Internet DRAFT - draft-ietf-drip-rid
draft-ietf-drip-rid
DRIP R. Moskowitz
Internet-Draft HTT Consulting
Updates: 7401, 7343 (if approved) S. Card
Intended status: Standards Track A. Wiethuechter
Expires: 5 June 2023 AX Enterprize, LLC
A. Gurtov
Linköping University
2 December 2022
DRIP Entity Tag (DET) for Unmanned Aircraft System Remote ID (UAS RID)
draft-ietf-drip-rid-37
Abstract
This document describes the use of Hierarchical Host Identity Tags
(HHITs) as self-asserting IPv6 addresses and thereby a trustable
identifier for use as the Unmanned Aircraft System Remote
Identification and tracking (UAS RID).
This document updates RFC7401 and RFC7343.
Within the context of RID, HHITs will be called DRIP Entity Tags
(DETs). HHITs provide claims to the included explicit hierarchy that
provides registry (via, e.g., DNS, RDAP) discovery for 3rd-party
identifier endorsement.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 June 2023.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. HHIT Statistical Uniqueness different from UUID or X.509
Subject . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 4
2.2. Notations . . . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 5
3. The Hierarchical Host Identity Tag (HHIT) . . . . . . . . . . 6
3.1. HHIT Prefix for RID Purposes . . . . . . . . . . . . . . 7
3.2. HHIT Suite IDs . . . . . . . . . . . . . . . . . . . . . 7
3.2.1. HDA custom HIT Suite IDs . . . . . . . . . . . . . . 8
3.3. The Hierarchy ID (HID) . . . . . . . . . . . . . . . . . 8
3.3.1. The Registered Assigning Authority (RAA) . . . . . . 9
3.3.2. The Hierarchical HIT Domain Authority (HDA) . . . . . 9
3.4. Edwards-Curve Digital Signature Algorithm for HHITs . . . 10
3.4.1. HOST_ID . . . . . . . . . . . . . . . . . . . . . . . 10
3.4.2. HIT_SUITE_LIST . . . . . . . . . . . . . . . . . . . 11
3.5. ORCHIDs for Hierarchical HITs . . . . . . . . . . . . . . 12
3.5.1. Adding Additional Information to the ORCHID . . . . . 13
3.5.2. ORCHID Encoding . . . . . . . . . . . . . . . . . . . 14
3.5.3. ORCHID Decoding . . . . . . . . . . . . . . . . . . . 16
3.5.4. Decoding ORCHIDs for HIPv2 . . . . . . . . . . . . . 16
4. Hierarchical HITs as DRIP Entity Tags . . . . . . . . . . . . 16
4.1. Nontransferablity of DETs . . . . . . . . . . . . . . . . 17
4.2. Encoding HHITs in CTA 2063-A Serial Numbers . . . . . . . 17
4.3. Remote ID DET as one Class of Hierarchical HITs . . . . . 18
4.4. Hierarchy in ORCHID Generation . . . . . . . . . . . . . 18
4.5. DRIP Entity Tag (DET) Registry . . . . . . . . . . . . . 19
4.6. Remote ID Authentication using DETs . . . . . . . . . . . 19
5. DRIP Entity Tags (DETs) in DNS . . . . . . . . . . . . . . . 20
6. Other UAS Traffic Management (UTM) Uses of HHITs Beyond
DET . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
7. Summary of Addressed DRIP Requirements . . . . . . . . . . . 21
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
8.1. New Well-Known IPv6 prefix for DETs . . . . . . . . . . . 21
8.2. New IANA DRIP Registry . . . . . . . . . . . . . . . . . 22
8.3. IANA CGA Registry Update . . . . . . . . . . . . . . . . 23
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8.4. IANA HIP Registry Updates . . . . . . . . . . . . . . . . 23
9. Security Considerations . . . . . . . . . . . . . . . . . . . 24
9.1. Post Quantum Computing out of scope . . . . . . . . . . . 26
9.2. DET Trust in ASTM messaging . . . . . . . . . . . . . . . 26
9.3. DET Revocation . . . . . . . . . . . . . . . . . . . . . 27
9.4. Privacy Considerations . . . . . . . . . . . . . . . . . 27
9.5. Collision Risks with DETs . . . . . . . . . . . . . . . . 28
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
10.1. Normative References . . . . . . . . . . . . . . . . . . 28
10.2. Informative References . . . . . . . . . . . . . . . . . 30
Appendix A. EU U-Space RID Privacy Considerations . . . . . . . 32
Appendix B. The 14/14 HID split . . . . . . . . . . . . . . . . 33
B.1. DET Encoding Example . . . . . . . . . . . . . . . . . . 34
Appendix C. Base32 Alphabet . . . . . . . . . . . . . . . . . . 35
Appendix D. Calculating Collision Probabilities . . . . . . . . 35
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
1. Introduction
Drone Remote ID Protocol (DRIP) Requirements [RFC9153] describe an
Unmanned Aircraft System Remote ID (UAS ID) as unique (ID-4), non-
spoofable (ID-5), and identify a registry where the ID is listed (ID-
2); all within a 19-character identifier (ID-1).
This DRIP foundational document (i.e., all else in DRIP enables or
uses it) describes (per Section 3 of [drip-architecture]) the use of
Hierarchical Host Identity Tags (HHITs) (Section 3) as self-asserting
IPv6 addresses and thereby a trustable identifier for use as the UAS
Remote ID. HHITs add explicit hierarchy to the 128-bit HITs,
enabling DNS HHIT queries (Host ID for authentication, e.g.,
[drip-authentication]) and for use with a Differentiated Access
Control (e.g. Registration Data Access Protocol (RDAP) [RFC9224])
for 3rd-party identification endorsement (e.g.,
[drip-authentication]).
This addition of hierarchy to HITs is an extension to [RFC7401] and
requires an update to [RFC7343]. As this document also adds EdDSA
(Section 3.4) for Host Identities (HIs), a number of Host Identity
Protocol (HIP) parameters in [RFC7401] are updated, but these should
not be needed in a DRIP implementation that does not use HIP.
HHITs as used within the context of Unmanned Aircraft System (UAS)
are labeled as DRIP Entity Tags (DETs). Throughout this document
HHIT and DET will be used appropriately. HHIT will be used when
covering the technology, and DET for their context within UAS RID.
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Hierarchical HITs provide self-claims of the HHIT registry. A HHIT
can only be in a single registry within a registry system (e.g.
DNS).
Hierarchical HITs are valid, though non-routable, IPv6 addresses
[RFC8200]. As such, they fit in many ways within various IETF
technologies.
1.1. HHIT Statistical Uniqueness different from UUID or X.509 Subject
HHITs are statistically unique through the cryptographic hash feature
of second-preimage resistance. The cryptographically-bound addition
of the hierarchy and a HHIT registration process [drip-registries]
provide complete, global HHIT uniqueness. If the HHITs cannot be
looked up with services provided by the DRIP Identity Management
Entity (DIME) identified via the embedded hierarchical information or
its registration validated by registration endorsement messages
[drip-authentication], then the HHIT is either fraudulent or revoked/
expired. In-depth discussion of these processes are out of scope for
this document.
This contrasts with using general identifiers (e.g., a Universally
Unique IDentifiers (UUID) [RFC4122] or device serial numbers as the
subject in an X.509 [RFC5280] certificate. In either case, there can
be no unique proof of ownership/registration.
For example, in a multi-Certificate Authority (multi-CA) PKI
alternative to HHITs, a Remote ID as the Subject (Section 4.1.2.6 of
[RFC5280]) can occur in multiple CAs, possibly fraudulently. CAs
within the PKI would need to implement an approach to enforce
assurance of the uniqueness achieved with HHITs.
2. Terms and Definitions
2.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here.
The document includes a set of algorithms with a guidance on the ones
that are recommended to be supported by implementations. The
following term is used for that purpose: RECOMMENDED.
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2.2. Notations
| Signifies concatenation of information - e.g., X | Y is the
concatenation of X and Y.
