Abstract
The keys of modern cryptographic algorithms
have an enormous size, so the testing of the algorithm performance for all key
combinations, will take practically an infinite time. To avoid this, the
sampling method is used, where a much smaller number of keys is tested and then
the estimation of the algorithm performance for all the keys is calculated with
a predetermined sampling error. For each sampling key, an output sample of the
algorithm must be generated and tested. Therefore, in order to have sampling
results as close as possible to the real performance of the algorithm, the key
question is whether the selection of the keys should be random or it must
follow some rules. If the selection of the keys is completely random, there is
a high probability that the tests will not find some "weak" or
"equivalent" keys, which give non-random or similar outputs and
therefore reduce the total number of active keys. But if the sampling keys are
selected with some specific criteria, there is a much greater probability of
detecting any weak or equivalent key. In this study an optimal key selection
methodology is proposed, which combines the random and the non-random key
selection.