A new distinguisher for clock controlled stream ciphers

In English In this paper we present a distinguisher targeting towards irregularly clocked filter generators. The attack is applied on the irregularly. clocked stream cipher called LILI-II. LILI-II is the successor of the cipher LILI-128 and its design was published in 1. There have been no known attacks better than exhaustive key search on LILI-II. Our attack is-the first of this kind that distinguishes the cipher output from a random source using 2(103) bits of keystream using computational complexity of approximately 2(103) operations.