Add option to enable encryption by default for new rooms (#7639)

Fixes #2431

Adds config option `encryption_enabled_by_default_for_room_type`, which determines whether encryption should be enabled with the default encryption algorithm in private or public rooms upon creation. Whether the room is private or public is decided based upon the room creation preset that is used.

Part of this PR is also pulling out all of the individual instances of `m.megolm.v1.aes-sha2` into a constant variable to eliminate typos ala #7637

Based on #7637

changelog.d/7639.feature

@@ -0,0 +1 @@
+Add an option to enable encryption by default for new rooms.

docs/sample_config.yaml

@@ -1973,6 +1973,26 @@ spam_checker:
    #    example_stop_events_from: ['@bad:example.com']
 
 
+## Rooms ##
+
+# Controls whether locally-created rooms should be end-to-end encrypted by
+# default.
+#
+# Possible options are "all", "invite", and "off". They are defined as:
+#
+# * "all": any locally-created room
+# * "invite": any room created with the "private_chat" or "trusted_private_chat"
+#             room creation presets
+# * "off": this option will take no effect
+#
+# The default value is "off".
+#
+# Note that this option will only affect rooms created after it is set. It
+# will also not affect rooms created by other servers.
+#
+#encryption_enabled_by_default_for_room_type: invite
+
+
 # Uncomment to allow non-server-admin users to create groups on this server
 #
 #enable_group_creation: true

synapse/api/constants.py

@@ -150,3 +150,8 @@ class EventContentFields(object):
     # Timestamp to delete the event after
     # cf https://github.com/matrix-org/matrix-doc/pull/2228
     SELF_DESTRUCT_AFTER = "org.matrix.self_destruct_after"
+
+
+class RoomEncryptionAlgorithms(object):
+    MEGOLM_V1_AES_SHA2 = "m.megolm.v1.aes-sha2"
+    DEFAULT = MEGOLM_V1_AES_SHA2

synapse/config/homeserver.py

@@ -36,6 +36,7 @@
 from .redis import RedisConfig
 from .registration import RegistrationConfig
 from .repository import ContentRepositoryConfig
+from .room import RoomConfig
 from .room_directory import RoomDirectoryConfig
 from .saml2_config import SAML2Config
 from .server import ServerConfig
@@ -79,6 +80,7 @@ class HomeServerConfig(RootConfig):
         PasswordAuthProviderConfig,
         PushConfig,
         SpamCheckerConfig,
+        RoomConfig,
         GroupsConfig,
         UserDirectoryConfig,
         ConsentConfig,

synapse/config/room.py

@@ -0,0 +1,80 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 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 logging
+
+from synapse.api.constants import RoomCreationPreset
+
+from ._base import Config, ConfigError
+
+logger = logging.Logger(__name__)
+
+
+class RoomDefaultEncryptionTypes(object):
+    """Possible values for the encryption_enabled_by_default_for_room_type config option"""
+
+    ALL = "all"
+    INVITE = "invite"
+    OFF = "off"
+
+
+class RoomConfig(Config):
+    section = "room"
+
+    def read_config(self, config, **kwargs):
+        # Whether new, locally-created rooms should have encryption enabled
+        encryption_for_room_type = config.get(
+            "encryption_enabled_by_default_for_room_type",
+            RoomDefaultEncryptionTypes.OFF,
+        )
+        if encryption_for_room_type == RoomDefaultEncryptionTypes.ALL:
+            self.encryption_enabled_by_default_for_room_presets = [
+                RoomCreationPreset.PRIVATE_CHAT,
+                RoomCreationPreset.TRUSTED_PRIVATE_CHAT,
+                RoomCreationPreset.PUBLIC_CHAT,
+            ]
+        elif encryption_for_room_type == RoomDefaultEncryptionTypes.INVITE:
+            self.encryption_enabled_by_default_for_room_presets = [
+                RoomCreationPreset.PRIVATE_CHAT,
+                RoomCreationPreset.TRUSTED_PRIVATE_CHAT,
+            ]
+        elif encryption_for_room_type == RoomDefaultEncryptionTypes.OFF:
+            self.encryption_enabled_by_default_for_room_presets = []
+        else:
+            raise ConfigError(
+                "Invalid value for encryption_enabled_by_default_for_room_type"
+            )
+
+    def generate_config_section(self, **kwargs):
+        return """\
+        ## Rooms ##
+
+        # Controls whether locally-created rooms should be end-to-end encrypted by
+        # default.
+        #
+        # Possible options are "all", "invite", and "off". They are defined as:
+        #
+        # * "all": any locally-created room
+        # * "invite": any room created with the "private_chat" or "trusted_private_chat"
+        #             room creation presets
+        # * "off": this option will take no effect
+        #
+        # The default value is "off".
+        #
+        # Note that this option will only affect rooms created after it is set. It
+        # will also not affect rooms created by other servers.
+        #
+        #encryption_enabled_by_default_for_room_type: invite
+        """

