Disabling key backups and then trying to re-enable fails without an error (if you have an untrusted key backup version on your account

[Half-Shot]

Steps to reproduce

1. "Allow key storage" is enabled (suspected broken)
2. Disable key storage (click yes on warnings)
3. Toggle "Allow key storage"

Outcome

What did you expect?

Key storage to be enabled

What happened instead?

The spinner span for a second and then the toggle went back. No errors to indicate what I must to do to correct this.

Operating system

Arch Linux

Application version

Element Nightly version: 2025083001 Crypto version: Rust SDK 0.13.0 (f64839e), Vodozemac 0.9.0

How did you install the app?

AUR

Homeserver

half-shot.uk

Will you send logs?

Yes

[Half-Shot]

Right, so I think I am starting to understand the state of this a little. The total absence of logging in this area is not helpful.

element-web/src/components/viewmodels/settings/encryption/KeyStoragePanelViewModel.ts

Lines 47 to 113 in be3778b

	const checkStatus = useCallback(async () => {
	const crypto = matrixClient.getCrypto();
	if (!crypto) {
	logger.error("Can't check key backup status: no crypto module available");
	return;
	}
	// The toggle is enabled only if this device will upload megolm keys to the backup.
	// This is consistent with EX.
	const activeBackupVersion = await crypto.getActiveSessionBackupVersion();
	setIsEnabled(activeBackupVersion !== null);
	}, [matrixClient]);
	useEffect(() => {
	(async () => {
	await checkStatus();
	setLoading(false);
	})();
	}, [checkStatus]);
	const setEnabled = useCallback(
	async (enable: boolean) => {
	setPendingValue(enable);
	try {
	// stop the device listener since enabling or (especially) disabling key storage must be
	// done with a sequence of API calls that will put the account in a slightly different
	// state each time, so suppress any warning toasts until the process is finished (when
	// we'll turn it back on again.)
	DeviceListener.sharedInstance().stop();
	const crypto = matrixClient.getCrypto();
	if (!crypto) {
	logger.error("Can't change key backup status: no crypto module available");
	return;
	}
	if (enable) {
	// If there is no existing key backup on the server, create one.
	// `resetKeyBackup` will delete any existing backup, so we only do this if there is no existing backup.
	const currentKeyBackup = await crypto.checkKeyBackupAndEnable();
	if (currentKeyBackup === null) {
	await crypto.resetKeyBackup();
	// resetKeyBackup fires this off in the background without waiting, so we need to do it
	// explicitly and wait for it, otherwise it won't be enabled yet when we check again.
	await crypto.checkKeyBackupAndEnable();
	}
	// Set the flag so that EX no longer thinks the user wants backup disabled
	await matrixClient.setAccountData(BACKUP_DISABLED_ACCOUNT_DATA_KEY, { disabled: false });
	} else {
	// This method will delete the key backup as well as server side recovery keys and other
	// server-side crypto data.
	await crypto.disableKeyStorage();
	// Set a flag to say that the user doesn't want key backup.
	// Element X uses this to determine whether to set up automatically,
	// so this will stop EX turning it back on spontaneously.
	await matrixClient.setAccountData(BACKUP_DISABLED_ACCOUNT_DATA_KEY, { disabled: true });
	}
	await checkStatus();
	} finally {
	setPendingValue(undefined);
	DeviceListener.sharedInstance().start(matrixClient);
	}
	},
	[setPendingValue, checkStatus, matrixClient],
	);

1. KeyStoragePanelViewModel checks to see if there is a currentKeyBackup. I still have one, so it is not null, skipping the following if block
2. We set the "backup disabled account key" to false.
3. In checkStatus, activeBackupVersion is still null so we toggle back to false.

[Half-Shot]

Aha, this is what I believe the bug is:

