Patent Publication Number: US-2020279233-A1

Title: Data structure, transmission device, receiving device, settlement device, method, and computer program

Description:
TECHNICAL FIELD 
     The present invention relates to a virtual currency (virtual cash). 
     BACKGROUND ART 
     In recent years, various proposals related to FinTech have been made, and some of the proposals have already been put into practical use. 
     Some of the proposals are called virtual currency. For example, Bitcoin (trademark), which began with a thesis published by someone using the name Satoshi Nakamoto and is realized by a system constructed on the Internet, is also generally called a virtual currency. On the other hand, bitcoin is sometimes referred to as cryptocurrency or crypto cash. 
     First, a structure of bitcoin will be described. Bitcoin is generally established by the following structure. 
     First, bitcoin is generated as follows. 
     A person who has the right to generate bitcoins is limited to an administrator who manages nodes to be described below. The node administrator participates in a certain game played on the Internet. The game is repeated, and the node administrator, who has won the game, can obtain a predetermined number of bitcoins every time the administrator wins the game. 
     The bitcoins generated in this way are transferred to a third party including a person other than the node administrator from the node administrator who obtains the bitcoins, for example, for “payment” in the same manner as general currency, and will be distributed as a result. 
     By the way, how to prevent double transfer is very important problem in the field of virtual currency or virtual money without being limited to bitcoin. Since general money, which is a tangible object, disappears from the transferor&#39;s hands when transferred from the transferor to the transferee, after the transferor transfers the money to the transferee, it is not possible for the transfer to transfer the same money to another transferee in principle. However, since the virtual currency is easy to duplicate and it is possible that the virtual currency as data owned by the transferor is not extinguished even when the transferor transfers the virtual currency to the transferee, it is very easy to transfer the same virtual currency to many people. Unless the same virtual currency can be prevented from being transferred to many people, such virtual currency cannot gain any trust as currency. 
     Bitcoin intends to solve such a problem of double transfer through a method of preserving all transaction records. The transaction records are as follows, for example. For simplicity, it is assumed that only four persons A to D participate in the structure of bitcoin and the node administrators are only two persons A and B. Assuming that the node administrator A wins the above-described game and gains 1,000 bitcoins, and the node administrator B wins the above-described game and gains 500 bitcoins. 
     In this state, A to D respectively have bitcoins described as follows. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
            
               
                   
                 A 
                 +1000 
               
               
                   
                 B 
                 +500 
               
               
                   
                 C 
                 0 
               
               
                   
                 D 
                 0 
               
               
                   
                   
               
            
           
         
       
     
     Next, assuming that A has paid 100 bitcoins to C and B has paid 200 bitcoins to D. 
     In this state, A to D respectively have bitcoins described as follows. 
     
       
         
           
               
               
               
               
               
             
               
                   
                 TABLE 2 
               
               
                   
                   
               
             
            
               
                   
                 A 
                 +1000 
                 −100 
                 (to C) 
               
               
                   
                 B 
                 +500 
                 −200 
                 (to D) 
               
               
                   
                 C 
                 0 
                 +100 
                 (from A) 
               
               
                   
                 D 
                 0 
                 +200 
                 (from B) 
               
               
                   
                   
               
            
           
         
       
     
     Next, assuming that A has paid 300 bitcoins to B and D has paid 100 bitcoins to C. 
     In this state, A to D respectively have bitcoins described as follows. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                   
                 TABLE 3 
               
               
                   
                   
               
             
            
               
                   
                 A 
                 +1000 
                 −100 
                 (to C) 
                 −300 
                 (to B) 
               
               
                   
                 B 
                 +500 
                 −200 
                 (to D) 
                 +300 
                 (from A) 
               
               
                   
                 C 
                 0 
                 +100 
                 (from A) 
                 +100 
                 (from D) 
               
               
                   
                 D 
                 0 
                 +200 
                 (from B) 
                 −100 
                 (to C) 
               
               
                   
                   
               
            
           
         
       
