Replace with pure rust implementation of libsecp256k1

[Gauthamastro]

PR replaces the secp256k1 with paritytech's libsecp256k1 which is a pure rust implementation.

[elichai]

Thanks for opening a PR :) May I ask what is the motivation behind this PR? Thanks!

[Gauthamastro]

We are using this library inside Intel's software extension guard (SGX) environment, which has issues with C code the current version of libsecp256k1 has. It would be great to have a pure rust version, so we don't need to maintain a fork just for this.

Other than that,

1. Pretty much no change in API
2. Pure rust version well maintained and used in production blockchains ( Polkadot, Kusama, to name a few)

So I really don't see a reason why not to add it.

[elichai]

Thanks for responding, Does this patch works for you? because it only changed test related stuff, the actual usage of secp256k1 is inside of the underlying math library https://github.com/ZenGo-X/curv

Also, I'd love to try and help you compile this as is on SGX, there's no reason this won't work.

As for repalcing the secp256k1 backend of curv please see https://github.com/ZenGo-X/curv/pull/44 and https://github.com/ZenGo-X/curv/issues/43

[Gauthamastro]

Thanks for responding, Does this patch works for you? because it only changed test related stuff, the actual usage of secp256k1 is inside of the underlying math library https://github.com/ZenGo-X/curv

Also, I'd love to try and help you compile this as is on SGX, there's no reason this won't work.

As for repalcing the secp256k1 backend of curv please see ZenGo-X/curv#44 and ZenGo-X/curv#43

Here you go, please check this: https://github.com/ZenGo-X/curv/pull/135

Right now, I am using a fork of libsecp256k1 for the PR but as soon as https://github.com/paritytech/libsecp256k1/pull/80 merges, I will change the dependency to official repo

[Gauthamastro]

Closing this as per our discussion in telegram.