A Method to Estimate the Number of Ciphertext Pairs for Differential Cryptanalysis

Differential cryptanalysis introduced by Biham and Shamir in 1990 is one of the most powerful attacks to DES-like cryptosystems. This attack presumes on some tendency of the target cryptosystem. So the efficiency of the attack depends upon the conspicuousness of this tendency. S/N ratio introduced in the paper is to evaluate this conspicuousness. In other words, the S/N ratio is a measure of the efficiency of the attack. Nevertheless, S/N ratio does NOT suggest how many pairs of ciphertexts are needed.