Initialization vector definition
An initialization vector is a fixed-size random or pseudo-random value that is used as an input parameter for cryptographic algorithms, like block ciphers and symmetric-key encryption algorithms. Initialization vectors are used to ensure that the encryption process is more secure. It makes it harder for an attacker to break the encryption by introducing randomness into the encryption process.
When using a symmetric encryption algorithm, like AES, the same key is used for both encryption and decryption. Without an initialization vector, if the same plaintext is encrypted multiple times using the same key, the resulting ciphertext would be identical. This could potentially allow an attacker to deduce information about the plaintext as well as the key used to encrypt it. By using a unique initialization vector for each encryption operation, even if the same key is used, the resulting ciphertext will be different.
Furthermore, using an initialization vector helps prevent dictionary attacks and other types of attacks that rely on finding patterns in the plaintext or ciphertext. The randomness introduced by the initialization vector makes it harder for an attacker to identify patterns in the ciphertext even if they have access to multiple messages encrypted with the same key.
See also: asymmetric encryption, handshake, cryptographic key