     
     All of the records indicated in Tables 1 to 3 described above are transaction records. According to the transaction records described above, it can be seen at the time of Table 3 that A has bitcoins of 600 (=+1000−100−300), B similarly has bitcoins of 600, C has bitcoins of 200, and D has bitcoins of 100. 
     The bitcoin having such a structure is interesting in that some data as a main body of bitcoin is not delivered from the transferor to the transferee in the transfer of bitcoin between A to D in the example described above. In spite of this, attraction of the bitcoin structure is to specify the current balance of bitcoin of A to D as long as the transaction records exist. Again, in the bitcoin structure, there is no data corresponding to a coin entity, even though a naming of “coin” is used to recall a tangible object. 
     Noted that the phenomenon that the node administrator in the bitcoin structure wins the game and gains bitcoins can occur after the transaction is advanced to some extent, for example, after the time of Table 3. 
     In the bitcoin structure, as described above, each participant who participates in the bitcoin structure does not have data corresponding to his/her bitcoin. In other words, even though each participant&#39;s wallet is empty, since all past transaction records exist so as to be accessible and the balance of bitcoin at that time is specified in this way from the access record, the bitcoin structure is established based on mutual understanding or common illusion that the bitcoin of each participant should be like this. 
     For that reason, in order for all participants to believe in the common illusion, it is necessary to guarantee that the transaction record is accurate at any time or the transaction record cannot be falsified. 
     Bitcoin ensures the guarantee with block chain and the technology and idea of proof-of-work. The transaction records of bitcoin have a structure in which new transaction records are linked to previous transaction records. As new transaction record data (blocks) are continuously linked to the past transaction records, the transaction record data are linked in the form of chain of blocks. This is called a block chain. When a new block added to the block chain is generated, a value obtained by encryption of the previous block (more precisely, a hash value created from the data of the past block) is added to the new block. Thus, if the past block is falsified after the time when the new block is added to the block chain, the hash value is changed and the falsification is detected, and thus the data of the past block created previously cannot be falsified in actual fact. 
     In addition, blockchain data is recorded in a server called a node, which exists in large numbers on the Internet. The same blockchain data is recorded in each of the nodes. As described above, the administrator of the node is a participant in a certain kind of game described above. A person who can add a new transaction record block to the past transaction record is only a winner of the game described above. That is, when the number of persons, who can add a new block to a node, is limited to only one person, appropriate block data is ensured. 
     With the structure described above, since the blockchain recorded in each node cannot be falsified by the hash value or the hash value is changed when the falsification is made, the evidence of falsification is detected. Even when some of the blockchains recorded in each node are falsified likewise, including the hash value (for example, even when some of the blockchains recorded in multiple nodes are also falsified) so that the falsification of the past block data is not detected, if a large number of non-falsified blockchains exist out of the blockchains recorded in a large number of nodes, the falsification of the past block data can be made helpless including the hash value by setting this state to true, and the theory of majority rule is adopted in actual bitcoin. As described above, the node administrator can obtain bitcoins as a reward by winning the game. Using the bitcoins as motivation, the node administrators improve computing power of his/her computer. In order for a malicious third party to falsify a majority of the blockchains recorded in the node, it is necessary to prepare a computer having computing power of at least half of the sum of the computing power of many computers of the node administrators. A person who participates in the bitcoin structure trusts that the computer having such computing power cannot be prepared in actual fact. Such trust or confidential relationship guarantees the legitimacy of not only the blockchain but also the transaction record, and gives a certain kind of trust to the bitcoin. 
     SUMMARY OF INVENTION 
     Technical Problem 
     The structure of bitcoin is as described above, but the inventor of the present invention has big doubts that bitcoin is called virtual currency or bitcoin is even called crypto cash. 
     This is because, in the structure of bitcoin, a cryptographic technique is only used to guarantee the legitimacy of transaction records. That is, when a new block is added to the blockchain described above, a hash value of the previous block is taken. 
     Moreover, as described above, there is no data that is delivered from the value transferor to the transferee at the time of transferring the value. This means that currency (banknote or coin) of a tangible object is not used which mediates the transfer of value through the transfer thereof in functioning the currency. 
     That is, bitcoin may function as currency, but has not entity as money and is also extremely limited in the use of cryptography. The problem with the lack of entity as money is that all of the past transaction records are required to be recorded, resulting in causing great efforts and waste in recording of the large amount of data. Actually, the amount of blockchain data recorded in bitcoin is already enormous, and recording of the enormous blockchain data and recording of the same blockchain data in a large number of nodes cause tremendous waste. On the other hand, when data is circulated among users in replace of money, the safety of the data becomes a problem. 
     From such a point of view, although being very vague, there is an idea that a cryptographic technique should be utilized to establish virtual currency, and there is a possibility that safe virtual currency, more specifically, safe virtual money can be established using appropriately the cryptographic technique. Bitcoin may be referred to as cryptocurrency or the like, and this is a way to give the user an “image” of safety due to use of cryptography. 
     In the bitcoin as described above, however, the use of the cryptographic technique is extremely limited. 
     In a case of exchanging a value called DigiCash or e-cash between users, virtual currency using data in replace of money to be exchanged has existed in the past, and the cryptographic technique has also been used for such virtual currency. However, the cryptographic technique used in such virtual currency merely means that data for authentication indicating the used data is authentic data is encrypted and attached to data having a monetary value. 
     An object of the present invention is to provide virtual currency that is data created as crypto cash in a true meaning. 
     Solution to Problem 
     In order to solve such a problem, the inventor of the present invention proposes the invention to be described below. 
     The present invention is to provide data structure of virtual currency data that is data of virtual currency having a monetary value and is used in combination with a settlement device that accepts settlement when the virtual currency data is received from a predetermined device via a network and when predetermined conditions are satisfied. 
     The data structure of virtual currency data includes virtual currency encryption data which is data obtained by, according to a predetermined encryption method, encryption of: issuer information including at least information on an issuer of the virtual currency data; amount information that is information for specifying a monetary value; and settlement condition information that is information on conditions for accepting payment with virtual currency. 
     The virtual currency data having such a data structure is used in combination with the settlement device that determines whether the settlement is accepted. As will be described below, there are three types of settlement devices, all of which use encryption technology. The virtual currency data having the data structure as described above may be naturally required to satisfy other conditions, but the settlement device can accept the settlement when the following conditions are satisfied. As will be described below, since virtual currency realized by the virtual currency data of the present invention has the virtual currency data to be exchanged at the time of value exchange, it is not necessary to record a large number of transaction record data, and the virtual currency data has high safety because, so to speak, the body of its monetary value is encrypted. 
     In addition, the term “encryption” in the present invention means that the data is converted so that the data cannot be read (not understood) without special knowledge even when a third party looks at the data, and includes not only conversion in which data can be decrypted but also a case of irreversible conversion as in a case of taking a hash value. 
