FAQ

How long does paper last?

Much longer than most storage media, if it is kept well. Ordinary office paper stored dry, dark and at room temperature lasts for decades; acid-free or archival paper is made to last far longer. Laser toner is fused plastic and very stable. The main enemies are water, heat, direct sunlight, mould and pests — store the pages in an envelope or folder in a dry place, and keep a second copy somewhere else.

How much data fits on a page?

It depends on how fine the dots are, which in turn depends on your printer, your scanner and the profile. As a rough guide for an A4 page, the raw capacity ranges from around ten kilobytes with the coarsest, crumple-tolerant 0.5 mm dots, through about 50 KB at 100 dpi dots, to a few hundred kilobytes with the finest dots. Part of that is used for parity. Your data is compressed first, so text, spreadsheets and source code take up much less room than their size on disk; photos and already-compressed files don’t shrink.

For your actual data, run

pabaru plan ./your-folder --printer laser600 --scanner-dpi 600 --paper a4

or just drop the folder into the app: it shows the page count for each profile.

Pabaru is meant for small, important data — keys, passwords, documents, notes. The current version supports backups up to about 8 MB after compression.

What if I lose a page or a page gets damaged?

Damaged dots inside a block are corrected by the block’s own Reed-Solomon code, and missing or unreadable blocks are rebuilt from parity blocks spread across all pages. With the Archival profile (or --survive-page-loss), you can lose any one whole page and still restore everything. Crumpled and torn pages can be scanned as they are — see Durability.

If you printed several copies, scan the surviving pages of all of them; Pabaru combines them.

Is it secure?

Without a password, a Pabaru backup is not secret: anyone with the pages and Pabaru (or the specification) can read it — like any printed document. File names are not printed on the paper, though, and original folder paths are never stored.

With a password, the data is encrypted with XChaCha20-Poly1305 and the key is derived with Argon2id, both well-established modern algorithms. The password is never printed. The security then rests on the strength of your password. See Encryption.

Can I recover my data without Pabaru?

Yes. That is a design goal. The paper format is completely described in the specification: page geometry, the order of dots, whitening, both error-correcting codes, encryption and the archive format. Everything else is standard: CRC32C, Reed-Solomon, zstd, tar, BLAKE3, Argon2id and XChaCha20-Poly1305. A programmer can write a decoder from the document alone. Pabaru itself is open source, so its code is a reference implementation too.

Which scanner and printer do I need?

Any laser printer and any flatbed scanner (or a multifunction printer) will do. Tell Pabaru which ones you have and it chooses dots that they can handle; the scanner needs about three times the dot density. See Printing & scanning.

Can I use my phone camera instead of a scanner?

Perspective distortion from phone photos has not been tested yet; use a flatbed scanner for now.

How does Pabaru compare with PaperBack?

Pabaru is directly inspired by PaperBack by Oleg Yuschuk, the program that showed how much data an ordinary printer and scanner can carry, and by the projects that continued it. Pabaru takes the same idea and builds a new format around it: it runs on Windows, macOS and Linux, backs up whole folders, uses a two-level error correction that spans pages (so a whole page can be lost), offers modern authenticated encryption, tolerates crumpled and torn paper, and has an open specification. The formats are not compatible.

Why not just print QR codes?

QR codes are great for small things — a single key or a recovery code — and every phone can read them. But a QR code holds at most a few kilobytes, so larger data needs many codes, and you have to manage their order and the redundancy between them yourself. Pabaru fills a whole page with a much denser grid, spreads error correction over all pages, restores folders with their structure and checks every file. For a short secret, a QR code may be all you need; for documents and folders, Pabaru is the better fit.

What does Pabaru cost?

Nothing. It is open source under the MIT or Apache-2.0 licence. There is no account, no telemetry and no network access — everything runs on your computer.