Hmm, as far as I'm aware, you can't do cryptanalysis on 2 characters. Marxos A factoid which is irrelevant in this context. If you only wanted to encrypt two characters, once, you could use ROT-13 and nobody would be the wiser.
Not a factoid. I'm making the claim that you can't decrypt it. I don't want to do the proof, because I can deduce it, with Pretty Good Certainty (TM). If you have a key approx 1/2 the size of the text, AND you do NOT know the length of the key, you have essentially two characters to do cryptanalysis. Now the key may be a small enough dictionary to do more analysis, and since you know that each set of the same modulus is using the same key character, but without knowing the length of the key, it's going to be next to impossible. There are many false leads (key-text combinations which result in what seems like valid plaintext) and the search space becomes too large. Marxos