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Journal of Applied Mathematics
Volume 2014, Article ID 457275, 7 pages
http://dx.doi.org/10.1155/2014/457275
Research Article

Cryptanalysis of Loiss Stream Cipher-Revisited

Information Science and Technology Institute, Zhengzhou 450000, China

Received 15 November 2013; Revised 5 May 2014; Accepted 5 May 2014; Published 27 May 2014

Academic Editor: Renat Zhdanov

Copyright © 2014 Lin Ding et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Loiss is a novel byte-oriented stream cipher proposed in 2011. In this paper, based on solving systems of linear equations, we propose an improved Guess and Determine attack on Loiss with a time complexity of 2231 and a data complexity of 268, which reduces the time complexity of the Guess and Determine attack proposed by the designers by a factor of 216. Furthermore, a related key chosen IV attack on a scaled-down version of Loiss is presented. The attack recovers the 128-bit secret key of the scaled-down Loiss with a time complexity of 280, requiring 264 chosen IVs. The related key attack is minimal in the sense that it only requires one related key. The result shows that our key recovery attack on the scaled-down Loiss is much better than an exhaustive key search in the related key setting.