Signal has completed the rollout of its secure backup feature across all supported operating systems, including Android, iOS, Linux, macOS, and Windows, with the release of version 8.30. This update introduces end-to-end encrypted local backups for iOS and desktop applications, while also revamping the Android backup system to utilize a new cross-platform format. The feature, initially launched on Android nearly a year ago, enables users to create encrypted backups of their chats and restore them on new devices.
The backup system offers two options: Signal-hosted backups and on-device local backups. Signal-hosted backups are limited to 45 days of media and 128 KB per message for free users, with paid plans offering up to 100 GB. Local backups, however, have no size restrictions. Both backup methods are encrypted and require a recovery key for decryption. Signal-hosted backups include an additional supplemental key that rotates daily within a Trusted Execution Environment, enhancing protection and forward secrecy.
According to Signal, a single on-device backup recovery key can decrypt all past backup files it encrypted, regardless of their storage location. The value of this key has been noted by threat actors, who reportedly began targeting it shortly after the feature's initial introduction.
The latest update also introduces several enhancements. When linking a new device from a primary device, the new device will now retrieve older attachments that may be missing from the chat history. Media files are now stored separately from the backup archive, and duplicate files are stored only once, which aims to reduce excessive backing up and syncing. Paying users will also gain an option to purge old media from local storage, retaining only thumbnails, with the ability to automatically retrieve full media from hosted backups.
The backup system is designed to ignore disappearing messages set to vanish within 24 hours, preventing them from being included in either backup method. For users who utilize both hosted and on-device backups, Signal clarifies that hosted backups do not overwrite local backups. During restoration, however, expired disappearing messages from local backups will be skipped.
The iOS client release, version 8.30, also enables direct iPhone-to-iPhone transfers using a local end-to-end encrypted Wi-Fi Aware link, which Signal states improves both speed and reliability. Signal has indicated that this rollout marks the completion of the first phase of its backup project, and engineers will now focus on improving non-backup systems.
