Network Working Group A. Mayrhofer Internet-Draft nic.at GmbH Intended status: Standards Track D. Klesev Expires: March 13, 2021 M. Sabadello Danube Tech GmbH September 9, 2020 The Decentralized Identifier (DID) in the DNS draft-mayrhofer-did-dns-04 Abstract This document specifies the use of the URI Resource Record Type to publish Decentralized Identifiers (DIDs) in the DNS. 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 March 13, 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 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. Mayrhofer, et al. Expires March 13, 2021 [Page 1] Internet-Draft draft-mayrhofer-did-dns September 2020 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Use of the 'URI' RRType . . . . . . . . . . . . . . . . . . . 3 3.1. Owner Name Scoping, Target . . . . . . . . . . . . . . . 3 3.2. Weight, Priority . . . . . . . . . . . . . . . . . . . . 3 4. Location of the Records . . . . . . . . . . . . . . . . . . . 4 4.1. Host Names . . . . . . . . . . . . . . . . . . . . . . . 4 4.2. Email Addresses (Experimental) . . . . . . . . . . . . . 4 5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 6. Considered Alternatives . . . . . . . . . . . . . . . . . . . 4 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 9. Security Considerations . . . . . . . . . . . . . . . . . . . 5 10. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 10.1. draft-mayrhofer-did-dns-04 . . . . . . . . . . . . . . . 6 10.2. draft-mayrhofer-did-dns-03 . . . . . . . . . . . . . . . 6 10.3. draft-mayrhofer-did-dns-02 . . . . . . . . . . . . . . . 6 10.4. draft-mayrhofer-did-dns-01 . . . . . . . . . . . . . . . 6 10.5. draft-mayrhofer-did-dns-00 . . . . . . . . . . . . . . . 6 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 11.1. Normative References . . . . . . . . . . . . . . . . . . 6 11.2. Informative References . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction Decentralized Identifiers (DIDs) [W3C-DID] use a Uniform Resource Identifier (URI) scheme [RFC3986] to identify persons, organizations, or things in decentralized infrastructure, such as blockchains and distributed ledgers. DIDs are structured around "methods", each method defining the syntax of the "method specific identifier" and the operations on the respective DIDs (See Section 3.2 of [W3C-DID] and [DID-METHODS]). For many methods, the method specific identifier is not human- friendly (such as hash values, referring to transactions on a blockchain). Most DIDs are therefore inherently hard to memorize for humans. By referring to DIDs from the Domain Name System (DNS), those hard to memorize identifiers can be discovered via well known, human friendly and widely established names. This document specifies how DIDs can be published in the DNS for discovery on the base of host names and email addresses. Mayrhofer, et al. Expires March 13, 2021 [Page 2] Internet-Draft draft-mayrhofer-did-dns September 2020 Since DIDs use a URI scheme ('did'), this specification leverages the existing URI DNS Resource Record Type (RRType) [RFC7553]. Records are scoped using the '_did' global underscore node name, as described in Section 3.1. 2. Terminology "Owner name", "Priority", "Weight" and "Target" refer to the respective fields of the URI RRType, as specified in Section 4 of RFC 7553. 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. 3. Use of the 'URI' RRType DIDs use an URI scheme ('did:'), so the most suitable option to publish DIDs in the DNS is the use of the 'URI' RRType. During the development of this document, various alternatives were considered, see Section 6 for a list. o When Decentralized Identifiers (DIDs) are published in the DNS, the 'URI' RRType MUST be used. 3.1. Owner Name Scoping, Target [RFC8552] describes the advantages of scoping an existing RRType over the definition (and complex deployment) of a new RRType. The "URI" RRType is specifically mentioned as one example where scoping is particularly useful (and part of the design). When DIDs are published in the DNS o the records MUST be scoped by setting the global (highest-level) underscore name of the URI RRset to '_did' (0x5F 0x64 0x69 0x64), o and the Target field of all records in the RRset MUST contain a URI of the 'did:' URI scheme. 3.2. Weight, Priority The semantics of the Weight and Priority fields remain. When a client encounters a DID method it does not support, it SHOULD consider the respective URI "unreachable" for the purpose of record Mayrhofer, et al. Expires March 13, 2021 [Page 3] Internet-Draft draft-mayrhofer-did-dns September 2020 selection, and proceed to the record with the next-lowest-numbered Priority, in accordance with Section 4.2 of RFC 7553. 4. Location of the Records 4.1. Host Names In order to discover the set of DIDs associated with a Host Name, a client prepends the given Host Name with the '_did' global underscore name to create the Owner name, and then queries the resulting Query Name for the URI RRType set. 4.2. Email Addresses (Experimental) To discover DIDs associated with email addresses, the (experimental) model from DNS-Based Authentication of Named Entities (DANE) Bindings for OpenPGP [RFC7929] is used. A client prepares the email address following the procedure outlined in Section 5 in RFC7929 the form the Query Name, but in step 5 MUST use the string '_mailto._did' instead of '_openpgpkey' as the second left-most label. Subsequently, the client performs a DNS query, but MUST use the URI RRType as Query Type (rather than the OPENPGPKEY RRType described in said section). 