The BFR gang takes you inside the world of electronic signatures. I personally haven't messed around with them since I quit using PGP back in the late 90's, so this should be a good refresher.

"On June 30, 2000 U.S. President Clinton signed the 'Electronic Signatures in Global and National Commerce Act' (ESIGN) using his electronic signature ID, and thereby established the validity of electronic signatures for interstate and international commerce."