Why Hash instead of Digest?

[skaunov]

Why was it chosen for Bls12 to implement Hash? It seems to me that Hash doesn't suppose a cryptographic function and mostly used for HashMap and such things; while cryptohash are defined by something like Digest trait.

[burdges]

Bls12 is a ZST, so hashing it does nothing. It likely supports Hash to help derive Hash elsewhere.

Hasher is the non-cryptographic analog of Digest. Afaik Digest only handles bytes, so no analog of Hash exists for Digest

[skaunov]

Thank you! Sorry in advance if I ask anything stupid...

AFAIU its Hash is used so that user could hash something to curve for further pairing. Now I wonder if it's possible it was intended to be HashToCurve (maybe indirectly), but ended up this way... 🤔 Did you ever encounter arkworks-rs Hash in the wild? Now I want to see one! 👓

Bls12 is a ZST, so hashing it does nothing. It likely supports Hash to help derive Hash elsewhere.

Isn't it on purpose? I mean representing anything as bytearray enables few usefull properties for cryptography, and isn't that restrictive. (Just not needed outside of crypto context, but I feel like Bls12 very much in.)

Hasher is the non-cryptographic analog of Digest. Afaik Digest only handles bytes, so no analog of Hash exists for Digest

[skaunov]

On the second look it really looks like to be able to HashMap points and elements if one would need this: https://docs.rs/ark-ec/0.4.2/ark_ec/?search=Hasher.

I would add that hashing to curve is currently so confusing I was quite sure it doesn't work yet until I found some code from a fellow who actually run it. I mean having it more clear would prevent this discussion. X) At least some note at hashing module...