Abstract: In the encryption/decryption method, a random number sequence {ri} is generated on the basis of a given multiple-affine key system K and encryption is performed by an exclusive OR of the random number sequence {ri} with a plain text. Further, the multiple-affine key system K is automatically sequentially rewritten into a series of new multiple-affine key systems each time when the number of use times of the multiple-affine key system reaches a predetermined number and encryption of plain texts thereafter is continued while generating random numbers using the series of the rewritten multiple-affine key systems. Likewise, in decryption as well, since decryption is performed using a multiple-affine key system automatically rewritten each time when the number of use times reaches a predetermined number, a third party cannot reproduce the multiple-affine key system and therefore cannot decipher a cipher text.

Abstract: In one aspect of this invention, a control unit generates a frame having control data, and transmits it to a controlled apparatus via a transmission/reception unit or the like at a predetermined priority. In the controlled apparatus, a transmission/reception unit receives the frame, and a control unit analyzes it to generate a predetermined signal on the basis of the analysis result. The signal is output to a driving system or the like via an external I/O or the like. The controlled apparatus generates a response frame and transmits it to the control apparatus. In the control apparatus, the control unit analyzes the contents of the response frame, and a predetermined display is provided on the LED of an output unit on the basis of the analysis result.