SYN-75 Verify signatures on server to server transactions

1 files changed, 125 insertions, 0 deletions

diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py
new file mode 100644
index 0000000000..ce19c69bd5
--- /dev/null
+++ b/synapse/crypto/keyring.py
@@ -0,0 +1,125 @@
+# -*- 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.crypto.keyclient import fetch_server_key
+from twisted.internet import defer
+from syutil.crypto.jsonsign import verify_signed_json, signature_ids
+from syutil.crypto.signing_key import (
+    is_signing_algorithm_supported, decode_verify_key_bytes
+)
+from syutil.base64util import decode_base64, encode_base64
+
+from OpenSSL import crypto
+
+import logging
+
+
+logger = logging.getLogger(__name__)
+
+
+class Keyring(object):
+    def __init__(self, hs):
+        self.store = hs.get_datastore()
+        self.clock = hs.get_clock()
+        self.hs = hs
+
+    @defer.inlineCallbacks
+    def verify_json_for_server(self, server_name, json_object):
+        key_ids = signature_ids(json_object, server_name)
+        verify_key = yield self.get_server_verify_key(server_name, key_ids)
+        verify_signed_json(json_object, server_name, verify_key)
+
+    @defer.inlineCallbacks
+    def get_server_verify_key(self, server_name, key_ids):
+        """Finds a verification key for the server with one of the key ids.
+        Args:
+            server_name (str): The name of the server to fetch a key for.
+            keys_ids (list of str): The key_ids to check for.
+        """
+
+        # Check the datastore to see if we have one cached.
+        cached = yield self.store.get_server_verify_keys(server_name, key_ids)
+
+        if cached:
+            defer.returnValue(cached[0])
+            return
+
+        # Try to fetch the key from the remote server.
+        # TODO(markjh): Ratelimit requests to a given server.
+
+        (response, tls_certificate) = yield fetch_server_key(
+            server_name, self.hs.tls_context_factory
+        )
+
+        # Check the response.
+
+        x509_certificate_bytes = crypto.dump_certificate(
+            crypto.FILETYPE_ASN1, tls_certificate
+        )
+
+        if ("signatures" not in response
+            or server_name not in response["signatures"]):
+            raise ValueError("Key response not signed by remote server")
+
+        if "tls_certificate" not in response:
+            raise ValueError("Key response missing TLS certificate")
+
+        tls_certificate_b64 = response["tls_certificate"]
+
+        if encode_base64(x509_certificate_bytes) != tls_certificate_b64:
+            raise ValueError("TLS certificate doesn't match")
+
+        verify_keys = {}
+        for key_id, key_base64 in response["verify_keys"].items():
+            if is_signing_algorithm_supported(key_id):
+                key_bytes = decode_base64(key_base64)
+                verify_key = decode_verify_key_bytes(key_id, key_bytes)
+                verify_keys[key_id] = verify_key
+
+        for key_id in response["signatures"][server_name]:
+            if key_id not in response["verify_keys"]:
+                raise ValueError(
+                    "Key response must include verification keys for all"
+                    " signatures"
+                )
+            if key_id in verify_keys:
+                verify_signed_json(
+                    response,
+                    server_name,
+                    verify_keys[key_id]
+                )
+
+        # Cache the result in the datastore.
+
+        time_now_ms = self.clock.time_msec()
+
+        self.store.store_server_certificate(
+            server_name,
+            server_name,
+            time_now_ms,
+            tls_certificate,
+        )
+
+        for key_id, key in verify_keys.items():
+            self.store.store_server_verify_key(
+                server_name, server_name, time_now_ms, key
+            )
+
+        for key_id in key_ids:
+            if key_id in verify_keys:
+                defer.returnValue(verify_keys[key_id])
+                return
+
+        raise ValueError("No verification key found for given key ids")