Tobias Looker and I have published an updated Barreto-Lynn-Scott Elliptic Curve Key Representations for JOSE and COSE specification in preparation for IETF 118 in Prague. This one of suite of IETF and IRTF specifications, including BLS Signatures and JSON Web Proofs that are coming together to enable standards for the use of JSON-based and CBOR-based tokens utilizing zero-knowledge proofs.
The specification is available at:
Tobias Looker and I have published an updated CBOR Web Token (CWT) Claims in COSE Headers specification that addresses the IETF Last Call (WGLC) comments received. Changes made were:
The specification is available at:
The specification is scheduled for the IESG telechat on November 30, 2023.
Orie Steele and I have updated the “Fully-Specified Algorithms for JOSE and COSE” specification in preparation for presentation and discussions at IETF 118 in Prague. The updates address comments received during the discussions at IETF 117 and afterwards. Specifically, this draft adds descriptions of key representations and of algorithms not updated by the specification. See my original post about the spec for why fully-specified algorithms matter.
Hopefully working group adoption will be considered by the JOSE working group during IETF 118.
The specification is available at:
I’ve had two different IETF specifications adopted by two different working groups in the last two days – a pleasant coincidence! Yesterday, the COSE “typ” (type) Header Parameter specification was adopted by the COSE working group. Today, the OAuth 2.0 Protected Resource Metadata specification was adopted by the OAuth working group. Their journeys from individual drafts to working group drafts couldn’t have been more different!
As I was musing with Phil Hunt, who wrote the original individual draft of OAuth 2.0 Protected Resource Metadata with me, I’m pretty sure that this is the longest time from writing an individual draft to it becoming a working group draft in my experience: August 3, 2016 to September 6, 2023 – seven years and a month!
Whereas, the time from the individual draft of COSE “typ” (type) Header Parameter to the first working group draft was only three months: July 8, 2023 to September 5, 2023. Which got me thinking… Is that the fastest progression I’ve had?
It turns out that my fastest time from individual draft to working group draft was for the JWK Thumbprint URI specification which I wrote with Kristina Yasuda. It went from individual draft to working group draft in only two months: November 24, 2021 to January 28, 2022. (And it became RFC 9278 on August 9, 2022 – less than nine months from start to finish, which I believe is also a personal record.)
Ironically, while OAuth 2.0 Protected Resource Metadata took over seven years from individual to working group drafts, a closely-related draft, OAuth 2.0 Discovery (which became RFC 8414) was previously my fastest from individual draft to working group draft: 2.5 months! (The journey to becoming an RFC took 2.5 years.)
The other relative speed demon was Proof-Of-Possession Semantics for JSON Web Tokens (JWTs): 3.5 months from individual draft to working group draft and two years from start to RFC 7800.
What are my takeaways from all these musings about starting things?
Orie Steele and I have written a new specification creating algorithm identifiers for JOSE and COSE that fully specify the cryptographic operations to be performed – something we’d promised to do during our presentation to the JOSE working group at IETF 117. The introduction to the specification (quoted below) describes why this matters.
The IANA algorithm registries for JOSE [IANA.JOSE.Algorithms] and COSE [IANA.COSE.Algorithms] contain two kinds of algorithm identifiers:
RS256 and ES256K in both JOSE and COSE and ES256 in JOSE.EdDSA in both JOSE and COSE and ES256 in COSE.This matters because many protocols negotiate supported operations using only algorithm identifiers. For instance, OAuth Authorization Server Metadata [RFC8414] uses negotiation parameters like these (from an example in the specification):
"token_endpoint_auth_signing_alg_values_supported": ["RS256", "ES256"]
OpenID Connect Discovery [OpenID.Discovery] likewise negotiates supported algorithms using alg and enc values. W3C Web Authentication [WebAuthn] and FIDO Client to Authenticator Protocol (CTAP) [FIDO2] negotiate using COSE alg numbers.