2.3. Definitions
This document uses the terms defined in Section 2.2 of [RFC9153] and
in Section 2 of [drip-architecture]. The following new terms are
used in the document:
cSHAKE (The customizable SHAKE function [NIST.SP.800-185]):
Extends the SHAKE [NIST.FIPS.202] scheme to allow users to
customize their use of the SHAKE function.
HDA (HHIT Domain Authority):
The 14-bit field that identifies the HHIT Domain Authority under a
Registered Assigning Authority (RAA). See Figure 1.
HHIT
Hierarchical Host Identity Tag. A HIT with extra hierarchical
information not found in a standard HIT [RFC7401].
HI
Host Identity. The public key portion of an asymmetric key pair
as defined in [RFC9063].
HID (Hierarchy ID):
The 28-bit field providing the HIT Hierarchy ID. See Figure 1.
HIP (Host Identity Protocol)
The origin [RFC7401] of HI, HIT, and HHIT.
HIT
Host Identity Tag. A 128-bit handle on the HI. HITs are valid
IPv6 addresses.
Keccak (KECCAK Message Authentication Code):
The family of all sponge functions with a KECCAK-f permutation as
the underlying function and multi-rate padding as the padding
rule. It refers in particular to all the functions referenced
from [NIST.FIPS.202] and [NIST.SP.800-185].
KMAC (KECCAK Message Authentication Code [NIST.SP.800-185]):
A Pseudo Random Function (PRF) and keyed hash function based on
KECCAK.
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RAA (Registered Assigning Authority):
The 14-bit field identifying the business or organization that
manages a registry of HDAs. See Figure 1.
RVS (Rendezvous Server):
A Rendezvous Server such as the HIP Rendezvous Server for enabling
mobility, as defined in [RFC8004].
SHAKE (Secure Hash Algorithm KECCAK [NIST.FIPS.202]):
A secure hash that allows for an arbitrary output length.
XOF (eXtendable-Output Function [NIST.FIPS.202]):
A function on bit strings (also called messages) in which the
output can be extended to any desired length.
3. The Hierarchical Host Identity Tag (HHIT)
The Hierarchical HIT (HHIT) is a small but important enhancement over
the flat Host Identity Tag (HIT) space, constructed as an Overlay
Routable Cryptographic Hash IDentifier (ORCHID) [RFC7343]. By adding
two levels of hierarchical administration control, the HHIT provides
for device registration/ownership, thereby enhancing the trust
framework for HITs.
The 128-bit HHITs represent the HI in only a 64-bit hash, rather than
the 96 bits in HITs. 4 of these 32 freed up bits expand the Suite ID
to 8 bits, and the other 28 bits are used to create a hierarchical
administration organization for HIT domains. Hierarchical HIT
construction is defined in Section 3.5. The input values for the
Encoding rules are described in Section 3.5.1.
A HHIT is built from the following fields (Figure 1):
* p = an IPV6 prefix (max 28 bit)
* 28-bit Hierarchy ID (HID) which provides the structure to organize
HITs into administrative domains. HIDs are further divided into
two fields:
- 14-bit Registered Assigning Authority (RAA) (Section 3.3.1)
- 14-bit Hierarchical HIT Domain Authority (HDA) (Section 3.3.2)
* 8-bit HHIT Suite ID (HHSI)
* ORCHID hash (92 - prefix length, e.g., 64) See Section 3.5 for
more details.
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14 bits| 14 bits 8 bits
+-------+-------+ +--------------+
| RAA | HDA | |HHIT Suite ID |
+-------+-------+ +--------------+
\ | ____/ ___________/
\ \ _/ ___/
\ \/ /
| p bits | 28 bits |8bits| o=92-p bits |
+--------------+------------+-----+------------------------+
| IPV6 Prefix | HID |HHSI | ORCHID hash |
+--------------+------------+-----+------------------------+
Figure 1: HHIT Format
The Context ID (generated with openssl rand) for the ORCHID hash is:
Context ID := 0x00B5 A69C 795D F5D5 F008 7F56 843F 2C40
Context IDs are allocated out of the namespace introduced for
Cryptographically Generated Addresses (CGA) Type Tags [RFC3972].
3.1. HHIT Prefix for RID Purposes
The IPv6 HHIT prefix MUST be distinct from that used in the flat-
space HIT as allocated in [RFC7343]. Without this distinct prefix,
the first 4 bits of the RAA would be interpreted as the HIT Suite ID
per HIPv2 [RFC7401].
Initially, for DET use, one 28-bit prefix should be assigned out of
the IANA IPv6 Special Purpose Address Block ([RFC6890]).
HHIT Use Bits Value
DET 28 TBD6 (suggested value 2001:30::/28)
Other prefixes may be added in the future either for DET use or other
applications of HHITs. For a prefix to be added to the registry in
Section 8.2, its usage and HID allocation process have to be publicly
available.
3.2. HHIT Suite IDs
The HHIT Suite IDs specify the HI and hash algorithms. These are a
superset of the 4/8-bit HIT Suite ID as defined in Section 5.2.10 of
[RFC7401].
The HHIT values of 1 - 15 map to the basic 4-bit HIT Suite IDs. HHIT
values of 17 - 31 map to the extended 8-bit HIT Suite IDs. HHIT
values unique to HHIT will start with value 32.
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As HHIT introduces a new Suite ID, EdDSA/cSHAKE128, and since this is
of value to HIPv2, it will be allocated out of the 4-bit HIT space
and result in an update to HIT Suite IDs. Future HHIT Suite IDs may
be allocated similarly, or may come out of the additional space made
available by going to 8 bits.
The following HHIT Suite IDs are defined:
HHIT Suite Value
RESERVED 0
RSA,DSA/SHA-256 1 [RFC7401]
ECDSA/SHA-384 2 [RFC7401]
ECDSA_LOW/SHA-1 3 [RFC7401]
EdDSA/cSHAKE128 TBD3 (suggested value 5)
3.2.1. HDA custom HIT Suite IDs
Support for 8-bit HHIT Suite IDs allows for HDA custom HIT Suite IDs.
These will be assigned values greater than 15 as follows:
HHIT Suite Value
HDA Private Use 1 TBD4 (suggested value 254)
HDA Private Use 2 TBD5 (suggested value 255)
These custom HIT Suite IDs, for example, may be used for large-scale
experimenting with post quantum computing hashes or similar domain
specific needs. Note that currently there is no support for domain-
specific HI algorithms.
They should not be used to create a "de facto standardization".
Section 8.2 states that additional Suite IDs can be made through IETF
Review.
3.3. The Hierarchy ID (HID)
The Hierarchy ID (HID) provides the structure to organize HITs into
administrative domains. HIDs are further divided into two fields:
* 14-bit Registered Assigning Authority (RAA)
* 14-bit Hierarchical HIT Domain Authority (HDA)
The rationale for the 14/14 HID split is described in Appendix B.
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The two levels of hierarchy allows for Civil Aviation Authorities
(CAAs) to have it least one RAA for their National Air Space (NAS).
Within its RAA(s), the CAAs can delegate HDAs as needed. There may
be other RAAs allowed to operate within a given NAS; this is a policy
decision of each CAA.
3.3.1. The Registered Assigning Authority (RAA)
An RAA is a business or organization that manages a registry of HDAs.
For example, the Federal Aviation Authority (FAA) or Japan Civil
Aviation Bureau (JCAB) could be an RAA.
The RAA is a 14-bit field (16,384 RAAs). The management of this
space is further elaborated in [drip-registries]. An RAA MUST
provide a set of services to allocate HDAs to organizations. It
SHOULD have a public policy on what is necessary to obtain an HDA.
The RAA need not maintain any HIP related services. It MUST maintain
a DNS zone minimally for the HDA zone delegation for discovering HIP
RVS servers [RFC8004] for the HID. The zone delegation is covered in
[drip-registries].
As DETs under an administrative control may be used in many different
domains (e.g., commercial, recreation, military), RAAs should be
allocated in blocks (e.g. 16-19) with consideration on the likely
size of a particular usage. Alternatively, different prefixes can be
used to separate different domains of use of HHITs.
The RAA DNS zone within the UAS DNS tree may be a PTR for its RAA.
