Public key validation service

(57) a summary public key reasonableness test agent (PKVA) (701), The off-line registration authority (702) who connects the public key (801) of the subject concerned to the 1st public key serial number (PKVN) (802) and who publishes the 1st unsigned public key reasonableness test certificate (signing no PKVC) (800) off-line is included to a subject (706). Moreover, a registration authority maintains the certificate database which is not signed PKVC, and stores no 1st signing PKVC into it. A trust certificate server (703) publishes a disposable public key reasonableness test certificate (disposable PKVC) (900) on-line to a subject. This disposable PKVC connects the public key of the subject from no 1st signing PKVC to the 1st PKVN from no 1st signing PKVC. Furthermore, a trust certificate server maintains a table (704) including the entry corresponding to no effective signing which was stored in the certificate database PKVC. Before using this PKVA in public key reasonableness test service and using the pair of the secret key/public key of a subject for the purpose of attestation, the reasonableness test of the public key of the subject concerned can be conducted.