a random number, usually the same number of bits as the block size, that is used as a starting point when encrypting a set of data

When a block cipher is used in CBC mode, the initialization vector is exclusive-ORed with the first plaintext block prior to encryption.

(IV) A sequence of random bytes appended to the front of the plaintext before encryption by a block cipher. Adding the initialization vector to the beginning of the plaintext eliminates the possibility of having the initial ciphertext block the same for any two messages. For example, if messages always start with a common header (a letterhead or "From" line) their initial ciphertext would always be the same, assuming that the same cryptographic algorithm and symmetric key was used. Adding a random initialization vector eliminates this from happening.

A value used to initialize a cryptographic algorithm. Often, the implication is that the value must be random. See Also: Nonce, Salt

A series of random bytes tagged on to the front of the plaintext before encryption by a block cipher. It is also used as a piece of the initial step in a block cipher process using some kind of chaining. It eliminates having the initial ciphertext block become the same for any two messages. Closely related topics are challenge/response, initialization vector, nonce, and salt. Challenge/response is by and large used to refer to password and authentication schemes used for secure SSL authentication or secure SSL validation for online security to accept credit cards, or initialization vectors to block ciphers with short, automated secure server network messages and password storage.

One of the problems with encrypting such things as files in specific formats (i.e., that of a word processor, email, etc.) is that there is a high degree of predictability about the first bytes of the message. This could be used to break the encrypted message easier than by brute force. In ciphers where one block of data is used to influence the ciphertext of the next (such as CBC), a random block of data is encrypted and used as the first block of the encrypted message, resulting in a less predictable ciphertext message. This random block is known as the initialization vector. The decryption process also performs the function of removing the first block, resulting in the original plaintext.

In cryptography, an initialization vector (IV) is a block of bits that is required to allow a stream cipher or a block cipher executed in any of several streaming modes of operation to produce a unique stream independent from other streams produced by the same encryption key, without having to go through a (usually lengthy) re-keying process. The size of IV depends on the encryption algorithm and on the cryptographic protocol in use and is normally as large as the block or as large as the encryption key. The IV must be known to the recipient of the encrypted information to be able to decrypt it.