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I am looking for an application (Windows) or code example that might help me find patterns in an encrypted file. I have a ciphertext for which I want to see when a key is repeated. I am not trying to break the encryption - just test for when a pattern repeats if it does so.

I've searched, but haven't found anything yet.

Thanks.!

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    $\begingroup$ If you find a pattern that is considered breaking the cipher (or just a broken cipher), by many definitions. $\endgroup$ – Thomas M. DuBuisson May 21 '15 at 15:06
  • $\begingroup$ If the encryption uses proper IVs, key re-use won't harm (the defender). You probably won't even notice IV reuse as it's unlikely that in your file the plaintexts repeat.. $\endgroup$ – SEJPM May 21 '15 at 15:32
  • $\begingroup$ Let's restate the problem for two parties. Consider a prover that knows both pattern and the text, and a verifier only having commitments (that hide plaintext just like encryption). Such a prover can efficiently convince a verifier there is a repeated pattern in the text. IACR preprint 2008/357. $\endgroup$ – Vadym Fedyukovych May 21 '15 at 15:43
  • $\begingroup$ I understand that while that IS technically considered breaking the cipher, until the attacker can actually read/use the plaintext - they haven't really accomplished anything. Anyway, that said, I am testing different IVs, key lengths and patterns and trying to test for repeating keys. Surely someone has already created something that can take a file and search for repeating patterns. Why reinvent :) Thanks everyone. $\endgroup$ – Andy M May 24 '15 at 11:05

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