Add support for countersign.

cwt/cose_message.py

@@ -1,13 +1,8 @@
 from typing import Any, Dict, List, Optional
 
-from cbor2 import CBORTag, dumps, loads
+from cbor2 import loads
 
 from .cbor_processor import CBORProcessor
-from .const import (
-    COSE_KEY_OPERATION_VALUES,
-    COSE_KEY_TYPES,
-    COSE_NAMED_ALGORITHMS_SUPPORTED,
-)
 from .cose_key_interface import COSEKeyInterface
 from .enums import COSEType
 from .signer import Signer
@@ -44,7 +39,7 @@ def unprotected(self) -> Dict[int, Any]:
         """
         return self._unprotected
 
-    
+
 class COSESignature(COSEHeaders):
     """
     The COSE signature.

cwt/enums.py

@@ -1,5 +1,6 @@
 import enum
 
+
 class COSEType(enum.Enum):
     ENCRYPT0 = 16
     ENCRYPT = 96