Unmanned Aircraft System Remote Identification (UAS RID)
draft-ietf-drip-rid-08
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9374.
|
|
|---|---|---|---|
| Authors | Robert Moskowitz , Stuart W. Card , Adam Wiethuechter , Andrei Gurtov | ||
| Last updated | 2021-07-25 | ||
| Replaces | draft-ietf-drip-uas-rid | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
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| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
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| Document shepherd | Mohamed Boucadair | ||
| IESG | IESG state | Became RFC 9374 (Proposed Standard) | |
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| Send notices to | mohamed.boucadair@orange.com |
draft-ietf-drip-rid-08
DRIP R. Moskowitz
Internet-Draft HTT Consulting
Updates: 7401, 7343 (if approved) S. Card
Intended status: Standards Track A. Wiethuechter
Expires: 26 January 2022 AX Enterprize, LLC
A. Gurtov
Linköping University
25 July 2021
Unmanned Aircraft System Remote Identification (UAS RID)
draft-ietf-drip-rid-08
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). HHITs self-attest to the
included explicit hierarchy that provides Registrar discovery for
3rd-party identifier attestation.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 26 January 2022.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 4
2.2. Notations . . . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
3. The Hierarchical Host Identity Tag (HHIT) . . . . . . . . . . 5
3.1. HHIT prefix . . . . . . . . . . . . . . . . . . . . . . . 6
3.2. HHIT Suite IDs . . . . . . . . . . . . . . . . . . . . . 6
3.2.1. 8 bit HIT Suite IDs . . . . . . . . . . . . . . . . . 6
3.3. The Hierarchy ID (HID) . . . . . . . . . . . . . . . . . 7
3.3.1. The Registered Assigning Authority (RAA) . . . . . . 7
3.3.2. The Hierarchical HIT Domain Authority (HDA) . . . . . 7
3.4. Edward Digital Signature Algorithm for HITs . . . . . . . 8
3.4.1. HOST_ID . . . . . . . . . . . . . . . . . . . . . . . 8
3.4.2. HIT_SUITE_LIST . . . . . . . . . . . . . . . . . . . 8
3.5. ORCHIDs for Hierarchical HITs . . . . . . . . . . . . . . 9
3.5.1. Adding additional information to the ORCHID . . . . . 10
3.5.2. ORCHID Encoding . . . . . . . . . . . . . . . . . . . 11
3.5.3. ORCHID Decoding . . . . . . . . . . . . . . . . . . . 12
3.5.4. Decoding ORCHIDs for HITv2 . . . . . . . . . . . . . 12
4. Hierarchical HITs as Remote ID . . . . . . . . . . . . . . . 13
4.1. Nontransferablity of HHITs . . . . . . . . . . . . . . . 13
4.2. Encoding HHITs in CTA 2063-A Serial Numbers . . . . . . . 13
4.3. Remote ID as one class of Hierarchical HITs . . . . . . . 14
4.4. Hierarchy in ORCHID Generation . . . . . . . . . . . . . 14
4.5. Hierarchical HIT Registry . . . . . . . . . . . . . . . . 15
4.6. Remote ID Authentication using HHITs . . . . . . . . . . 15
5. UAS ID HHIT in DNS . . . . . . . . . . . . . . . . . . . . . 15
6. DRIP Proofs . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. Claim / Assertion: HHIT . . . . . . . . . . . . . . . . . 17
6.2. Self-Attestation: Attestation(X,X) . . . . . . . . . . . 17
6.2.1. Concise Self-Attestation: Attestation(X, ConciseX) . 19
6.3. Certificate(X, Y) . . . . . . . . . . . . . . . . . . . . 21
6.3.1. Concise Certificate(X, Concise Y) . . . . . . . . . . 22
6.4. Offline Broadcast Attestation: Attestation(X, Offline
Y) . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
6.5. Timestamps . . . . . . . . . . . . . . . . . . . . . . . 25
6.6. Signatures . . . . . . . . . . . . . . . . . . . . . . . 25
7. Other UTM uses of HHITs . . . . . . . . . . . . . . . . . . . 25
8. DRIP Requirements addressed . . . . . . . . . . . . . . . . . 25
9. ASTM Considerations . . . . . . . . . . . . . . . . . . . . . 25
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10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26
10.1. New IPv6 prefix needed for HHITs . . . . . . . . . . . . 26
11. Security Considerations . . . . . . . . . . . . . . . . . . . 27
11.1. Hierarchical HIT Trust . . . . . . . . . . . . . . . . . 27
11.2. Collision risks with Hierarchical HITs . . . . . . . . . 28
11.3. Proofs Considerations . . . . . . . . . . . . . . . . . 28
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
12.1. Normative References . . . . . . . . . . . . . . . . . . 29
12.2. Informative References . . . . . . . . . . . . . . . . . 29
Appendix A. EU U-Space RID Privacy Considerations . . . . . . . 32
Appendix B. Example HHIT Self Attestation . . . . . . . . . . . 32
B.1. HHIT Offline Self Attestation . . . . . . . . . . . . . . 33
Appendix C. Calculating Collision Probabilities . . . . . . . . 34
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
[drip-requirements] describes an Unmanned Aircraft System Remote
Identification and tracking (UAS ID) as unique (ID-4), non-spoofable
(ID-5), and identify a registry where the ID is listed (ID-2); all
within a 20 character identifier (ID-1).
