Patent ID: 7222108

Claim:
In an electronic cash system which comprises issuer equipment as an institution for issuing electronic cash, user equipment as a user for receiving said electronic cash issued from said issuer equipment and shop equipment as an institution for receiving payment by said electronic cash, said issuer equipment comprising: key generating means for generating a secret key SKI and a public key PKI; storage means for storing said secret key SKI, said public key PKI and a user public key PKU as a user pseudonym; signature generating means for generating a signature SKI(PKU, x) for said user pseudonym PKU and the amount of withdrawal x with said secret key SKI; a balance counter set in said storage means in correspondence with said user pseudonym PKU; signature verifying means for verifying the validity of a user signature and a license contained in history information H received from said shop equipment; balance updating means for receiving said amount of withdrawal x from said user and said user public key PKU and for incrementing said balance counter of said user pseudonym PKU by said amount of withdrawal x, said balance updating means storing said history information H in said storage means and decrementing said balance counter of said user pseudonym PKU by the amount paid when said user signature and said license are both valid by said signature verifying means; sending means for sending said signature SKI(PKU, x) from said signature generating means to said user equipment; receiving means for receiving pieces of information from the other institutions; and control means for controlling each of said means to execute its process.