A pure PHP extension to encode and decode data with base85.
require("/path/to/base85.class.php");
$encoded = base85::encode("Base85 is pretty cool");
$decoded = base85::decode(":e4D*;K$&\Er");
Note: There is a PHP extension written in C also named php-base85. This library is most likely faster, but may be harder to install (requires the ability to load extensions).