The initialization vector is used in combination with a secret key only once for encryption. This makes it difficult for hackers to determine the combination and crack the cipher. The constant changes to the initialization vector mean that there are no identical sequences of encrypted data from which hackers can derive a pattern.
The initialization vector is used in block ciphers, such as Cipher Block Chain( CBC) and Cipher Feedback( CFB), and forms the initial value for the first plaintext block to be encrypted. The length of the initialization vector is a measure of transmission security and is usually as long as the key. For example, the initialization vector in Wired Equivalent Privacy(WEP) comprises 24 bits, while that in Temporal Key Integrity Protocol( TKIP) comprises 48 bits.