Shorter bit sequence is enough to break stream cipher LILI-128

LILI-128 is the stream cipher proposed as a candidate cipher for the New European Schemes for Signatures, Integrity, and Encryption (NESSIE) Project. Some methods of breaking it more efficiently than an exhaustive search for its secret key have been found already. The authors propose a new method, which uses shorter bit sequence to break LILI-128 successfully. An attack that can be made with less data can be a more practical threat. With only 2⁷ bits of keystream, this method can break LILI-128 successfully. The efficiency of our attack depends on the memory size. For example, with 2^99.1 computations, our attack breaks LILI-128, if 2^28.6-bit memory is available.