This paper describes an LSI digital encryption processor (DEP) for data ciphering. The DEP combines a fast hardware implementation of the Data Encryption Standard (DES) published by the National Bureau of Standards (PJBS) with a set of multiplexers and registers under the control of a user programmed sequencer. This architecture enables the user to program any of the DES modes of operation published by NBS. In addition, multiple ciphering operations and multiplexed ciphering operations using up to four different keys may be programmed and internally executed without any external hardware.
The DEP is designed as a standard microprocessor peripheral. This LSI device should reduce the current cost and simplify the process of encrypting digital data to a point where it is feasible to include a ciphering function in modems, terminals, and work stations. The ability to internally program cascaded ciphers should substantially increase the security of the DES algorithm and hence, the life of the encryption equipment.