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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...

marked as duplicate by Steffen Ullrich, ThoriumBR, Anders, grochmal, HashHazard Oct 24 '16 at 19:46

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  • 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 '16 at 19:28
  • i guess brute forcing a 256 bit key would be quite time consuming.... – Tomer waldman Oct 25 '16 at 4:35
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No, knowing the plaintext of a given ciphertext does not improve an attackers attempt to break AES-CBC.

https://crypto.stackexchange.com/questions/1512/why-is-aes-resistant-to-known-plaintext-attacks

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