Patent Publication Number: US-7590591-B2

Title: Electronic value exchange system and electronic value exchange method

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a technology of exchanging electronic values as information electronically representing values. 
   2. Related Background Art 
   There is the conventionally proposed technology of safely circulating information electronically representing values (hereinafter referred to as “electronic values”), including electronic money and electronic tickets. For example, the original data circulation method disclosed in Japanese Patent Application Laid-Open No. 2001-143009 implements safe circulation by enabling device-device exchange and use of electronic values issued to users, while preventing reproduction and forgery of the electronic values. 
   The above original data circulation method provides the safety of circulation but does not always assure fairness of trade. Here the fair trade is a trade satisfying the condition that “neither of two parties involved in an attempt of mutual exchange of electronic values loses the electronic value of itself, without acquiring an electronic value as a consideration or without obtaining a guarantee for acquisition thereof”. Namely, in the case of the aforementioned original data circulation method, when an exchange transaction is interrupted, for example, by an abnormality of communication or a fraud of a transaction partner on the occasion of exchanging electronic values E 1 , E 2  held by respective devices D 1 , D 2  of users, D 1  could lose E 1  without acquisition of E 2 . 
   A document disclosing a technology to overcome this disadvantage is, for example, Japanese Patent Application Laid-Open No. 2004-341643. This technology enables an exchange of electronic values in a transaction under a normal condition, i.e., in a transaction satisfying the condition that a communication line between the devices D 1  and D 2  is not interrupted from start to end of the transaction and that D 1  and D 2  both cooperate to fulfill the transaction. On the other hand, under abnormal conditions, a third-party device is used to enable recovery of fairness of the transaction even from a midway point of the transaction. 
   SUMMARY OF THE INVENTION 
   In the conventional electronic value exchange technology described above, however, the device D 1  to start a trade must fix E 1  as an object of the trade at the start of the trade, and this raises the following problem of concern. For example, suppose D 1  holds E 1   a  and E 1   b  as electronic values. The user of D 1  desires to exchange only either one of E 1   a  and E 1   b , for E 2  held by D 2 . At this time, the user of D 1  needs to decide which electronic value is used as E 1  and needs to give D 2  the electronic value which is not used as E 1 , prior to the start of the exchange transaction. 
   However, in the case where the user of D 1  selects E 1   a  as an exchange object, let us assume that the user of D 2  has such preference that “E 2  may be exchanged for E 1   b  but not for E 1   a ”. In this case, the devices D 1 , D 2  will interrupt the exchange transaction once started, and again execute a new exchange transaction. This situation can be prevented if the users are informed of the exchange objects in advance. However, it requires an additional procedure and this can be a factor to degrade processing efficiency and system performance. 
   An object of the present invention is therefore to implement such an exchange of electronic values that a user is allowed to arbitrarily designate any electronic value to satisfy a condition, as an exchange object, while maintaining high security. 
   An electronic value exchange system according to the present invention is an electronic value exchange system for implementing an exchange of electronic values stored in a first storage device of a first communication terminal and in a second storage device of a second communication terminal, respectively, the first communication terminal comprising: output means for acquiring condition information containing a first condition for a first electronic value as an exchange object on the first communication terminal, and a second condition for a second electronic value as an exchange object on the second communication terminal, and for outputting the condition information to the first storage device; and transmitting means for transmitting offer information containing the condition information and a first random number generated by the first storage device, to the second communication terminal; the second communication terminal comprising: determining means for determining the first and second electronic values as exchange objects, using the condition information contained in the offer information transmitted by the transmitting means; the second storage device comprising: generating means for performing: generation of session information from a second random number generated by the second storage device; generation of agreement object information from the first and second electronic values and the first random number; and generation of a first electronic signature from first signature object information using the session information and the agreement object information; and managing means for deleting the second electronic value; the second communication terminal further comprising: transmitting means for transmitting agreement information containing the first signature object information, the first electronic signature, and the first and second electronic values, to the first communication terminal; the first communication terminal further comprising: verifying means for verifying the agreement information and for outputting the agreement information as confirmation request information to the first storage device; the first storage device further comprising: authenticating means for performing an authentication of the second storage device, based on whether the first electronic signature and the agreement object information contained in the confirmation request information satisfy a predetermined condition; generating means for, when the authentication is successfully done, generating a second electronic signature from second signature object information using the session information and sending a first confirmation information containing the session information and the second electronic signature, to the second storage device; and managing means for deleting the first electronic value when the authentication is successfully done; the second storage device further comprising: authenticating means for performing an authentication of the first storage device, based on whether the second electronic signature and the session information satisfy a predetermined condition, out of the first confirmation information containing the session information and the second electronic signature; wherein the managing means makes the first electronic value stored in storage means when the authentication is successfully done; wherein the transmitting means of the second communication terminal transmits second confirmation information containing the second random number to the first communication terminal; wherein the authenticating means of the first storage device performs an authentication of the second storage device, based on whether the second random number contained in the second confirmation information is one corresponding to the session information of the first signature object information contained in the confirmation request information; and wherein the managing means of the first storage device makes the second electronic value stored in storage means when the authentication is successfully done. 
