[Cfrg] request for comments: hashing to ristretto255
rsw@cs.stanford.edu Wed, 12 August 2020 20:20 UTC
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Date: Wed, 12 Aug 2020 13:20:21 -0700
From: rsw@cs.stanford.edu
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Subject: [Cfrg] request for comments: hashing to ristretto255
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Hello, I'm writing on behalf of the hash-to-curve authors to request feedback on a proposed appendix for the hash-to-curve draft that specifies a method for hashing to ristretto255. The proposed appendix is here: https://github.com/cfrg/draft-irtf-cfrg-hash-to-curve/pull/294 The goal is to give a hash_to_ristretto255 function that is a drop-in replacement for the hash_to_curve function, in the sense that it gives the same API, the same security properties, and the same domain separation strategy. This should make it easy for protocols using a hash-to-curve function to migrate to ristretto255. (Note that hash_to_ristretto255 *does not* aim to return group elements with any particular relationship to the ones returned by hash_to_curve functions targeting curve25519 or edwards25519, as this would seemingly violate the ristretto255 abstraction.) In more detail: the ristretto255 draft specifies a FROM_UNIFORM_BYTES function that, on input a uniformly random 64-byte string, outputs a random ristretto255 element. The hash_to_ristretto function simply composes FROM_UNIFORM_BYTES with the same hashing primitives used in the hash_to_curve function. Your feedback, by email or on GitHub, would be very much appreciated! Best regards, -=rsw