I understand that "anagramming" is often used after frequency analysis of a traditional substitution cipher, but anagramming requires prior frequency analysis to provide a starting point. Is there any technique other than frequency analysis for a cipher-text only attack on a traditional substitution cipher?

  • $\begingroup$ Brute force, maybe? $\endgroup$ – mikeazo Jan 8 '16 at 12:56

Yes, there are many. Here are the few that I know:

  1. Brute-Force: Simply trying all possible keys.
  2. Kasiski examination: Exploiting the repeated words in the ciphertext to figure out the key length in Vigenere Cipher.
  3. Friedman test aka Kappa Test: Measures the unevenness of the cipher letter frequencies to break the Vigenere cipher.
  4. Key elimination: Eleminate the key by XORing two plaintexts with the same key.
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  • $\begingroup$ You seem to target Vigenère ciphers, but Ned was asking for attacks on substitution. These do not immediately translate, as well; this is why they're listed precisely like you listed them, on the Vigenère wikipedia page. $\endgroup$ – Joost Jan 9 '16 at 10:13
  • $\begingroup$ @Joost Vigenere Cipher is a substitution Cipher, so the answer fits in perfectly. $\endgroup$ – Switch Jan 9 '16 at 15:43
  • $\begingroup$ I agree that I (perhaps falsely) jumped to the conclusion that Ned was talking about a monoalphabetic substitution, but I still think that picking out Vigenere and attacking that instead is a gross over-specification. At the very least, it needs an "if your cipher is actually Vigenere" note. $\endgroup$ – Joost Jan 19 '16 at 14:43
  • $\begingroup$ @Joost I have done that (specifying that the attack is for Vigenere). Only the middle two are Vigenere specific, and I have mentioned it. The rest work for others as well. $\endgroup$ – Switch Jan 19 '16 at 16:30

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