Archive for the 'Cryptography' Category

August 10, 2022
JWK Thumbprint URI is now RFC 9278

IETF logoThe JWK Thumbprint URI specification has been published as RFC 9278. Congratulations to my co-author, Kristina Yasuda, on the publication of her first RFC!

The abstract of the RFC is:


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.

The need for this arose during specification work in the OpenID Connect working group. In particular, JWK Thumbprint URIs are used as key identifiers that can be syntactically distinguished from other kinds of identifiers also expressed as URIs in the Self-Issued OpenID Provider v2 specification.

May 16, 2022
JWK Thumbprint URI Draft Addressing IETF Last Call Comments

OAuth logoKristina Yasuda and I have published a new JWK Thumbprint URI draft that addresses the IETF Last Call comments received. Changes made were:

  • Clarified the requirement to use registered hash algorithm identifiers.
  • Acknowledged IETF Last Call reviewers.

The specification is available at:

February 15, 2022
JWK Thumbprint URI Draft Addressing Working Group Last Call Comments

OAuth logoKristina Yasuda and I have published an updated JWK Thumbprint URI draft that addresses the OAuth Working Group Last Call (WGLC) comments received. Changes made were:

  • 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.
  • Acknowledged WGLC reviewers.

The specification is available at:

January 29, 2022
Working Group Adoption of the JWK Thumbprint URI Specification

OAuth logoThe IETF OAuth working group has adopted the JWK Thumbprint URI specification. The abstract of the specification is:

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.

The need for this arose during specification work in the OpenID Connect working group. In particular, JWK Thumbprint URIs are used as key identifiers that can be syntactically distinguished from other kinds of identifiers also expressed as URIs in the Self-Issued OpenID Provider v2 specification.

Given that the specification does only one simple thing in a straightforward manner, we believe that it is ready for working group last call.

The specification is available at:

January 12, 2022
Described more of the motivations for the JWK Thumbprint URI specification

OAuth logoAs requested by the chairs during today’s OAuth Virtual Office Hours call, Kristina Yasuda and I have updated the JWK Thumbprint URI specification to enhance the description of the motivations for the specification. In particular, it now describes using JWK Thumbprint URIs as key identifiers that can be syntactically distinguished from other kinds of identifiers also expressed as URIs. It is used this way in the Self-Issued OpenID Provider v2 specification, for instance. No normative changes were made.

As discussed on the call, we are requesting that that the chairs use this new draft as the basis for a call for working group adoption.

The specification is available at:

November 24, 2021
JWK Thumbprint URI Specification

IETF logoThe JSON Web Key (JWK) Thumbprint specification [RFC 7638] defines a method for computing a hash value over a JSON Web Key (JWK) [RFC 7517] and encoding that hash in a URL-safe manner. Kristina Yasuda and I have just created the JWK Thumbprint URI specification, which defines how to represent JWK Thumbprints as URIs. This enables JWK Thumbprints to be communicated in contexts requiring URIs, including in specific JSON Web Token (JWT) [RFC 7519] claims.

Use cases for this specification were developed in the OpenID Connect Working Group of the OpenID Foundation. Specifically, its use is planned in future versions of the Self-Issued OpenID Provider v2 specification.

The specification is available at:

June 23, 2021
Second Version of FIDO2 Client to Authenticator Protocol (CTAP) Now a Standard

FIDO logoThe FIDO Alliance has completed the CTAP 2.1 Specification. This follows the publication of the closely-related second version of the W3C Web Authentication (WebAuthn) specification.

Today’s FIDO Alliance announcement describes the enhancements in the second version as follows:

Enhancements to FIDO standards to accelerate passwordless in the enterprise

The FIDO Alliance has announced enhancements to its FIDO2 specifications, which include several new features that will be helpful for passwordless enterprise deployments and other complex security applications. Both FIDO2 specifications were recently updated by their governing bodies – with the World Wide Web Consortium (W3C) approving WebAuthn Level 2 and FIDO doing the same for CTAP 2.1.

