DRIP Entity Tags (DET) in the Domain Name System (DNS)

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Table of Contents

1. Introduction

Registries are fundamental to Unmanned Aircraft System (UAS) Remote Identification (RID). Only very limited operational information can be sent via Broadcast RID, but extended information is sometimes needed. The most essential element of information from RID is the UAS ID, the unique key for lookup of extended information in relevant registries (see Figure 4 of [RFC9434]).¶

When a DRIP Entity Tag (DET) [RFC9374] is used as the UAS ID in RID, extended information can be retrieved from a DRIP Identity Management Entity (DIME) which manages registration of and associated lookups from DETs. In this document we assume the DIME is a function of UAS Service Suppliers (USS) (Appendix A.2 of [RFC9434]) but a DIME can be independent or handled by another entity as well.¶

2. Terminology

3. DET Hierarchy in DNS

[RFC9374] defines the Hierarchical Host Identity Tag (HHIT) and further specifies an instance of them used for UAS RID called DETs. The HHIT is a 128-bit value that is as an IPv6 address intended primarily as an identifier rather than locator. It's format is in Figure 1 and further information is in [RFC9374].¶

+-------------+--------------+---------------+-------------+
| IPv6 Prefix | Hierarchy ID | HHIT Suite ID | ORCHID Hash |
| (28-bits)   | (28-bits)    | (8-bits)      | (64-bits)   |
+-------------+--------------+---------------+-------------+
             /                \
            /                  \
           /                    \-----------------------------\
          /                                                    \
         /                                                      \
        +--------------------------------+-----------------------+
        | Registered Assigning Authority | HHIT Domain Authority |
        | (14-bits)                      | (14-bits)             |
        +--------------------------------+-----------------------+

The IPv6 Prefix, assigned by IANA for DETs is 2001:30::/28. The corresponding domain (nibble reversed as 3.0.0.1.0.0.2.ip6.arpa) is owned by the IAB.¶

Due to the nature of the hierarchy split and its relationship to nibble reversing of the IPv6 address, the upper level of hierarchy (i.e. RAAs) "borrows" the upper two bits of their respective HDA space for DNS delegation. As such the IPv6 prefix of RAAs are 2001:3x:xxx::/44 and HDAs are 2001:3x:xxxx:xx::/56 with respective nibble reverse domains of x.x.x.x.3.0.0.1.0.0.2.ip6.arpa and y.y.y.x.x.x.x.3.0.0.1.0.0.2.ip6.arpa.¶

Preallocations have been made based on the ISO 3166-1 Numeric Nation Code [ISO3166-1]. This is to support the initial use case of DETs in UAS RID on an international level. See Section 6.2.1 for the RAA allocations.¶

The HDA values of 0, 4096, 8192 and 12288 are reserved for operational use of an RAA (a by-product of the above mentioned borrowing of bits), specifically when to register with the Apex and endorse delegations of HDAs in their namespace.¶

The administration, management and policy for operation a DIME at any level in the hierarchy (Apex, RAA or HDA), be it external or from a parent level, is out of scope for this document. In some cases, such as the RAAs and HDAs of a nation, these are National Matters which are to be dealt with by those parties accordingly.¶

4. Public Information Registry

Per [RFC9434] all information classified, by all parties involved, as public is stored in the DNS, specifically Authoritative Name Servers, to satisfy REG-1 from [RFC9153].¶

Authoritative Name Servers use domain names as handles and data is stored in Resource Records (RR) with associated RRTypes. This document defines two new RRTypes, one for HHIT metadata (HHIT, Section 5.1) and another for UAS Broadcast RID information (BRID, Section 5.2). The former RRType is particularly important as it contains a URI (as part of the certificate) that point to Private Information resources.¶

DETs, being IPv6 addresses, are to be under ip6.arpa (nibble reversed per convention) with at minimum an HHIT RRType. Depending on local circumstances or additional use cases other RRTypes MAY be present. For UAS RID the BRID RRType MUST be present to provide the Broadcast Endorsements defined in [RFC9575].¶

DNSSEC is strongly RECOMMENDED (especially for RAA-level and higher zones). When a DIME decides to use DNSSEC they SHOULD define a framework for cryptographic algorithms and key management [RFC6841]. This may be influenced by frequency of updates, size of the zone, and policies.¶

UAS specific information, such as physical characteristics, MAY also be stored in DNS but is out of scope for this document. This specification information is currently drafted in [uas-sn-dns].¶

An example, from Apex to client, of the DNS zones in available in Appendix A.¶

Lookups of the above RRTypes are performed with the standard DNS methodology using the nibble reversed DET as the query name affixed to the ip6.arpa domain apex and asking for the specific RRType. The HHIT RRType provides the public key for signature verification and URIs via the certificate. The BRID RRType provides static Broadcast RID information such as the Broadcast Endorsements sent following [RFC9575].¶

