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

Fixes https://github.com/matrix-org/synapse/issues/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 https://github.com/matrix-org/synapse/pull/7637

Based on #7637

4 files changed, 110 insertions, 7 deletions

diff --git a/tests/federation/test_federation_sender.py b/tests/federation/test_federation_sender.py
index ff12539041..1a9bd5f37d 100644
--- a/tests/federation/test_federation_sender.py
+++ b/tests/federation/test_federation_sender.py
@@ -21,6 +21,7 @@ from signedjson.types import BaseKey, SigningKey
 
 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),
diff --git a/tests/handlers/test_e2e_keys.py b/tests/handlers/test_e2e_keys.py
index e1e144b2e7..6c1dc72bd1 100644
--- a/tests/handlers/test_e2e_keys.py
+++ b/tests/handlers/test_e2e_keys.py
@@ -25,6 +25,7 @@ from twisted.internet import defer
 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 @@ class E2eKeysHandlerTestCase(unittest.TestCase):
         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 @@ class E2eKeysHandlerTestCase(unittest.TestCase):
         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 @@ class E2eKeysHandlerTestCase(unittest.TestCase):
         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 @@ class E2eKeysHandlerTestCase(unittest.TestCase):
                         "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",
diff --git a/tests/handlers/test_user_directory.py b/tests/handlers/test_user_directory.py
index c15bce5bef..23fcc372dd 100644
--- a/tests/handlers/test_user_directory.py
+++ b/tests/handlers/test_user_directory.py
@@ -17,12 +17,13 @@ from mock import Mock
 from twisted.internet import defer
 
 import synapse.rest.admin
-from synapse.api.constants import UserTypes
+from synapse.api.constants import EventTypes, RoomEncryptionAlgorithms, UserTypes
 from synapse.rest.client.v1 import login, room
 from synapse.rest.client.v2_alpha import user_directory
 from synapse.storage.roommember import ProfileInfo
 
 from tests import unittest
+from tests.unittest import override_config
 
 
 class UserDirectoryTestCase(unittest.HomeserverTestCase):
@@ -147,6 +148,94 @@ class UserDirectoryTestCase(unittest.HomeserverTestCase):
         s = self.get_success(self.handler.search_users(u1, "user3", 10))
         self.assertEqual(len(s["results"]), 0)
 
+    @override_config({"encryption_enabled_by_default_for_room_type": "all"})
+    def test_encrypted_by_default_config_option_all(self):
+        """Tests that invite-only and non-invite-only rooms have encryption enabled by
+        default when the config option encryption_enabled_by_default_for_room_type is "all".
+        """
+        # Create a user
+        user = self.register_user("user", "pass")
+        user_token = self.login(user, "pass")
+
+        # Create an invite-only room as that user
+        room_id = self.helper.create_room_as(user, is_public=False, tok=user_token)
+
+        # Check that the room has an encryption state event
+        event_content = self.helper.get_state(
+            room_id=room_id, event_type=EventTypes.RoomEncryption, tok=user_token,
+        )
+        self.assertEqual(event_content, {"algorithm": RoomEncryptionAlgorithms.DEFAULT})
+
+        # Create a non invite-only room as that user
+        room_id = self.helper.create_room_as(user, is_public=True, tok=user_token)
+
+        # Check that the room has an encryption state event
+        event_content = self.helper.get_state(
+            room_id=room_id, event_type=EventTypes.RoomEncryption, tok=user_token,
+        )
+        self.assertEqual(event_content, {"algorithm": RoomEncryptionAlgorithms.DEFAULT})
+
+    @override_config({"encryption_enabled_by_default_for_room_type": "invite"})
+    def test_encrypted_by_default_config_option_invite(self):
+        """Tests that only new, invite-only rooms have encryption enabled by default when
+        the config option encryption_enabled_by_default_for_room_type is "invite".
+        """
+        # Create a user
+        user = self.register_user("user", "pass")
+        user_token = self.login(user, "pass")
+
+        # Create an invite-only room as that user
+        room_id = self.helper.create_room_as(user, is_public=False, tok=user_token)
+
+        # Check that the room has an encryption state event
+        event_content = self.helper.get_state(
+            room_id=room_id, event_type=EventTypes.RoomEncryption, tok=user_token,
+        )
+        self.assertEqual(event_content, {"algorithm": RoomEncryptionAlgorithms.DEFAULT})
+
+        # Create a non invite-only room as that user
+        room_id = self.helper.create_room_as(user, is_public=True, tok=user_token)
+
+        # Check that the room does not have an encryption state event
+        self.helper.get_state(
+            room_id=room_id,
+            event_type=EventTypes.RoomEncryption,
+            tok=user_token,
+            expect_code=404,
+        )
+
+    @override_config({"encryption_enabled_by_default_for_room_type": "off"})
+    def test_encrypted_by_default_config_option_off(self):
+        """Tests that neither new invite-only nor non-invite-only rooms have encryption
+        enabled by default when the config option
+        encryption_enabled_by_default_for_room_type is "off".
+        """
+        # Create a user
+        user = self.register_user("user", "pass")
+        user_token = self.login(user, "pass")
+
+        # Create an invite-only room as that user
+        room_id = self.helper.create_room_as(user, is_public=False, tok=user_token)
+
+        # Check that the room does not have an encryption state event
+        self.helper.get_state(
+            room_id=room_id,
+            event_type=EventTypes.RoomEncryption,
+            tok=user_token,
+            expect_code=404,
+        )
+
+        # Create a non invite-only room as that user
+        room_id = self.helper.create_room_as(user, is_public=True, tok=user_token)
+
+        # Check that the room does not have an encryption state event
+        self.helper.get_state(
+            room_id=room_id,
+            event_type=EventTypes.RoomEncryption,
+            tok=user_token,
+            expect_code=404,
+        )
+
     def test_spam_checker(self):
         """
         A user which fails to the spam checks will not appear in search results.
diff --git a/tests/test_federation.py b/tests/test_federation.py
index c662195eec..89dcc58b99 100644
--- a/tests/test_federation.py
+++ b/tests/test_federation.py
@@ -30,7 +30,7 @@ class MessageAcceptTests(unittest.HomeserverTestCase):
         room_creator = self.homeserver.get_room_creation_handler()
         room_deferred = ensureDeferred(
             room_creator.create_room(
-                our_user, room_creator.PRESETS_DICT["public_chat"], ratelimit=False
+                our_user, room_creator._presets_dict["public_chat"], ratelimit=False
             )
         )
         self.reactor.advance(0.1)