synapse/handlers/federation.py

@@ -33,7 +33,12 @@
 from twisted.internet import defer
 
 from synapse import event_auth
-from synapse.api.constants import EventTypes, Membership, RejectedReason
+from synapse.api.constants import (
+    EventTypes,
+    Membership,
+    RejectedReason,
+    RoomEncryptionAlgorithms,
+)
 from synapse.api.errors import (
     AuthError,
     CodeMessageException,
@@ -742,7 +747,10 @@ async def _process_received_pdu(
                 if device:
                     keys = device.get("keys", {}).get("keys", {})
 
-                    if event.content.get("algorithm") == "m.megolm.v1.aes-sha2":
+                    if (
+                        event.content.get("algorithm")
+                        == RoomEncryptionAlgorithms.MEGOLM_V1_AES_SHA2
+                    ):
                         # For this algorithm we expect a curve25519 key.
                         key_name = "curve25519:%s" % (device_id,)
                         current_keys = [keys.get(key_name)]

synapse/handlers/room.py

@@ -26,7 +26,12 @@
 
 from six import iteritems, string_types
 
-from synapse.api.constants import EventTypes, JoinRules, RoomCreationPreset
+from synapse.api.constants import (
+    EventTypes,
+    JoinRules,
+    RoomCreationPreset,
+    RoomEncryptionAlgorithms,
+)
 from synapse.api.errors import AuthError, Codes, NotFoundError, StoreError, SynapseError
 from synapse.api.room_versions import KNOWN_ROOM_VERSIONS, RoomVersion
 from synapse.events.utils import copy_power_levels_contents
@@ -56,31 +61,6 @@
 
 
 class RoomCreationHandler(BaseHandler):
-
-    PRESETS_DICT = {
-        RoomCreationPreset.PRIVATE_CHAT: {
-            "join_rules": JoinRules.INVITE,
-            "history_visibility": "shared",
-            "original_invitees_have_ops": False,
-            "guest_can_join": True,
-            "power_level_content_override": {"invite": 0},
-        },
-        RoomCreationPreset.TRUSTED_PRIVATE_CHAT: {
-            "join_rules": JoinRules.INVITE,
-            "history_visibility": "shared",
-            "original_invitees_have_ops": True,
-            "guest_can_join": True,
-            "power_level_content_override": {"invite": 0},
-        },
-        RoomCreationPreset.PUBLIC_CHAT: {
-            "join_rules": JoinRules.PUBLIC,
-            "history_visibility": "shared",
-            "original_invitees_have_ops": False,
-            "guest_can_join": False,
-            "power_level_content_override": {},
-        },
-    }
-
     def __init__(self, hs):
         super(RoomCreationHandler, self).__init__(hs)
 
@@ -89,6 +69,39 @@ def __init__(self, hs):
         self.room_member_handler = hs.get_room_member_handler()
         self.config = hs.config
 
+        # Room state based off defined presets
+        self._presets_dict = {
+            RoomCreationPreset.PRIVATE_CHAT: {
+                "join_rules": JoinRules.INVITE,
+                "history_visibility": "shared",
+                "original_invitees_have_ops": False,
+                "guest_can_join": True,
+                "power_level_content_override": {"invite": 0},
+            },
+            RoomCreationPreset.TRUSTED_PRIVATE_CHAT: {
+                "join_rules": JoinRules.INVITE,
+                "history_visibility": "shared",
+                "original_invitees_have_ops": True,
+                "guest_can_join": True,
+                "power_level_content_override": {"invite": 0},
+            },
+            RoomCreationPreset.PUBLIC_CHAT: {
+                "join_rules": JoinRules.PUBLIC,
+                "history_visibility": "shared",
+                "original_invitees_have_ops": False,
+                "guest_can_join": False,
+                "power_level_content_override": {},
+            },
+        }
+
+        # Modify presets to selectively enable encryption by default per homeserver config
+        for preset_name, preset_config in self._presets_dict.items():
+            encrypted = (
+                preset_name
+                in self.config.encryption_enabled_by_default_for_room_presets
+            )
+            preset_config["encrypted"] = encrypted
+
         self._replication = hs.get_replication_data_handler()
 