This document describes 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 include
explicit hierarchy to enable DNS HHIT queries (Host ID for
authentication, e.g. Section 6.2.1) and for EPP Registrar discovery
[RFC7484] for 3rd-party identification attestation (e.g.
Section 6.2.1).
HITs are statistically unique through the cryptographic hash feature
of second-preimage resistance. The cryptographically-bound addition
of the Hierarchy and a HHIT registration process (TBD; e.g. based on
Extensible Provisioning Protocol, [RFC5730]) provide complete, global
HHIT uniqueness. This is in contrast to using general identifiers
(e.g. a Universally Unique IDentifier (UUID) [RFC4122] or device
serial number) as the subject in an X.509 [RFC5280] certificate.
In a multi-CA (multi Certificate Authority) 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.
Hierarchical HITs provide self-attestation of the HHIT registry. A
HHIT can only be in a single registry within a registry system (e.g.
Extensible Provisioning Protocol (EPP) [RFC5730] and DNS).
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Hierarchical HITs are valid, though non-routable, IPv6 addresses
[RFC8200]. As such, they fit in many ways within various IETF
technologies.
2. Terms and Definitions
2.1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Notations
| Signifies concatenation of information - e.g., X | Y is the
concatenation of X and Y.
Claim(X,Y):
Form of a predicate (X is Y, X has property Y, and most
importantly X owns Y).
Assertion({X...}):
A set of one or more claims. This definition is borrowed from
JWT/CWT ([RFC7519]/[RFC8392]).
Attestation(X,Y):
A signed claim. X attests to Y.
Certificate(X,Y):
A claim or attestation, Y, signed exclusively by a third party, X,
and are only over identities.
2.3. Definitions
This document uses the terms defined in [drip-requirements]. 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 (Hierarchical HIT Domain Authority):
The 16-bit field that identifies the HHIT Domain Authority under
an Registered Assigning Authority (RAA).
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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
used in HIP.
HID (Hierarchy ID):
The 32 bit field providing the HIT Hierarchy ID.
HIP (Host Identity Protocol)
The origin of HI, HIT, and HHIT, required for DRIP.
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. In particular all the functions referenced from
[NIST.FIPS.202] and [NIST.SP.800-185].
KMAC (KECCAK Message Authentication Code [NIST.SP.800-185]):
A PRF and keyed hash function based on KECCAK.
RAA (Registered Assigning Authority):
The 16 bit field identifying the business or organization that
manages a registry of HDAs.
RVS (Rendezvous Server):
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 HIT space. By adding two levels of hierarchical
administration control, the HHIT provides for device registration/
ownership, thereby enhancing the trust framework for HITs.
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HHITs represent the HI in only a 64 bit hash and uses the other 32
bits 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 in Section 3.5.1.
A HHIT is built from the following fields:
* IANA prefix (max 28 bit)
* 32 bit Hierarchy ID (HID)
* 4 (or 8) bit HIT Suite ID
* ORCHID hash (96 - prefix length - Suite ID length bits, e.g. 64)
See Section 3.5
The Context ID for the ORCHID hash is:
Context ID := 0x00B5 A69C 795D F5D5 F008 7F56 843F 2C40
3.1. HHIT prefix
A unique IANA IPv6 prefix, no larger than 28 bit, for HHITs is
recommended. It clearly separates the flat-space HIT processing from
HHIT processing per Section 3.5.
Without a unique prefix, the first 4 bits of the RRA would be
interpreted as the HIT Suite ID per HIPv2 [RFC7401].
3.2. HHIT Suite IDs
The HIT Suite IDs specifies the HI and hash algorithms. Any HIT
Suite ID can be used for HHITs. The 8 bit format is supported (only
when the first 4 bits are ZERO), but this reduces the ORCHID hash
length.
3.2.1. 8 bit HIT Suite IDs
Support for 8 bit HIT Suite IDs is allowed in Section 5.2.10 of
[RFC7401], but not specified in how ORCHIDs are generated with these
longer OGAs. Section 3.5 provides the algorithmic flexibility,
allowing for HDA custom HIT Suite IDs as follows:
HIT Suite Four-bit ID Eight-bit encoding
HDA Assigned 1 NA TBD3 (suggested value 0x0E)
HDA Assigned 2 NA TBD4 (suggested value 0x0F)
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This feature 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.
3.3. The Hierarchy ID (HID)
The Hierarchy ID (HID) provides the structure to organize HITs into
administrative domains. HIDs are further divided into 2 fields:
* 16 bit Registered Assigning Authority (RAA)
* 16 bit Hierarchical HIT Domain Authority (HDA)
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) could be an RAA.
