Security evaluation of a new analog speech scrambling device using a nonlinear DES-based keystream generator

A novel nonlinear data-encryption-standard-based keystream generator algorithm, which provides eight very long random and mutually independent keystreams, is used to operate a speech-scrambling algorithm which processes the analog signal in the two dimensions of time and frequency, and uses a preamplifier to synchronize the operation of the receiver with that of the transmitter. Both the scrambling and generator algorithms can be implemented on one device, providing security against a ciphertext-only attack, as well as against a known-plaintext attack. The operation and security evaluation of the analog speech scrambling algorithm are summarized. The operation and security evaluations of the keystream generator algorithm are then described. The different possible known plaintext attacks are outlined, and it is shown that none can compromise the security of this algorithm