On the Existence of secure Keystream Generators

摘要

Desginers of stream ciphers have generally used ad hoc methods to build systems that are secure against known attacks. There is often a sense that this is the best that can be done, that any system will eventually fall to a practical attack. In this paper we show that there are families of keystream generators that resist all possible attacks of a very general type in which a small number of known bits of a keytream are used to synthesize a generator of the keystream (called a synthesizing algorithm).