Initialization vector: Difference between revisions

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== SSL 2.0 IV ==

In [[Block cipher mode of operation#Cipher-block chaining Cipher_block_chaining_(CBC)|cipher-block chaining mode]] (CBC mode), the IV need not be secret, but must be unpredictable (In particular, for any given

plaintext, it must not be possible to predict the IV that will be associated to the plaintext in advance of the generation of the IV.) at encryption time. Additionally for the [[Block cipher mode of operation#OFB|output feedback mode]] (OFB mode), the IV must be unique.<ref>{{citation |author = Morris Dworkin |title = NIST Recommendation for Block Cipher Modes of Operation; Chapters 6.2 and 6.4 |date = 2001 |url = https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38a.pdf }}

</ref>

In particular, the (previously) common practice of re-using the last ciphertext block of a message as the IV for the next message is insecure (for example, this method was used by SSL 2.0).