Computer systems such as smart cards having memory architectures that can protect security information, and methods of using same

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;
• means for executing a general application program in the first memory area including a subroutine call to the second memory area, wherein the means for executing comprises means for transmitting an address of a memory location that is being accessed;
• means for unlocking the third memory area only upon executing a 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 means for unlocking comprises means for unlocking the third memory area when the means for transmitting transmits an address of a memory location in the second memory area;
• and
• means for locking the third memory area when the means for transmitting transmits an address of a memory location in the first memory area.

A method of executing a security program embodied in a computer usable storage medium while executing an application program embodied in a computer usable storage medium, the method comprising:

• executing the application program;
• transmitting an address of a memory location that is being accessed responsive to executing the application program on an address bus;
• locking the security program when the address of the memory location does not correspond to a vector table area containing therein at least one subroutine call to the security program to prevent direct access thereto;
• unlocking the security program upon execution of a subroutine call to the vector table area and when the address of the memory location corresponds to the vector table area to allow indirect access thereto via the subroutine call;
• and
• executing the security program that is unlocked to access a data area associated with the security program.