A secret sequence of alphanumeric characters and other symbols used for necessary authentication prior to log-in onto a computer system. Password protection allows a system to assign log-in names to users for file or programme access. The Password Authentication Protocol (PAP) is a means of restricting access to authorised users by validating their input code during log-in; this is often called a "handshake". Most log-in environments display bullets or asterisks instead of the password, and leave the field uncalibrated so crackers cannot predict the code count. A computer account whose password is the user's name, called a "Joe account", is easily invaded by crackers, because the security access code can be readily guessed. Password accountability can also trace user activity, since each increment of access is recorded; this demonstrable trail is often called a "footprint". See RSA, PGP, Secure MIME @MIME, SSL, firewall, proxy, trap door, escrow key, Clipper.