When I was about ten years old, I played with some children who exchanged coded messages with their friends. Their codes were very simple and usually consisted of substituting another letter or a number for the correct letter. I amazed them by being able to quickly decode their secret messages.

I then created my own code, which no one else would be able to decode. Actually the other children didn't have any idea as to how to decode the simple codes that they were using. I found that other children usually did not understand many of the things I was doing. Therefore, I often did things by myself without trying to get anyone else involved. This was true for my coding system. My system used two letters for each letter, space or punctuation mark. The number of letter combinations I used for each letter, space or punctuation mark matched the frequency of that item in normal use. This made it almost impossible to decode. I felt that my system was brilliant. I even had fantasies about selling it to the US Government, but I never got around to doing that.