Why using AES in ECB (Electronic Code Book) mode a bad idea? is CTR mode better? Given only these two can be used for parallelization.

  • $\begingroup$ On the other hand, that makes your post's title completely different from your post's body. $\;$ $\endgroup$
    – user991
    May 31, 2015 at 9:56
  • $\begingroup$ There are other parallelizable modes as well. Such as XTS and OCB. But to recommend a mode we need to understand your requirements. $\endgroup$ May 31, 2015 at 11:51

1 Answer 1


ECB is bad because identical plaintext blocks result in identical ciphertext blocks. Encrypted data is therefore not pseudo-random.

This is how Tux looks like after ECB encryption:


CTR mode doesn't have this problem. Data encrypted with CTR mode is pseudo-random and doesn't show any pattern. So CTR is much better.

CBC and CFB can also decrypt parallel, but not encrypt.


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