Use the v2 lookup API for 3PID invites (#5897)

Fixes https://github.com/matrix-org/synapse/issues/5861

Adds support for the v2 lookup API as defined in [MSC2134](https://github.com/matrix-org/matrix-doc/pull/2134). Currently this is only used for 3PID invites.

Sytest PR: https://github.com/matrix-org/sytest/pull/679

4 files changed, 166 insertions, 9 deletions

diff --git a/changelog.d/5897.feature b/changelog.d/5897.feature
new file mode 100644
index 0000000000..7b10774c96
--- /dev/null
+++ b/changelog.d/5897.feature
@@ -0,0 +1 @@
+Switch to the v2 lookup API for 3PID invites.
\ No newline at end of file
diff --git a/synapse/handlers/identity.py b/synapse/handlers/identity.py
index d199521b58..97daca5fee 100644
--- a/synapse/handlers/identity.py
+++ b/synapse/handlers/identity.py
@@ -282,3 +282,16 @@ class IdentityHandler(BaseHandler):
         except HttpResponseException as e:
             logger.info("Proxied requestToken failed: %r", e)
             raise e.to_synapse_error()
+
+
+class LookupAlgorithm:
+    """
+    Supported hashing algorithms when performing a 3PID lookup.
+
+    SHA256 - Hashing an (address, medium, pepper) combo with sha256, then url-safe base64
+        encoding
+    NONE - Not performing any hashing. Simply sending an (address, medium) combo in plaintext
+    """
+
+    SHA256 = "sha256"
+    NONE = "none"
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 249a6d9c5d..4605cb9c0b 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -29,9 +29,11 @@ from twisted.internet import defer
 from synapse import types
 from synapse.api.constants import EventTypes, Membership
 from synapse.api.errors import AuthError, Codes, HttpResponseException, SynapseError
+from synapse.handlers.identity import LookupAlgorithm
 from synapse.types import RoomID, UserID
 from synapse.util.async_helpers import Linearizer
 from synapse.util.distributor import user_joined_room, user_left_room
+from synapse.util.hash import sha256_and_url_safe_base64
 
 from ._base import BaseHandler
 
@@ -523,7 +525,7 @@ class RoomMemberHandler(object):
             event (SynapseEvent): The membership event.
             context: The context of the event.
             is_guest (bool): Whether the sender is a guest.
-            room_hosts ([str]): Homeservers which are likely to already be in
+            remote_room_hosts (list[str]|None): Homeservers which are likely to already be in
                 the room, and could be danced with in order to join this
                 homeserver for the first time.
             ratelimit (bool): Whether to rate limit this request.
@@ -634,7 +636,7 @@ class RoomMemberHandler(object):
             servers.remove(room_alias.domain)
         servers.insert(0, room_alias.domain)
 
-        return (RoomID.from_string(room_id), servers)
+        return RoomID.from_string(room_id), servers
 
     @defer.inlineCallbacks
     def _get_inviter(self, user_id, room_id):
@@ -697,6 +699,44 @@ class RoomMemberHandler(object):
             raise SynapseError(
                 403, "Looking up third-party identifiers is denied from this server"
             )
+
+        # Check what hashing details are supported by this identity server
+        use_v1 = False
+        hash_details = None
+        try:
+            hash_details = yield self.simple_http_client.get_json(
+                "%s%s/_matrix/identity/v2/hash_details" % (id_server_scheme, id_server)
+            )
+        except (HttpResponseException, ValueError) as e:
+            # Catch HttpResponseExcept for a non-200 response code
+            # Catch ValueError for non-JSON response body
+
+            # Check if this identity server does not know about v2 lookups
+            if e.code == 404:
+                # This is an old identity server that does not yet support v2 lookups
+                use_v1 = True
+            else:
+                logger.warn("Error when looking up hashing details: %s" % (e,))
+                return None
+
+        if use_v1:
+            return (yield self._lookup_3pid_v1(id_server, medium, address))
+
+        return (yield self._lookup_3pid_v2(id_server, medium, address, hash_details))
+
+    @defer.inlineCallbacks
+    def _lookup_3pid_v1(self, id_server, medium, address):
+        """Looks up a 3pid in the passed identity server using v1 lookup.
+
+        Args:
+            id_server (str): The server name (including port, if required)
+                of the identity server to use.
+            medium (str): The type of the third party identifier (e.g. "email").
+            address (str): The third party identifier (e.g. "foo@example.com").
+
+        Returns:
+            str: the matrix ID of the 3pid, or None if it is not recognized.
+        """
         try:
             data = yield self.simple_http_client.get_json(
                 "%s%s/_matrix/identity/api/v1/lookup" % (id_server_scheme, id_server),
@@ -711,8 +751,83 @@ class RoomMemberHandler(object):
 
