From c12bc704fe7e09ec00de0aceccef2f3af9c98e48 Mon Sep 17 00:00:00 2001
From: Hubert Chathi <hubertc@matrix.org>
Date: Tue, 3 Aug 2021 20:57:11 -0400
Subject: [PATCH 1/2] Send and handle cross-signing messages using the stable
 prefix.

---
 synapse/handlers/e2e_keys.py               | 8 ++++++--
 synapse/storage/databases/main/devices.py  | 4 +++-
 tests/federation/test_federation_sender.py | 5 +++--
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index d92370859fb6..c4b4c7c003db 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -65,8 +65,12 @@ def __init__(self, hs: "HomeServer"):
         else:
             # Only register this edu handler on master as it requires writing
             # device updates to the db
-            #
-            # FIXME: switch to m.signing_key_update when MSC1756 is merged into the spec
+            federation_registry.register_edu_handler(
+                "m.signing_key_update",
+                self._edu_updater.incoming_signing_key_update,
+            )
+            # also handle the unstable version
+            # FIXME: remove this when enough servers have upgraded
             federation_registry.register_edu_handler(
                 "org.matrix.signing_key_update",
                 self._edu_updater.incoming_signing_key_update,
diff --git a/synapse/storage/databases/main/devices.py b/synapse/storage/databases/main/devices.py
index 3816a0ca5382..7092740c10b3 100644
--- a/synapse/storage/databases/main/devices.py
+++ b/synapse/storage/databases/main/devices.py
@@ -240,7 +240,9 @@ async def get_device_updates_by_remote(
         # add the updated cross-signing keys to the results list
         for user_id, result in cross_signing_keys_by_user.items():
             result["user_id"] = user_id
-            # FIXME: switch to m.signing_key_update when MSC1756 is merged into the spec
+            results.append(("m.signing_key_update", result))
+            # also send the unstable version
+            # FIXME: remove this when enough servers have upgraded
             results.append(("org.matrix.signing_key_update", result))
 
         return now_stream_id, results
diff --git a/tests/federation/test_federation_sender.py b/tests/federation/test_federation_sender.py
index b00dd143d677..335fc7a3a277 100644
--- a/tests/federation/test_federation_sender.py
+++ b/tests/federation/test_federation_sender.py
@@ -266,7 +266,8 @@ def test_upload_signatures(self):
         )
 
         # expect signing key update edu
-        self.assertEqual(len(self.edus), 1)
+        self.assertEqual(len(self.edus), 2)
+        self.assertEqual(self.edus.pop(0)["edu_type"], "m.signing_key_update")
         self.assertEqual(self.edus.pop(0)["edu_type"], "org.matrix.signing_key_update")
 
         # sign the devices
@@ -491,7 +492,7 @@ def check_signing_key_update_txn(
     ) -> None:
         """Check that the txn has an EDU with a signing key update."""
         edus = txn["edus"]
-        self.assertEqual(len(edus), 1)
+        self.assertEqual(len(edus), 2)
 
     def generate_and_upload_device_signing_key(
         self, user_id: str, device_id: str

From a4f5aff9aee2ef54d26a2602368608aa9ea66e58 Mon Sep 17 00:00:00 2001
From: Hubert Chathi <hubertc@matrix.org>
Date: Tue, 3 Aug 2021 21:01:42 -0400
Subject: [PATCH 2/2] add changelog

---
 changelog.d/10520.misc | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 changelog.d/10520.misc

diff --git a/changelog.d/10520.misc b/changelog.d/10520.misc
new file mode 100644
index 000000000000..a911e165da80
--- /dev/null
+++ b/changelog.d/10520.misc
@@ -0,0 +1 @@
+Send and handle cross-signing messages using the stable prefix.