A Method of Evaluating the Security of Snow 2.0-Like Ciphers Against Correlation Attacks Over the Finite Extensions of Two Element Field

Abstract

A method is proposed for evaluation of the security of SNOW 2.0-like ciphers against correlation attacks that are generated by analogy with the well-known attacks on the SNOW 2.0 cipher. Unlike the available methods, the proposed one focuses on proving the security and allows obtaining lower bounds of effectiveness of attacks of the considered class directly by the parameters of stream ciphers components in the same way as it proves the security of block ciphers against linear cryptanalysis. Application of the method to SNOW 2.0 and Strumok ciphers shows that any of the considered correlation attacks on them over the field of order 256 has an average time complexity no less than 2146 . 20 and 2249. 40 , respectively, and requires no less than 2142.77 and 2249. 38 keystream symbols, respectively.