Viewing Single Post From: Brute Forcing The Adfgvx Cipher

Viewing Single Post From: Brute Forcing The Adfgvx Cipher
jdege	Mar 20 2009, 04:57 PM
Elite member Posts: 263 Group: Admin Member #246 Joined: December 7, 2006	osric Mar 20 2009, 03:35 PM For each perm of the transposition key, a transposed ciphertext is created. This is then hillclimbed, using 10 successive random substitution keys. The hillclimbing of each of these 10 substitution keys is prolonged for approx 15,000 key changes. Each plaintext produced is scored with log tetragraphs. The highest scoring plaintexts, transposition keys and substitution keys are displayed. Once all perms have been considered, the highest scoring is usually the correct transposition key. The plaintext is not good at this stage, though it's good enough for the log tetragraphs to have distinguished between the right transposition key and the rest. Ah-ha. I'd been looking at this problem, trying to find a statistic that would come through the substitution cipher, and not finding any that would work on short texts. I'd considered doing a full hill-climb on the result of every trial transposition decrypt, but eliminated that as being far too expensive. I hadn't considered that doing a fast, limited hill-climb might provide good enough results to use as a scoring function. This is a new idea, to me. Is this your own insight? Or have you seen this technique used elsewhere? (As for the challenge, there were never more than a handful of active participants in this forum, and we've all pretty much gone silent for the last year or so. Throw it out, if you like. You may draw some of them out of the woodwork. Personally, I'm not going to be able to look at it until July or August.)
	When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

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