A Base45 encoder/decoder in pure Erlang.
Implements the encoding scheme defined in RFC 9285. It was notably used for encoding the EU Digital COVID Certificate in QR codes.
About Base45
Base45 encodes pairs of bytes (16 bit) into 3 characters, and a remaining single byte into 2 characters. It uses a 45-character subset of US-ASCII that is compatible with the Alphanumeric mode of QR codes.
The number 45 comes from the QR code standard (ISO/IEC 18004). In Alphanumeric mode, a QR code supports exactly 45 characters: the digits 0-9, the uppercase letters A-Z, and 9 special characters. This mode is more compact than Byte mode, encoding two characters in just 11 bits. Base45 takes advantage of this by mapping binary data exclusively to these 45 characters, resulting in smaller QR codes than e.g. Base64 (which would require the less efficient Byte mode).
Usage
base45:encode(<<1,2,3>>). %% => <<"X5030">>
base45:decode(<<"X5030">>). %% => <<1,2,3>>
Import
Erlang (rebar3):
{deps, [base45]}.
Elixir (Mix):
{:base45, "~> 3.0"}
Available via Hex.pm. Source code and releases on GitHub.
Licensed under Apache 2.0.