i am currently trying to encrypt a set of files safely (using AES encryption in CBC mode), but knowing that plain text copies of some of these files may be floating around the file system i am worried that the content of these copied files can help break the key to the entire set of files i am trying to encrypt (with the same key). i know a very obvious solution is to encrypt every file with it's own key but, it seems quite an awkward solution...

  • The only benefit to an attacker would be not having to compute a plaintext analysis for each key during a bruteforce. Otherwise, this is designed to specifically be strong against this attack. I'd suggest looking at "chosen plaintext attacks".
    – d1str0
    Oct 24, 2016 at 19:28
  • i guess brute forcing a 256 bit key would be quite time consuming.... Oct 25, 2016 at 4:35

1 Answer 1


No, knowing the plaintext of a given ciphertext does not improve an attackers attempt to break AES-CBC.


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