Anonymous Digicash

I want to write a simple digicash program. This will use code from PGP as much as possible. It will probably be online digicash, but it needs strong anonymity. For that you need a blind signature protocol. What is the best one, and where can I get a description of it? What is the best/simplest digicash system to implement? Is it possible to have a partially blind signature? For example, the customer generates the cash (random string), blinds it, and sends it to the bank. The bank adds an expiration date and signs it. The customer unblinds the random string, leaving a signature on both the cash and the expiration date. --- MikeIngle@delphi.com