a data processing apparatus comprises a memory store ; a data bus connected to the memory store , the data bus being adapted for transporting data to and from the memory store ; a processing entity operative to release read and write commands towards the memory store , the write command being accompanied by first data intended to be written to the memory store ; and an encryption module communicatively coupled to the processing entity and to the data bus . upon the processing entity releasing a write command accompanied by said first data , the encryption module encrypts , in accordance with an encryption key , said first data and send an encrypted version of said first data onto the data bus for writing into the memory store . the reverse operation is performed upon the processing entity releasing a read command .