A while back I received a card in the post. The card seemed to be a Japanese advertisement for some sort of gelatinised sea water, which turns out to be the most normal part of the card. On the back of the card are 13 two cent stamps and a load of gibberish. Of course this could only be from a few people and they’re all hoyhoy.
This particular gibberish is in the form of a pile of made up characters, I did a frequency analysis to confirm my suspicion (and hope) that it was a substitution cipher. My first though was to further substitute each character with an ASCII character so that I could easily test it against the library of presumably similar plaintext insanity but in listing the characters for frequency analysis I realized that due to penmanship issues and postmarks I wasn’t really able to identify a few of the characters and there were a some that may or may not have been discrete characters. For example there is a hash mark and an slightly italic hashmark; these turned out to be different characters.
My first attempt was a “same word” attack. I simply went throught the ciphertext looking for strings that occur more than once. I found a string of 8 characters doubled with a doubled character within, but it yielded nothing very promising in /usr/share/dict/words. It turns out it was two words and contained an apostrophe, so analysing it on real plaintext with punctuation and spaces removed would have been helpful, but just running the pattern against the words file was not.
Next I tried an attack I remember using against the krauts in the big one. The Nazis couldn’t keep from beginning a transmission with some formal address and I hoped my writer would have started this note in some fairly normal way. My task was made a lot easier by the fact that the first seven characters contained two sets of doubles. It’s not unthinkable that hoyhoy may begin a letter with the word “smorgasbord” or “monkeychow”, but in this case it was “Hey dude”. After that it was surprisingly easy to fill in the rest. Why he chose to solve the traveling salesman problem in that format is beyond me, but I guess it does add a little flair.