Implement message signing and verification logic

lib/tfw/crypto.py

@@ -2,12 +2,32 @@
 # All Rights Reserved. See LICENSE file for details.
 
 from functools import wraps
+from base64 import b64encode, b64decode
+from copy import deepcopy
 
 from cryptography.hazmat.backends import default_backend
 from cryptography.hazmat.primitives.hashes import SHA256
 from cryptography.hazmat.primitives.hmac import HMAC as _HMAC
 from cryptography.exceptions import InvalidSignature
 
+from tfw.networking import message_bytes
+
+
+def sign_message(key, message):
+    signature = HMAC(key, message_bytes(message)).signature
+    message['signature'] = b64encode(signature).decode()
+
+
+def verify_message(key, message):
+    message = deepcopy(message)
+    try:
+        signature_b64 = message.pop('signature')
+        signature = b64decode(signature_b64)
+        actual_signature = HMAC(key, message_bytes(message)).signature
+        return signature == actual_signature
+    except KeyError:
+        return False
+
 
 class HMAC:
     def __init__(self, key, message):