The RAA is a 16 bit field (65,536 RAAs) assigned by a numbers
management organization, perhaps ICANN's IANA service. An RAA must
provide a set of services to allocate HDAs to organizations. It must
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 discovering HID RVS servers.
As HHITs may be used in many different domains, RAA should be
allocated in blocks with consideration on the likely size of a
particular usage. Alternatively, different Prefixes can be used to
separate different domains of use of HHTs.
This DNS zone may be a PTR for its RAA. It may be a zone in a HHIT
specific DNS zone. Assume that the RAA is 100. The PTR record could
be constructed:
100.hhit.arpa IN PTR raa.bar.com.
3.3.2. The Hierarchical HIT Domain Authority (HDA)
An HDA may be an ISP or any third party that takes on the business to
provide RVS and other needed services for HIP enabled devices.
The HDA is an 16 bit field (65,536 HDAs per RAA) assigned by an RAA.
An HDA should maintain a set of RVS servers that its client HIP-
enabled customers use. How this is done and scales to the
potentially millions of customers is outside the scope of this
document. This service should be discoverable through the DNS zone
maintained by the HDA's RAA.
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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.
3.4. Edward Digital Signature Algorithm for HITs
Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032] are
specified here for use as Host Identities (HIs) per HIPv2 [RFC7401].
Further the HIT_SUITE_LIST is specified as used in [RFC7343].
See Section 3.2 for use of the HIT Suite for this document.
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 5.2.19 of [RFC7401].
Algorithm
profiles Values
EdDSA TBD1 (suggested value 13) [RFC8032] (RECOMMENDED)
For hosts that implement EdDSA as the algorithm, the following EdDSA
curves are available:
Algorithm Curve Values
EdDSA RESERVED 0
EdDSA EdDSA25519 1 [RFC8032]
EdDSA EdDSA25519ph 2 [RFC8032]
EdDSA EdDSA448 3 [RFC8032]
EdDSA EdDSA448ph 4 [RFC8032]
3.4.2. HIT_SUITE_LIST
The HIT_SUITE_LIST parameter contains a list of the supported HIT
suite IDs of the Responder. Based on the HIT_SUITE_LIST, the
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, and the relationship between
the four-bit ID value used in the OGA ID field and the eight-bit
encoding within the HIT_SUITE_LIST ID field is clarified:
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HIT Suite 4-bit ID 8-bit encoding
RESERVED 0 0x00
EdDSA/cSHAKE128 TBD2 (suggested value 5) 0x50 (RECOMMENDED)
The following table provides more detail on the above HIT Suite
combinations. The input for each generation algorithm is the
encoding of the HI as defined in this Appendix.
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 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.
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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 addendum to ORCHIDv2 [RFC7343], as it can
produce ORCHIDv2 output.
3.5.1. Adding additional information to the ORCHID
ORCHIDv2 [RFC7343] is currently defined as consisting of three
components:
ORCHID := Prefix | OGA ID | Encode_96( Hash )
where:
Prefix : A constant 28-bit-long bitstring value
(IANA IPv6 assigned).
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.
This addendum will be constructed as follows:
ORCHID := Prefix (p) | Info (n) | OGA ID (o) | Hash (m)
where:
Prefix (p) : An IANA IPv6 assigned prefix (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.
Hash (m) : An extraction function in which output is m bits.
p + n + o + m = 128 bits
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With a 28 bit IPv6 Prefix, the remaining 100 bits can be divided in
any manner between the additional information, OGA ID, and the hash
output. Care must be taken in determining the size of the hash
portion, taking into account risks like pre-image attacks. Thus 64
bits as used in Hierarchical HITs may be as small as is acceptable.
3.5.2. ORCHID Encoding
This addendum 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, 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 32 bits for the HID and 4 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 the cSHAKE function call for this addendum is:
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 Prefix of /28 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.
Hierarchical HIT uses the same context as all other HIPv2 HIT Suites
as they are clearly separated by the distinct HIT Suite ID.
3.5.2.1. Encoding ORCHIDs for HITv2
This section is included to provide backwards compatibility for
ORCHIDv2 [RFC7343] as used for HITv2 [RFC7401].
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For HITv2s, the Prefix MUST be 2001:20::/28. Info is length ZERO
(not included), and OGA ID is length 4. Thus the HI Hash is length
96. 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:
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 addendum, the decoding of an ORCHID is determined by the
Prefix and OGA ID (HIT Suite 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 the HHIT document.
3.5.4. Decoding ORCHIDs for HITv2
This section is included to provide backwards compatibility for
ORCHIDv2 [RFC7343] as used for HITv2 [RFC7401].
HITv2s are identified by a Prefix of 2001:20::/28. The next 4 bits
are the OGA ID. is length 4. The remaining 96 bits are the HI Hash.
