Refactor: Keccak Permutation #3675
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* replace single-shot ::expand() with more versatile ::squeeze() * use BufferStuffer/BufferSlicer in ::squeeze() and ::absorb() * remove low-level access to Keccak state * remove static Keccak state mutation methods * ::permute() is now private
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This was referenced Aug 19, 2023
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Closing, after @falko-strenzke squashed my changes into #3673. |
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Pull Request Dependencies
This builds on top of #3673. @falko-strenzke feel free to incorporate my two patches into your PR and squash it all together. We could then just close this one and merge your's.
Description
This applies further cleanup to
Keccak_Permutationand widens its versatility somewhat. Most notably:Replace single-shot
::expand()with more versatile::squeeze()Just like
::absorb()before,::squeeze()can be called multiple times with arbitrary-length buffers. That's really useful for implementing XOFs (see eXtendable Output Functions as first-class citizen #3671).use
BufferStuffer/BufferSlicerin::squeeze()and::absorb()That's more of a style thing to avoid some raw pointers and lots of offset shifting. IMHO, that makes the code as "readable" as it gets. 🤡
remove low-level access to Keccak state and static mutation methods
I believe that's actually the whole point of this new class: No more fiddling with Keccak-states and offset positions in the implementations of "SHA3", "SHAKE" and the "Keccak" hash. @falko-strenzke please make sure that this interface is enough to implement KMAC as well.
::permute() is now private
Its an implementation detail of the sponge construction and should be handled that way, I think. Or are there use cases where a downstream user would want to have control over when exactly
permute()should be called?My two cents
Was this refactoring worth it? I think so! The implementations of "SHA3", "SHAKE" and the upcoming "SHAKE" XOF are now super slim an concise. Note though, that the implementations for
SHA_3andKeccak_1600(the hash) are basically identical. I hope that's roughly what @randombit had in mind when we started arguing about the architecture back in February (#3279)