To provide a technique for fault attack detection in IC card authentication using an elliptic curve cryptosystem method, by overcoming the problem that any fault attack can not be detected in many cases because a conventional technique utilizes a decoding message as a point on an elliptic curve.

In IC card, a cipher input from an authentication device is decrypted by a secret key to obtain a decrypted message, and then the correspondence between the decrypted message and the cipher is verified by using a degenerated pairing function on an elliptic curve, thus detecting the fact of fault attack.