To enhance the security of authentication processing relating to transmission/reception of information.

When a mail address of a sender is inputted from the sender in a procedure A1, a server of each provider generates a file ID of an electronic mail received in a procedure A2, an optional setting value set by a manager of a home page or a bulletin board in a procedure A3, a random number is generated, based on the file ID and the setting value in a procedure A4, and the random number is set as a basis of a random number array. A character string is converted one by one character each into an ASKII code in a procedure A5 and all the converted codes are obtained, A numeral obtained in the procedure A5 is used for a basis of the random number again in a procedure A6. Character codes are added by a random number by the number of times set by the random number in a procedure A7 to generate a password character string. The password character string is a confirmation key this time. Every time a sender transmits a mail, a different password character string is used to generate the mail.