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4. Hierarchical HITs as Remote ID
Hierarchical HITs are a refinement on the Host Identity Tag (HIT) of
HIPv2 [RFC7401]. HHITs require a new Overlay Routable Cryptographic
Hash Identifier (ORCHID [RFC7343]) mechanism as described in
Section 3.5. HHITs for UAS ID also use the new EdDSA/SHAKE128 HIT
suite defined in Section 3.4 (GEN-2 in [drip-requirements]). This
hierarchy, cryptographically embedded within the HHIT, provides the
information for finding the UA's HHIT registry (ID-3 in
[drip-requirements]).
ASTM Standard Specification for Remote ID and Tracking [F3411-19]
specifies three UAS ID types:
TYPE-1 A static, manufacturer assigned, hardware serial number per
ANSI/CTA-2063-A "Small Unmanned Aerial System Serial Numbers"
[CTA2063A].
TYPE-2 A CAA assigned (presumably static) ID.
TYPE-3 A UTM system assigned UUID [RFC4122]. These can be dynamic,
but do not need to be.
For HHITs to be used effectively as UAS IDs, F3411 should add UAS ID
type 4 as HHIT.
4.1. Nontransferablity of HHITs
A HI and its HHIT 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 a HHIT within the 2063-A format is not simple. There is no
place for the HID; there will need to be a mapping service from
Manufacturer Code to HID. The HIT Suite ID and ORCHID hash will take
14 characters (see below), leaving only 1 character for the
Manufacturer's use of other information.
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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 HIT Suite ID and ORCHID hash. Although,
programatically, 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).
The low-order 68 bits (HIT Suite ID | ORCHID hash) of the HHIT SHALL
be left-padded with 2 bits of ZERO. This 70 bit number will be
encoded into 14 characters using the digit/letters above. The
Manufacturer MAY use a Length Code of 14 or 15. If 15, the first
character after the Length Code is set by the Manufacturer with the
low order 14 characters for the encoded HIT Suite ID and ORCHID hash.
A mapping service (e.g. DNS) MUST provide a trusted (e.g. via
DNSSEC) conversion of the 4 character Manufacturer Code to high-order
60 bits (Prefix | HID) of the HHIT. Definition of this mapping
service is currently out of scope of this document.
4.3. Remote ID as one class of Hierarchical HITs
UAS Remote ID 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 10.
4.4. Hierarchy in ORCHID Generation
ORCHIDS, as defined in [RFC7343], do not cryptographically bind an
IPv6 prefix nor the Orchid Generation Algorithm (OGA) ID (the HIT
Suite ID) to the hash of the HI. The rational at the time of
developing ORCHID was attacks against these fields are 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 HHIT
that has the underlying HI can directly trust and act on all content
in the HHIT. This provides a strong, self-attestation for using the
hierarchy to find the HHIT Registry.
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4.5. Hierarchical HIT Registry
HHITs are registered to Hierarchical HIT Domain Authorities (HDAs).
A registration process, [drip-registries], ensures UAS ID global
uniqueness (ID-4 in [drip-requirements]). It also provides the
mechanism to create UAS Public/Private data that are associated with
the HHIT UAS ID (REG-1 and REG-2 in [drip-requirements]).
The two levels of hierarchy within an HHIT allows for CAAs to have
their own Registered Assigning Authority (RAA) for their National Air
Space (NAS). Within the RAA, the CAAs can delegate HDAs as needed.
There may be other RAAs allowed to operate within a given NAS; this
is a policy decision by the CAA.
4.6. Remote ID Authentication using HHITs
The EdDSA25519 Host Identity (HI) [Section 3.4] underlying the HHIT
can be used in an 84-byte self proof attestation as shown in
Appendix B to provide proof of Remote ID ownership (GEN-1 in
[drip-requirements]). An lookup service like DNS can provide the HI
and registration proof (GEN-3 in [drip-requirements]).
Similarly the 200-byte offline self-attestation shown in Appendix B.1
provides the same proofs without Internet access and with a small
cache that contains the HDA's HI/HHIT and HDA meta-data. These self-
attestations are carried in the ASTM Authentication Message (Msg Type
0x2).
Hashes of previously sent ASTM messages can be placed in a signed
"Manifest" Authentication Message (GEN-2 in [drip-requirements]).
This can be either a standalone Authentication Message, or an
enhanced self attestation Authentication Message. Alternatively the
ASTM Message Pack (Msg Type 0xF) can provide this feature, but only
over Bluetooth 5 or WiFi NAN broadcasts.
5. UAS ID HHIT in DNS
There are two approaches for storing and retrieving the HHIT using
DNS. These are:
* As FQDNs in the .aero TLD.
* Reverse DNS lookups as IPv6 addresses per [RFC8005].
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An HHIT 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
[drip-requirements]). For example, the USS for the HHIT could be
found via the following: Assume the RAA is 100 and the HDA is 50.
The PTR record is constructed as:
100.50.hhit.uas.aero IN PTR foo.uss.aero.
