the invention is directed to a data - processing system comprising a processor and first encrypted information in a first persistent memory whose level of information leakage is higher than that of a second persistent memory . in the second persistent memory is stored a first cryptographic key for decrypting the first encrypted information , thereby generating therefrom first unencrypted information that is usable by the processor for executing an operation . the same cryptographic key may also be used for encrypting the first unencrypted information , thereby generating the first encrypted information . it is also directed to a method of processing such a data - processing system with an operating system , comprising a writing step for writing first unencrypted information into the first persistent memory , an encryption step for encrypting the first unencrypted information under use of the first cryptographic key , creating therefrom first encrypted information in the first persistent memory , and an access - limitation step for setting the data - processing system to a state in which writing into the first persistent memory is controlled by the operating system . it also relates to a method of executing an operation on such a data - processing system comprising a decryption step for decrypting the first encrypted information under use of the first cryptographic key , thereby generating therefrom first unencrypted information and an execution step for executing an operation by the processor , using the first unencrypted information .