UAS Remote ID
draft-moskowitz-drip-uas-rid-05
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| Authors | Robert Moskowitz , Stuart W. Card , Adam Wiethuechter , Andrei Gurtov | ||
| Last updated | 2020-08-13 | ||
| Replaced by | draft-ietf-drip-uas-rid | ||
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draft-moskowitz-drip-uas-rid-05
DRIP R. Moskowitz
Internet-Draft HTT Consulting
Intended status: Standards Track S. Card
Expires: 14 February 2021 A. Wiethuechter
AX Enterprize
A. Gurtov
Linköping University
13 August 2020
UAS Remote ID
draft-moskowitz-drip-uas-rid-05
Abstract
This document describes the use of Hierarchical Host Identity Tags
(HHITs) as a self-asserting and thereby 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.
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Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Terminology . . . . . . . . . . . . . . . . 3
2.2. Notation . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3
3. Hierarchical HITs as Remote ID . . . . . . . . . . . . . . . 5
3.1. Hierarchy in ORCHID Generation . . . . . . . . . . . . . 5
3.2. Hierarchical HIT Registry . . . . . . . . . . . . . . . . 5
3.3. 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 . . . . . . . . . . . . . . . . . . . 7
9.1. Hierarchical HIT Trust . . . . . . . . . . . . . . . . . 8
9.2. Collision risks with Hierarchical HITs . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Appendix A. EU U-Space RID Privacy Considerations . . . . . . . 11
Appendix B. The Hierarchical Host Identity Tag (HHIT) . . . . . 12
B.1. HHIT prefix . . . . . . . . . . . . . . . . . . . . . . . 13
B.2. HHIT Suite IDs . . . . . . . . . . . . . . . . . . . . . 13
B.3. The Hierarchy ID (HID) . . . . . . . . . . . . . . . . . 13
B.3.1. The Registered Assigning Authority (RAA) . . . . . . 13
B.3.2. The Hierarchical HIT Domain Authority (HDA) . . . . . 13
Appendix C. ORCHIDs for Hierarchical HITs . . . . . . . . . . . 14
C.1. Adding additional information to the ORCHID . . . . . . . 14
C.2. ORCHID Decoding . . . . . . . . . . . . . . . . . . . . . 15
C.3. ORCHID Encoding . . . . . . . . . . . . . . . . . . . . . 15
Appendix D. Edward Digital Signature Algorithm for HITs . . . . 16
D.1. HOST_ID . . . . . . . . . . . . . . . . . . . . . . . . . 16
D.2. HIT_SUITE_LIST . . . . . . . . . . . . . . . . . . . . . 17
Appendix E. Calculating Collision Probabilities . . . . . . . . 17
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
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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 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 thus HHIT Registries [hhit-registries] 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.
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
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.
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HI
Host Identity. The public key portion of an asymmetric keypair
used in HIP.
HIP
Host Identity Protocol. The origin of HI, HIT, and HHIT, required
for DRIP. Optional full use of HIP enables additional DRIP
functionality.
HDA (Hierarchical HIT Domain Authority):
The 16 bit field identifying the HIT Domain Authority under an
RAA.
HHIT
Hierarchical Host Identity Tag. A HIT with extra hierarchical
information not found in a standard HIT.
HID (Hierarchy ID):
The 32 bit field providing the HIT Hierarchy ID.
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 Hierarchical HIT Assigning
Authority.
RVS (Rendezvous Server):
The HIP Rendezvous Server for enabling mobility, as defined in
[RFC8004].
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.
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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] supports three types of UAS IDs, namely
the [CTA2063A] serial number, CAA registration ID, and UTM-provided
UUID session ID. For HHITs to be used effectively as UAS IDs,
F3411-19 SHOULD add HHIT as the fourth UAS ID type.
3.1. Hierarchy in ORCHID Generation
ORCHIDS, as defined in [RFC7343], do not cryptographically bind the
IPv6 prefix nor the Orchid Generation Algorithm (OGA) 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 though 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.
