Add MSC4243 flag, verify event signatures from the user ID

2025-09-09 13:11:34 +01:00
parent 39e4f27347
commit aefeb3cb58
4 changed files with 150 additions and 15 deletions
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -116,6 +116,8 @@ class RoomVersion:
    msc4289_creator_power_enabled: bool
    # MSC4291: Room IDs as hashes of the create event
    msc4291_room_ids_as_hashes: bool
+    # MSC4243: User ID localparts as Account Keys
+    msc4243_account_keys: bool


 class RoomVersions:
@@ -140,6 +142,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    V2 = RoomVersion(
        "2",
@@ -162,6 +165,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    V3 = RoomVersion(
        "3",
@@ -184,6 +188,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    V4 = RoomVersion(
        "4",
@@ -206,6 +211,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    V5 = RoomVersion(
        "5",
@@ -228,6 +234,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    V6 = RoomVersion(
        "6",
@@ -250,6 +257,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    V7 = RoomVersion(
        "7",
@@ -272,6 +280,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    V8 = RoomVersion(
        "8",
@@ -294,6 +303,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    V9 = RoomVersion(
        "9",
@@ -316,6 +326,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    V10 = RoomVersion(
        "10",
@@ -338,6 +349,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    MSC1767v10 = RoomVersion(
        # MSC1767 (Extensible Events) based on room version "10"
@@ -361,6 +373,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    MSC3757v10 = RoomVersion(
        # MSC3757 (Restricting who can overwrite a state event) based on room version "10"
@@ -384,6 +397,7 @@ class RoomVersions:
        msc3757_enabled=True,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    V11 = RoomVersion(
        "11",
@@ -406,6 +420,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    MSC3757v11 = RoomVersion(
        # MSC3757 (Restricting who can overwrite a state event) based on room version "11"
@@ -429,6 +444,7 @@ class RoomVersions:
        msc3757_enabled=True,
        msc4289_creator_power_enabled=False,
        msc4291_room_ids_as_hashes=False,
+        msc4243_account_keys=False,
    )
    HydraV11 = RoomVersion(
        "org.matrix.hydra.11",
@@ -451,6 +467,7 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=True,  # Changed from v11
        msc4291_room_ids_as_hashes=True,  # Changed from v11
+        msc4243_account_keys=False,
    )
    V12 = RoomVersion(
        "12",
@@ -473,6 +490,30 @@ class RoomVersions:
        msc3757_enabled=False,
        msc4289_creator_power_enabled=True,  # Changed from v11
        msc4291_room_ids_as_hashes=True,  # Changed from v11
+        msc4243_account_keys=False,
+    )
+    MSC4243v12 = RoomVersion(
+        "org.matrix.12.4243",
+        RoomDisposition.STABLE,
+        EventFormatVersions.ROOM_V11_HYDRA_PLUS,
+        StateResolutionVersions.V2_1,  # Changed from v11
+        enforce_key_validity=False,  # No longer enforce key validity.
+        special_case_aliases_auth=False,
+        strict_canonicaljson=True,
+        limit_notifications_power_levels=True,
+        implicit_room_creator=True,  # Used by MSC3820
+        updated_redaction_rules=True,  # Used by MSC3820
+        restricted_join_rule=True,
+        restricted_join_rule_fix=True,
+        knock_join_rule=True,
+        msc3389_relation_redactions=False,
+        knock_restricted_join_rule=True,
+        enforce_int_power_levels=True,
+        msc3931_push_features=(),
+        msc3757_enabled=False,
+        msc4289_creator_power_enabled=True,
+        msc4291_room_ids_as_hashes=True,
+        msc4243_account_keys=True,
    )


@@ -494,6 +535,7 @@ KNOWN_ROOM_VERSIONS: Dict[str, RoomVersion] = {
        RoomVersions.MSC3757v10,
        RoomVersions.MSC3757v11,
        RoomVersions.HydraV11,
+        RoomVersions.MSC4243v12,
    )
 }

