You're thinking of SIGSALY. Not only was it not analog, it was the first digital system to use PCM for audio. https://en.m.wikipedia.org/wiki/SIGSALY https://e

You're thinking of SIGSALY. Not only was it not analog, it was the first digital system to use PCM for audio. https://en.m.wikipedia.org/wiki/SIGSALY https://en.m.wikipedia.org/wiki/SIGSALY The analog TV stuff isn't encryption, it's scrambling. Those systems used proper digital crypto to generate the keystream, then scrambled video lines using a digital line buffer. They aren't secure (you can decode the picture by correlating lines without having the key) and they still rely on digital bits to do the processing, even if the image itself is transmitted as analog. So no, analog crypto doesn't exist, though you can certainly obfuscate analog signals in various ways. For crypto to be analog the actual cryptography would have to be performed in the analog domain. To my knowledge, that doesn't exist and can't exist.