Key to these enhancements is enterprise attestation, which provides enterprise IT with improved management of FIDO authenticators used by employees. Enterprise attestation enables better binding of an authenticator to an account, assists with usage tracking and other management functions including credential and pin management, and biometric enrollment required in the enterprise.

Other updates include support for cross-origin iFrames and Apple attestation, as well as improvements to resident credentials. More details on these and other FIDO specification enhancements are available here.

April 14, 2021
Second Version of W3C Web Authentication (WebAuthn) Now a Standard

W3C logoThe World Wide Web Consortium (W3C) has published this Recommendation for the Web Authentication (WebAuthn) Level 2 specification, meaning that it now a completed standard. While remaining compatible with the original standard, this second version adds additional features, among them for user verification enhancements, manageability, enterprise features, and an Apple attestation format. The companion second FIDO2 Client to Authenticator Protocol (CTAP) specification is also approaching becoming a completed standard.

See the W3C announcement of this achievement. Also, see Tim Cappalli‘s summary of the changes in the second versions of WebAuthn and FIDO2.

March 31, 2021
Second Version of FIDO2 Client to Authenticator Protocol (CTAP) advanced to Public Review Draft

FIDO logoThe FIDO Alliance has published this Public Review Draft for the FIDO2 Client to Authenticator Protocol (CTAP) specification, bringing the second version of FIDO2 one step closer to becoming a completed standard. While remaining compatible with the original standard, this second version adds additional features, among them for user verification enhancements, manageability, enterprise features, and an Apple attestation format.

This parallels the similar progress of the closely related second version of the W3C Web Authentication (WebAuthn) specification, which recently achieved Proposed Recommendation (PR) status.

February 28, 2021
Second Version of W3C Web Authentication (WebAuthn) advances to Proposed Recommendation (PR)

W3C logoThe World Wide Web Consortium (W3C) has published this Proposed Recommendation (PR) for the Web Authentication (WebAuthn) Level 2 specification, bringing the second version of WebAuthn one step closer to becoming a completed standard. While remaining compatible with the original standard, this second version adds additional features, among them for user verification enhancements, manageability, enterprise features, and an Apple attestation format.

December 31, 2020
Near-Final Second W3C WebAuthn and FIDO2 CTAP Specifications

W3C logoFIDO logoThe W3C WebAuthn and FIDO2 working groups have been busy this year preparing to finish second versions of the W3C Web Authentication (WebAuthn) and FIDO2 Client to Authenticator Protocol (CTAP) specifications. While remaining compatible with the original standards, these second versions add additional features, among them for user verification enhancements, manageability, enterprise features, and an Apple attestation format. Near-final review drafts of both have been published:

Expect these to become approved standards in early 2021. Happy New Year!

August 14, 2020
COSE and JOSE Registrations for Web Authentication (WebAuthn) Algorithms is now RFC 8812

IETF logoThe W3C Web Authentication (WebAuthn) working group and the IETF COSE working group created “CBOR Object Signing and Encryption (COSE) and JSON Object Signing and Encryption (JOSE) Registrations for Web Authentication (WebAuthn) Algorithms” to make some algorithms and elliptic curves used by WebAuthn and FIDO2 officially part of COSE and JOSE. The RSA algorithms are used by TPMs. The “secp256k1” curve registered (a.k.a., the Bitcoin curve) is also used in some decentralized identity applications. The completed specification has now been published as RFC 8812.

As described when the registrations recently occurred, the algorithms registered are:

  • RS256 – RSASSA-PKCS1-v1_5 using SHA-256 – new for COSE
  • RS384 – RSASSA-PKCS1-v1_5 using SHA-384 – new for COSE
  • RS512 – RSASSA-PKCS1-v1_5 using SHA-512 – new for COSE
  • RS1 – RSASSA-PKCS1-v1_5 using SHA-1 – new for COSE
  • ES256K – ECDSA using secp256k1 curve and SHA-256 – new for COSE and JOSE

The elliptic curves registered are:

  • secp256k1 – SECG secp256k1 curve – new for COSE and JOSE

See them in the IANA COSE Registry and the IANA JOSE Registry.

