Network Working Group A. Mayrhofer
Internet-Draft GmbH
Intended status: Standards Track D. Klesev
Expires: February 27, 2020
M. Sabadello
Danube Tech GmbH
August 26, 2019

The Decentralized Identifier (DID) in the DNS


This document specifies the use of the URI Resource Record Type to publish Decentralized Identifiers (DIDs) in the DNS.

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Table of Contents

1. Introduction

Decentralized Identifiers (DIDs) use a Uniform Resource Identifier (URI) scheme 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 (for example, hash values referring to transactions on a blockchain). Most DIDs are therefore inherently hard to memorize for humans.

By referring to DIDs from the 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.

Since DIDs use a URI scheme ('did'), this specification leverages the existing URI DNS Resource Record Type (RRType). 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 RFC7553.

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.

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

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 DID "unreachable" for the purpose of record selection, and proceed to the URI 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 is used. A client prepares the email address following the procedure outlined in Section 5 in RFC7929, except that the second left-most label in step 5 of that procedure MUST be replaced with the label sequence '_mailto._did' instead to form the Query Name. Subsequently, the client performs a DNS query for the URI RRType (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 "" to a Decentralized Identifier using the 'sov' method:

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. Updating the URI specification was found to be the option with the highest likeliness of interoperability combined with the lowest effort in standardization and implementation/deployment.

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.

7. Acknowledgements

Acknowledgements will be added here.

8. IANA Considerations

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 (such as a backreference to the DNS domain name).

Including a DID in the DNS allows to correlate that DID with DNS information, and is therefore NOT RECOMMENDED for DIDs which are supposed to be private.

10. Changes

[Note to RFC Editors: This whole section is to be removed before publication]

10.1. draft-mayrhofer-did-dns-02

10.2. draft-mayrhofer-did-dns-01

10.3. draft-mayrhofer-did-dns-00

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.
[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) v0.11", July 2018.

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.

Authors' Addresses

Alexander Mayrhofer GmbH Karlsplatz 1/2/9 Vienna, 1010 Austria EMail:
Dimitrij Klesev EMail:
Markus Sabadello Danube Tech GmbH Annagasse 8/1/8 Vienna, 1010 Austria EMail: