Add ability to verify signature in xfile dchange.

Every round, the master node checks the federations file to add xfield and
member nodes verify their federations file signature and block xfield before signing the block
Add tests to verify max block size and aggregated pubkey changes with signatures

src/bin/tapyrus-signerd.rs

@@ -256,7 +256,7 @@ mod tests {
     }
 
     #[test]
-    fn test_load_federations_has_max_block_size() {
+    fn test_load_federations_ihas_max_block_size() {
         let pubkey = PublicKey::from_str(
             "0302f5584e30d2ee32e772d04ff8ee1efc90a7a91ac5b7c4025da7a42a67d06a25",
         )
@@ -266,4 +266,15 @@ mod tests {
         load_federations(&pubkey, path);
     }
 
+    #[test]
+    #[should_panic(expected = "federations_file: InvalidSig")]
+    fn test_load_federations_has_invalid_signature() {
+        let pubkey = PublicKey::from_str(
+            "039af53a49a365576de41a2e70cc148353d7d1f4cad45f888fd8bc6d2c94a97657",
+        )
+        .unwrap();
+
+        let path = Path::new("tests/resources/federations_has_invalid_signature.toml");
+        load_federations(&pubkey, path);
+    }
 }

src/crypto/vss.rs

@@ -185,15 +185,15 @@ impl Vss {
         let local_sig_for_positive = Sign::sign_xfield(
             &shared_keys_for_positive,
             &priv_shared_keys,
-            xfield.signature_hash()?,
+            xfield.signature_hash().unwrap(),
         );
 
         let shared_keys_for_negative =
             Sign::verify_vss_and_construct_key(&shared_block_secrets.for_negative(), &index)?;
         let local_sig_for_negative = Sign::sign_xfield(
             &shared_keys_for_negative,
             &priv_shared_keys,
-            xfield.signature_hash()?,
+            xfield.signature_hash().unwrap(),
         );
         Self::create_local_sig_from_shares(
             priv_shared_keys,

src/errors.rs

@@ -31,7 +31,9 @@ pub enum Error {
     /// Error when the aggregated public key included the candidate block is invalid.
     InvalidAggregatedPublicKey,
     /// xField is not supported by signer.
-    UnsupportedXField,
+    UnsupportedXField(String),
+    UnauthorizedFederationChange(u32),
+    XfieldFederationMismatch(Option<u32>, &'static str),
 }
 
 impl std::fmt::Display for Error {