Unify the computation of digests and challenges in different folding schemes #94
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…`PoseidonTranscript{Var}`
Note that now `absorb_point` only supports hashing points whose BaseField is equal to the sponge's field
arnaucube
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This is great! Very nice!
Unifying the transcripts and hashes and polishing the absorbs of points and nonnative elements was a pending task!
Really like the approach of extending the arkworks Sponge trait.
Also, as with your previous PRs, thanks a lot for all the good comments/docs along the code, they are very insightful!
Just a couple of small questions.
| pub trait AbsorbNonNative<F: PrimeField> { | ||
| /// Converts the object into field elements that can be absorbed by a `CryptographicSponge`. | ||
| /// Append the list to `dest` | ||
| fn to_native_sponge_field_elements(&self, dest: &mut Vec<F>); |
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One question, I've tried to find where the to_native_sponge_field_elements is used and haven't succeed (other than structs implementing the method to implement the AbsorbNonNative trait). The usages of the AbsorbNonNative trait that I've found use the one that returns the Vec<F> instead of modifying a given dest input value.
Does the AbsorbNonNative have the method with the dest param in order to match the native Absorb trait, which internally uses a similar method from arkworks (also modifying the dest param)?
I observed that in Nova, we compute the challenges and digests by manually constructing the input vectors to
CRH{Var}::evaluate, while in ProtoGalaxy, we haveProtoGalaxyTranscriptfor absorbing the inputs to a sponge.It would be beneficial to unify the way we derive challenges and digests in different folding schemes, and thus I created this PR and made several changes in challenge generation and digest computation. Notably,
PoseidonTranscript{Var}, the wrappers ofPoseidonSponge{Var}, are removed. Instead,PoseidonSponge{Var}now implements theTranscript{Var}traits directly and supports both digest computation and challenge generation.PoseidonSponge{Var}for both purposes. One still needs to create two separate instances, e.g.,spongeandtranscript, for digest computation and challenge generation respectively.Transcript{Var}traits now allow absorbing any non-native values (e.g., integers, points, CycleFold instances), as long as they implementAbsorbNonNative{Gadget}.Transcript{Var}::absorb_pointmethod now is solely for absorbing native points (i.e., those whose base field is also the sponge's field), so someabsorb_pointcalls are replaced withabsorb_nonnative.CommittedInstance{Var}::hashand{CycleFold}ChallengeGadget::get_challenge_{native, gadget}now use the absorb methods provided byPoseidonSponge{Var}andTranscript{Var}.ProtoGalaxyTranscriptis removed in favor of implementingAbsorb{Gadget}forCommittedInstance{Var}.Yet, as this PR focuses on code quality and does not introduce bug fixes or new functionalities, we can lower the priority of merging it.