even by Observers lacking Internet access. This document
defines DRIP message types and formats to be sent in Broadcast RID defines DRIP message types and formats to be sent in Broadcast RID
Authentication Messages to verify that attached and recent detached Authentication Messages to verify that attached and recently detached
messages were signed by the registered owner of the DRIP Entity Tag messages were signed by the registered owner of the DRIP Entity Tag
(DET) claimed. (DET) claimed.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
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Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 24 August 2024. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9575.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
1.1. DRIP Entity Tag (DET) Authentication Goals for Broadcast 1.1. DRIP Entity Tag (DET) Authentication Goals for Broadcast
RID . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 RID
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 2. Terminology
2.1. Required Terminology . . . . . . . . . . . . . . . . . . 5 2.1. Required Terminology
2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5 2.2. Definitions
3. UAS RID Authentication Background & Procedures . . . . . . . 5 3. UAS RID Authentication Background and Procedures
3.1. DRIP Authentication Protocol Description . . . . . . . . 6 3.1. DRIP Authentication Protocol Description
3.1.1. Usage of DNS . . . . . . . . . . . . . . . . . . . . 6 3.1.1. Usage of DNS
3.1.2. Providing UAS RID Trust . . . . . . . . . . . . . . . 7 3.1.2. Providing UAS RID Trust
3.2. ASTM Authentication Message Framing . . . . . . . . . . . 8 3.2. ASTM Authentication Message Framing
3.2.1. Authentication Page . . . . . . . . . . . . . . . . . 8 3.2.1. Authentication Page
3.2.2. Authentication Payload Field . . . . . . . . . . . . 9 3.2.2. Authentication Payload Field
3.2.3. Specific Authentication Method (SAM) . . . . . . . . 10 3.2.3. SAM Data Format
3.2.4. ASTM Broadcast RID Constraints . . . . . . . . . . . 11 3.2.4. ASTM Broadcast RID Constraints
4. DRIP Authentication Formats . . . . . . . . . . . . . . . . . 13 4. DRIP Authentication Formats
4.1. UA Signed Evidence Structure . . . . . . . . . . . . . . 13 4.1. UA-Signed Evidence Structure
4.2. DRIP Link . . . . . . . . . . . . . . . . . . . . . . . . 15 4.2. DRIP Link
4.3. DRIP Wrapper . . . . . . . . . . . . . . . . . . . . . . 17 4.3. DRIP Wrapper
4.3.1. Wrapped Count & Format Validation . . . . . . . . . . 18 4.3.1. Wrapped Count and Format Validation
4.3.2. Wrapper over Extended Transports . . . . . . . . . . 18 4.3.2. Wrapper over Extended Transports
4.3.3. Wrapper Limitations . . . . . . . . . . . . . . . . . 20 4.3.3. Wrapper Limitations
4.4. DRIP Manifest . . . . . . . . . . . . . . . . . . . . . . 20 4.4. DRIP Manifest
4.4.1. Hash Count & Format Validation . . . . . . . . . . . 21 4.4.1. Hash Count and Format Validation
4.4.2. Manifest Ledger Hashes . . . . . . . . . . . . . . . 22 4.4.2. Manifest Ledger Hashes
4.4.3. Hash Algorithms and Operation . . . . . . . . . . . . 22 4.4.3. Hash Algorithms and Operation
4.5. DRIP Frame . . . . . . . . . . . . . . . . . . . . . . . 23 4.5. DRIP Frame
5. Forward Error Correction . . . . . . . . . . . . . . . . . . 24 5. Forward Error Correction
5.1. Encoding . . . . . . . . . . . . . . . . . . . . . . . . 25 5.1. Encoding
5.2. Decoding . . . . . . . . . . . . . . . . . . . . . . . . 26 5.2. Decoding
5.3. FEC Limitations . . . . . . . . . . . . . . . . . . . . . 29 5.3. FEC Limitations
6. Requirements & Recommendations . . . . . . . . . . . . . . . 29 6. Requirements and Recommendations
6.1. Legacy Transports . . . . . . . . . . . . . . . . . . . . 29 6.1. Legacy Transports
6.2. Extended Transports . . . . . . . . . . . . . . . . . . . 29 6.2. Extended Transports
6.3. Authentication . . . . . . . . . . . . . . . . . . . . . 29 6.3. Authentication
6.4. Operational . . . . . . . . . . . . . . . . . . . . . . . 30 6.4. Operational
6.4.1. DRIP Wrapper . . . . . . . . . . . . . . . . . . . . 31 6.4.1. DRIP Wrapper
6.4.2. UAS RID Trust Assessment . . . . . . . . . . . . . . 31 6.4.2. UAS RID Trust Assessment
7. Summary of Addressed DRIP Requirements . . . . . . . . . . . 31 7. Summary of Addressed DRIP Requirements
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 8. IANA Considerations
8.1. IANA DRIP Registry . . . . . . . . . . . . . . . . . . . 32 8.1. IANA DRIP Registry
9. Security Considerations . . . . . . . . . . . . . . . . . . . 33 9. Security Considerations
9.1. Replay Attacks . . . . . . . . . . . . . . . . . . . . . 33 9.1. Replay Attacks
9.2. Wrapper vs Manifest . . . . . . . . . . . . . . . . . . . 34 9.2. Wrapper vs Manifest
9.3. VNA Timestamp Offsets for DRIP Authentication Formats . . 35 9.3. VNA Timestamp Offsets for DRIP Authentication Formats
9.4. DNS Security in DRIP . . . . . . . . . . . . . . . . . . 36 9.4. DNS Security in DRIP
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36 10. References
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 37 10.1. Normative References
11.1. Normative References . . . . . . . . . . . . . . . . . . 37 10.2. Informative References
11.2. Informative References . . . . . . . . . . . . . . . . . 38 Appendix A. Authentication States
Appendix A. Authentication States . . . . . . . . . . . . . . . 38 A.1. None: Black
A.1. None: Black . . . . . . . . . . . . . . . . . . . . . . . 40 A.2. Partial: Gray
A.2. Partial: Gray . . . . . . . . . . . . . . . . . . . . . . 40 A.3. Unsupported: Brown
A.3. Unsupported: Brown . . . . . . . . . . . . . . . . . . . 41 A.4. Unverifiable: Yellow
A.4. Unverifiable: Yellow . . . . . . . . . . . . . . . . . . 41 A.5. Verified: Green
A.5. Verified: Green . . . . . . . . . . . . . . . . . . . . . 41 A.6. Trusted: Blue
A.6. Trusted: Blue . . . . . . . . . . . . . . . . . . . . . . 41 A.7. Questionable: Orange
A.7. Questionable: Orange . . . . . . . . . . . . . . . . . . 41 A.8. Unverified: Red
A.8. Unverified: Red . . . . . . . . . . . . . . . . . . . . . 42 A.9. Conflicting: Purple
A.9. Conflicting: Purple . . . . . . . . . . . . . . . . . . . 42 Appendix B. Operational Recommendation Analysis
Appendix B. Operational Recommendation Analysis . . . . . . . . 42 B.1. Page Counts vs Frame Counts
B.1. Page Counts vs Frame Counts . . . . . . . . . . . . . . . 42 B.1.1. Special Cases
B.1.1. Special Cases . . . . . . . . . . . . . . . . . . . . 44 B.2. Full Authentication Example
B.2. Full Authentication Example . . . . . . . . . . . . . . . 44 B.2.1. Raw Example
B.2.1. Raw Example . . . . . . . . . . . . . . . . . . . . . 46 Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47 Authors' Addresses
1. Introduction 1. Introduction
The initial regulations (e.g., [FAA-14CFR]) and standards (e.g., The initial regulations (e.g., [FAA-14CFR]) and standards (e.g.,
[F3411]) for Unmanned Aircraft (UA) Systems (UAS) Remote [F3411]) for Unmanned Aircraft Systems (UAS) Remote Identification
Identification and tracking (RID) do not address trust. However, (RID) and tracking do not address trust. However, this is a
this is a requirement that needs to be addressed for various requirement that needs to be addressed for various different parties
different parties that have a stake in the safe operation of National that have a stake in the safe operation of National Airspace Systems
Airspace Systems (NAS). Drone Remote ID Protocol's (DRIP's) goal is (NAS). Drone Remote ID Protocol's (DRIP's) goal is to specify how
to specify how RID can be made trustworthy and available in both RID can be made trustworthy and available in both Internet and local-
Internet and local-only connected scenarios, especially in emergency only connected scenarios, especially in emergency situations.
situations.
UAS often operate in a volatile environment. Small UA offer little UAS often operate in a volatile environment. A small Unmanned
capacity for computation and communication. UAS RID must also be Aircraft (UA) offers little capacity for computation and
accessible with ubiquitous and inexpensive devices without communication. UAS RID must also be accessible with ubiquitous and
modification. This limits options. Most current small UAS are IoT inexpensive devices without modification. This limits options. Most
devices even if not typically thought of as such. Thus many IoT current small UAS are Internet of Things (IoT) devices even if they
considerations apply here. Some DRIP work, currently strongly scoped are not typically thought of as such. Thus many IoT considerations
to UAS RID, is likely to be applicable to some other IoT use-cases. apply here. Some DRIP work, currently strongly scoped to UAS RID, is
likely to be applicable to some other IoT use cases.
Generally, two communication schemes for UAS RID are considered: Generally, two communication schemes for UAS RID are considered:
Broadcast and Network. This document focuses on adding trust to Broadcast and Network. This document focuses on adding trust to
Broadcast RID (Section 3.2 of [RFC9153] and Section 1.2.2 of Broadcast RID (Section 3.2 of [RFC9153] and Section 1.2.2 of
[RFC9434]). As defined in [F3411] and outlined in [RFC9153] and [RFC9434]). As defined in [F3411] and outlined in [RFC9153] and
[RFC9434], Broadcast RID is a one-way RF transmission of MAC layer [RFC9434], Broadcast RID is a one-way Radio Frequency (RF)
messages over Bluetooth or Wi-Fi. transmission of Media Access Control (MAC) layer messages over
Bluetooth or Wi-Fi.
Senders can make any claims the RID message formats allow. Observers Senders can make any claims the RID message formats allow. Observers
have no standardized means to assess the trustworthiness of message have no standardized means to assess the trustworthiness of message
content, nor verify whether the messages were sent by the UA content, nor verify whether the messages were sent by the UA
identified therein, nor confirm that the UA identified therein is the identified therein, nor confirm that the UA identified therein is the
one they are visually observing. Indeed, Observers have no way to one they are visually observing. Indeed, Observers have no way to
detect whether the messages were sent by a UA, or spoofed by some detect whether the messages were sent by a UA or spoofed by some
other transmitter (e.g., a laptop or smartphone) anywhere in direct other transmitter (e.g., a laptop or smartphone) anywhere in direct
wireless broadcast range. Authentication is the primary strategy for wireless broadcast range. Authentication is the primary strategy for
mitigating this issue. mitigating this issue.
1.1. DRIP Entity Tag (DET) Authentication Goals for Broadcast RID 1.1. DRIP Entity Tag (DET) Authentication Goals for Broadcast RID
ASTM [F3411] Authentication Messages (Message Type 0x2), when used ASTM [F3411] Authentication Messages (Message Type 0x2), when used
with DRIP Entity Tag (DET) [RFC9374] based formats, enable a high with DET-based formats [RFC9374], enable a high level of trust that
level of trust that the content of other ASTM Messages was generated the content of other ASTM Messages was generated by their claimed
by their claimed registered source. These messages are designed to registered source. These messages are designed to provide the
provide the Observers with trustworthy and immediately actionable Observers with trustworthy and immediately actionable information.
information. Appendix A provides a high-level overview of the Appendix A provides a high-level overview of the various states of
various states of trustworthiness that may be used along with these trustworthiness that may be used along with these formats.
formats.
This authentication approach also provides some error correction This authentication approach also provides some error correction
(Section 5) as mandated by the United States (US) Federal Aviation (Section 5) as mandated by the United States (US) Federal Aviation
Administration (FAA) [FAA-14CFR], which is missing from [F3411] over Administration (FAA) [FAA-14CFR], which is missing from [F3411] over
Legacy Transports (Bluetooth 4.x). Legacy Transports (Bluetooth 4.x).
These DRIP enhancements to ASTM's [F3411] further support the These DRIP enhancements to ASTM's specification for RID and tracking
important use case of Observers who may be offline at the time of [F3411] further support the important use case of Observers who may
observation. be offline at the time of observation.
A summary of DRIP requirements [RFC9153] addressed herein is provided
in Section 7.
Note: The Endorsement (used in Section 4.2) that proves that a DET Section 7 summarizes the DRIP requirements [RFC9153] addressed
is registered MUST come from its immediate parent in the herein.
registration hierarchy, e.g., a DRIP Identity Management Entity
(DIME) [drip-registries]. In the definitive hierarchy, the parent
of the UA is its HHIT Domain Authority (HDA), the parent of an HDA
is its Registered Assigning Authority (RAA), etc. It is also
assumed that all DRIP-aware entities use a DET as their identifier
during interactions with other DRIP-aware entities.
2. Terminology 2. Terminology
2.1. Required Terminology 2.1. Required Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2.2. Definitions 2.2. Definitions
This document makes use of the terms (CAA, Observer, USS, UTM, etc.) This document makes use of the terms (CAA, Observer, USS, UTM, etc.)
defined in [RFC9153]. Other terms (such as DIME) are from [RFC9434], defined in [RFC9153]. Other terms (such as DIME) are from [RFC9434],
while others (HI, DET, RAA, HDA, etc.) are from [RFC9374]. while others (HI, DET, RAA, HDA, etc.) are from [RFC9374].
In addition, the following terms are defined for this document: In addition, the following terms are defined for this document:
Extended Transports: Extended Transports: Use of extended advertisements (Bluetooth 5.x),
service info (Wi-Fi Neighbor Awareness Networking (NAN)), or IEEE
802.11 Beacons with the vendor-specific information element as
specified in [F3411]. Must use ASTM Message Pack (Message Type
0xF).
Use of extended advertisements (Bluetooth 5.x), service info (Wi- Legacy Transports: Use of broadcast frames (Bluetooth 4.x) as
Fi Neighbor Awareness Networking (NAN)), or IEEE 802.11 Beacons specified in [F3411].
with vendor specific information element as specified in [F3411].
Must use ASTM Message Pack (Message Type 0xF).
Legacy Transports: Manifest: An immutable list of items being transported (in this
specific case over wireless communication).
Use of broadcast frames (Bluetooth 4.x) as specified in [F3411]. Observation Session: The period of time during which a given
Observer's receiver is processing (even if only intermittently) a
series of UAS RID messages, at least some of which use DRIP
extensions to [F3411], all nominally from the same UA executing a
single flight operation.
Manifest: Note: For the remainder of this document, _Broadcast Endorsement:
Parent, Child_ will be abbreviated as _BE: Parent, Child_. For
example, _Broadcast Endorsement: RAA, HDA_ will be abbreviated as
_BE: RAA, HDA_.
an immutable list of items being transported (in this specific 3. UAS RID Authentication Background and Procedures
case over wireless communication).
3. UAS RID Authentication Background & Procedures
3.1. DRIP Authentication Protocol Description 3.1. DRIP Authentication Protocol Description
[F3411] defines Authentication Message framing only. It does not [F3411] defines Authentication Message framing only. It does not
define authentication formats or methods. It explicitly anticipates define authentication formats or methods. It explicitly anticipates
several signature options but does not fully define those. Annex A1 several signature options but does not fully define those. Annex A1
of [F3411] defines a Broadcast Authentication Verifier Service, which of [F3411] defines a Broadcast Authentication Verifier Service, which
has a heavy reliance on Observer real-time connectivity to the has a heavy reliance on Observer real-time connectivity to the
Internet. Fortunately, [F3411] also allows third party standard Internet. Fortunately, [F3411] also allows third-party standard
Authentication Types using Type 5 Specific Authentication Method Authentication Types using the Type 0x5 Specific Authentication
(SAM), several of which DRIP defines herein. Method (SAM), several of which DRIP defines herein.
The standardization of specific formats to support the DRIP The standardization of specific formats to support the DRIP
requirements in UAS RID for trustworthy communications over Broadcast requirements in UAS RID for trustworthy communications over Broadcast
RID is an important part of the chain of trust for a UAS ID. Per RID is an important part of the chain of trust for a UAS ID. Per
Section 5 of [RFC9434], Authentication formats are needed to relay Section 5 of [RFC9434], Authentication formats are needed to relay
information for Observers to determine trust. No existing formats information for Observers to determine trust. No existing formats
(defined in [F3411] or other organizations leveraging this feature) (defined in [F3411] or other organizations leveraging this feature)
provide the functionality to satisfy this goal resulting in the work provide functionality to satisfy this goal, resulting in the work
reflected in this document. reflected in this document.
