Contracts pallet - Add support for recovering public key from elliptic curve signatures (ECDSA)

[PierreOssun]

Can we add support for recovering public key from elliptic curve signatures (ECDSA) to !ink ?

We are trying to implement an ECDSA verifier in a contract. For this we are using recover function from the libsecp256k1 library developed by Parity and also used in Substrate.
The problem is that it uses a big list of constants that made cargo build fail due to its huge file size.
As a note : We could compile the contract using rustflags to increase memory and the optimized WASM file size was 1.3 Mb

In Ethereum, the ecrecover function is implemented as a precompiled contract and can be called from any contract.
A suggested solution is to implement the EDCSA recover pub key logic in contracts-pallet level, so that it can be used by !ink contracts via ext calls (as it was implemented for hashes).
What do you think ?

[cmichi]

If we want to have this it would have to be implemented in the contracts pallet. I'm moving the issue to the appropriate repository.

cc @athei

[athei]

Makes sense to me. Contracts should not contain cryptographic code as it makes them way to big.

For this we are using recover function from the libsecp256k1 library developed by Parity and also used in Substrate.

A quick grep in substrate seems to suggest that it is in some Cargo.toml files but in no source file. Maybe an unused dependency. @gilescope what do you think?

[PierreOssun]

Hello @athei
It is used here:

substrate/primitives/core/src/ecdsa.rs

Line 511 in 16e17ae

/// Verify a signature on a message. Returns true if the signature is good.

[bkchr]

@athei you probably want to use this here:

substrate/primitives/io/src/lib.rs

Line 784 in b79e2b9

fn secp256k1_ecdsa_recover(

And as @PierreOssun already pointed out, we use it in several places.

[athei]

Yeah I messed up my grep. This is great. We can use existing client functions for that.

[PierreOssun]

@athei
If you agree to implement it, Supercolony can take care of it and do a Pull Request

[athei]

@athei
If you agree to implement it, Supercolony can take care of it and do a Pull Request

That would be great. But keep in mind that the biggest part of implementing this feature will be adding tests and benchmarks.

[atenjin]

related to #8989, we think we not only need ecdsa recover, we also need more functions.

[xgreenx]

related to #8989, we think we not only need ecdsa recover, we also need more functions.

Yea, but recovery is a feature only for ECDSA when verifying and signing must be implemented for all three supported key pairs.