Block Cipher

A block cipher is a very unique part of cryptography. For instance, during encryption, the cipher may take a 128-bit block of plaintext for the input, and produce an 128-bit output block of ciphertext. The exact transformation of this procedure is controlled by a secondary input - the secret key. The decryption process is quite similar. Following our example, the decryption algorithm uses a 128-bit block of ciphertext with a secret key and produces the initial 128-bit block of plaintext. A mode of operation is required to encrypt messages longer than the block size mentioned above. Block ciphers are often contrasted against stream ciphers, a type of cipher that functions on one digit at a time. Unlike a block cipher, the transformation of a stream cipher varies during the encryption process. The difference between the two is not always evident . When used in specific modes of operation, a block cipher functions just as effectively as a stream cipher.