3.1.1. Usage of DNS 3.1.1. Usage of DNS
Like most aviation matters, the overall objectives here are security Like most aviation matters, the overall objectives here are security
and ultimately safety oriented. Since DRIP depends on DNS for some and ultimately safety oriented. Since DRIP depends on DNS for some
of its functions, DRIP usage of DNS needs to be protected as per best of its functions, DRIP usage of DNS needs to be protected per best
security practices. Many participating nodes will have limited local security practices. Many participating nodes will have limited local
processing power and/or poor, low bandwidth QoS paths. Appropriate processing power and/or poor, low-bandwidth QoS paths. Appropriate
and feasible security techniques will be highly UAS and Observer and feasible security techniques will be highly dependent on the UAS
situation dependent. Therefore specification of particular DNS and Observer situation. Therefore, specification of particular DNS
security options, transports, etc. is outside the scope of this security options, transports, etc. is outside the scope of this
document (see also Section 9.4). document (see also Section 9.4).
In DRIP Observers MUST validate all signatures received. This In DRIP, Observers MUST validate all signatures received. This
requires the Host Identity (HI) corresponding to a DET [RFC9374]. requires that the Host Identity (HI) correspond to a DET [RFC9374].
HI's MAY be retrieved from a local cache, if present. The local HI's MAY be retrieved from a local cache, if present. The local
cache is pre-configured with well knowns HIs (such as those of CAA cache is pre-configured with well-known HIs (such as those of CAA
DIMEs) and further populated by received Broadcast Endorsements (BEs) DIMEs) and is further populated by received Broadcast Endorsements
(Section 3.1.2.1) and DNS lookups (when available). (BEs) (Section 3.1.2.1) and DNS lookups (when available).
The Observer MUST perform a DNS query, when connectivity allows, to The Observer MUST perform a DNS query, when connectivity allows, to
obtain an HI not previously known. If a query can not be performed, obtain a previously unknown HI. If a query cannot be performed, the
the message SHOULD be cached by the Observer to be validated once the message SHOULD be cached by the Observer to be validated once the HI
HI is obtained. is obtained.
A more comprehensive specification of DRIP's use of DNS is out of A more comprehensive specification of DRIP's use of DNS is out of
scope for this document and can be found in [drip-registries]. scope for this document and can be found in [DRIP-REG].
3.1.2. Providing UAS RID Trust 3.1.2. Providing UAS RID Trust
For DRIP, two actions together provide a mechanism for an Observer to For DRIP, two actions together provide a mechanism for an Observer to
trust in UAS RID using Authentication Messages. trust in UAS RID using Authentication Messages.
First is the transmission of an entire trust chain via Broadcast First is the transmission of an entire trust chain via Broadcast
Endorsements (Section 3.1.2.1). This provides a hierarchy of DIMEs Endorsements (Section 3.1.2.1). This provides a hierarchy of DIMEs
down to and including an individual UA's registration of a claimed down to and including an individual UA's registration of a claimed
DET and corresponding HI (public key). This alone cannot be trusted DET and corresponding HI (public key). This alone cannot be trusted
as having any relevance to the observed UA because replay attacks are as having any relevance to the observed UA because replay attacks are
trivial. trivial.
After an Observer has gathered such a complete key trust chain (from After an Observer has gathered such a complete key trust chain (from
pre-configured cache entries, Broadcast Endorsements received over pre-configured cache entries, Broadcast Endorsements received over
the air and/or DNS lookups) and verified all of its links, that the air and/or DNS lookups) and verified all of its links, that
device can trust that claimed DET and corresponding public key are device can trust that the claimed DET and corresponding public key
properly registered, but the UA has not yet been proven to possess are properly registered, but the UA has not yet been proven to
the corresponding private key. possess the corresponding private key.
It is necessary for the UA to prove possession by dynamically signing Second is for the UA to prove possession by dynamically signing data
data that is unique and unpredictable but easily verified by the that is unique and unpredictable but easily verified by the Observer
Observer (Section 3.1.2.2). Verification of this signed data MUST be (Section 3.1.2.2). Verification of this signed data MUST be
performed by the Observer as part of the received UAS RID information performed by the Observer as part of the received UAS RID information
trust assessment (Section 6.4.2). trust assessment (Section 6.4.2).
3.1.2.1. DIME Endorsements of Subordinate DETs 3.1.2.1. DIME Endorsements of Subordinate DETs
Observers receive DRIP Link Authentication Messages (Section 4.2) Observers receive DRIP Link Authentication Messages (Section 4.2)
containing Broadcast Endorsements by DIMEs of child DET containing Broadcast Endorsements by DIMEs of child DET
registrations. A series of these Endorsements confirms a path registrations. A series of these Endorsements confirms a path
through the hierarchy, defined in [drip-registries], from the DET through the hierarchy, defined in [DRIP-REG], from the DET Prefix
Prefix Owner all the way to an individual UA DET registration. Owner all the way to an individual UA DET registration.
Note: For the remainder of this document Broadcast Endorsement:
Parent, Child will be abbreviated to BE: Parent, Child. For
example Broadcast Endorsement: RAA, HDA will be abbreviated to BE:
RAA, HDA.
3.1.2.2. UA Signed Evidence 3.1.2.2. UA-Signed Evidence
To prove possession of the private key associated to the DET, the UA To prove possession of the private key associated with the DET, the
MUST send data that is unique and unpredictable but easily validated UA MUST sign and send data that is unique and unpredictable but
by the Observer, that is signed over. The data can be an ASTM easily validated by the Observer. The data can be an ASTM Message
Message that fulfills the requirements to be unpredictable but easily that fulfills the requirements to be unpredictable but easily
validated. An Observer receives this UA-signed Evidence from DRIP- validated. An Observer receives this UA-signed Evidence from DRIP-
based Authentication Messages (Section 4.3 or Section 4.4). based Authentication Messages (Sections 4.3 or 4.4). The Observer
must verify the signature (cryptographically, as specified in
Section 3.1.1) and validate the signed content (via non-cryptographic
means, as specified in Section 6.3).
Whether the content is true is a separate question which DRIP cannot Whether the content is true is a separate question that DRIP cannot
address, but validation performed using observable and/or out of band address, but validation performed using observable and/or out-of-band
data (Section 6) are possible and encouraged. data (Section 6) is possible and encouraged.
3.2. ASTM Authentication Message Framing 3.2. ASTM Authentication Message Framing
The Authentication Message (Message Type 0x2) is unique in the ASTM The Authentication Message (Message Type 0x2) is unique in the ASTM
[F3411] Broadcast standard as it is the only message that can be [F3411] Broadcast standard, as it is the only message that can be
larger than the Legacy Transport size. To address this limitation larger than the Legacy Transport size. To address this limitation
around transport size, it is defined as a set of "pages", each of around transport size, it is defined as a set of "pages", each of
which fits into a single Legacy Transport frame. For Extended which fits into a single Legacy Transport frame. For Extended
Transports, pages are still used but all are in a single frame. Transports, pages are still used but they are all in a single frame.
Informational Note: Message Pack (Message Type 0xF) is also larger | Informational Note: Message Pack (Message Type 0xF) is also
than the Legacy Transport size but is limited for use only on | larger than the Legacy Transport size but is limited for use
Extended Transports where is can be supported. | only on Extended Transports where it can be supported.
The following sub-sections are a brief overview of the Authentication The following subsections are a brief overview of the Authentication
Message format defined in [F3411] for better context on how DRIP Message format defined in [F3411] for better context on how DRIP
Authentication fills and uses various fields already defined by ASTM Authentication fills and uses various fields already defined by ASTM
[F3411]. [F3411].
3.2.1. Authentication Page 3.2.1. Authentication Page
This document leverages Authentication Type 0x5, Specific This document leverages Authentication Type 0x5 (Specific
Authentication Method (SAM), as the principal authentication Authentication Method (SAM)) as the principal authentication
container, defining a set of SAM Types in Section 4. Authentication container, defining a set of SAM Types in Section 4. Authentication
Type is encoded in every Authentication Page in the Page Header. The Type is encoded in every Authentication Page in the _Page Header_.
SAM Type is defined as a field in the Authentication Payload (see The SAM Type is defined as a field in the _Authentication Payload_
Section 3.2.3.1). (see Section 3.2.3).
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Page Header | | | Page Header | |
+---------------+ | +---------------+ |
| | | |
| | | |
| Authentication Payload | | Authentication Payload |
| | | |
| | | |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 1: Standard ASTM Authentication Message Page Figure 1: Standard ASTM Authentication Message Page
Page Header: (1 octet) _Page Header_: (1 octet)
Authentication Type (4 bits) and Page Number (4 bits) Authentication Type (4 bits) and Page Number (4 bits)
Authentication Payload: (23 octets per page) _Authentication Payload_: (23 octets per page)
Authentication Payload, including headers. Null padded. See Authentication Payload, including headers. Null padded. See
Section 3.2.2. Section 3.2.2.
The Authentication Message is structured as a set of pages per The Authentication Message is structured as a set of pages per
Figure 1. There is a technical maximum of 16 pages (indexed 0 to 15) Figure 1. There is a technical maximum of 16 pages (indexed 0 to 15)
that can be sent for a single Authentication Message, with each page that can be sent for a single Authentication Message, with each page
carrying a maximum 23 octet Authentication Payload. See carrying a maximum 23-octet _Authentication Payload_. See
Section 3.2.4 for more details. Over Legacy Transports, these Section 3.2.4 for more details. Over Legacy Transports, these
messages are "fragmented", with each page sent in a separate Legacy messages are "fragmented", with each page sent in a separate Legacy
Transport frame. Transport frame.
Either as a single Authentication Message or a set of fragmented Either as a single Authentication Message or a set of fragmented
Authentication Message Pages, the structure is further wrapped by Authentication Message Pages, the structure is further wrapped by
outer ASTM framing and the specific link framing. outer ASTM framing and the specific link framing.
3.2.2. Authentication Payload Field 3.2.2. Authentication Payload Field
Figure 2 is the source data view of the data fields found in the Figure 2 is the source data view of the data fields found in the
Authentication Message as defined by [F3411]. This data is placed Authentication Message as defined by [F3411]. This data is placed
into Figure 1's Authentication Payload, spanning multiple into the _Authentication Payload_ shown in Figure 1, which spans
Authentication Pages. multiple _Authentication Pages_.
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Authentication Headers | | Authentication Headers |
| +---------------+---------------+ | +---------------+---------------+
| | | | | |
+---------------+---------------+ | +---------------+---------------+ |
. . . .
. Authentication Data / Signature . . Authentication Data / Signature .
skipping to change at page 9, line 51 skipping to change at line 412
| ADL | | | ADL | |
+---------------+ | +---------------+ |
. . . .
. Additional Data . . Additional Data .
. . . .
| | | |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 2: ASTM Authentication Message Fields Figure 2: ASTM Authentication Message Fields
Authentication Headers: (6 octets) _Authentication Headers_: (6 octets)
As defined in [F3411]. As defined in [F3411].
Authentication Data / Signature: (0 to 255 octets) _Authentication Data / Signature_: (0 to 255 octets)
Opaque authentication data. The length of this payload is known Opaque authentication data. The length of this payload is known
through a field in the Authentication Headers (defined in through a field in the _Authentication Headers_ (defined in
[F3411]). [F3411]).
Additional Data Length (ADL): (1 octet - unsigned) _Additional Data Length (ADL)_: (1 octet - unsigned)
Length in octets of Additional Data. The value of ADL is Length in octets of _Additional Data_. The value of _ADL_ is
calculated as the minimum of 361 - Authentication Data / Signature calculated as the minimum of 361 - Authentication Data / Signature
Length and 255. Only present with Additional Data. Length and 255. Only present with _Additional Data_.
Additional Data: (ADL octets)
Data that follows the Authentication Data / Signature but is not _Additional Data:_ (_ADL_ octets)
considered part of the Authentication Data thus is not covered by
a signature. For DRIP, this field is used to carry Forward Error
Correction (FEC) generated by transmitters and parsed by receivers
as defined in Section 5.
3.2.3. Specific Authentication Method (SAM) Data that follows the _Authentication Data / Signature_ but is not
considered part of the _Authentication Data_, and thus is not
covered by a signature. For DRIP, this field is used to carry
Forward Error Correction (FEC) generated by transmitters and
parsed by receivers as defined in Section 5.
3.2.3.1. SAM Data Format 3.2.3. SAM Data Format
Figure 3 is the general format to hold authentication data when using Figure 3 is the general format to hold authentication data when using
SAM and is placed inside the Authentication Data/Signature field in SAM and is placed inside the _Authentication Data / Signature_ field
Figure 2. in Figure 2.
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| SAM Type | | | SAM Type | |
+---------------+ | +---------------+ |
. . . .
. SAM Authentication Data . . SAM Authentication Data .
. . . .
| | | |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 3: SAM Data Format Figure 3: SAM Data Format
SAM Type: (1 octet) _SAM Type_: (1 octet)
The following SAM Types are allocated to DRIP: The following SAM Types are allocated to DRIP:
+==========+=============================+ +==========+=============================+
| SAM Type | Description | | SAM Type | Description |
+==========+=============================+ +==========+=============================+
| 0x01 | DRIP Link (Section 4.2) | | 0x01 | DRIP Link (Section 4.2) |
+----------+-----------------------------+ +----------+-----------------------------+
| 0x02 | DRIP Wrapper (Section 4.3) | | 0x02 | DRIP Wrapper (Section 4.3) |
+----------+-----------------------------+ +----------+-----------------------------+
| 0x03 | DRIP Manifest (Section 4.4) | | 0x03 | DRIP Manifest (Section 4.4) |
+----------+-----------------------------+ +----------+-----------------------------+
| 0x04 | DRIP Frame (Section 4.5) | | 0x04 | DRIP Frame (Section 4.5) |
+----------+-----------------------------+ +----------+-----------------------------+
Table 1: DRIP SAM Types Table 1: DRIP SAM Types
Note: ASTM International is the owner of these code points as they | Note: ASTM International is the owner of these code points as
are defined in [F3411]. In accordance with Annex 5 of the ASTM's | they are defined in [F3411]. In accordance with Annex 5 of
[F3411], the International Civil Aviation Organization (ICAO) has | [F3411], the International Civil Aviation Organization (ICAO)
been selected by ASTM as the registrar to manage allocations of | has been selected by ASTM as the registrar to manage
these code points. The list of which can be found at | allocations of these code points. The list is available at
[ASTM-Remote-ID]. | [ASTM-Remote-ID].
SAM Authentication Data: (0 to 200 octets) _SAM Authentication Data_: (0 to 200 octets)
Contains opaque authentication data formatted as defined by the Contains opaque authentication data formatted as defined by the
preceding SAM Type. preceding SAM Type.
3.2.4. ASTM Broadcast RID Constraints 3.2.4. ASTM Broadcast RID Constraints
3.2.4.1. Wireless Frame Constraints 3.2.4.1. Wireless Frame Constraints
A UA has the option of broadcasting using Bluetooth (4.x and 5.x), A UA has the option to broadcast using Bluetooth (4.x and 5.x), Wi-Fi
Wi-Fi NAN, or IEEE 802.11 Beacon, see Section 6. With Bluetooth, FAA NAN, or IEEE 802.11 Beacon; see Section 6. With Bluetooth, FAA and
and other Civil Aviation Authorities (CAA) mandate transmitting other Civil Aviation Authorities (CAA) mandate transmitting
simultaneously over both 4.x and 5.x. The same application layer simultaneously over both 4.x and 5.x. The same application-layer
information defined in [F3411] MUST be transmitted over all the information defined in [F3411] MUST be transmitted over all the
physical layer interfaces performing the function of RID. This is physical-layer interfaces performing RID, because Observer transports
because Observer transports may be limited. If an Observer can may be limited. If an Observer can support multiple transports, it
support multiple transports it should be assumed to use the latest should use (display, report, etc.) the latest data regardless of the
data regardless of the transport received over. transport over which that data was received.
Bluetooth 4.x presents a payload size challenge in that it can only Bluetooth 4.x presents a payload-size challenge in that it can only
transmit 25 octets of payload per frame while other transports can transmit 25 octets of payload per frame, while other transports can
support larger payloads per frame. However, the [F3411] messaging support larger payloads per frame. As [F3411] message formats are
framing dictated by Bluetooth 4.x constraints is inherited by [F3411] the same for all media, and their framing was designed to fit within
over other media. these legacy constraints, Extended Transports cannot send larger
messages; instead, the Message Pack format encapsulates multiple
messages (each of which fits within these legacy constraints).
It should be noted that Extended Transports by definition have Error By definition Extended Transports provide FEC, but Legacy Transports
Correction built in, unlike Legacy Transports. For Authentication lack FEC. Thus over Legacy Transports, paged Authentication Messages
Messages this means that over Legacy Transport pages could be not may suffer the loss of one or more pages. This would result in
received by Observers resulting in incomplete messages during delivery to the Observer application of incomplete (typically
operation, although the use of DRIP FEC (Section 5) reduces the unusable) messages, so DRIP FEC (Section 5) is specified to enable
likelihood of this. Authentication Messages sent using Extended recovery of a single lost page and thereby reduce the likelihood of
Transports do not suffer this issue as the full message (all pages) receiving incompletely reconstructable Authentication Messages.
are sent using a single Message Pack. Furthermore the use of one-way Authentication Messages sent using Extended Transports do not suffer
RF broadcasts prohibits the use of any congestion control or loss this issue, as the full message (all pages) is sent using a single
recovery schemes that require ACKs or NACKs. Message Pack. Furthermore, the use of one-way RF broadcasts
prohibits the use of any congestion-control or loss-recovery schemes
that require ACKs or NACKs.
