Details:
Title  ElimLin algorithm revisited.  Author(s)  Nicolas T. Courtois, Pouyan Sepehrdad, Petr Suvsil, Serge Vaudenay  Type  Book, Chapter in Book, Conference Proceeding  Abstract  ElimLin is a simple algorithm for solving polynomial systems of multivariate equations over small finite fields. It was initially proposed as a single tool by Courtois to attack DES. It can reveal some hidden linear equations existing in the ideal generated by the system. We report a number of key theorems on ElimLin. Our main result is to characterize ElimLin in terms of a sequence of intersections of vector spaces. It implies that the linear space generated by ElimLin is invariant with respect to any variable ordering during elimination and substitution. This can be seen as surprising given the fact that it eliminates variables. On the contrary, monomial ordering is a crucial factor in Gröbner basis algorithms such as F4. Moreover, we prove that the result of ElimLin is invariant with respect to any affine bijective variable change. Analyzing an overdefined dense system of equations, we argue that to obtain more linear equations in the succeeding iteration in ElimLin some restrictions should be satisfied. Finally, we compare the security of LBlock and MIBS block ciphers with respect to algebraic attacks and propose several attacks on Courtois Toy Cipher version 2 (CTC2) with distinct parameters using ElimLin.  Keywords  block ciphers, algebraic cryptanalysis, systems of sparse polynomial equations of low degree  ISBN  9783642340468/pbk 
URL 
http://link.springer.com/chapter/10.1007%2F9783642340475_18 
Language  English  Pages  306325  Publisher  Berlin: Springer  Year  2012  Edition  0  Translation 
No  Refereed 
No 
