Viewing Single Post From: Brute Forcing The Adfgvx Cipher

Viewing Single Post From: Brute Forcing The Adfgvx Cipher
osric	Mar 20 2009, 03:35 PM
Advanced Member Posts: 51 Group: Members Member #3,254 Joined: March 15, 2009	jdege, I am afraid you have got completely the wrong impression from my description of what the algorithm is doing! The log tetragraphs are used for scoring plaintext, not the transposed ciphertext. 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. Having found the correct transposition key, my Churn program finds the correct substitution key and plaintext in 10 seconds or less. This stage, as you say, is easy. As a general comment, ic's and log digraphs are useless for solving ciphers based on short plaintexts of 100 letters or so -- as in this case. Here you need log tetragraphs. For long ciphers, like Simon Singh's Playfair challenge which had 540 letters of ciphertext, scoring with ic or log digraphs will provide a solution. It sounds from what you've said that an ADFGVX cipher would be a good challenge for this group. Let me know when you have read this and I shall delete it all prior to issuing a challenge on the main page.


Brute Forcing The Adfgvx Cipher · General