1. A system for processing encrypted information, the system comprising: key generator hardware for processing an input key associated with the encrypted information according to an alogorithm to generate a unique output key, the decryption key generator comprising a single chip microprocessor programmed as a finite state machine which, in each of a plurality of states, responds to one of a plurality of predetermined input words to change to another of a plurality of states and output a corresponding output key word, a plurality of repeatable output key word sequences being generated only with predetermined input key word sequences with each word of a repeatable output sequence being dependent on the present state of the microprocessor and on an input word to the microprocessor which is acceptable at that state; and decryptor means for receiving the encrypted information and a corresponding output key from the key generator hardware and for decrypting the received encrypted information based on the received output key.