June 19, 2020
Registrations for all WebAuthn algorithm identifiers completed

IETF logoWe wrote the specification COSE and JOSE Registrations for WebAuthn Algorithms to create and register COSE and JOSE algorithm and elliptic curve identifiers for algorithms used by WebAuthn and CTAP2 that didn’t yet exist. I’m happy to report that all these registrations are now complete and the specification has progressed to the RFC Editor. Thanks to the COSE working group for supporting this work.

Search for WebAuthn in the IANA COSE Registry and the IANA JOSE Registry to see the registrations. These are now stable and can be used by applications, both in the WebAuthn/FIDO2 space and for other application areas, including decentralized identity (where the secp256k1 “bitcoin curve” is in widespread use).

The algorithms registered are:

  • RS256 – RSASSA-PKCS1-v1_5 using SHA-256 – new for COSE
  • RS384 – RSASSA-PKCS1-v1_5 using SHA-384 – new for COSE
  • RS512 – RSASSA-PKCS1-v1_5 using SHA-512 – new for COSE
  • RS1 – RSASSA-PKCS1-v1_5 using SHA-1 – new for COSE
  • ES256K – ECDSA using secp256k1 curve and SHA-256 – new for COSE and JOSE

The elliptic curves registered are:

  • secp256k1 – SECG secp256k1 curve – new for COSE and JOSE
May 31, 2020
secp256k1 curve and algorithm registered for JOSE use

IETF logoIANA has registered the “secp256k1” elliptic curve in the JSON Web Key Elliptic Curve registry and the corresponding “ES256K” signing algorithm in the JSON Web Signature and Encryption Algorithms registry. This curve is widely used among blockchain and decentralized identity implementations.

The registrations were specified by the COSE and JOSE Registrations for WebAuthn Algorithms specification, which was created by the W3C Web Authentication working group and the IETF COSE working group because WebAuthn also allows the use of secp256k1. This specification is now in IETF Last Call. The corresponding COSE registrations will occur after the specification becomes an RFC.

May 14, 2020
Nearing completion on two WebAuthn-related specs at the IETF

IETF logoThis week we published updates to two IETF specifications that support the WebAuthn/FIDO2 ecosystem, as well as other uses, such as decentralized identity.

One is COSE and JOSE Registrations for WebAuthn Algorithms. It registers algorithm and elliptic curve identifiers for algorithms used by WebAuthn and FIDO2. The “secp256k1” curve being registered is also used for signing in some decentralized identity applications. The specification has completed the Area Director review and has been submitted to the IESG for publication.

The other is Registries for Web Authentication (WebAuthn). This creates IANA registries enabling multiple kinds of extensions to W3C Web Authentication (WebAuthn) implementations to be registered. This specification has completed IETF last call and is scheduled for review by the IESG.

Thanks to the COSE working group for their adoption of the algorithms specification, and to Ivaylo Petrov and Murray Kucherawy for their reviews of it. Thanks to Kathleen Moriarty and Benjamin Kaduk for their Area Director sponsorships of the registries specification and to Jeff Hodges for being primary author of it.

The specifications are available at:

March 9, 2020
Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs) is now RFC 8747

IETF logoI’m pleased to report that Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs) is now RFC 8747. The abstract of the specification is:

This specification describes how to declare in a CBOR Web Token (CWT) (which is defined by RFC 8392) that the presenter of the CWT possesses a particular proof-of-possession key. Being able to prove possession of a key is also sometimes described as being the holder-of-key. This specification provides equivalent functionality to “Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)” (RFC 7800) but using Concise Binary Object Representation (CBOR) and CWTs rather than JavaScript Object Notation (JSON) and JSON Web Tokens (JWTs).

This is one of a series of specifications, including CWT [RFC 8392] – which mirrors JWT [RFC 7519], in which we are intentionally bringing functionality that is available in JSON to the CBOR and IoT world.

March 3, 2020
Two New OAuth RFCs: MTLS (RFC 8705) and Resource Indicators (RFC 8707)

OAuth logoTwo widely used OAuth specifications have recently become RFCs. Here’s a bit about both specs.