3.2. Hierarchical HIT Registry
HHITs are registered to Hierarchical HIT Domain Authorities (HDAs) as
described in [hhit-registries]. This registration process 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.
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3.3. Remote ID Authentication using HHITs
The EdDSA25519 Host Identity (HI) [Appendix D] underlying the HHIT is
used for the Message Wrapper, Sec 4.2 [drip-auth] (requirements GEN-
2). It and the HDA's HI/HHIT are used for the Auth Certificate, sec
5.1 [drip-auth] (requirements GEN-3). These messages also establish
that the UA owns the HHIT and that no other UA can assert ownership
of the HHIT (GEN-1).
The number of HDAs authorized to register UAs within an NAS
determines the size of the HDA credential cache a device processing
the Offline Authentication. This cache contains the HDA's HI/HHIT
and HDA meta-data; it could be very small.
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:
100.50.hhit.uas.areo IN PTR foo.uss.areo.
The individual HHITs are potentially too numerous (e.g. 63M) 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.a3ad14.28.14.2001.20.10.hhit.arpa.
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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:
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:
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).
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.
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Another mitigation of HHIT hijacking is if the HI owner supplies an
object containing the HHIT and signed by the HI private key of the
HDA.
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 as in HHIT Registries [hhit-registries]
provides a level of assured uniqueness unattainable without mirroring
this approach.
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 (the actual Remote ID
message) does not provide any assertion of trust. The best that
might be done is 4 bytes truncated from a HI signing of the HHIT (the
UA ID field is 20 bytes and a HHIT is 16). It is in the ASTM
Authentication Messages as defined in [drip-auth] that provide all of
the 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 Location/Vector Message 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.
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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 E for the collision probability formula.
However, this risk of collision is within a single "Additional
Information" value. Some registration process should be used to
reject a collision, forcing the client to generate a new HI and thus
HIT and reapplying to the registration process.
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>.
[hhit-registries]
Moskowitz, R., Card, S., and A. Wiethuechter,
"Hierarchical HIT Registries", Work in Progress, Internet-
Draft, draft-moskowitz-hip-hhit-registries-02, 9 March
2020, <https://tools.ietf.org/html/draft-moskowitz-hip-
hhit-registries-02>.
[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>.
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[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>.
[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,
20 May 2020, <https://tools.ietf.org/html/draft-moskowitz-
drip-crowd-sourced-rid-04>.
[CTA2063A] ANSI, "Small Unmanned Aerial Systems Serial Numbers",
September 2019.
[drip-auth]
Wiethuechter, A., Card, S., and R. Moskowitz, "DRIP
Authentication Formats", Work in Progress, Internet-Draft,
draft-wiethuechter-drip-auth-03, 27 July 2020,
<https://tools.ietf.org/html/draft-wiethuechter-drip-auth-
03>.
[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-03, 13 July 2020,
<https://tools.ietf.org/html/draft-ietf-drip-reqs-03>.
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[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-c2-00, 6 April 2020, <https://tools.ietf.org/html/
draft-moskowitz-drip-secure-nrid-c2-00>.
[Keccak] Bertoni, G., Daemen, J., Peeters, M., Van Assche, G., and
R. Van Keer, "The Keccak Function",
<https://keccak.team/index.html>.
[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>.
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.
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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 HITs are "Using cSHAKE in ORCHIDs"
(Appendix C). The input values for the Encoding rules are in
Appendix C.1.
A HHIT is built from the following fields:
* 28 bit IANA prefix
* 4 bit HIT Suite ID
* 32 bit Hierarchy ID (HID)
* 64 bit ORCHID hash
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B.1. HHIT prefix
A unique 28 bit prefix for HHITs is recommended. It clearly
separates the flat-space HIT processing from HHIT processing per
"Using cSHAKE in ORCHIDs" (Appendix C).
