Algebraic attacks on two kinds of special nonlinear filter generators

• Published in: 高技术通讯（英文版） Vol. 18; no. 2; pp. 151 - 154
• Main Author: 杨文峰 Hu Yupu Qiu Hua
• Format: Journal Article
• Language: English
• Published: Key Laboratory of Computer Networks & Information Security, Ministry of Education,Xidian University, Xi'an 710071, P.R.China%Navy Submarine Academy, Qingdao 266071, P.R.China 01.06.2012
• Subjects: LFSR; 代数关系; 代数攻击; 发电机; 布尔函数; 线性反馈移位寄存器; 过滤功能; 非线性滤波; cryptanalysis; linear feedback shift register (LFSR); stream cipher; Boolean function,algebraic attack
• ISSN: 1006-6748
• DOI: 10.3772/j.issn.1006-6748.2012.02.008

This letter proposes algebraic attacks on two kinds of nonlinear filter generators with symmetric Boolean functions as the filter fimctions. Different fxom the classical algebraic attacks, the proposed attacks take the advantage of the combinational property of a linear feedback shift register （LFSR） and the symmetric Boolean function to obtain a tow-degree algebraic relation, and hence the complexities of the proposed attacks are independent of the algebraic immunity （AI） of the filter functions. It is shown that improper combining of the LFSR with the filter function can make the filter generator suffer from algebraic attacks. As a result, the bits of the LFSR must be selected properly to input the filter function with large AI in order to withstand the proposed algebraic attacks.