Signal will let you sync old messages when linking new devices

Signal is finally adding a new feature that allows users to synchronize their old message history from their primary iOS or Android devices to newly linked devices like desktops and iPads.

The transfer process is fully end-to-end encrypted, ensuring privacy and data security. It will employ a QR code verification step to ensure the action is authorized.

“Signal’s upcoming beta releases will also introduce the option to transfer your messages and media when you link your primary Signal device to a new Desktop or iPad,” explains Signal.

“Instead of starting fresh, and having only new messages show up, you can choose to bring your chats and your last 45 days of media with you. Or, you can choose not to.”

Syncing without centralization

Signal’s operational model dictates that all messages are end-to-end encrypted and all user communications are stored locally on their devices, not on the platform’s servers.

Since each linked device has unique encryption keys, messages cannot be practically transferred to newly linked devices.

Signal’s engineers have devised a new mechanism that solves this problem by creating an encrypted archive of past messages on the primary device and transferring it to the newly linked device using a one-time 256-bit AES key.

Users can start the process by generating a QR code on the newly linked device and scanning it from their primary device, creating a secure “provisioning address” to receive encrypted data.

Before the archive transfer begins, a provisioning message is sent to the new device, which is encrypted with the public key from the QR code.

The message contains shared account information, a one-time encryption key to decrypt the archive containing the message history, and cryptographic proofs of legitimate account linking for the new device.

The archive includes all text messages, stickers, call history, group updates, quotes, reactions, and delivery and read receipts.

The transfer of the archive takes place via a direct channel between the devices, with the Signal servers acting only as a temporary relay.

Media files (images, videos, documents) are not included in the archive. Instead, links to the attachments stored in encrypted form on Signal servers are relayed.

A limitation of 45 days applies to media, as Signal automatically deletes anything older than that from its servers.

Signal says it is looking into extending the media retention period beyond 45 days, but the limit applies for now.

In addition to pushing the retention period further, Signal says its new, secure message archiving system will hopefully act as the basis for developing message restoration mechanisms for users who lost or damaged their phones.

Those eager to participate in testing the new feature and help Signal’s engineers squash any bugs in the process may do so by installing Signal Beta.