Since almost any byte chain can be used as a key (the length of the chain must meet the requirements of the algorithm used), random-number generators are used to generate keys. The main goal of a random-number generator is to create a unique key, since security depends greatly on key uniqueness. The best key generator is a generator for which it is difficult (almost impossible) to guess what number (key) will be generated next. Special statistic random sequence tests are used to check the security level of random-number generators.