     The settlement conditions specified by the settlement condition information included in the state of being encrypted in the data structure of virtual currency data in the present invention may be arbitrary. Examples of the settlement conditions include a restriction on a value transferor or transferee, a restriction on the place of a value transferor or transferee, a restriction on the time at which the value can be transferred, and a restriction on the number of times the same person can transfer the value within a certain period of time. 
     For example, in the data structure of virtual currency data according to the present invention, the settlement condition information may include recipient information that is information for specifying a person who receives the payment. Since the virtual currency data having such a data structure can limit the person who can receive the payment, even when such virtual currency data is stolen by a malicious third party, the third party is not a person specified by the recipient information, and thus the malicious third party cannot receive the monetary value. 
     In addition, the settlement condition information may include time information that is information for specifying a time (period) at which the payment is accepted. Since the virtual currency data having such a data structure can limit the time at which the payment can be received, even when such virtual currency data is stolen by a malicious third party, the malicious third party cannot receive the monetary value when the stolen data passes the due date at which the payment is received. Further, when the payment time is set as the validated date of the virtual currency data, those who have the virtual currency data have to be settled it urgently, or the use of the virtual currency data can be promoted to use it. 
     The settlement condition information may be information for changing an amount of money specified by the amount information. 
     For example, the amount of money specified by the amount information can be changed with the passage of time by the settlement condition information. Specifically, the amount of money specified by the amount information can be gradually reduced with the passage of time by the settlement condition information, or the amount of money specified by the amount information can be reduced in a step-by-step manner with the passage of time by the settlement condition information, but this urges a person who has the virtual currency data including the virtual currency encryption data including the data obtained by encryption of the settlement condition information to use the virtual currency data. Naturally, the amount of money specified by the amount information may be increased, or may be increased and reduced. Thus, it is possible to induce the consumption behavior of the user(s) having such virtual currency data, for example, to accelerate the payment using the virtual currency data, to delay the payment using the virtual currency data, and to concentrate the payment using the virtual currency data at a certain time or avoid it at a certain time. 
     In addition, the amount of money specified by the amount information can be changed by the settlement condition information, depending on the payment place, the transferor or transferee at the time of the payment, and the number of times the payment is performed by the same person at a certain time or the same person receives the payment. Thus, the consumption behavior of the user(s) can also be induced. 
     The issuer information encrypted and included in the data structure of virtual currency data according to the present invention may include information other than an issuer. For example, the issuer information further may include not only issuer information that is information for specifying an issuer of the virtual currency data but also at least one of: authentication information that is information to guarantee authenticity of the virtual currency data, the information being issued by a person having authority to guarantee the authenticity of the virtual currency data; serial number information that is information unique to each virtual currency data for distinguishing the virtual currency data from other virtual currency data; and timing information that is information for specifying a timing at which the virtual currency data is issued. 
     In the data structure of virtual currency data according to the present invention, encryption condition information, which is information for specifying a condition when the issuer information, the amount information, and the settlement condition information are encrypted, may be further attached. This is useful in a settlement device to be described below, and particularly useful in virtual currency data used in combination with first and third types of settlement devices to be described below. Note that the encryption condition information may or may not be encrypted. 
     The data structure of virtual currency data according to the present invention may be further attached with at least a part of the issuer information, the amount information, and the settlement condition information in an unencrypted state. As described above, the issuer information, the amount information, and the settlement condition information are encrypted virtual currency encryption data in the present invention. This makes it possible to increase the safety of the virtual currency data, but to cause inconvenience that the value transferee out of the value transferor and transferee does not know he/she receives how much the amount of money under certain conditions. Such inconvenience can be solved in a manner that at least a part of the issuer information, the amount information, and the settlement condition information is made as readable plaintext data, for example, is read without being decrypted by a receiving device or a transmission device to be described below. 
     Naturally, the virtual currency data having the data structure of the virtual currency data described above may be recorded in a recording medium. The recording medium is not limited to a portable recording medium, and may be a recording medium built in a predetermined device. The recording medium built in the predetermined device is, for example, a random access memory (RAM) or a hard disk drive (HDD). 
     The predetermined device may be a receiving device including a terminal device receiving means receiving data via the network, the recording medium described above built therein, and the virtual currency data may be recorded on the recording medium after being received by the terminal device receiving means. 
     The predetermined device may be a transmission device including a first transmission means transmitting data via the network, the recording medium described above built therein, and the virtual currency data may be transmitted to the settlement device via the network by the transmission means. 
     Next, three types of settlement devices will be described. 
     A first type of settlement device is a settlement device including: a settlement device receiving means that receives virtual currency data, which is data of virtual currency having a monetary value, via a network from a predetermined device for requesting settlement, the virtual currency data including virtual currency encryption data which is data obtained by, according to a predetermined encryption method, encryption of issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency; a decryption means that decrypts the virtual currency encryption data received by the settlement device receiving means; a settlement condition determining means that determines whether a condition specified by the settlement condition information obtained by decryption of the virtual currency encryption data with the decryption means is satisfied; and a settlement means that accepts settlement of an amount of money specified by the amount information obtained by decryption of the virtual currency encryption data with the decryption means when the settlement condition determining means determines that the condition specified by the settlement condition information is satisfied. 
     The virtual currency data used in combination with the first type of settlement device is the virtual currency data having the data structure of the virtual currency data according to the present invention, and the virtual currency encryption data included therein is limited to encrypted data capable of being decrypted. Upon receiving the virtual currency data, the first settlement device decrypts the virtual currency encryption data included in the virtual currency data. Then, the settlement device accepts the settlement of the amount of money specified by the amount information on condition that the condition specified by the settlement condition information included in the decrypted virtual currency encryption data is satisfied. In this case, the authenticity of the virtual currency data may be authenticated by the issuer information, the authenticity is proved by the fact that the virtual currency encryption data can be originally decrypted. By setting whether the decryption can be made as an authentication condition, it is possible to increase the accuracy of confirmation of the authenticity of the virtual currency data executed by such a settlement device, and as a result, to increase the safety of the virtual currency data used together with a settlement device executed by such a settlement device. The issuer information may also be used for confirming the validity of the virtual currency encryption data as in second and third types of settlement devices to be described below. 
