Add a test for batch verification

crypto/frost/src/tests/schnorr.rs

@@ -30,3 +30,43 @@ pub(crate) fn verify<R: RngCore + CryptoRng, C: Curve>(rng: &mut R) {
   );
 }
 
+pub(crate) fn batch_verify<R: RngCore + CryptoRng, C: Curve>(rng: &mut R) {
+  // Create 3 signatures
+  let mut keys = vec![];
+  let mut challenges = vec![];
+  let mut sigs = vec![];
+  for i in 0 .. 3 {
+    keys.push(C::F::random(&mut *rng));
+    challenges.push(C::F::random(&mut *rng));
+    sigs.push(schnorr::sign::<C>(keys[i], C::F::random(&mut *rng), challenges[i]));
+  }
+
+  // Batch verify
+  let mut triplets = (0 .. 3).map(
+    |i| (u16::try_from(i + 1).unwrap(), C::generator_table() * keys[i], challenges[i], sigs[i])
+  ).collect::<Vec<_>>();
+  schnorr::batch_verify(rng, &triplets).unwrap();
+
+  // Shift 1 from s from one to another and verify it fails
+  // This test will fail if unique factors aren't used per-signature, hence its inclusion
+  {
+    let mut triplets = triplets.clone();
+    triplets[1].3.s += C::F::one();
+    triplets[2].3.s -= C::F::one();
+    if let Err(blame) = schnorr::batch_verify(rng, &triplets) {
+      assert_eq!(blame, 2);
+    } else {
+      assert!(false);
+    }
+  }
+  // Sanity
+  schnorr::batch_verify(rng, &triplets).unwrap();
+
+  // Make sure a completely invalid signature fails when included
+  triplets[0].3.s = C::F::random(&mut *rng);
+  if let Err(blame) = schnorr::batch_verify(rng, &triplets) {
+    assert_eq!(blame, 1);
+  } else {
+    assert!(false);
+  }
+}