Refined Method of Impossible Differentials Search with Application to Kalyna-Like Ciphers

This work addresses the problem of evaluating the security of block ciphers against impossible differential cryptanalysis, with a particular focus on Kalyna-like ciphers. Based on formalized methods—specifically the Wu-Wang method—this work introduces refined rules tailored to AES- and Kalyna-like ciphers. These refinements simplify compatibility checks by replacing large systems of linear equations with computationally efficient conditions. Experimental results have identified several classes of impossible differentials for three-round versions of certain Kalyna cipher variants, thereby demonstrating the security of full-round ciphers against this method of cryptanalysis.