3.2.4.2. Paged Authentication Message Constraints 3.2.4.2. Paged Authentication Message Constraints
To keep consistent formatting across the different transports (Legacy To keep consistent formatting across the different transports (Legacy
and Extended) and their independent restrictions, the authentication and Extended) and their independent restrictions, the authentication
data being sent is REQUIRED to fit within the page limit that the data being sent is REQUIRED to fit within the page limit that the
most constrained existing transport can support. Under Broadcast most constrained existing transport can support. Under Broadcast
RID, the Extended Transport that can hold the least amount of RID, the Extended Transport that can hold the least amount of
authentication data is Bluetooth 5.x at 9 pages. authentication data is Bluetooth 5.x at 9 pages.
As such DRIP transmitters are REQUIRED to adhere to the following As such, DRIP transmitters are REQUIRED to adhere to the following
when using the Authentication Message: when using the Authentication Message:
1. Authentication Data / Signature data MUST fit in the first 9 1. _Authentication Data / Signature_ data MUST fit in the first 9
pages (Page Numbers 0 through 8). pages (Page Numbers 0 through 8).
2. The Length field in the Authentication Headers (which encodes the 2. The _Length_ field in the _Authentication Headers_ (which encodes
length in octets of Authentication Data / Signature only) MUST the length in octets of _Authentication Data / Signature_ only)
NOT exceed the value of 201. This includes the SAM Type but MUST NOT exceed the value of 201. This includes the SAM Type but
excludes Additional Data. excludes _Additional Data_.
3.2.4.3. Timestamps 3.2.4.3. Timestamps
In ASTM [F3411] timestamps are a Unix-style timestamp with an epoch In ASTM [F3411], timestamps are a Unix-style timestamp with an epoch
of 2019-01-01 00:00:00 UTC. For DRIP this format is adopted for of 2019-01-01 00:00:00 UTC. For DRIP, this format is adopted for
Authentication to keep a common time format in Broadcast payloads. Authentication to keep a common time format in Broadcast payloads.
Under DRIP there are two timestamps defined Valid Not Before (VNB) Under DRIP, there are two timestamps defined: Valid Not Before (VNB)
and Valid Not After (VNA). and Valid Not After (VNA).
Valid Not Before (VNB) Timestamp: (4 octets) Valid Not Before (VNB) Timestamp: (4 octets)
Timestamp denoting recommended time to start trusting data in. Timestamp denoting the recommended time at which to start trusting
MUST follow the format defined in [F3411] as described above. data. MUST follow the format defined in [F3411] as described
MUST be set no earlier than the time the signature (across a given above. MUST be set no earlier than the time the signature (across
structure) is generated. a given structure) is generated.
Valid Not After (VNA) Timestamp: (4 octets) Valid Not After (VNA) Timestamp: (4 octets)
Timestamp denoting recommended time to stop trusting data. MUST
follow the format defined in [F3411] as described above. Has an Timestamp denoting the recommended time at which to stop trusting
additional offset to push a short time into the future (relative data. MUST follow the format defined in [F3411] as described
to VNB) to avoid replay attacks. The exact offset is not defined above. Has an offset (relative to VNB) to avoid replay attacks.
in this document. Best practice identifying an acceptable offset The exact offset is not defined in this document. Best practice
should be used taking into consideration the UA environment, and for identifying an acceptable offset should be used and should
propagation characteristics of the messages being sent, and clock take into consideration the UA environment, propagation
differences between the UA and Observers. A reasonable time would characteristics of the messages being sent, and clock differences
be to set VNA 2 minutes after VNB. between the UA and Observers. For UA signatures in scenarios
typical as of 2024, a reasonable offset would be to set VNA
approximately 2 minutes after VNB; see Appendix B for examples
that may aid in tuning this value.
4. DRIP Authentication Formats 4. DRIP Authentication Formats
All formats defined in this section are the content of the All formats defined in this section are contained in the
Authentication Data / Signature field in Figure 2 and use the _Authentication Data / Signature_ field in Figure 2 and use the
Specific Authentication Method (SAM, Authentication Type 0x5). The Specific Authentication Method (SAM, Authentication Type 0x5). The
first octet of the Authentication Data / Signature of Figure 2 is first octet of the _Authentication Data / Signature_ of Figure 2 is
used to multiplex among these various formats. used to multiplex among these various formats.
When sending data over a medium that does not have underlying FEC, When sending data over a medium that does not have underlying FEC,
for example Legacy Transports, then Section 5 MUST be used. for example Legacy Transports, then FEC (per Section 5) MUST be used.
Examples of Link, Wrapper and Manifest are shown as part of an Examples of Link, Wrapper, and Manifest are shown as part of an
operational schedule in Appendix B.2.1. operational schedule in Appendix B.2.1.
4.1. UA Signed Evidence Structure 4.1. UA-Signed Evidence Structure
The UA Signed Evidence Structure (Figure 4) is used by the UA during The _UA-Signed Evidence Structure_ (Figure 4) is used by the UA
flight to sign over information elements using the private key during flight to sign over information elements using the private key
associated with the current UA DET. It is encapsulated by the SAM associated with the current UA DET. It is encapsulated by the _SAM
Authentication Data field of Figure 3. Authentication Data_ field of Figure 3.
This structure is used by the DRIP Wrapper (Section 4.3), Manifest This structure is used by the DRIP Wrapper (Section 4.3), Manifest
Section 4.4, and Frame (Section 4.5). DRIP Link (Section 4.2) MUST (Section 4.4), and Frame (Section 4.5). DRIP Link (Section 4.2) MUST
NOT use it as it will not fit in the ASTM Authentication Message with NOT use it, as it will not fit in the ASTM Authentication Message
its intended content (i.e., a Broadcast Endorsement). with its intended content (i.e., a Broadcast Endorsement).
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| VNB Timestamp by UA | | VNB Timestamp by UA |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| VNA Timestamp by UA | | VNA Timestamp by UA |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| | | |
. . . .
skipping to change at page 14, line 41 skipping to change at line 632
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 4: Endorsement Structure for UA Signed Evidence Figure 4: Endorsement Structure for UA-Signed Evidence
Valid Not Before (VNB) Timestamp by UA: (4 octets) _Valid Not Before (VNB) Timestamp by UA_: (4 octets)
See Section 3.2.4.3. Set by the UA. See Section 3.2.4.3. Set by the UA.
Valid Not After (VNA) Timestamp by UA: (4 octets) _Valid Not After (VNA) Timestamp by UA_: (4 octets)
See Section 3.2.4.3. Set by the UA. See Section 3.2.4.3. Set by the UA.
Evidence: (0 to 112 octets) _Evidence_: (0 to 112 octets)
The evidence section MUST be filled in with data in the form of an
The _Evidence_ field MUST be filled in with data in the form of an
opaque object specified in the DRIP Wrapper (Section 4.3), opaque object specified in the DRIP Wrapper (Section 4.3),
Manifest (Section 4.4), or Frame (Section 4.5). Manifest (Section 4.4), or Frame (Section 4.5).
UA DRIP Entity Tag: (16 octets) _UA DRIP Entity Tag_: (16 octets)
This is the current DET [RFC9374] being used by the UA assumed to This is a DET [RFC9374] currently being used by the UA for
be a Specific Session ID (a type of UAS ID). authentication; it is assumed to be a Specific Session ID (a type
of UAS ID typically also used by the UA in the Basic ID Message).
UA Signature: (64 octets) _UA Signature_: (64 octets)
Signature over concatenation of preceding fields (VNB, VNA, Signature over the concatenation of preceding fields (_VNB_,
Evidence, and UA DET) using the keypair of the UA DET. The _VNA_, _Evidence_, and _UA DET_) using the keypair of the UA DET.
signature algorithm is specified by the HHIT Suite ID of the DET. The signature algorithm is specified by the Hierarchical Host
Identity Tags (HHIT) Suite ID of the DET.
When using this structure, the UA is minimally self-endorsing its When using this structure, the UA is minimally self-endorsing its
DET. The HI of the UA DET can be looked up by mechanisms described DET. The HI of the UA DET can be looked up by mechanisms described
in [drip-registries] or by extracting it from a Broadcast Endorsement in [DRIP-REG] or by extracting it from a Broadcast Endorsement (see
(see Section 4.2 and Section 6.3). Sections 4.2 and 6.3).
4.2. DRIP Link 4.2. DRIP Link
This SAM Type is used to transmit Broadcast Endorsements. For This SAM Type (Figure 5) is used to transmit Broadcast Endorsements.
example, the BE: HDA, UA is sent (see Section 6.3) as a DRIP Link For example, the _BE: HDA, UA_ is sent (see Section 6.3) as a DRIP
message. Link message.
DRIP Link is important as its contents are used to provide trust in DRIP Link is important as its contents are used to provide trust in
the DET/HI pair that the UA is currently broadcasting. This message the DET/HI pair that the UA is currently broadcasting. This message
does not require Internet connectivity to perform signature does not require Internet connectivity to perform signature
verification of the contents when the DIME DET/HI is in the verification of the contents when the DIME DET/HI is in the
Observer's cache. It also provides the UA HI, when it is filled with Observer's cache. It also provides the UA HI, when it is filled with
a BE: HDA, UA, so that connectivity is not required when performing a BE: HDA, UA, so that connectivity is not required when performing
signature verification of other DRIP Authentication Messages. signature verification of other DRIP Authentication Messages.
Various Broadcast Endorsements are sent during operation to ensure Various Broadcast Endorsements are sent during each UAS flight
that the full Broadcast Endorsement chain is available offline. See operation to ensure that the full Broadcast Endorsement chain is
Section 6.3 for further details. available offline. See Section 6.3 for further details.
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| VNB Timestamp by Parent | | VNB Timestamp by Parent |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| VNA Timestamp by Parent | | VNA Timestamp by Parent |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| | | |
| DET | | DET |
skipping to change at page 16, line 51 skipping to change at line 730
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 5: Broadcast Endorsement / DRIP Link Figure 5: Broadcast Endorsement / DRIP Link
VNB Timestamp by Parent: (4 octets) _VNB Timestamp by Parent_: (4 octets)
See Section 3.2.4.3. Set by Parent Entity. See Section 3.2.4.3. Set by Parent Entity.
VNA Timestamp by Parent: (4 octets) _VNA Timestamp by Parent_: (4 octets)
See Section 3.2.4.3. Set by Parent Entity. See Section 3.2.4.3. Set by Parent Entity.
DET of Child: (16 octets) _DET of Child_: (16 octets)
DRIP Entity Tag of Child Entity. DRIP Entity Tag of Child Entity.
HI of Child: (32 octets) _HI of Child_: (32 octets)
Host Identity of Child Entity. Host Identity of Child Entity.
DET of Parent: (16 octets) _DET of Parent_: (16 octets)
DRIP Entity Tag of Parent Entity in DIME Hierarchy. DRIP Entity Tag of Parent Entity in DIME Hierarchy.
Signature by Parent: (64 octets) _Signature by Parent_: (64 octets)
Signature over concatenation of preceding fields (VNB, VNA, DET of Signature over concatenation of preceding fields (_VNB_, _VNA_,
Child, HI of Child, and DET of Parent) using the keypair of the _DET of Child_, _HI of Child_, and _DET of Parent_) using the
Parent DET. keypair of the Parent DET.
This DRIP Authentication Message is used in conjunction with other This DRIP Authentication Message is used in conjunction with other
DRIP SAM Types (such as the Manifest or the Wrapper) that contain DRIP SAM Types (such as the Manifest or the Wrapper) that contain
data (e.g., the ASTM Location/Vector Message, Message Type 0x2) that data (e.g., the ASTM Location/Vector Message, Message Type 0x2) that
is guaranteed to be unique, unpredictable, and easily cross-checked is guaranteed to be unique, unpredictable, and easily cross-checked
by the receiving device. by the receiving device.
A hash of the final link (BE: HDA on UA) in the Broadcast Endorsement A hash of the final link (BE: HDA on UA) in the Broadcast Endorsement
chain MUST be included in each DRIP Manifest Section 4.4. chain MUST be included in each DRIP Manifest (Section 4.4).
Note: The Endorsement that proves a DET is registered MUST come from
its immediate parent in the registration hierarchy, e.g., a DRIP
Identity Management Entity (DIME) [DRIP-REG]. In the definitive
hierarchy, the parent of the UA is its HHIT Domain Authority (HDA),
the parent of an HDA is its Registered Assigning Authority (RAA),
etc. It is also assumed that all DRIP-aware entities use a DET as
their identifier during interactions with other DRIP-aware entities.
4.3. DRIP Wrapper 4.3. DRIP Wrapper
This SAM Type is used to wrap and sign over a list of other [F3411] This SAM Type is used to wrap and sign over a list of other [F3411]
Broadcast RID messages. Broadcast RID messages.
The evidence section of the UA Signed Evidence Structure The _Evidence_ field of the _UA-Signed Evidence Structure_
(Section 4.1) is populated with up to four ASTM [F3411] Messages in a (Section 4.1) is populated with up to four ASTM Messages [F3411] in a
contiguous octet sequence. Only ASTM Message Types 0x0, 0x1, 0x3, contiguous octet sequence. Only ASTM Message Types 0x0, 0x1, 0x3,
0x4, and 0x5 are allowed and must be in Message Type order as defined 0x4, and 0x5 are allowed and must be in Message Type order as defined
by [F3411]. These messages MUST include the Message Type and by [F3411]. These messages MUST include the Message Type and
Protocol Version octet and MUST NOT include the Message Counter octet Protocol Version octet and MUST NOT include the Message Counter octet
(thus are fixed at 25 octets in length). (thus are fixed at 25 octets in length).
4.3.1. Wrapped Count & Format Validation 4.3.1. Wrapped Count and Format Validation
When decoding a DRIP Wrapper on a receiver, a calculation of the When decoding a DRIP Wrapper on a receiver, a calculation of the
number of messages wrapped and a validation MUST be performed by number of messages wrapped and a validation MUST be performed by
using the number of octets (defined as wrapperLength) between the VNA using the number of octets (defined as wrapperLength) between the
Timestamp by UA and the UA DET as shown in Figure 6. _VNA Timestamp by UA_ and the _UA DET_ as shown in Figure 6.
<CODE BEGINS> <CODE BEGINS>
if (wrapperLength MOD 25) != 0 { if (wrapperLength MOD 25) != 0 {
return DECODE_FAILURE; return DECODE_FAILURE;
} }
wrappedCount = wrapperLength / 25; wrappedCount = wrapperLength / 25;
if (wrappedCount == 0) { if (wrappedCount == 0) {
// DECODE_SUCCESS; treat as DRIP Wrapper over extended transport // DECODE_SUCCESS; treat as DRIP Wrapper over extended transport
} }
else if (wrappedCount > 4) { else if (wrappedCount > 4) {
return DECODE_FAILURE; return DECODE_FAILURE;
} else { } else {
// DECODE_SUCCESS; treat as standard DRIP Wrapper // DECODE_SUCCESS; treat as standard DRIP Wrapper
} }
<CODE ENDS> <CODE ENDS>
Figure 6: Pseudo-code for Wrapper validation and number of Figure 6: Pseudocode for Wrapper Validation and Number of
messages calculation Messages Calculation
4.3.2. Wrapper over Extended Transports 4.3.2. Wrapper over Extended Transports
When using Extended Transports an optimization can be made to DRIP When using Extended Transports, an optimization to DRIP Wrapper can
Wrapper to sign over co-located data in an ASTM Message Pack (Message be made to sign over co-located data in an ASTM Message Pack (Message
Type 0xF). Type 0xF).
To perform this optimization the UA Signed Evidence Structure is To perform this optimization, the _UA-Signed Evidence Structure_ is
filled with the ASTM Messages to be in the ASTM Message Pack, the filled with the ASTM Messages to be in the ASTM Message Pack, the
signature is generated, then the evidence field is cleared leaving signature is generated, and then the _Evidence_ field is cleared,
the encoded form shown in Figure 7. leaving the encoded form shown in Figure 7.
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| VNB Timestamp by UA | | VNB Timestamp by UA |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| VNA Timestamp by UA | | VNA Timestamp by UA |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| | | |
| UA | | UA |
skipping to change at page 19, line 38 skipping to change at line 855
| | | |
| | | |
| | | |
| | | |
| | | |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 7: DRIP Wrapper over Extended Transports Figure 7: DRIP Wrapper over Extended Transports
To verify the signature, the receiver MUST concatenate all the To verify the signature, the receiver MUST concatenate all the
messages in the Message Pack (excluding Authentication Message found messages in the Message Pack (excluding the Authentication Message
in the same Message Pack) in ASTM Message Type order and set the found in the same Message Pack) in ASTM Message Type order and set
evidence section of the UA Signed Evidence Structure before the _Evidence_ field of the _UA-Signed Evidence Structure_ before
performing signature verification. performing signature verification.
