VALIDITY TERM EXTENSION SYSTEM FOR DIGITAL SIGNATURE, VALIDITY TERM EXTENDING DEVICE FOR THE SAME, VERIFYING METHOD FOR THE SAME AND VALIDITY TERM EXTENDING METHOD FOR THE SAME

摘要

PROBLEM TO BE SOLVED: To enable a person different from an original signatory to perform the extending of the validity term of an original digital signature. SOLUTION: The validity term extending device 4 for a digital signature transmits an original digital signature 42 to a time stamp issuing server 10 within the validity term and the time stamp issuing server 10 combines time information 43 concerning a time when the original digital signature 42 is received with the signature to generate a digital signature as a time stamp 45. The device 4 successively repeats an operation that a new digital signature having the new validity term is generated by combining the digital signature 42 with the time stamp 45 and the new digital signature is transmitted to the time stamp server 10 within the new validity term.