Patent ID: 9350551
Filing Date: 2016-05-24
CPC Classification: H04L

Claim Text:
1. A validity determination method comprising: having a first Central Processing Unit (CPU) of a receiving apparatus of electronic data identify a first public key corresponding to an electronic signature attached to the received electronic data based on current date and time, among multiple public keys having respective valid terms, identify a second public key corresponding to the electronic signature based on a creation date and time, among the multiple public keys having respective valid terms, when the first public key corresponding to the electronic signature is not identified based on the current date and time, determine that the electronic signature of the electronic data has expired when a digest value, which is acquired by decrypting the electronic signature by using the second public key being identified, is valid, and send a resend-request for the electronic data, and determine that the electronic data are valid, when the electronic data are received with respect to the resend-request; having a second Central Processing Unit (CPU) of a sending apparatus of the electronic data resend the electronic data to the receiving apparatus in response to receiving the resend-request if the sending apparatus has sent the electronic data relevant to the resend-request in a past; and further having the first CPU of the receiving apparatus of the electronic data determine the electronic data, in which the electronic signature is expired, as a spoofing electronic data, when content of the electronic data is different from content of authenticated electronic data.