It may be a zone in an HHIT specific DNS zone. Assume that the RAA
is decimal 100. The PTR record could be constructed as follows
(where 20010030 is the DET prefix):
100.20010030.hhit.arpa. IN PTR raa.example.com.
Note that if the zone 20010030.hhit.arpa is ultimately used, some
registrar will need to manage this for all HHIT applications. Thus
further thought will be needed in the actual zone tree and
registration process [drip-registries].
3.3.2. The Hierarchical HIT Domain Authority (HDA)
An HDA may be an Internet Service Provider (ISP), UAS Service
Supplier (USS), or any third party that takes on the business to
provide UAS services management, HIP RVSs or other needed services
such as those required for HHIT and/or HIP-enabled devices.
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The HDA is a 14-bit field (16,384 HDAs per RAA) assigned by an RAA is
further elaborated in [drip-registries]. An HDA must maintain public
and private UAS registration information and should maintain a set of
RVS servers for UAS clients that may use HIP. How this is done and
scales to the potentially millions of customers are outside the scope
of this document, though covered in [drip-registries]. This service
should be discoverable through the DNS zone maintained by the HDA's
RAA.
An RAA may assign a block of values to an individual organization.
This is completely up to the individual RAA's published policy for
delegation. Such policy is out of scope.
3.4. Edwards-Curve Digital Signature Algorithm for HHITs
The Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032] is
specified here for use as HIs per HIPv2 [RFC7401].
The intent in this document is to add EdDSA as a HI algorithm for
DETs, but doing so impacts the HIP parameters used in a HIP exchange.
The subsections of this section document the required updates of HIP
parameters. Other than the HIP DNS RR (Resource Record) [RFC8005],
these should not be needed in a DRIP implementation that does not use
HIP.
See Section 3.2 for use of the HIT Suite in the context of DRIP.
3.4.1. HOST_ID
The HOST_ID parameter specifies the public key algorithm, and for
elliptic curves, a name. The HOST_ID parameter is defined in
Section 5.2.9 of [RFC7401].
Algorithm
profile Value
EdDSA TBD1 (suggested value 13) [RFC8032]
3.4.1.1. HIP Parameter support for EdDSA
The addition of EdDSA as a HI algorithm requires a subfield in the
HIP HOST_ID parameter (Section 5.2.9 of [RFC7401]) as was done for
ECDSA when used in a HIP exchange.
For HIP hosts that implement EdDSA as the algorithm, the following
EdDSA curves are represented by the following fields:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EdDSA Curve | NULL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Public Key |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
EdDSA Curve Curve label
Public Key Represented in Octet-string format [RFC8032]
Figure 2
For hosts that implement EdDSA as a HIP algorithm the following EdDSA
curves are defined; recommended curves are tagged accordingly:
Algorithm Curve Values
EdDSA RESERVED 0
EdDSA EdDSA25519 1 [RFC8032] (RECOMMENDED)
EdDSA EdDSA25519ph 2 [RFC8032]
EdDSA EdDSA448 3 [RFC8032] (RECOMMENDED)
EdDSA EdDSA448ph 4 [RFC8032]
3.4.1.2. HIP DNS RR support for EdDSA
The HIP DNS RR is defined in [RFC8005]. It uses the values defined
for the 'Algorithm Type' of the IPSECKEY RR [RFC4025] for its PK
Algorithm field.
The new EdDSA HI uses [ipseckey-eddsa] for the IPSECKEY RR encoding.
3.4.2. HIT_SUITE_LIST
The HIT_SUITE_LIST parameter contains a list of the supported HIT
suite IDs of the HIP Responder. Based on the HIT_SUITE_LIST, the HIP
Initiator can determine which source HIT Suite IDs are supported by
the Responder. The HIT_SUITE_LIST parameter is defined in
Section 5.2.10 of [RFC7401].
The following HIT Suite ID is defined:
HIT Suite Value
EdDSA/cSHAKE128 TBD3 (suggested value 5)
Table 1 provides more detail on the above HIT Suite combination.
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The output of cSHAKE128 is variable per the needs of a specific
ORCHID construction. It is at most 96 bits long and is directly used
in the ORCHID (without truncation).
+=======+===========+=========+===========+====================+
| Index | Hash | HMAC | Signature | Description |
| | function | | algorithm | |
| | | | family | |
+=======+===========+=========+===========+====================+
| 5 | cSHAKE128 | KMAC128 | EdDSA | EdDSA HI hashed |
| | | | | with cSHAKE128, |
| | | | | output is variable |
+-------+-----------+---------+-----------+--------------------+
Table 1: HIT Suites
3.5. ORCHIDs for Hierarchical HITs
This section improves on ORCHIDv2 [RFC7343] with three enhancements:
* Optional "Info" field between the Prefix and ORCHID Generation
Algorithm (OGA) ID.
* Increased flexibility on the length of each component in the
ORCHID construction, provided the resulting ORCHID is 128 bits.
* Use of cSHAKE, NIST SP 800-185 [NIST.SP.800-185], for the hashing
function.
The Keccak [Keccak] based cSHAKE XOF hash function is a variable
output length hash function. As such it does not use the truncation
operation that other hashes need. The invocation of cSHAKE specifies
the desired number of bits in the hash output. Further, cSHAKE has a
parameter 'S' as a customization bit string. This parameter will be
used for including the ORCHID Context Identifier in a standard
fashion.
This ORCHID construction includes the fields in the ORCHID in the
hash to protect them against substitution attacks. It also provides
for inclusion of additional information, in particular the
hierarchical bits of the Hierarchical HIT, in the ORCHID generation.
This should be viewed as an update to ORCHIDv2 [RFC7343], as it can
produce ORCHIDv2 output.
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The follow sub-sections define the general, new, ORCHID construct
with the specific application here for HHITs. Thus items like the
hash size is only discussed as it impacts HHIT's 64-bit hash. Other
hash sizes should be discussed in any other specific use of this new
ORCHID construct.
3.5.1. Adding Additional Information to the ORCHID
ORCHIDv2 [RFC7343] is defined as consisting of three components:
ORCHID := Prefix | OGA ID | Encode_96( Hash )
where:
Prefix : A constant 28-bit-long bitstring value
(IPV6 prefix)
OGA ID : A 4-bit long identifier for the Hash_function
in use within the specific usage context. When
used for HIT generation this is the HIT Suite ID.
Encode_96( ) : An extraction function in which output is obtained
by extracting the middle 96-bit-long bitstring
from the argument bitstring.
The new ORCHID function is as follows:
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ORCHID := Prefix (p) | Info (n) | OGA ID (o) | Hash (m)
where:
Prefix (p) : An IPv6 prefix of length p (max 28-bit-long).
Info (n) : n bits of information that define a use of the
ORCHID. 'n' can be zero, that is no additional
information.
OGA ID (o) : A 4- or 8-bit long identifier for the Hash_function
in use within the specific usage context. When
used for HIT generation this is the HIT Suite ID
[IANA-HIP]. When used for HHIT generation this is
the HHIT Suite ID [TBC_DRIP_REGISTRY].
Note to the RFC Editor: Please replace [TBC_DRIP_REGISTRY]
with the pointer to the IANA registry created in
Section 8.2.
Hash (m) : An extraction function in which output is 'm' bits.
Sizeof(p + n + o + m) 128 bits
The ORCHID length MUST be 128 bits. For HHITs with a 28-bit IPv6
prefix, there are 100 bits remaining to be divided in any manner
between the additional information ("Info"), OGA ID, and the hash
output. Consideration must be given to the size of the hash portion,
taking into account risks like pre-image attacks. 64 bits, as used
here for HHITs, may be as small as is acceptable. The size of 'n',
for the HID, is then determined as what is left; in the case of the
8-bit OGA used for HHIT, this is 28 bits.
3.5.2. ORCHID Encoding
This update adds a different encoding process to that currently used
in ORCHIDv2. The input to the hash function explicitly includes all
the header content plus the Context ID. The header content consists
of the Prefix, the Additional Information ("Info"), and OGA ID (HIT
Suite ID). Secondly, the length of the resulting hash is set by sum
of the length of the ORCHID header fields. For example, a 28-bit
prefix with 28 bits for the HID and 8 bits for the OGA ID leaves 64
bits for the hash length.
