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Security OAuth Working Group RFC Request for Comments I-D Internet-Draft JSON Web Key JWK Thumbprint URI URN OAuth This specification registers a kind of URI that represents a JSON Web Key (JWK) Thumbprint value. JWK Thumbprints are defined in RFC 7638. This enables JWK Thumbprints to be used, for instance, as key identifiers in contexts requiring URIs.

A JSON Web Key (JWK) Thumbprint is a URL-safe representation of a hash value over a JSON Web Key (JWK) . This specification defines a URI prefix indicating that the portion of the URI following the prefix is a JWK Thumbprint. This enables JWK Thumbprints to be communicated in contexts requiring URIs, including in specific JSON Web Token (JWT) claims. JWK Thumbprints URIs are being used in the specification as one kind of subject identifier in a context requiring that the identifier be a URI. In this case, the subject identifier is derived from a public key represented as a JWK. Expressing the identifier as JWK Thumbprint URI enables this kind of identifier to be differentiated from other kinds of identifiers that are also URIs, such as Decentralized Identifiers (DIDs) .

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.

The following URI prefix is defined to indicate that the portion of the URI following the prefix is a JWK Thumbprint: urn:ietf:params:oauth:jwk-thumbprint To make it explicit in a URI which hash algorithm is used, the prefix is followed by a hash algorithm identifier and a JWK Thumbprint value, each separated by a colon character to form a URI representing a JWK Thumbprint.

Hash algorithm identifiers used in JWK Thumbprint URIs are strings registered in the IANA "Named Information Hash Algorithm Registry" .

To promote interoperability among implementations, the SHA-256 hash algorithm is mandatory to implement.

Section 3.1 of contains the following example JWK Thumbprint value:

A complete JWK Thumbprint URI using the above JWK Thumbprint and SHA-256 hash algorithm is:

The security considerations of also apply when using this specification.

There are cryptographic algorithms for which multiple public keys correspond to the same private key. This is described in the security considerations of as follows: Designers using these curves should be aware that for each public key, there are several publicly computable public keys that are equivalent to it, i.e., they produce the same shared secrets. Thus using a public key as an identifier and knowledge of a shared secret as proof of ownership (without including the public keys in the key derivation) might lead to subtle vulnerabilities. This consideration for public keys as identifiers equally applies to JWK Thumbprint URIs used as identifiers. A recommended way to ensure that the JWK Thumbprint URI corresponds to the actual public key used is to sign a message containing the correct public key with the private key. This signed message could also contain the JWK Thumbprint URI (although, by definition, it could also be computed directly from the public key).

This specification registers the following value in the IANA "OAuth URI" registry established by .

URN: urn:ietf:params:oauth:jwk-thumbprint Common Name: JWK Thumbprint URI Change controller: IESG Specification Document: [[ this specification ]]

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Use cases for this specification were developed in the OpenID Connect Working Group of the OpenID Foundation. Specifically, it is being used a key identifier in the specification. The following individuals also contributed to this specification: John Bradley, Brian Campbell, Vladimir Dzhuvinov, Adam Lemmon, Neil Madden, Aaron Parecki, and David Waite.

[[ to be removed by the RFC Editor before publication as an RFC ]] -01 Added security considerations about multiple public keys coresponding to the same private key. Added hash algorithm identifier after the JWK thumbprint URI prefix to make it explicit in a URI which hash algorithm is used. Added reference to a registry for hash algorithm identifiers. Added SHA-256 as a mandatory to implement hash algorithm to promote interoperability. -00 Created initial working group draft from draft-jones-oauth-jwk-thumbprint-uri-01.