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Arkworks bindings to Circom's R1CS, for Groth16 Proof and Witness generation in Rust.

Clone the repository and runcd ark-circom/ && cargo doc --open

[dependencies]ark-circom ="0.5.0"

// Load the WASM and R1CS for witness and proof generationlet cfg =CircomConfig::<Bn254>::new("./test-vectors/mycircuit.wasm","./test-vectors/mycircuit.r1cs",)?;// Insert our public inputs as key value pairsletmut builder =CircomBuilder::new(cfg);builder.push_input("a",3);builder.push_input("b",11);// Create an empty instance for setting it uplet circom = builder.setup();// Run a trusted setupletmut rng =thread_rng();let params =generate_random_parameters_with_reduction(circom,&mut rng)?;// Get the populated instance of the circuit with the witnesslet circom = builder.build()?;let inputs = circom.get_public_inputs().unwrap();// Generate the prooflet proof =prove(&params, circom,&mut rng)?;// Check that the proof is validlet pvk =process_vk(&params.vk)?;let verified =verify_with_processed_vk(&pvk,&inputs,&proof)?;assert!(verified);

Tests require the following installed:

1. solc. We also recommend usingsolc-select for more flexibility.
2. ganache-cli

• Witness generation using Circom's WASM witness code
• ZKey parsing into Arkworks Proving Key over BN254
• Compatibility layer for Ethereum types, so that proofs can be used in Solidity verifiers
• Proof generations and verification using Arkworks
• CLI for common operations

The prover key generated by circom differs from the one generated by arkworks' groth16 library. While the format is the same, it represents different values.Circom 'prepares' the powers of tau by converting them to Lagrange base, i.e. froms^i.G ->L_i(s).G. This affects the witness generation process, and the caller needs to ensure the correctR1CSToQAP implementer is used:

• useCircomReduction for working with circom-generated files,
• useLibsnarkReduction for setup produced using the arkworks backend.

This library would not have been possibly without the great work done in:

• zkutil
• snarkjs

Special shoutout toKobi Gurkan for all the help in parsing SnarkJS' ZKey file format.