The functionality of a Wrapper in this form is equivalent to Message The functionality of a Wrapper in this form is equivalent to Message
Set Signature (Authentication Type 0x3) when running over Extended Set Signature (Authentication Type 0x3) when running over Extended
Transports. What the Wrapper provides is the same format but over Transports. The Wrapper provides the same format but over both
both Extended and Legacy Transports allowing the transports to be Extended and Legacy Transports, which allows the transports to be
similar. Message Set Signature also implies using the ASTM validator similar. Message Set Signature also implies using the ASTM validator
system architecture which depends on Internet connectivity for system architecture, which depends on Internet connectivity for
verification which the receiver may not have at the time of receipt verification that the receiver may not have at the time an
of an Authentication Message. This is something the Wrapper, and all Authentication Message is received. This is something the Wrapper,
DRIP Authentication Formats, avoid when the UA key is obtained via a and all DRIP Authentication Formats, avoid when the UA key is
DRIP Link Authentication Message. obtained via a DRIP Link Authentication Message.
4.3.3. Wrapper Limitations 4.3.3. Wrapper Limitations
The primary limitation of the Wrapper is the bounding of up to 4 ASTM The primary limitation of the Wrapper is the bounding of up to four
Messages that can be sent within it. Another limitation is that the ASTM Messages that can be sent within it. Another limitation is that
format cannot be used as a surrogate for messages it is wrapping due the format cannot be used as a surrogate for messages it is wrapping
to the potential that an Observer on the ground does not support due to the potential that an Observer on the ground does not support
DRIP. Thus, when a Wrapper is being used, the wrapped data must DRIP. Thus, when a Wrapper is being used, the wrapped data must
effectively be sent twice, once as a single framed message (as effectively be sent twice, once as a single-framed message (as
specified in [F3411]) and then again within the Wrapper. specified in [F3411]) and again within the Wrapper.
4.4. DRIP Manifest 4.4. DRIP Manifest
This SAM Type is used to create message manifests that contain hashes This SAM Type is used to create message manifests that contain hashes
of previously sent ASTM Messages. of previously sent ASTM Messages.
By hashing previously sent messages and signing them, we gain trust By hashing previously sent messages and signing them, we gain trust
in a UA's previous reports without re-transmitting them. This is a in a UA's previous reports without retransmitting them. This is a
way to evade the limitation of a maximum of 4 messages in the Wrapper way to evade the limitation of a maximum of four messages in the
(Section 4.3.3) and greatly reduce overhead. Wrapper (Section 4.3.3) and greatly reduce overhead.
Observers MUST hash all received ASTM Messages and cross-check them Observers MUST hash all received ASTM Messages and cross-check them
against hashes in received Manifests. against hashes in received Manifests.
Judicious use of a Manifest enables an entire Broadcast RID message Judicious use of a Manifest enables an entire Broadcast RID message
stream to be strongly authenticated with less than 100% overhead stream to be strongly authenticated with less than 100% overhead
relative to a completely unauthenticated message stream (see relative to a completely unauthenticated message stream (see
Section 6.3 and Appendix B). Section 6.3 and Appendix B).
The evidence section of the UA Signed Evidence Structure The _Evidence_ field of the _UA-Signed Evidence Structure_
(Section 4.1) is populated with 8-octet hashes of [F3411] Broadcast (Section 4.1) is populated with 8-octet hashes of [F3411] Broadcast
RID messages (up to 11) and three special hashes (Section 4.4.2). RID messages (up to 11) and three special hashes (Section 4.4.2).
All these hashes MUST be concatenated to form a contiguous octet All of these hashes MUST be concatenated to form a contiguous octet
sequence in the evidence section. It is RECOMMENDED the max number sequence in the _Evidence_ field. It is RECOMMENDED that the maximum
of ASTM Message Hashes be used is 10 (see Appendix B.1.1.2). number of ASTM Message Hashes used be 10 (see Appendix B.1.1.2).
The Previous Manifest Hash, Current Manifest Hash, and DRIP Link (BE: The _Previous Manifest Hash_, _Current Manifest Hash_, and _DRIP Link
HDA, UA) Hash MUST always come before the ASTM Message Hashes as seen (BE: HDA, UA) Hash_ MUST always come before the _ASTM Message Hashes_
in Figure 8. as seen in Figure 8.
An Observer MUST use the Manifest to verify each ASTM Message hashed An Observer MUST use the Manifest to verify each ASTM Message hashed
therein that it has previously received. It can do this without therein that it has previously received. It can do this without
having received them all. A Manifest SHOULD typically encompass a having received them all. A Manifest SHOULD typically encompass a
single transmission cycle of messages being sent, see Section 6.4 and single transmission cycle of messages being sent; see Section 6.4 and
Appendix B. Appendix B.
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Previous Manifest | | Previous Manifest |
| Hash | | Hash |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Current Manifest | | Current Manifest |
| Hash | | Hash |
skipping to change at page 21, line 26 skipping to change at line 937
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| | | |
. . . .
. ASTM Message Hashes . . ASTM Message Hashes .
. . . .
| | | |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 8: DRIP Manifest Evidence Structure Figure 8: DRIP Manifest Evidence Structure
Previous Manifest Hash: (8 octets) _Previous Manifest Hash_: (8 octets)
Hash of the previously sent Manifest Message. Hash of the previously sent Manifest Message.
Current Manifest Hash: (8 octets) _Current Manifest Hash_: (8 octets)
Hash of the current Manifest Message. Hash of the current Manifest Message.
DRIP Link (BE: HDA, UA): (8 octets) _DRIP Link (BE: HDA, UA)_: (8 octets)
Hash of the DRIP Link Authentication Message carrying BE: HDA, UA Hash of the DRIP Link Authentication Message carrying BE: HDA, UA
(see Section 4.2). (see Section 4.2).
ASTM Message Hash: (8 octets) _ASTM Message Hash_: (8 octets)
Hash of a single full ASTM Message using hash operations described Hash of a single full ASTM Message using hash operations described
in Section 4.4.3. in Section 4.4.3.
4.4.1. Hash Count & Format Validation 4.4.1. Hash Count and Format Validation
When decoding a DRIP Manifest on a receiver, a calculation of the When decoding a DRIP Manifest on a receiver, a calculation of the
number of hashes and a validation can be performed by using the number of hashes and a validation can be performed by using the
number of octets (defined as manifestLength) between the UA DET and number of octets between the _UA DET_ and the _VNB Timestamp by UA_
the VNB Timestamp by UA such as shown in Figure 9. (defined as manifestLength) such as shown in Figure 9.
<CODE BEGINS> <CODE BEGINS>
if (manifestLength MOD 8) != 0 { if (manifestLength MOD 8) != 0 {
return DECODE_FAILURE return DECODE_FAILURE
} }
hashCount = (manifestLength / 8) - 3; hashCount = (manifestLength / 8) - 3;
<CODE ENDS> <CODE ENDS>
Figure 9: Pseudo-code for Manifest Sanity Check and Number of Hashes Figure 9: Pseudocode for Manifest Sanity Check and Number of
Calculation Hashes Calculation
4.4.2. Manifest Ledger Hashes 4.4.2. Manifest Ledger Hashes
Three special hashes are included in all Manifests. The Previous The following three special hashes are included in all Manifests:
Manifest Hash, links to the previous Manifest, and the Current
Manifest Hash is of the Manifest in which it appears. These two
hashes act as a ledger of provenance to the Manifest that could be
traced back if the Observer was present for extended periods of time.
The DRIP Link (BE: HDA, UA) is included so there is a direct * the _Previous Manifest Hash_ links to the previous Manifest.
* the _Current Manifest Hash_ is of the Manifest in which it
appears.
* the _DRIP Link (BE: HDA, UA) Hash_ ties the endorsed UA key to the
Manifest chain.
The Previous and Current hashes act as a ledger of provenance for the
Manifest chain, which should be traced back if the Observer and UA
were within Broadcast RID wireless range of each other for an
extended period of time.
The _DRIP Link (BE: HDA, UA)_ is included so there is a direct
signature by the UA over the Broadcast Endorsement (see Section 4.2). signature by the UA over the Broadcast Endorsement (see Section 4.2).
Typical operation would expect that the list of ASTM Message Hash's Typical operation would expect that the list of _ASTM Message Hashes_
contain nonce-link data. To enforce a binding between the BE: HDA, contain nonce-like data. To enforce a binding between the BE: HDA,
UA and avoid trivial replay attack vectors (see Section 9.1) at least UA and avoid trivial replay attack vectors (see Section 9.1), at
1 ASTM Message Hash MUST be from an [F3411] message that satisfies least one _ASTM Message Hash_ MUST be from an [F3411] message that
the 4th requirement in Section 6.3. satisfies the fourth requirement in Section 6.3. At least once per
Observation Session, the Observer must process that message as
specified in Section 6.3.
4.4.3. Hash Algorithms and Operation 4.4.3. Hash Algorithms and Operation
The hash algorithm used for the Manifest is the same hash algorithm The hash algorithm used for the Manifest is the same hash algorithm
used in creation of the DET [RFC9374] that is signing the Manifest. used in creation of the DET [RFC9374] that is signing the Manifest.
This is encoded as part of the DET using the HHIT Suite ID. This is encoded as part of the DET using the HHIT Suite ID.
DET's using cSHAKE128 [NIST.SP.800-185] compute the hash as follows: DETs that use cSHAKE128 [NIST.SP.800-185] compute the hash as
follows:
cSHAKE128(ASTM Message, 64, "", "Remote ID Auth Hash") cSHAKE128(ASTM Message, 64, "", "Remote ID Auth Hash")
For OGAs other than "5" [RFC9374], use the construct appropriate for For ORCHID Generation Algorithms (OGAs) other than "5" (EdDSA/
the associated hash. For example, for "2" which is ECDSA/SHA-384: cSHAKE128) [RFC9374], use the construct appropriate for the
associated hash. For example, the hash for "2" (ECDSA/SHA-384) is
computed as follows:
Ltrunc( SHA-384( ASTM Message | "Remote ID Auth Hash" ), 8 ) Ltrunc( SHA-384( ASTM Message | "Remote ID Auth Hash" ), 8 )
When building the list of hashes, the Previous Manifest Hash is known
from the previous Manifest. For the first built Manifest this value When building a Manifest, this process MUST be followed:
is filled with a random nonce. The Current Manifest Hash is null
filled while ASTM Messages are hashed and fill the ASTM Messages 1. The _Previous Manifest Hash_
Hashes section. When all messages are hashed, the Current Manifest
Hash is computed over the Previous Manifest Hash, Current Manifest a. is filled with a random nonce if and only if this is the
Hash (null filled) and ASTM Messages Hashes. This hash value first manifest being generated;
replaces the null filled Current Manifest Hash and becomes the
Previous Manifest Hash for the next Manifest. b. otherwise, it contains the previous manifest's _Current
Manifest Hash_.
2. The _Current Manifest Hash_ is filled with null.
3. _ASTM Message Hashes_ are filled per Section 4.4.3.1 or
Section 4.4.3.2.
4. A hash, as defined above in this section, is calculated over the
_Previous Manifest Hash_, _Current Manifest Hash_ (null filled),
and _ASTM Message Hashes_.
5. The _Current Manifest Hash_ (null filled) is replaced with the
hash generated in Step r.
4.4.3.1. Legacy Transport Hashing 4.4.3.1. Legacy Transport Hashing
Under this transport DRIP hashes the full ASTM Message being sent Under this transport, DRIP hashes the full ASTM Message being sent
over the Bluetooth Advertising frame. This is the 25-octet object over the Bluetooth Advertising frame. This is the 25-octet object
start with the Message Type and Protocol Version octet along with the that starts with the Message Type and Protocol Version octet along
24 octets of message data. The hash MUST NOT included the Message with the 24 octets of message data. The hash MUST NOT include the
Counter octet. Message Counter octet.
For paged ASTM Messages (currently only Authentication Messages) all For paged ASTM Messages (currently only Authentication Messages), all
the pages are concatenated together in Page Number order and hashed of the pages are concatenated together in Page Number order and
as one object. hashed as one object.
4.4.3.2. Extended Transport Hashing 4.4.3.2. Extended Transport Hashing
Under this transport DRIP hashes the full ASTM Message Pack (Message Under this transport, DRIP hashes the full ASTM Message Pack (Message
Type 0xF) regardless of its content. The hash MUST NOT included the Type 0xF) regardless of its content. The hash MUST NOT include the
Message Counter octet. Message Counter octet.
4.5. DRIP Frame 4.5. DRIP Frame
This SAM Type is defined to enable the use of Section 4.1 in the This SAM Type is defined to enable use of the _UA-Signed Evidence
future beyond the previously defined formats (Wrapper and Manifest) Structure_ (Section 4.1) in the future beyond the previously defined
by the inclusion of a single octet to signal the format of evidence formats (Wrapper and Manifest) by the inclusion of a single octet to
data (up to 111 octets). signal the format of _Evidence_ data (up to 111 octets).
The content format of Frame Evidence Data is not defined in this The content format of _Frame Evidence Data_ is not defined in this
document. Other specifications MUST define the contents and register document. Other specifications MUST define the contents and register
for a Frame Type. At the time of publication there are no defined for a _Frame Type_. At the time of publication (2024), there are no
Frame Types other than an Experimental range. defined Frame Types; only an Experimental range has been defined.
Observers MUST check the signature of the structure (Section 4.1) per Observers MUST check the signature of the structure (Section 4.1) per
Section 3.1.2.2 and MAY, if the specification of Frame Type is known, Section 3.1.2.2 and MAY, if the specification of _Frame Type_ is
parse the content in Frame Evidence Data. known, parse the content in _Frame Evidence Data_.
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Frame Type | | | Frame Type | |
+---------------+ . +---------------+ .
. Frame Evidence Data . . Frame Evidence Data .
. . . .
| | | |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 10: DRIP Frame Figure 10: DRIP Frame
Frame Type: (1 octet) _Frame Type_: (1 octet)
Byte to sub-type for future different DRIP Frame formats. It As shown in Figure 10, the _Frame Type_ takes the first octet,
takes the first octet in Figure 10, leaving 111 octets available which leaves 111 octets available for _Frame Evidence Data_. See
for Frame Evidence Data. See Section 8.1 for Frame Type Section 8.1 for Frame Type allocations.
allocations.
5. Forward Error Correction 5. Forward Error Correction
For Broadcast RID, FEC is provided by the lower layers in Extended For Broadcast RID, FEC is provided by the lower layers in Extended
Transports. The Bluetooth 4.x Legacy Transport does not have Transports. The Bluetooth 4.x Legacy Transport does not support FEC,
supporting FEC, so with DRIP Authentication the following application so the following application-level scheme is used with DRIP
level scheme is used to add some FEC. When sending data over a Authentication to add some FEC. When sending data over a medium that
medium that does not have underlying FEC, for example Bluetooth 4.x, does not have underlying FEC, for example Bluetooth 4.x, this section
then this section MUST be used. MUST be used.
The Bluetooth 4.x lower layers have error detection but not The Bluetooth 4.x lower layers have error detection but not
correction. Any frame in which Bluetooth detects an error is dropped correction. Any frame in which Bluetooth detects an error is dropped
and not delivered to higher layers (in our case, DRIP). Thus it can and not delivered to higher layers (in our case, DRIP). Thus it can
be treated as an erasure. be treated as an erasure.
DRIP standardizes a single page FEC scheme using XOR parity across DRIP standardizes a single page FEC scheme using XOR parity across
all page data of an Authentication Message. This allows the all page data of an Authentication Message. This allows the
correction of single erased page in an Authentication Message. If correction of a single erased page in an Authentication Message. If
more than a single page is missing then handling of an incomplete more than a single page is missing, then handling of an incomplete
Authentication Message is determined by higher layers. Authentication Message is determined by higher layers.
Other FEC schemes, to protect more than a single page of an Other FEC schemes, to protect more than a single page of an
Authentication Message or multiple [F3411] Messages, is left for Authentication Message or multiple [F3411] Messages, are left for
future standardization if operational experience proves it necessary future standardization if operational experience proves it necessary
and/or practical. and/or practical.
The data added during FEC is not included in the Authentication Data The data added during FEC is not included in the _Authentication Data
/ Signature, but instead in the Additional Data field of Figure 2. / Signature_, but instead in the _Additional Data_ field of Figure 2.
This may cause the Authentication Message to exceed 9-pages, up to a This may cause the Authentication Message to exceed 9 pages, up to a
maximum of 16-pages. maximum of 16 pages.
5.1. Encoding 5.1. Encoding
When encoding two things are REQUIRED: When encoding, two things are REQUIRED:
1. The FEC data MUST start on a new Authentication Page. To do 1. The FEC data MUST start on a new Authentication Page. To do
this, the results of parity encoding MUST be placed in the this, the results of parity encoding MUST be placed in the
Additional Data field of Figure 2 with null padding before it to _Additional Data_ field of Figure 2 with null padding before it
line up with the next page. The Additional Data Length field to line up with the next page. The _Additional Data Length_
MUST be set to number of padding octets + number of parity field MUST be set to number of padding octets + number of parity
octets. octets.
