Authors: Mihaljević, Miodrag J. 
Gangopadhyay, Sugata
Paul, Goutam
Imai, Hideki
Affiliations: Mathematical Institute of the Serbian Academy of Sciences and Arts 
Title: Internal state recovery of keystream generator LILI-128 based on a novel weakness of the employed Boolean function
Journal: Information Processing Letters
Volume: 112
Issue: 21
First page: 805
Last page: 810
Issue Date: 15-Nov-2012
Rank: M23
ISSN: 0020-0190
DOI: 10.1016/j.ipl.2012.07.013
This paper proposes an algorithm for internal state recovery of the keystream generator LILI-128 and introduces a novel approach for cryptanalysis of certain stream ciphers which belong to the class of nonlinear filters. The proposed cryptanalysis is based on a cryptographic feature/weakness of the Boolean function employed as the nonlinear filter. It is shown that the developed algorithm is significantly more efficient than the previously reported ones against LILI-128 and can recover the internal state with time complexities of pre-processing and processing of the order of 2 47 and 2 35, respectively, the space complexity of 2 47, and a sample of dimension approximately equal to 2 46. The developed cryptanalysis is also a practical confirmation on the significance of the so-called "non-normality" design criterion for Boolean functions.
Keywords: Boolean functions | Cryptography | Internal state recovery | LILI-128 keystream generator | Stream ciphers
Publisher: Elsevier
Project: Department of Science and Technology, Ministry of Science and Technology, India
Advanced Techniques of Cryptology, Image Processing and Computational Topology for Information Security 

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