Security3 publishers2 min readPublished
Signal's new on-device backups restore across five platforms under one recovery key
Signal finished rolling out on-device encrypted backups for iOS and desktop in iOS version 8.30, restorable on Android, iOS, Linux, macOS and Windows. Teams that require Signal can now keep message history on their own drives, protected by the recovery key alone.
The Watch · Security desk
What happened
- Disappearing messages set to vanish within 24 hours are left out of both hosted and on-device backups.
- The free hosted tier keeps text plus the last 45 days of media, and a monthly fee raises media storage to 100GB.
- The iOS release also reworks iPhone-to-iPhone transfer to run over a local end-to-end encrypted Wi-Fi Aware link.
Compiled by The WatchSomething wrong?How this is made
Why it matters
- exposure Anyone who obtains a user's recovery key and any copy of that user's local archive, including a NAS mirror, can decrypt every snapshot in it, old ones included.
- decision Teams deciding where Signal history lives now weigh hosted backups with a daily-rotating TEE key against local archives they control that have no forward secrecy.
- constraint A disappearing timer longer than 24 hours no longer guarantees the text is gone from every copy, because Signal skips expired messages when a backup is restored.
- capability A team on mixed Android, iPhone and desktop hardware can move users between platforms without sending their history through Signal's hosted service.
The local archive changes what an attacker has to steal. Hosted backups belong to Signal Secure Backups, the service Signal introduced in September 2025 [4], and they need two keys. One is the user's recovery key. The other rotates daily inside a Trusted Execution Environment. It cannot decrypt a backup by itself, and it gives hosted copies forward secrecy [7]. Signal said TEEs are "currently the best way to protect this supplemental key." [8]
On-device backups can be written to any drive or service, so they cannot use the TEE [9]. Their recovery key decrypts all past backups, and Signal warns users never to share it [9]. A thief who has one user's key and one copy of that user's archive can read every snapshot in that copy, however old [9].
Signal expects those copies to spread. Explaining the rebuilt format, the company said "backup media gets stored in a separate folder so it's easier to periodically sync, and duplicate files are only stored once, which also helps save space if you decide to mirror an on-device backup to an external hard drive or NAS server on your home network." [5] Each mirror opens with the same recovery key [9].
Disappearing messages set to vanish within 24 hours stay out of both backup types [10]. Messages on longer timers go in and are filtered later. Signal wrote: "Expired disappearing messages in an on-device backup are automatically skipped during the transfer process when you restore that backup, but you may want to take additional steps such as setting a shorter expiration timer for disappearing messages in on-device backups." [11] By that description, a message on a timer longer than a day can sit in an archive after it has expired on the phone [11].
For a team that requires Signal on mixed hardware, the pieces for moving history now exist. A backup restores on Android, iOS, Linux, macOS or Windows [2]. Android now writes the same format as iOS and desktop [3]. The iOS release adds an iPhone-to-iPhone transfer over a local end-to-end encrypted Wi-Fi Aware link [12]. The hosted free tier keeps only the last 45 days of media [6]. A newly linked laptop that scrolls past that window can, Signal said, "securely request a copy of any missing files directly from your primary device as an end-to-end encrypted attachment." [13] Help Net Security's report does not mention administrative controls over where archives are stored or who holds the keys.
Signal said the release "wraps up the first phase of the backups project, but we're hard at work on several non-backup improvements too." [15]
What to watch
- Whether a later phase of Signal's backups project gives on-device archives key rotation or forward secrecy comparable to the hosted TEE key.
- Whether Signal changes on-device backups to drop expired disappearing messages when the backup is written, instead of skipping them at restore.
- Any Signal controls aimed at organisations for where backup archives are stored and who holds recovery keys.