Signal completes rollout of encrypted backups across all platforms

The Signal messenger has released version 8.30, completing the rollout of its secure backups feature to every supported operating system: Android, iOS, Linux, macOS and Windows. The capability first appeared on Android nearly a year ago, letting users create end-to-end encrypted copies of their chats and restore them on another device if their phone is lost.

Two storage options

The system offers two approaches. Signal-hosted backups are limited for free users to 45 days of media and 128 KB per message (up to 100 GB on paid plans). On-device local backups have no size restrictions.

Both are encrypted and require a recovery key to decrypt. Hosted backups gain extra protection from a supplemental key that rotates daily inside a Trusted Execution Environment, providing forward secrecy. The recovery key for a local backup, however, can decrypt every past file it encrypted, wherever those files are stored.

Threat actors have already recognised the key's value: shortly after the feature launched, they added it to their targeting scope.

What's new in 8.30

The update brings local backups to iOS and desktop, and moves Android backups to the same cross-platform format. When linking a new device, it now retrieves older attachments missing from the chat. Media is stored separately from the archive, and duplicate files are kept only once, eliminating redundant copying and syncing.

Paying users get an option to purge old media while keeping only thumbnails, with full versions pulled automatically from hosted backups. 'Disappearing messages' set to vanish within 24 hours are excluded from the archive; during restoration, expired ones from a local backup are skipped. A hosted backup does not wipe a local one.

The iOS client also enables direct iPhone-to-iPhone transfer over a local encrypted Wi-Fi Aware link, which Signal says improves speed and reliability.

Signal says this first phase of the backups project is now complete, and its engineers will turn to improving non-backup systems.

Source: Bleeping Computer