| 摘要 |
PURPOSE:To secure the same input and output instructions while improving the secrecy of these instructions by applying different decoding methods between an executing mode and an external output mode for instructions ciphered and stored. CONSTITUTION:When an instruction is carried out, a changeover switch 6 is closed at the side of an instruction decoding circuit 8. Then the instruction stored in an instruction storing circuit 4 that is shown by an address inputted through an address input terminal 5 is sent to a 1st decoding circuit 7 having the adverse characteristics to those of a ciphering circuit 2 and decoded there. Then the switch 6 is closed at the side of an output terminal 12 when an instruction is read to outside. The instruction stored in the circuit 4 that is shown by an address inputted through the terminal 5 is sent to a 2nd decoding circuit 10 having a decoding method which is different from that of the circuit 7 and supplied via a cipher key 11 and decoded there. |
