Chameleon — A new kind of stream cipher

Abstract

Stream cipher systems are used to protect intellectual property in pay-TV and a number of other applications. In some of these, it would be convenient if a single ciphertext could be broadcast, and subscribers given slightly different deciphering keys that had the effect of producing slightly different plaintexts. In this way, a subscriber who illegally resold material licensed to him could be traced. Previously, such tracing could be done using a one-time pad, or with complicated key management schemes. In this paper we show how to endow any stream cipher with this potentially useful property. We also present a simple traitor tracing scheme based on random coding with which it can be used.