analog transmission automatic gain control bell labs cable television cross modulation cryptochannel cryptography descramble diffie-hellman key exchange digital digitizing donald duck encryption engineer family radio service forward error correction frequency range germans intermodulation jamming leonard adleman line code linear feedback shift register martin hellman message microwave radio relay noise one-time pad phonograph public-key cryptography rsa read-only memory recording sigsaly satellite modem security set shamir telecommunication telephone television encryption transfer function voice inversion whitfield diffie winston churchill world war ii z-transform