For storing rarely used secrets that should not be kept on a networked computer, it is convenient to print them on paper. However, ordinary barcodes can store not much more than 2000 octets of data, and in practice even such small amounts cannot be reliably read by widely used software (e.g. ZXing).

In this note I show a script for splitting small amounts of data across multiple barcodes and generating a printable document. Specifically, this script is limited to less than 7650 alphanumeric characters, such as from the Base-64 alphabet. It can be used for archiving Tarsnap keys, GPG keys, SSH keys, etc.

The script is implemented in Python, since this is one of the most widespread interpreters, is compatible with both Python 2 and Python 3, and has one external dependency, the iec16022 binary. On Debian-based systems these can be installed using
apt-get install python3 iec16022

The script accepts any ASCII sequence and generates an HTML page sized adequately for printing on A5 paper that contains multiple ISO/IEC 16022 (Data Matrix) barcodes. The barcodes can be read with any off-the-shelf software, e.g. ZXing. Even if up to 30% of the barcode area is corrupted, the data can still be recovered. //

This page can now be printed on a laser printer (with no margins) and laminated. If done properly, it is likely to outlast the service for which it holds the secrets.