BytestringSplitter for #114.

nkms/crypto/signature.py

@@ -1,7 +1,7 @@
 from nkms.crypto import api as API
 
 
-class Signature(object):
+class Signature(bytes):
     """
     The Signature object allows signatures to be made and verified.
     """
@@ -29,6 +29,9 @@ class Signature(object):
         self._r = r
         self._s = s
 
+    def __repr__(self):
+        return "{} v{}: {} - {}".format(__class__.__name__, self._v, self._r, self._s)
+
     def verify(self, message: bytes, pubkey: bytes) -> bool:
         """
         Verifies that a message's signature was valid.

nkms/crypto/utils.py

@@ -1,7 +1,27 @@
-from nkms.crypto import api
 
 
-def verify(signature: bytes, message: bytes, pubkey: bytes) -> bool:
-    msg_digest = api.keccak_digest(message)
-    ecdsa_sig = api.ecdsa_load_sig(bytes(signature))
-    return api.ecdsa_verify(*ecdsa_sig, msg_digest, pubkey)
+class BytestringSplitter(object):
+
+    def __init__(self, *message_types):
+        """
+        :param message_types:  A collection of types of messages to parse.
+        """
+        self.message_types = message_types
+
+    def __call__(self, splittable):
+        if self.total_expected_length() != len(splittable):
+            raise ValueError("Wrong number of bytes to constitute message types {} - need {}, got {}".format(self.message_types, self.total_expected_length(), len(splittable)))
+
+        cursor = 0
+        message_objects = []
+
+        for message_type in self.message_types:
+            expected_end_of_object_bytes = cursor + message_type._EXPECTED_LENGTH
+            bytes_for_this_object = splittable[cursor:cursor + expected_end_of_object_bytes]
+            message_objects.append(message_type(bytes_for_this_object))
+            cursor = expected_end_of_object_bytes
+
+        return message_objects
+
+    def total_expected_length(self):
+        return sum(m._EXPECTED_LENGTH for m in self.message_types)

tests/crypto/test_bytestring_types.py

@@ -0,0 +1,13 @@
+from nkms.crypto.api import secure_random
+from nkms.crypto.signature import Signature
+from nkms.crypto.utils import BytestringSplitter
+
+
+def test_split_two_signatures():
+    """
+    We make two random Signatures and concat them.  Then split them and show that we got the proper result.
+    """
+    sig1, sig2 = Signature(secure_random(65)), Signature(secure_random(65))
+    two_signature_splitter = BytestringSplitter(Signature, Signature)
+    rebuilt_sig1, rebuilt_sig2 = two_signature_splitter(sig1 + sig2)
+    assert (sig1, sig2) == (rebuilt_sig1, rebuilt_sig2)