| 摘要 |
PURPOSE:To improve the safety and the crime prevention of data by caliculating a received check code and a past check code as prescribed to generate a new check code, and allowing a text to contain this check code to transmit it at the next transmission time. CONSTITUTION:The text transmitted and received between a center device 1 and plural terminal devices 2 is provided with a check code CKC consisting of codes M and N. With respect to the code N, random numbers are generated optionally in the transmission side and the updated and stored in a table 3 of the terminal in order as the latest code N1 - the i-th code Ni. In the center device, terminal numbers and codes of terminals are stored in the order of N1-Ni in a table 4. Contents of the code N in tables 3 and 4 are subjected to a prescribed arithmetic processing to generate the code M in the transmission side and is included in the text and is transmitted. When data is received from the terminal in the center device 1, it is decided wshether the received CKC has prescribed relations to the stored past CKC or not; and if it has not prescribed relations, wrong use is judged to disconnect a line.
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