     The first type of settlement device includes the decryption means, and decrypts the virtual currency encryption data using the decryption means. Needless to say, a large number of pieces of the virtual currency data exist at the same time, for example, on the network, on the recording medium described above, or in the predetermined device described above. When the encryption method, for example, both a key and an algorithm are always the same, the decryption means of the settlement device can always decrypt the virtual currency encryption data with a combination of one kind of key and algorithm. However, if the safety of the virtual currency data is desired to be increased, it is obvious that at least one of the virtual currency encryption data included in a large number of pieces of virtual currency data, or if possible, all the virtual currency encryption data is preferably encrypted by a method different from that used for other virtual currency encryption data. However, when such a technique is adopted, the decryption means should grasp how to encrypt the virtual currency encryption data to be decrypted. This can be achieved by the encryption condition information described above. 
     When the settlement device includes means that grasps, from the encryption condition information attached to the virtual currency encryption data to be decrypted by the decryption means, a condition when the virtual currency encryption data is encrypted, the decryption means can know the condition when the virtual currency encryption data is encrypted, and thus there is no inconvenience in decrypting the virtual currency encryption data even if the virtual currency encryption data are respectively encrypted under different conditions. The encryption condition information may or may not be encrypted as described above. The encryption condition information, which is not encrypted, can be used as it is. On the other hand, if the encryption condition information is encrypted, the encryption condition information cannot be used unless being decrypted. Even when the virtual currency encryption data are respectively encrypted under different conditions, the encrypted encryption condition data can be decrypted by a predetermined means of the settlement device, for example, by the decryption means if the encrypting condition of the encryption condition information is equal any time. 
     The encryption condition information may be the above-described key or algorithm itself used when the virtual currency encryption data is encrypted, or may be information for specifying which key or algorithm is used when the virtual currency encryption data is encrypted. For example, when the virtual currency data is encrypted, the encryption is assumed to be performed with different keys, which are sequentially changed, such as a first key when the first virtual currency data is encrypted, a second key when the second virtual currency data is encrypted, a third key when the third virtual currency data is encrypted, and so on. Then, these keys are assumed to be pseudo-random numbers generated continuously by the following formula, for example. Then, since an N-th pseudo-random number is always the same when an initial value X 0  is specified from the beginning, a means for grasping the condition when the virtual currency encryption data is encrypted can reproduce the N-th pseudo-random number at any time from X 0 . Thereby, the decryption means can decrypt the virtual currency encryption data using the pseudo-random number as a key. If the initial value X 0  is hidden, even when the encryption condition information (a numerical value indicating what number pseudo-random number) included in the virtual currency data is included in the virtual currency data in plaintext, a malicious third party who obtains the virtual currency data cannot grasp the condition when the virtual currency encryption data is encrypted from encryption condition information. Further, as described above, at least a part of the issuer information, the amount information, and the settlement condition information may be further attached to the virtual currency data in an unencrypted state, but, for example, some of the data may also serve as encryption condition information. 
         X   N   =f ( X   N-1 ) 
     (X N  is the N-th pseudo-random number, and the pseudo-random number is formed from numbers, characters, symbols, or an enumeration of two or more of them.) 
     The inventor of the present invention also proposes a method executed by the first type of settlement device described above, as one aspect. The effect thereof is equal to that of the first settlement device. For example, the method is as follow. 
     The method is a settlement method executed by a settlement device capable of receiving data via a network and including a computer for performing data processing. 
     The settlement method includes steps executed by the computer of: a settlement device receiving step of receiving virtual currency data, which is data of virtual currency having a monetary value, via a network from a predetermined device for requesting settlement, the virtual currency data including virtual currency encryption data which is data obtained by, according to a predetermined encryption method, encryption of issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency; a decryption step of decrypting the virtual currency encryption data received in the settlement device receiving step; a settlement condition determining step of determining whether a condition specified by the settlement condition information obtained by decryption of the virtual currency encryption data in the decryption step is satisfied; and a settlement step of accepting settlement of an amount of money specified by the amount information obtained by decryption of the virtual currency encryption data in the decryption step when being determined in the settlement condition determining step that the condition specified by the settlement condition information is satisfied. 
     The inventor of the present invention also proposes, for example, a computer program for causing a general-purpose computer to function as the first type of settlement device described above, as one aspect of the present invention. For example, the computer program is as follow. 
     The computer program is a computer program for causing a computer capable of receiving data via a network and performing data processing to function as a settlement device. 
     The computer program is a computer program for causing the computer to function as: a settlement device receiving means that receives virtual currency data, which is data of virtual currency having a monetary value, via a network from a predetermined device for requesting settlement, the virtual currency data including virtual currency encryption data which is data obtained by, according to a predetermined encryption method, encryption of issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency; a decryption means that decrypts the virtual currency encryption data received by the settlement device receiving means; a settlement condition determining means that determines whether a condition specified by the settlement condition information obtained by decryption of the virtual currency encryption data with the decryption means is satisfied; and a settlement means that accepts settlement of an amount of money specified by the amount information obtained by decryption of the virtual currency encryption data with the decryption means when the settlement condition determining means determines that the condition specified by the settlement condition information is satisfied. 
     A second type of settlement device is a settlement device including: a settlement device receiving means that receives virtual currency data, which is data of virtual currency having a monetary value, via a network from a predetermined device for requesting settlement, the virtual currency data including virtual currency encryption data which is data obtained by, according to a predetermined encryption method, encryption of issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency; a copy data recording means that records copy virtual currency encryption data that is data equal to the virtual currency encryption data; a second authentication means that compares the virtual currency encryption data received by the settlement device receiving means with the copy virtual currency encryption data to determine whether both of the data coincide with each other, and determines that the virtual currency data sent from the predetermined device is authentic when both of the data coincide with each other; a settlement condition determining means that determines whether a condition specified by the settlement condition information is satisfied; and a settlement means that accepts settlement of an amount of money specified by the amount information when the second authentication means determines that the virtual currency data sent from the predetermined device is authentic and the settlement condition determining means determines that the condition specified by the settlement condition information is satisfied. 