2025-09-05T06:50:37.271Z D FetchHttpApi: --> DELETE https://chaotic.half-shot.uk/_matrix/client/v3/room_keys/version/2
2025-09-05T06:50:38.562Z D FetchHttpApi: <-- DELETE https://chaotic.half-shot.uk/_matrix/client/v3/room_keys/version/2 [1291ms 200]
2025-09-05T06:50:38.562Z D DEBUG matrix_sdk_crypto::backups: Disabling key backup and resetting backup state for room keys
    at /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/matrix-sdk-crypto-0.13.0/src/backups/mod.rs:413
    in matrix_sdk_crypto::backups::disable_backup
2025-09-05T06:50:47.254Z D FetchHttpApi: <-- GET https://chaotic.half-shot.uk/_matrix/client/v3/sync?filter=xxx&timeout=xxx&org.matrix.msc4222.use_state_after=xxx&set_presence=xxx&since=xxx [15683ms 200]
2025-09-05T06:50:47.867Z D DEBUG matrix_sdk_crypto::backups: Done disabling backup
    at /home/runner/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/matrix-sdk-crypto-0.13.0/src/backups/mod.rs:420
    in matrix_sdk_crypto::backups::disable_backup
2025-09-05T06:50:47.867Z I DeviceListener: Backup status changed
2025-09-05T06:50:47.867Z D [PerSessionKeyBackupDownloader] Got current backup version from server: undefined
2025-09-05T06:50:47.867Z I [PerSessionKeyBackupDownloader] Unsupported algorithm undefined
2025-09-05T06:50:47.868Z D FetchHttpApi: --> PUT https://chaotic.half-shot.uk/_matrix/client/v3/user/%40Half-Shot%3Ahalf-shot.uk/account_data/m.cross_signing.master
2025-09-05T06:50:48.028Z D FetchHttpApi: <-- PUT https://chaotic.half-shot.uk/_matrix/client/v3/user/%40Half-Shot%3Ahalf-shot.uk/account_data/m.cross_signing.master [160ms 200]
2025-09-05T06:50:49.363Z W Ending non-existent watcher ID 1757052492688_17_deviceClientInformationOptIn_null
2025-09-05T06:50:49.363Z D Checking key backup status...
2025-09-05T06:50:49.364Z D FetchHttpApi: --> GET https://chaotic.half-shot.uk/_matrix/client/v3/room_keys/version
2025-09-05T06:50:49.577Z D FetchHttpApi: <-- GET https://chaotic.half-shot.uk/_matrix/client/v3/room_keys/version [213ms 200]
2025-09-05T06:50:49.579Z D TRACE matrix_sdk_crypto::backups: Verifying backup auth data

1. Element has deleted the version 2 backup off my account with DELETE https://chaotic.half-shot.uk/_matrix/client/v3/room_keys/version/2
2. I still have a backup on my account, from some previous iteration.
3. Element checks /version and sees that I have a backup, so it thinks everything is fine when I click enable.
4. But this fails later on in checkStatus because my version 1 backup isn't an active backup, so I'm stuck in a broken situation.

https://github.com/matrix-org/matrix-js-sdk/blob/ccd825fb39477b8340946907e6977078f01f879c/src/rust-crypto/backup.ts#L315-L325

So why isn't my version 1 backup active? Well, apparently it's neither trusted nor matchesDecryptionKey so ignores the backup.

[Half-Shot]

I managed to cheat the system by forcing currentKeyBackup to be null in

element-web/src/components/viewmodels/settings/encryption/KeyStoragePanelViewModel.ts

Lines 47 to 113 in be3778b

	const checkStatus = useCallback(async () => {
	const crypto = matrixClient.getCrypto();
	if (!crypto) {
	logger.error("Can't check key backup status: no crypto module available");
	return;
	}
	// The toggle is enabled only if this device will upload megolm keys to the backup.
	// This is consistent with EX.
	const activeBackupVersion = await crypto.getActiveSessionBackupVersion();
	setIsEnabled(activeBackupVersion !== null);
	}, [matrixClient]);
	useEffect(() => {
	(async () => {
	await checkStatus();
	setLoading(false);
	})();
	}, [checkStatus]);
	const setEnabled = useCallback(
	async (enable: boolean) => {
	setPendingValue(enable);
	try {
	// stop the device listener since enabling or (especially) disabling key storage must be
	// done with a sequence of API calls that will put the account in a slightly different
	// state each time, so suppress any warning toasts until the process is finished (when
	// we'll turn it back on again.)
	DeviceListener.sharedInstance().stop();
	const crypto = matrixClient.getCrypto();
	if (!crypto) {
	logger.error("Can't change key backup status: no crypto module available");
	return;
	}
	if (enable) {
	// If there is no existing key backup on the server, create one.
	// `resetKeyBackup` will delete any existing backup, so we only do this if there is no existing backup.
	const currentKeyBackup = await crypto.checkKeyBackupAndEnable();
	if (currentKeyBackup === null) {
	await crypto.resetKeyBackup();
	// resetKeyBackup fires this off in the background without waiting, so we need to do it
	// explicitly and wait for it, otherwise it won't be enabled yet when we check again.
	await crypto.checkKeyBackupAndEnable();
	}
	// Set the flag so that EX no longer thinks the user wants backup disabled
	await matrixClient.setAccountData(BACKUP_DISABLED_ACCOUNT_DATA_KEY, { disabled: false });
	} else {
	// This method will delete the key backup as well as server side recovery keys and other
	// server-side crypto data.
	await crypto.disableKeyStorage();
	// Set a flag to say that the user doesn't want key backup.
	// Element X uses this to determine whether to set up automatically,
	// so this will stop EX turning it back on spontaneously.
	await matrixClient.setAccountData(BACKUP_DISABLED_ACCOUNT_DATA_KEY, { disabled: true });
	}
	await checkStatus();
	} finally {
	setPendingValue(undefined);
	DeviceListener.sharedInstance().start(matrixClient);
	}
	},
	[setPendingValue, checkStatus, matrixClient],
	);

, which seems to have given me a new key backup version thats happily backing up keys.

[richvdh]

after all of 5 seconds triage, sounds like a dup of #29856

[Half-Shot]

That sounds exactly like it. Unfortunately due to the sheer lack of any leads on the UI or logs, you only know it's a dupe after a few hours of debugging 🫠