The individual HHITs are potentially too numerous (e.g. 60 - 600M)
and dynamic to actually store in a signed, DNS zone. The HDA SHOULD
provide DNS service for its zone and provide the HHIT detail
response.
The HHIT reverse lookup can be a standard IPv6 reverse look up, or it
can leverage off the HHIT structure. Assume a prefix of
2001:30::/28, the RAA is 10 and the HDA is 20 and the HHIT is:
2001:30:a0:145:a3ad:1952:ad0:a69e
An HHIT reverse lookup could be to:
a69e.ad0.1952.a3ad.145.a0.30.2001.20.10.hhit.arpa.
A 'standard' ip6.arpa RR has the advantage of only one Registry
service supported.
$ORIGIN 5.4.1.0.0.a.0.0.0.3.0.0.1.0.0.2.ip6.arpa.
e.9.6.a.0.d.a.0.2.5.9.1.d.a.3.a IN PTR
6. DRIP Proofs
The DRIP Proofs are a set of custom objects to be used in the USS/UTM
system. They are created during the enrollment of an Operator and
the provisioning of an Aircraft and are tied to the Operator ID and
UAS RID.
These structures, when chained together, create two distinct roots of
trust. One back to the UAS manufacturer, back to the initial
production of a given Aircraft. The other back to the authorizing
CAA. These chains can also be used by authorized entities to trace
an Aircraft through all owners and flights in the Aircraft's lifetime
(something of interest to ICAO).
The rest of this section will define the formats of proofs in DRIP as
forms of certificates and attestations and their common uses.
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6.1. Claim / Assertion: HHIT
The HHIT can be taken in its entirety as a single claim or broken
into various claims and thus be classified as an assertion.
There are a number of different claims that an HHIT can be broken
into:
* Valid ORCHID construction. To validate would require the Host
Identity used.
* Ownership of the asymmetric keypair used to generate the hash.
* Being a member of a specified Registry. This is defined by the
RAA and HDA pairing encoded. This is a baseless claim on its own
that is attested to by the Registry.
6.2. Self-Attestation: Attestation(X,X)
This DRIP Proof is a self-signed attestation (by an entity known as
'X') staking an unverified claim on a HHIT/HI pairing until an
expiration date/time.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| |
| Hierarchical |
| Host Identity Tag |
| |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| Host |
| Identity |
| |
| |
| |
+---------------+---------------+---------------+---------------+
| Expiration Timestamp |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| Signature |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
HHIT The HHIT of the entity, derived from the HI and
other information.
HI The HI of the entity. This is the public half of
an EdDSA25519 asymmetric keypair.
Expiration A timestamp signaling the expiration of the
Timestamp attestation.
Signature Generated using the asymmetric keypair of the entity.
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Figure 1: Self-Attestation: Attestation(X,X)
This Self-Attestation is 116 bytes attesting to a number of claims
and assertions. Overall the entire structure creates an assertion of
the ownership of this first two claims (HHIT and HI), a binding
(between HHIT and HI) and an upper time bound of relevance (the
Expiration Timestamp).
The offset of the Expiration Timestamp (ETS) SHOULD be of significant
length (possibly years).
These are 5 (five) Self-Attestations that can be created in a
standard DRIP UAS RID system:
* Attestation(Manufacturer, Manufacturer)
* Attestation(RAA, RAA)
* Attestation(HDA, HDA) or Attestation(Registry, Registry)
* Attestation(Operator, Operator)
* Attestation(Aircraft, Aircraft)
This is not an exhaustive list as any entity with the DRIP UAS system
SHOULD have a Self-Attestation for itself.
The Timestamp formatting is covered in Section 6.5.
6.2.1. Concise Self-Attestation: Attestation(X, ConciseX)
A smaller version of Attestation(X, X) exists where the Host Identity
is removed allowing a claim to be made in 84 bytes.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| |
| Hierarchical |
| Host Identity Tag |
| |
+---------------+---------------+---------------+---------------+
| Expiration Timestamp |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| Signature |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
HHIT The HHIT of the entity, derived from the HI and
other information.
Expiration A timestamp signaling the expiration of the
Timestamp attestation.
Signature Generated using the asymmetric keypair of the entity.
Figure 2: Concise Self-Attestation: Attestation(X, ConciseX)
This form would require that the Host Identity associated with the
HHIT be in a public Registry to be requested (nominally with a DNS
lookup using a HIP RR type) and checked against.
The Timestamp formatting is covered in Section 6.5.
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6.3. Certificate(X, Y)
This DRIP Proof is an attestation where Entity X asserts trust in the
binding claimed by Entity Y (in Assertion Y) and signs this asserting
with a timestamp and an expiration of when the binding is no longer
asserted by Entity X.
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
+---------------+---------------+---------------+---------------+
| Length Ax | Length Ay |
+---------------+---------------+---------------+---------------+
| |
. .
. Assertion X .
. .
| |
+---------------+---------------+---------------+---------------+
| |
. .
. Assertion Y .