B.2. HHIT Suite IDs
The HIT Suite IDs specifies the HI and hash algorithms. Any HIT
Suite ID can be used for HHITs, provided that the prefix for HHITs is
different from flat space HITs. Without a unique prefix,
Appendix B.1, additional HIT Suite IDs would be needed for HHITs.
This would risk exhausting the limited Suite ID space of only 15 IDs.
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)
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.
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.
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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 adds the [Keccak] based cSHAKE XOF hash function from
NIST SP 800-185 [NIST.SP.800-185] to ORCHIDv2 [RFC7343]. cSHAKE 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.
This ORCHID construction includes the Prefix in the hash to protect
against Prefix subsitution attacks. It also provides for inclusion
of additional information, in particular the hierarchical bits of the
Hierarchical HIT, in the ORCHID generation. It should be viewed as
an addendum to ORCHIDv2 [RFC7343].
cSHAKE is used, rather than SHAKE from NIST FIPS 202 [NIST.FIPS.202],
as 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.
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.
Encode_96( ) : An extraction function in which output is obtained
by extracting the middle 96-bit-long bitstring
from the argument bitstring.
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This addendum will be constructed as follows:
ORCHID := Prefix | OGA ID | Info (n) | Hash (m)
where:
Prefix (p) : A (max 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.
Info (n) : n bits of information that define a use of the
ORCHID. n can be zero, that is no additional
information.
Hash (m) : An extraction function in which output is m bits.
p + n + m = 124 bits
With a 28 bit IPv6 Prefix, the 96 bits currently allocated to the
Encode_96 function can be divided in any manner between the
additional information 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 Decoding
With this addendum, the decoding of an ORCHID is determined by the
Prefix and OGA ID. ORCHIDv2 [RFC7343] decoding is selected when the
Prefix is: 2001:20::/28.
For Heirarchical HITs, the decoding is determined by the presence of
the HHIT Prefix as specified in the HHIT document.
C.3. ORCHID Encoding
ORCHIDv2 has a number of inputs including a Context ID, some header
bits, the hash algorithm, and the input bitstream, normally just the
public key. The output is a 96 bit value.
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This addendum adds a different encoding process to that currently
used. The input to the hash function explicitly includes all the
fixed header content plus the Context ID. The fixed header content
consists of the Prefix, OGA ID, and the Additional Information.
Secondly, the length of the resulting hash is set by the rules set by
the Prefix/OGA ID. In the case of Hierarchical HITs, this is 64
bits.
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 | OGA ID | Additional Information | HOST_ID
L := Length in bits of hash portion of ORCHID
Hierarchical HIT uses the same context as all other HIPv2 HIT Suites
as they are clearly separated by the distinct HIT Suite ID.
Appendix D. Edward Digital Signature Algorithm for HITs
Edwards-Curve Digital Signature Algorithm (EdDSA) [RFC8032] are
specified here for use as Host Identities (HIs).
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:
Algorithm Curve Values
EdDSA RESERVED 0
EdDSA EdDSA25519 1 [RFC8032]
EdDSA EdDSA25519ph 2 [RFC8032]
EdDSA EdDSA448 3 [RFC8032]
EdDSA EdDSA448ph 4 [RFC8032]
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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 is 96
bits long and is directly used in the ORCHID.
+=======+===========+=========+===========+===================+
| Index | Hash | HMAC | Signature | Description |
| | function | | algorithm | |
| | | | family | |
+=======+===========+=========+===========+===================+
| 5 | cSHAKE128 | KMAC128 | EdDSA | EdDSA HI hashed |
| | | | | with cSHAKE128, |
| | | | | output is 96 bits |
+-------+-----------+---------+-----------+-------------------+
Table 1: HIT Suites
Appendix E. 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
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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
4947 Commercial Drive
Yorkville, NY 13495
United States of America
Email: stu.card@axenterprize.com
Adam Wiethuechter
AX Enterprize
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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