base64
Instead of base64, it's probably a good idea to use cl-base64 instead, which, unlike base64, is maintained.

base64 implements the Base64 transfer encoding algorithm as defined in RFC 1521 by Borenstein & Freed, September 1993.

Written by Juri Pakaste. It is in the public domain.

Available at http://www.iki.fi/juri/store/dl/base64.lisp.