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Print a file as QR codes, and scan it back
Some computers have a printer and nothing else: no network, no USB, no camera. Kionel prints a file as pages of encrypted QR codes; any phone with a browser reads the pages back, in any order, and rebuilds the file byte for byte. The same pages make a paper backup that can be restored years later.
Written by Taha Bayar, a biologist working on laboratory data handover.
How to print a file
- Open Kionel on the computer with the printer (the offline package works without a network) and choose the file.
- Open No camera and no cable? Print the file as pages of codes, choose a density and press Print the file as codes.
- Kionel shows a 12-character code. Write it down and keep it apart from the pages: the pages are encrypted and cannot be read without it. If a receiving device already showed you its code, type that one first and it is used instead.
How to read the pages back
- On a phone or any computer, open Kionel, choose Receive → Printed pages and enter the code. You can also scan first; Kionel asks for the code when it has every code it needs, and a wrong code never throws away what was read.
- Point the camera at the pages, one at a time, in any order. Or, with a business licence, open photos or scans of the pages.
- When enough codes are read, the file is rebuilt and checked against its signed record.
How much fits on a page
| Density | Codes a page | File data a page | Printer |
|---|---|---|---|
| Standard | 6, each about 6.4 cm | about 4 KB | Any laser or inkjet |
| Dense | 12, each about 4.8 cm | about 11 KB | A laser printer at 600 dpi |
Text and CSV files are compressed before printing, often four to ten times, so a 40 KB instrument export usually fits on two or three standard pages. Up to 60 pages are printed; larger files belong on a serial cable or a screen recording.
What happens if a code is smudged or a page is torn
About 30% of the codes are spares. They are not copies: each one mixes a third of the file, so it can stand in for whichever code is lost. In our tests, a 30 KB file still came back in 93 out of 100 trials with eight of its 48 codes missing, and files over 150 KB came back every time with twelve missing. If a read stops short, Kionel says how much it has and keeps it; scan the remaining pages.
How safe the pages are
- The file is encrypted with a key derived from the 12-character code (60 bits); every guess costs an attacker 600,000 PBKDF2 rounds.
- With the option to print the code on the pages, anyone holding the pages can read the file. Leave it off for anything confidential.
- For a backup kept for years, store the code as carefully as the file itself would need.
Compared with other paper backup tools
Paper backup is not new. qr-backup (a Linux command-line tool) fits more on a page at its densest setting, and paperize and papyrus do the same from Python. Kionel's difference is where it runs: in a browser on the printing PC, and restored by pointing a phone at the pages, with no software to install on either side, plus a signed record of what was printed when a business licence is loaded.