This does not work for polymorphic algorithms. For instance, with EdDSA, you do not know which of the curves Ed25519 and/or Ed448 are supported! This causes real problems in practice.
WebAuthn contains this de-facto algorithm definition to work around this problem:
-8 (EdDSA), where crv is 6 (Ed25519)
This redefines the COSE EdDSA algorithm identifier for the purposes of WebAuthn to restrict it to using the Ed25519 curve – making it non-polymorphic so that algorithm negotiation can succeed, but also effectively eliminating the possibility of using Ed448. Other similar workarounds for polymorphic algorithm identifiers are used in practice.
This specification creates fully-specified algorithm identifiers for all registered polymorphic JOSE and COSE algorithms and their parameters, enabling applications to use only fully-specified algorithm identifiers. It furthermore deprecates the practice of registering polymorphic algorithm identifiers.
The specification is available at:
Orie Steele and I have updated the COSE “typ” (type) Header Parameter Specification to address feedback received during IETF 117 in San Francisco. Specifically, the spec now requires that the typ header parameter only be used in the protected header parameters. And we described the implications of the unprotected header parameters changing.
The specification is available at:
We believe that having done this, the spec is now ready for working group adoption.
Orie Steele and I have created a specification to add a typ header parameter to COSE – something increasingly widely used in JOSE but currently missing in COSE. The introduction to the spec tells the story:
CBOR Object Signing and Encryption (COSE) [RFC9052] defines header parameters that parallel many of those defined by the JSON Object Signing and Encryption (JOSE) [RFC7515] [RFC7516] specifications. However, one way in which COSE does not provide equivalent functionality to JOSE is that it does not define an equivalent of the
typ(type) header parameter, which is used for declaring the type of the entire JOSE data structure. The security benefits of havingtyp(type) are described in the JSON Web Token Best Current Practices [RFC8725], which recommends its use for “explicit typing” — usingtypvalues to distinguish between different kinds of objects.This specification adds the equivalent of the JOSE
typ(type) header parameter to COSE so that the benefits of explicit typing can be brought to COSE objects. The syntax of the COSE type header parameter value is the same as the existing COSE content type header parameter, allowing both integer CoAP Content-Formats [IANA.CoAP.ContentFormats] values and string Media Type [IANA.MediaTypes] values to be used.
The specification is available at:
We plan to socialize this specification at IETF 117 in San Francisco later this month.
Tobias Looker and I have published an updated CBOR Web Token (CWT) Claims in COSE Headers draft that addresses the COSE Working Group Last Call (WGLC) comments received. Changes made were:
The specification is available at:
Following a call for adoption by the restarted JSON Object Signing and Encryption (JOSE) Working Group, I’m pleased to report that the three initial working group specifications have been published. They are:
JSON Web Proof, with abstract:
This document defines a new container format similar in purpose and design to JSON Web Signature (JWS) called a JSON Web Proof (JWP). Unlike JWS, which integrity-protects only a single payload, JWP can integrity-protect multiple payloads in one message. It also specifies a new presentation form that supports selective disclosure of individual payloads, enables additional proof computation, and adds a protected header to prevent replay and support binding mechanisms.
JSON Proof Algorithms, with abstract:
The JSON Proof Algorithms (JPA) specification registers cryptographic algorithms and identifiers to be used with the JSON Web Proof (JWP) and JSON Web Key (JWK) specifications. It defines several IANA registries for these identifiers.
JSON Proof Token, with abstract:
JSON Proof Token (JPT) is a compact, URL-safe, privacy-preserving representation of claims to be transferred between three parties. The claims in a JPT are encoded as base64url-encoded JSON objects that are used as the payloads of a JSON Web Proof (JWP) structure, enabling them to be digitally signed and selectively disclosed. JPTs also support reusability and unlinkability when using Zero-Knowledge Proofs (ZKPs).