   An electronic value exchange method according to the present invention is an electronic value exchange method of implementing an exchange of electronic values stored in a first storage device of a first communication terminal and in a second storage device of a second communication terminal, respectively, the electronic value exchange method comprising the following steps: letting the first communication terminal execute: a step of acquiring condition information containing a first condition for a first electronic value as an exchange object on the first communication terminal and a second condition for a second electronic value as an exchange object on the second communication terminal, and outputting the condition information to the first storage device; and a step of transmitting offer information containing the condition information and a first random number generated by the first storage device, to the second communication terminal; letting the second communication terminal execute: a step of determining first and second electronic values as exchange objects, using the condition information contained in the transmitted offer information; letting the second storage device execute: a step of performing: generation of session information from a second random number generated by the second storage device; generation of agreement object information from the first and second electronic values and the first random number; and generation of a first electronic signature from first signature object information using the session information and the agreement object information; and a step of deleting the second electronic value; letting the second communication terminal execute: a step of transmitting agreement information containing the first signature object information, the first electronic signature, and the first and second electronic values to the first communication terminal; letting the first communication terminal execute: a step of verifying the agreement information and outputting the agreement information as confirmation request information to the first storage device; letting the first storage device execute: a step of performing an authentication of the second storage device, based on whether the first electronic signature and the agreement object information contained in the confirmation request information satisfy a predetermined condition; a step of, when the authentication is successfully done, generating a second electronic signature from the second signature object information using the session information and sending a first confirmation information containing the session information and the second electronic signature, to the second storage device; and a step of deleting the first electronic value when the authentication is successfully done; letting the second storage device execute: a step of performing an authentication of the first storage device, based on whether the second electronic signature and the session information satisfy a predetermined condition, out of the first confirmation information containing the session information and the second electronic signature; and a step of storing the first electronic value when the authentication is successfully done; letting the second communication terminal execute a step of transmitting second confirmation information containing the second random number to the first communication terminal; letting the first storage device execute a step of performing an authentication of the second storage device, based on whether the second random number contained in the second confirmation information is one corresponding to the session information of the first signature object information contained in the confirmation request information; and letting the first storage device execute a step of storing the second electronic value when the authentication is successfully done. 
   According to these aspects of the invention, the second communication terminal first selects an electronic value out of those satisfying the exchange object condition acquired by the first communication terminal, and then the exchange of electronic values starts. In other words, the first communication terminal does not have to fix an electronic value as an exchange object but simply presents the condition for it to the second communication terminal, and then the second communication terminal can start the exchange of desired electronic values with the first communication terminal. The electronic value deleting process and storing process at the two terminals, for implementing the exchange of electronic values, are executed only if the aforementioned conditions are met. In the process of exchanging the electronic values, therefore, the system and method permit the user to arbitrarily designate any electronic value satisfying the conditions, as an exchange object, while maintaining high security. 
   On the occasion of verifying the agreement information, the verifying means verifies, for example, whether the first electronic value in the agreement information satisfies the first condition and whether the second electronic value in the agreement information satisfies the second condition. If the two conditions are met, the agreement information can be outputted as the confirmation request information to the first storage device. Among the predetermined conditions, the predetermined condition in the authentication by the authenticating means of the first storage device is, for example, a condition including at least that the first electronic signature is a regular signature for the first signature object information and that the agreement object information is one corresponding to the first and second electronic values and the first random number. On the other hand, the predetermined condition in the authentication by the authenticating means of the second storage device is, for example, a condition including at least that the second electronic signature is a regular signature for the second signature object information and that the session information is one corresponding to the second random number. 
