refactor: update block header signature field type (#834)

Author: agaffney

ledger/babbage/babbage.go

@@ -173,7 +173,7 @@ type BabbageBlockHeader struct {
 			Minor uint64
 		}
 	}
-	Signature interface{}
+	Signature []byte
 }
 
 func (h *BabbageBlockHeader) UnmarshalCBOR(cborData []byte) error {

ledger/shelley/shelley.go

@@ -151,7 +151,7 @@ type ShelleyBlockHeader struct {
 		ProtoMajorVersion    uint64
 		ProtoMinorVersion    uint64
 	}
-	Signature interface{}
+	Signature []byte
 }
 
 func (h *ShelleyBlockHeader) UnmarshalCBOR(cborData []byte) error {

ledger/verify_kes.go

@@ -129,7 +129,6 @@ func VerifyKes(
 	slotsPerKesPeriod uint64,
 ) (bool, error) {
 	// Ref: https://github.com/IntersectMBO/ouroboros-consensus/blob/de74882102236fdc4dd25aaa2552e8b3e208448c/ouroboros-consensus-cardano/src/shelley/Ouroboros/Consensus/Shelley/Protocol/Praos.hs#L125
-	sigBytes := header.Signature.([]byte)
 	// Ref: https://github.com/IntersectMBO/cardano-ledger/blob/master/libs/cardano-protocol-tpraos/src/Cardano/Protocol/TPraos/BHeader.hs#L189
 	msgBytes, err := cbor.Encode(header.Body)
 	if err != nil {
@@ -144,7 +143,7 @@ func VerifyKes(
 	if currentKesPeriod >= startOfKesPeriod {
 		t = currentKesPeriod - startOfKesPeriod
 	}
-	return verifySignedKES(opCertVkHotBytes, t, msgBytes, sigBytes), nil
+	return verifySignedKES(opCertVkHotBytes, t, msgBytes, header.Signature), nil
 }
 
 func verifySignedKES(vkey []byte, period uint64, msg []byte, sig []byte) bool {