A computer readable storage medium encoded with computer instructions for causing a tamper resistant microprocessor which has a function for decrypting and executing encrypted codes and a table formed by a plurality of regions for storing a plurality of encryption keys corresponding to at least one program and at least one shared library to be called up by the at least one program, to use a shared library called up from a calling source program, the instructions including the steps of causing the tamper resistant microprocessor to create a task for the shared library, causing the tamper resistant microprocessor to allocate a task identifier to the task, causing the tamper resistant microprocessor to acquire an instruction key from a header of the shared library, causing the tamper resistant microprocessor to store the instruction key into a region of the table corresponding to the task identifier allocated to the task for the shared library in the microprocessor, causing the tamper resistant microprocessor to initialize by executing a loader in the shared library, and causing the tamper resistant microprocessor to return a control to the calling source program via an entry point in the shared library.