Block cipher mode of operation

In cryptography, a block cipher mode of operation is an algorithm that uses a <a href="/facts/Block_cipher/MJywAyfQ">block cipher</a> to provide <a href="/facts/Information_security/horlrCln">information security</a> such as <a href="/facts/Confidentiality/JFMubsQm">confidentiality</a> or <a href="/facts/Authentication/64y4S69b">authenticity</a>. A block cipher by itself is only suitable for the secure cryptographic transformation (encryption or decryption) of one fixed-length group of <a href="/facts/Bit/S972NSaD">bits</a> called a <a href="/facts/Block_(data_storage)/S3vT7c6N">block</a>. 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.
Most modes require a unique binary sequence, often called an <a href="/facts/Initialization_vector/qlVQjCS3">initialization vector</a> (IV), for each encryption operation. The IV must be non-repeating, and for some modes must also be random. The initialization vector is used to ensure that distinct <a href="/facts/Ciphertext/luNTs4sY">ciphertexts</a> are produced even when the same <a href="/facts/Plaintext/tWnBDCgE">plaintext</a> is encrypted multiple times independently with the same <a href="/facts/Key_(cryptography)/5W5PAmT4">key</a>. Block ciphers may be capable of operating on more than one <a href="/facts/Block_size_(cryptography)/QdUI7u7v">block size</a>, but during transformation the block size is always fixed. Block cipher modes operate on whole blocks and require that the final data fragment be <a href="/facts/Padding_(cryptography)/okxl18q9">padded</a> to a full block if it is smaller than the current block size. There are, however, modes that do not require padding because they effectively use a block cipher as a <a href="/facts/Stream_cipher/BxU0aWmJ">stream cipher</a>.
Historically, encryption modes have been studied extensively in regard to their error propagation properties under various scenarios of data modification. Later development regarded <a href="/facts/Integrity_protection/g3XGbKIH">integrity protection</a> as an entirely separate cryptographic goal. Some modern modes of operation combine <a href="/facts/Confidentiality/JFMubsQm">confidentiality</a> and <a href="/facts/Authentication/64y4S69b">authenticity</a> in an efficient way, and are known as <a href="/facts/Authenticated_encryption/u3229wI2">authenticated encryption</a> modes.

Block cipher mode of operation open-in-new

Block cipher mode of operation