Patent ID: 8423766

Claim:
A method of authenticating a subject device to be authenticated, comprising: acquiring current authentication information that is created using an arbitrary value, and that is used for a current authentication process, from the subject device; acquiring encryption information that is the arbitrary value encrypted using next authentication information as an encryption key, from the subject device; receiving first transmission information that is expressed as the next authentication information exclusive-OR the current authentication information, the next authentication information being used for a next authentication process, and second transmission information in which the arbitrary value is hidden using the next authentication information, from the subject device; calculating the next authentication information based on the first transmission information and the current authentication information; calculating the arbitrary value based on calculated next authentication information and the second transmission information; and determining whether to authenticate the subject device based on a calculated arbitrary value and the current authentication information, wherein the acquiring includes acquiring the current authentication information that is created by performing, two times, an operation using a one-way function on the arbitrary value, and wherein the determining includes decrypting the encryption information using the next authentication information; determining whether to authenticate the subject device based on decrypted encryption information; performing, two times, the operation using the one-way function on the calculated arbitrary value; and determining whether to authenticate the subject device based on whether a value obtained by performing, two times, the operation using the one-way function on the calculated arbitrary value is identical to the current authentication information.