UAS Remote ID
draft-ietf-drip-rid-03
The information below is for an old version of the document.
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| Authors | Robert Moskowitz , Stuart W. Card , Adam Wiethuechter , Andrei Gurtov | ||
| Last updated | 2020-10-27 (Latest revision 2020-10-24) | ||
| Replaces | draft-ietf-drip-uas-rid | ||
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draft-ietf-drip-rid-03
DRIP R. Moskowitz
Internet-Draft HTT Consulting
Updates: 7401, 7343 (if approved) S. Card
Intended status: Standards Track A. Wiethuechter
Expires: April 30, 2021 AX Enterprize, LLC
A. Gurtov
Linköping University
October 27, 2020
UAS Remote ID
draft-ietf-drip-rid-03
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 UAS Remote ID. HHITs include explicit
hierarchy to provide Registrar discovery for 3rd-party ID
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
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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 April 30, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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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
1.1. Nontransferablity of HHITs . . . . . . . . . . . . . . . 3
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 3
2.2. Notation . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
3. Hierarchical HITs as Remote ID . . . . . . . . . . . . . . . 5
3.1. Remote ID as one class of Hierarchical HITs . . . . . . . 5
3.2. Hierarchy in ORCHID Generation . . . . . . . . . . . . . 5
3.3. Hierarchical HIT Registry . . . . . . . . . . . . . . . . 6
3.4. Remote ID Authentication using HHITs . . . . . . . . . . 6
4. UAS ID HHIT in DNS . . . . . . . . . . . . . . . . . . . . . 6
5. Other UTM uses of HHITs . . . . . . . . . . . . . . . . . . . 7
6. DRIP Requirements addressed . . . . . . . . . . . . . . . . . 7
7. ASTM Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9.1. Hierarchical HIT Trust . . . . . . . . . . . . . . . . . 9
9.2. Collision risks with Hierarchical HITs . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. EU U-Space RID Privacy Considerations . . . . . . . 12
Appendix B. The Hierarchical Host Identity Tag (HHIT) . . . . . 12
B.1. HHIT prefix . . . . . . . . . . . . . . . . . . . . . . . 13
B.2. HHIT Suite IDs . . . . . . . . . . . . . . . . . . . . . 13
B.2.1. 8 bit HIT Suite IDs . . . . . . . . . . . . . . . . . 13
B.3. The Hierarchy ID (HID) . . . . . . . . . . . . . . . . . 13
B.3.1. The Registered Assigning Authority (RAA) . . . . . . 14
B.3.2. The Hierarchical HIT Domain Authority (HDA) . . . . . 14
Appendix C. ORCHIDs for Hierarchical HITs . . . . . . . . . . . 14
C.1. Adding additional information to the ORCHID . . . . . . . 15
C.2. ORCHID Encoding . . . . . . . . . . . . . . . . . . . . . 16
C.2.1. Encoding ORCHIDs for HITv2 . . . . . . . . . . . . . 17
C.3. ORCHID Decoding . . . . . . . . . . . . . . . . . . . . . 18
C.4. Decoding ORCHIDs for HITv2 . . . . . . . . . . . . . . . 18
Appendix D. Edward Digital Signature Algorithm for HITs . . . . 18
D.1. HOST_ID . . . . . . . . . . . . . . . . . . . . . . . . . 18
D.2. HIT_SUITE_LIST . . . . . . . . . . . . . . . . . . . . . 19
Appendix E. Example HHIT Self Claim . . . . . . . . . . . . . . 20
E.1. HHIT Offline Self Claim . . . . . . . . . . . . . . . . . 20
Appendix F. Calculating Collision Probabilities . . . . . . . . 21
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Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
[drip-requirements] describes a UAS ID as a "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 HITs (HHITs)
(Appendix B) as self-asserting IPv6 addresses and thereby a trustable
Identifier for use as the UAS Remote ID. HHITs include explicit
hierarchy to provide Registrar discovery for 3rd-party ID
attestation.
