darkfi/src/blake.rs

use bellman::{
    gadgets::{
        blake2s,
        boolean::{AllocatedBit, Boolean},
        multipack,
    },
    groth16, Circuit, ConstraintSystem, SynthesisError,
};
use bls12_381::Bls12;
use ff::PrimeField;
use rand::rngs::OsRng;

pub const CRH_IVK_PERSONALIZATION: &[u8; 8] = b"Zcashivk";

struct MyCircuit {
    /// The input to SHA-256d we are proving that we know. Set to `None` when we
    /// are verifying a proof (and do not have the witness data).
    preimage: Option<[u8; 80]>,
}

impl<Scalar: PrimeField> Circuit<Scalar> for MyCircuit {
    fn synthesize<CS: ConstraintSystem<Scalar>>(self, cs: &mut CS) -> Result<(), SynthesisError> {
        // Compute the values for the bits of the preimage. If we are verifying a proof,
        // we still need to create the same constraints, so we return an equivalent-size
        // Vec of None (indicating that the value of each bit is unknown).
        let bit_values = if let Some(preimage) = self.preimage {
            preimage
                .iter()
                .map(|byte| (0..8).map(move |i| (byte >> i) & 1u8 == 1u8))
                .flatten()
                .map(|b| Some(b))
                .collect()
        } else {
            vec![None; 80 * 8]
        };
        assert_eq!(bit_values.len(), 80 * 8);

        // Witness the bits of the preimage.
        let preimage_bits = bit_values
            .into_iter()
            .enumerate()
            // Allocate each bit.
            .map(|(i, b)| AllocatedBit::alloc(cs.namespace(|| format!("preimage bit {}", i)), b))
            // Convert the AllocatedBits into Booleans (required for the sha256 gadget).
            .map(|b| b.map(Boolean::from))
            .collect::<Result<Vec<_>, _>>()?;

        let hash = blake2s::blake2s(
            cs.namespace(|| "computation of ivk"),
            &preimage_bits,
            CRH_IVK_PERSONALIZATION,
        )?;

        // Expose the vector of 32 boolean variables as compact public inputs.
        multipack::pack_into_inputs(cs.namespace(|| "pack hash"), &hash)
    }
}

fn main() {
    use blake2s_simd::Params as Blake2sParams;
    use std::time::Instant;

    let start = Instant::now();
    println!("Starting...");
    // Create parameters for our circuit. In a production deployment these would
    // be generated securely using a multiparty computation.
    let params = {
        let c = MyCircuit { preimage: None };
        groth16::generate_random_parameters::<Bls12, _, _>(c, &mut OsRng).unwrap()
    };
    println!("Generated random params. [{:?}]", start.elapsed());

    let start = Instant::now();
    // Prepare the verification key (for proof verification).
    let pvk = groth16::prepare_verifying_key(&params.vk);
    println!("Prepared verify key [{:?}]", start.elapsed());

    let start = Instant::now();
    // Pick a preimage and compute its hash.
    let preimage = [42; 80];
    //let hash = Sha256::digest(&Sha256::digest(&preimage));
    println!(
        "Computed blake2s(preimage) witness data [{:?}]",
        start.elapsed()
    );

    // Create an instance of our circuit (with the preimage as a witness).
    let c = MyCircuit {
        preimage: Some(preimage),
    };

    let start = Instant::now();
    // Create a Groth16 proof with our parameters.
    let proof = groth16::create_random_proof(c, &params, &mut OsRng).unwrap();
    println!("Generated random proof [{:?}]", start.elapsed());

    let start = Instant::now();

    let hash_result = {
        let mut h = Blake2sParams::new()
            .hash_length(32)
            .personal(CRH_IVK_PERSONALIZATION)
            .to_state();
        h.update(&preimage);
        h.finalize()
    };

    // Pack the hash as inputs for proof verification.
    let hash_bits = multipack::bytes_to_bits_le(hash_result.as_bytes());
    let inputs = multipack::compute_multipacking(&hash_bits);

    println!("Packed data and verifying proof... [{:?}]", start.elapsed());

    let start = Instant::now();
    // Check the proof!
    assert!(groth16::verify_proof(&pvk, &proof, &inputs).is_ok());
    println!("Done! [{:?}]", start.elapsed());
}