Patent ID: 7228436

Claim:
A semiconductor integrated circuit device comprising: a first RAM for inputting and outputting data between a bus and itself; a second RAM for inputting and outputting data between the bus and itself; a secret key holder for holding a secret key; a bus port for controlling access from outside to the bus; a CPU for storing an encrypted program and a decryption program in the first memory RAM via the bus port, decrypting the encrypted program by using the decryption program and the secret key, and executing the decrypted program; and a controller for causing, the bus port to disable access from the outside and enable access to the first and second RAMs when the encrypted program and the decryption program are stored in the first RAM, thereby transferring the encrypted program and the decryption program from the first RAM to the second RAM, disabling access to the first RAM when the transfer is completed, and disabling access to the second RAM when the decryption and the execution of the decrypted program are completed.