Allow resigning of events with a new signing key#19668
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Add `resign_event` and `event_needs_resigning` utility functions to `event_signing.py`, and a `_resign_events` background update handler that iterates through locally-sent events and re-signs any that aren't signed with the current signing key. Co-Authored-By: Kegan Dougall <kegan@element.io> Co-Authored-By: Erik Johnston <erikj@element.io>
Allow admins to trigger the event re-signing background update via POST /_synapse/admin/v1/background_updates/start_job with job_name "event_resign".
Add unit tests for `resign_event` and `event_needs_resigning` in test_event_signing.py, and an integration test for the event_resign background update in test_events_bg_updates.py.
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erikjohnston
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Apr 8, 2026
Use -(1 << 31) as the initial stream position instead of 0, matching the precedent set by POPULATE_STREAM_ORDERING2. This ensures events with negative stream orderings (from backfill) are also covered.
Allow filtering which events to re-sign: - old_key_id: only re-sign events signed with a specific key (filtered in Python since signatures are stored as JSON) - before_ts: only re-sign events with received_ts < value (filtered in SQL alongside the existing stream_ordering scan) These parameters are passed through the admin API POST body and preserved in the background update progress across batches.
erikjohnston
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Apr 8, 2026
Instead of matching on the key ID string, accept the full public key (format: "algorithm:key_id base64key") and verify the event signature against it. This is more secure as it ensures we only re-sign events genuinely signed by the specified key. Events without a signature for the key ID are fast-path skipped. A warning is logged if a signature exists but fails verification.
Co-authored-by: Erik Johnston <erikj@element.io>
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erikjohnston
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Apr 9, 2026
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This adds a way to re-sign all locally-created events with a new signing key, which is useful when rotating server signing keys.
This doesn't trigger automatically, instead needs to be triggered when needed via the admin API.
c.f. https://github.com/matrix-org/internal-config/issues/1670#issuecomment-4206020126 for internal discussion.