First and second nodes generate numeric string elements from time interval by their physical changes. The first node generates a basic numeric string from the numeric string elements and similar numeric strings, encrypts the generated basic numeric string and the similar numeric strings, and generates a cipher value list that stores the numeric strings with corresponding cipher values. The second node generates a basic numeric string based on the numeric string elements generated by the second node, encrypts the generated basic numeric string in accordance with the same encryption rule as that for the first node, and transmits the generated cipher value to the first node. The first node receives a cipher value from the second node, and compares the received cipher value with the cipher values in the cipher value list to find a match, and transmits a match signal if a match is found.