   In the foregoing electronic value exchange system, the first and second communication terminals can be portable terminals and the first and second storage devices can be IC cards. When the present invention is applied to the exchange of electronic values between IC cards connected to portable terminals with excellent portability as in this case, it becomes feasible to implement the exchange of electronic values with higher flexibility and with higher security. As a result, circulation of electronic values is promoted. 
   The present invention enables implementation of such exchange of electronic values that the user is allowed to arbitrarily designate any electronic value satisfying the condition, as an exchange object, while maintaining high security. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an illustration showing a functional configuration of an electronic value exchange system in an embodiment of the present invention. 
       FIG. 2  is an illustration for explaining the first phase of the operation of the electronic value exchange system according to the present invention. 
       FIG. 3  is an illustration for explaining the second phase of the operation of the electronic value exchange system according to the present invention. 
       FIG. 4  is an illustration for explaining the third phase of the operation of the electronic value exchange system according to the present invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   An embodiment of the present invention will be described below with reference to the accompanying drawings presented for illustrative purposes only. Electronic value exchange system  1  in the present embodiment, as shown in  FIG. 1 , comprises two portable terminals  10 ,  20  (corresponding to communication terminals) capable of transmission/reception of data to and from each other. The portable terminals  10 ,  20  are provided with respective IC cards  10   a,    20   a  (corresponding to storage devices) detachably mounted. The portable terminal  10  is, for example, a cell phone or PDA (Personal Digital Assistance), but can be any terminal device with a communication function, without any restrictions on its function and use. 
   The portable terminal  10  is comprised of exchange object condition acquirer  11  (corresponding to the outputting means), data transmitter/receiver  12  (corresponding to the transmitting means), data verifier  13  (corresponding to the verifying means), and IC card  10   a . Furthermore, the IC card  10   a  is comprised of electronic value retainer  14 , electronic value manager  15  (corresponding to the managing means), data generator  16  (corresponding to the generating means), and data authenticator  17  (corresponding to the authenticating means). These components are connected so as to be able to import and export signals from and to each other through a bus. The IC card  10   a  has tamper resistance enough to secure high confidentiality and resistance to external programs and devices. 
   The functions of the respective components will be described below. The exchange object condition acquirer  11  acquires an exchange object condition C entered by a user of the portable terminal  10  and outputs a Start Exchange signal with this condition C as a parameter to the IC card  10   a . The data transmitter/receiver  12  performs transmission/reception of various signals to and from the portable terminal  20 . For example, it performs transmission of an Offer signal containing condition C and random number n 1  as elements, or reception of a Commitment signal containing random number n 2  as an element. 
   When detecting reception of an Agreement signal, the data verifier  13  verifies whether V 1  (corresponding to the first electronic value) in the signal belongs to list C 1  of the condition C, and outputs the result of the verification. Similarly, it also verifies whether V 2  (corresponding to the second electronic value) in the Agreement signal belongs to list C 2 . 
   The electronic value retainer  14  retains electronic values including the electronic values V 1 , V 2  as exchange objects. The electronic value manager  15  performs deletion of an electronic value retained in the electronic value retainer  14 , and storage of an electronic value not retained. 
   The data generator  16  retains a public key P 1 , together with its certificate CertP 1  issued by a certificate authority, and generates an electronic signature SigP 1 (m) that can be verified by the public key P 1 . The parameter m represents a message as a signature object. The detailed processing contents will be described later in the description of the operation, but the data generator  16  generates the foregoing random number n 1  and generates an Offer signal with this n 1  and condition C as elements. In addition, it generates an electronic signature Se=SigP 1 (s 2 ). 
   The data authenticator  17  performs authentication of IC card  20   a  being an exchange partner of electronic values, based on an after-described Confirm Exchange signal {s 1 |s 2 ,Sa,CertP 2 ,V 1 ,V 2 }. 
   The portable terminal  20  is an exchange partner of the portable terminal  10  and selects electronic values V 1 , V 2  as exchange objects. For this reason, the portable terminal  20  basically has much the same configuration as the portable terminal  10 , but is different therefrom in that the portable terminal  20  has exchange object determiner  22 . The portable terminal  20  is comprised of data transmitter/receiver  21  (corresponding to the transmitting means), exchange object determiner  22  (corresponding to the determining means), and IC card  20   a . Just as the IC card  10   a  was, the IC card  20   a  is comprised of electronic value retainer  23 , electronic value manager  24  (corresponding to the managing means), data generator  25  (corresponding to the generating means), and data authenticator  26  (corresponding to the authenticating means). These components are connected so as to be able to import and export signals from and to each other through a bus. 