To achieve the variable length output in a consistent manner, the
cSHAKE hash is used. For this purpose, cSHAKE128 is appropriate.
The cSHAKE function call for this update is:
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cSHAKE128(Input, L, "", Context ID)
Input := Prefix | Additional Information | OGA ID | HOST_ID
L := Length in bits of hash portion of ORCHID
For full Suite ID support (those that use fixed length hashes like
SHA256), the following hashing can be used (Note: this does not
produce output Identical to ORCHIDv2 for a /28 prefix and Additional
Information of zero-length):
Hash[L](Context ID | Input)
Input := Prefix | Additional Information | OGA ID | HOST_ID
L := Length in bits of hash portion of ORCHID
Hash[L] := An extraction function in which output is obtained
by extracting the middle L-bit-long bitstring
from the argument bitstring.
The middle L-bits are those bits from the source number where either
there is an equal number of bits before and after these bits, or
there is one more bit prior (when the difference between hash size
and L is odd).
Hierarchical HITs use the Context ID defined in Section 3.
3.5.2.1. Encoding ORCHIDs for HIPv2
This section discusses how to provide backwards compatibility for
ORCHIDv2 [RFC7343] as used in HIPv2 [RFC7401].
For HIPv2, the Prefix is 2001:20::/28 (Section 6 of [RFC7343]).
'Info' is zero-length (i.e., not included), and OGA ID is 4-bit.
Thus, the HI Hash is 96-bit length. Further, the Prefix and OGA ID
are not included in the hash calculation. Thus, the following ORCHID
calculations for fixed output length hashes are used:
Hash[L](Context ID | Input)
Input := HOST_ID
L := 96
Context ID := 0xF0EF F02F BFF4 3D0F E793 0C3C 6E61 74EA
Hash[L] := An extraction function in which output is obtained
by extracting the middle L-bit-long bitstring
from the argument bitstring.
For variable output length hashes use:
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Hash[L](Context ID | Input)
Input := HOST_ID
L := 96
Context ID := 0xF0EF F02F BFF4 3D0F E793 0C3C 6E61 74EA
Hash[L] := The L-bit output from the hash function
Then, the ORCHID is constructed as follows:
Prefix | OGA ID | Hash Output
3.5.3. ORCHID Decoding
With this update, the decoding of an ORCHID is determined by the
Prefix and OGA ID. ORCHIDv2 [RFC7343] decoding is selected when the
Prefix is: 2001:20::/28.
For Hierarchical HITs, the decoding is determined by the presence of
the HHIT Prefix as specified in Section 8.2.
3.5.4. Decoding ORCHIDs for HIPv2
This section is included to provide backwards compatibility for
ORCHIDv2 [RFC7343] as used for HIPv2 [RFC7401].
HITs are identified by a Prefix of 2001:20::/28. The next 4 bits are
the OGA ID. The remaining 96 bits are the HI Hash.
4. Hierarchical HITs as DRIP Entity Tags
HHITs for UAS ID (called, DETs) use the new EdDSA/SHAKE128 HIT suite
defined in Section 3.4 (GEN-2 in [RFC9153]). This hierarchy,
cryptographically bound within the HHIT, provides the information for
finding the UA's HHIT registry (ID-3 in [RFC9153]).
The ASTM Standard Specification for Remote ID and Tracking
[F3411-22a] adds support for DETs. This is only available via the
new UAS ID type 4, "Specific Session ID (SSI)".
This new SSI uses the first byte of the 20-byte UAS ID for the SSI
Type, thus restricting the UAS ID of this type to a maximum of 19
bytes. The SSI Types initially assigned are:
SSI 1 IETF - DRIP Drone Remote ID Protocol (DRIP) entity ID.
SSI 2 3GPP - IEEE 1609.2-2016 HashedID8
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4.1. Nontransferablity of DETs
A HI and its DET SHOULD NOT be transferable between UA or even
between replacement electronics (e.g., replacement of damaged
controller CPU) for a UA. The private key for the HI SHOULD be held
in a cryptographically secure component.
4.2. Encoding HHITs in CTA 2063-A Serial Numbers
In some cases, it is advantageous to encode HHITs as a CTA 2063-A
Serial Number [CTA2063A]. For example, the FAA Remote ID Rules
[FAA_RID] state that a Remote ID Module (i.e., not integrated with UA
controller) must only use "the serial number of the unmanned
aircraft"; CTA 2063-A meets this requirement.
Encoding an HHIT within the CTA 2063-A format is not simple. The CTA
2063-A format is defined as follows:
Serial Number := MFR Code | Length Code | MFR SN
where:
MFR Code : 4 character code assigned by ICAO
(International Civil Aviation Organization,
a UN Agency).
Length Code : 1 character Hex encoding of MFR SN length (1-F).
MFR SN : US-ASCII alphanumeric code (0-9, A-Z except O and I).
Maximum length of 15 characters.
There is no place for the HID; there will need to be a mapping
service from Manufacturer Code to HID. The HHIT Suite ID and ORCHID
hash will take the full 15 characters (as described below) of the MFR
SN field.
A character in a CTA 2063-A Serial Number "shall include any
combination of digits and uppercase letters, except the letters O and
I, but may include all digits". This would allow for a Base34
encoding of the binary HHIT Suite ID and ORCHID hash in 15
characters. Although, programmatically, such a conversion is not
hard, other technologies (e.g., credit card payment systems) that
have used such odd base encoding have had performance challenges.
Thus, here a Base32 encoding will be used by also excluding the
letters Z and S (too similar to the digits 2 and 5). See Appendix C
for the encoding scheme.
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The low-order 72 bits (HHIT Suite ID | ORCHID hash) of the HHIT SHALL
be left-padded with 3 bits of zeros. This 75-bit number will be
encoded into the 15-character MFR SN field using the digit/letters
above. The manufacturer MUST use a Length Code of F (15).
Note: The manufacturer MAY use the same Manufacturer Code with a
Length Code of 1 - E (1 - 14) for other types of serial numbers.
Using the sample DET from Section 5 that is for HDA=20 under RAA=10
and having the ICAO CTA MFR Code of 8653, the 20-character CTA 2063-A
Serial Number would be:
8653F02T7B8RA85D19LX
A mapping service (e.g., DNS) MUST provide a trusted (e.g., via
DNSSEC [RFC4034]) conversion of the 4-character Manufacturer Code to
high-order 58 bits (Prefix | HID) of the HHIT. That is, given a
Manufacturer Code, a returned Prefix|HID value is reliable.
Definition of this mapping service is out of scope of this document.
It should be noted that this encoding would only be used in the Basic
ID Message (Section 2.2 of [RFC9153]). The DET is used in the
Authentication Messages (i.e., the messages that provide framing for
authentication data only).
4.3. Remote ID DET as one Class of Hierarchical HITs
UAS Remote ID DET may be one of a number of uses of HHITs. However,
it is out of the scope of the document to elaborate on other uses of
HHITs. As such these follow-on uses need to be considered in
allocating the RAAs (Section 3.3.1) or HHIT prefix assignments
(Section 8).
4.4. Hierarchy in ORCHID Generation
ORCHIDS, as defined in [RFC7343], do not cryptographically bind an
IPv6 prefix nor the OGA ID (the HIT Suite ID) to the hash of the HI.
The rationale at the time of developing ORCHID was attacks against
these fields are Denial-of-Service (DoS) attacks against protocols
using ORCHIDs and thus up to those protocols to address the issue.
HHITs, as defined in Section 3.5, cryptographically bind all content
in the ORCHID through the hashing function. A recipient of a DET
that has the underlying HI can directly trust and act on all content
in the HHIT. This provides a strong, self-claim for using the
hierarchy to find the DET Registry based on the HID (Section 4.5).
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4.5. DRIP Entity Tag (DET) Registry
DETs are registered to HDAs. A registration process,
[drip-registries], ensures DET global uniqueness (ID-4 in [RFC9153]).
It also provides the mechanism to create UAS public/private data that
are associated with the DET (REG-1 and REG-2 in [RFC9153]).
