initial commit

Cargo.toml

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+[package]
+name = "sapvi"
+version = "0.1.0"
+authors = ["narodnik <x@x.org>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+ff = { git = "https://github.com/zcash/librustzcash" }
+group = { git = "https://github.com/zcash/librustzcash" }
+pairing = { git = "https://github.com/zcash/librustzcash" }
+bellman = { git = "https://github.com/zcash/librustzcash" }
+#zcash_primitives = { git = "https://github.com/zcash/librustzcash" }
+#zcash_proofs = { git = "https://github.com/zcash/librustzcash" }
+#bench-utils = { git = "https://github.com/scipr-lab/zexe", features = ["print-trace"]}
+rand = "0.7.3"
+sha2 = "0.9.1"
+

src/main.rs

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+// Say we want to write a circuit that proves we know the preimage to some hash computed
+// using SHA-256d (calling SHA-256 twice). The preimage must have a fixed length known in
+// advance (because the circuit parameters will depend on it), but can otherwise have any value.
+// We take the following strategy:
+//
+// * Witness each bit of the preimage.
+// * Compute hash = SHA-256d(preimage) inside the circuit.
+// * Expose hash as a public input using multiscalar packing.
+//
+use bellman::{
+    gadgets::{
+        boolean::{AllocatedBit, Boolean},
+        multipack,
+        sha256::sha256,
+    },
+    groth16, Circuit, ConstraintSystem, SynthesisError,
+};
+use ff::PrimeField;
+use pairing::{bls12_381::Bls12, Engine};
+use rand::rngs::OsRng;
+use sha2::{Digest, Sha256};
+
+/// Our own SHA-256d gadget. Input and output are in little-endian bit order.
+fn sha256d<Scalar: PrimeField, CS: ConstraintSystem<Scalar>>(
+    mut cs: CS,
+    data: &[Boolean],
+) -> Result<Vec<Boolean>, SynthesisError> {
+    // Flip endianness of each input byte
+    // NOTE: data is a vec of Bool so it is iterating over 8 'bits' at a time
+    // This is needed because Rust sha256 and ZC sha256 have different endianness.
+    let input: Vec<_> = data
+        .chunks(8)
+        .map(|c| c.iter().rev())
+        .flatten()
+        .cloned()
+        .collect();
+
+    let mid = sha256(cs.namespace(|| "SHA-256(input)"), &input)?;
+    let res = sha256(cs.namespace(|| "SHA-256(mid)"), &mid)?;
+
+    // Flip endianness of each output byte
+    Ok(res
+        .chunks(8)
+        .map(|c| c.iter().rev())
+        .flatten()
+        .cloned()
+        .collect())
+}
+
+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
+                .into_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<_>, _>>()?;
+
+        // Compute hash = SHA-256d(preimage).
+        let hash = sha256d(cs.namespace(|| "SHA-256d(preimage)"), &preimage_bits)?;
+
+        // Expose the vector of 32 boolean variables as compact public inputs.
+        multipack::pack_into_inputs(cs.namespace(|| "pack hash"), &hash)
+    }
+}
+
+fn main() {
+    use std::time::{Duration, 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 sha256(sha256(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();
+    // Pack the hash as inputs for proof verification.
+    let hash_bits = multipack::bytes_to_bits_le(&hash);
+    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());
+}