1. An apparatus for decryption using cache storage, the apparatus comprising: a memory for storing at least one number sequence; a control signal responsive to the contents of the memory which indicates whether a selected number sequence is stored in the a switch having a first sequence input coupled to the output of the memory, for selectively outputting the first sequence input responsive to the indication of the control signal; and a decoder which receives the output of the switch as a first input and receives encrypted data as a second input, and combines these first and second inputs to produce decrypted data.