Re: [Cfrg] Adoption request: draft-hdevalence-cfrg-ristretto

"Filippo Valsorda" <> Wed, 24 July 2019 10:24 UTC

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Date: Wed, 24 Jul 2019 12:24:52 +0200
From: "Filippo Valsorda" <>
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Subject: Re: [Cfrg] Adoption request: draft-hdevalence-cfrg-ristretto
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What are the next steps in discussing adoption of this draft?

I believe it would be especially timely, as ristretto255 provides a
better prime-order group than Curve25519 for OPRFs and PAKEs that are
being discussed by this group.

Moreover, Cas Cremers and Dennis Jackson recently published a new round
of small subgroup attacks that would have been avoided by Ristretto
adoption, as they mention in the paper.

2019-05-18 00:22 GMT+02:00 Filippo Valsorda <>io>:
> Hello,
> I'd like to request for the group to adopt
> draft-hdevalence-cfrg-ristretto for publication as an Informational RFC.
> Ristretto255 is a prime-order group designed by Henry de Valence,
> based on Mike Hamburg's Decaf. It provides a safe, efficient, and
> implementor-friendly abstraction for a prime-order group, enabling safer
> and simpler design of higher-level protocols. Its order is the same as
> the prime-order subgroup of Curve25519.
> Ristretto255 can easily be implemented on top of an existing Curve25519
> library, and the authors are providing multiple implementations in
> different languages: curve25519-dalek in Rust, by Isis Lovecruft
> and Henry de Valence; curve25519-elisabeth in Java, by Jack Grigg;
> ristretto255 in Go (implemented clean-room from the spec),
> by George Tankersley and myself; and ristretto-donna (forthcoming) in
> C, by Isis Lovecruft. We are also aware of other implementations we
> have not personally tested for interoperability, including one in Frank
> Denis's libsodium.
> Importantly, ristretto255 is a flexible abstraction, and can be
> implemented with different, more efficient curves than Curve25519. The
> draft only provides implementation details for a Curve25519 backend,
> but it defines the interface contract which is required of compliant
> implementations, allowing alternate backends.
> The group has already been adopted by some higher level protocols,
> including Bulletproofs by Chain, and has been subject of discussion on
> this list, including some good posts by Tony Arcieri. More information
> is available at and in the draft, and the
> authors and I are available to answer questions.
> Best, Filippo