TIME RESTRICTION ENCRYPTION SYSTEM

摘要

PROBLEM TO BE SOLVED: To obtain the system that is able to decode encryption data only when a decoding condition is satisfied by adopting the method where a user B requests issue of a time key certificate including disclosure time information to a time key certificate management device, the user B sends data encrypted by the acquired encryption public key to a user A, and the user A that requests a decoding key can acquire the decoding key only when the decoding condition is satisfied. SOLUTION: An information user requests service of information to an information server. The information server receiving the request of the information service from the information user requests provision of a time key certificate including encryption public key KEt to a time key certificate management device. The time key certificate management device sends G time key certificate including the encryption public key KEt the information server. The information user requests a decoding key to the time key certificate management device, receives the decoding key sent after a disclosure time, decodes the encrypted information M by using the decoding key to obtain the object information M.