testudo/src/spartan.rs

use super::dense_mlpoly::EqPolynomial;
use super::errors::ProofVerifyError;
use super::r1csinstance::{
  R1CSCommitment, R1CSCommitmentGens, R1CSDecommitment, R1CSEvalProof, R1CSInstance,
  R1CSInstanceEvals, R1CSInstanceSize,
};
use super::r1csproof::{R1CSGens, R1CSProof};
use super::random::RandomTape;
use super::scalar::Scalar;
use super::timer::Timer;
use super::transcript::{AppendToTranscript, ProofTranscript};
use merlin::Transcript;
use serde::{Deserialize, Serialize};

pub struct SNARKGens {
  gens_r1cs_sat: R1CSGens,
  gens_r1cs_eval: R1CSCommitmentGens,
}

impl SNARKGens {
  pub fn new(size: &R1CSInstanceSize) -> Self {
    let gens_r1cs_sat = R1CSGens::new(size.get_num_cons(), size.get_num_vars(), b"gens_r1cs_sat");
    let gens_r1cs_eval = R1CSCommitmentGens::new(size, b"gens_r1cs_eval");
    SNARKGens {
      gens_r1cs_sat,
      gens_r1cs_eval,
    }
  }
}

#[derive(Serialize, Deserialize, Debug)]
pub struct SNARK {
  r1cs_sat_proof: R1CSProof,
  inst_evals: R1CSInstanceEvals,
  r1cs_eval_proof: R1CSEvalProof,
}

impl SNARK {
  fn protocol_name() -> &'static [u8] {
    b"Spartan SNARK proof"
  }

  /// A public computation to create a commitment to an R1CS instance
  pub fn encode(inst: &R1CSInstance, gens: &SNARKGens) -> (R1CSCommitment, R1CSDecommitment) {
    inst.commit(&gens.gens_r1cs_eval)
  }

  /// A method to produce a proof of the satisfiability of an R1CS instance
  pub fn prove(
    inst: &R1CSInstance,
    decomm: &R1CSDecommitment,
    vars: Vec<Scalar>,
    input: &[Scalar],
    gens: &SNARKGens,
    transcript: &mut Transcript,
  ) -> Self {
    // we create a Transcript object seeded with a random Scalar
    // to aid the prover produce its randomness
    let mut random_tape = RandomTape::new(b"proof");
    transcript.append_protocol_name(SNARK::protocol_name());
    let (r1cs_sat_proof, rx, ry) = {
      let (proof, rx, ry) = R1CSProof::prove(
        inst,
        vars,
        input,
        &gens.gens_r1cs_sat,
        transcript,
        &mut random_tape,
      );
      let proof_encoded: Vec<u8> = bincode::serialize(&proof).unwrap();
      Timer::print(&format!("len_r1cs_sat_proof {:?}", proof_encoded.len()));

      (proof, rx, ry)
    };

    // We send evaluations of A, B, C at r = (rx, ry) as claims
    // to enable the verifier complete the first sum-check
    let timer_eval = Timer::new("eval_sparse_polys");
    let inst_evals = {
      let eval_table_rx = EqPolynomial::new(rx.clone()).evals();
      let eval_table_ry = EqPolynomial::new(ry.clone()).evals();
      inst.evaluate_with_tables(&eval_table_rx, &eval_table_ry)
    };
    inst_evals.append_to_transcript(b"r1cs_inst_evals", transcript);
    timer_eval.stop();

    let r1cs_eval_proof = {
      let proof = R1CSEvalProof::prove(
        decomm,
        &rx,
        &ry,
        &inst_evals,
        &gens.gens_r1cs_eval,
        transcript,
        &mut random_tape,
      );

      let proof_encoded: Vec<u8> = bincode::serialize(&proof).unwrap();
      Timer::print(&format!("len_r1cs_eval_proof {:?}", proof_encoded.len()));
      proof
    };

    SNARK {
      r1cs_sat_proof,
      inst_evals,
      r1cs_eval_proof,
    }
  }

  /// A method to verify the proof of the satisfiability of an R1CS instance
  pub fn verify(
    &self,
    comm: &R1CSCommitment,
    input: &[Scalar],
    transcript: &mut Transcript,
    gens: &SNARKGens,
  ) -> Result<(), ProofVerifyError> {
    transcript.append_protocol_name(SNARK::protocol_name());

    let timer_sat_proof = Timer::new("verify_sat_proof");
    assert_eq!(input.len(), comm.get_num_inputs());
    let (rx, ry) = self
      .r1cs_sat_proof
      .verify(
        comm.get_num_vars(),
        comm.get_num_cons(),
        input,
        &self.inst_evals,
        transcript,
        &gens.gens_r1cs_sat,
      )
      .unwrap();
    timer_sat_proof.stop();

