Add a Sha256 bench (#188)

* add sha256 bench

* feat: Refactor sha256 benchmark and update dependencies

- Refactored the `sha256.rs` benchmarking file by replacing the former `hex_literal::hex` usage with a newly created `decode_hex` function.
- Updated the "Test vectors" section to work with the new `decode_hex` function to compute digests in `Sha256Circuit` instances.
- adapted to new APIs for RecursiveSNARK
- Amended the `Cargo.toml` file to include the `sha2` package dependency, version `0.10.7`.
- added the bench target

* cargo fmt

---------

Co-authored-by: Srinath Setty <srinath@microsoft.com>

Cargo.toml

@@ -42,6 +42,7 @@ rand = "0.8.4"
 hex = "0.4.3"
 pprof = { version = "0.11" }
 cfg-if = "1.0.0"
+sha2 = "0.10.7"
 
 [[bench]]
 name = "recursive-snark"
@@ -55,6 +56,10 @@ harness = false
 name = "compute-digest"
 harness = false
 
+[[bench]]
+name = "sha256"
+harness = false
+
 [features]
 default = []
 # Compiles in portable mode, w/o ISA extensions => binary can be executed on all systems.

benches/sha256.rs

@@ -0,0 +1,233 @@
+//! Benchmarks Nova's prover for proving SHA-256 with varying sized messages.
+//! We run a single step with the step performing the entire computation.
+//! This code invokes a hand-written SHA-256 gadget from bellman/bellperson.
+//! It also uses code from bellman/bellperson to compare circuit-generated digest with sha2 crate's output
+#![allow(non_snake_case)]
+type G1 = pasta_curves::pallas::Point;
+type G2 = pasta_curves::vesta::Point;
+use ::bellperson::{
+  gadgets::{
+    boolean::{AllocatedBit, Boolean},
+    num::{AllocatedNum, Num},
+    sha256::sha256,
+    Assignment,
+  },
+  ConstraintSystem, SynthesisError,
+};
+use core::time::Duration;
+use criterion::*;
+use ff::{PrimeField, PrimeFieldBits};
+use nova_snark::{
+  traits::{
+    circuit::{StepCircuit, TrivialTestCircuit},
+    Group,
+  },
+  PublicParams, RecursiveSNARK,
+};
+use sha2::{Digest, Sha256};
+
+#[derive(Clone, Debug)]
+struct Sha256Circuit<Scalar: PrimeField> {
+  preimage: Vec<u8>,
+  digest: Scalar,
+}
+
+impl<Scalar: PrimeField + PrimeFieldBits> StepCircuit<Scalar> for Sha256Circuit<Scalar> {
+  fn arity(&self) -> usize {
+    1
+  }
+
+  fn synthesize<CS: ConstraintSystem<Scalar>>(
+    &self,
+    cs: &mut CS,
+    _z: &[AllocatedNum<Scalar>],
+  ) -> Result<Vec<AllocatedNum<Scalar>>, SynthesisError> {
+    let mut z_out: Vec<AllocatedNum<Scalar>> = Vec::new();
+
+    let bit_values: Vec<_> = self
+      .preimage
+      .clone()
+      .into_iter()
+      .flat_map(|byte| (0..8).map(move |i| (byte >> i) & 1u8 == 1u8))
+      .map(Some)
+      .collect();
+    assert_eq!(bit_values.len(), self.preimage.len() * 8);
+
+    let preimage_bits = bit_values
+      .into_iter()
+      .enumerate()
+      .map(|(i, b)| AllocatedBit::alloc(cs.namespace(|| format!("preimage bit {i}")), b))
+      .map(|b| b.map(Boolean::from))
+      .collect::<Result<Vec<_>, _>>()?;
+
+    let hash_bits = sha256(cs.namespace(|| "sha256"), &preimage_bits)?;
+
+    for (i, hash_bits) in hash_bits.chunks(256_usize).enumerate() {
+      let mut num = Num::<Scalar>::zero();
+      let mut coeff = Scalar::ONE;
+      for bit in hash_bits {
+        num = num.add_bool_with_coeff(CS::one(), bit, coeff);
+
+        coeff = coeff.double();
+      }
+
+      let hash = AllocatedNum::alloc(cs.namespace(|| format!("input {i}")), || {
+        Ok(*num.get_value().get()?)
+      })?;
+
+      // num * 1 = hash
+      cs.enforce(
+        || format!("packing constraint {i}"),
+        |_| num.lc(Scalar::ONE),
+        |lc| lc + CS::one(),
+        |lc| lc + hash.get_variable(),
+      );
+      z_out.push(hash);
+    }
+
+    // sanity check with the hasher
+    let mut hasher = Sha256::new();
+    hasher.update(&self.preimage);
+    let hash_result = hasher.finalize();
+
+    let mut s = hash_result
+      .iter()
+      .flat_map(|&byte| (0..8).rev().map(move |i| (byte >> i) & 1u8 == 1u8));
+
+    for b in hash_bits {
+      match b {
+        Boolean::Is(b) => {
+          assert!(s.next().unwrap() == b.get_value().unwrap());
+        }
+        Boolean::Not(b) => {
+          assert!(s.next().unwrap() != b.get_value().unwrap());
