| 摘要 |
PURPOSE:To improve the protection of software by providing a microprocessor, a memory, a peripheral LSI with a conversion table for ciphering and deciphering data to cipher information flowing on a data bus. CONSTITUTION:A microprocessor 10, a memory and other LSI 21 are constituted by separate chips. In the microprocessor system above, the microprocessor 10, the memory peripheral LSI 21, data bus and data ciphering means 12, 23 and deciphering means 13, 22 are provided to cipher the information in the data bus at the outside of the chip. Thus, since the its own software under execution cannot be known even analyzing the data by means of, e.g, a logic analyzer, and even a ROM of the firmware is stolen, it is meaningless as the program as it is then the software is protected surely. |
