apollo_propeller: add ShardSignatureVerificationError

crates/apollo_propeller/Cargo.toml

@@ -10,8 +10,10 @@ description = "Implementation of the Propeller algorithm for the Starknet sequen
 testing = []
 
 [dependencies]
+libp2p.workspace = true
 reed-solomon-simd.workspace = true
 sha2.workspace = true
+thiserror.workspace = true
 
 [dev-dependencies]
 rstest.workspace = true

crates/apollo_propeller/src/types.rs

@@ -1,5 +1,8 @@
 //! Core types for the Propeller protocol.
 
+use libp2p::identity::PeerId;
+use thiserror::Error;
+
 use crate::MerkleHash;
 
 #[derive(Debug, Default, PartialEq, Clone, Copy, Ord, PartialOrd, Eq, Hash)]
@@ -12,3 +15,15 @@ pub struct ShardIndex(pub u32);
 
 #[derive(Debug, Default, PartialEq, Clone, Copy, Ord, PartialOrd, Eq, Hash)]
 pub struct MessageRoot(pub MerkleHash);
+
+/// Errors that can occur when verifying a shard signature.
+#[derive(Debug, Clone, PartialEq, Eq, Error)]
+pub enum ShardSignatureVerificationError {
+    #[error(
+        "We could not find a public key for signer/publisher {0}. This suggests that the public \
+         key cannot be extracted form the peer ID and needs to be provided explicitly."
+    )]
+    NoPublicKeyAvailable(PeerId),
+    #[error("Received a shard with an invalid signature. Sender should be reported...")]
+    VerificationFailed,
+}