Electronic cash implementing method with a surveillance institution, and user apparatus and surveillance institution apparatus for implementing the same

Claim 2

The method of claim 1, wherein in said step (1) said surveillance institution stores in said surveillance database a total amount of spent money Y in correspondence with said management data and in said step (4) said user sends to the shop a ballance of the electronic cash included in information of the electronic cash.

Claim 3

The method of claim 2, wherein said step (4) comprises: step (4a) wherein said shop generates arbitrary challenge information e and sends it to said user; step (4b) wherein said user generates his signature S U (e,y) for said amount of payment y and said challenge information e sent to him and sends said electronic cash C, said amount of payment y and said signature S U (e,y) of said user to said shop; and step (4c) wherein said shop verifies the validity of said signature S B (X,N U ) of said bank, verifies the validity of said signature S U (e,y) of said user by said verification key N U , and verifies that said amount of payment y is smaller than said balance x of said electronic cash, and if the results of any of said verifications are valid, said shop approves of the payment of said amount y with said electronic cash.

Claim 4

The method of claim 2 or 3, wherein said step (6) comprises: step (6a) wherein said surveillance institution makes a check to see if said management data n obtainable from said communication data H has been registered in said surveillance database; step (6b) wherein if said data H has been registered, said surveillance institution updates said total amount of payments Y corresponding to said management data n with Y+y; step (6c) wherein said surveillance institution makes a check to see if said updated total amount of payments Y+y is smaller than said face value X, and if so, instructs said bank to transfer the amount of money y to a bank account of said shop; step (6d) wherein if Y+y=X , said surveillance institution erases from said surveillance database said management data n and said total amount of payments Y corresponding thereto; and step (6e) wherein when the result of any one of said checks is invalid, said surveillance institution decides that said user committed overspending, then erases from said surveillance database said management data n and said corresponding total amount of payments Y, and sends said management data n to said bank to specify the name of an overspending user from said user database.

Claim 5

The method of claim 4, wherein said management data n comprises a pair of said face value X and said signature verification key N U .

Claim 6

The method of claim 1, 2 or 3, wherein said step (1) includes a step wherein said user produces said verification key N U .

Claim 7

The method of claim 1, 2 or 3, wherein said step (1) includes a step wherein said user generates a variable number R and sends it together with said verification key N U to said bank and further to said surveillance institution and said step (2) includes a step wherein said bank records, as said management data, information including said verification key N U and said variable number R, and said step (3) includes a step wherein said surveillance institution registers, as said management data, information including said verification key N U and variable number R.

Claim 8

The method of claim 1, 2 or 3, further includes a step wherein said surveillance institution produces said verification key NU and sends it to said user.

Claim 9

The method of claim 1, 2 or 3, wherein said management data n is obtained by processing a set of said face value X and said signature verification key N U with a predetermined one-way hash function h.

Claim 10

An electronic cash implementing method for an electronic cash system which is composed of a surveillance institution which keeps the issuance of electronic cash under its surveillance, a bank which issues electronic cash, a user who uses electronic cash, and a shop which receives a payment with electronic cash, and wherein said surveillance institution makes public an encipher function E T and said bank makes public a bank signature verification key PK B , said method comprising: step (1) wherein said user sends user information U and an amount of money X corresponding to the face value of electronic cash to said bank and requests the bank to withdraw said amount of money X from a bank account of said user, while at the same time said user enciphers information including signature verification key N U and said face value X to produce enciphered information E T (X,n) and send it to said bank; step (2) wherein said bank withdraws said amount of money X from said bank account of said user and sends said amount of money X and said enciphered information E T (X,n) to said surveillance institution, while at the same time said bank records said user information U and said enciphered information E T (X,n) in a user database in correspondence with each other; step (3) wherein said surveillance institution deciphers said encipherd information E T to obtain signature verification key information and registers at least one of said signature verification key information and said enciphered information E T in a surveillance database in correspondence with a total amount of payments Y; step (4) wherein said user requests said bank to attach a blind signature to said management data n and said amount of money X, obtains a bank signature S B (n) of said bank for said amount of money X; step (5) wherein said user pays an amount of money y to said shop, using, as electronic cash C of said face value X, second information including said bank signature S B (n), a balance x, said face value X and said user signature verification key N U and said shop receives said electronic cash C after verifying its validity; step (6) wherein said shop sends to said surveillance institution, for the settlement of an account, whole data H of communication between said shop and said user, including information on said electronic cash C; and step (7) wherein said surveillance institution verifies the validity of said electronic cash C contained in said communication data H and instructs said bank to transfer said amount of payment y to a bank account of said shop.

