Initialization vector

The initialization vector (IV ) is a term used in cryptography and refers to 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 must be avoided that the same plaintext blocks always give equal ciphertext blocks. A formal letter begins in German usually with " Dear Sir / Madam " followed by the name. Based on this knowledge, an attacker could try to draw conclusions on the key used (see known- plaintext attack). To avoid this, the first plaintext block with a IV is XORed. Since the IV is randomly generated so that the resulting ciphertexts are different even if the plaintexts start with identical data.

As can be selected in the encryption algorithms usually modes in which the ciphertext of one block depends on the ciphertext of his predecessor block, the IV must not be kept secret. In the described case, the ciphertext of block IV would act as the block, such that for the initialization cryptanalysts anyway would be known.