In
cryptography, a
mode of operation is an algorithm that uses a
block cipher to provide an
information service such as
confidentiality or
authenticity. 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. 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.