Patent ID: 8281130

Claim:
An authentication system having an authentication target device having a processor and an authentication requesting device having a processor for carrying out an authentication process for the authentication target device, in which the authentication target device and the authentication requesting device respectively hold at least one common encryption key, wherein the authentication requesting device comprises: a first encrypted code production unit that encrypts an authentication code, using the encryption key, to thereby produce a first encrypted code, wherein the authentication code is divided into a plurality of portions having an assigned numeric value; a switching target portion selecting unit that selects at least one pair of the assigned numeric values of the authentication code as switching target portions; a transmission unit that sends the first encrypted code and switching target portion specifying information which specifies the switching target portions to the authentication target device; and a switching unit that switches the switching target portions of the authentication code using the switching target portion specifying information, to thereby produce a comparing code, and the authentication target device comprises: an authentication code decrypting unit that decrypts the first encrypted code sent, using the encryption key, to thereby restore the authentication code; a switching unit that switches the switching target portions of the restored authentication code, based on the switching target portion specifying information sent, to thereby produce a switched authentication code; a second encrypted code production unit that encrypts the switched authentication code, using the encryption key, to thereby produce a second encrypted code; and a transmission unit that sends the second encrypted code to the authentication requesting device, and the authentication requesting device decrypts the second encrypted code sent, using the encryption key, to thereby restore the switched authentication code, and compares the restored switched authentication code with the comparing code to carry out an authentication process for the authentication target device.