JWK Thumbprint URI

JWK Thumbprint URI Microsoft

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Microsoft

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Security OAuth 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.

Introduction A JSON Web Key (JWK) Thumbprint is a URL-safe representation of a hash value over a 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 Thumbprint 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 a 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) .

Requirements Notation and Conventions 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.

JWK Thumbprint URI 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 the hash algorithm being used explicit in a URI, 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 Algorithms Identifier Hash algorithm identifiers used in JWK Thumbprint URIs MUST be values from the "Hash Name String" column in the IANA "Named Information Hash Algorithm Registry" . JWK Thumbprint URIs with hash algorithm identifiers not found in this registry are not considered valid and applications will need to detect and handle this error, should it occur.

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

Example JWK Thumbprint URI contains the following example JWK Thumbprint value: NzbLsXh8uDCcd-6MNwXF4W_7noWXFZAfHkxZsRGC9Xs A complete JWK Thumbprint URI using the above JWK Thumbprint and SHA-256 hash algorithm is as follows: urn:ietf:params:oauth:jwk-thumbprint:sha-256:NzbLsXh8uDCcd-6MNwXF4W_7noWXFZAfHkxZsRGC9Xs

Security Considerations The security considerations of also apply when using this specification.

Multiple Public Keys per Private Key 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).

IANA Considerations

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

Registry Contents

URN:: urn:ietf:params:oauth:jwk-thumbprint
Common Name:: JWK Thumbprint URI
Change controller:: IESG
Specification Document:: RFC 9278

References Normative References OAuth Parameters IANA Informative References Named Information Hash Algorithm Registry IANA Self-Issued OpenID Provider v2 Microsoft Microsoft yes.com Decentralized Identifiers (DIDs) v1.0 Digital Bazaar Digital Bazaar Danube Tech Evernym

Acknowledgements Use cases for this specification were developed in the OpenID Connect Working Group of the OpenID Foundation. Specifically, it is being used as a key identifier in the specification. The following individuals also contributed to the creation of this specification: , , , , , , , , , , , , , , , , , and .