     The virtual currency data used in combination with the second type of settlement device is the virtual currency data having the data structure of the virtual currency data according to the present invention, but the virtual currency encryption data included therein is not limited to encrypted data capable of being decrypted. The second settlement device includes the copy data recording means that records the copy virtual currency encryption data that is data equal to the virtual currency encryption data included in a large number of pieces of virtual currency data scheduled to be sent to the settlement device. Upon receiving the virtual currency data, the settlement device compares the virtual currency encryption data included in the virtual currency data with the copy virtual currency encryption data recorded in the copy data recording means. As a result, the settlement device determines whether one of the copy virtual currency encryption data recorded in the copy data recording means coincides with the virtual currency encryption data included in the received virtual currency data, determines that the virtual currency encryption data is authentic when the virtual currency encryption data coincides with one of the copy virtual currency encryption data, and accepts the settlement for the data of the amount of money specified by the amount information on condition that the condition specified by the settlement condition information is satisfied. In short, according to the first settlement device, whether the virtual currency data including the virtual currency encryption data is authentic is determined depending on whether the virtual currency encryption data can be decrypted, but, alternatively, according to the second settlement device, whether the virtual currency data is authentic is determined depending on the comparison between the virtual currency encryption data and the copy virtual currency encryption data prepared in advance by copying the virtual currency encryption data. Therefore, even in the second settlement device as in the first settlement device, it is possible to increase the accuracy of confirmation of the authenticity of the virtual currency data executed by such a settlement device, and as a result, to increase the safety of the virtual currency data used together with a settlement device executed by such a settlement device. 
     As described above, the second settlement device determines whether the settlement condition specified by the settlement condition information is satisfied. For this purpose, naturally, the settlement condition information is required. The settlement condition information may be recorded in, for example, the copy data recording means in association with each of the copy virtual currency encryption data corresponding the settlement condition information, or may be obtained by decrypting the copy virtual currency encryption data or the virtual currency encryption data as needed. Similarly, the issuer information may also be recorded in, for example, the copy data recording means in association with each of the copy virtual currency encryption data corresponding the issuer information, or may be obtained by decrypting the copy virtual currency encryption data or the virtual currency encryption data, and thus the issuer information can be used to confirm the authenticity of the virtual currency data. 
     The inventor of the present invention also proposes a method executed by the second type of settlement device described above, as one aspect of the present invention. The effect thereof is equal to that of the second settlement device. For example, the method is as follow. 
     The method is a settlement method executed by a settlement device capable of receiving data via a network and including a recording medium and a computer for performing data processing. 
     The settlement method includes steps executed by the computer of: a settlement device receiving step of receiving virtual currency data, which is data of virtual currency having a monetary value, via a network from a predetermined device for requesting settlement, the virtual currency data including virtual currency encryption data which is data obtained by, according to a predetermined encryption method, encryption of issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency; a copy data recording step of recording copy virtual currency encryption data, which is data equal to the virtual currency encryption data, in the recording medium; a second authentication step of comparing the virtual currency encryption data received by the settlement device receiving unit with the copy virtual currency encryption data recorded in the recording medium to determine whether both of the data coincide with each other, and determining that the virtual currency data sent from the predetermined device is authentic when both of the data coincide with each other; a settlement condition determining step of determining whether a condition specified by the settlement condition information is satisfied; and a settlement step of accepting settlement of an amount of money specified by the amount information when being determined in the second authentication step that the virtual currency data sent from the predetermined device is authentic and being determined in the settlement condition determining step that the condition specified by the settlement condition information is satisfied. 
     The inventor of the present invention also proposes, for example, a computer program for causing a general-purpose computer to function as the second type of settlement device described above, as one aspect of the present invention. For example, the computer program is as follow. 
     The computer program is a computer program for causing a computer capable of receiving data via a network and performing data processing to function as a settlement device. 
     The computer program is a computer program causing the computer to function as: a settlement device receiving means that receives virtual currency data, which is data of virtual currency having a monetary value, via a network from a predetermined device for requesting settlement, the virtual currency data including virtual currency encryption data which is data obtained by, according to a predetermined encryption method, encryption of issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency; a copy data recording means that records copy virtual currency encryption data that is data equal to the virtual currency encryption data; a second authentication means that compares the virtual currency encryption data received by the settlement device receiving means with the copy virtual currency encryption data to determine whether both of the data coincide with each other, and determines that the virtual currency data sent from the predetermined device is authentic when both of the data coincide with each other; a settlement condition determining means that determines whether a condition specified by the settlement condition information is satisfied; and a settlement means that accepts settlement of an amount of money specified by the amount information when the second authentication means determines that the virtual currency data sent from the predetermined device is authentic and the settlement condition determining means determines that the condition specified by the settlement condition information is satisfied. 
     A third type of settlement device is a settlement device including: a settlement device receiving means that receives virtual currency data, which is data of virtual currency having a monetary value, via a network from a predetermined device for requesting settlement, the virtual currency data including virtual currency encryption data which is data obtained by, according to a predetermined encryption method, encryption of issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency; a plaintext information recording means that records, in association with each other, the issuer information, the amount information, and the settlement condition information included in one virtual currency encryption data in an encrypted state; an encryption means that encrypts the issuer information, the amount information, and the settlement condition information recorded in the plaintext information recording means using an encryption method equal to the predetermined encryption method used when the issuer information, the amount information, and the settlement condition information are encrypted into the virtual currency encryption data; a third authentication means that compares the virtual currency encryption data received by the settlement device receiving means with the data obtained by encryption of the issuer information, the amount information, and the settlement condition information recorded in the plaintext information recording means with the encryption means to determine whether both of the data coincide with each other, and determines that the virtual currency data sent from the predetermined device is authentic when both of the data coincide with each other; a settlement condition determining means that determines whether a condition specified by the settlement condition information recorded in the plaintext information recording means is satisfied; and a settlement means that accepts settlement of an amount of money specified by the amount information when the third authentication means determines that the virtual currency data sent from the predetermined device is authentic and the settlement condition determining means determines that the condition specified by the settlement condition information is satisfied. 
