Abstract
Kiyomoto-Fukushima-Tanaka proposed a perfectly ano-nymous attribute authentication scheme that realizes unidentifiable and untraceable authentication with offline revocation checking. The Kiyomoto-Fukushima-Tanaka scheme uses a self-blindable certificate that a user can change randomly. Thus, the certificate is modified for each authentication and the authentication scheme has the unidentifiable property and the untraceable property. However, in this letter, we show that the Kiyomoto-Fukushima-Tanaka scheme is insecure against the impersonation attack.