. .
| |
+---------------+---------------+---------------+---------------+
| Timestamp |
+---------------+---------------+---------------+---------------+
| Expiration Timestamp |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| Signature |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
Length Length in bytes of Assertion(X). Encoded as an
Ax unsigned integer.
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Length Length in bytes of Assertion(Y). Encoded as an
Ay unsigned integer.
Assertion(X) The attestation/certificate of entity X.
Assertion(Y) The attestation/certificate of entity Y.
Timestamp A timestamp signaling the current time at
signing of the certificate.
Expiration A timestamp signaling the expiration of the
Timestamp attestation.
Signature Generated using the asymmetric keypair of the
entity.
Figure 3: Certificate(X, Y)
Cxy Form wraps both Self-Attestations of the entities and is signed
by Entity X. Two timestamps, one taken at the time of signing and
one as an expiration time are used to set boundaries to the
assertion. Care should be given to how far into the future the
Expiration Timestamp is set, but is left up to system policy.
Most attestations of this form have a length of 304 bytes; some may
be 84 or 116 bytes. Certificate(Registry,
Certificate(Operator,Aircraft)) is unique in that is 680 bytes long,
binding of two Cxy forms (in this specific case Certificate(Registry,
Operator) with Certificate(Operator, Aircraft).
The Timestamp formatting is covered in Section 6.5.
6.3.1. Concise Certificate(X, Concise Y)
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| |
| Hierarchical Host Identity Tag |
| of Entity X |
| |
+---------------+---------------+---------------+---------------+
| |
. .
. Ayy .
. .
| |
+---------------+---------------+---------------+---------------+
| Expiration Timestamp |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| Signature |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
Figure 4: Concise Certificate(X, Concise Y)
The short form of the Cxy this attestation is 200 bytes long and is
designed to fit inside the framing of the ASTM F3411 Authentication
Message. The HHIT of Entity X is used in place of the full Axx (see
Section 11.3 for comments). The timestamp is removed and only an
expiration timestamp is present. Ayy MUST NOT be the in Concise
Form.
During creation the Expiration Timestamp MUST be no later than the
Expiration Timestamp found in Ayy.
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6.4. Offline Broadcast Attestation: Attestation(X, Offline Y)
A special attestation that is the basis for a certificate finalized
onboard the aircraft during flight. It is used in Broadcast RID to
provide the trustworthiness of the Aircraft without the need of the
Observer to be connected to the Internet.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+---------------+---------------+
| |
| Hierarchical Host Identity Tag |
| of Entity X |
| |
+---------------+---------------+---------------+---------------+
| |
| Hierarchical Host Identity Tag |
| of Entity Y |
| |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| Host Identity of Entity Y |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
| Expiration Timestamp |
+---------------+---------------+---------------+---------------+
| |
| |
| |
| |
| |
| |
| |
| Signature |
| |
| |
| |
| |
| |
| |
| |
| |
+---------------+---------------+---------------+---------------+
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Figure 5: Offline Form: Attestation(X, Offline Y)
The signature is generated using Entity X's keypair.
6.5. Timestamps
Timestamps MAY be the standard UNIX time or a protocol specific
timestamp, to avoid programming complexities. For example [F3411-19]
uses a 00:00:00 01/01/2019 offset. When a Expiration Timestamp is
required a desired offset is added, setting the timestamp into the
future. The amount of offset for specific timestamps is left to best
practice.
6.6. Signatures
Signatures are ALWAYS taken over the preceding fields in the
certificate/attestation. For DRIP the EdDSA25519 algorithm from
[RFC8032] is used.
7. Other UTM uses of HHITs
HHITs might be used within the UTM architecture beyond UA ID (and USS
in UA ID registration and authentication). This includes a GCS HHIT
ID. The GCS may use its HIIT if it is the source of Network Remote
ID for securing the transport and for secure C2 transport (e.g.
[drip-secure-nrid-c2]).
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 (this use is
currently outside the scope). Further, they can be used by FINDER
observers, (e.g. [crowd-sourced-rid]).
8. DRIP Requirements addressed
This document in the previous sections provides the details to
solutions for GEN 1 - 3, ID 1 - 5, and REG 1 - 2 as describled in
[drip-requirements].
9. ASTM Considerations
ASTM will need to make the following additional value to the "UA ID"
in the Basic Message (Msg Type 0x0):
Type 4:
This document UA ID of Hierarchical HITs (see Section 4).
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The HHIT RID authors will participate in ASTM to enact this change.
10. IANA Considerations
This document requests IANA to make the following changes to the IANA
"Host Identity Protocol (HIP) Parameters" registry:
Host ID:
This document defines the new EdDSA Host ID with value TBD1
(suggested: 13) (see Section 3.4.1) in the "HI Algorithm"
subregistry of the "Host Identity Protocol (HIP) Parameters"
registry.
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.
HIT Suite ID:
This document defines the new HIT Suite of EdDSA/cSHAKE with value
TBD2 (suggested: 5) (see Section 3.4.2) in the "HIT Suite ID"
subregistry of the "Host Identity Protocol (HIP) Parameters"
registry.