--- a/synapse/crypto/keyring.py
+++ b/synapse/crypto/keyring.py
@@ -47,7 +47,7 @@ from synapse.events import EventBase
 from synapse.events.utils import prune_event_dict
 from synapse.logging.context import make_deferred_yieldable, run_in_background
 from synapse.storage.keys import FetchKeyResult
-from synapse.types import JsonDict
+from synapse.types import JsonDict, UserID
 from synapse.util import unwrapFirstError
 from synapse.util.async_helpers import yieldable_gather_results
 from synapse.util.batching_queue import BatchingQueue
@@ -83,6 +83,7 @@ class VerifyJsonRequest:
    get_json_object: Callable[[], JsonDict]
    minimum_valid_until_ts: int
    key_ids: List[str]
+    key_ids_are_public_keys: bool = False

    @staticmethod
    def from_json_object(
@@ -118,6 +119,7 @@ class VerifyJsonRequest:
            lambda: prune_event_dict(event.room_version, event.get_pdu_json()),
            minimum_valid_until_ms,
            key_ids=key_ids,
+            key_ids_are_public_keys=False,
        )


@@ -265,6 +267,38 @@ class Keyring:
            )
        )

+    async def verify_event_for_account_key(
+        self,
+        user_id_str: str,
+        event: EventBase,
+    ) -> None:
+        """Verify that the given event has been signed by the provided account key, as determined by
+        the user_id provided.
+
+        Args:
+            user_id_str: The MSC4243 user ID, consisting of an account key localpart and a domain.
+            event: The PDU that should be signed with the account key. Room version must support MSC4243.
+        """
+        assert event.room_version.msc4243_account_keys
+        user_id = UserID.from_string(user_id_str)
+        key_ids = list(event.signatures.get(user_id.domain, []))
+        # only keep the key ID that matches the desired user ID we want to verify as.
+        # Events can be signed by multiple parties e.g invites, restricted joins
+        expected_key_id = "ed25519:" + user_id.localpart
+        key_ids = [key_id for key_id in key_ids if key_id == expected_key_id]
+        assert len(key_ids) == 1  # the user must have signed the event.
+        await self.process_request(
+            VerifyJsonRequest(
+                user_id.domain,
+                # We defer creating the redacted json object, as it uses a lot more
+                # memory than the Event object itself.
+                lambda: prune_event_dict(event.room_version, event.get_pdu_json()),
+                0,  # No validity times
+                key_ids=key_ids,
+                key_ids_are_public_keys=True,
+            )
+        )
+
    async def process_request(self, verify_request: VerifyJsonRequest) -> None:
        """Processes the `VerifyJsonRequest`. Raises if the object is not signed
        by the server, the signatures don't match or we failed to fetch the
@@ -278,6 +312,15 @@ class Keyring:
                Codes.UNAUTHORIZED,
            )

+        if verify_request.key_ids_are_public_keys:
+            # No need to fetch keys as we have them already.
+            assert len(verify_request.key_ids) == 1
+            key_id = verify_request.key_ids[0]
+            key_bytes = decode_base64(key_id.removeprefix("ed25519:"))
+            verify_key = decode_verify_key_bytes(key_id, key_bytes)
+            await self._process_json(verify_key, verify_request)
+            return
+
        found_keys: Dict[str, FetchKeyResult] = {}