2. The Last Page Index field (in Page 0) MUST be incremented from 2. The _Last Page Index_ field (in Page 0) MUST be incremented from
what it would have been without FEC by the number of pages what it would have been without FEC by the number of pages
required for the Additional Data Length field, null padding and required for the _Additional Data Length_ field, null padding,
FEC. and FEC.
To generate the parity, a simple XOR operation using the previous To generate the parity, a simple XOR operation using the previous
parity page and current page is used. Only the 23-octet parity page and current page is used. Only the 23-octet
Authentication Payload field of Figure 1 is used in the XOR _Authentication Payload_ field of Figure 1 is used in the XOR
operations. For Page 0, a 23-octet null pad is used for the previous operations. For Page 0, a 23-octet null pad is used for the previous
parity page. parity page.
Figure 11 shows an example of the last two pages (out of N) of an Figure 11 shows an example of the last two pages (out of N) of an
Authentication Message using DRIP Single Page FEC. The Additional Authentication Message using DRIP Single Page FEC. The _Additional
Data Length is set to 33 as there are always 23 octets of FEC data Data Length_ is set to 33, as there are always 23 octets of FEC data
and in this example 10 octets of padding to line it up into Page N. and there are 10 octets of padding in this example to line it up into
Page N.
Page N-1: Page N-1:
0 1 2 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 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
| Page Header | | | Page Header | |
+---------------+ | +---------------+ |
| Authentication Data / Signature | | Authentication Data / Signature |
| | | |
| +---------------+---------------+---------------+ | +---------------+---------------+---------------+
skipping to change at page 26, line 37 skipping to change at line 1181
| Forward Error Correction | | Forward Error Correction |
| | | |
| | | |
| | | |
+---------------+---------------+---------------+---------------+ +---------------+---------------+---------------+---------------+
Figure 11: Example Single Page FEC Encoding Figure 11: Example Single Page FEC Encoding
5.2. Decoding 5.2. Decoding
Frame decoding is independent of the transmit media. However the Frame decoding is independent of the transmit media. However, the
decoding process can determine from the first Authentication page decoding process can determine from the first Authentication Page
that there may be a Bluetooth 4.x FEC page at the end. The decoding that there may be a Bluetooth 4.x FEC page at the end. The decoding
process MUST test for the presence of FEC and apply it as follows. process MUST test for the presence of FEC and apply it as follows.
To determine if FEC has been used, a check of the Last Page Index is To determine if FEC has been used, a check of the _Last Page Index_
performed. In general if the Last Page Index field is one greater is performed. In general, if the _Last Page Index_ field is one
than that necessary to hold Length octets of Authentication Data then greater than that necessary to hold _Length_ octets of Authentication
FEC has been used. Note that if Length octets are exhausted exactly Data, then FEC has been used. Note that if _Length_ octets are
at the end of an Authentication Page, the Additional Data Length exhausted exactly at the end of an Authentication Page, the
field will occupy the first octet of the following page. The _Additional Data Length_ field will occupy the first octet of the
remainder of this page will be null padded under DRIP to align the following page. The remainder of this page will be null padded under
FEC to its own page. In this case the Last Page Index will have been DRIP to align the FEC to its own page. In this case, the _Last Page
incremented once for initializing the Additional Data Length field Index_ will have been incremented once for initializing the
and once for FEC page, for a total of two additional pages, as in the _Additional Data Length_ field and once for the FEC page, for a total
last row of Table 5. of two additional pages, as in the last row of Table 5.
To decode FEC in DRIP, a rolling XOR is used on each Authentication To decode FEC in DRIP, a rolling XOR is used on each _Authentication
Page received in the current Authentication Message. A Message Page_ received in the current Authentication Message. A Message
Counter, outside of the ASTM Message but specified in [F3411], is Counter, outside of the ASTM Message but specified in [F3411], is
used to signal a different Authentication Message and to correlate used to signal a different Authentication Message and to correlate
pages to messages. This Message Counter is only single octet in pages to messages. This Message Counter is only a single octet in
length, so it will roll over (to 0x00) after reaching its maximum length, so it will roll over (to 0x00) after reaching its maximum
value (0xFF). If only a single page is missing in the Authentication value (0xFF). If only a single page is missing in the Authentication
Message the resulting parity octets should be the data of the erased Message the resulting parity octets should be the data of the erased
page. page.
Authentication Page 0 contains various important fields, only located Authentication Page 0 contains various important fields, only located
on that page, that help decode the full ASTM Authentication Message. on that page, that help decode the full ASTM Authentication Message.
If Page 0 has been reconstructed, the Last Page Index and Length If Page 0 has been reconstructed, the _Last Page Index_ and _Length_
fields MUST be validated by DRIP. The pseudo-code in Figure 12 can fields MUST be validated by DRIP. The pseudocode in Figure 12 can be
be used for both checks. used for both checks.
<CODE BEGINS> <CODE BEGINS>
function decode_check(auth_pages[], decoded_lpi, decoded_length) { function decode_check(auth_pages[], decoded_lpi, decoded_length) {
// check decoded_lpi does not exceed maximum value // check decoded_lpi does not exceed maximum value
if (decoded_lpi >= 16) { if (decoded_lpi >= 16) {
return DECODE_FAILURE return DECODE_FAILURE
} }
// check that decoded length does not exceed DRIP maximum value // check that decoded length does not exceed DRIP maximum value
if (decoded_length > 201) { if (decoded_length > 201) {
skipping to change at page 28, line 34 skipping to change at line 1243
return DECODE_FAILURE return DECODE_FAILURE
} }
// check that byte directly after last auth byte is null // check that byte directly after last auth byte is null
if (auth_data[last_auth_byte + 1] equals null) { if (auth_data[last_auth_byte + 1] equals null) {
return DECODE_FAILURE return DECODE_FAILURE
} }
// we set our presumed Additional Data Length (ADL) // we set our presumed Additional Data Length (ADL)
presumed_adl = auth_data[last_auth_byte + 1] presumed_adl = auth_data[last_auth_byte + 1]
// use the presumed ADL to calculate a presumed LPI // use the presumed ADL to calculate a presumed
//Last Page Index (LPI, a field defined in [F3411])
presumed_lpi = (presumed_adl + decoded_length - 17) / 23 presumed_lpi = (presumed_adl + decoded_length - 17) / 23
// check that presumed LPI and decoded LPI match // check that presumed LPI and decoded LPI match
if (presumed_lpi not equal decoded_lpi) { if (presumed_lpi not equal decoded_lpi) {
return DECODE_FAILURE return DECODE_FAILURE
} }
return DECODE_SUCCESS return DECODE_SUCCESS
} }
<CODE ENDS> <CODE ENDS>
Figure 12: Pseudo-code for Decode Checks Figure 12: Pseudocode for Decode Checks
5.3. FEC Limitations 5.3. FEC Limitations
The worst-case scenario is when the Authentication Data / Signature The worst-case scenario is when the _Authentication Data / Signature_
ends perfectly on a page boundary (Page N-1). This means the ends perfectly on a page boundary (Page N-1). This means the
Additional Data Length would start the next page (Page N) and have 22 _Additional Data Length_ would start the next page (Page N) and have
octets worth of null padding to align the FEC to begin at the start 22 octets worth of null padding to align the FEC to begin at the
of the next page (Page N+1). In this scenario, an entire page (Page start of the next page (Page N+1). In this scenario, an entire page
N) is being wasted just to carry the Additional Data Length. (Page N) is being wasted just to carry the _Additional Data Length_.
6. Requirements & Recommendations 6. Requirements and Recommendations
6.1. Legacy Transports 6.1. Legacy Transports
Under DRIP, the goal is to attempt to bring reliable receipt of the Under DRIP, the goal is to bring reliable receipt of the paged
paged Authentication Message using Legacy Transports. FEC Authentication Message using Legacy Transports. FEC (Section 5) MUST
(Section 5) MUST be used, per mandated RID rules (for example the US be used, per mandated RID rules (for example, the US FAA RID Rules
FAA RID Rule [FAA-14CFR]), when using Legacy Transports (such as [FAA-14CFR]), when using Legacy Transports (such as Bluetooth 4.x).
Bluetooth 4.x).
Under [F3411], Authentication Messages are transmitted at the static Under [F3411], Authentication Messages are transmitted at the static
rate (at least every 3 seconds). Any DRIP Authentication Messages rate (at least every 3 seconds). Any DRIP Authentication Messages
containing dynamic data (such as the DRIP Wrapper) MAY be sent at the containing dynamic data (such as the DRIP Wrapper) MAY be sent at the
dynamic rate (at least every 1 second). dynamic rate (at least every 1 second).
6.2. Extended Transports 6.2. Extended Transports
Under the ASTM specification, Extended Transports of RID must use the Under the ASTM specification, Extended Transports of RID must use the
Message Pack (Message Type 0xF) format for all transmissions. Under Message Pack (Message Type 0xF) format for all transmissions. Under
Message Pack, ASTM Messages are sent together (in Message Type order) Message Pack, ASTM Messages are sent together (in Message Type order)
in a single frame (up to 9 single frame equivalent messages under in a single frame (up to 9 single-frame equivalent messages under
Legacy Transports). Message Packs are required by [F3411] to be sent Legacy Transports). Message Packs are required by [F3411] to be sent
at a rate of 1 per second (like dynamic messages). at a rate of 1 per second (like dynamic messages).
Message Packs are sent only over Extended Transports that provide Message Packs are sent only over Extended Transports that provide
FEC. Thus, the DRIP decoders will never be presented with a Message FEC. Thus, the DRIP decoders will never be presented with a Message
Pack from which a constituent Authentication Page has been dropped; Pack from which a constituent Authentication Page has been dropped;
DRIP FEC could never provide a benefit to a Message Pack, only DRIP FEC could never provide benefit to a Message Pack, only consume
consume its precious payload space. Therefore, DRIP FEC (Section 5) its precious payload space. Therefore, DRIP FEC (Section 5) MUST NOT
MUST NOT be used in Message Packs. be used in Message Packs.
6.3. Authentication 6.3. Authentication
To fulfill the requirements in [RFC9153], a UA: To fulfill the requirements in [RFC9153], a UA MUST:
1. MUST: send DRIP Link (Section 4.2) using the BE: Apex, RAA 1. send DRIP Link (Section 4.2) using the _BE: Apex, RAA_ (partially
(partially satisfying GEN-3); at least once per 5 minutes. Apex satisfying GEN-3); at least once per 5 minutes. Apex in this
in this context is the DET prefix owner context is the DET prefix owner.
2. MUST: send DRIP Link (Section 4.2) using the BE: RAA, HDA 2. send DRIP Link (Section 4.2) using the BE: RAA, HDA (partially
(partially satisfying GEN-3); at least once per 5 minutes satisfying GEN-3); at least once per 5 minutes.
3. MUST: send DRIP Link (Section 4.2) using the BE: HDA, UA 3. send DRIP Link (Section 4.2) using the BE: HDA, UA (satisfying
(satisfying ID-5, GEN-1 and partially satisfying GEN-3); at least ID-5, GEN-1 and partially satisfying GEN-3); at least once per
once per minute minute.
4. MUST: send any other DRIP Authentication Format (non-DRIP Link) 4. send any other DRIP Authentication Format (non-DRIP Link) where
where the UA is dynamically signing data that is guaranteed to be the UA is dynamically signing data that is guaranteed to be
unique, unpredictable and easily cross checked by the receiving unique, unpredictable, and easily cross checked by the receiving
device (satisfying ID-5, GEN-1 and GEN-2); at least once per 5 device (satisfying ID-5, GEN-1 and GEN-2); at least once per 5
seconds seconds.
These four transmission requirements collectively satisfy GEN-3. An Observer's receiver must verify the signature (cryptographically,
as specified in Section 3.1.1) on each of the 4 messages sent in the
operations specified immediately above and the Observer MUST validate
the signed content (via non-cryptographic means) of the 4th message
sent in the last operation immediately above (the non-DRIP Link
message).
These transmission, receiver verification, and Observer validation
requirements collectively satisfy GEN-3.
6.4. Operational 6.4. Operational
UAS operation may impact the frequency of sending DRIP Authentication UAS operation may impact the frequency of sending DRIP Authentication
messages. When a UA dwells at an approximate location, and the Messages. When a UA dwells at an approximate location, and the
channel is heavily used by other devices, less frequent message channel is heavily used by other devices, less frequent message
authentication may be effective (to minimize RF packet collisions) authentication may be effective (to minimize RF packet collisions)
for an Observer. Contrast this with a UA transiting an area, where for an Observer. Contrast this with a UA transiting an area, where
authenticated messages SHOULD be sufficiently frequent for an authenticated messages SHOULD be sufficiently frequent for an
Observer to have a high probability of receiving an adequate number Observer to have a high probability of receiving an adequate number
for validation during the transit. for validation during the transit.
A RECOMMENDED operational configuration (in alignment with A RECOMMENDED operational configuration (in alignment with
Section 6.3) with reasoning can be found in Appendix B. It consists Section 6.3) with rationale can be found in Appendix B. It
of the following recommendations for every second: recommends the following once per second:
* Under Legacy Transport: * Under Legacy Transport:
- Two sets of those ASTM Messages required by a CAA in its - Two sets of those ASTM Messages required by a CAA in its
jurisdiction (example: Basic ID, Location and System) and one jurisdiction (example: Basic ID, Location/Vector, and System)
set of other ASTM Messages (example: Self ID, Operator ID) and one set of other ASTM Messages (example: Self ID, Operator
ID)
- An FEC protected DRIP Manifest enabling authentication of those - An FEC-protected DRIP Manifest enabling authentication of those
ASTM Messages sent ASTM Messages sent
- A single page of an FEC protected DRIP Link - A single page of an FEC-protected DRIP Link
* Under Extended Transport: * Under Extended Transport:
- A Message Pack of ASTM Messages (up to 4) and a DRIP Wrapper - A Message Pack of ASTM Messages (up to 4) and a DRIP Wrapper
(per Section 4.3.2) (per Section 4.3.2)
- A Message Pack of a DRIP Link - A Message Pack of a DRIP Link
6.4.1. DRIP Wrapper 6.4.1. DRIP Wrapper
If DRIP Wrappers are sent, they MUST be sent in addition to any If DRIP Wrappers are sent, they MUST be sent in addition to any
required ASTM Messages in a given jurisdiction. An implementation required ASTM Messages in a given jurisdiction. An implementation
MUST NOT send DRIP Wrappers in place of any required ASTM Messages it MUST NOT send DRIP Wrappers in place of any required ASTM Messages it
may encapsulate. Thus, messages within a Wrapper are sent twice: may encapsulate. Thus, messages within a Wrapper are sent twice:
once in the clear and once authenticated within the Wrapper. once in the clear and once authenticated within the Wrapper.
The DRIP Wrapper has a specific use case for DRIP aware Observers. The DRIP Wrapper has a specific use case for DRIP-aware Observers.
For an Observer plotting Location Messages (Message Type 0x2) on a For an Observer plotting Location/Vector Messages (Message Type 0x2)
map, display an embedded Location Message in a DRIP Wrapper can be on a map, display of an embedded Location/Vector Message in a DRIP
marked differently (e.g., via color) to signify trust in the Location Wrapper can be marked differently (e.g., via color) to signify trust
data. in the Location/Vector data.
6.4.2. UAS RID Trust Assessment 6.4.2. UAS RID Trust Assessment
As described in Section 3.1.2, the Observer MUST perform validation As described in Section 3.1.2, the Observer MUST perform validation
of the data being received in Broadcast RID. This is because trust of the data being received in Broadcast RID. This is because trust
in a key is different from trust that an observed UA possesses that in a key is different from trust that an observed UA possesses that
key. key.
A chain of DRIP Links provides trust in a key. A message containing A chain of DRIP Links provides trust in a key. A message, signed by
rapidly changing, not predictable far in advance (relative to typical that key, containing data that changes rapidly and is not predictable
operational flight times) that can be validated by Observers, signed far in advance (relative to typical operational flight times) but
by that key, provides trust that some agent with access to that data that can be validated by Observers, provides trust that some agent
also possesses that key. If the validation involves correlating with access to that data also possesses that key. If the validation
physical world observations of the UA with claims in that data, then involves correlating physical world observations of the UA with
the probability is high that the observed UA is (or is collaborating claims in that data, then the probability is high that the observed
with or observed in real time by) the agent with the key. UA is (or is collaborating with or observed in real time by) the
agent with the key.
After signature verification of any DRIP Authentication Message At least once per Observation session, after signature verification
containing UAS RID information elements (e.g., DRIP Wrapper of any DRIP Authentication Message containing UAS RID information
Section 4.3) the Observer MUST use other sources of information to elements (e.g., DRIP Wrapper, Section 4.3), the Observer must use
correlate against and perform validation. An example of another other sources of information to correlate against and perform
validation (as specified in Section 6.3). An example of another
source of information is a visual confirmation of the UA position. source of information is a visual confirmation of the UA position.
When correlation of these different data streams does not match in When correlation of these different data streams does not match in
acceptable thresholds, the data MUST be rejected as if the signature acceptable thresholds, the data MUST be rejected as if the signature
failed to validate. Acceptable thresholds limits and what happens failed to validate. Acceptable threshold limits and what happens
after such a rejection are out of scope for this document. after such a rejection are out of scope for this document.
