Block ciphers may be capable of operating on more than one block size, but during transformation the block size is always fixed. The initialization vector is used to ensure distinct ciphertexts are produced even when the same plaintext is encrypted multiple times independently with the same key. The IV has to be non-repeating and, for some modes, random as well. Most modes require a unique binary sequence, often called an initialization vector (IV), for each encryption operation. A mode of operation describes how to repeatedly apply a cipher's single-block operation to securely transform amounts of data larger than a block. A block cipher by itself is only suitable for the secure cryptographic transformation (encryption or decryption) of one fixed-length group of bits called a block. In cryptography, a block cipher mode of operation is an algorithm that uses a block cipher to provide information security such as confidentiality or authenticity. For "method of operation", see Modus operandi.
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