Encryption/decryption apparatus with non-accessible table of keys

Abstract

An encryption/decryption unit (EDU) that handles management of encryption keys used in the secure exchange of data over non-secure communication links. Each EDU includes a central processing unit (CPU) that controls its operation, random access memory (RAM) in which tables of key exchange keys (KEKs) are stored, and a data encryption standard (DES) coprocessor that implements a data encryption algorithm developed by the U.S. National Bureau of Standards--all comprising a module that is embedded in a potting material. Attempts to remove the potting material either by mechanical or solvent means are likely to result in loss of the data and program code stored in the module. The CPU includes special circuitry enabling it to operate in an encrypted mode so that it can not be interrogated to discover the program or data stored therein. This program enables the EDU to establish secure communications with another similar EDU over a non-secure link. Each EDU establishing a secure communications session randomly generates a portion of a session data encryption key (DEK) that is encoded by using a KEK from either a public or private table of keys stored in the embedded RAM. The two EDUs exchange the encrypted portions of the DEK, decrypt the portions, and then logically combine them to determine the current session DEK. Use of a stored EDU ID in each EDU comprising the link prevents a third EDU from bridging the link to tap into the communications between two stations.