x/crypto/sha3: add Keccak 256 support

[pascaldekloe]

Ethereum and other crypto chains use the "original" Keccak hash. The difference is a dsbyte of 1 instead of 6 as in func NewKeccak256() hash.Hash { return &state{rate: 136, outputLen: 32, dsbyte: 0x01} }.

Can we support this Hash in the library or allow the specification of the domain separation byte in some way?

[odeke-em]

/cc @agl @aead and other crypto folks.

[aead]

I'm not a member of the Go team and this my personal opinion.

@pascaldekloe
I think adding more functions to the sha3 package isn't a good idea. The package already contains some complexity for its users (see the long doc). Further the package is named sha3 (not keccak), so it should implement the SHA-3 standard (and the "improved version" SHAKE).

Adam (@agl) once said:

Go only tries to meet the 90%-need in order to keep things simple.

I'm not sure whether it's worth to add a new keccak package - probably not. It would be basically a copy of the sha3 package - but of course @agl has to decide about this.

Keccak256 is just very small modification (1 byte modification!) to sha3, similar to shake better to extend sha3 package, not create a new one.

[FiloSottile]

Based on discussion with @agl, @bradfitz, @ianlancetaylor, accepted with symbol name NewLegacyKeccak256.

Let us know if Ethereum also uses the 128 variant.

[splix]

@FiloSottile Ethereum's Go code uses only 256 variant

for reference https://github.com/ethereumproject/go-ethereum/blob/master/crypto/sha3/hashes.go

[pascaldekloe]

Shall CL106462 be used to make the change or should I create a new one?

[leonklingele]

s/NewKeccak/NewLegacyKeccak/g and jettison the non-256bit variants?