Modified SNOW 3G: Stream Cipher Algorithm Using Piecewise Linear Chaotic Map

SNOW 3G is a synchronous stream cipher developed by Thomas Johansson and Patrik Ekhdal at Lund University. In 2006, it was chosen as the main part of the second set of Universal Mobile Telecommunications System (UMTS) confidentiality and integrity algorithms [2]. In 2008, Patrik Bohm published a report entitled "Statistical Evaluation of Stream Cipher SNOW 3G". He tested the randomness properties of SNOW 3G key stream generator. Bohm using NIST statistical test suite as randomness test tool with three kinds of test, i.e. long key stream data set, short key stream data set, and initialization vector data set. The result of the report shows that from three kind of tests, only short key stream data set has not passed eight randomness tests. He state that the suggests SNOW 3G fail because there is a weakness in the initialization of the cipher. In this paper we modify SNOW 3G algorithm using piecewise linear chaotic map (PLCM) on the key initialization mode and keystream generation mode. We use the same statistical test that have been used by Bohm [5]. The experiment shows that modified SNOW 3G stream cipher algorithm has passed all the statistical test. The results prove that PLCM impact on algorithm's randomness.