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The point of using an IV is that you can use the same key for multiple messages. You're not supposed to repeat (key, nonce) pairs for a stream cipher, and CBC's
by JoachimSchipper 15y ago
The point of using an IV is that you can use the same key for multiple messages. You're not supposed to repeat (key, nonce) pairs for a stream cipher, and CBC's IV is sort-of equivalent to the nonce. (AES-CBC is not technically a stream cipher. Not all stream ciphers have nonces.)
- tptacek 15y agoUsing the same key+nonce pair in a stream cipher has the effect of generating an identical keystream. It's a much, much worse problem than repeating IVs; it makes decrypting the resulting ciphertext stream almost a pencil/paper exercise. Sorry for the pedantry.