HIT Suite ID eight-bit encoding:
This document defines the first eight-bit encoded HIT Suite IDs as
defined in Section 5.2.10 of [RFC7401]. These are the new HDA
domain HIT Suites with values TBD3 and TBD4 (suggested: 0x0E and
0x0F) (see Section 3.2.1). IANA is requested to expand the "HIT
Suite ID" subregistry of the "Host Identity Protocol (HIP)
Parameters" registry to show both the four-bit and eight-bit
values as shown in Section 5.2.10 of [RFC7401] and add these new
values that only have eight bit representations.
10.1. New IPv6 prefix needed for HHITs
Because HHIT format is not compatible with [RFC7343], IANA is
requested to allocated a new 28-bit prefix out of the IANA IPv6
Special Purpose Address Block, namely 2001:0000::/23, as per
[RFC6890] (suggested: 2001:30::/28).
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11. Security Considerations
A 64-bit hash space presents a real risk of second pre-image
cryptographic hash attack Section 11.2. The HHIT Registry services
effectively block attempts to "take over" or "hijack" a HHIT. It
does not stop a rogue attempting to impersonate a known HHIT. This
attack can be mitigated by the receiver of the HHIT using DNS to find
the HI for the HHIT. As such, use of DNSSEC by the HHIT registries
is recommended.
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 Appendix B.1 as discussed in Section 4.6.
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.
"hhit.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 HIT hash collisions.
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
(attestation) process of the HHIT by the HI private key and the
further signing (attestation) 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 HHIT, 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.
11.1. Hierarchical HIT Trust
The HHIT UAS RID in the ASTM Basic 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 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. Minimally, it takes 84 bytes,
Appendix B, to prove ownership of a HHIT.
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The ASTM Authentication Messages (Msg Type 0x2) as shown in
Section 4.6 can provide practical actual ownership proofs. These
attestations include timestamps to defend against replay attacks.
But in themselves, they do not prove which UA actually sent the
message. They could have been sent by a dog running down the street
with a Broadcast Remote ID device strapped to its back.
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 [crowd-sourced-rid]. Only then does an
observer gain full trust in the HHIT Remote ID.
HHIT Remote IDs obtained via the Network Remote ID path provides a
different approach to trust. Here the UAS SHOULD be securely
communicating to the USS (see [drip-secure-nrid-c2]), thus asserting
HHIT RID trust.
11.2. Collision risks with Hierarchical HITs
The 64 bit hash size does have an increased risk of collisions over
the 96 bit hash size used for the other HIT Suites. 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 C 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 HHIT and MUST reject a
collision, forcing the UAS to generate a new HI and thus HHIT and
reapplying to the registration process.
11.3. Proofs Considerations
A major consideration is the optimization done in Certificate: X on Y
(Concise Form) to get its length down to 200 bytes. The truncation
of Certificate: HDA on HDA down to just its HHIT is one that could be
used against the system to act as a false Registry. For this to
occur an attacker would need to find a hash collision on that
Registry HHIT and then manage to spoof all of DNS being used in the
system.
The authors believe that the probability of such an attack is low
when Registry operators are using best practices in security. If
such an attack can occur (especially in the time frame of "one-time
use IDs") then there are more serious issues present in the system.
12. References
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12.1. Normative References
[F3411-19] ASTM International, "Standard Specification for Remote ID
and Tracking", February 2020,
<http://www.astm.org/cgi-bin/resolver.cgi?F3411>.
[NIST.FIPS.202]
Dworkin, M., "SHA-3 Standard: Permutation-Based Hash and
Extendable-Output Functions", National Institute of
Standards and Technology report,
DOI 10.6028/nist.fips.202, July 2015,
<https://doi.org/10.6028/nist.fips.202>.
[NIST.SP.800-185]
Kelsey, J., Change, S., and R. Perlner, "SHA-3 derived
functions: cSHAKE, KMAC, TupleHash and ParallelHash",
National Institute of Standards and Technology report,
DOI 10.6028/nist.sp.800-185, December 2016,
<https://doi.org/10.6028/nist.sp.800-185>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[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>.
[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>.
[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>.
12.2. Informative References
[corus] CORUS, "U-space Concept of Operations", September 2019,
<https://www.sesarju.eu/node/3411>.
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[crowd-sourced-rid]
Moskowitz, R., Card, S. W., Wiethuechter, A., Zhao, S.,
and H. Birkholz, "Crowd Sourced Remote ID", Work in
Progress, Internet-Draft, draft-moskowitz-drip-crowd-
sourced-rid-06, 26 May 2021, <https://tools.ietf.org/html/
draft-moskowitz-drip-crowd-sourced-rid-06>.
[CTA2063A] ANSI/CTA, "Small Unmanned Aerial Systems Serial Numbers",
September 2019, <https://shop.cta.tech/products/small-
unmanned-aerial-systems-serial-numbers>.
