Unable to connect to key backup

[richvdh]

On one of my test accounts, this is shown in backup settings:

When I click "Connect to backup", I get:

But when I go back to settings, it is still the same as before.

In the console:

22:37:24.716 FetchHttpApi: --> GET http://localhost:8008/_matrix/client/v3/room_keys/version [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
22:37:24.745 FetchHttpApi: <-- GET http://localhost:8008/_matrix/client/v3/room_keys/version [30ms 200] [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
22:37:24.754 FetchHttpApi: --> GET http://localhost:8008/_matrix/client/v3/room_keys/keys?version=xxx [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
22:37:24.811 FetchHttpApi: <-- GET http://localhost:8008/_matrix/client/v3/room_keys/keys?version=xxx [56ms 200] [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
22:37:24.820    INFO matrix_sdk_crypto::machine: Successfully imported room keys, total_count: 1, imported_count: 0, room_keys: {}
    at /home/rav/work/matrix-rust-sdk/crates/matrix-sdk-crypto/src/machine.rs:1775 [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
22:37:24.820 Checking key backup status... [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
22:37:24.821 FetchHttpApi: --> GET http://localhost:8008/_matrix/client/v3/room_keys/version [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
22:37:25.028 FetchHttpApi: <-- GET http://localhost:8008/_matrix/client/v3/room_keys/version [208ms 200] [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
22:37:25.053 Key backup present on server but not trusted: not enabling key backup [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)

[richvdh]

Legacy crypto behaves much the same way. In the console:

15:06:40.724 Checking key backup status... [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
15:06:40.724 FetchHttpApi: --> GET http://localhost:8008/_matrix/client/v3/room_keys/version [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
15:06:40.785 FetchHttpApi: <-- GET http://localhost:8008/_matrix/client/v3/room_keys/version [61ms 200] [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
15:06:40.787 Backup is trusted locally [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
15:06:40.787 Ignoring signature from unknown key ed25519:T4lieB66JX4oVLHGYE7h+19mAX4LRXMh1Bc2vFpznO0 [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
15:06:40.787 Ignoring signature from unknown key ed25519:JLBLBBZUGL [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
15:06:40.787 No usable key backup: not enabling key backup [rageshake.ts:74:27](webpack:///matrix-react-sdk/src/rageshake/rageshake.ts)
15:06:40.788 RestoreKeyBackupDialog: found cached backup key

[richvdh]

The specific problem with this account is that the backup appears to have been signed with an old cross-signing key (and a device that no longer exists).

[BillCarsonFr]

We should create several issues for that:

• Create a new settings UX backup
• Troubleshooting desynchronised backup (bad signature)
• Define the identity reset sementic properly (reset cross signing keys should sign the exisisting backup? if trusted)

See https://github.com/matrix-org/internal-config/issues/1315

[richvdh]

See:

• Key Backup section in User Settings is very confusing #26468
• "Connect to backup" does not report failures to connect backup #26530
• Define semantics for resetting cross-signing keys element-meta#2181