+        }
+        Boolean::Constant(_b) => {
+          panic!("Can't reach here")
+        }
+      }
+    }
+
+    Ok(z_out)
+  }
+
+  fn output(&self, _z: &[Scalar]) -> Vec<Scalar> {
+    vec![self.digest]
+  }
+}
+
+type C1 = Sha256Circuit<<G1 as Group>::Scalar>;
+type C2 = TrivialTestCircuit<<G2 as Group>::Scalar>;
+
+criterion_group! {
+name = recursive_snark;
+config = Criterion::default().warm_up_time(Duration::from_millis(3000));
+targets = bench_recursive_snark
+}
+
+criterion_main!(recursive_snark);
+
+fn bench_recursive_snark(c: &mut Criterion) {
+  let bytes_to_scalar = |bytes: [u8; 32]| -> <G1 as Group>::Scalar {
+    let mut bytes_le = bytes;
+    bytes_le.reverse();
+    <G1 as Group>::Scalar::from_repr(bytes_le).unwrap()
+  };
+
+  let decode_hex = |s: &str| -> <G1 as Group>::Scalar {
+    let bytes = (0..s.len())
+      .step_by(2)
+      .map(|i| u8::from_str_radix(&s[i..i + 2], 16))
+      .collect::<Result<Vec<u8>, _>>()
+      .unwrap();
+    let bytes_arr: [u8; 32] = bytes.try_into().unwrap();
+    bytes_to_scalar(bytes_arr)
+  };
+
+  // Test vectors
+  let circuits = vec![
+    Sha256Circuit {
+      preimage: vec![0u8; 64],
+      digest: decode_hex("12df9ae4958c1957170f9b04c4bc00c27315c5d75a391f4b672f952842bfa5ac"),
+    },
+    Sha256Circuit {
+      preimage: vec![0u8; 128],
+      digest: decode_hex("13abfac9782cb9c13c4508bde596f1914fe2f744f6a661c0c9a16659745c4e1b"),
+    },
+    Sha256Circuit {
+      preimage: vec![0u8; 256],
+      digest: decode_hex("0f5a007b5aef126a58f9bbd937842967c44253e7f97d98b5cd10bfe44d6782c8"),
+    },
+    Sha256Circuit {
+      preimage: vec![0u8; 512],
+      digest: decode_hex("06a6cfaad91d49366f18443cd4e11576ff27c174bb9fe2bc54735a79e3e456e0"),
+    },
+    Sha256Circuit {
+      preimage: vec![0u8; 1024],
+      digest: decode_hex("3763c73508f5fbb36daae8257d6c5c07db08ec5df0549ccf692b9fa218fd0ef7"),
+    },
+    Sha256Circuit {
+      preimage: vec![0u8; 2048],
+      digest: decode_hex("35c18d6c3cf49e42b3ffcb54ea04bdc16617efba0e673abc8c858257955005a5"),
+    },
+    Sha256Circuit {
+      preimage: vec![0u8; 4096],
+      digest: decode_hex("25349112d1bd5ba15e3e2d3effa01af1da02c097ce6208cdf28f34b74d35feb2"),
+    },
+    Sha256Circuit {
+      preimage: vec![0u8; 8192],
+      digest: decode_hex("22bc891155c7d423039a2206ed4a5342755948baeb13a54b61dbead7c3d3b8f6"),
+    },
+    Sha256Circuit {
+      preimage: vec![0u8; 16384],
+      digest: decode_hex("3fda713dc72ddcd42ce625c75f7e41d526d30647278a3dfcda95904e59ade7f1"),
+    },
+    Sha256Circuit {
+      preimage: vec![0u8; 32768],
+      digest: decode_hex("1e2091bd3e3cedffebb7316b52414fff82511cbd232561874a4ae11ae2040ac1"),
+    },
+    Sha256Circuit {
+      preimage: vec![0u8; 65536],
+      digest: decode_hex("0c33953975c438ce357912f27b0fbcf98bae6eb68a1a913386672ee406a4f479"),
+    },
+  ];
+
+  for circuit_primary in circuits {
+    let mut group = c.benchmark_group(format!(
+      "NovaProve-Sha256-message-len-{}",
+      circuit_primary.preimage.len()
+    ));
+    group.sample_size(10);
+
+    // Produce public parameters
+    let pp =
+      PublicParams::<G1, G2, C1, C2>::setup(circuit_primary.clone(), TrivialTestCircuit::default());
+
+    let circuit_secondary = TrivialTestCircuit::default();
+    let z0_primary = vec![<G1 as Group>::Scalar::from(2u64)];
+    let z0_secondary = vec![<G2 as Group>::Scalar::from(2u64)];
+
+    group.bench_function("Prove", |b| {
+      b.iter(|| {
+        let mut recursive_snark = RecursiveSNARK::new(
+          black_box(&pp),
+          black_box(&circuit_primary),
+          black_box(&circuit_secondary),
+          black_box(z0_primary.clone()),
+          black_box(z0_secondary.clone()),
+        );
+        // produce a recursive SNARK for a step of the recursion
+        assert!(recursive_snark
+          .prove_step(
+            black_box(&pp),
+            black_box(&circuit_primary),
+            black_box(&circuit_secondary),
+            black_box(z0_primary.clone()),
+            black_box(z0_secondary.clone()),
+          )
+          .is_ok());
+      })
+    });
+    group.finish();
+  }
+}