Secure communication system having long-term keying variable

摘要

A secure communication apparatus incorporates a longterm, non-extractable master key variable which is held in common by all terminals. A pseudorandom bit sequence generator within the transmitter provides a binary bit stream which is transmitted unencrypted to the intended receiver. Both terminals simultaneously mix the master variable with the transmitted pseudorandom bit stream in an identical manner to create a common separate working variable which is subsequently used for data encryption and decryption.