UAS Remote ID
HTT Consulting
Oak Park
MI
48237
USA
rgm@labs.htt-consult.com
AX Enterprize
4947 Commercial Drive
Yorkville
NY
13495
USA
stu.card@axenterprize.com
AX Enterprize
4947 Commercial Drive
Yorkville
NY
13495
USA
adam.wiethuechter@axenterprize.com
Linköping University
IDA
Linköping
58183
Sweden
gurtov@acm.org
Internet
DRIP
RFC
Request for Comments
I-D
Internet-Draft
RID
This document describes using 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 registration discovery for 3rd-party ID assertion.
Further, HHITs can also be used elsewhere in the UTM architecture
to facilitate UAS communications.
Introduction
This document describes the use of Hierarchical HITs (HHITs) as self-asserting
and thereby a trustable Identifier for use as the UAS Remote ID.
HHITs include explicit hierarchy to provide registration discovery
for 3rd-party ID assertion.
The Drip
Requirements describe 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).
HITs are statistically unique through the cryptograhic hash feature
of second-preimage resistance. The cryptograhically-bound addition
of the Hierarchy and 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. All CAs within a PKI would
have to check each other for duplicate (possibly fraudulent) IDs to
approach this assurance of uniqueness.
Hierarchical HITs are valid, though non-routable, IPv6 addresses.
As such, they fit in many ways within various IETF technologies.
Terms and Definitions
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 when, and only when, they appear in all
capitals, as shown here.
Definitions
- CAA
-
Civil Aeronautics Administration. Two CAAs are the US
Federal Aviation Administration (FAA) and European Union
Aviation Safety Agency (EASA).
- C2
-
Command and Control. A set of organizational and technical
attributes and processes that employs human, physical, and
information resources to solve problems and accomplish
missions. Previously primarily used in military contexts.
- CS-RID
-
Crowd Sourced Remote Identification. An optional DRIP WG
service that gateways Broadcast RID to Network RID, and
supports verification of RID positon/velocity claims with
independent measurements (e.g. by multilateration), via a
SDSP.
- GCS
-
Ground Control Station. The part of the UAS that the remote
pilot uses to exercise C2 over the UA, whether by remotely
exercising UA flight controls to fly the UA, by setting GPS
waypoints, or otherwise directing its flight.
- HI
-
Host Identity. The public key portion of an asymmetric
keypair from 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
information not found in a standard HIT.
- HIT
-
Host Identity Tag. A 128 bit handle on the HI. HITs are
valid IPv6 addresses.
- Observer
-
Referred to in some UAS documents as a "user", but there
are also other classes of RID users; "observer" is
preferred here to denote an individual who has observed an
UA and needs to know something about it, starting with its
RID.
- RID
-
Remote ID. A unique identifier found on all UA to be used
in communication and in regulation of UA operation.
- UA
-
Unmanned Aircraft. In this document UA's are typically
thought of as drones of commercial or military variety. This
is a very strict definition which can be relaxed to include
any and all aircraft that are unmanned.
- UAS
-
Unmanned Aircraft System. Composed of Unmanned Aircraft
and all required on-board subsystems, payload, control
station, other required off-board subsystems, any required
launch and recovery equipment, all required crew members,
and C2 links between UA and the control station.
- USS
-
UAS Service Supplier. Provide UTM services to support the
UAS community, to connect Operators and other entities to
enable information flow across the USS network, and to
promote shared situational awareness among UTM
participants. (From FAA UTM ConOps V1, May 2018).
- UTM
-
UAS Traffic Management. A "traffic management" ecosystem
for uncontrolled operations that is separate from, but
complementary to, Air Traffic Management (ATM) systems for
manned aircraft.
Hierarchical HITs as Remote ID
Hierarchical HITs are a refinement on the Host Identity Tag (HIT)
of HIPv2. HHITs
require a new ORCHID mechanism as described in . HHITs for
UAS ID also use the new EdDSA/SHAKE128 HIT suite defined in
(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
supports three types of UAS IDs, namely the 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.
Hierarchy in ORCHID generation
ORCHIDS, as defined in ,
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 , 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.
Hierarchical HIT Registry
HHITs are registered to Hierarchical HIT Domain Authorities (HDAs)
as described in . 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 (GEN-4 and
GEN-5).
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.
Remote ID Authentication using HHITs
The EdDSA25519 Host Identity (HI) underlying the HHIT is used for
the Message Wrapper, Sec 4.1
(requirements GEN-2). It and the HDA's HI/HHIT are used for the
Offline Claim, sec 4.3 (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.
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 .
The HHIT can be used to construct an FQDN that points to the USS
that has the Public/Private information for the UA (GEN-4 and
GEN-5). 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:
The individual HHITs are potentially too numerous to actually store
in DNS. 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:
An HHIT reverse lookup would be to is:
Other UTM uses of HHITs
HHITs can be used extensively within the UTM architecture beyond for
UA ID (and USS in UA ID registration and authentication). The GCS
SHOULD have its own HHIT as an ID. It could use this if it is the
source of Network Remote ID for securing the transport and for
secure C2 transport .
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, .
DRIP Requirements addressed
This document provides solutions to GEN 1 - 6 and ID 1 - 5.
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 ).
Security Considerations
The security considerations with Hierarchical HITs, most notably
the short hash of the HI, are discussed in . The
binding of the hierarchy to the hash of the HI is covered in .
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 its implied
second-preimage resistance) makes it statistically challenging to
attacks. A registration process as in 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.
Hierarchical HIT Trust
The HHIT UAS RID in the ASTM Basic Message (the actual Remote ID
message) does not provide any assertions 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 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 . 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 ),
thus asserting HHIT RID trust.
Acknowledgments
Dr. Gurtov is an advisor on Cybersecurity to the Swedish Civil Aviation Administration.
Standard Specification for Remote ID and Tracking
ASTM International
Small Unmanned Aerial Systems Serial Numbers
ANSI
U-space Concept of Operations
CORUS
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 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).