4.6. Remote ID Authentication using DETs
The EdDSA25519 HI (Section 3.4) underlying the DET can be used in an
88-byte self-proof evidence (timestamp, HHIT, and signature of these)
to provide proof to Observers of Remote ID ownership (GEN-1 in
[RFC9153]). In practice, the Wrapper and Manifest authentication
formats (Sections 6.3.3 and 6.3.4 of [drip-authentication])
implicitly provide this self-evidence. A lookup service like DNS can
provide the HI and registration proof (GEN-3 in [RFC9153]).
Similarly, for Observers without Internet access, a 200-byte offline
self-endorsement (Section 3.1.2 of [drip-authentication]) could
provide the same Remote ID ownership proof. This endorsement would
contain the HDA's signing of the UA's HHIT, itself signed by the UA's
HI. Only a small cache (also Section 3.1.2 of [drip-authentication])
that contains the HDA's HI/HHIT and HDA meta-data is needed by the
Observer. However, such an object would just fit in the ASTM
Authentication Message (Section 2.2 of [RFC9153]) with no room for
growth. In practice, [drip-authentication] provides this offline
self-endorsement in two authentication messages: the HDA's
endorsement of the UA's HHIT registration in a Link authentication
message whose hash is sent in a Manifest authentication message.
Hashes of any previously sent ASTM messages can be placed in a
Manifest authentication message (GEN-2 in [RFC9153]). When a
Location/Vector Message (i.e., a message that provides UA location,
altitude, heading, speed, and status) hash along with the hash of the
HDA's UA HHIT endorsement are sent in a Manifest authentication
message and the Observer can visually see a UA at the claimed
location, the Observer has a very strong proof of the UA's Remote ID.
All this behavior and how to mix these authentication messages into
the flow of UA operation messages are detailed in
[drip-authentication].
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5. DRIP Entity Tags (DETs) in DNS
There are two approaches for storing and retrieving DETs using DNS.
The following are examples of how this may be done. This will serve
as guidance to the actual deployment of DETs in DNS. However, this
document does not provide a recommendation. Further DNS-related
considerations are covered in [drip-registries].
* As FQDNs, for example, "20010030.hhit.arpa.".
* Reverse DNS lookups as IPv6 addresses per [RFC8005].
A DET can be used to construct an FQDN that points to the USS that
has the public/private information for the UA (REG-1 and REG-2 in
[RFC9153]). For example, the USS for the HHIT could be found via the
following: assume the RAA is decimal 100 and the HDA is decimal 50.
The PTR record is constructed as follows:
100.50.20010030.hhit.arpa. IN PTR foo.uss.example.org.
The HDA SHOULD provide DNS service for its zone and provide the HHIT
detail response.
The DET reverse lookup can be a standard IPv6 reverse look up, or it
can leverage off the HHIT structure. Using the allocated prefix for
HHITs TBD6 [suggested value 2001:30::/28] (See Section 3.1), the RAA
is decimal 10 and the HDA is decimal 20, the DET is:
2001:30:280:1405:a3ad:1952:ad0:a69e
See Appendix B.1 for how the upper 64 bits, above, are constructed.
A DET reverse lookup could be to:
a69e.0ad0.1952.a3ad.1405.0280.20.10.20010030.hhit.arpa..
or:
a3ad19520ad0a69e.5.20.10.20010030.hhit.arpa.
A 'standard' ip6.arpa RR has the advantage of only one Registry
service supported.
$ORIGIN 5.0.4.1.0.8.2.0.0.3.0.0.1.0.0.2.ip6.arpa.
e.9.6.a.0.d.a.0.2.5.9.1.d.a.3.a IN PTR
a3ad1952ad0a69e.20.10.20010030.hhit.arpa.
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This DNS entry for the DET can also provide a revocation service.
For example, instead of returning the HI RR it may return some record
showing that the HI (and thus DET) has been revoked. Guidance on
revocation service will be provided in [drip-registries].
6. Other UAS Traffic Management (UTM) Uses of HHITs Beyond DET
HHITs will be used within the UTM architecture beyond DET (and USS in
UA ID registration and authentication), for example, as a Ground
Control Station (GCS) HHIT ID. Some GCS will use its HHIT for
securing its Network Remote ID (to USS HHIT) and Command and Control
(C2, Section 2.2.2 of [RFC9153]) transports.
Observers may have their own HHITs to facilitate UAS information
retrieval (e.g., for authorization to private UAS data). They could
also use their HHIT for establishing a HIP connection with the UA
Pilot for direct communications per authorization. Details about
such issues are out of the scope of this document).
7. Summary of Addressed DRIP Requirements
This document provides the details to solutions for GEN 1 - 3, ID 1 -
5, and REG 1 - 2 requirements that are described in [RFC9153].
8. IANA Considerations
8.1. New Well-Known IPv6 prefix for DETs
Since the DET format is not compatible with [RFC7343], IANA is
requested to allocate a new prefix following this template for the
IPv6 Special-Purpose Address Registry.
Address Block:
IANA is requested to allocate a new 28-bit prefix out of the IANA
IPv6 Special Purpose Address Block, namely 2001::/23, as per
[RFC6890] (TBD6, suggested: 2001:30::/28).
Name:
This block should be named "DRIP Entity Tags (DETs) Prefix".
RFC:
This document.
Allocation Date:
Date this document published.
Termination Date:
Forever.
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Source:
False.
Destination:
False.
Forwardable:
False.
Globally Reachable:
False.
Reserved-by-Protocol:
False.
8.2. New IANA DRIP Registry
This document requests IANA to create a new registry titled "Drone
Remote ID Protocol" registry. It is suggested that multiple
designated experts be appointed for registry change requests.
Criteria that should be applied by the designated experts include
determining whether the proposed registration duplicates existing
functionality and whether the registration description is clear and
fits the purpose of this registry.
Registration requests MUST be sent to drip-reg-review@ietf.org and
are evaluated within a three-week review period on the advice of one
or more designated experts. Within the review period, the designated
experts will either approve or deny the registration request,
communicating this decision to the review list and IANA. Denials
should include an explanation and, if applicable, suggestions as to
how to make the request successful.
Registration requests that are undetermined for a period longer than
28 days can be brought to the IESG's attention for resolution.
The following two subregistries should be created under that
registry.
Hierarchical HIT (HHIT) Prefixes:
Initially, for DET use, one 28-bit prefix should be assigned out
of the IANA IPv6 Special Purpose Address Block, namely 2001::/23,
as per [RFC6890]. Future additions to this subregistry are to be
made through Expert Review (Section 4.5 of [RFC8126]). Entries
with network-specific prefixes may be present in the registry.
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HHIT Use Bits Value Reference
DET 28 TBD6 (suggested value 2001:30::/28) [This]
Hierarchical HIT (HHIT) Suite ID:
This 8-bit valued subregistry is a superset of the 4/8-bit "HIT
Suite ID" subregistry of the "Host Identity Protocol (HIP)
Parameters" registry in [IANA-HIP]. Future additions to this
subregistry are to be made through IETF Review (Section 4.8 of
[RFC8126]). The following HHIT Suite IDs are defined:
HHIT Suite Value Reference
RESERVED 0
RSA,DSA/SHA-256 1 [RFC7401]
ECDSA/SHA-384 2 [RFC7401]
ECDSA_LOW/SHA-1 3 [RFC7401]
EdDSA/cSHAKE128 TBD3 (suggested value 5) [This]
HDA Private Use 1 TBD4 (suggested value 254) [This]
HDA Private Use 2 TBD5 (suggested value 255) [This]
The HHIT Suite ID values 1 - 31 are reserved for IDs that MUST be
replicated as HIT Suite IDs (Section 8.4) as is TBD3 here. Higher
values (32 - 255) are for those Suite IDs that need not or cannot
be accommodated as a HIT Suite ID.
