Initialization vector
The initialization vector ( IV ) is a term from cryptography and describes a block of random data that is used in certain modes of some block ciphers , such as the cipher block chaining mode .
When encrypting messages, it must be avoided that the same plaintext blocks result in the same ciphertext blocks over and over again . A formal letter in German usually starts with "Dear Mr. / Ms." followed by the name. From this knowledge, an attacker could attempt to draw conclusions about the key used (see known plain text attack ). To avoid this, the first plaintext block with an IV is XOR -linked. Since the IV was generated randomly, the resulting ciphertexts differ even if the plaintexts begin with identical data.
Since modes are usually selected for the encryption algorithms in which the ciphertext of a block depends on the ciphertext of its predecessor block, the IV does not have to be kept secret. In the case described, the ciphertext of the block would function as the IV of the block , so that initialization vectors would be known to the cryptanalysts anyway .
