PERFORMANCE BOUNDS FOR ANALOG SIGNAL ENCRYPTION

Abstract

It is sometimes desirable to perform analog scrambling on an analog signal rather than digitizing the signal and performing digital encryption and transmission. Analog signal encryption is usually assumed to offer only a very limited degree of security. However, it is in fact possible to achieve perfect secrecy (just as is obtained with the one-time pad, for example) in encrypting an analog signal. The price paid for perfect secrecy is an inevitable degradation in the quality of the recovered analog signal. Under the constraint of perfect secrecy, the minimum possible degradation can be specified, at least in principle. This minimal degradation is a decreasing function of the key size for a fixed length message or key rate for an ongoing message. This bound on performance is determined by the rate distortion bounds for optimal digitization of the analog message.