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I came across a problem very similar recently and wondered if anyone knew how to solve this.

So say for example I have an RAR archive called archiveA.rar and a password to protect it the password is known as keyA. keyA is stored on the server but I can send the server any file and it will compress it into a RAR file and encrypt it with keyA. I can keep sending files to the server to retrieve encrypted versions of different files. So my question is with all this given information and the fact that I can send unlimited files to the server can I solve for keyA, if so please explain how I would do so?

  • Could you explain why are you asking specifically about RAR? – techraf Mar 22 '16 at 6:52
  • Because the scenario I was in recently was dealing with a RAR, and I can't seem to find any resources on how RAR files are encrypted. – munim_R Mar 22 '16 at 6:54
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RAR uses AES256 for encryptionsource, thus the question is whether AES is cryptographically resistant to a known-plaintext attack.

At present there is no known method that allows retrieving AES encryption key given unlimited number of plaintext inputs and corresponding outputs faster than brute-force. Although there is no proof that it is impossible.

See related posts on Cryptography SE.

  • thanks a bunch for helping me understand this concept :) – munim_R Mar 22 '16 at 7:15

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