7. Summary of Addressed DRIP Requirements 7. Summary of Addressed DRIP Requirements
The following [RFC9153] requirements are addressed in this document: The following requirements as defined in [RFC9153] are addressed in
this document:
ID-5: Non-spoofability
ID-5: Non-spoofability
Addressed using the DRIP Wrapper (Section 4.3), DRIP Manifest Addressed using the DRIP Wrapper (Section 4.3), DRIP Manifest
(Section 4.4) or DRIP Frame (Section 4.5). (Section 4.4), or DRIP Frame (Section 4.5).
GEN-1: Provable Ownership GEN-1: Provable Ownership
Addressed using the DRIP Link (Section 4.2) and DRIP Wrapper Addressed using the DRIP Link (Section 4.2) and DRIP Wrapper
(Section 4.3), DRIP Manifest (Section 4.4) or DRIP Frame (Section 4.3), DRIP Manifest (Section 4.4), or DRIP Frame
(Section 4.5). (Section 4.5).
GEN-2: Provable Binding GEN-2: Provable Binding
Addressed using the DRIP Wrapper (Section 4.3), DRIP Manifest Addressed using the DRIP Wrapper (Section 4.3), DRIP Manifest
(Section 4.4) or DRIP Frame (Section 4.5). (Section 4.4) or DRIP Frame (Section 4.5).
GEN-3: Provable Registration GEN-3: Provable Registration
Addressed using the DRIP Link (Section 4.2). Addressed using the DRIP Link (Section 4.2).
8. IANA Considerations 8. IANA Considerations
8.1. IANA DRIP Registry 8.1. IANA DRIP Registry
This document requests two new registries, for DRIP SAM Type and DRIP IANA has created the "DRIP SAM Types" and "DRIP Frame Types"
Frame Type, under the DRIP registry group registries within the "Drone Remote ID Protocol" registry group
(https://www.iana.org/assignments/drip/drip.xhtml). (https://www.iana.org/assignments/drip).
DRIP SAM Type: This registry is a mirror for SAM Types containing DRIP SAM Types:
the subset of allocations used by DRIP Authentication Messages. This registry is a mirror for SAM Types containing the subset of
Future additions MUST be done through ASTM's designated registrar allocations used by DRIP Authentication Messages. Future
which at the time of publication of this RFC is ICAO additions MUST be done through ASTM's designated registrar, which
[ASTM-Remote-ID]. Additions for DRIP will be coordinated by IANA is ICAO [ASTM-Remote-ID] at the time of publication of this RFC
and the ASTM designated registrar before final publication as (2024). The registration procedure for DRIP (only) SAM Types is
Standards Track RFCs. The following values have been allocated to Standards Action [RFC8126]. Requests for new DRIP SAM Type
the IETF and are defined here: registrations will be coordinated by IANA and the ASTM-designated
registrar of all SAM Types before being documented in Standards
Track RFCs. The following values have been allocated to the IETF:
+==========+===============+=======================================+ +==========+===========+=======================================+
| SAM Type | Name | Description | | SAM Type | Name | Description |
+==========+===============+=======================================+ +==========+===========+=======================================+
| 0x01 | DRIP Link | Format to hold Broadcast Endorsements | | 0x01 | DRIP Link | Format to hold Broadcast Endorsements |
+----------+---------------+---------------------------------------+ +----------+-----------+---------------------------------------+
| 0x02 | DRIP Wrapper | Authenticate full ASTM Messages | | 0x02 | DRIP | Authenticate full ASTM Messages |
+----------+---------------+---------------------------------------+ | | Wrapper | |
| 0x03 | DRIP Manifest | Authenticate hashes of ASTM Messages | +----------+-----------+---------------------------------------+
+----------+---------------+---------------------------------------+ | 0x03 | DRIP | Authenticate hashes of ASTM Messages |
| 0x04 | DRIP Frame | Format for future DRIP authentication | | | Manifest | |
+----------+---------------+---------------------------------------+ +----------+-----------+---------------------------------------+
| 0x04 | DRIP | Format for future DRIP authentication |
| | Frame | |
+----------+-----------+---------------------------------------+
Table 2: DRIP SAM Types Table 2: DRIP SAM Types
DRIP Frame Type: This 8-bit valued registry is for Frame Types in DRIP Frame Types:
DRIP Frame Authentication Messages. Future additions to this This 8-bit value registry is for Frame Types in DRIP Frame
registry are to be made through Expert Review (Section 4.5 of Authentication Messages. Future additions to this registry are to
[RFC8126]) for the values of 0x01 to 0x9F and First Come, First be made through Expert Review (Section 4.5 of [RFC8126]) for
Served (Section 4.4 of [RFC8126]) for values 0xA0 to 0xEF. The values 0x01 to 0x9F and First Come First Served (Section 4.4 of
following values are defined: [RFC8126]) for values 0xA0 to 0xEF. The following values are
defined:
+=============+==============+====================================+ +=============+==============+===============================+
| Frame Type | Name | Description | | Frame Type | Name | Description |
+=============+==============+====================================+ +=============+==============+===============================+
| 0x00 | Reserved | Reserved | | 0x00 | Reserved | Reserved |
+-------------+--------------+------------------------------------+ +-------------+--------------+-------------------------------+
| 0x01 - 0x9F | Reserved | Reserved: Expert Review | | 0x01 - 0xEF | Unassigned | |
+-------------+--------------+------------------------------------+ +-------------+--------------+-------------------------------+
| 0xA0 - 0xEF | Reserved | Reserved: First Come, First Served | | 0xF0-0xFF | Experimental | Reserved for Experimental Use |
+-------------+--------------+------------------------------------+ +-------------+--------------+-------------------------------+
| 0xF0 - 0xFF | Experimental | Experimental Use |
+-------------+--------------+------------------------------------+
Table 3: DRIP Frame Types Table 3: DRIP Frame Types
Criteria that should be applied by the designated experts includes Criteria that should be applied by the designated experts includes
determining whether the proposed registration duplicates existing determining whether the proposed registration duplicates existing
functionality and whether the registration description is clear and functionality and whether the registration description is clear and
fits the purpose of this registry. fits the purpose of this registry.
Registration requests MUST be sent to drip-reg-review@ietf.org Registration requests MUST be sent to drip-reg-review@ietf.org
(mailto:drip-reg-review@ietf.org) and be evaluated within a three- (mailto:drip-reg-review@ietf.org) and be evaluated by one or more
week review period on the advice of one or more designated experts. designated experts within a three-week review period. Within that
Within that review period, the designated experts will either approve review period, the designated experts will either approve or deny the
or deny the registration request, and communicate their decision to registration request, and communicate their decision to the review
the review list and IANA. Denials should include an explanation and, list and IANA. Denials should include an explanation and, if
if applicable, suggestions to successfully register the DRIP Frame applicable, suggestions to successfully register the DRIP Frame Type.
Type.
Registration requests that are undetermined for a period longer than Registration requests that are undetermined for a period longer than
28 days can be brought to the IESG's attention for resolution. 28 days can be brought to the IESG's attention for resolution.
9. Security Considerations 9. Security Considerations
9.1. Replay Attacks 9.1. Replay Attacks
[F3411] (regardless of transport) lacks replay protection, as it more [F3411] (regardless of transport) lacks replay protection, as it more
fundamentally lacks fully specified authentication. An attacker can fundamentally lacks fully specified authentication. An attacker can
spoof the UA sender MAC address and UAS ID, replaying (with or spoof the UA sender MAC address and UAS ID, replaying (with or
without modification) previous genuine messages, and/or crafting without modification) previous genuine messages, and/or crafting
entirely new messages. Using DRIP in [F3411] Authentication message entirely new messages. Using DRIP in [F3411] Authentication Message
framing enables verification that messages were signed with framing enables verification that messages were signed with
registered keys, but when naively used may be vulnerable to replay registered keys, but when naively used may be vulnerable to replay
attacks. Technologies such as Single Emitter Identification can attacks. Technologies such as Single Emitter Identification can
detect such attacks, but are not readily available and can be detect such attacks, but they are not readily available and can be
prohibitively expensive, especially for typical Observer devices such prohibitively expensive, especially for typical Observer devices such
as smartphones. as smartphones.
Replay attack detection using DRIP requires Observer devices to Replay attack detection using DRIP requires Observer devices to
combine information from multiple messages and sources other than combine information from multiple Broadcast RID messages and from
Broadcast RID. A complete chain of Link messages (Section 4.2), from sources other than Broadcast RID. A complete chain of Link messages
an Endorsement root of trust to the claimed sender, must be collected (Section 4.2) from an Endorsement root of trust to the claimed sender
and verified by the Observer device to provide trust in a key. must be collected and verified by the Observer device to provide
Successful signature verification, using that key, of a Wrapper trust in a key. Successful signature verification, using that public
(Section 4.3) or Manifest (Section 4.4) message, authenticating key, of a Wrapper (Section 4.3) or Manifest (Section 4.4) message,
content that is nonce-like, provides trust that the sender actually authenticating content that is nonce-like (see below), provides trust
possesses that key. that the sender actually possesses the corresponding private key.
By "nonce-like" is meant data that is unique, not accurately The term "nonce-like" describes data that is unique, changes
predictable long in advance, and readily validated by the Observer. frequently, is not accurately predictable long in advance, and is
This is described in Section 6.3 (requirement 4) and Section 3.1.2.2. easily validated (i.e., can be checked quickly at low computational
The [F3411] Location message reporting precise UA position and cost using readily available data) by the Observer. A Location/
velocity at a precise very recent time, to be checked by the Observer Vector Message is an obvious choice. This is described in
against visual observations of the UA within RF and thus typically Section 3.1.2.2 and Section 6.3 (requirement 4). A Location/Vector
visual Line Of Sight is the recommended form of this data. For Message [F3411] reporting precise UA position and velocity at a
specification of the foregoing, see Section 3.1.2 and Section 6.4.2. precise and very recent time can be checked by the Observer against
visual observations of UA within both RF and Visual Line of Sight.
For normative specification of the foregoing, see Sections 3.1.2 and
6.4.2. As non-normative clarification, the requirements are
satisfied as follows:
The public key corresponding to a given DET (i.e., the key attested
in the DRIP Link (BE: HDA, UA) that is the last link in the relevant
chain of DRIP Links) is used by an Observer's receiver to try to
authenticate some signed message.
If the signature check passes,
_and_ the message was a Wrapper or Manifest,
_and_ the wrapped or manifested message contained content that was
nonce-like,
_and_ the Observer validated that content by non-cryptographic
means (e.g., if the wrapped or manifested message was a Location/
Vector Message and the UA was visually observed to be in
approximately the claimed location at the reported time),
_only then_ can the Observer trust that the currently observed
sending UA actually possesses the corresponding private key (and thus
owns the corresponding DET).
Messages that pass signature verification with trusted keys could Messages that pass signature verification with trusted keys could
still be replays if they contain only static information (e.g., still be replays if they contain only static information (e.g.,
Broadcast Endorsements (Section 4.2), [F3411] Basic ID or [F3411] Broadcast Endorsements (Section 4.2), [F3411] Basic ID, or [F3411]
Operator ID) or information that cannot be readily validated (e.g., Operator ID), or information that cannot be readily validated (e.g.,
[F3411] Self-ID). Replay of Link messages is harmless (unless sent [F3411] Self-ID). Replay of Link messages is harmless (unless sent
so frequently as to cause RF data link congestion) and indeed can so frequently as to cause RF data link congestion) and indeed can
increase the likelihood of an Observer device collecting an entire increase the likelihood of an Observer device collecting an entire
trust chain in a short time window. Replay of other messages trust chain in a short time window. Replay of other messages
([F3411] Basic ID, [F3411] Operator ID, or [F3411] Self-ID) remains a ([F3411] Basic ID, [F3411] Operator ID, or [F3411] Self-ID) remains a
vulnerability, unless they are combined with messages containing vulnerability, unless they are combined with messages containing
nonce-like data ([F3411] Location or [F3411] System) in a Wrapper or nonce-like data ([F3411] Location/Vector or [F3411] System) in a
Manifest. For specification of this last requirement, see Wrapper or Manifest. For specification of this last requirement, see
Section 4.4.2. Section 4.4.2.
9.2. Wrapper vs Manifest 9.2. Wrapper vs Manifest
Implementations have a choice on using Wrapper (Section 4.3), Implementations have a choice of using Wrapper (Section 4.3),
Manifest (Section 4.4), or a combination to satisfy the 4th Manifest (Section 4.4), or a combination to satisfy the fourth
requirement in Section 6.3. requirement in Section 6.3.
Wrapper is an attached signature of the full content of one or more Wrapper is an attached signature on the full content of one or more
[F3411] messages, providing strong authentication. However, the size [F3411] messages, providing strong authentication. Wrapper is an
limitation means it can not support such signatures over other attached signature of the full content of one or more [F3411]
Authentication Messages, thus it can not provide a direct binding to messages, providing strong authentication. However, the size
any part of the trust chain (Section 3.1.2 and Section 6.4.2). limitation means it cannot support such signatures over other
Authentication Messages; thus, it cannot provide a direct binding to
any part of the trust chain (Sections 3.1.2 and 6.4.2).
Manifest explicitly provides the binding of the last link in the Manifest explicitly provides the binding of the last link in the
trust chain (with the inclusion of the hash of the Link containing trust chain (with the inclusion of the hash of the Link containing
BE: HDA, UA). The use of hashes and their length also allows for a BE: HDA, UA). The use of hashes and their length also allows for a
larger (11 vs 4) number of any [F3411] messages to be authenticated, larger number (11 vs 4) of [F3411] messages to be authenticated,
making it more efficient compared to the Wrapper. However, the making it more efficient compared to the Wrapper. However, the
detached signature requires additional Observer overhead in storing detached signature requires additional Observer overhead in storing
and comparing hashes of received messages (some that may not be and comparing hashes of received messages (some of which may not be
received) of those in a Manifest. received) with those in a Manifest.
Appendix B contains a breakdown of frame counts and an example of a Appendix B contains a breakdown of frame counts and an example of a
schedule using both Manifest and Wrapper. Typical operation may see schedule using both Manifest and Wrapper. Typical operation may see
(as an example) 2x Basic ID, 2x Location, 2x System, 1x Operator ID (as an example) 2x Basic ID, 2x Location/Vector, 2x System, 1x
and 1x Self ID broadcast per second to comply with jurisdiction Operator ID and 1x Self ID broadcast per second to comply with
mandates. Each of these messages are a single frame in size. A Link jurisdiction mandates. Each of these messages is a single frame in
message is 8 frames long (including FEC). This is a base frame count size. A Link message is 8 frames long (including FEC). This is a
of *16 frames*. base frame count of *16 frames*.
When Wrapper is used, up to 4 of the previous messages (except the When Wrapper is used, up to four of the previous messages (except the
Link) can be authenticated. For this comparison, we will sign all Link) can be authenticated. For this comparison, we will sign all
the messages we can in two Wrappers. This results in _20 frames_ the messages we can in two Wrappers. This results in _20 frames_
(with FEC). Due to not being able to fit, the Link message is left (with FEC). Due to size constraints, the Link message is left
unauthenticated. The total frame count using Wrappers is *36 frames* unauthenticated. The total frame count using Wrappers is *36 frames*
(wrapper frame count + base frame count). (wrapper frame count + base frame count).
When Manifest is used, up to 10 previous messages can be When Manifest is used, up to 10 previous messages can be
authenticated. For this example all messages (8) are hashed authenticated. For this example, all messages (8) are hashed
(including the Link) resulting in a single Manifest that is _9 (including the Link) resulting in a single Manifest that is _9
frames_ (with FEC). The total frame count using Manifest is *25 frames_ (with FEC). The total frame count using Manifest is *25
frames* (manifest frame count + base frame count). frames* (manifest frame count + base frame count).
9.3. VNA Timestamp Offsets for DRIP Authentication Formats 9.3. VNA Timestamp Offsets for DRIP Authentication Formats
Note the discussion of VNA Timestamp offsets here is in the context Note the discussion of VNA Timestamp offsets here is in the context
of the DRIP Wrapper (Section 4.3), DRIP Manifest (Section 4.4), and of the DRIP Wrapper (Section 4.3), DRIP Manifest (Section 4.4), and
DRIP Frame (Section 4.5). For DRIP Link (Section 4.2) these offsets DRIP Frame (Section 4.5). For DRIP Link (Section 4.2), these offsets
are set by the DIME and have their own set of considerations in are set by the DIME and have their own set of considerations in
[drip-registries]. [DRIP-REG].
The offset of the VNA Timestamp by UA is one that needs careful The offset of the _VNA Timestamp by UA_ is one that needs careful
consideration for any implementation. The offset should be shorter consideration for any implementation. The offset should be shorter
than any given flight duration (typically less than an hour) but be than any given flight duration (typically less than an hour) but be
long enough to be received and processed by Observers (larger than a long enough to be received and processed by Observers (larger than a
few seconds). It is recommended that 3-5 minutes should be few seconds). It is recommended that 3-5 minutes should be
sufficient to serve this purpose in any scenario, but is not limited sufficient to serve this purpose in any scenario, but it is not
by design. limited by design.
