Patent ID: 7409551

Claim:
A certificate validating device that validates a public key certificate, which was issued by an end entity certificate issuing certification authority and which is used to verify a digital signature generated by the end entity certificate issuing certification authority, in a public key infrastructure (PKI) system comprising a plurality of certification authorities including the end entity certificate issuing certification authority which issues a public key certificate to an end entity, the certificate validating device comprising: a database that registers information including a valid path from a start certification authority to any end entity certificate issuing certification authority; a storage device that stores the database; and a processor including program means for searching the database to obtain the information registered in the database, wherein the certificate validating device receives from a first end entity a certificate validation request for the public key certificate, validates the public key certificate by using the information registered in the database, and sends the validation result to the first end entity, wherein the public key certificate is received by the first end entity from the second end entity, and the certificate validation request for the public key certificate is attached to the digital signature which is to be verified, and wherein the certificate validating device determines that the public key certificate is validated under at least one condition that a path between a start certification authority and an end entity certificate issuing certification authority that issues a public key certificate to the second end entity is registered as the valid path.