5. Resource Records

hhit-rr = [
    type: uint .size(2),
    abbreviation: tstr .size(15),
    registration-cert: bstr / #6.TBD
]

[
  0,
  "APEX",
  WQGC..uAo=
]

bcast-rr = {
    uas_type: nibble-field,
    uas_ids: [+ uas-id-grp],
    ? auth: [+ auth-grp],
    ? self-grp,
    ? op_type: 0..3,
    ? area-grp,
    ? classification-grp,
    ? operator-grp
}
uas-id-grp = (
    id_type: &uas-id-types,
    uas_id: bstr .size(20)
)
uas-id-types = (none: 0, serial: 1, caa_id: 2, utm_id: 3, session_id: 4)
auth-grp = (
    a_type: nibble-field,
    a_data: bstr .size(1..362)
)
area-grp = (
    area_count: 1..255,
    area_radius: float,
    area_floor: float,
    area_ceiling: float
)
classification-grp = (
    ua_class: 0..8,
    eu_class: nibble-field,
    eu_category: nibble-field
)
self-grp = (
    desc_type: nibble-field,
    description: tstr .size(23)
)
operator-grp = (
    operator_id_type: nibble-field,
    operator_id: bstr .size(20)
)
nibble-field = 0..15

{
  "uas_type": 0,
  "uas_ids": [
    [4, h'012001003FFE0001056A2621D4EF572EF5']
  ],
  "auths": [
    [5, b64'AYDQ..dwo='],
    [5, b64'AYDQ..Wgs='],
    [5, b64'AYDQ..NAw='],
    [5, b64'AYDQ..7gA=']
  ]
}

6. IANA Considerations

7. Security Considerations

8. Public Key Exposure

DETs are built upon asymmetric keys. As such the public key must be revealed to enable clients to perform signature verifications. [RFC9374] security considerations cover various attacks on such keys.¶

While unlikely the forging of a corresponding private key is possible if given enough time (and computational power). As such it is RECOMMENDED that the public key for any DET not be exposed in DNS (under any RRType) until it is required.¶

Optimally this requires the UAS somehow signal the DIME that a flight using a Specific Session ID will soon be underway or complete. It may also be facilitated under UTM if the USS (which may or may not be a DIME) signals when a given operation using a Session ID goes active.¶

9. Contributors

Thanks to Stuart Card (AX Enterprize, LLC) and Bob Moskowitz (HTT Consulting, LLC) for their early work on the DRIP registries concept. Their early contributions laid the foundations for the content and processes of this architecture and document. Bob Moskowitz is also instrumental in the PKIX work defined in this document with his parallel work in ICAO.¶

Appendix A. DET DNS Zone Examples

This appendix is informative, showing an example of the DNS zone setup/content from Apex to a client.¶

For this example the following DETs are shown:¶

• Apex = 2001:0030:0000:0005:fad8:7fea:e0f6:90ad¶
• RAA = 2001:003f:fe00:0005:618a:cd8e:76d3:b790¶
• HDA = 2001:003f:fe00:0105:ad79:a278:1c10:5443¶
• Client = 2001:003f:fe00:0105:6a26:21d4:ef57:2ef5¶

The RAA allocation of 16376 and an HDA of 1 have been selected.¶

$ORIGIN 3.0.0.1.0.0.2.ip6.arpa.
0.e.f.f IN NS ns1.raa-16376.example.com
1.e.f.f IN NS ns1.raa-16376.example.com
2.e.f.f IN NS ns1.raa-16376.example.com
3.e.f.f IN NS ns1.raa-16376.example.com

$ORIGIN 0.e.f.f.3.0.0.1.0.0.2.ip6.arpa.
1.0.0 IN NS ns1.hda-1.example.com

$ORIGIN 5.0.0.0.0.0.e.f.f.3.0.0.1.0.0.2.ip6.arpa.
0.9.7.b.3.d.6.7.e.8.d.c.a.8.1.6 IN BRID ( a368..5a0b )
0.9.7.b.3.d.6.7.e.8.d.c.a.8.1.6 IN HHIT ( 0 RAA 5901..0d0c )

$ORIGIN 5.0.1.0.0.0.e.f.f.3.0.0.1.0.0.2.ip6.arpa.
3.4.4.5.0.1.c.1.8.7.2.a.9.7.d.a IN BRID ( a368..340c )
3.4.4.5.0.1.c.1.8.7.2.a.9.7.d.a IN HHIT ( 0 HDA 5901..ac0a )
5.f.e.2.7.5.f.e.4.d.1.2.6.2.a.6 IN BRID ( a368..ee00 )
5.f.e.2.7.5.f.e.4.d.1.2.6.2.a.6 IN HHIT ( 0 CHILD 5901..0306 )

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