Initialization vector
lastmod 2020-03-06created 2020-03-061 edits
An initialization vector (IV) is the value used when encrypting the first block.
Each mode of operation uses the initialization vector differently, and the properties required of it may differ slightly, but they share the property that the same initialization vector must not be reused. This is because if the initialization vector is the same, security problems arise, such as the leading blocks becoming identical when two similar plaintexts are encrypted.
Some modes of operation, such as CTR, use the term nonce (number used once) instead of initialization vector. This term is usually used when there is no requirement other than that the initialization vector differ every time.