I first heard about this in The Code Book, by Simon Singh, which he mentions and is excellent! It's unfortunate that they invented this when they did - it was o

I first heard about this in The Code Book, by Simon Singh, which he mentions and is excellent! It's unfortunate that they invented this when they did - it was obviously useful, but a practical implementation was not plausible at the time, so I guess the idea got put in a filing cabinet under "how to communicate without pre-shared keys," and forgot about it.