Cracking the Adventure Time cipher
This seems like as good a time as any to bring up a question I've been wondering. I've seen enough examples like this to know that, for monoalphabetic substitution ciphers, frequency analysis is the way to go with attacking them. But what about ciphers that are just slightly more complicated than that, but nowhere near the strength of "real" crypto. How does one go about attacking these?Like, imagine a cipher where you shift each letter once (modulo 'Z') for each character of the text thus far (e.g. "HELLO WORLD" becomes "HFNOS BUYTM"). I'm sure someone has a name for this that I don't know. This seems immune to frequency analysis (unless you have such a large ciphertext that you begin to notice recurring strings with 1/26th the probability of a monoalphabetic cipher), but still trivial enough that an experienced cryptanalyist should crack it immediately. My question is, how would they do it? What's the "next step" if frequency analysis fails?