ECB and CBC modes

We'll compare Electronic Codebook (ECB) and Cipher Block Chaining (CBC) and show you how to implement AES CBC in Python.

ECB

In the ECB method, each block of plaintext is encrypted with the key separately, so if you have two blocks of plaintext that are the same, they will result in identical ciphertext:

If you have something like an image here with large areas of solid colors such as gray and black and then you encrypt it, you'll just get different colors but the pattern won't change:

That's not good. You can still see that this is a picture of a penguin, and that's not what most people expect out of encryption. You expect the encryption to conceal the data so attackers looking at the encrypted data can't tell what the message is, and here that property is not present.

Thus, CBC is considered the best solution to this problem.

CBC

In addition to the key, you add an initialization vector, which is XOR'd with the plaintext before encryption. Then for the next block, you take the...