         except IOError as e:
             logger.warn("Error from identity server lookup: %s" % (e,))
+
+        return None
+
+    @defer.inlineCallbacks
+    def _lookup_3pid_v2(self, id_server, medium, address, hash_details):
+        """Looks up a 3pid in the passed identity server using v2 lookup.
+
+        Args:
+            id_server (str): The server name (including port, if required)
+                of the identity server to use.
+            medium (str): The type of the third party identifier (e.g. "email").
+            address (str): The third party identifier (e.g. "foo@example.com").
+            hash_details (dict[str, str|list]): A dictionary containing hashing information
+                provided by an identity server.
+
+        Returns:
+            Deferred[str|None]: the matrix ID of the 3pid, or None if it is not recognised.
+        """
+        # Extract information from hash_details
+        supported_lookup_algorithms = hash_details["algorithms"]
+        lookup_pepper = hash_details["lookup_pepper"]
+
+        # Check if any of the supported lookup algorithms are present
+        if LookupAlgorithm.SHA256 in supported_lookup_algorithms:
+            # Perform a hashed lookup
+            lookup_algorithm = LookupAlgorithm.SHA256
+
+            # Hash address, medium and the pepper with sha256
+            to_hash = "%s %s %s" % (address, medium, lookup_pepper)
+            lookup_value = sha256_and_url_safe_base64(to_hash)
+
+        elif LookupAlgorithm.NONE in supported_lookup_algorithms:
+            # Perform a non-hashed lookup
+            lookup_algorithm = LookupAlgorithm.NONE
+
+            # Combine together plaintext address and medium
+            lookup_value = "%s %s" % (address, medium)
+
+        else:
+            logger.warn(
+                "None of the provided lookup algorithms of %s%s are supported: %s",
+                id_server_scheme,
+                id_server,
+                hash_details["algorithms"],
+            )
+            raise SynapseError(
+                400,
+                "Provided identity server does not support any v2 lookup "
+                "algorithms that this homeserver supports.",
+            )
+
+        try:
+            lookup_results = yield self.simple_http_client.post_json_get_json(
+                "%s%s/_matrix/identity/v2/lookup" % (id_server_scheme, id_server),
+                {
+                    "addresses": [lookup_value],
+                    "algorithm": lookup_algorithm,
+                    "pepper": lookup_pepper,
+                },
+            )
+        except (HttpResponseException, ValueError) as e:
+            # Catch HttpResponseExcept for a non-200 response code
+            # Catch ValueError for non-JSON response body
+            logger.warn("Error when performing a 3pid lookup: %s" % (e,))
+            return None
+
+        # Check for a mapping from what we looked up to an MXID
+        if "mappings" not in lookup_results or not isinstance(
+            lookup_results["mappings"], dict
+        ):
+            logger.debug("No results from 3pid lookup")
             return None
 
+        # Return the MXID if it's available, or None otherwise
+        mxid = lookup_results["mappings"].get(lookup_value)
+        return mxid
+
     @defer.inlineCallbacks
     def _verify_any_signature(self, data, server_hostname):
         if server_hostname not in data["signatures"]:
@@ -962,9 +1077,7 @@ class RoomMemberMasterHandler(RoomMemberHandler):
         )
 
         if complexity:
-            if complexity["v1"] > max_complexity:
-                return True
-            return False
+            return complexity["v1"] > max_complexity
         return None
 
     @defer.inlineCallbacks
@@ -980,10 +1093,7 @@ class RoomMemberMasterHandler(RoomMemberHandler):
         max_complexity = self.hs.config.limit_remote_rooms.complexity
         complexity = yield self.store.get_room_complexity(room_id)
 
-        if complexity["v1"] > max_complexity:
-            return True
-
-        return False
+        return complexity["v1"] > max_complexity
 
     @defer.inlineCallbacks
     def _remote_join(self, requester, remote_room_hosts, room_id, user, content):
diff --git a/synapse/util/hash.py b/synapse/util/hash.py
new file mode 100644
index 0000000000..359168704e
--- /dev/null
+++ b/synapse/util/hash.py
@@ -0,0 +1,33 @@
+# -*- coding: utf-8 -*-
+
+# Copyright 2019 The Matrix.org Foundation C.I.C.
+#
+# 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.
+
+import hashlib
+
+import unpaddedbase64
+
+
+def sha256_and_url_safe_base64(input_text):
+    """SHA256 hash an input string, encode the digest as url-safe base64, and
+    return
+
+    :param input_text: string to hash
+    :type input_text: str
+
+    :returns a sha256 hashed and url-safe base64 encoded digest
+    :rtype: str
+    """
+    digest = hashlib.sha256(input_text.encode()).digest()
+    return unpaddedbase64.encode_base64(digest, urlsafe=True)