9.4. DNS Security in DRIP 9.4. DNS Security in DRIP
As stated in Section 3.1 specification of particular DNS security As stated in Section 3.1 specification of particular DNS security
options, transports, etc. is outside the scope of this document. options, transports, etc. is outside the scope of this document. The
[drip-registries] is the main specification for DNS operations in main specification for DNS operations in DRIP [DRIP-REG] will specify
DRIP and as such will specify DRIP usage of best common practices for applicable best common security practices (e.g., from [RFC9364]).
security (such as [RFC9364]).
10. Acknowledgments
* Ryan Quigley, James Mussi and Joseph Stanton of AX Enterprize, LLC
for early prototyping to find holes in the draft specifications
* Carsten Bormann for the simple approach of using bit-column-wise
parity for erasure (dropped frame) FEC
* Soren Friis for pointing out that Wi-Fi implementations would not
always give access to the MAC Address, originally used in
calculation of the hashes for DRIP Manifest. Also, for confirming
that Message Packs (0xF) can only carry up to 9 ASTM frames worth
of data (9 Authentication pages)
* Gabriel Cox (chair of the working group that produced [F3411]) in
reviewing the specification for the SAM Type request as the ASTM
Designated Expert
* Mohamed Boucadair (Document Shepherd) for his many patches and
comments
* Eric Vyncke (DRIP AD) for his guidance through the documents path
to publication
* Thanks to the following reviewers:
- Rick Salz (secdir)
- Matt Joras (genart)
- Di Ma (dnsdir)
- Gorry Fairhurst (tsvart)
- Carlos Bernardos (intdir)
- Behcet Sarikaya (iotdir)
- Martin Duke (IESG)
- Roman Danyliw (IESG)
- Murray Kucherawy (IESG)
- Erik Kline (IESG)
- Warren Kumari (IESG)
- Paul Wouters (IESG)
11. References 10. References
11.1. Normative References 10.1. Normative References
[F3411] ASTM International, "Standard Specification for Remote ID [F3411] ASTM International, "Standard Specification for Remote ID
and Tracking", ASTM F3411-22A, DOI 10.1520/F3411-22A, July and Tracking", ASTM F3411-22A, DOI 10.1520/F3411-22A, July
2022, <https://www.astm.org/f3411-22a.html>. 2022, <https://www.astm.org/f3411-22a.html>.
[NIST.SP.800-185] [NIST.SP.800-185]
Kelsey, J., Change, S., Perlner, R., and NIST, "SHA-3 Kelsey, J., Chang, S., and R. Perlner, "SHA-3 Derived
derived functions: cSHAKE, KMAC, TupleHash and Functions: cSHAKE, KMAC, TupleHash and ParallelHash", NIST
ParallelHash", NIST Special Publications Special Publication 800-185, DOI 10.6028/NIST.SP.800-185,
(General) 800-185, DOI 10.6028/NIST.SP.800-185, December December 2016,
2016,
<https://nvlpubs.nist.gov/nistpubs/SpecialPublications/ <https://nvlpubs.nist.gov/nistpubs/SpecialPublications/
NIST.SP.800-185.pdf>. NIST.SP.800-185.pdf>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
skipping to change at page 38, line 15 skipping to change at line 1684
[RFC9374] Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov, [RFC9374] Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
"DRIP Entity Tag (DET) for Unmanned Aircraft System Remote "DRIP Entity Tag (DET) for Unmanned Aircraft System Remote
ID (UAS RID)", RFC 9374, DOI 10.17487/RFC9374, March 2023, ID (UAS RID)", RFC 9374, DOI 10.17487/RFC9374, March 2023,
<https://www.rfc-editor.org/info/rfc9374>. <https://www.rfc-editor.org/info/rfc9374>.
[RFC9434] Card, S., Wiethuechter, A., Moskowitz, R., Zhao, S., Ed., [RFC9434] Card, S., Wiethuechter, A., Moskowitz, R., Zhao, S., Ed.,
and A. Gurtov, "Drone Remote Identification Protocol and A. Gurtov, "Drone Remote Identification Protocol
(DRIP) Architecture", RFC 9434, DOI 10.17487/RFC9434, July (DRIP) Architecture", RFC 9434, DOI 10.17487/RFC9434, July
2023, <https://www.rfc-editor.org/info/rfc9434>. 2023, <https://www.rfc-editor.org/info/rfc9434>.
11.2. Informative References 10.2. Informative References
[ASTM-Remote-ID] [ASTM-Remote-ID]
"ICAO Remote ID Number Registration", December 2023, International Civil Aviation Organization (ICAO), "Remote
ID Number Registration", December 2023,
<https://www.icao.int/airnavigation/IATF/Pages/ASTM- <https://www.icao.int/airnavigation/IATF/Pages/ASTM-
Remote-ID.aspx>. Remote-ID.aspx>.
[drip-registries] [DRIP-REG] Wiethuechter, A. and J. Reid, "DRIP Entity Tag (DET)
Wiethuechter, A. and J. Reid, "DRIP Entity Tag (DET)
Identity Management Architecture", Work in Progress, Identity Management Architecture", Work in Progress,
Internet-Draft, draft-ietf-drip-registries-14, 4 December Internet-Draft, draft-ietf-drip-registries-16, 31 May
2023, <https://datatracker.ietf.org/doc/html/draft-ietf- 2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
drip-registries-14>. drip-registries-16>.
[FAA-14CFR] [FAA-14CFR]
"Remote Identification of Unmanned Aircraft", January Federal Aviation Administration (FAA), "Remote
2021, <https://www.govinfo.gov/content/pkg/FR-2021-01-15/ Identification of Unmanned Aircraft", January 2021,
<https://www.govinfo.gov/content/pkg/FR-2021-01-15/
pdf/2020-28948.pdf>. pdf/2020-28948.pdf>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC9364] Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237, [RFC9364] Hoffman, P., "DNS Security Extensions (DNSSEC)", BCP 237,
RFC 9364, DOI 10.17487/RFC9364, February 2023, RFC 9364, DOI 10.17487/RFC9364, February 2023,
<https://www.rfc-editor.org/info/rfc9364>. <https://www.rfc-editor.org/info/rfc9364>.
Appendix A. Authentication States Appendix A. Authentication States
ASTM Authentication has only three states: None, Invalid, and Valid. ASTM Authentication has only three states: None, Invalid, and Valid.
This is because, under ASTM, the authentication is done by an This is because, under ASTM, the authentication is done by an
external service hosted somewhere on the Internet so it is assumed an external service hosted somewhere on the Internet so it is assumed an
authoritative response will always be returned. This classification authoritative response will always be returned. This classification
becomes more complex in DRIP with the support of "offline" scenarios becomes more complex in DRIP with the support of "offline" scenarios
where a Observer does not have Internet connectivity. With the use where an Observer does not have Internet connectivity. With the use
of asymmetric cryptography this means that the public key (PK) must of asymmetric cryptography, this means that the public key (PK) must
somehow be obtained. [drip-registries] gets more into detail how somehow be obtained. [DRIP-REG] provides more detail on how these
these keys are stored on DNS and one use of DRIP Authentication keys are stored on the DNS and how DRIP Authentication Messages can
messages is to send PK's over Broadcast RID. be used to send PK's over Broadcast RID.
There are a few keys of interest: the PK of the UA and the PK's of There are a few keys of interest: the PK of the UA and the PKs of
relevant DIMEs. This document describes how to send the PK of the UA relevant DIMEs. This document describes how to send the PK of the UA
over the Broadcast RID messages. The key of DIMEs are sent over over the Broadcast RID messages. The keys of DIMEs are sent over
Broadcast RID using the same mechanisms (see Section 4.2 and Broadcast RID using the same mechanisms (see Sections 4.2 and 6.3)
Section 6.3) but MAY be sent at a far lower rate due to potential but MAY be sent at a far lower rate due to potential operational
operational constraints (such as saturation of limited bandwidth). constraints (such as saturation of limited bandwidth). As such,
As such, there are scenarios where part of the key-chain may be there are scenarios where part of the key-chain may be unavailable at
unavailable at the moment a full Authentication Message is received the moment a full Authentication Message is received and processed.
and processed.
The intent of this informative appendix is to give a recommended way The intent of this informative appendix is to recommend a way to
to classify these various states and convey it to the user through classify these various states and convey it to the user through
colors and state names/text. These states can apply to either a colors and state names/text. These states can apply to either a
single authentication message, a DET (and its associated public key), single Authentication Message, a DET (and its associated public key),
and/or a sender. and/or a sender.
The table below lays out the recommended colors to associate with Table 4 briefly describes each state and recommends an associated
state and a brief description of each. color.
+==============+========+=================================+ +==============+========+===================================+
| State | Color | Details | | State | Color | Details |
+==============+========+=================================+ +==============+========+===================================+
| None | Black | No Authentication being | | None | Black | No Authentication has been or is |
| | | received (as yet) | | | | being received (as yet) |
+--------------+--------+---------------------------------+ +--------------+--------+-----------------------------------+
| Partial | Gray | Authentication being received | | Partial | Gray | Authentication being received but |
| | | but missing pages | | | | missing pages |
+--------------+--------+---------------------------------+ +--------------+--------+-----------------------------------+
| Unsupported | Brown | Authentication Type/SAM Type of | | Unsupported | Brown | Authentication Type / SAM Type of |
| | | received message not supported | | | | received message not supported |
+--------------+--------+---------------------------------+ +--------------+--------+-----------------------------------+
| Unverifiable | Yellow | Data needed for signature | | Unverifiable | Yellow | Data needed for signature |
| | | verification is missing | | | | verification is missing |
+--------------+--------+---------------------------------+ +--------------+--------+-----------------------------------+
| Verified | Green | Valid signature verification | | Verified | Green | Valid signature verification and |
| | | and content validation | | | | content validation |
+--------------+--------+---------------------------------+ +--------------+--------+-----------------------------------+
| Trusted | Blue | evidence of Verified and DIME | | Trusted | Blue | Evidence of Verified and DIME is |
| | | is marked as only registering | | | | marked as only registering DETs |
| | | DETs for trusted entities | | | | for trusted entities |
+--------------+--------+---------------------------------+ +--------------+--------+-----------------------------------+
| Unverified | Red | Invalid signature verification | | Unverified | Red | Invalid signature verification or |
| | | or content validation | | | | content validation |
+--------------+--------+---------------------------------+ +--------------+--------+-----------------------------------+
| Questionable | Orange | evidence of both Verified & | | Questionable | Orange | Evidence of both"Verified and |
| | | Unverified for the same claimed | | | | Unverified for the same claimed |
| | | sender | | | | sender |
+--------------+--------+---------------------------------+ +--------------+--------+-----------------------------------+
| Conflicting | Purple | evidence of both Trusted & | | Conflicting | Purple | Evidence of both Trusted and |
| | | Unverified for the same claimed | | | | Unverified for the same claimed |
| | | sender | | | | sender |
+--------------+--------+---------------------------------+ +--------------+--------+-----------------------------------+
Table 4: Authentication State Names, Colors & Descriptions Table 4: Authentication State Names, Colors, and Descriptions
A.1. None: Black A.1. None: Black
The default state where no authentication information has yet to be The default state where authentication information has not yet been
received. received and is not currently being received.
A.2. Partial: Gray A.2. Partial: Gray
A pending state where authentication pages are being received but a A pending state where Authentication Pages are being received, but a
full authentication message has yet to be compiled. full Authentication Message has yet to be compiled.
A.3. Unsupported: Brown A.3. Unsupported: Brown
A state wherein authentication data is being or has been received, A state wherein authentication data is being or has been received but
but cannot be used, as the Authentication Type or SAM Type is not cannot be used, as the Authentication Type or SAM Type is not
supported by the Observer. supported by the Observer.
A.4. Unverifiable: Yellow A.4. Unverifiable: Yellow
A pending state where a full authentication message has been received A pending state where a full Authentication Message has been received
but other information, such as public keys to verify signatures, is but other information, such as public keys to verify signatures, is
missing. missing.
A.5. Verified: Green A.5. Verified: Green
A state where all authentication messages that have been received, up A state where all Authentication Messages that have been received
to that point from that claimed sender, pass signature verification from that claimed sender up to that point pass signature verification
and the requirement of Section 6.4.2 has been met. and the requirement of Section 6.4.2 has been met.
A.6. Trusted: Blue A.6. Trusted: Blue
A state where all authentication messages that have been received, up A state where all Authentication Messages that have been received
to that point, from that claimed sender, have passed signature from that claimed sender up to that point have passed signature
verification, the requirement of Section 6.4.2 has been met, and the verification, the requirement of Section 6.4.2 has been met, and the
public key of the sending UA is marked as trusted. public key of the sending UA has been marked as trusted.
The sending UA key will have been marked as trusted if the relevant The sending UA key will have been marked as trusted if the relevant
DIMEs only register DETs (of subordinate DIMEs, UAS operators, and DIMEs only register DETs (of subordinate DIMEs, UAS operators, and
UA) that have been vetted as per their published registration UA) that have been vetted as per their published registration
policies, and those DIMEs have been marked, by the owner (individual policies, and those DIMEs have been marked, by the owner (individual
or organizational) of the Observer, as per that owner's policy, as or organizational) of the Observer, as per that owner's policy, as
trusted to register DETs only for trusted parties. trusted to register DETs only for trusted parties.
A.7. Questionable: Orange A.7. Questionable: Orange
A state where there is a mix of authentication messages received that A state where there is a mix of Authentication Messages received that
are Verified (Appendix A.5) and Unverified (Appendix A.8). are Verified (Appendix A.5) and Unverified (Appendix A.8).
Transition to this state is from Verified if a subsequent message State transitions from Verified to Questionable if a subsequent
fails verification so would have otherwise been marked Unverified, or message fails verification, so it would have otherwise been marked
from Unverified if a subsequent message passes verification or Unverified. State transitions from Unverified to Questionable if a
validation so would otherwise have been marked Verified, or from subsequent message passes verification or validation, so it would
either of those state upon mixed results on the requirement of otherwise have been marked Verified. It may transition from either
of those states upon mixed results on the requirement of
Section 6.4.2. Section 6.4.2.
A.8. Unverified: Red A.8. Unverified: Red
A state where all authentication messages that have been received, up A state where all Authentication Messages that have been received
to that point, from that claimed sender, failed signature from that claimed sender up to that point failed signature
verification or the requirement of Section 6.4.2. verification or the requirement of Section 6.4.2.
A.9. Conflicting: Purple A.9. Conflicting: Purple
A state where there is a mix of authentication messages received that A state where there is a mix of Authentication Messages received that
are Trusted (Appendix A.6) and Unverified (Appendix A.8) and the are Trusted (Appendix A.6) and Unverified (Appendix A.8) and the
public key of the aircraft is marked as trusted. public key of the aircraft is marked as trusted.
Transition to this state is from Trusted if a subsequent message State transitions from Trusted to Conflicting if a subsequent message
fails verification so would have otherwise been marked Unverified, or fails verification, so it would have otherwise been marked
from Unverified if a subsequent message passes verification or Unverified. State transitions from Unverified to Conflicting if a
validation and policy checks so would otherwise have been marked subsequent message passes verification or validation and policy
Trusted, or from either of those state upon mixed results on the checks, so it would otherwise have been marked Trusted. It may
transition from either of those states upon mixed results on the
requirement of Section 6.4.2. requirement of Section 6.4.2.
Appendix B. Operational Recommendation Analysis Appendix B. Operational Recommendation Analysis
The recommendations found in Section 6.4 may seem heavy handed and The recommendations in Section 6.4 may seem heavy-handed and
specific. This informative appendix lays out the math and specific. This informative appendix lays out the math and
assumptions made to come to the recommendations listed there as well assumptions made that resulted in those recommendations and provides
as an example. an example.
In many jurisdictions, the required ASTM Messages to be transmitted In all jurisdictions known to the authors of this document as of its
every second are: Basic ID (0x1), Location (0x2), and System (0x4). publication (2024), at least the following ASTM Messages are required
Typical implementations will most likely send at a higher rate (2x to be transmitted at least once per second:
sets per cycle) resulting in 6 frames sent per cycle. Transmitting
this set of message more than once a second is not discouraged but
awareness is needed to avoid congesting the RF spectrum, causing
further issues.
Informational Note: In Europe, the Operator ID Message (0x5) is * Basic ID (0x1)
also required. In Japan, two Basic ID (0x0), Location (0x1), and
Authentication (0x2) are required. Self ID (0x3) is optional but * Location (0x2)
can carry Emergency Status information.
* System (0x4)
Europe also requires:
* Operator ID Message (0x5)
Japan requires not one but two Basic ID messages:
* one carrying a manufacturer assigned serial number
* one carrying a CAA assigned registration number
Japan also requires:
* Authentication (0x2) using their own unique scheme
In all jurisdictions, one further message is optional, but highly
recommended for carriage of additional information on the nature of
the emergency if the Emergency value is sent in the Operational
Status field of the Location/Vector Message:
* Self ID (0x3)
To improve the likelihood of successful timely receipt of regulator
required RID data elements, most implementations send at a higher
rate, whether by repeating the same messages in the same one second
interval, or updating message content and sending messages more
frequently than once per second. Excessive sending rate, however,
could congest the RF spectrum, leading to collisions and counter-
intuitively actually reducing the likelihood of timely receipt of RID
data.
