Cryptanalysis of block-wise stream ciphers suitable for the protection of multimedia and ubiquitous systems

In this paper we introduce a general framework of related-key attack on block-wise stream ciphers which are suitable for the protection of multimedia and ubiquitous systems. As a case study, we show how our cryptanalytic framework is applied to a block-wise stream cipher TWOPRIME: we construct various related-key differentials of TWOPRIME and use them to show that recovering related keys of TWOPRIME can be performed with a data complexity of 214 known plaintext blocks and a time complexity of 232 8-bit table lookups. We expect that our general framework for a related-key attack would be useful tool for analyzing many of block-wise stream ciphers. D.G. Lee ETRI (Electronics and Telecommunications Research Institute), 138, Gajeongno, Yuseong-gu, Daejeon, Korea e-mail: [email protected] J. Kim Division of e-Business, Kyungnam University, 449, Wolyeong-dong, Masan, Kyungnam, Korea e-mail: [email protected] J. Sung ( ) Department of Mathematics, University of Seoul, 90 Cheonnong-Dong, Dongdaemun-gu, Seoul 130-743, Korea e-mail: [email protected] Y.S. Lee Department of Information & Communication Engineering, Chosun University, 375 Seosuk-dong, Dong-gu, Gwangju, Korea e-mail: [email protected] S. Rho School of Electrical Engineering, Korea University, Anam-Dong, Seongbuk-gu, Seoul, 136-713, Korea e-mail: [email protected]