[CFRG] Re: Call for adoption: draft-google-cfrg-libzk-03 (Longfellow ZK)

[David Cook <[e-mail]>]

I support adoption of this draft. I have previously reviewed earlier
versions of the document, and helped implement a prior version with my
colleagues at ISRG. I would be willing to review the document if it is
adopted.

I had previously expressed hesitation about whether an IRTF RG was the
appropriate venue for this work, but I trust the judgement of the authors
and the chairs on this point. I am glad to see that the adoption call was
made for this document, and not for the topic of zero knowledge proofs, or
post-quantum secure zero knowledge proofs, as that allays my concerns. It's
great to see this work moving forward, and to see more people contributing
to it.
--David Cook

On Fri, Sep 25, 2026 at 12:09 PM Nick Sullivan <[e-mail]>
wrote:

> Dear CFRG,
>
> This message starts a two-week call for adoption of
> draft-google-cfrg-libzk-03, "Longfellow ZK", by Matteo Frigo and Abhi
> Shelat. The call ends on Friday October 9, 2026.
>
> https://www.ietf.org/archive/id/draft-google-cfrg-libzk-03.html
>
> The document specifies a post-quantum zero-knowledge argument system built
> to run on constrained devices while remaining expressive enough for
> real-world statements: ECDSA, SHA-256 and ML-DSA signature verification,
> string, integer and date comparisons, and basic parsing. Its Fiat-Shamir
> layer builds on the transformation the research group has already adopted,
> draft-irtf-cfrg-fiat-shamir-03.
>
> The authors presented the work at IETF 122 through 125. The current
> revision has taken feedback from a large number of external reviewers, at
> least two independent groups have implemented it from the specification,
> and the authors have a Lean 4 formalization of the protocol and of the
> circuits for ECDSA verification and SHA-256, which they intend to release
> for external audit once internal review is done.
>
> On relevance: drafts inside the IETF intend to build on this protocol, and
> outside the IETF it appears in eIDAS and EU age assurance documentation and
> is deployed in Google Wallet for digital identities and in India's UIDAI
> identity application.
>
> Please reply on the list with whether you support adoption, and whether
> you would review or implement the document if it is adopted. Objections
> should name a specific problem with the document or with CFRG taking it on.
> Adoption means change control passes to the research group; the authors
> have indicated they are ready for that.
>
> Thank you,
> Nick, for the CFRG chairs
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