8.3. IANA CGA Registry Update
This document requests that this document be added to the reference
field for the "CGA Extension Type Tags" registry [IANA-CGA], where
IANA registers the following Context ID:
Context ID:
The Context ID (Section 3) shares the namespace introduced for CGA
Type Tags. Defining new Context IDs follow the rules in Section 8
of [RFC3972]:
Context ID := 0x00B5 A69C 795D F5D5 F008 7F56 843F 2C40 [This]
8.4. IANA HIP Registry Updates
This document requests IANA to make the following changes to the IANA
"Host Identity Protocol (HIP) Parameters" [IANA-HIP] registry:
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Host ID:
This document defines the new EdDSA Host ID with value TBD1
(suggested: 13) (Section 3.4.1) in the "HI Algorithm" subregistry
of the "Host Identity Protocol (HIP) Parameters" registry.
Algorithm
profile Value Reference
EdDSA TBD1 (suggested value 13) [RFC8032]
EdDSA Curve Label:
This document specifies a new algorithm-specific subregistry named
"EdDSA Curve Label". The values for this subregistry are defined
in Section 3.4.1.1. Future additions to this subregistry are to
be made through IETF Review (Section 4.8 of [RFC8126]).
Algorithm Curve Values Reference
EdDSA RESERVED 0
EdDSA EdDSA25519 1 [RFC8032]
EdDSA EdDSA25519ph 2 [RFC8032]
EdDSA EdDSA448 3 [RFC8032]
EdDSA EdDSA448ph 4 [RFC8032]
5-65535 Unassigned
HIT Suite ID:
This document defines the new HIT Suite of EdDSA/cSHAKE with value
TBD3 (suggested: 5) (Section 3.4.2) in the "HIT Suite ID"
subregistry of the "Host Identity Protocol (HIP) Parameters"
registry.
HIT Suite Value Reference
EdDSA/cSHAKE128 TBD3 (suggested value 5) [This]
The HIT Suite ID 4-bit values 1 - 15 and 8-bit values 0x00 - 0x0F
MUST be replicated as HHIT Suite IDs (Section 8.2) as is TBD3
here.
9. Security Considerations
The 64-bit hash in HHITs presents a real risk of second pre-image
cryptographic hash attack Section 9.5. There are no known (to the
authors) studies of hash size to cryptographic hash attacks.
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However, with today's computing power, producing 2^64 EdDSA keypairs
and then generating the corresponding HHIT is economically feasible.
Consider that a *single* bitcoin mining ASIC can do on the order of
2^46 sha256 hashes a second or about 2^62 hashes in a single day.
The point being, 2^64 is not prohibitive, especially as this can be
done in parallel.
Now it should be noted that the 2^64 attempts is for stealing a
specific HHIT. Consider a scenario of a street photography company
with 1,024 UAs (each with its own HHIT); an attacker may well be
satisfied stealing any one of them. Then rather than needing to
satisfy a 64-bit condition on the cSHAKE128 output, an attacker needs
only to satisfy what is equivalent to a 54-bit condition (since there
are 2^10 more opportunities for success).
Thus, although the probability of a collision or pre-image attack is
low in a collection of 1,024 HHITs out of a total population of 2^64,
per Section 9.5, it is computationally and economically feasible.
Therefore, the HHIT registration is a MUST and HHIT/HI registration
validation SHOULD be performed by Observers either through registry
lookups or via broadcasted registration proofs (Section 3.1.2 of
[drip-authentication]).
The DET Registry services effectively block attempts to "take over"
or "hijack" a DET. It does not stop a rogue attempting to
impersonate a known DET. This attack can be mitigated by the
receiver of messages containing DETs using DNS to find the HI for the
DET. As such, use of DNSSEC by the DET registries is recommended to
provide trust in HI retrieval.
Another mitigation of HHIT hijacking is if the HI owner (UA) supplies
an object containing the HHIT and signed by the HI private key of the
HDA such as detailed in [drip-authentication].
The two risks with hierarchical HITs are the use of an invalid HID
and forced HIT collisions. The use of a DNS zone (e.g., "det.arpa.")
is a strong protection against invalid HIDs. Querying an HDA's RVS
for a HIT under the HDA protects against talking to unregistered
clients. The Registry service [drip-registries], through its HHIT
uniqueness enforcement, provides against forced or accidental HHIT
hash collisions.
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Cryptographically Generated Addresses (CGAs) provide an assurance of
uniqueness. This is two-fold. The address (in this case the UAS ID)
is a hash of a public key and a Registry hierarchy naming. Collision
resistance (more important that it implied second-preimage
resistance) makes it statistically challenging to attacks. A
registration process [drip-registries] within the HDA provides a
level of assured uniqueness unattainable without mirroring this
approach.
The second aspect of assured uniqueness is the digital signing
(evidence) process of the DET by the HI private key and the further
signing (evidence) of the HI public key by the Registry's key. This
completes the ownership process. The observer at this point does not
know what owns the DET, but is assured, other than the risk of theft
of the HI private key, that this UAS ID is owned by something and is
properly registered.
9.1. Post Quantum Computing out of scope
As stated in Section 8.1 of [drip-architecture], there has been no
effort, at this time, to address post quantum computing cryptography.
UAs and Broadcast Remote ID communications are so constrained that
current post quantum computing cryptography is not applicable. Plus
since a UA may use a unique DET for each operation, the attack window
could be limited to the duration of the operation.
HHITs contain the ID for the cryptographic suite used in its
creation, a future post quantum computing safe algorithm that fits
the Remote ID constraints may readily be added.
9.2. DET Trust in ASTM messaging
The DET in the ASTM Basic ID Message (Msg Type 0x0, the actual Remote
ID message) does not provide any assertion of trust. The best that
might be done within this Basic ID Message is 4 bytes truncated from
a HI signing of the HHIT (the UA ID field is 20 bytes and a HHIT is
16). This is not trustable; that is, too open to a hash attack.
Minimally, it takes 84 bytes (Section 4.6) to prove ownership of a
DET with a full EdDSA signature. Thus, no attempt has been made to
add DET trust directly within the very small Basic ID Message.
The ASTM Authentication Message (Msg Type 0x2) as shown in
Section 4.6 can provide practical actual ownership proofs. These
endorsements and evidences include timestamps to defend against
replay attacks. But in themselves, they do not prove which UA sent
the message. They could have been sent by a dog running down the
street with a Broadcast Remote ID module strapped to its back.
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Proof of UA transmission comes when the Authentication Message
includes proofs for the ASTM Location/Vector Message (Msg Type 0x1)
and the observer can see the UA or that information is validated by
ground multilateration. Only then does an observer gain full trust
in the DET of the UA.
DETs obtained via the Network RID path provides a different approach
to trust. Here the UAS SHOULD be securely communicating to the USS,
thus asserting DET trust.
9.3. DET Revocation
The DNS entry for the DET can also provide a revocation service. For
example, instead of returning the HI RR it may return some record
showing that the HI (and thus DET) has been revoked. Guidance on
revocation service will be provided in [drip-registries].
9.4. Privacy Considerations
There is no expectation of privacy for DETs; it is not part of the
privacy normative requirements listed in, Section 4.3.1, of
[RFC9153]. DETs are broadcast in the clear over the open air via
Bluetooth and Wi-Fi. They will be collected and collated with other
public information about the UAS. This will include DET registration
information and location and times of operations for a DET. A DET
can be for the life of a UA if there is no concern about DET/UA
activity harvesting.
Further, the MAC address of the wireless interface used for Remote ID
broadcasts are a target for UA operation aggregation that may not be
mitigated through MAC address randomization. For Bluetooth 4 Remote
ID messaging, the MAC address is used by observers to link the Basic
ID Message that contains the RID with other Remote ID messages, thus
must be constant for a UA operation. This message linkage use of MAC
addresses may not be needed with the Bluetooth 5 or Wi-Fi PHYs.
These PHYs provide for a larger message payload and can use the
Message Pack (Msg Type 0xF) and the Authentication Message to
transmit the RID with other Remote ID messages. However, it is not
mandatory to send the RID in a Message Pack or Authentication
Message, so allowance for using the MAC address for UA message
linking must be maintained. That is, the MAC address should be
stable for at least a UA operation.
Finally, it is not adequate to simply change the DET and MAC for a UA
per operation to defeat historically tracking a UA's activity.
