base85

I read about the UUID v4 and it's virtually unique, and that's what I need. The problem is, it's a too large number, is it possible to generate UUID's like Facebook or Twitter with fewer characters? I read some post, where you can shrink this code to 20 with Ascii85, but don't see a reliable PHP script doing the job. Someone knows a tested class?? for random ID's it the best way to store this 20 char, right? --- Edit --- @David Schwartz Thanks. I need a random unique identifier in a single server, between 8 and 16 chars (ok 20 is fine if its the lowest). The idea it's to identify objets with