Thanks to Jeremie Miller and David Waite for helping us get there!
I’m thrilled that the IETF has restarted the JSON Object Signing and Encryption (JOSE) Working Group. It’s chartered to work on JSON- and CBOR-based representations for Zero-Knowledge Proofs (ZKPs), selective disclosure enabling minimal disclosure, and non-correlatable presentation. The representations are planned to use the three-party model of Issuer, Holder, and Verifier utilized by Verifiable Credentials.
See the newly approved JOSE charter at https://datatracker.ietf.org/doc/charter-ietf-jose/03/. The working group will be chaired by Karen O’Donoghue, John Bradley, and John Mattsson, with the assigned area director being Roman Danyliw.
I believe this is a great outcome because the JOSE working group participants already have expertise creating simple, widely-adopted JSON-based cryptographic formats, such as JSON Web Signature (JWS), JSON Web Encryption (JWE), and JSON Web Key (JWK). The new formats will be peers to JWS, JWE, and COSE, reusing elements that make sense, while enabling use of new cryptographic algorithms whose inputs and outputs are not representable in the existing JOSE and COSE formats.
If you’re interested in the work, please join the JOSE mailing list at https://www.ietf.org/mailman/listinfo/jose if you’re not already a member. Also, plan to participate in IETF 116 Yokohama, where we should be able to have the first meeting of the reconstituted working group. I hope to see you there!
As background, the first step in the JOSE rechartering was the JSON Web Proofs (JWP) BoF at IETF 114 in Philadelphia sponsored by Security Area Director Roman Danyliw and chaired by Karen O’Donoghue and John Bradley, during which Jeremie Miller, Kristina Yasuda, Tobias Looker, and I presented. That was follwed by a Virtual Interim JWP BoF in October, 2022, review on the ietf-announce mailing list, and multiple IESG discussions.
All of which brings us back to the (now recurring!) question: “What Would JOSE Do?” Join us and be part of answering it!
This week, Tobias Looker and I submitted two individual Internet Drafts for consideration by the COSE working group.
The first is “Barreto-Lynn-Scott Elliptic Curve Key Representations for JOSE and COSE“, the abstract of which is:
This specification defines how to represent cryptographic keys for the pairing-friendly elliptic curves known as Barreto-Lynn-Scott (BLS), for use with the key representation formats of JSON Web Key (JWK) and COSE (COSE_Key).
These curves are used in Zero-Knowledge Proof (ZKP) representations for JOSE and COSE, where the ZKPs use the CFRG drafts “Pairing-Friendly Curves” and “BLS Signatures“.
The second is “CBOR Web Token (CWT) Claims in COSE Headers“, the abstract of which is:
This document describes how to include CBOR Web Token (CWT) claims in the header parameters of any COSE structure. This functionality helps to facilitate applications that wish to make use of CBOR Web Token (CWT) claims in encrypted COSE structures and/or COSE structures featuring detached signatures, while having some of those claims be available before decryption and/or without inspecting the detached payload.
JWTs define a mechanism for replicating claims as header parameter values, but CWTs have been missing the equivalent capability to date. The use case is the same as that which motivated Section 5.3 of JWT “Replicating Claims as Header Parameters” – encrypted CWTs for which you’d like to have unencrypted instances of particular claims to determine how to process the CWT prior to decrypting it.
We plan to discuss both with the COSE working group at IETF 113 in Vienna.
The Concise Binary Object Representation (CBOR) Tags for Date specification has now been published as RFC 8943. In particular, the full-date tag requested for use by the ISO Mobile Driver’s License specification in the ISO/IEC JTC 1/SC 17 “Cards and security devices for personal identification” working group has been created by this RFC. The abstract of the RFC is:
The Concise Binary Object Representation (CBOR), as specified in RFC 7049, is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation.