   The description of the components common to the portable terminals  10 ,  20  is omitted herein, and the exchange object determiner  22  will be described below. When detecting reception of an Offer signal transmitted from the portable terminal  10 , the exchange object determiner  22  extracts the condition C for exchange objects from the signal. The exchange object determiner  22  acquires lists C 1 , C 2  from the condition C and makes them displayed on a display device (not shown), and thereafter awaits selection of exchange objects V 1 , V 2 . When a user of the portable terminal  20  selects V 1  out of electronic values listed in list C 1  and selects V 2  out of electronic values listed in list C 2 , the exchange object determiner  22  outputs these exchange objects V 1 , V 2 , together with first random number n 1 , to the IC card  20   a.    
   Next, the operation of the electronic value exchange system  1  in the present embodiment and each of steps constituting an electronic value exchange method according to the present invention will be described with reference to  FIGS. 2 to 4 . The description of the operation is based on the assumption that the electronic value exchange system  1  enables any portable terminal user to perform an exchange of any electronic values within the scope of the exchange object condition. It is presumed in the present embodiment, particularly, that the user of portable terminal  20  selects any one electronic value as electronic value V 1  of an exchange object out of the list C 1  of electronic values provided by the portable terminal  10  and that the user of the portable terminal  20  selects any one electronic value as electronic value V 2  of an exchange object out of the electronic value list C 2  on the portable terminal  20  side disclosed on a sales board or the like by himself or herself. 
   First, at S 1  in  FIG. 2 , the portable terminal  10  acquires the condition C (corresponding to the condition information) for exchange objects through the exchange object condition acquirer  11  in accordance with user&#39;s input manipulation. The condition C for exchange objects includes constituent elements of lists C 1 , C 2  (corresponding to the first condition and the second condition) containing all the electronic values as candidates for exchange objects. In other words, electronic values meeting the condition C for exchange objects, i.e., electronic values in the lists C 1 , C 2  as elements of C can be deemed as the aforementioned electronic values “satisfying the condition C”. 
   The condition C acquired at S 1  is fed as a parameter of a Start Exchange signal to IC card  10   a  (S 2 ). When the IC card  10   a  receives the input, the data generator  16  thereof generates a first random number n 1  (S 3 ), and thereafter generates an Offer signal (={n 1 ,C}) including this n 1  and C (S 4 ). The Offer signal thus generated is outputted from the IC card  10   a  and the data transmitter/receiver  12  transmits it from portable terminal  10  to portable terminal  20  (S 5 ). 
   The portable terminal  20  receives the Offer signal through the data transmitter/receiver  21  (S 5 ), and the exchange object determiner  22  presents lists C 1 , C 2  of condition C to the user and awaits selection of exchange objects V 1 , V 2 . The presentation to the user is, for example, a display on the display device. The selection of exchange objects is designated by the user of portable terminal  20 . For example, let us suppose as to the condition C=(C 1 ,C 2 ) that three types of electronic values [V 1   a, V 1   b, V 1   c ] are listed as candidates for an exchange object in the list C 1  and that two types of electronic values [V 2   a, V 2   b ] are listed as candidates for an exchange object in the list C 2 . When the user selects any one electronic value out of the electronic values V 1   a , V 1   b , V 1   c , the selected electronic value becomes an exchange object V 1 . When the user selects the electronic value V 1   a,  “V 1  =V 1   a ”. Similarly, the user selects any one electronic value out of the electronic values V 2   a , V 2   b , and the selected electronic value becomes an exchange object V 2 . When the user selects the electronic value V 2   b , “V 2 =V 2   b ”. As a result, V 1  and V 2  are determined (S 6 ). 
   The determined electronic values V 1 , V 2  of exchange objects, together with the random number n 1  generated on the portable terminal  10  side, are outputted as an Agree Exchange (={n 1 ,V 1 ,V 2 }) signal to the IC card  20   a  (S 7 ). When the IC card  20   a  receives the Agree Exchange signal, the data generator  25  generates a second random number n 2  (S 8 ). 
