Encrypted backup

Back your history up to a single encrypted file, and restore it on a new device. The file is protected by a recovery code that only you ever see.

How it works

Z writes a .zbk archive: your messages, attachments, contacts and identity, encrypted with a key derived from a 25-character recovery code using Argon2id.
The code is shown once, and you type it back before the archive is written — the last moment a mis-copied code can be fixed.
The archive streams, so a large history never has to fit in memory, and a truncated or altered file fails outright rather than restoring a quietly incomplete history.
You choose where it goes. Z does not upload it anywhere.

Lose the code and the archive is gone. There is no copy, no reset link and no support route, because there is no account and no server-side storage to hold one. That is the trade that makes the backup safe to keep anywhere — treat the code like a key, not a password.

Restoring

Install Z on the new device, choose restore, pick the file and enter the code. History and contacts come back; sessions do not — your device re-establishes them with each contact, so no key material is ever replayed. Contacts may see your safety number change, which is why verification exists.

Automatic backups

Optional, and off by default. Enabling it stores your recovery code in the encrypted vault, because an unattended backup cannot ask you for one. That is a real trade-off and the app says so where you switch it on rather than leaving it implicit.