B.1. Page Counts vs Frame Counts B.1. Page Counts vs Frame Counts
There are two formulas to determine the number of Authentication There are two formulas to determine the number of Authentication
Pages required, one for Wrapper: Pages required. The following formula is for Wrapper:
<CODE BEGINS> <CODE BEGINS>
wrapper_struct_size = 89 + (25 * num_astm_messages) wrapper_struct_size = 89 + (25 * num_astm_messages)
wrapper_page_count = ceiling((wrapper_struct_size - 17) / 23) + 1 wrapper_page_count = ceiling((wrapper_struct_size - 17) / 23) + 1
<CODE ENDS> <CODE ENDS>
and one for Manifest:
The following formula is for Manifest:
<CODE BEGINS> <CODE BEGINS>
manifest_struct_size = 89 + (8 * (num_astm_hashes + 3)) manifest_struct_size = 89 + (8 * (num_astm_hashes + 3))
manifest_page_count = ceiling((manifest_struct_size - 17) / 23) + 1 manifest_page_count = ceiling((manifest_struct_size - 17) / 23) + 1
<CODE ENDS> <CODE ENDS>
A similar formula can be applied to Link as they are of fixed size: A similar formula can be applied to Links, as they are of fixed size:
<CODE BEGINS> <CODE BEGINS>
link_page_count = ceiling((137 - 17) / 23) + 1 = 7 link_page_count = ceiling((137 - 17) / 23) + 1 = 7
<CODE ENDS> <CODE ENDS>
Comparing Wrapper and Manifest Authentication Message page counts Comparing Wrapper and Manifest Authentication Message page counts
against total frame counts we have the following: against total frame counts, we have the following:
+==========+=========+==========+=================+===============+ +==========+=========+==========+=================+===============+
| ASTM | Wrapper | Manifest | ASTM Messages + | ASTM Messages | | ASTM | Wrapper | Manifest | ASTM Messages + | ASTM Messages |
| Messages | (w/FEC) | (w/FEC) | Wrapper (w/FEC) | + Manifest | | Messages | (w/FEC) | (w/FEC) | Wrapper (w/FEC) | + Manifest |
| | | | | (w/FEC) | | | | | | (w/FEC) |
+==========+=========+==========+=================+===============+ +==========+=========+==========+=================+===============+
| 0 | 5 (6) | 6 (7) | 5 (6) | 6 (7) | | 0 | 5 (6) | 6 (7) | 5 (6) | 6 (7) |
+----------+---------+----------+-----------------+---------------+ +----------+---------+----------+-----------------+---------------+
| 1 | 6 (7) | 6 (7) | 7 (8) | 7 (8) | | 1 | 6 (7) | 6 (7) | 7 (8) | 7 (8) |
+----------+---------+----------+-----------------+---------------+ +----------+---------+----------+-----------------+---------------+
skipping to change at page 43, line 50 skipping to change at line 1958
+----------+---------+----------+-----------------+---------------+ +----------+---------+----------+-----------------+---------------+
| 8 | N/A | 8 (9) | N/A | 16 (17) | | 8 | N/A | 8 (9) | N/A | 16 (17) |
+----------+---------+----------+-----------------+---------------+ +----------+---------+----------+-----------------+---------------+
| 9 | N/A | 9 (10) | N/A | 18 (19) | | 9 | N/A | 9 (10) | N/A | 18 (19) |
+----------+---------+----------+-----------------+---------------+ +----------+---------+----------+-----------------+---------------+
| 10 | N/A | 9 (10) | N/A | 19 (20) | | 10 | N/A | 9 (10) | N/A | 19 (20) |
+----------+---------+----------+-----------------+---------------+ +----------+---------+----------+-----------------+---------------+
| 11 | N/A | 9 (11) | N/A | 20 (22) | | 11 | N/A | 9 (11) | N/A | 20 (22) |
+----------+---------+----------+-----------------+---------------+ +----------+---------+----------+-----------------+---------------+
Table 5: Page & Frame Counts Table 5: Page and Frame Counts
Link shares the same page counts as Manifest with 5 ASTM Messages. Link shares the same page counts as Manifest with 5 ASTM Messages.
B.1.1. Special Cases B.1.1. Special Cases
B.1.1.1. Zero ASTM Messages B.1.1.1. Zero ASTM Messages
Zero ASTM Messages in Table 5 is where Extended Wrapper Zero ASTM Messages (see Table 5) is where Extended Wrapper
(Section 4.3.2) without FEC is used in Message Packs. With a max of (Section 4.3.2) without FEC is used in Message Packs. With a maximum
9 "message slots" in a Message Pack an Extended Wrapper fills 5 of nine "message slots" in a Message Pack, an Extended Wrapper fills
slots, thus can authenticate up to 4 ASTM Messages co-located in the five slots; thus it can authenticate up to four ASTM Messages co-
same Message Pack. located in the same Message Pack.
B.1.1.2. Eleven ASTM Messages B.1.1.2. Eleven ASTM Messages
Eleven ASTM Messages in Table 5 is where a Manifest with FEC invokes Eleven ASTM Messages (see Table 5) is where a Manifest with FEC
the situation mentioned in Section 5.3. invokes the situation mentioned in Section 5.3.
Eleven is the max number of ASTM Messages Hashes that can be Eleven is the maximum number of ASTM Message Hashes that can be
supported resulting in 14 total hashes. This completely fills the supported resulting in 14 total hashes. This completely fills the
evidence section of the structure making its total size 200 octets. _Evidence_ field of the _UA-Signed Evidence Structure_ making its
This fits on exactly 9 Authentication Pages ((201 - 17) / 23 == 8) so total size 200 octets. This fits on exactly 9 Authentication Pages
when the ADL is added it is placed on the next page (Page 10). Per ((201 - 17) / 23 == 8), so when the ADL is added, it is placed on the
rule 1 in Section 5.1 this means that all of Page 10 is null padded next page (Page 10). Per rule 1 in Section 5.1, this means that all
(expect the ADL octet) and FEC data fills Page 11, resulting in a of Page 10 is null padded (expect the ADL octet) and FEC data fills
plus two page count when FEC is applied. Page 11, resulting in a plus-two page count when FEC is applied.
This drives the recommendation is Section 4.4 to only use up to 10 This drives the recommendation is Section 4.4 to only use up to 10
ASTM Message Hashes and not 11. ASTM Message Hashes, not 11.
B.2. Full Authentication Example B.2. Full Authentication Example
This example is focused on showing that 100% of ASTM Messages can be This example (Figure 13) is focused on showing that 100% of ASTM
authenticated over Legacy Transports with up to 125% overhead in Messages can be authenticated over Legacy Transports with up to 125%
Authentication Pages. Extended Transports is not shown as overhead in Authentication Pages. Extended Transports are not shown
Authentication with DRIP in that case is covered using Extended in this example, because, for those, Authentication with DRIP is
Wrapper (Section 4.3.2). Two ASTM Message Packs are sent in a given achieved using Extended Wrapper (Section 4.3.2). Two ASTM Message
cycle: one containing up to 4 ASTM Messages and an Extended Wrapper Packs are sent in a given cycle: one containing up to four ASTM
(authenticating the pack) and one containing a Link message with a Messages and an Extended Wrapper (authenticating the pack), and one
Broadcast Endorsement and up to two other ASTM Messages. containing a Link message with a Broadcast Endorsement and up to two
other ASTM Messages.
This example transmit scheme covers and meets every known regulatory This example transmit scheme covers and meets every known regulatory
case enabling manufacturers to use the same firmware worldwide. case enabling manufacturers to use the same firmware worldwide.
+------------------------------------------------------+ +------------------------------------------------------+
| Frame Slots | | Frame Slots |
| 00 - 04 | 05 - 07 | 08 - 16 | 17 | | 00 - 04 | 05 - 07 | 08 - 16 | 17 |
+-------------------+---------------+---------+--------+ +-------------------+---------------+---------+--------+
| {A|B|C|D},V,S,I,O | {A|B|C|D},V,S | M[0,8] | L/W[0] | | {A|B|C|D},V,S,I,O | {A|B|C|D},V,S | M[0,8] | L/W[0] |
+-------------------+---------------+---------+--------+ +-------------------+---------------+---------+--------+
skipping to change at page 45, line 44 skipping to change at line 2043
L[y,z] = DRIP Link Authentication Message (0x2) L[y,z] = DRIP Link Authentication Message (0x2)
W[y,z] = DRIP Wrapper Authentication Message (0x2) W[y,z] = DRIP Wrapper Authentication Message (0x2)
M[y,z] = DRIP Manifest Authentication Message (0x2) M[y,z] = DRIP Manifest Authentication Message (0x2)
y = Start Page y = Start Page
z = End Page z = End Page
# = Empty Frame Slot # = Empty Frame Slot
* = Message in DRIP Manifest Authentication Message * = Message in DRIP Manifest Authentication Message
Figure 13: Full Authenticated Legacy Transport Transmit Schedule Figure 13: Example of a Fully Authenticated Legacy Transport
Example Transmit Schedule
Every common required message (Basic ID, Location and System) is sent Every common required message (Basic ID, Location/Vector, and System)
twice plus Operator ID and Self ID in a single second. The Manifest is sent twice along with Operator ID and Self ID in a single second.
is over all messages (8) in slots 00 - 04 and 05 - 07. The Manifest is over all messages (8) in slots 00 - 04 and 05 - 07.
In two seconds either a Link or Wrapper are sent. The content and In two seconds, either a Link or Wrapper is sent. The content and
order of Links and Wrappers runs as follows: order of Links and Wrappers runs as follows:
Link: HDA on UA Link: HDA on UA
Link: RAA on HDA Link: RAA on HDA
Link: HDA on UA Link: HDA on UA
Link: Apex on RAA Link: Apex on RAA
Link: HDA on UA Link: HDA on UA
Link: RAA on HDA Link: RAA on HDA
Link: HDA on UA Link: HDA on UA
Wrapper: Location (0x1), System (0x4) Wrapper: Location/Vector (0x1), System (0x4)
Link: HDA on UA Link: HDA on UA
Link: RAA on HDA Link: RAA on HDA
Link: HDA on UA Link: HDA on UA
Link: Apex on RAA Link: Apex on RAA
Link: HDA on UA Link: HDA on UA
Link: RAA on HDA Link: RAA on HDA
Link: HDA on UA Link: HDA on UA
Wrapper: Location (0x1), System (0x4) Wrapper: Location/Vector (0x1), System (0x4)
Link: IANA on UAS RID Apex Link: IANA on UAS RID Apex
With perfect receipt of all messages, in 8 seconds all messages (up After perfect receipt of all messages for a period of 8 seconds, all
to that point then all in future) are authenticated using the messages sent during that period have been authenticated using the
Manifest. Within 136 seconds the entire Broadcast Endorsement chain Manifest (except for the Authentication Messages themselves). Within
is received and can be validated; interspersed with 4 messages 136 seconds, the entire Broadcast Endorsement chain is received and
directly signed over via Wrapper. can be validated. Interspersed in this schedule are 4 messages sent
not only in their basic [F3411] form, but also in DRIP Wrapper
messages, together with their attached signatures, to defend against
the possibility of attack against the detached signatures provided by
the Manifest messages.
B.2.1. Raw Example B.2.1. Raw Example
Assuming the following DET and HI: Assuming the following DET and HI:
2001:3f:fe00:105:a29b:3ff4:2226:c04e 2001:3f:fe00:105:a29b:3ff4:2226:c04e
b5fef530d450dedb59ebafa18b00d7f5ed0ac08a81975034297bea2b00041813 b5fef530d450dedb59ebafa18b00d7f5ed0ac08a81975034297bea2b00041813
The following ASTM Messages to be sent in a single second: The following ASTM Messages are to be sent in a single second:
0240012001003ffe000105a29b3ff42226c04e000000000000 0240012001003ffe000105a29b3ff42226c04e000000000000
12000000000000000000000000000000000000000060220000 12000000000000000000000000000000000000000060220000
32004578616d706c652053656c662049440000000000000000 32004578616d706c652053656c662049440000000000000000
420000000000000000000100000000000000000010ea510900 420000000000000000000100000000000000000010ea510900
52004578616d706c65204f70657261746f7220494400000000 52004578616d706c65204f70657261746f7220494400000000
0240012001003ffe000105a29b3ff42226c04e000000000000 0240012001003ffe000105a29b3ff42226c04e000000000000
12000000000000000000000000000000000000000060220000 12000000000000000000000000000000000000000060220000
420000000000000000000100000000000000000010ea510900 420000000000000000000100000000000000000010ea510900
This is Link with FEC that would be spread out over 8 seconds: This is a Link with FEC that would be spread out over 8 seconds:
2250078910ea510904314b8564b17e66662001003ffe000105 2250078910ea510904314b8564b17e66662001003ffe000105
2251a29b3ff42226c04eb5fef530d450dedb59ebafa18b00d7 2251a29b3ff42226c04eb5fef530d450dedb59ebafa18b00d7
2252f5ed0ac08a81975034297bea2b000418132001003ffe00 2252f5ed0ac08a81975034297bea2b000418132001003ffe00
22530105b82bf1c99d87273103fc83f6ecd9b91842f205c222 22530105b82bf1c99d87273103fc83f6ecd9b91842f205c222
2254dd71d8e165ad18ca91daf9299a73eec850c756a7e9be46 2254dd71d8e165ad18ca91daf9299a73eec850c756a7e9be46
2255f51dddfa0f09db7bfdde14eec07c7a6dd1061c1d5ace94 2255f51dddfa0f09db7bfdde14eec07c7a6dd1061c1d5ace94
2256d9ad97940d280000000000000000000000000000000000 2256d9ad97940d280000000000000000000000000000000000
2257a03b0f7a6feb0d198167045058cfc49f73129917024d22 2257a03b0f7a6feb0d198167045058cfc49f73129917024d22
skipping to change at page 47, line 38 skipping to change at line 2134
225008b110ea510903e0dd7c6560115e670000000000000000 225008b110ea510903e0dd7c6560115e670000000000000000
2251d57594875f8608b4d61dc9224ecf8b842bd4862734ed01 2251d57594875f8608b4d61dc9224ecf8b842bd4862734ed01
22522ca2e5f2b8a3e61547b81704766ba3eeb651be7eafc928 22522ca2e5f2b8a3e61547b81704766ba3eeb651be7eafc928
22538884e3e28a24fd5529bc2bd4862734ed012ca2e5f2b8a3 22538884e3e28a24fd5529bc2bd4862734ed012ca2e5f2b8a3
2254e61547b81704766ba3eeb62001003ffe000105a29b3ff4 2254e61547b81704766ba3eeb62001003ffe000105a29b3ff4
22552226c04efb729846e7d110903797066fd96f49a77c5a48 22552226c04efb729846e7d110903797066fd96f49a77c5a48
2256c4c3b330be05bc4a958e9641718aaa31aeabad368386a2 2256c4c3b330be05bc4a958e9641718aaa31aeabad368386a2
22579ed2dce2769120da83edbcdc0858dd1e357755e7860317 22579ed2dce2769120da83edbcdc0858dd1e357755e7860317
2258e7c06a5918ea62a937391cbfe0983539de1b2e688b7c83 2258e7c06a5918ea62a937391cbfe0983539de1b2e688b7c83
Acknowledgments
The authors acknowledge the following individuals:
* Ryan Quigley, James Mussi, and Joseph Stanton of AX Enterprize,
LLC for early prototyping to find holes in earlier drafts of this
specification.
* Carsten Bormann for the simple approach of using bit-column-wise
parity for erasure (dropped frame) FEC.
* Soren Friis for pointing out that Wi-Fi implementations would not
always give access to the MAC Address, as was 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).
* Gabriel Cox (chair of the working group that produced [F3411]) for
reviewing the specification for the SAM Type request as the ASTM
Designated Expert.
* Mohamed Boucadair (Document Shepherd) for his many patches and
comments.
* Eric Vyncke (DRIP AD) for his guidance regarding the document's
path to publication.
The authors also thank the following reviewers:
* Rick Salz (secdir)
* Matt Joras (genart)
* Di Ma (dnsdir)
* Gorry Fairhurst (tsvart)
* Carlos Bernardos (intdir)
* Behcet Sarikaya (iotdir)
* Martin Duke (IESG)
* Roman Danyliw (IESG)
* Murray Kucherawy (IESG)
* Erik Kline (IESG)
* Warren Kumari (IESG)
* Paul Wouters (IESG)
Authors' Addresses Authors' Addresses
Adam Wiethuechter (editor) Adam Wiethuechter (editor)
AX Enterprize, LLC AX Enterprize, LLC
4947 Commercial Drive 4947 Commercial Drive
Yorkville, NY 13495 Yorkville, NY 13495
United States of America United States of America
Email: adam.wiethuechter@axenterprize.com Email: adam.wiethuechter@axenterprize.com
Stuart Card Stuart Card
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