Groth16 bls12-381 Solidity Verifier Template

[rubydusa]

I wrote a solidity verifier template for Groth16 that uses the new BLS12-381 precompiles as defined in EIP-2537

feats:

• different format for verification key json export using -bls12381-solidity flag in zkey export verificationkey
• export solidity calldata for new verifier

I implemented this in a way so it could be easy to extend bls12381 solidity verifiers for other zk proof types.

Manual test instructions:

fib.circom:

pragma circom 2.1.4;

template Fib(N) {
	signal input a1;
	signal input a2;

	signal output out;

	if (N == 1) {
		out <== a1; 
	}
	else if (N == 2) {
		out <== a2;
	}
	else {
		var b1 = a1;
		var b2 = a1 + a2;
		var i = N - 2;

		var inter = 0;

		while (i > 0) {
			inter = b2;
			b2 = b2 + b1;
			b1 = inter;
			
			i--;
		}

		out <== b2;
	}

}

component main = Fib(5);

input.json:

{
    "a1": 1,
    "a2": 1
}

run:

# compile
circom fib.circom --r1cs --wasm --prime bls12381

# powers of tau
snarkjs powersoftau new bls12381 10 pot_0000.ptau
snarkjs powersoftau contribute pot_0000.ptau pot_0001.ptau --name="Ram" --entropy="entropy"
snarkjs powersoftau beacon pot_0001.ptau pot_beacon.ptau 0102030405060708090a0b0c0d0e0f101112131415161718191a1b1c1d1e1f 10
snarkjs powersoftau prepare phase2 pot_beacon.ptau pot_final.ptau

# genrerate solidity verifier
snarkjs groth16 setup fib.r1cs pot_final.ptau fib.zkey
snarkjs zkey export verificationkey -bls12381-solidity fib.zkey verification_key.json
snarkjs zkey export solidityverifier fib.zkey verifier.sol

# generate proof calldata
node fib_js/generate_witness.js fib_js/fib.wasm input.json witness.wtns
snarkjs groth16 prove fib.zkey witness.wtns proof.json public.json
snarkjs zkey export soliditycalldata public.json proof.json