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Any changes to the UA MAC may have impacts to C2 setup and use. A
constant GCS MAC may well defeat any privacy gains in UA MAC and RID
changes. UA/GCS binding is complicated with changing MAC addresses;
historically UAS design assumed these to be "forever" and made setup
a one-time process. Additionally, if IP is used for C2, a changing
MAC may mean a changing IP address to further impact the UAS
bindings. Finally, an encryption wrapper's identifier (such as ESP
[RFC4303] SPI) would need to change per operation to insure operation
tracking separation.
Creating and maintaining UAS operational privacy is a multifaceted
problem. Many communication pieces need to be considered to truly
create a separation between UA operations. Simply changing the DET
only starts the changes that need to be implemented.
These privacy realities may present challenges for the EU U-space
(Appendix A) program.
9.5. Collision Risks with DETs
The 64-bit hash size here for DETs does have an increased risk of
collisions over the 96-bit hash size used for the ORCHID [RFC7343]
construct. There is a 0.01% probability of a collision in a
population of 66 million. The probability goes up to 1% for a
population of 663 million. See Appendix D for the collision
probability formula.
However, this risk of collision is within a single "Additional
Information" value, i.e., a RAA/HDA domain. The UAS/USS registration
process should include registering the DET and MUST reject a
collision, forcing the UAS to generate a new HI and thus HHIT and
reapplying to the DET registration process (Section 6 of
[drip-registries]).
Thus an adversary trying to generate a collision and 'steal' the DET
would run afoul of this registration process and associated
validation process mentioned in Section 1.1.
10. References
10.1. Normative References
[ipseckey-eddsa]
Moskowitz, R., Kivinen, T., and M. Richardson, "EdDSA
value for IPSECKEY", Work in Progress, Internet-Draft,
draft-moskowitz-ipsecme-ipseckey-eddsa-06, 23 November
2022, <https://datatracker.ietf.org/doc/html/draft-
moskowitz-ipsecme-ipseckey-eddsa-06>.
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[NIST.FIPS.202]
Dworkin, M. J. and National Institute of Standards and
Technology, "SHA-3 Standard: Permutation-Based Hash and
Extendable-Output Functions", DOI 10.6028/nist.fips.202,
July 2015, <http://dx.doi.org/10.6028/nist.fips.202>.
[NIST.SP.800-185]
Kelsey, J., Change, S., Perlner, R., and National
Institute of Standards and Technology, "SHA-3 derived
functions: cSHAKE, KMAC, TupleHash and ParallelHash",
DOI 10.6028/nist.sp.800-185, December 2016,
<http://dx.doi.org/10.6028/nist.sp.800-185>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6890] Cotton, M., Vegoda, L., Bonica, R., Ed., and B. Haberman,
"Special-Purpose IP Address Registries", BCP 153,
RFC 6890, DOI 10.17487/RFC6890, April 2013,
<https://www.rfc-editor.org/info/rfc6890>.
[RFC7343] Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay
Routable Cryptographic Hash Identifiers Version 2
(ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September
2014, <https://www.rfc-editor.org/info/rfc7343>.
[RFC7401] Moskowitz, R., Ed., Heer, T., Jokela, P., and T.
Henderson, "Host Identity Protocol Version 2 (HIPv2)",
RFC 7401, DOI 10.17487/RFC7401, April 2015,
<https://www.rfc-editor.org/info/rfc7401>.
[RFC8005] Laganier, J., "Host Identity Protocol (HIP) Domain Name
System (DNS) Extension", RFC 8005, DOI 10.17487/RFC8005,
October 2016, <https://www.rfc-editor.org/info/rfc8005>.
[RFC8032] Josefsson, S. and I. Liusvaara, "Edwards-Curve Digital
Signature Algorithm (EdDSA)", RFC 8032,
DOI 10.17487/RFC8032, January 2017,
<https://www.rfc-editor.org/info/rfc8032>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References
[cfrg-comment]
"A CFRG review of draft-ietf-drip-rid", September 2021,
<https://mailarchive.ietf.org/arch/msg/cfrg/
tAJJq60W6TlUv7_pde5cw5TDTCU/>.
[corus] CORUS, "U-space Concept of Operations", September 2019,
<https://www.sesarju.eu/node/3411>.
[CTA2063A] ANSI/CTA, "Small Unmanned Aerial Systems Serial Numbers",
September 2019, <https://shop.cta.tech/products/small-
unmanned-aerial-systems-serial-numbers>.
[drip-architecture]
Card, S. W., Wiethuechter, A., Moskowitz, R., Zhao, S.,
and A. Gurtov, "Drone Remote Identification Protocol
(DRIP) Architecture", Work in Progress, Internet-Draft,
draft-ietf-drip-arch-29, 16 August 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-drip-
arch-29>.
[drip-authentication]
Wiethuechter, A., Card, S. W., and R. Moskowitz, "DRIP
Entity Tag Authentication Formats & Protocols for
Broadcast Remote ID", Work in Progress, Internet-Draft,
draft-ietf-drip-auth-26, 14 October 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-drip-
auth-26>.
[drip-registries]
Wiethuechter, A. and J. Reid, "DRIP Entity Tag (DET)
Identity Management Architecture", Work in Progress,
Internet-Draft, draft-ietf-drip-registries-06, 17 November
2022, <https://datatracker.ietf.org/doc/html/draft-ietf-
drip-registries-06>.
[F3411-22a]
ASTM International, "Standard Specification for Remote ID
and Tracking - F3411−22a", July 2022,
<https://www.astm.org/f3411-22a.html>.
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[FAA_RID] United States Federal Aviation Administration (FAA),
"Remote Identification of Unmanned Aircraft", 2021,
<https://www.govinfo.gov/content/pkg/FR-2021-01-15/
pdf/2020-28948.pdf>.
[IANA-CGA] IANA, "Cryptographically Generated Addresses (CGA) Message
Type Name Space", <https://www.iana.org/assignments/cga-
message-types/cga-message-types.xhtml>.
[IANA-HIP] IANA, "Host Identity Protocol (HIP) Parameters",
<https://www.iana.org/assignments/hip-parameters/hip-
parameters.xhtml>.
[Keccak] Bertoni, G., Daemen, J., Peeters, M., Van Assche, G., and
R. Van Keer, "The Keccak Function",
<https://keccak.team/index.html>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[RFC4025] Richardson, M., "A Method for Storing IPsec Keying
Material in DNS", RFC 4025, DOI 10.17487/RFC4025, March
2005, <https://www.rfc-editor.org/info/rfc4025>.
[RFC4034] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Resource Records for the DNS Security Extensions",
RFC 4034, DOI 10.17487/RFC4034, March 2005,
<https://www.rfc-editor.org/info/rfc4034>.
[RFC4122] Leach, P., Mealling, M., and R. Salz, "A Universally
Unique IDentifier (UUID) URN Namespace", RFC 4122,
DOI 10.17487/RFC4122, July 2005,
<https://www.rfc-editor.org/info/rfc4122>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC8004] Laganier, J. and L. Eggert, "Host Identity Protocol (HIP)
Rendezvous Extension", RFC 8004, DOI 10.17487/RFC8004,
October 2016, <https://www.rfc-editor.org/info/rfc8004>.
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[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC9063] Moskowitz, R., Ed. and M. Komu, "Host Identity Protocol
Architecture", RFC 9063, DOI 10.17487/RFC9063, July 2021,
<https://www.rfc-editor.org/info/rfc9063>.
[RFC9153] Card, S., Ed., Wiethuechter, A., Moskowitz, R., and A.
Gurtov, "Drone Remote Identification Protocol (DRIP)
Requirements and Terminology", RFC 9153,
DOI 10.17487/RFC9153, February 2022,
<https://www.rfc-editor.org/info/rfc9153>.
[RFC9224] Blanchet, M., "Finding the Authoritative Registration Data
Access Protocol (RDAP) Service", STD 95, RFC 9224,
DOI 10.17487/RFC9224, March 2022,
<https://www.rfc-editor.org/info/rfc9224>.
Appendix A. EU U-Space RID Privacy Considerations
The EU is defining a future of airspace management known as U-space
within the Single European Sky ATM Research (SESAR) undertaking.
Concept of Operation for EuRopean UTM Systems (CORUS) project
proposed low-level Concept of Operations [corus] for UAS in the EU.