        # If we are the originating server, short-circuit the key-fetch for any keys
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -241,16 +241,28 @@ async def _check_sigs_on_pdu(
    sender_domain = get_domain_from_id(pdu.sender)
    if not _is_invite_via_3pid(pdu):
        try:
-            await keyring.verify_event_for_server(
-                sender_domain,
-                pdu,
-                pdu.origin_server_ts if room_version.enforce_key_validity else 0,
-            )
+            if pdu.room_version.msc4243_account_keys:
+                await keyring.verify_event_for_account_key(
+                    pdu.sender,
+                    pdu,
+                )
+            else:
+                await keyring.verify_event_for_server(
+                    sender_domain,
+                    pdu,
+                    pdu.origin_server_ts if room_version.enforce_key_validity else 0,
+                )
        except Exception as e:
-            raise InvalidEventSignatureError(
-                f"unable to verify signature for sender domain {sender_domain}: {e}",
-                pdu.event_id,
-            ) from None
+            if pdu.room_version.msc4243_account_keys:
+                raise InvalidEventSignatureError(
+                    f"unable to verify signature for account key {pdu.sender}: {e}",
+                    pdu.event_id,
+                ) from None
+            else:
+                raise InvalidEventSignatureError(
+                    f"unable to verify signature for sender domain {sender_domain}: {e}",
+                    pdu.event_id,
+                ) from None

    # now let's look for events where the sender's domain is different to the
    # event id's domain (normally only the case for joins/leaves), and add additional
@@ -283,11 +295,17 @@ async def _check_sigs_on_pdu(
            pdu.content[EventContentFields.AUTHORISING_USER]
        )
        try:
-            await keyring.verify_event_for_server(
-                authorising_server,
-                pdu,
-                pdu.origin_server_ts if room_version.enforce_key_validity else 0,
-            )
+            if pdu.room_version.msc4243_account_keys:
+                await keyring.verify_event_for_account_key(
+                    pdu.content[EventContentFields.AUTHORISING_USER],
+                    pdu,
+                )
+            else:
+                await keyring.verify_event_for_server(
+                    authorising_server,
+                    pdu,
+                    pdu.origin_server_ts if room_version.enforce_key_validity else 0,
+                )
        except Exception as e:
            raise InvalidEventSignatureError(
                f"unable to verify signature for authorising serve {authorising_server}: {e}",
--- a/tests/crypto/test_keyring.py
+++ b/tests/crypto/test_keyring.py
@@ -34,12 +34,15 @@ from twisted.internet.defer import Deferred, ensureDeferred
 from twisted.internet.testing import MemoryReactor

 from synapse.api.errors import SynapseError
+from synapse.api.room_versions import RoomVersions
 from synapse.crypto import keyring
+from synapse.crypto.event_signing import compute_event_signature
 from synapse.crypto.keyring import (
    PerspectivesKeyFetcher,
    ServerKeyFetcher,
    StoreKeyFetcher,
 )
+from synapse.events import make_event_from_dict
 from synapse.logging.context import (
    ContextRequest,
    LoggingContext,
@@ -388,6 +391,35 @@ class KeyringTestCase(unittest.HomeserverTestCase):
        mock_fetcher1.get_keys.assert_called_once()
        mock_fetcher2.get_keys.assert_called_once()

+    def test_verify_event_for_account_key(self) -> None:
+        """Test basic functionality of verify_event_for_account_key.
+        - That it parses the user ID correctly.
+        - That it doesn't rely on key fetchers.
+        """
+        room_version = RoomVersions.MSC4243v12
+
+        # Make a signing key and replace the key ID from '1' to be the base64 public key
+        signing_key = signedjson.key.generate_signing_key("1")
+        verify_key_str = encode_verify_key_base64(get_verify_key(signing_key))
+        signing_key.version = verify_key_str
+        domain = "can.be.anything.com"
+        signing_user_id = f"@{verify_key_str}:{domain}"
+
+        event_dict = {
+            "type": "m.room.create",
+            "state_key": "",
+            "sender": signing_user_id,
+            "content": {
+                "room_version": room_version.identifier,
+            },
+        }
+        event_dict["signatures"] = compute_event_signature(
+            room_version, event_dict, signature_name=domain, signing_key=signing_key
+        )
+        event = make_event_from_dict(event_dict, room_version)
+        kr = keyring.Keyring(self.hs, key_fetchers=None)
+        self.get_success(kr.verify_event_for_account_key(signing_user_id, event))
+

@logcontext_clean
 class ServerKeyFetcherTestCase(unittest.HomeserverTestCase):