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 general IDs (e.g. a UUID or
device serial number) as the subject in an X.509 certificate.
In a multi-CA PKI, a subject can occur in multiple CAs, possibly
fraudulently. CAs within the PKI would need to implement an approach
to enforce assurance of uniqueness.
Hierarchical HITs are valid, though non-routable, IPv6 addresses. As
such, they fit in many ways within various IETF technologies.
1.1. Nontransferablity of HHITs
HIs and its HHITs SHOULD NOT be transferable between UA or even
between replacement electronics for a UA. The private key for the HI
SHOULD be held in a cryptographically secure component.
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. Notation
| Signifies concatenation of information - e.g., X | Y is the
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concatenation of X and Y.
2.3. Definitions
See [drip-requirements] for common DRIP terms.
cSHAKE (The customizable SHAKE function):
Extends the SHAKE scheme to allow users to customize their use of
the function.
HDA (Hierarchical HIT Domain Authority):
The 16 bit field identifying the HHIT Domain Authority under an
RAA.
HHIT
Hierarchical Host Identity Tag. A HIT with extra hierarchical
information not found in a standard HIT.
HI
Host Identity. The public key portion of an asymmetric keypair
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. Optional full use of HIP enables additional DRIP
functionality.
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.
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].
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SHAKE (Secure Hash Algorithm KECCAK):
A secure hash that allows for an arbitrary output length.
XOF (eXtendable-Output Function):
A function on bit strings (also called messages) in which the
output can be extended to any desired length.
3. Hierarchical HITs as Remote ID
Hierarchical HITs are a refinement on the Host Identity Tag (HIT) of
HIPv2 [RFC7401]. HHITs require a new ORCHID mechanism as described
in Appendix C. HHITs for UAS ID also use the new EdDSA/SHAKE128 HIT
suite defined in Appendix D (requirements GEN-2). This hierarchy,
cryptographically embedded within the HHIT, provides the information
for finding the UA's HHIT registry (ID-3).
The current ASTM [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], which can but need not
be dynamic.
For HHITs to be used effectively as UAS IDs, F3411-19 SHOULD add UAS
ID type 4 as HHIT.
3.1. Remote ID as one class of Hierarchical HITs
UAS Remote ID may be one of a number of uses of HHITs. As such these
follow-on uses need to be considered in allocating the RAAs
Appendix B.3.1 or HHIT prefix assignments Section 8.
3.2. Hierarchy in ORCHID Generation
ORCHIDS, as defined in [RFC7343], do not cryptographically bind the
IPv6 prefix nor the Orchid Generation Algorithm (OGA) ID (the HIT
Suite ID) to the hash of the HI. The justification then was attacks
against these fields are DoS attacks against protocols using them.
HHITs, as defined in Appendix C, cryptographically bind all content
in the ORCHID through the hashing function. Thus a recipient of a
HHIT that has the underlying HI can directly act on all content in
the HHIT. This is especially important to using the hierarchy to
find the HHIT Registry.
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3.3. Hierarchical HIT Registry
HHITs are registered to Hierarchical HIT Domain Authorities (HDAs).
A registration process (TBD) ensures UAS ID global uniqueness (ID-4).
It also provides the mechanism to create UAS Public/Private data
associated with the HHIT UAS ID (REG-1 and REG-2).
The 2 levels of hierarchy within the 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.
3.4. Remote ID Authentication using HHITs
The EdDSA25519 Host Identity (HI) [Appendix D] underlying the HHIT
can be used in an 84 byte self proof claim as shown in Appendix E to
provide proof of Remote ID ownership (requirements GEN-1). An
Internet lookup service like DNS can provide the HI and registration
proof (requirements GEN-3).
