Add proof of work verification error. (#503)

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src/core/proof_of_work.rs

@@ -1,3 +1,5 @@
+use thiserror::Error;
+
 use super::channel::Blake2sChannel;
 use crate::commitment_scheme::blake2_hash::{Blake2sHash, Blake2sHasher};
 use crate::commitment_scheme::hasher::Hasher;
@@ -26,17 +28,23 @@ impl ProofOfWork {
         proof
     }
 
-    pub fn verify(&self, channel: &mut Blake2sChannel, proof: &ProofOfWorkProof) -> bool {
+    pub fn verify(
+        &self,
+        channel: &mut Blake2sChannel,
+        proof: &ProofOfWorkProof,
+    ) -> Result<(), ProofOfWorkVerificationError> {
         let seed = channel.get_digest().as_ref().to_vec();
         let verified = check_leading_zeros(
             self.hash_with_nonce(&seed, proof.nonce).as_ref(),
             self.n_bits,
         );
 
-        if verified {
-            channel.mix_nonce(proof.nonce);
+        if !verified {
+            return Err(ProofOfWorkVerificationError::ProofOfWorkVerificationFailed);
         }
-        verified
+
+        channel.mix_nonce(proof.nonce);
+        Ok(())
     }
 
     fn grind(&self, seed: Vec<u8>) -> ProofOfWorkProof {
@@ -76,6 +84,12 @@ fn check_leading_zeros(bytes: &[u8], bound_bits: u32) -> bool {
     n_bits >= bound_bits
 }
 
+#[derive(Clone, Copy, Debug, Error)]
+pub enum ProofOfWorkVerificationError {
+    #[error("Proof of work verification failed.")]
+    ProofOfWorkVerificationFailed,
+}
+
 #[cfg(test)]
 mod tests {
     use crate::commitment_scheme::blake2_hash::Blake2sHash;
@@ -88,7 +102,7 @@ mod tests {
         let proof_of_work_prover = ProofOfWork { n_bits: 11 };
         let proof = ProofOfWorkProof { nonce: 133 };
 
-        assert!(proof_of_work_prover.verify(&mut channel, &proof));
+        proof_of_work_prover.verify(&mut channel, &proof).unwrap();
     }
 
     #[test]
@@ -97,7 +111,9 @@ mod tests {
         let proof_of_work_prover = ProofOfWork { n_bits: 1 };
         let invalid_proof = ProofOfWorkProof { nonce: 0 };
 
-        assert!(!proof_of_work_prover.verify(&mut channel, &invalid_proof));
+        proof_of_work_prover
+            .verify(&mut channel, &invalid_proof)
+            .unwrap_err();
     }
 
     #[test]
@@ -109,9 +125,8 @@ mod tests {
         let verifier = ProofOfWork::new(n_bits);
 
         let proof = prover.prove(&mut prover_channel);
-        let verified = verifier.verify(&mut verifier_channel, &proof);
+        verifier.verify(&mut verifier_channel, &proof).unwrap();
 
-        assert!(verified);
         assert_eq!(prover_channel.get_digest(), verifier_channel.get_digest());
     }
 }

src/core/prover/mod.rs

@@ -5,6 +5,7 @@ use thiserror::Error;
 
 use super::fri::FriVerificationError;
 use super::poly::circle::{CanonicCoset, MAX_CIRCLE_DOMAIN_LOG_SIZE};
+use super::proof_of_work::ProofOfWorkVerificationError;
 use super::queries::SparseSubCircleDomain;
 use super::ColumnVec;
 use crate::commitment_scheme::blake2_hash::Blake2sHasher;
@@ -193,7 +194,7 @@ pub fn verify(
     let fri_config = FriConfig::new(LOG_LAST_LAYER_DEGREE_BOUND, LOG_BLOWUP_FACTOR, N_QUERIES);
     let mut fri_verifier = FriVerifier::commit(channel, fri_config, proof.fri_proof, bounds)?;
 
-    ProofOfWork::new(PROOF_OF_WORK_BITS).verify(channel, &proof.proof_of_work);
+    ProofOfWork::new(PROOF_OF_WORK_BITS).verify(channel, &proof.proof_of_work)?;
     let opening_positions = fri_verifier
         .column_opening_positions(channel)
         .into_values()
@@ -311,6 +312,8 @@ pub enum VerificationError {
     OodsNotMatching,
     #[error(transparent)]
     Fri(#[from] FriVerificationError),
+    #[error(transparent)]
+    ProofOfWork(#[from] ProofOfWorkVerificationError),
 }
 
 #[cfg(test)]