Patent ID: 7889862

Claim:
A semiconductor integrated circuit for updating encryption or decryption keys used to encrypt or decrypt data in a secure system in which data is stored in an encrypted form in a memory, the circuit comprising: a device; a store for storing a boundary address defining a boundary separating at least a portion of the memory into a first region and a second region; a cryptographic circuit for encrypting or decrypting data flowing between the memory and the device; a key selector arranged to select either a first key or a second key and provide the selected key to the cryptographic circuit, wherein the selected key is selected such that data transferred between the device and the first region of the memory is encrypted or decrypted by the cryptographic circuit using the first key, and data transferred between the device and the second region of the memory is encrypted or decrypted by the cryptographic circuit using the second key, and updating means for incrementing or decrementing the boundary address in response to data being written to the boundary address; wherein the boundary address is variable between a minimum value and a maximum value and wherein the updating means set the boundary address to the minimum value if the boundary address exceeds the maximum value, set the first key to the value of the second key, and generate a new second key.