Signal 8.30 Adds Encrypted Local Backups to iPhone and Desktop Apps

Signal has released version 8.30, completing the rollout of secure backup features across Android, iOS, Linux, macOS, and Windows. The update adds on-device encrypted backups to iOS and desktop apps while standardizing Android on the same cross-platform backup format.

Signal backups are protected with end-to-end encryption

Signal introduced its encrypted backup system on Android nearly a year ago. It allows users to create protected copies of their chats and restore them on another device if they lose their phone.

Users can choose between two backup options:

• Signal-hosted backups: Free users can store 45 days of media and messages up to 128 KB. Paid plans provide 100 GB of storage.
• On-device local backups: Local backups have no size limit and are stored on the user’s device.

Both backup types are encrypted and require a recovery key for decryption. Hosted backups also use an auxiliary key that is rotated daily within a trusted execution environment, providing additional protection and forward confidentiality.

Signal says the recovery key stored on a user’s device can decrypt all previously encrypted backup files, regardless of where those files are stored.

Threat actors took note of the value of these recovery keys shortly after Signal introduced the backup feature and began incorporating them into their targeting efforts.

Local backups arrive on iOS and desktop

Signal’s latest update brings on-device backups to iOS and desktop platforms. It also updates Android backups to use the same cross-platform format, making it easier to move backup data between supported operating systems.

Signal improves media storage and device transfers

When users link a new device from their primary device, Signal currently retrieves old attachments that are missing from chats.

Signal also says media will now be stored separately from backup archives. Duplicate files will be saved only once, reducing the need for excessive backups and synchronization.

Paid users will additionally be able to remove older media from local storage and keep only thumbnails. Signal will automatically retrieve the full media files from hosted backups when needed.

Disappearing messages are excluded from backups

Both backup methods exclude disappearing messages that are set to disappear within 24 hours. These messages are not included in the backup archive.

Users who enable both hosted and on-device backups should also note that hosted backups do not erase local backups. However, during a restore, expired messages that are missing from local backups are skipped.

iPhone-to-iPhone transfers use encrypted Wi-Fi Aware

The Signal 8.30 iOS release enables direct iPhone-to-iPhone transfers over a local end-to-end encrypted Wi-Fi Aware link. Signal says the change improves transfer speed and reliability.

Signal says the deployment completes the first phase of its backup project. Its engineers will now focus on improving the system beyond backups.

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