Patent ID: 8612774

Claim:
A semiconductor integrated circuit for restricting data access to and from an external memory that includes one or more regions and stores data in an encrypted form, the circuit comprising: a first cryptographic circuit for encrypting data transmitted from the circuit to the external memory and for decrypting data transmitted from the external memory to the circuit, the encrypting and decrypting being performed using a secret encryption or decryption key; and one or more fuses, each fuse corresponding to one of the regions of the external memory, and which are initially in a first state and which may be irreversibly changed to a second state; in which the circuit is arranged to cause a change in state of a selected fuse from the first state to the second state, the selected fuse corresponding to a region of the external memory to which data has been written and in which the circuit is further arranged to block data writes to the external memory if data is being written to a region for which the corresponding fuse is in the second state.