Similarly the 200 byte offline self claim shown in Appendix E.1
provide the same proofs without Internet access and with a small
cache that contains the HDA's HI/HHIT and HDA meta-data. These self
claims 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 (requirements GEN-2). This can be
either a standalone Authentication Message, or an enhanced self claim
Authentication Message. Alternatively the ASTM Message Pack (Msg
Type 0xF) can provide this feature, but only over Bluetooth 5 or WiFi
NAN broadcasts.
4. UAS ID HHIT in DNS
There are 2 approaches for storing and retrieving the HHIT from DNS.
These are:
* As FQDNs in the .aero TLD.
* Reverse DNS lookups as IPv6 addresses per [RFC8005].
The 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). For
example the USS for the HHIT could be found via the following.
Assume that the RAA is 100 and the HDA is 50. The PTR record is
constructed as:
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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. Rather the USS
would 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 that the RAA is 10 and
the HDA is 20 and the HHIT is:
2001:14:28:14:a3ad:1952:ad0:a69e
An HHIT reverse lookup would be to is:
a69e.ad0.1952.a3ad.14.28.14.2001.20.10.hhit.arpa.
5. Other UTM uses of HHITs
HHITs can be used extensively within the UTM architecture beyond UA
ID (and USS in UA ID registration and authentication). This includes
a GCS HHIT ID. It could use this if it is the source of Network
Remote ID for securing the transport and for secure C2 transport
[drip-secure-nrid-c2].
Observers SHOULD have 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. Further, they can be used
by FINDER observers, [crowd-sourced-rid].
6. DRIP Requirements addressed
This document provides solutions to GEN 1 - 3, ID 1 - 5, and REG 1 -
2.
7. ASTM Considerations
ASTM will need to make the following changes to the "UA ID" in the
Basic Message (Msg Type 0x0):
Type 4:
This document UA ID of Hierarchical HITs (see Section 3).
8. IANA Considerations
IANA will need to make the following changes to the "Host Identity
Protocol (HIP) Parameters" registries:
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Host ID:
This document defines the new EdDSA Host ID (see Appendix D.1).
HIT Suite ID:
This document defines the new HIT Suite of EdDSA/cSHAKE (see
Appendix D.2).
HIT Suite ID:
This document defines two new HDA domain HIT Suites (see
Appendix B.2.1).
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].
9. Security Considerations
A 64 bit hash space presents a real risk of second pre-image attacks
Section 9.2. The HHIT Registry services effectively block attempts
to "take over" 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.
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 E.1 as shown in Section 3.4.
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 has direct protection
against forced or accidental HIT hash collisions.
Cryptographically Generated Addresses (CGAs) provide a unique
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 (TBD) within the HDA provides a level of
assured uniqueness unattainable without mirroring this approach.
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The second aspect of assured uniqueness is the digital signing
process of the HHIT by the HI private key and the further signing 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.
9.1. 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 E, to prove ownership of a HHIT.
The ASTM Authentication Messages (Msg Type 0x2) as shown in
Section 3.4 can provide practical actual ownership proofs. These
claims 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.
9.2. 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 F 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.
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10. References
10.1. 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.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>.
10.2. Informative References
[corus] CORUS, "U-space Concept of Operations", September 2019,
<https://www.sesarju.eu/node/3411>.
[crowd-sourced-rid]
Moskowitz, R., Card, S., Wiethuechter, A., Zhao, S., and
H. Birkholz, "Crowd Sourced Remote ID", Work in Progress,
Internet-Draft, draft-moskowitz-drip-crowd-sourced-rid-04,
May 20, 2020, <https://tools.ietf.org/html/draft-
moskowitz-drip-crowd-sourced-rid-04>.
[CTA2063A] ANSI, "Small Unmanned Aerial Systems Serial Numbers",
September 2019.
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[drip-requirements]
Card, S., Wiethuechter, A., Moskowitz, R., and A. Gurtov,
"Drone Remote Identification Protocol (DRIP)
Requirements", Work in Progress, Internet-Draft, draft-
ietf-drip-reqs-04, August 25, 2020,
<https://tools.ietf.org/html/draft-ietf-drip-reqs-04>.