     The virtual currency data used in combination with the third type of settlement device is the virtual currency data having the data structure of the virtual currency data according to the present invention, but the virtual currency encryption data included therein is not limited to encrypted data capable of being decrypted. The third settlement device includes the plaintext information recording means that records, in association with each other, the issuer information, the amount information, and the settlement condition information which are used to generate the virtual currency encryption data included in a large number of pieces of virtual currency data scheduled to be sent to the settlement device. Upon receiving the virtual currency data, the settlement device generates the data by encrypting the issuer information, the amount information, and the settlement condition information which are recorded in the plaintext information recording means described above and in association with each other. Then, the settlement device determines that the virtual currency data is authentic when the data coincides with the virtual currency encryption data included in the received virtual currency data. The settlement device accepts the settlement for the data of the amount of money specified by the amount information on condition that the virtual currency data is determined to be authentic and the condition specified by the settlement condition information is satisfied. In short, according to the first settlement device, whether the virtual currency data including the virtual currency encryption data is authentic is determined depending on whether the virtual currency encryption data can be decrypted, but, alternatively, according to the third settlement device, whether the virtual currency data is authentic is determined depending on whether the same data as the virtual currency encryption data can be created again by the encryption of the issuer information, the amount information, and the settlement condition information. Therefore, even in the third settlement device as in the first settlement device, it is possible to increase the accuracy of confirmation of the authenticity of the virtual currency data executed by such a settlement device, and as a result, to increase the safety of the virtual currency data used together with a settlement device executed by such a settlement device. 
     The third type of settlement device includes the encryption means, and encrypts the issuer information, the amount information, and the settlement condition information which are recorded in the plaintext information recording means by the encryption means. Needless to say, a large number of pieces of the virtual currency data exist at the same time, for example, on the network, on the recording medium described above, or in the predetermined device described above. When the encryption method, for example, both a key and an algorithm are always the same, the encryption means of the settlement device encrypts the issuer information, the amount information, and the settlement condition information which are recorded in the plaintext information recording means, with a combination of one kind of key and algorithm, and the data obtained in this way coincides with the virtual currency encryption data included in the virtual currency data sent to the settlement device, unless the virtual currency encryption data is particularly falsified. On the other hand, at least one of the virtual currency encryption data included in a large number of pieces of virtual currency data, or if possible, all the virtual currency encryption data may be encrypted by a method different from that used for other virtual currency encryption data. In this case, when the method of encrypting the issuer information, the amount information, and the settlement condition information using the encryption means does not coincide with the method used when the virtual currency encryption data is encrypted to be compared therewith, the data obtained by the encryption of the issuer information, the amount information, and the settlement condition information recorded in the plaintext information recording means does not coincide with the virtual currency encryption data included in the virtual currency data sent to the settlement device. That is, the settlement device should grasp how to encrypt the virtual currency encryption data included in the virtual currency data sent to the settlement device. This can be achieved by the encryption condition information described above. The contents and usage of the data may be the same as those described in the first settlement device. 
     The inventor of the present invention also proposes a method executed by the third type of settlement device described above, as one aspect of the present invention. The effect thereof is equal to that of the third settlement device. For example, the method is as follow. 
     The method is a settlement method executed by a settlement device capable of receiving data via a network and including a computer for performing data processing. 
     The settlement method includes steps executed by the computer of: a settlement device receiving step of receiving virtual currency data, which is data of virtual currency having a monetary value, via a network from a predetermined device for requesting settlement, the virtual currency data including virtual currency encryption data which is data obtained by, according to a predetermined encryption method, encryption of issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency; a plaintext information recording step of recording the issuer information, the amount information, and the settlement condition information, which are included in one virtual currency encryption data in an encrypted state, in the recording medium in association with each other; an encryption step of encrypting the issuer information, the amount information, and the settlement condition information recorded in the plaintext information recording step using an encryption method equal to the predetermined encryption method used when the issuer information, the amount information, and the settlement condition information are encrypted into the virtual currency encryption data; a third authentication step of comparing the virtual currency encryption data received in the settlement device receiving step with the data obtained by encryption, in the encryption step, of the issuer information, the amount information, and the settlement condition information recorded in the plaintext information recording step to determine whether both of the data coincide with each other, and determining that the virtual currency data sent from the predetermined device is authentic when both of the data coincide with each other; a settlement condition determining step of determining whether a condition specified by the settlement condition information recorded in the plaintext information recording step is satisfied; and a settlement step of accepting settlement of an amount of money specified by the amount information when being determined in the third authentication step that the virtual currency data sent from the predetermined device is authentic and being determined in the settlement condition determining step that the condition specified by the settlement condition information is satisfied. 
     The inventor of the present invention also proposes, for example, a computer program for causing a general-purpose computer to function as the third type of settlement device described above, as one aspect of the present invention. For example, the computer program is as follow. 
     The computer program is a computer program for causing a computer capable of receiving data via a network and performing data processing to function as a settlement device. 
     The computer program causes the computer to function as: a settlement device receiving means that receives virtual currency data, which is data of virtual currency having a monetary value, via a network from a predetermined device for requesting settlement, the virtual currency data including virtual currency encryption data which is data obtained by, according to a predetermined encryption method, encryption of issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency; a plaintext information recording means that records, in association with each other, the issuer information, the amount information, and the settlement condition information included in one virtual currency encryption data in an encrypted state; an encryption means that encrypts the issuer information, the amount information, and the settlement condition information recorded in the plaintext information recording means using an encryption method equal to the predetermined encryption method used when the issuer information, the amount information, and the settlement condition information are encrypted into the virtual currency encryption data; a third authentication means that compares the virtual currency encryption data received by the settlement device receiving means with the data obtained by encryption of the issuer information, the amount information, and the settlement condition information recorded in the plaintext information recording means with the encryption means to determine whether both of the data coincide with each other, and determines that the virtual currency data sent from the predetermined device is authentic when both of the data coincide with each other; a settlement condition determining means that determines whether a condition specified by the settlement condition information recorded in the plaintext information recording means is satisfied; and a settlement means that accepts settlement of an amount of money specified by the amount information when the third authentication means determines that the virtual currency data sent from the predetermined device is authentic and the settlement condition determining means determines that the condition specified by the settlement condition information is satisfied. 
