diff --git a/synapse/crypto/keyclient.py b/synapse/crypto/keyclient.py
new file mode 100644
index 0000000000..b53d1c572b
--- /dev/null
+++ b/synapse/crypto/keyclient.py
@@ -0,0 +1,118 @@
+# -*- coding: utf-8 -*-
+# Copyright 2014 matrix.org
+#
+# 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 twisted.web.http import HTTPClient
+from twisted.internet import defer, reactor
+from twisted.internet.protocol import ClientFactory
+from twisted.names.srvconnect import SRVConnector
+import json
+import logging
+
+
+logger = logging.getLogger(__name__)
+
+
+@defer.inlineCallbacks
+def fetch_server_key(server_name, ssl_context_factory):
+ """Fetch the keys for a remote server."""
+
+ factory = SynapseKeyClientFactory()
+
+ SRVConnector(
+ reactor, "matrix", server_name, factory,
+ protocol="tcp", connectFuncName="connectSSL", defaultPort=443,
+ connectFuncKwArgs=dict(contextFactory=ssl_context_factory)).connect()
+
+ server_key, server_certificate = yield factory.remote_key
+
+ defer.returnValue((server_key, server_certificate))
+
+
+class SynapseKeyClientError(Exception):
+ """The key wasn't retireved from the remote server."""
+ pass
+
+
+class SynapseKeyClientProtocol(HTTPClient):
+ """Low level HTTPS client which retrieves an application/json response from
+ the server and extracts the X.509 certificate for the remote peer from the
+ SSL connection."""
+
+ def connectionMade(self):
+ logger.debug("Connected to %s", self.transport.getHost())
+ self.sendCommand(b"GET", b"/key")
+ self.endHeaders()
+ self.timer = reactor.callLater(
+ self.factory.timeout_seconds,
+ self.on_timeout
+ )
+
+ def handleStatus(self, version, status, message):
+ if status != b"200":
+ logger.info("Non-200 response from %s: %s %s",
+ self.transport.getHost(), status, message)
+ self.transport.abortConnection()
+
+ def handleResponse(self, response_body_bytes):
+ try:
+ json_response = json.loads(response_body_bytes)
+ except ValueError:
+ logger.info("Invalid JSON response from %s",
+ self.transport.getHost())
+ self.transport.abortConnection()
+ return
+
+ certificate = self.transport.getPeerCertificate()
+ self.factory.on_remote_key((json_response, certificate))
+ self.transport.abortConnection()
+ self.timer.cancel()
+
+ def on_timeout(self):
+ logger.debug("Timeout waiting for response from %s",
+ self.transport.getHost())
+ self.transport.abortConnection()
+
+
+class SynapseKeyClientFactory(ClientFactory):
+ protocol = SynapseKeyClientProtocol
+ max_retries = 5
+ timeout_seconds = 30
+
+ def __init__(self):
+ self.succeeded = False
+ self.retries = 0
+ self.remote_key = defer.Deferred()
+
+ def on_remote_key(self, key):
+ self.succeeded = True
+ self.remote_key.callback(key)
+
+ def retry_connection(self, connector):
+ self.retries += 1
+ if self.retries < self.max_retries:
+ connector.connector = None
+ connector.connect()
+ else:
+ self.remote_key.errback(
+ SynapseKeyClientError("Max retries exceeded"))
+
+ def clientConnectionFailed(self, connector, reason):
+ logger.info("Connection failed %s", reason)
+ self.retry_connection(connector)
+
+ def clientConnectionLost(self, connector, reason):
+ logger.info("Connection lost %s", reason)
+ if not self.succeeded:
+ self.retry_connection(connector)
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