   The data generator  25  uses a one-way function to generate session information s 2  corresponding to the above n 2 . Examples of the one-way function to be applicable include safe hash functions such as SHA-1 (Secure Hash Algorithm 1) and MD 5 (Message Digest 5). The session information s 2  is calculated as H(n 2 ) (S 9 ). Subsequently, the data generator  25  generates agreement object information s 1  by the aforementioned one-way function (S 10 ). The agreement object information s 1  can be expressed as s 1 =H(V 1 |V 2 |n 1 ) using V 1  and V 2  determined at S 6 , and the random number n 1  as parameters. The notation “|” represents a concatenation between character strings. 
   Furthermore, the data generator  25  generates an electronic signature Sa=SigP 2 (s 1 |s 2 ) from s 1  and s 2  generated at S 9  and at S 10 , respectively (S 11 ). Here SigP 2  represents a function for generating an electronic signature that can be verified by the public key P 2 . For example, it is RSA (Rivest Shamir Adleman) or ECDSA (Elliptic Curve Digital Signature Algorithm). In addition, SigP 2 (x) is an electronic signature generated for x as a signature object. The electronic signature Sa corresponds to the first electronic signature, and s 1 |s 2  to the first signature object information. 
   In conjunction with the generation of Sa, V 2  (e.g., V 2   b  determined at S 6 ) retained in the electronic value retainer  23  is deleted by the electronic value manager  24  (S 12 ). At S 13 , the IC card  20   a  makes the data generator  25  generate an Agreement signal with {s 1 |s 2 ,Sa,CertP 2 ,V 1 ,V 2 } as information elements, and instructs the data transmitter/receiver  21  to transmit it. The data transmitter/receiver  21  transmits the foregoing Agreement signal to the portable terminal  10  (S 14 ). 
   Referring now to  FIG. 3 , the portable terminal  10 , receiving the Agreement signal, confirms whether “V 1 ” contained in the signal belongs to the list C 1  of the condition C acquired at S 1  (S 15 ). This confirmation process is executed by the data verifier  13 . When V 1  belongs to C 1  (S 15 ; YES), the portable terminal  10  moves to S 17 . On the other hand, when V 1  does not belong to C 1  (S 15 ; NO), the portable terminal  10  sends an error message to indicate that, to the portable terminal  20  (S 16 ), thereby interrupting the sequential processing. 
   S 17  and S 18  are to execute processes similar to S 15  and S 16 , for “V 2 ” in the Agreement signal. Namely, the data verifier  13  confirms whether “V 2 ” belongs to list C 2  and, when it belongs to the list C 2 , the portable terminal  10  moves to the next process S 19 . Even if at S 15  or S 17  the exchange object V 1  or V 2  is not listed in the list C 1  or C 2 , respectively, and if the user of the portable terminal  10  agrees, the portable terminal  10  can continue the next process, without sending an error. 
   The Agreement signal received at S 14  in  FIG. 2  by the portable terminal  10 , after subjected to the aforementioned verification process, is outputted as a Confirm Exchange signal to the IC card  10   a  (S 19 ). In the IC card  10   a , the data authenticator  17  performs authentication of the above Confirm Exchange signal {s 1 |s 2 ,Sa,CertP 2 ,V 1 ,V 2 } (S 20 ). Authentication items are the following three items.
     1) CertP 2  is a valid public key certificate certified by a certificate authority.   2) Signature verification of Sa=SigP 2 (s 1 |s 2 ) is successfully done by use of P 2 .   3) A relation of s 1 =H(V 1 |V 2 |n 1 ) holds among s 1 , V 1 , V 2 , and random number n 1 .   

   When the Confirm Exchange signal satisfies all the above items, the authentication is successfully completed (S 20 ; YES), and the flow goes to S 22 . However, if one or more items are not satisfied, the authentication is unsuccessful (S 20 ; NO), and the portable terminal  10  is notified of interruption of processing through an error message (S 21 ). At S 22  the data generator  16  generates an electronic signature Se=SigP 1 (s 2 ). Here SigP 1  is a function for generating an electronic signature that can be verified by the public key P 1 , and is, for example, RSA (Rivest Shamir Adleman) or ECDSA (Elliptic Curve Digital Signature Algorithm). SigP 1 (x) is an electronic signature generated for x as a signature object. 
   In conjunction with the generation of electronic signature Se, V 1  as an exchange object is deleted from the electronic value retainer  14  (S 23 ). Thereafter, a Confirmation signal with {s 2 ,Se,CertP 1 } as elements is transmitted from portable terminal  10  to portable terminal  20  (S 24 ). 
