Importance

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Abstract

A user U generates a signature verification key N.sub.U, a signature key SS.sub.U and a cipher key K, enciphers (X,N.sub.U) by a public key into E.sub.I (X,K,N.sub.U) and sends the enciphered information to a bank together with user information U and the amount of money X. The bank registers the information U and E.sub.I in a user data base in correspondence with each other, then withdraws the amount of money X from a user's bank account and sends information (X,E.sub.I) to an electronic cash issuer together with a bank signature S.sub.B (X,E.sub.I) for the information. The issuer deciphers the enciphered information E.sub.I by a secret key to obtain the information (X,N.sub.U), then registers the information E.sub.I and the key N.sub.U in an inspection data base in correspondence with each other, and enciphers the signature S.sub.I (X,N.sub.U) attached to the key N.sub.U by the key K into E.sub.K (S.sub.I), which is sent to the user via the bank. The user deciphers the information E.sub.K by the key K to obtain the issuer signature S.sub.I and sends to a shop, as electronic cash C, information containing the key N.sub.U and the issuer signature S.sub.I. The shop verifies the validity of the issuer signature and the user signature and, if they are valid, approves payment in an amount y. The shop sends data H of communication with the user to the issuer for settlement of accounts, and the issuer makes a check to see if the key N.sub.U in the data H is registered in the inspection data base.

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First Claim