A data processing apparatus includes a volatile memory, a random number generator adapted for generating random numbers from which one or more keys are generated, and a memory encryption unit (MEU). The MEU is configured to receive an N-bit block of data and to divide the N-bit block of data into two more sub-blocks of data, where each sub-block contains fewer than N-bits. The MEU is further configured to encrypt each sub-block of data using the one more keys, to combine the encrypted sub-blocks into an N-bit block of encrypted data, and to write the encrypted N-bit block of data to the volatile memory.