Poseidon hash supported in gnark

[devon1209]

Consensys/gnark-crypto#553

In this PR, I saw that Poseidon2 has been partially implemented.
I’d like to know whether this hash has been audited, and whether there are any plans to also implement the original Poseidon hash for interoperability.

[ivokub]

Hi, thanks for the interest!

Our Poseidon2 afaik is not audited yet. There are still some optimizations we're working on. We probably will audit next year, but don't have timeline for that. And if we do, then I'm not sure we would audit all instances, but perhaps for BLS12-377 and Koalabear.

We don't plan to implement Poseidon.

[devon1209]

Thanks for the reply.
In an EVM environment (bn254), which hash functions does gnark target for zk proving?
I’m also wondering whether there are plans to support Poseidon2 for cases with t > 4 as well.

[ivokub]

For zk proving its best to use Legacy Keccak. See https://pkg.go.dev/github.com/consensys/gnark@v0.14.0/backend/solidity#WithProverTargetSolidityVerifier
It is cheapest for verifying the Groth16 proofs.

And if you want to verify the proofs locally, then you should use https://pkg.go.dev/github.com/consensys/gnark@v0.14.0/backend/solidity#WithVerifierTargetSolidityVerifier option, otherwise the default native verifier uses SHA2 afaik.

[devon1209]

Thanks, but I was actually asking about zk-friendly hash functions that can be used inside the circuit.

[devon1209]

Hi @ivokub
I’ve made a contribution to this issue.
Could you please review it? Thanks :)