| 摘要 |
PROBLEM TO BE SOLVED: To obtain the external ROM information protection system with high safety by providing a means which divides and decodes an execution program to be written to a ROM and a means which reads the program out of the ROM and decodes it. SOLUTION: Random data are inputted from a data input terminal to a cyclic code part 204 and data generated through the cyclic encoding of the cyclic code part 204 are set as a 2nd key in a 2nd key hold part 207. Then data size, the number of divisions of the data, whether or not the divided data are coded by the divided data, and information for selecting a 1st key in divided data units are set in a control part A205 from an external setting terminal. There are multiple 1st keys at a 1st key hold part 206 and the control part 205 controls a selecting circuit B202 to make a choice. Coding or noncoding can be selected in the divided data units and a cyclic code for error detection is added to easily detect ciphered divided data not being decoded into the original data in such as case. |