[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-c2-01, September 27, 2020,
<https://tools.ietf.org/html/draft-moskowitz-drip-secure-
nrid-c2-01>.
[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>.
[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>.
[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>.
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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. 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.
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 Appendix C.
The input values for the Encoding rules are in Appendix C.1.
A HHIT is built from the following fields:
* IANA prefix (max 28 bit)
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* 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 Appendix C
B.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 Appendix C.
Without a unique prefix, the first 4 bits of the RRA would be
interpreted as the HIT Suite ID per HIPv2 [RFC7401].
B.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.
B.2.1. 8 bit HIT Suite IDs
Support for 8 bit HIT Suite IDs is allowed in Sec 5.2.10, [RFC7401],
but not specified in how ORCHIDs are generated with these longer
OGAs. Appendix C provides the algorithmic flexiblity, allowing for
HDA custom HIT Suite IDs as follows:
HIT Suite Four-bit ID Eight-bit encoding
HDA Assigned 1 NA 0x0E
HDA Assigned 2 NA 0x0F
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.
B.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)
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B.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.
B.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.
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.
Appendix C. 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.
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* Use of cSHAKE, NIST SP 800-185 [NIST.SP.800-185], for the hashing
function.
The [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 addendum to ORCHIDv2 [RFC7343], as it can
produce ORCHIDv2 output.
C.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:
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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
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.
C.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
Context ID := 0x00B5 A69C 795D F5D5 F008 7F56 843F 2C40
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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
Context ID := 0x00B5 A69C 795D F5D5 F008 7F56 843F 2C40
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.
C.2.1. Encoding ORCHIDs for HITv2
This section is included to provide backwards compatibility for
ORCHIDv2 [RFC7343] as used for HITv2 [RFC7401].
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
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Then the ORCHID is constructed as follows:
Prefix | OGA ID | Hash Output
C.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.
C.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.
Appendix D. 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 Appendix B.2 for use of the HIT Suite for this document.
D.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 13 [RFC8032] (RECOMMENDED)
For hosts that implement EdDSA as the algorithm, the following ECC
curves are available:
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Algorithm Curve Values
EdDSA RESERVED 0
EdDSA EdDSA25519 1 [RFC8032]
EdDSA EdDSA25519ph 2 [RFC8032]
EdDSA EdDSA448 3 [RFC8032]
EdDSA EdDSA448ph 4 [RFC8032]
D.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:
HIT Suite Four-bit ID Eight-bit encoding
RESERVED 0 0x00
EdDSA/cSHAKE128 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
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Appendix E. Example HHIT Self Claim
This section shows example uses of HHIT RID to prove trustworthiness
of the RID. These are examples only and other documents will provide
fully specified claims. Care has been taken in the example design to
minimize the risk of replay attacks.
Ownership of a HHIT can be proved in 84 bytes via the following HHIT
Self Claim:
* 4 byte Signing Timestamp
* 16 byte HHIT
* 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
Claim, with a new timestamp, at least once a minute. The UA MAY
precompute these claims and transmit during the appropriate 1 minute
window. 1 minute is chosen as a balance between claim 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 a claim 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 Claim could
include the EdDSA25519 HI.
E.1. HHIT Offline Self Claim
Ownership of a HHIT can be proved in 200 bytes without Internet
access and a small cache via the following HHIT Offline Self Claim:
* 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)
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* 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.
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 Claim to the HDA. The HDA would construct its
claim of registry with an Expiry Timestamp, its own HHIT, and its
signature, returning a 132 byte HDA Registry Claim to the UA. The UA
would use this much the same way as its HHIT only in the Self Claim
above, creating a 200 byte Offline Self Claim.
The receiver of such a claim would need a cache of RAA ID, HDA ID,
HDA HHIT, and HDA HI (min 80 bytes per RAA/HDA).
Appendix F. 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
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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
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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