5. Example The following example is a URI Resource Record which refers from the host name "example.net" to a Decentralized Identifier using the 'sov' method: _did.example.net. IN URI 100 10 "did:sov:1234abcd" 6. Considered Alternatives During the development of this document, the following alternatives were considered: A dedicated RRType, TXT records, an Enumservice, Well-Known URIs, direct registration in the Service Name Registry. Using the URI RRType was found to be the option with the least impact on existing specifications and highest interoperability potential. Support for URI RRTypes is widespread in DNS software, which means that implementation and deployment of the proposed protocol should be possible without any changes to underlying infrastructure. Furthermore, the Identifiers and Discovery Working Group of the Decentralized Identity Foundation (DIF) is considering a .well-known URL based approach to discovering DIDs from web sites. Mayrhofer, et al. Expires March 13, 2021 [Page 4] Internet-Draft draft-mayrhofer-did-dns September 2020 7. Acknowledgements Acknowledgements will be added here. 8. IANA Considerations Per [RFC8552] IANA is requested to add the following entry to the DNS Underscore Global Scoped Entry Registry: +---------+-------------+-----------+ | RR Type | _NODE NAME | REFERENCE | +---------+-------------+-----------+ | URI | _did | {THISRFC} | +---------+-------------+-----------+ Table 1: Underscore Global Registry Entry Registration for '_did' Note to RFC Editor: Please replace the above "{THISRFC}" text with a reference to this document's RFC number. Note that IANA has already created a provisional URI scheme registration for the 'did:' scheme itself. 9. Security Considerations Most of the considerations outlined in the base specification of the URI RRType (RFC7553) also apply to the DID use case - particularly the concerns around downgrade attacks when the record is not signed with the help of DNSSEC. Note that the DID resolving process itself (out of scope of this document) can provide additional security information. The "Linked Domain Service Endpoint" of a DID document can be used to back-reference to the Domain which was originally used to discover that DID. Such a "closed loop" (similar to verifying DNS reverse lookups against their corresponding forward lookups) would increase the confidence in non-DNSSEC scenarios. Including a DID in the DNS allows for correlation of that DID with DNS information (and potentially registration information of that DNS name). Therefore DIDs which are supposed to be private SHOULD NOT be added to the DNS. 10. Changes [Note to RFC Editors: This whole section is to be removed before publication] Mayrhofer, et al. Expires March 13, 2021 [Page 5] Internet-Draft draft-mayrhofer-did-dns September 2020 10.1. draft-mayrhofer-did-dns-04 o Reworded "Alternatives" o Added text about backreference using DID's Linked Domain Service Endpoint. 10.2. draft-mayrhofer-did-dns-03 o Updated DID spec to v1.0 document o Minor editorial changes to make text more clear. 10.3. draft-mayrhofer-did-dns-02 o Updated attrleaf reference to RFC8552 o Changed author information for D. Klesev o Added sentence on .well-known discovery scheme 10.4. draft-mayrhofer-did-dns-01 o email addresses further scoped with '_mailto._did' o Changed protocol registration to attrleaf drafts o Made clear requirements regarding use of the URI scheme o Added privacy aspect to security considerations 10.5. draft-mayrhofer-did-dns-00 o Initial version 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7553] Faltstrom, P. and O. Kolkman, "The Uniform Resource Identifier (URI) DNS Resource Record", RFC 7553, DOI 10.17487/RFC7553, June 2015, . Mayrhofer, et al. Expires March 13, 2021 [Page 6] Internet-Draft draft-mayrhofer-did-dns September 2020 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8552] Crocker, D., "Scoped Interpretation of DNS Resource Records through "Underscored" Naming of Attribute Leaves", BCP 222, RFC 8552, DOI 10.17487/RFC8552, March 2019, . [W3C-DID] W3C, W3C., "Decentralized Identifiers (DIDs) v1.0", February 2020, . 11.2. Informative References [DID-METHODS] W3C, W3C., "DID Method Registry", June 2018, . [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, . [RFC6116] Bradner, S., Conroy, L., and K. Fujiwara, "The E.164 to Uniform Resource Identifiers (URI) Dynamic Delegation Discovery System (DDDS) Application (ENUM)", RFC 6116, DOI 10.17487/RFC6116, March 2011, . [RFC6117] Hoeneisen, B., Mayrhofer, A., and J. Livingood, "IANA Registration of Enumservices: Guide, Template, and IANA Considerations", RFC 6117, DOI 10.17487/RFC6117, March 2011, . [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. Cheshire, "Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry", BCP 165, RFC 6335, DOI 10.17487/RFC6335, August 2011, . [RFC7929] Wouters, P., "DNS-Based Authentication of Named Entities (DANE) Bindings for OpenPGP", RFC 7929, DOI 10.17487/RFC7929, August 2016, . Mayrhofer, et al. Expires March 13, 2021 [Page 7] Internet-Draft draft-mayrhofer-did-dns September 2020 Authors' Addresses Alexander Mayrhofer nic.at GmbH Karlsplatz 1/2/9 Vienna 1010 Austria Email: alex.mayrhofer.ietf@gmail.com Dimitrij Klesev Email: dimitrij.klesev@gmail.com Markus Sabadello Danube Tech GmbH Annagasse 8/1/8 Vienna 1010 Austria Email: markus@danubetech.com Mayrhofer, et al. Expires March 13, 2021 [Page 8]