The present invention is an authenticating
system including: a
client (hereinafter, referred to as C) including a creator for, by employing a first hash
algorithm (hereinafter, referred to as 1A), creating a first hash value (hereinafter, referred to as 1V) from
authentication information including an ID and a
password, and creating 2V from the 1V and a random number, and a
receiver for receiving the random number and an 1A identifier from a
server (hereinafter, referred to as S), transmitting the ID and the 2V to the S, and receiving an
authentication result from the S; and the S including a storage for storing 3V created from the
authentication information by employing an 2A identifier and the 2A ID by ID, and a device for transmitting the random number and the 1A identifier to a PC, receiving the ID and the 2V from the PC, determining whether the 2A identifier, which corresponds to the ID, coincides with the 1A identifier, creating 4V from the 3V and the random number by employing the 1A in a case where it coincides, determining whether the 2V coincides with the 4V, transmitting the effect that the authentication is successful to the PC in a case where it coincides, and transmitting the effect that the authentication is unsuccessful to the PC in a case where it does not coincide. Even in a case where a hash
algorithm (hereinafter, referred to as A) that is used in the
authentication system is changed, employing such a configuration enables the
system to be successively utilized.