Algebraic Attacks on SOBER-t32 and SOBER-t16 without Stuttering

This paper presents algebraic attacks on SOBER-t32 and SOBER-t16 without stuttering. For unstuttered SOBER-t32, two different attacks are implemented. In the first attack, we obtain multivariate equations of degree 10. Then, an algebraic attack is developed using a collection of output bits whose relation to the initial state of the LFSR can be described by low-degree equations. The resulting system of equations contains 269 equations and monomials, which can be solved using the Gaussian elimination with the complexity of 2196.5 . For the second attack, we build a multivariate equation of degree 14. We focus on the property of the equation that the monomials which are combined with output bit are linear. By applying the Berlekamp-Massey algorithm, we can obtain a system of linear equations and the initial states of the LFSR can be recovered. The complexity of attack is around O(2100 ) with 292 keystream observations. The second algebraic attack is applicable to SOBER-t16 without stut...

• Type: Conference
• Year: 2004
• Where: FSE
• Authors: Joo Yeon Cho, Josef Pieprzyk
• Keywords: Algebraic Attack, Cryptography, FSE 2004, Multivariate Equations, Output Bit