circom-prover spec

[vivianjeng]

Problem

Related to #224

1. Current mopro depends on ark-circom version but we need to patch it to get the correct version: zkmopro/circom-compat
   • we replace wasmer with rust-witness. So we remove whole wasmer dependencies in zkmopro/circom-compat
   • There are a lot of problems with wasmer in mobile. Checkout issues
   • See: Circom Comparison for more details
2. We only use a few functions in mopro and we write prove in mopro with ark-groth16
   • What we use in mopro
     

     mopro/mopro-ffi/src/circom/mod.rs

     Lines 16 to 18 in e424efd

     	use ark_circom::{
     	read_proving_key, read_zkey, CircomReduction, FieldSerialization, ZkeyHeaderReader,
     	};

   • how we prove in circom
     

     mopro/mopro-ffi/src/circom/mod.rs

     Lines 198 to 206 in e424efd

     	let ark_proof = Groth16::<T, CircomReduction>::create_proof_with_reduction_and_matrices(
     	&pkey,
     	r,
     	s,
     	&matrices,
     	matrices.num_instance_variables,
     	matrices.num_constraints,
     	witness_fr.as_slice(),
     	);

   • We can maintain our own circom-prover to perform these functions.
3. We have several adapters (now or in the future). We need to easily switch between adapters
   • We are doing research on GPU acceleration: https://github.com/zkmopro/gpu-acceleration
     If it improves the performance enough, we can switch from ark-groth16 to e.g. gpu-groth16
   • We might have other witness generator in the future. e.g. circom-witnesscalc or witnesscalc

We can maintain our own circom-prover for cross-platform solution, and we can publish our packages.
In the future, we can encourage ZK applications (e.g. Semaphore) to use the crate circom-prover instead of circom-compat for cross-platform proving.

Details

Similar to circom-compat
It maintains the functions we need in mopro-ffi

mopro/mopro-ffi/src/circom/mod.rs

Lines 16 to 18 in e424efd

	use ark_circom::{
	read_proving_key, read_zkey, CircomReduction, FieldSerialization, ZkeyHeaderReader,
	};

mopro/mopro-ffi/src/circom/serialization.rs

Line 3 in e424efd

use ark_circom::ethereum;

It can also export functions called prove, verify
like it does in mopro-ffi

mopro/mopro-ffi/src/circom/mod.rs

Lines 198 to 206 in e424efd

	let ark_proof = Groth16::<T, CircomReduction>::create_proof_with_reduction_and_matrices(
	&pkey,
	r,
	s,
	&matrices,
	matrices.num_instance_variables,
	matrices.num_constraints,
	witness_fr.as_slice(),
	);

mopro/mopro-ffi/src/circom/mod.rs

Lines 248 to 252 in e424efd

	let verified = Groth16::<T, CircomReduction>::verify_with_processed_vk(
	&pvk,
	&public_inputs_fr,
	&proof_parsed.0,
	)?;

so we can remove duplicated dependencies e.g. ark_groth16, ark_ec in mopro-ffi

Acceptance criteria

• Create a repo in zkmopro called circom-prover (or other name)
• replace the ark-circom dependency in mopro-ffi with circom-prover

Next steps (optional)

Publish the crate so we can close #224