The pam_usb Project: www.pamusb.org

“What Is Linux-PAM?”: www.kernel.org/pub/linux/libs/pam/whatispam.html

The USB Guide: www.linux-usb.org

“What Key Size Should Be Used?”: www.rsasecurity.com/rsalabs/node.asp?id=2264

“The Failure of Two-Factor Authentication”, by Bruce Schneier: www.schneier.com/crypto-gram-0503.html#2