In CBOR, one point of extensibility is the definition of CBOR tags. RFC 7049 defines two tags for time: CBOR tag 0 (date/time string as per RFC 3339) and tag 1 (POSIX “seconds since the epoch”). Since then, additional requirements have become known. This specification defines a CBOR tag for a date text string (as per RFC 3339) for applications needing a textual date representation within the Gregorian calendar without a time. It also defines a CBOR tag for days since the date 1970-01-01 in the Gregorian calendar for applications needing a numeric date representation without a time. This specification is the reference document for IANA registration of the CBOR tags defined.
Note that a gifted musical singer/songwriter appears in this RFC in a contextually appropriate fashion, should you need an additional incentive to read the specification. ;-)
The “Concise Binary Object Representation (CBOR) Tags for Date” specification has completed IETF last call and advanced to evaluation by the Internet Engineering Steering Group (IESG). This is the specification that defines the full-date tag requested for use by the ISO Mobile Driver’s License specification in the ISO/IEC JTC 1/SC 17 “Cards and security devices for personal identification” working group.
The specification is available at:
An HTML-formatted version is also available at:
The 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 COSERS384 — RSASSA-PKCS1-v1_5 using SHA-384 — new for COSERS512 — RSASSA-PKCS1-v1_5 using SHA-512 — new for COSERS1 — RSASSA-PKCS1-v1_5 using SHA-1 — new for COSEES256K — ECDSA using secp256k1 curve and SHA-256 — new for COSE and JOSEThe elliptic curves registered are:
secp256k1 — SECG secp256k1 curve — new for COSE and JOSESee them in the IANA COSE Registry and the IANA JOSE Registry.
We 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 COSERS384 — RSASSA-PKCS1-v1_5 using SHA-384 — new for COSERS512 — RSASSA-PKCS1-v1_5 using SHA-512 — new for COSERS1 — RSASSA-PKCS1-v1_5 using SHA-1 — new for COSEES256K — ECDSA using secp256k1 curve and SHA-256 — new for COSE and JOSEThe elliptic curves registered are:
secp256k1 — SECG secp256k1 curve — new for COSE and JOSEThe CBOR tags for the date representations defined by the “Concise Binary Object Representation (CBOR) Tags for Date” specification have been registered in the IANA Concise Binary Object Representation (CBOR) Tags registry. This means that they’re now ready for use by applications. In particular, the full-date tag requested for use by the ISO Mobile Driver’s License specification in the ISO/IEC JTC 1/SC 17 “Cards and security devices for personal identification” working group is now good to go.
FYI, I also updated the spec to incorporate a few editorial suggestions by Carsten Bormann. The new draft changed “positive or negative” to “unsigned or negative” and added an implementation note about the relationship to Modified Julian Dates. Thanks Carsten, for the useful feedback, as always!
It’s my sense that the spec is now ready for working group last call in the CBOR Working Group.
The specification is available at:
An HTML-formatted version is also available at:
IANA 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.
This 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:
The IETF CBOR working group has adopted the specification Concise Binary Object Representation (CBOR) Tags for Date. The abstract of the specification is:
The Concise Binary Object Representation (CBOR, RFC 7049) is a data format whose design goals include the possibility of extremely small code size, fairly small message size, and extensibility without the need for version negotiation.
In CBOR, one point of extensibility is the definition of CBOR tags. RFC 7049 defines two tags for time: CBOR tag 0 (RFC 3339 date/time string) and tag 1 (Posix “seconds since the epoch”). Since then, additional requirements have become known. This specification defines a CBOR tag for an RFC 3339 date text string, for applications needing a textual date representation without a time. It also defines a CBOR tag for days since the Posix epoch, for applications needing a numeric date representation without a time. It is intended as the reference document for the IANA registration of the CBOR tags defined.
The need for this arose for the ISO Mobile Driver’s License specification in the working group ISO/IEC JTC 1/SC 17 “Cards and security devices for personal identification”.
The specification is available at:
An HTML-formatted version is also available at:
I’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.
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