RFC 8705: OAuth 2.0 Mutual-TLS Client Authentication and Certificate-Bound Access Tokens

Abstract: This document describes OAuth client authentication and certificate-bound access and refresh tokens using mutual Transport Layer Security (TLS) authentication with X.509 certificates. OAuth clients are provided a mechanism for authentication to the authorization server using mutual TLS, based on either self-signed certificates or public key infrastructure (PKI). OAuth authorization servers are provided a mechanism for binding access tokens to a client’s mutual-TLS certificate, and OAuth protected resources are provided a method for ensuring that such an access token presented to it was issued to the client presenting the token.

Client certificates are widely used in the financial industry to authenticate OAuth clients. Indeed, this specification was developed in part because it was needed by the OpenID Financial-Grade API (FAPI) specifications. It is in production use by numerous Open Banking deployments today.

RFC 8707: Resource Indicators for OAuth 2.0

Abstract: This document specifies an extension to the OAuth 2.0 Authorization Framework defining request parameters that enable a client to explicitly signal to an authorization server about the identity of the protected resource(s) to which it is requesting access.

This specification standardizes the “resource” request parameter that is used by Azure Active Directory (AAD) V1 to specify the target resource for an OAuth authorization request.

February 19, 2020
JSON Web Token Best Current Practices is now RFC 8725 and BCP 225

OAuth logoThe JSON Web Token Best Current Practices specification is now RFC 8725 and BCP 225. The abstract of the specification is:

JSON Web Tokens, also known as JWTs, are URL-safe JSON-based security tokens that contain a set of claims that can be signed and/or encrypted. JWTs are being widely used and deployed as a simple security token format in numerous protocols and applications, both in the area of digital identity and in other application areas. This Best Current Practices document updates RFC 7519 to provide actionable guidance leading to secure implementation and deployment of JWTs.

The JSON Web Token (JWT) specification [RFC 7519] was approved in May 2015, almost five years ago, and has been in production use since at least 2013. This Best Current Practices specification contains a compendium of lessons learned from real JWT deployments and implementations over that period. It describes pitfalls and how to avoid them as well as new recommended practices that enable proactively avoiding problems that could otherwise arise. Importantly, the BCP introduces no breaking changes to the JWT specification and does not require changes to existing deployments.

The BCP came about as JWTs were starting to be used in new families of protocols and applications, both in the IETF and by others. For instance, JWTs are being used by the IETF STIR working group to enable verification of the calling party’s authorization to use a particular telephone number for an incoming call, providing verified Caller ID to help combat fraudulent and unwanted telephone calls. The advice in the BCP can be used by new JWT profiles and applications to take advantage of what’s been learned since we created the JSON Web Token (JWT) specification over a half decade ago.

January 27, 2020
COSE and JOSE Registrations for WebAuthn Algorithms spec adding explanatory comments on design decisions

IETF logoThe “COSE and JOSE Registrations for WebAuthn Algorithms” specification has been updated to add explanatory comments on design decisions made that were discussed on the mailing list that Jim Schaad requested be added to the draft.

The specification is available at:

An HTML-formatted version is also available at:

November 6, 2019
Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs) sent to the RFC Editor

OAuth logoI’m pleased to report that the Proof-of-Possession Key Semantics for CBOR Web Tokens (CWTs) specification is now technically stable and will shortly be an RFC – an Internet standard. Specifically, it has now progressed to the RFC Editor queue, meaning that the only remaining step before finalization is editorial due diligence. Thus, implementations can now utilize the draft specification with confidence that that breaking changes will not occur as it is finalized.

The abstract of the specification is:

This specification describes how to declare in a CBOR Web Token (CWT) (which is defined by RFC 8392) that the presenter of the CWT possesses a particular proof-of-possession key. Being able to prove possession of a key is also sometimes described as being the holder-of-key. This specification provides equivalent functionality to “Proof-of-Possession Key Semantics for JSON Web Tokens (JWTs)” (RFC 7800) but using Concise Binary Object Representation (CBOR) and CWTs rather than JavaScript Object Notation (JSON) and JSON Web Tokens (JWTs).

Thanks to the ACE working group for completing this important specification.

The specification is available at:

An HTML-formatted version is also available at:

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