Stephan Brands is a cryptographer
who specializes in identity management techniques. He is presently employed by Zero Knowledge Systems
, who also has aquired the rights to his patents.
Brands has worked a lot on certificates that can be used to reveal what you are allowed to do without revealing who you are (or only revealing a 'suitable part' of who you are.)
He has also developed a digital cash system called Choiceless Digital Cash, which allows non-interactive signing of coins, along with much smaller coins than the simplistic systems. Writeup coming soon (my references contains some errors I need to fix, which is why this is delayed.)