Sampling methods for cryptographic tests

Abstract

Modern cryptographic algorithms have an enormous key diversity, therefore the procedures for the testing of the algorithm strength for all the keys, will take practically an infinite time. To avoid this, the sampling method must be used, in which a much smaller number n of the total key combinations N is tested, and then the performance of the algorithm for all the keys is calculated with a predefined sampling error. For each sampling key n, a cipher output (sample) is produced and the critical questions are how many samples must be tested and how large must be the size of each sample. The general rule is that, the sampling error is decreased as the number of the samples is increased. But since the tests must be executed in an acceptable time, the above rule should be considered together with some additional factors, such as the type of the cryptographic cipher, the kind and the size of the plain information and the available computer power. In this study the interrelations of all the above factors are examined and applicable solutions are proposed. Keywords: Cryptography, Data encryption, Communication security, Computer security, Data security, Information security.