1/// This example does the hash chain but in the naive approach: instead of using folding, it does a
  2/// big circuit containing n instantiations of the sha256 constraints.
  3
  4#[cfg(test)]
  5mod tests {
  6    use ark_bn254::{Bn254, Fr};
  7
  8    use ark_groth16::Groth16;
  9    use ark_snark::SNARK;
 10
 11    use ark_ff::PrimeField;
 12
 13    use std::time::Instant;
 14
 15    use ark_crypto_primitives::crh::sha256::{constraints::Sha256Gadget, digest::Digest, Sha256};
 16    use ark_r1cs_std::fields::fp::FpVar;
 17    use ark_r1cs_std::{alloc::AllocVar, eq::EqGadget};
 18    use ark_r1cs_std::{bits::uint8::UInt8, boolean::Boolean, ToBitsGadget, ToBytesGadget};
 19    use ark_relations::r1cs::{
 20        ConstraintSynthesizer, ConstraintSystem, ConstraintSystemRef, SynthesisError,
 21    };
 22
 23    use crate::utils::tests::*;
 24
 25    /// Test circuit to be folded
 26    #[derive(Clone, Debug)]
 27    pub struct SHA256ChainCircuit<F: PrimeField, const N: usize, const HASHES_PER_STEP: usize> {
 28        z_0: Option<Vec<F>>,
 29        z_n: Option<Vec<F>>,
 30    }
 31    impl<F: PrimeField, const N: usize, const HASHES_PER_STEP: usize> ConstraintSynthesizer<F>
 32        for SHA256ChainCircuit<F, N, HASHES_PER_STEP>
 33    {
 34        fn generate_constraints(self, cs: ConstraintSystemRef<F>) -> Result<(), SynthesisError> {
 35            let z_0 = Vec::<FpVar<F>>::new_witness(cs.clone(), || {
 36                Ok(self.z_0.unwrap_or(vec![F::zero()]))
 37            })?;
 38            let z_n =
 39                Vec::<FpVar<F>>::new_input(cs.clone(), || Ok(self.z_n.unwrap_or(vec![F::zero()])))?;
 40            let mut z_i: Vec<FpVar<F>> = z_0.clone();
 41            for _ in 0..N {
 42                let mut b: Vec<UInt8<F>> = z_i
 43                    .iter()
 44                    .map(|f| UInt8::<F>::from_bits_le(&f.to_bits_le().unwrap()[..8]))
 45                    .collect::<Vec<_>>();
 46
 47                for _ in 0..HASHES_PER_STEP {
 48                    let mut sha256_var = Sha256Gadget::default();
 49                    sha256_var.update(&b).unwrap();
 50                    b = sha256_var.finalize()?.to_bytes()?;
 51                }
 52
 53                // update z_i = z_{i+1}
 54                z_i = b
 55                    .iter()
 56                    .map(|e| {
 57                        let bits = e.to_bits_le().unwrap();
 58                        Boolean::<F>::le_bits_to_fp_var(&bits).unwrap()
 59                    })
 60                    .collect();
 61            }
 62
 63            z_i.enforce_equal(&z_n)?;
 64            Ok(())
 65        }
 66    }
 67    // compute natively in rust the expected result
 68    fn rust_native_result(z_0: Vec<Fr>, n_steps: usize, hashes_per_step: usize) -> Vec<Fr> {
 69        let mut z_i: Vec<Fr> = z_0.clone();
 70        for _ in 0..n_steps {
 71            let mut b = f_vec_to_bytes(z_i.to_vec());
 72
 73            for _ in 0..hashes_per_step {
 74                let mut sha256 = Sha256::default();
 75                sha256.update(b);
 76                b = sha256.finalize().to_vec();
 77            }
 78
 79            z_i = bytes_to_f_vec(b.to_vec()).unwrap();
 80        }
 81        z_i.clone()
 82    }
 83
 84    #[test]
 85    fn full_flow() {
 86        // set how many iterations of the SHA256ChainCircuit circuit internal loop we want to
 87        // compute
 88        const N_STEPS: usize = 100;
 89        const HASHES_PER_STEP: usize = 10;
 90        println!("running the 'naive' SHA256ChainCircuit, with N_STEPS={}, HASHES_PER_STEP={}. Total hashes = {}", N_STEPS, HASHES_PER_STEP, N_STEPS* HASHES_PER_STEP);
 91
 92        // set the initial state
 93        // let z_0_aux: Vec<u32> = vec![0_u32; 32 * 8];
 94        let z_0_aux: Vec<u8> = vec![0_u8; 32];
 95        let z_0: Vec<Fr> = z_0_aux.iter().map(|v| Fr::from(*v)).collect::<Vec<Fr>>();
 96
 97        // run the N iterations 'natively' in rust to compute the expected `z_n`
 98        let z_n = rust_native_result(z_0.clone(), N_STEPS, HASHES_PER_STEP);
 99
100        let circuit = SHA256ChainCircuit::<Fr, N_STEPS, HASHES_PER_STEP> {
101            z_0: Some(z_0),
102            z_n: Some(z_n.clone()),
103        };
104
105        let cs = ConstraintSystem::<Fr>::new_ref();
106        circuit.clone().generate_constraints(cs.clone()).unwrap();
107        println!(
108            "number of constraints of the (naive) SHA256ChainCircuit with N_STEPS*HASHES_PER_STEP={} sha256 hashes in total: {}",
109            N_STEPS * HASHES_PER_STEP,
110            cs.num_constraints()
111        );
112
113        // now let's generate an actual Groth16 proof
114        let mut rng = rand::rngs::OsRng;
115        let (g16_pk, g16_vk) =
116            Groth16::<Bn254>::circuit_specific_setup(circuit.clone(), &mut rng).unwrap();
117
118        let start = Instant::now();
119        let proof = Groth16::<Bn254>::prove(&g16_pk, circuit.clone(), &mut rng).unwrap();
120        println!(
121            "Groth16 proof generation (for the naive SHA256ChainCircuit): {:?}",
122            start.elapsed()
123        );
124
125        let public_inputs = z_n;
126        let valid_proof = Groth16::<Bn254>::verify(&g16_vk, &public_inputs, &proof).unwrap();
127
128        assert!(valid_proof);
129
130        println!("finished running the 'naive' SHA256ChainCircuit, with N_STEPS={}, HASHES_PER_STEP={}. Total hashes = {}", N_STEPS, HASHES_PER_STEP, N_STEPS* HASHES_PER_STEP);
131    }
132}