     The inventor of the present invention also proposes the virtual currency data generating device for generating the virtual currency data having the data structure of the virtual currency data according to the present invention, as one aspect of the present invention. The effect according to this aspect is equal to that described in the data structure of the virtual currency data according to the present invention. 
     An example of the virtual currency data generating device is a virtual currency data generating device including: a currency generating and encrypting means that encrypts, according to a predetermined encryption method, issuer information including at least information on an issuer of a virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency, and thus generates virtual currency encryption data which is data obtained by encryption of the issuer information, the amount information, and the settlement condition information, the virtual currency data generating device being capable of generating virtual currency data which includes the virtual currency encryption data and is data of virtual currency having a monetary value. 
     The above-described virtual currency data generating device may be integrated with one of the above-described settlement devices according to the present invention, the virtual currency data generating device including: a currency generating and encrypting means that encrypts, according to a predetermined encryption method, issuer information including at least information on an issuer of a virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency, and thus generates virtual currency encryption data which is data obtained by encryption of the issuer information, the amount information, and the settlement condition information, the virtual currency data generating device thus being capable of generating virtual currency data which includes the virtual currency encryption data and is data of virtual currency having a monetary value. 
     The inventor of the present invention also proposes the method executed by the virtual currency data generating device described so far, as one aspect of the present invention. The effect thereof is equal to that of the virtual currency data generating device. 
     An example of the method is a method executed by a virtual currency data generating device including a computer and capable of generating virtual currency data which is data of virtual currency having a monetary value, the method including a step executed by the computer for encrypting, according to a predetermined encryption method, issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency, and thus generating virtual currency encryption data which is data obtained by encryption of the issuer information, the amount information, and the settlement condition information, and thus generating virtual currency data which includes the virtual currency encryption data and is data of virtual currency having a monetary value. 
     The inventor of the present invention also proposes, for example, a computer program for causing a general-purpose computer to function as the virtual currency data generating device described above, as one aspect of the present invention. For example, the computer program is as follow. 
     This is a computer program for causing a computer to function as the virtual currency data generating device capable of generating virtual currency data which is the data of the virtual currency having the monetary value. 
     The computer program is a computer program for causing the computer to function as: a currency generating and encrypting means that encrypts, according to a predetermined encryption method, issuer information including at least information on an issuer of the virtual currency data, amount information that is information for specifying a monetary value, and settlement condition information that is information on conditions for accepting payment with virtual currency, and thus generates virtual currency encryption data which is data obtained by encryption of the issuer information, the amount information, and the settlement condition information, and thus the computer program causing the computer to generate virtual currency data which includes the virtual currency encryption data and is data of virtual currency having a monetary value. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing an overall structure of a settlement system according to a first embodiment; 
         FIG. 2  is a diagram showing an external appearance of a user terminal included in the settlement system shown in  FIG. 1 ; 
         FIG. 3  is a diagram showing a configuration of hardware of the user terminal included in the settlement system shown in  FIG. 1 ; 
         FIG. 4  is a block diagram showing functional blocks generated inside the user terminal included in the settlement system shown in  FIG. 1 ; 
         FIG. 5  is a diagram showing a configuration of hardware of a settlement device included in the settlement system shown in  FIG. 1 ; 
         FIG. 6  is a block diagram showing functional blocks generated inside the settlement device included in the settlement system shown in  FIG. 1 ; 
         FIG. 7  is a diagram showing a configuration of hardware of a settlement terminal included in the settlement system shown in  FIG. 1 ; 
         FIG. 8  is a block diagram showing functional blocks generated inside the settlement terminal included in the settlement system shown in  FIG. 1 ; 
         FIG. 9  is a diagram showing a flow of a process to be executed at the time of settlement on the settlement system shown in  FIG. 1 ; 
         FIGS. 10(A) and 10(B)  are diagrams showing an example of an image displayed on a display of the user terminal included in the settlement system shown in  FIG. 1 ; 
         FIG. 11  is a diagram showing notionally the content of a part of data recorded on a basic data recording unit in the settlement device included in the settlement system shown in  FIG. 1 ; 
         FIG. 12(A)  is a diagram showing notionally a data structure of plaintext data serving as an origin of virtual currency encryption data contained in virtual currency data used in the settlement system shown in  FIG. 1 , and  FIG. 12(B)  is a diagram showing notionally a data structure of the virtual currency data used in the settlement system shown in  FIG. 1 ; 
         FIG. 13  is a diagram showing another example of an image displayed on the display of the user terminal included in the settlement system shown in  FIG. 1 ; 
         FIG. 14  is a diagram showing further another example of an image displayed on the display of the user terminal included in the settlement system shown in  FIG. 1 ; 
         FIG. 15  is a block diagram showing functional blocks generated inside a settlement device included in a settlement system of Modification Example 1; 
         FIG. 16  is a block diagram showing functional blocks generated inside a settlement device included in a settlement system of a second embodiment; 
         FIG. 17  is a block diagram showing functional blocks generated inside a settlement device included in a settlement system of a third embodiment; and 
         FIG. 18  is a block diagram showing a functional block generated inside a settlement device included in a settlement system of Modification Example 2. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First to third embodiments of the present invention will be described below. In the description of each embodiment and modification example, the same element is denoted by the same reference numeral and duplication description will not be presented in some cases. 
     First Embodiment 
       FIG. 1  schematically shows an overall configuration of a settlement system according to a first embodiment. 
     The settlement system is configured to include a plurality of user terminals  100 - 1  to  100 -N (which may also hereinafter simply be described as “user terminal  100 .”), a settlement device  200 , and settlement terminals  300 - 1  to  300 - n  (which may also hereinafter simply be described as “settlement terminal  300 .”). These are all connectable to a network  400 . 
     The network  400  is the Internet in this embodiment without being limited thereto. 
     The user terminal  100  is an example of a receiving device according to the present invention, the settlement terminal  300  is an example of a transmission device according to the present invention, and the settlement device  200  is an example of a settlement device according to the present invention. 
