Patent ID: 7353403

Claim:
A computer system comprising: first, second and third memory areas, the first memory area storing therein at least one general application program including at least one subroutine call to the second memory area, the second memory area storing therein at least one subroutine call to the third memory area, and the third memory area storing therein at least one security application program that is callable by a subroutine call from the second memory area; and a processing system that is configured to execute a general application program in the first memory area including a subroutine call to the second memory area and to unlock the third memory area upon executing the subroutine call from the first memory area to the second memory area to allow the general application program in the first memory area to indirectly access the security program in the third memory area via the subroutine call to the second memory area but prevent the general application program stored in the first memory area from directly accessing the security application program stored in the third memory area, wherein the processing system includes an address bus that transmits an address of a memory location that is being accessed, and wherein the processing system is configured to unlock the third memory area when the address bus transmits an address of a memory location in the second memory area and is configured to lock the third memory area when the address bus transmits an address of a memory location in the first memory area.