Certificate validity authentication method and apparatus

A certificate validity authentication method wherein validity of a public key certificate issued by a certification authority which is different from a certification authority trusted by a terminal is authenticated in compliance with a request made by the terminal, comprising:

• the path search step of executing a process in which, with any certification authority set as a start certification authority, an issue destination of a public key certificate issued by the start certification authority is checked, and subject to any certification authority included as the issue destination, an issue destination of a public key certificate issued by the issue-destination certification authority is further checked, the process being continued until all of the issue destinations of the public key certificates become terminals, thereby to search for paths which extend from said start certification authority to terminal admitting certification authorities having issued public key certificates to any terminals;
• the path verification step of executing for each of the paths detected by said path search step, a process in which, with said start certification authority set at an upstream side, a signature of the public key certificate issued by the terminal admitting certification authority on the pertinent path is verified in the light of the public key certificate issued by the certification authority located directly upstream, and subject to the verification having held good, a signature of the public key certificate issued by the terminal admitting certification authority located directly upstream is verified in the light of the public key certificate issued by the certification authority located directly upstream still further, the process being continued until said certification authority located directly upstream becomes said start certification authority, thereby to verify said paths;
• the path registration step of registering in a database those of said paths whose verifications have held good by said path verification step;
• and
• the validity authentication step of complying with the request of the terminal for authenticating the validity of the public key certificate issued by the terminal admitting certification authority which is different from the certification authority trusted by said terminal, to judge said validity of said public key certificate as having been authenticated when the path between said certification authority trusted by said terminal and said start certification authority and the path between the different terminal admitting certification authority and said start certification authority are held registered in the database.