It introduces strong requirements for UAS privacy based on European
GDPR regulations. It suggests that UAs are identified with agnostic
IDs, with no information about UA type, the operators or flight
trajectory. Only authorized persons should be able to query the
details of the flight with a record of access.
Due to the high privacy requirements, a casual observer can only
query U-space if it is aware of a UA seen in a certain area. A
general observer can use a public U-space portal to query UA details
based on the UA transmitted "Remote identification" signal. Direct
remote identification (DRID) is based on a signal transmitted by the
UA directly. Network remote identification (NRID) is only possible
for UAs being tracked by U-Space and is based on the matching the
current UA position to one of the tracks.
This is potentially a contrary expectation as that presented in
Section 9.4. U-space will have to deal with this reality within the
GDPR regulations. Still, DETs as defined here present a large step
in the right direction for agnostic IDs.
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The project lists "E-Identification" and "E-Registrations" services
as to be developed. These services can use DETs and follow the
privacy considerations outlined in this document for DETs.
If an "agnostic ID" above refers to a completely random identifier,
it creates a problem with identity resolution and detection of
misuse. On the other hand, a classical HIT has a flat structure
which makes its resolution difficult. The DET (Hierarchical HIT)
provides a balanced solution by associating a registry with the UA
identifier. This is not likely to cause a major conflict with
U-space privacy requirements, as the registries are typically few at
a country level (e.g., civil personal, military, law enforcement, or
commercial).
Appendix B. The 14/14 HID split
The following explains the logic behind selecting to divide the 28
bits of the HID into 2 14-bit components.
At this writing ICAO has 273 member "States", each may want to
control RID assignment within its National Air Space (NAS). Some
members may want separate RAAs to use for Civil, general Government,
and Military use. They may also want allowances for competing Civil
RAA operations. It is reasonable to plan for 8 RAAs per ICAO member
(plus regional aviation organizations like in the European Union).
Thus at a start a 4,096 RAA space is advised.
There will be requests by commercial entities for their own, RAA
allotments. Examples could include international organizations that
will be using UAS and international delivery service associations.
These may be smaller than the RAA space needed by ICAO member States
and could be met with a 2,048 space allotment, but as will be seen,
might as well be 4,096 as well.
This may well cover currently understood RAA entities. There will be
future new applications, branching off into new areas. So yet
another space allocation should be set aside. If this is equal to
all that has been reserved, we should allow for 16,384 (2^14) RAAs.
The HDA allocation follows a different logic from that of RAAs. Per
Appendix D, an HDA should be able to easily assign 63M RIDs and even
manage 663M with a "first come, first assigned" registration process.
For most HDAs this is more than enough, and a single HDA assignment
within their RAA will suffice. Most RAAs will only delegate to a
couple HDAs for their operational needs. But there are major
exceptions that point to some RAAs needing large numbers of HDA
assignments.
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Delivery service operators like Amazon (est. 30K delivery vans) and
UPS (est. 500K delivery vans) may choose, for anti-tracking reasons,
to use unique RIDs per day or even per operation. 30K delivery UA
could need 11M upwards to 44M RIDs. Anti-tracking would be hard to
provide if the HID were the same for a delivery service fleet, so
such a company may turn to an HDA that provides this service to
multiple companies so that who's UA is who's is not evident in the
HID. A USS providing this service could well use multiple HDA
assignments per year, depending on strategy.
Perhaps a single RAA providing HDAs for delivery service (or similar
behaving) UAS could 'get by' with a 2048 HDA space (11-bits). So the
HDA space could well be served with only 12 bits allocated out of the
28-bit HID space. But as this is speculation, and it will take years
of deployment experience, a 14-bit HDA space has been selected.
There may also be 'small' ICAO member States that opt for a single
RAA and allocate their HDAs for all UA that are permitted in their
NAS. The HDA space is large enough that some to use part for
government needs as stated above and for small commercial needs. Or
the State may use a separate, consecutive RAA for commercial users.
Thus it would be 'easy' to recognize State-approved UA by HID high-
order bits.
B.1. DET Encoding Example
The DET upper 64 bits appear to be oddly constructed from nibbled
fields, when typically seen in 8-bit representations. The following
works out the construction of the example in Section 5.
In that example the prefix is 2001:30::/28, the RAA is decimal 10 and
the HDA is decimal 20. Below is the RAA and HDA in 14-bit format:
RAA 10 = 00000000001010
HDA 20 = 00000000010100
The left most 4 bits of the RAA, all zeros, combine with the prefix
to form 2001:0030:, leaving remaining RAA and HDA combined to:
0000|0010|1000|0000|0001|0100|
Which, combined with the OGA of x05 is: 0280:1405, thus the whole
upper 64 bits are 2001:0030:0280:1405.
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Appendix C. Base32 Alphabet
The alphabet used in CTA 2063-A Serial Number does not lend to using
any published Base32 encoding scheme. Thus the following Base32
Alphabet is used.
Each 5-bit group is used as an index into an array of 32 printable
characters. The character referenced by the index is placed in the
output string. These characters, identified below, are selected from
US-ASCII digits and uppercase letters.
+=====+========+=====+==========+=====+==========+=====+==========+
|Value|Encoding|Value| Encoding |Value| Encoding |Value| Encoding |
+=====+========+=====+==========+=====+==========+=====+==========+
| 0|0 | 8| 8 | 16| G | 24| Q |
+-----+--------+-----+----------+-----+----------+-----+----------+
| 1|1 | 9| 9 | 17| H | 25| R |
+-----+--------+-----+----------+-----+----------+-----+----------+
| 2|2 | 10| A | 18| J | 26| T |
+-----+--------+-----+----------+-----+----------+-----+----------+
| 3|3 | 11| B | 19| K | 27| U |
+-----+--------+-----+----------+-----+----------+-----+----------+
| 4|4 | 12| C | 20| L | 28| V |
+-----+--------+-----+----------+-----+----------+-----+----------+
| 5|5 | 13| D | 21| M | 29| W |
+-----+--------+-----+----------+-----+----------+-----+----------+
| 6|6 | 14| E | 22| N | 30| X |
+-----+--------+-----+----------+-----+----------+-----+----------+
| 7|7 | 15| F | 23| P | 31| Y |
+-----+--------+-----+----------+-----+----------+-----+----------+
Table 2: The Base 32 Alphabet
Appendix D. Calculating Collision Probabilities
The accepted formula for calculating the probability of a collision
is:
p = 1 - e^{-k^2/(2n)}
P Collision Probability
n Total possible population
k Actual population
The following table provides the approximate population size for a
collision for a given total population.
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Deployed Population
Total With Collision Risk of
Population .01% 1%
2^96 4T 42T
2^72 1B 10B
2^68 250M 2.5B
2^64 66M 663M
2^60 16M 160M
Acknowledgments
Dr. Gurtov is an adviser on Cybersecurity to the Swedish Civil
Aviation Administration.
Quynh Dang of NIST gave considerable guidance on using Keccak and the
NIST supporting documents. Joan Deamen of the Keccak team was
especially helpful in many aspects of using Keccak. Nicholas
Gajcowski [cfrg-comment] provided a concise hash pre-image security
assessment via the CFRG list.
Many thanks to Michael Richardson and Brian Haberman for the iotdir
review, Magnus Nystrom for the secdir review, Elwyn Davies for genart
review and DRIP co-chair and draft shepherd, Mohamed Boucadair for
his extensive comments and help on document clarity. And finally,
many thanks to area directors: Roman Danyliw, Erik Kline, Murray
Kucherawy, Warren Kumari, John Scudder, Paul Wouters, and Sarker
Zaheduzzaman, for the IESG review.
Authors' Addresses
Robert Moskowitz
HTT Consulting
Oak Park, MI 48237
United States of America
Email: rgm@labs.htt-consult.com
Stuart W. Card
AX Enterprize, LLC
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: stu.card@axenterprize.com
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Adam Wiethuechter
AX Enterprize, LLC
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: adam.wiethuechter@axenterprize.com
Andrei Gurtov
Linköping University
IDA
SE-58183 Linköping
Sweden
Email: gurtov@acm.org
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