named
             after the three-headed watchdog of Greek mythology, is one of the best-known-
             private-key encryption technologies. It creates an encrypted data packet,
             called a ticket, which securely identifies the user. To make a purchase, you
             generate the ticket during a series of coded messages you exchange with a
             Kerberos server, which sits between your computer system and the one you are
             communicating with. These latter two systems share a secret key with the
             Kerberos server to protect information from prying eyes and to assure that your
             data has not been altered during the transmission. But this technology has a
             potentially weak link: Breach the server, and the watchdog rolls over and plays
             dead. An alternative to private-key cryptography is a public-key system that
             ...