Claim 11

The method according to claim 10, wherein in said step (3) said surveillance institution registers said at least one of said signature verification key information and said enciphered information E T in said surveillance database in correspondence with said total amount of payments Y.

Claim 12

The method of claim 11, wherein said step (4) comprises: step (4a) wherein said shop generates arbitrary challenge information e and sends it to said user; step (4b) wherein said user generates a user signature S U (e,y) for said amount of payment y and said challenge information e sent to him and sends said electronic cash C={x,X,N U ,S B (X,n)} and information {y,S U (e,y)}to said shop; and step (4c) wherein said shop verifies the validity of said bank signature S B (X,N U ) by said bank signature verification key PK B and the validity of said user signature S U (e,y) by said user signature verification key N U , and if both of said signatures are valid, said shop approves of the payment of said amount y with said electronic cash.

Claim 13

The method of claim 11 or 12, wherein said step (7) comprises: step (7a) wherein said surveillance institution makes a check to see if said at least one of said signature verification key information and said enciphered information E T obtainable from said communication data H has been registered in said surveillance database; step (7b) wherein if said management data n has been registered, said surveillance institution updates said total amount of payments Y corresponding to said at least one of said signature verification key information and said enciphered information E T with Y+y; step (7c) wherein said surveillance institution makes a check to see if said updated total amount of payments Y+y is smaller than said face value X, and if so, instructs said bank to transfer the amount of money y to a bank account of said shop; step (7d) wherein if Y+y=X , said surveillance institution erases from said surveillance database said management data n and said total amount of payments Y corresponding to said at least one of said signature verification key information and said enciphered information E T ; and step (7e) wherein when the result of any one of said checks is invalid, said surveillance institution decides that said user committed overspending, then erases from said surveillance database said management data corresponding to said at least one of said signature verification information and said enciphered information E T and said corresponding total amount of payments Y, and sends said at least one of said signature verification information and said enciphered information E T to said bank to specify the name of an overspending user from said user database.

Claim 14

The method of claim 13, wherein said management data n is composed of a pair of said face value X and said signature verification key N U .

Claim 15

The method of claim 10, 11 or 12, wherein said step (1) includes a step wherein said user produces said verification key N U .

Claim 16

The method of claim 10, 11 or 12, wherein said step (1) includes a step wherein said user generates a variable number R and sends it together with said verification key N U to said bank and further to said surveillance institution and said step (2) includes a step wherein said bank records, as said management data, information including said verification key N U and said variable number R, and said step (3) includes a step wherein said surveillance institution registers, as said management data, information including said verification key N U and variable number R.

Claim 17

The method of claim 10, 11 or 12, further includes a step wherein said surveillance institution produces said verification key NU and sends it to said user.

Claim 18

The method of claim 10, 11 or 12, wherein said management data n is obtained by processing said pair of said face value X and said signature verification key N U with a predetermined hash function h.

Claim 19

A user apparatus for implementing an electronic cash system which is composed of a surveillance institution which keeps the issuance of electronic cash under its surveillance, a bank which issues electronic cash, a user who uses electronic cash and a shop which receives a payment with electronic cash, said apparatus comprising: key generating means for generating user signature key SK U ; memory means for storing electronic cash C containing a bank signature S B (X,N U ) attached to an amount of money X and a signature verification key N U , a balance x, a face value X and a signature verification key N U , and said user signature key SK U ; signature generating means for attaching a signature to an amount of payment y and arbitrary challenge information e received from said shop by said signature key SK U to generate a signature S U (e,y); and balance updating means for subtracting said amount of payment y from said balance x to update the latter.