    let timer_eval_proof = Timer::new("verify_eval_proof");
    self
      .inst_evals
      .append_to_transcript(b"r1cs_inst_evals", transcript);
    assert!(self
      .r1cs_eval_proof
      .verify(
        comm,
        &rx,
        &ry,
        &self.inst_evals,
        &gens.gens_r1cs_eval,
        transcript
      )
      .is_ok());
    timer_eval_proof.stop();
    Ok(())
  }
}

pub struct NIZKGens {
  gens_r1cs_sat: R1CSGens,
}

impl NIZKGens {
  pub fn new(num_cons: usize, num_vars: usize) -> Self {
    let gens_r1cs_sat = R1CSGens::new(num_cons, num_vars, b"gens_r1cs_sat");
    NIZKGens { gens_r1cs_sat }
  }
}

#[derive(Serialize, Deserialize, Debug)]
pub struct NIZK {
  r1cs_sat_proof: R1CSProof,
  r: (Vec<Scalar>, Vec<Scalar>),
}

impl NIZK {
  fn protocol_name() -> &'static [u8] {
    b"Spartan NIZK proof"
  }

  /// A method to produce a proof of the satisfiability of an R1CS instance
  pub fn prove(
    inst: &R1CSInstance,
    vars: Vec<Scalar>,
    input: &[Scalar],
    gens: &NIZKGens,
    transcript: &mut Transcript,
  ) -> Self {
    // we create a Transcript object seeded with a random Scalar
    // to aid the prover produce its randomness
    let mut random_tape = RandomTape::new(b"proof");
    transcript.append_protocol_name(NIZK::protocol_name());
    let (r1cs_sat_proof, rx, ry) = {
      let (proof, rx, ry) = R1CSProof::prove(
        inst,
        vars,
        input,
        &gens.gens_r1cs_sat,
        transcript,
        &mut random_tape,
      );
      let proof_encoded: Vec<u8> = bincode::serialize(&proof).unwrap();
      Timer::print(&format!("len_r1cs_sat_proof {:?}", proof_encoded.len()));

      (proof, rx, ry)
    };

    NIZK {
      r1cs_sat_proof,
      r: (rx, ry),
    }
  }

  /// A method to verify the proof of the satisfiability of an R1CS instance
  pub fn verify(
    &self,
    inst: &R1CSInstance,
    input: &[Scalar],
    transcript: &mut Transcript,
    gens: &NIZKGens,
  ) -> Result<(), ProofVerifyError> {
    transcript.append_protocol_name(NIZK::protocol_name());

    // We send evaluations of A, B, C at r = (rx, ry) as claims
    // to enable the verifier complete the first sum-check
    let timer_eval = Timer::new("eval_sparse_polys");
    let (claimed_rx, claimed_ry) = &self.r;
    let inst_evals = {
      let eval_table_rx = EqPolynomial::new(claimed_rx.clone()).evals();
      let eval_table_ry = EqPolynomial::new(claimed_ry.clone()).evals();
      inst.evaluate_with_tables(&eval_table_rx, &eval_table_ry)
    };
    timer_eval.stop();

    let timer_sat_proof = Timer::new("verify_sat_proof");
    assert_eq!(input.len(), inst.get_num_inputs());
    let (rx, ry) = self
      .r1cs_sat_proof
      .verify(
        inst.get_num_vars(),
        inst.get_num_cons(),
        input,
        &inst_evals,
        transcript,
        &gens.gens_r1cs_sat,
      )
      .unwrap();

    // verify if claimed rx and ry are correct
    assert_eq!(rx, *claimed_rx);
    assert_eq!(ry, *claimed_ry);
    timer_sat_proof.stop();

    Ok(())
  }
}

#[cfg(test)]
mod tests {
  use super::*;

  #[test]
  pub fn check_snark() {
    let num_vars = 256;
    let num_cons = num_vars;
    let num_inputs = 10;
    let (inst, vars, input) = R1CSInstance::produce_synthetic_r1cs(num_cons, num_vars, num_inputs);
    let r1cs_size = inst.size();

    // produce public generators
    let gens = SNARKGens::new(&r1cs_size);

    // create a commitment to R1CSInstance
    let (comm, decomm) = SNARK::encode(&inst, &gens);

    // produce a proof
    let mut prover_transcript = Transcript::new(b"example");
    let proof = SNARK::prove(&inst, &decomm, vars, &input, &gens, &mut prover_transcript);

    // verify the proof
    let mut verifier_transcript = Transcript::new(b"example");
    assert!(proof
      .verify(&comm, &input, &mut verifier_transcript, &gens)
      .is_ok());
  }
}