Issuance system and certificate issuance server

1 . An issuance system comprising:

an information processing device that communicates with a time stamp server and stores an electronic certificate, a secret key having a relationship with the electronic certificate, and a preshared key; and

a certificate issuance server that stores the preshared key,

wherein

the information processing device

generates a signature based on the secret key and the preshared key in a term of validity of the electronic certificate, transmits a command for generating a time stamp to the time stamp server, and receives the time stamp from the time stamp server, and

transmits the signature and the time stamp to the certificate issuance server after expiration of the term of validity, and the certificate issuance server

verifies the signature by using a public key corresponding to the secret key and verifies the time stamp, and

when it is certified that the preshared key had been stored in the information processing device and it is certified that the signature was generated in the term of validity, issues an electronic certificate and transmits the issued electronic certificate to the information processing device.

2 . The issuance system according to claim 1 , wherein the information processing device deletes the preshared key after the signature is generated.

3 . The issuance system according to claim 1 , wherein the information processing device

after the signature is generated, repeats the generation of a signature based on the secret key and data, transmits the time stamp generation command to the time stamp server each time the signature is generated, and thereby receives a plurality of time stamps,

reduces a number of time stamps, and

after the expiration of the term of validity, transmits all the generated signatures, the data used for generating the signatures, and all the time stamps stored in the information processing device to the certificate issuance server.

4 . A certificate issuance server that communicates with an information processing device storing an electronic certificate, a secret key having a relationship with the electronic certificate, and a preshared key, the certificate issuance server comprising:

memory to store the preshared key;

communicating circuitry to receive a signature and a time stamp transmitted by the information processing device;

verifying circuitry to verify the signature by using a public key corresponding to the secret key and verify the time stamp; and

issuing circuitry to issue an electronic certificate when it is certified that the preshared key had been stored in the information processing device and it is certified that the signature was generated in a term of validity of the electronic certificate, wherein

the signature is generated in the term of validity based on the secret key and the preshared key,

the time stamp is information certifying timing of the generation of the signature, and

upon issuance of the electronic certificate, the communicating circuitry transmits the issued electronic certificate to the information processing device.

5 . The issuance system according to claim 2 , wherein the information processing device

after the signature is generated, repeats the generation of a signature based on the secret key and data, transmits the time stamp generation command to the time stamp server each time the signature is generated, and thereby receives a plurality of time stamps,

reduces a number of time stamps, and

after the expiration of the term of validity, transmits all the generated signatures, the data used for generating the signatures, and all the time stamps stored in the information processing device to the certificate issuance server.