Encryption

Pabaru can encrypt a backup with a password, so that the printed pages are useless to anyone who finds them.

How to use it

• App: under Password protection, tick the encryption box and enter the password twice.
• CLI: pabaru encode … --encrypt asks for the password twice. For scripts, use --password-env VAR to read it from an environment variable.

When restoring, Pabaru recognises an encrypted backup by itself and asks for the password. On the command line you get three attempts without reloading the scans.

What happens

• The compressed archive is encrypted before it is split into blocks, with XChaCha20-Poly1305 (authenticated encryption).
• The key is derived from your password with Argon2id, a memory-hard function that makes guessing passwords slow and expensive. Its salt and parameters are printed on every page, so the key can be derived again later.
• The password is never printed — the page only says encrypted.
• A wrong password or tampered data is detected reliably by the authentication tag, and nothing is written to disk.

Choose the password well

The paper may outlive your memory of the password. There is no recovery: without the password, the data is gone. Use a long passphrase and store it somewhere separate — for example in a password manager, or sealed in an envelope with someone you trust.

The exact algorithms and parameters are part of the specification.