A block cipher mode of operation implements a block cipher with an arbitrary block length and provides output ciphertext that is always the same size as the input plaintext. The mode can provide the best possible security in systems that cannot allow data expansion, such as disk-block encryption and some network protocols. The mode accepts an additional input, which can be used to protect against attacks that manipulate the ciphertext by rearranging the ciphertext blocks. The universal hash function from Galois/Counter Mode of operation for block ciphers may be used in an embodiment for hardware and software efficiency.