A Method for Security Estimation of the Spn-Based Block Cipher Against Related-Key Attacks

Abstract Symmetric block ciphers are the most widely used cryptographic primitives. In addition to providing privacy, block ciphers are used as basic components in the construction of hash functions, message authentication codes, pseudorandom number generators, as a part of various cryptographic protocols, etc. Nowadays the most popular block cipher is AES (Advanced Encryption Standard). It is used as a standard of symmetric encryption in many countries. Several years ago it was found a theoretical attack exploiting the AES key expansion algorithm that allows reducing significantly the complexity comparing to the brute force attack. This article presents an advanced method of finding the number of active substitutions that helps to estimate the security of encryption algorithms against related-key attacks. The method was applied to a prospective block cipher, which is a candidate for the Ukrainian standard