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.