Here's a simple class for what it's worth that will do simple base85 encoding and decoding. This only works with the required blocks of data and not large data structures or streams, and does no validation of the data. What it does do is encode a block of 4 8-bit bytes into 5 base85 characters and decode a block of 5 Base85 characters into 4 8-bit bytes. There's also a provision in the definition for base85 to represent 5 !'s with a single 'z'. However the definition I read wasn't clear on whether it was mandatory, so I didn't implement any checking for that.
Some may ask why one would want this. Ever tried to send an attachment through an email server that won't accept them? With this you can encode any 8-bit data to look like text and be reliably decoded on the other end.