Referring to FIG. 12, after a period of time, the shop encryption program encrypts the information including the challenge that was signed by the user [Rs,Ts,SID]pSKU, the digital cash token [x,Rd]SKI, and the user's digital cash issuer license [pPKU]SKI, using the public key of the digital cash issuer PKI, and sends the information to the digital cash issuer via a communications path.