[drip-registries]
Wiethuechter, A., Card, S., and R. Moskowitz, "DRIP
Registries", Work in Progress, Internet-Draft, draft-
wiethuechter-drip-registries-00, 22 February 2021,
<https://tools.ietf.org/html/draft-wiethuechter-drip-
registries-00>.
[drip-requirements]
Card, S. W., Wiethuechter, A., Moskowitz, R., and A.
Gurtov, "Drone Remote Identification Protocol (DRIP)
Requirements", Work in Progress, Internet-Draft, draft-
ietf-drip-reqs-17, 7 July 2021,
<https://tools.ietf.org/html/draft-ietf-drip-reqs-17>.
[drip-secure-nrid-c2]
Moskowitz, R., Card, S., Wiethuechter, A., and A. Gurtov,
"Secure UAS Network RID and C2 Transport", Work in
Progress, Internet-Draft, draft-moskowitz-drip-secure-
nrid-c2-02, 25 December 2020,
<https://tools.ietf.org/html/draft-moskowitz-drip-secure-
nrid-c2-02>.
[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>.
[Keccak] Bertoni, G., Daemen, J., Peeters, M., Van Assche, G., and
R. Van Keer, "The Keccak Function",
<https://keccak.team/index.html>.
[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>.
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[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>.
[RFC5730] Hollenbeck, S., "Extensible Provisioning Protocol (EPP)",
STD 69, RFC 5730, DOI 10.17487/RFC5730, August 2009,
<https://www.rfc-editor.org/info/rfc5730>.
[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>.
[RFC7484] Blanchet, M., "Finding the Authoritative Registration Data
(RDAP) Service", RFC 7484, DOI 10.17487/RFC7484, March
2015, <https://www.rfc-editor.org/info/rfc7484>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[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>.
[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>.
[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>.
[RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig,
"CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392,
May 2018, <https://www.rfc-editor.org/info/rfc8392>.
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Appendix A. EU U-Space RID Privacy Considerations
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 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.
The project lists "E-Identification" and "E-Registrations" services
as to be developed. These services can follow the privacy mechanism
proposed in this document. 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
Hierarchical HITs provide 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. Example HHIT Self Attestation
This section shows example uses of HHIT RID to prove trustworthiness
of the RID and attestation of registration to the RAA|HDA. These are
examples only and other documents will provide fully specified
attestations. Care has been taken in the example design to minimize
the risk of replay attacks.
This ownership/attestation of a HHIT can be proved in 84 bytes via
the following HHIT Self Attestation following Section 6.2.1 format:
* 4 byte Signing Timestamp
* 16 byte HHIT
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* 64 byte Signature (EdDSA25519 signature)
The Timestamp MAY be the standard UNIX time at the time of signing.
A protocol specific timestamp may be used to avoid programming
complexities. For example, [F3411-19] uses a 00:00:00 01/01/2019
offset.
To minimize the risk of replay, the UA SHOULD create a new Self
Attestation, with a new timestamp, at least once a minute. The UA
MAY precompute these attestations and transmit during the appropriate
1 minute window. 1 minute is chosen as a balance between attestation
compute time against risk. A shorter window of use lessens the risk
of replay.
The signature is over the 20 byte Timestamp + HHIT.
The receiver of such an attestation would need access to the
underlying public key (HI) to validate the signature. This may be
obtained via a DNS query using the HHIT. A larger (116 bytes) Self
Attestation could include the EdDSA25519 HI. This larger 116
attestation allows for signature validation before HHIT lookup to
prove registration attestation.
B.1. HHIT Offline Self Attestation
Ownership and RAA|HDA registration of a HHIT can be proved in 200
bytes without Internet access and a small cache via the following
HHIT Offline Self Attestation Section 6.2 format:
* 16 byte UA HHIT
* 32 byte UA EdDSA25519 HI
* 4 byte HDA Signing Expiry Timestamp
* 16 byte HDA HHIT
* 64 byte HDA Signature (EdDSA25519 signature)
* 4 byte UA Signing Timestamp
* 64 byte UA Signature (EdDSA25519 signature)
The Timestamps MAY be the standard UNIX time at the time of signing.
A protocol specific timestamp may be used to avoid programming
complexities. For example, [F3411-19] uses a 00:00:00 01/01/2019
offset.
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The HDA signature is over the 68 byte UA HHIT + UA HI + HDA Expiry
Timestamp + HDA HHIT. During the UA Registration process, the UA
would provide a Self Attestation to the HDA. The HDA would construct
its attestation of registry with an Expiry Timestamp, its own HHIT,
and its signature, returning a 132 byte HDA Registry Attestation to
the UA. The UA would use this much the same way as its HHIT only in
the Self Attestation above, creating a 200 byte Offline Self
Attestation.
The receiver of such an attestation would need a cache of RAA ID, HDA
ID, HDA HHIT, and HDA HI (min 80 bytes per RAA/HDA).
Appendix C. 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.
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.
Authors' Addresses
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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
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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