fix(blockchain): report a bad proposer signature as an invalid block proof

The proposer signature moved out of the attestation aggregate but stayed
inside `BlockProof`, so a failure there is still the spec's
INVALID_BLOCK_PROOF rejection, not INVALID_SIGNATURE. Reusing the
attestation-signature variants classified it as the latter, which the
`test_corrupt_proof_rejected` and
`test_proof_reused_under_different_message_rejected` fixtures reject now
that the runner asserts the reason (#547).

Separate variants keep the gossip attestation path on
INVALID_SIGNATURE.

Author: MegaRedHand

crates/blockchain/src/spec_test_runner.rs

@@ -83,9 +83,14 @@ pub fn rejection_reason(err: &StoreError) -> Option<RejectionReason> {
         StoreError::AttestationTooFarInFuture { .. } => RejectionReason::AttestationTooFarInFuture,
         StoreError::AggregateVerificationFailed(_) => RejectionReason::InvalidSignature,
         StoreError::BlockProofVerificationFailed(_) => RejectionReason::InvalidBlockProof,
-        // An attestation-free block carries no aggregate, so stray proof bytes
-        // are a malformed block proof rather than a distinct spec reason.
-        StoreError::UnexpectedAttestationProof => RejectionReason::InvalidBlockProof,
+        // The proposer signature and the attestation aggregate are both
+        // components of the block proof, so a failure in either is the same
+        // spec rejection even though we carry them as separate wire fields. An
+        // attestation-free block carries no aggregate at all, so stray proof
+        // bytes are a malformed block proof rather than a distinct reason.
+        StoreError::ProposerSignatureDecodingFailed
+        | StoreError::ProposerSignatureVerificationFailed
+        | StoreError::UnexpectedAttestationProof => RejectionReason::InvalidBlockProof,
         StoreError::EmptyAggregationBits => RejectionReason::EmptyAggregationBits,
         StoreError::NotProposer { .. } => RejectionReason::WrongProposer,
         StoreError::DuplicateAttestationData { .. } => RejectionReason::DuplicateAttestationData,

crates/blockchain/src/store.rs

@@ -1013,6 +1013,17 @@ pub enum StoreError {
     #[error("Validator signature verification failed")]
     SignatureVerificationFailed,
 
+    /// Kept apart from [`Self::SignatureDecodingFailed`] because the proposer
+    /// signature is a component of the block proof, so the spec reports its
+    /// failure as an invalid block proof rather than an invalid signature.
+    #[error("Block proposer signature could not be decoded")]
+    ProposerSignatureDecodingFailed,
+
+    /// See [`Self::ProposerSignatureDecodingFailed`] for why this is distinct
+    /// from [`Self::SignatureVerificationFailed`].
+    #[error("Block proposer signature verification failed")]
+    ProposerSignatureVerificationFailed,
+
     #[error("Block carries an attestation proof but has no attestations")]
     UnexpectedAttestationProof,
 
@@ -1193,9 +1204,9 @@ pub fn verify_block_signatures(
     let proposer_pubkey = ValidatorPublicKey::from_bytes(&proposer_validator.proposal_pubkey)
         .map_err(|_| StoreError::PubkeyDecodingFailed(block.proposer_index))?;
     let proposer_signature = ValidatorSignature::from_bytes(&signed_block.proof.proposer_signature)
-        .map_err(|_| StoreError::SignatureDecodingFailed)?;
+        .map_err(|_| StoreError::ProposerSignatureDecodingFailed)?;
     if !proposer_signature.is_valid(&proposer_pubkey, block_slot_u32, &block_root) {
-        return Err(StoreError::SignatureVerificationFailed);
+        return Err(StoreError::ProposerSignatureVerificationFailed);
     }
 
     // 2. Verify the attestation aggregate (Type-2 over the body attestations