   Referring now to  FIG. 4 , the IC card  20   a  of the portable terminal  20  makes the data authenticator  26  perform authentication for the foregoing Confirmation signal (S 25 ). The authentication is successfully done if the following three items all are met.
     i) CertP 1  is a valid public key certificate certified by a certificate authority.   ii) The signature verification of Se=SigP 1 (s 2 ) is successfully done by use of P 1 .   iii) A relation of s 2 =H(n 2 ) holds between s 2  and random number n 2 .   

   Here the electronic signature Se corresponds to the second electronic signature, and s 2  to the second signature object information. 
   When the Confirmation signal satisfies all the above items, the authentication is successfully done (S 25 ; YES) and the flow moves to S 26 . At S 26 , the electronic value manager  24  stores the electronic value V 1  determined as an exchange object at S 6 , into the electronic value retainer  23  (S 26 ). On the other hand, if one or more items are not met, the authentication is unsuccessful (S 25 ; NO), and the portable terminal  20  is notified of interruption of processing (S 27 ). Thereafter, the data transmitter/receiver  21  transmits a Commitment signal with the random number n 2  as an element to the portable terminal  10 . This Commitment signal is outputted through a bus to the IC card  10   a  (S 28 ). 
   The IC card  10   a , receiving the Commitment signal, collates the calculation result obtained by substituting the random number n 2  in the signal into the predetermined one-way function H, against s 2  transmitted at S 25 , to determine whether the relation s 2 =H(n 2 ) holds (S 29 ). This determination process is carried out by the data authenticator  17 . When it holds (S 29 ; YES), the electronic value V 2  of the exchange object (electronic value received at S 19 ) is stored into the electronic value retainer  14  (S 30 ). Then the user of the portable terminal  10  is notified of completion of the exchange. If it does not hold (S 29 ; NO), the user is notified of interruption of processing through an error message (S 31 ). 
   As described above, the electronic value exchange system  1  of the present embodiment enables the highly flexible and convenient exchange of electronic values, without loss of security. For example, let us suppose a case where the user of the portable terminal  20  has such preference that “V 2   a  may be exchanged for V 1   b  but not for V 1   a ”. If the conventional technology is applied to this case, the portable terminal  10  must once interrupt the electronic value exchange process started with the portable terminal  20  and again execute a new process. With the electronic value exchange system  1  of the present embodiment, after the start of the electronic value exchange process, the portable terminal  20  selects exchange objects out of electronic values satisfying the condition C presented by the portable terminal  10 , during the process. Namely, the portable terminal  20  selects electronic values V 1   b , V 2   a  as exchange objects V 1 , V 2  out of a plurality of electronic values listed in the lists C 1 , C 2  of the condition C. This permits the exchange of V 2   a  for V 1   b , without interruption of the once started processing. 
   In order to implement the exchange of electronic values between IC cards  10   a ,  20   a , it is necessary to perform the processes of deletion of V 1  and storage of V 2  in the IC card  10   a  and the processes of deletion of V 2  and storage of V 1  in the IC card  20   a . Among these, the deletion process of V 1  is not executed unless the conditions listed above at S 20  are met, and the storage process of V 1  is not executed unless the conditions listed above at S 25  are met. In addition, the storage process of V 2  is not executed unless the verification at above S 29  is successfully done. Namely, the exchange of exchange objects V 1  and V 2  is normally completed only if the two IC cards succeed in mutual authentication. This maintains a high security level even in cases where the user is allowed to select any exchange objects satisfying the conditions. 
   The mode described in the present embodiment is just a preferred example of the electronic value exchange system according to the present invention, and the present invention is by no means limited to this mode. For example, the above embodiment adopted the condition that the electronic values as exchange objects were listed in the lists C 1 , C 2  being the elements of C, as the condition C for electronic values as exchange objects, but, instead of such direct designation, it is also possible to use a criterion about an attribute of each electronic value. For example, it is also possible to set as the condition C for electronic values, e.g., a value is not less than a predetermined value, an issue date or an expiration date is after a predetermined date, or a scope of use or a user satisfies predetermined conditions. 
   The disclosure of Japanese Patent Application No. 2005-071744 filed Mar. 14, 2005 including specification, drawings and claims is incorporated herein by reference in its entirety.