persist hashes and origin signatures for PDUs

synapse/crypto/event_signing.py

@@ -0,0 +1,70 @@
+# -*- coding: utf-8 -*-
+
+# Copyright 2014 OpenMarket Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+from synapse.api.events.utils import prune_pdu
+from syutil.jsonutil import encode_canonical_json
+from syutil.base64util import encode_base64, decode_base64
+from syutil.crypto.jsonsign import sign_json, verify_signed_json
+
+import hashlib
+
+
+def hash_event_pdu(pdu, hash_algortithm=hashlib.sha256):
+    hashed = _compute_hash(pdu, hash_algortithm)
+    hashes[hashed.name] = encode_base64(hashed.digest())
+    pdu.hashes = hashes
+    return pdu
+
+
+def check_event_pdu_hash(pdu, hash_algorithm=hashlib.sha256):
+    """Check whether the hash for this PDU matches the contents"""
+    computed_hash = _compute_hash(pdu, hash_algortithm)
+    if computed_hash.name not in pdu.hashes:
+        raise Exception("Algorithm %s not in hashes %s" % (
+            computed_hash.name, list(pdu.hashes)
+        ))
+    message_hash_base64 = hashes[computed_hash.name]
+    try:
+        message_hash_bytes = decode_base64(message_hash_base64)
+    except:
+        raise Exception("Invalid base64: %s" % (message_hash_base64,))
+    return message_hash_bytes == computed_hash.digest()
+
+
+def _compute_hash(pdu, hash_algorithm):
+    pdu_json = pdu.get_dict()
+    pdu_json.pop("meta", None)
+    pdu_json.pop("signatures", None)
+    hashes = pdu_json.pop("hashes", {})
+    pdu_json_bytes = encode_canonical_json(pdu_json)
+    return hash_algorithm(pdu_json_bytes)
+
+
+def sign_event_pdu(pdu, signature_name, signing_key):
+    tmp_pdu = Pdu(**pdu.get_dict())
+    tmp_pdu = prune_pdu(tmp_pdu)
+    pdu_json = tmp_pdu.get_dict()
+    pdu_jdon = sign_json(pdu_json, signature_name, signing_key)
+    pdu.signatures = pdu_json["signatures"]
+    return pdu
+
+
+def verify_signed_event_pdu(pdu, signature_name, verify_key):
+    tmp_pdu = Pdu(**pdu.get_dict())
+    tmp_pdu = prune_pdu(tmp_pdu)
+    pdu_json = tmp_pdu.get_dict()
+    verify_signed_json(pdu_json, signature_name, verify_key)