Cryptography CS 555 Topic 3: One-time Pad and Perfect Secrecy CS555 Spring 2012/Topic 3 1 Outline and Readings • Outline • • • • One-time pad Perfect secrecy Limitation of perfect secrecy Usages of one-time pad • Readings: • Katz and Lindell: Chapter 2 CS555 Spring 2012/Topic 3 2 One-Time Pad • Fix the vulnerability of the Vigenere cipher by using very long keys • Key is a random string that is at least as long as the plaintext • Encryption is similar to shift cipher