         # linearizer to stop two upgrades happening at once
@@ -798,7 +811,7 @@ async def send(etype, content, **kwargs) -> int:
             )
             return last_stream_id
 
-        config = RoomCreationHandler.PRESETS_DICT[preset_config]
+        config = self._presets_dict[preset_config]
 
         creator_id = creator.user.to_string()
 
@@ -888,6 +901,13 @@ async def send(etype, content, **kwargs) -> int:
                 etype=etype, state_key=state_key, content=content
             )
 
+        if config["encrypted"]:
+            last_sent_stream_id = await send(
+                etype=EventTypes.RoomEncryption,
+                state_key="",
+                content={"algorithm": RoomEncryptionAlgorithms.DEFAULT},
+            )
+
         return last_sent_stream_id
 
     async def _generate_room_id(

tests/federation/test_federation_sender.py

@@ -21,6 +21,7 @@
 
 from twisted.internet import defer
 
+from synapse.api.constants import RoomEncryptionAlgorithms
 from synapse.rest import admin
 from synapse.rest.client.v1 import login
 from synapse.types import JsonDict, ReadReceipt
@@ -536,7 +537,10 @@ def build_device_dict(user_id: str, device_id: str, sk: SigningKey):
     return {
         "user_id": user_id,
         "device_id": device_id,
-        "algorithms": ["m.olm.curve25519-aes-sha2", "m.megolm.v1.aes-sha2"],
+        "algorithms": [
+            "m.olm.curve25519-aes-sha2",
+            RoomEncryptionAlgorithms.MEGOLM_V1_AES_SHA2,
+        ],
         "keys": {
             "curve25519:" + device_id: "curve25519+key",
             key_id(sk): encode_pubkey(sk),

tests/handlers/test_e2e_keys.py

@@ -25,6 +25,7 @@
 import synapse.handlers.e2e_keys
 import synapse.storage
 from synapse.api import errors
+from synapse.api.constants import RoomEncryptionAlgorithms
 
 from tests import unittest, utils
 
@@ -222,7 +223,10 @@ def test_reupload_signatures(self):
         device_key_1 = {
             "user_id": local_user,
             "device_id": "abc",
-            "algorithms": ["m.olm.curve25519-aes-sha2", "m.megolm.v1.aes-sha2"],
+            "algorithms": [
+                "m.olm.curve25519-aes-sha2",
+                RoomEncryptionAlgorithms.MEGOLM_V1_AES_SHA2,
+            ],
             "keys": {
                 "ed25519:abc": "base64+ed25519+key",
                 "curve25519:abc": "base64+curve25519+key",
@@ -232,7 +236,10 @@ def test_reupload_signatures(self):
         device_key_2 = {
             "user_id": local_user,
             "device_id": "def",
-            "algorithms": ["m.olm.curve25519-aes-sha2", "m.megolm.v1.aes-sha2"],
+            "algorithms": [
+                "m.olm.curve25519-aes-sha2",
+                RoomEncryptionAlgorithms.MEGOLM_V1_AES_SHA2,
+            ],
             "keys": {
                 "ed25519:def": "base64+ed25519+key",
                 "curve25519:def": "base64+curve25519+key",
@@ -315,7 +322,10 @@ def test_upload_signatures(self):
         device_key = {
             "user_id": local_user,
             "device_id": device_id,
-            "algorithms": ["m.olm.curve25519-aes-sha2", "m.megolm.v1.aes-sha2"],
+            "algorithms": [
+                "m.olm.curve25519-aes-sha2",
+                RoomEncryptionAlgorithms.MEGOLM_V1_AES_SHA2,
+            ],
             "keys": {"curve25519:xyz": "curve25519+key", "ed25519:xyz": device_pubkey},
             "signatures": {local_user: {"ed25519:xyz": "something"}},
         }
@@ -392,7 +402,7 @@ def test_upload_signatures(self):
                         "device_id": device_id,
                         "algorithms": [
                             "m.olm.curve25519-aes-sha2",
-                            "m.megolm.v1.aes-sha2",
+                            RoomEncryptionAlgorithms.MEGOLM_V1_AES_SHA2,
                         ],
                         "keys": {
                             "curve25519:xyz": "curve25519+key",