[Recorded Jan 26, 2005] Whitfield Diffie, a key figure in the discovery of public-key cryptography, traces the growth of information security through the 20th century and into the 21st. In the 1970s, the world of information security was transformed by public-key cryptography, the radical revision of cryptographic thinking that allowed people with no prior contact to communicate securely. "Public key" solved security problems born of the revolution in information technology that characterized the 20th century and made Internet commerce possible. Security problems rarely stay solved, however. Continuing growth in computing, networking, and wireless applications have given rise to new security problems that are already confronting us.