In 2001, the US National Institute of Standards and Technology (NIST) revised its list of approved modes of operation by including AES as a block cipher and adding CTR mode in SP800-38A, Recommendation for Block Cipher Modes of Operation. The earliest modes of operation, ECB, CBC, OFB, and CFB (see below for all), date back to 1981 and were specified in FIPS 81, DES Modes of Operation. 6 Other modes and other cryptographic primitives.4.2.2.2 Propagating cipher block chaining (PCBC).4.1.3 Synthetic initialization vector (SIV).4.1.2 Counter with cipher block chaining message authentication code (CCM).4.1 Authenticated encryption with additional data (AEAD) modes.Some modern modes of operation combine confidentiality and authenticity in an efficient way, and are known as authenticated encryption modes. Later development regarded integrity protection as an entirely separate cryptographic goal. Historically, encryption modes have been studied extensively in regard to their error propagation properties under various scenarios of data modification. There are, however, modes that do not require padding because they effectively use a block cipher as a stream cipher.
Block cipher modes operate on whole blocks and require that the last part of the data be padded to a full block if it is smaller than the current block size. 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.