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Journal of Information Science and Engineering, Vol. 31 No. 3, pp. 1085-1096


The Pseudorandomness of Many-Round Lai-Massey Scheme

YIYUAN LUO1,2, XUEJIA LAI2 AND JING HU1 
1School of Electronics and Information 
Shanghai Dian Ji University 
Shanghai, 200240 P.R. China 
E-mail: {luoyy; hujing}@sdju.edu.cn 
2Department of Computer Science and Engineering 
Shanghai Jiao Tong University 
Shanghai, 200240 P.R. China 
E-mail: lai-xj@cs.sjtu.edu.cnn

    In this paper we prove beyond-birthday-bound for the (strong) pseudorandomness of many-round Lai-Massey scheme. Motivated by Hoang and Rogaway's analysis of generalized Feistel networks, we use the coupling technology from Markov chain theory and prove that for any e > 0, with enough rounds, the Lai-Massey scheme is indistinguishable from a uniform random permutation by any computationally unbounded distinguisher making at most q~N1-t combined chosen plaintext/ciphertext (CCA) queries, where N is the range size of the round function. Previous works by Vaudenay et al. and Yunet al. only proved the birthday-bound CCA security of Lai-Massey scheme.

Keywords: cryptography, block cipher, Lai-Massey scheme, Pseudorandomness, coupling

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