Improved Fixed Point Attack on Gost2

One of the well known block cipher is Gost which was accepted as a Russian Standard, and was proposed to be included in ISO/IEC 18033-3. But, recent attacks on this cipher result in extracting more weaknesses of it and so the standardization of Gost was rejected. In 2015, the designers proposed a modified version of Gost, namely Gost2, which has a new key schedule and explicit choice for Sboxes. In this paper, we present an improved algorithm for fixed point attack on Gost2 with computational complexity of 2
²³³
. This computational complexity has a factor of 2
⁴
improvement in comparison to previous attack which has 2
²³⁷
computational complexity.