Claim 20

A surveillance institution apparatus for implementing an electronic cash system which is composed of a surveillance institution which keeps the issuance of electronic cash under its surveillance, a bank which issues electronic cash, a user who uses electronic cash and a shop which receives a payment with electronic cash, said apparatus comprising: a surveillance database wherein management data n corresponding to each user possessing electronic cash issued thereto is registered in correspondence with a total amount of payments Y; a history database for storing history data H which contains electronic cash C including a balance x, a face value X, a signature verification key N U and a bank signature S B (X,N U ), and an amount of payment y all received from said shop; means for making a check to see if there has been registered in the surveillance database said management data n corresponding to said amount of money X and said verification key N U in said history data H and, if not, for deciding that the electronic cash paid to the shop is overspent electronic cash; adding means for adding said amount of payment y in said history data to said total amount of payments Y in the surveillance database when said management data n has been registered therein; compare means for comparing the result of addition Y+y with said face value X; and control means which: if the result of said comparison by said compare means is Y+y<X , updates said total amount of payments Y in the surveillance database with the result of said addition Y+y; if Y+y=X , eliminates said management data n and said total amount of payments Y from said surveillance database; if Y+y>X , decides that electronic cash paid to said shop is overspent electronic cash, then eliminates said management data n and said amount of payments Y, and reports said eliminated management data n to said bank.

Claim 21

A user apparatus for implementing an electronic cash system which is composed of a surveillance institution which keeps the issuance of electronic cash under its surveillance, a bank which issues electronic cash, a user who uses electronic cash and a shop which receives a payment with electronic cash, said apparatus comprising: key generating means for generating user signature key SK U ; encipher means for enciphering said amount of money X and said signature verification key N U by a public encipher key PK T of said surveillance institution to generate enciphered information E T (X,N U ) and for sending it to said bank; blind signature pre-processing means for pre-processing said signature verification key N U to produce pre-processed signature verification key F(N U ), said pre-processed signature verification key F(N U ) being sent to said bank; blind signature post-processing means for post-processing a blind signature Z(N U ) for said signature verification key received from said bank to obtain a signature S B (N U ) of said bank; memory means for storing electronic cash C containing a balance x, a face value X, said signature verification key N U and said bank signature S B (X,N U ), said user signature key SK U and said public encipher key PK T of said surveillance institution; signature generating means for attaching a signature to an amount of payment y and arbitrary challenge information e received from said shop by said signature key SK U to generate a signature S U (e,y); and balance updating means for subtracting said amount of payment y from said balance x to update the latter.

Claim 22

A surveillance institution apparatus for implementing an electronic cash system which is composed of a surveillance institution which keeps the issuance of electronic cash under its surveillance, a bank which issues electronic cash, a user who uses electronic cash and a shop which receives a payment with electronic cash, and wherein said surveillance institution makes public an encipher function E T and said bank makes public a signature verification key PK B , said method comprising: a memory for storing a secret decipher key SK T for deciphering said public encipher function E T ; decipher means for deciphering, by using said secret decipher key SK T , enciphered information E T (n) for management data n containing a signature verification key N U to obtain said management data n; a surveillance database for registering therein said deciphered management data n and the total amount of payments Y corresponding thereto; a history database for storing history data H which contains electronic cash C including a balance x, a face value X, a signature verification key N U and a bank signature S B (X,N U ), and an amount of payment y all received from said shop; means for making a check to see if there has been registered in said surveillance database said management data n corresponding to said amount of money X and said verification key N U in said history data H and, if not, for deciding that the electronic cash paid to said shop is overspent electronic cash; adding means for adding said amount of payment y in said history data to said total amount of payments Y in said surveillance database when said management data n has been registered therein; compare means for comparing the result of said addition Y+y with said face value X; and control means which: if the result of said comparison by said compare means is Y+y<X , updates said total amount of payments Y in said surveillance database with the result of addition Y+y; if Y+y=X , eliminates said management data n and said total amount of payments Y from said surveillance database; if Y+y>X , decides that said electronic cash paid to said shop is overspent electronic cash, then eliminates said management data n and said total amount of payments Y, and reports said eliminated management data n to said bank.