DRIP R. Moskowitz Internet-Draft HTT Consulting Intended status: Standards Track S. Card Expires: 12 February 2021 A. Wiethuechter AX Enterprize A. Gurtov Linköping University 11 August 2020 UAS Remote ID draft-moskowitz-drip-uas-rid-04 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. 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 12 February 2021. Copyright Notice Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. Moskowitz, et al. Expires 12 February 2021 [Page 1] Internet-Draft UAS Remote ID August 2020 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 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 . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terms and Definitions . . . . . . . . . . . . . . . . . . . . 3 2.1. Requirements Terminology . . . . . . . . . . . . . . . . 3 2.2. Definitions . . . . . . . . . . . . . . . . . . . . . . . 3 3. Hierarchical HITs as Remote ID . . . . . . . . . . . . . . . 4 3.1. Hierarchy in ORCHID Generation . . . . . . . . . . . . . 4 3.2. Hierarchical HIT Registry . . . . . . . . . . . . . . . . 4 3.3. Remote ID Authentication using HHITs . . . . . . . . . . 5 4. UAS ID HHIT in DNS . . . . . . . . . . . . . . . . . . . . . 5 5. Other UTM uses of HHITs . . . . . . . . . . . . . . . . . . . 6 6. DRIP Requirements addressed . . . . . . . . . . . . . . . . . 6 7. ASTM Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 9. Security Considerations . . . . . . . . . . . . . . . . . . . 6 9.1. Hierarchical HIT Trust . . . . . . . . . . . . . . . . . 7 10. Normative References . . . . . . . . . . . . . . . . . . . . 7 11. Informative References . . . . . . . . . . . . . . . . . . . 8 Appendix A. EU U-Space RID Privacy Considerations . . . . . . . 9 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10 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) [hierarchical-hit] 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. Moskowitz, et al. Expires 12 February 2021 [Page 2] Internet-Draft UAS Remote ID August 2020 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. Definitions See [drip-requirements] for common DRIP terms. 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. HHIT Hierarchical Host Identity Tag. A HIT with extra hierarchical information not found in a standard HIT. HIT Host Identity Tag. A 128 bit handle on the HI. HITs are valid IPv6 addresses. Moskowitz, et al. Expires 12 February 2021 [Page 3] Internet-Draft UAS Remote ID August 2020 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 [new-orchid]. HHITs for UAS ID also use the new EdDSA/SHAKE128 HIT suite defined in [new-hip-crypto] (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 [new-orchid], 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. Moskowitz, et al. Expires 12 February 2021 [Page 4] Internet-Draft UAS Remote ID August 2020 3.3. Remote ID Authentication using HHITs The EdDSA25519 Host Identity (HI) 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. Moskowitz, et al. Expires 12 February 2021 [Page 5] Internet-Draft UAS Remote ID August 2020 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 TBD 9. Security Considerations The security considerations with Hierarchical HITs, most notably the short hash of the HI, are discussed in [hierarchical-hit]. The binding of the hierarchy to the hash of the HI is covered in [new-orchid]. 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. Moskowitz, et al. Expires 12 February 2021 [Page 6] Internet-Draft UAS Remote ID August 2020 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. 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. 10. Normative References [F3411-19] ASTM International, "Standard Specification for Remote ID and Tracking", February 2020, . [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, . [hierarchical-hit] Moskowitz, R., Card, S., and A. Wiethuechter, "Hierarchical HITs for HIPv2", Work in Progress, Internet- Moskowitz, et al. Expires 12 February 2021 [Page 7] Internet-Draft UAS Remote ID August 2020 Draft, draft-moskowitz-hip-hierarchical-hit-05, 13 May 2020, . [new-hip-crypto] Moskowitz, R., Card, S., and A. Wiethuechter, "New Cryptographic Algorithms for HIP", Work in Progress, Internet-Draft, draft-moskowitz-hip-new-crypto-05, 26 July 2020, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 11. Informative References [corus] CORUS, "U-space Concept of Operations", September 2019, . [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, . [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, . [drip-requirements] Card, S., Wiethuechter, A., and R. Moskowitz, "Drone Remote Identification Protocol (DRIP) Requirements", Work in Progress, Internet-Draft, draft-card-drip-reqs-02, 20 April 2020, . Moskowitz, et al. Expires 12 February 2021 [Page 8] Internet-Draft UAS Remote ID August 2020 [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, . [new-orchid] Moskowitz, R., Card, S., and A. Wiethuechter, "Using cSHAKE in ORCHIDs", Work in Progress, Internet-Draft, draft-moskowitz-orchid-cshake-01, 21 May 2020, . [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, . [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, . [RFC8005] Laganier, J., "Host Identity Protocol (HIP) Domain Name System (DNS) Extension", RFC 8005, DOI 10.17487/RFC8005, October 2016, . 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. Moskowitz, et al. Expires 12 February 2021 [Page 9] Internet-Draft UAS Remote ID August 2020 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). Acknowledgments Dr. Gurtov is an adviser on Cybersecurity to the Swedish Civil Aviation Administration. 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 Moskowitz, et al. Expires 12 February 2021 [Page 10] Internet-Draft UAS Remote ID August 2020 SE-58183 Linköping Sweden Email: gurtov@acm.org Moskowitz, et al. Expires 12 February 2021 [Page 11]