     Although not limited thereto, in this embodiment, payment of money using virtual currency data to be described below is, in principle, performed on an administrator (who manages or owns the settlement terminal  300 , for example) of the settlement terminal  300  from an administrator (owner) of the user terminal  100 , and is performed on an administrator of another user terminal  100  from an administrator of one user terminal  100  in some cases. 
     Normally, the user terminal  100  is possession of each user. The user terminal  100  includes a computer. The user terminal  100  is a mobile phone, a smartphone, a tablet, a notebook computer, a desktop computer, or the like. Among them, the smartphone or the tablet is particularly preferable for use as the user terminal  100 , considering that the smartphone or the tablet is portable and suitable for installation of computer programs to be described below. The smartphone is, for example, an iPhone that is manufactured and sold by Apple Japan, LLC. An example of the tablet is an iPad that is manufactured and sold by Apple Japan, LLC. Hereinafter, the description is made assuming that the user terminal is the smartphone, but is not limited thereto. 
     The user terminal  100  at least needs to be capable of receiving data, but may also be capable of transmitting data. In this embodiment, since the user terminal  100  is the smartphone, it is naturally possible to receive and transmit data. 
     A configuration of the user terminal  100  will be described below. Each of the user terminals  100 - 1  to  100 -N has the same configuration in relation to the present invention. 
     An example of external appearance of the user terminal  100  is shown in  FIG. 2 . 
     The user terminal  100  includes a display  101 . The display  101  is used to display still images or moving images, and a publicly known or well-known display can be used. The display  101  is, for example, a liquid crystal display. The user terminal  100  also includes an input device  102 . The input device  102  is used for the user to perform a desired input on the user terminal  100 . A publicly known or well-known input device can be used as the input device  102 . The input device  102  of the user terminal  100  in this embodiment is a button-type input device, but is not limited thereto, and a numeric keypad, a keyboard, a trackball, a mouse, or the like can also be used. Moreover, when the display  101  is a touch panel, the display  101  also has a function of the input device  102 , which is applied to this embodiment. 
     Data input from the input device  102  will be described in detail below, but include, for example, generation request information on a generation request of virtual currency data, payment information on use of virtual currency data, transfer information on transfer of virtual currency data, and a user ID. 
     A configuration of hardware of the user terminal  100  is shown in  FIG. 3 . 
     The hardware includes a CPU (central processing unit)  111 , a ROM (read only memory)  112 , a RAM (random access memory)  113 , and an interface  114 , which are interconnected by a bus  116 . 
     The CPU  111  is an arithmetic operation device that performs arithmetic operations. The CPU  111 , for example, executes a computer program recorded in the ROM  112  to execute processing to be described below. It should be noted that the computer program used herein includes at least a computer program for causing the user terminal  100  to function as a receiving device of the present invention. The computer program may be pre-installed in the user terminal  100 , or may be post-installed. The computer program may be installed in the user terminal  100  via a predetermined recording medium (not shown) such as a memory card, or may be installed via a network such as the Internet. 
     The ROM  112  records computer programs and data necessary for the CPU  111  to execute processing to be described below. The computer program recorded in the ROM  112  is not limited thereto. For example, when the user terminal  100  is the smartphone, a computer program and data are recorded, for example, for executing telephone calls or e-mails, which are required to cause the user terminal to function as the smartphone. The user terminal  100  can also browse a homepage based on data received via the network  400 , and is mounted with a publicly known web browser for enabling the browsing of the homepage. 
     The RAM  113  provides a work area necessary for the CPU  111  to perform processing. Virtual currency data to be described below may be recorded in the RAM  113 . 
     The interface  114  performs data exchange between the CPU  111  and the RAM  113  connected via the bus  116  and the outside. The display  101  and the input device  102  described above are connected to the interface  114 . The operation content input from the input device  102  is input to the bus  116  from the interface  114 , and image data to be described below is output to the display  101  from the interface  114 . The interface  114  is also connected to a transmission and reception unit, which is not shown. 
     The transmission and reception unit transmits and receives data via the network  400  that is the Internet. Such communication may also be performed in a wired manner, but when the user terminal  100  is the smartphone, the communication is wirelessly performed in general. As long as it is possible, the transmission and reception unit may have a publicly known or well-known configuration. The data (for example, virtual currency data) received by the transmission and reception unit from the network  400  is received through the interface  114 , and the data (for example, virtual currency data) passed from the interface  114  to the transmission and reception unit is sent to the outside, for example, to the settlement device  200  by the transmission and reception unit via the network  400 . 
     Functional blocks as shown in  FIG. 4  are generated within the user terminal  100  when the CPU  111  executes the computer program. It should be noted that while the following functional blocks may be generated with functions of the above-described computer program alone for causing the user terminal  100  to function as the user terminal of the present invention, the following functional blocks may be generated in cooperation with the above-described computer program and an OS and other computer programs installed in the user terminal  100 . 
     A control unit  120  to be described below is generated in the user terminal  100  in relation to functions of the present invention, and a main control unit  121 , a display control unit  122 , a data input/output unit  123 , and a user terminal recording unit  124  are generated in the control unit  120 . 
     The control unit  120  executes information processing as will be described below. 
     The main control unit  121  performs overall control within the control unit  120 . For example, the main control unit  121  controls the display control unit  122  based on data received from the data input/output unit  123  to be detailed below. 
     The main control unit  121  may receive virtual currency data to be described below from the data input/output unit  123  that will be described below. Upon receiving the data, the main control unit  121  sends it to the user terminal recording unit  124  or the display control unit  122 . The main control unit  121  may read the virtual currency data from the user terminal recording unit  124  as will be described below. The main control unit  121 , which has read the virtual currency data, instructs the display control unit  122  to display based on the virtual currency data, and sends it to the data input/output unit  123  in some cases. 
     From the data input/output unit  123 , the main control unit  121  may receive the above-described generation request information, payment information, or transfer information input from the input device  102 . Upon receiving such information, the main control unit  121  performs processing to be described below. For example, upon receiving the generation request information, the main control unit  121  adds necessary information thereto, sends it to the data input/output unit  123 , and sends it from the data input/output unit  123  to the settlement device  200 , via the transmission and reception unit and the network  400 . 
     The display control unit  122  controls images to be displayed on the display  101  under control of the main control unit  121 . An image based on the data sent from the display control unit  122  is displayed on the display  101 . The main control unit  121  sends an instruction on what image should be displayed on the display  101 , to the display control unit  122 . 
     The data input/output unit  123  inputs and outputs data to/from the control unit  120 . Specifically, the data input/output unit  123  receives the input from the input device  102 . For example, the generation request information, the payment information, or the transfer information is input from the input device  102  to the data input/output unit  123 . Such information is sent from data input/output unit  123  to the main control unit  121 . 
     In addition, the data input/output unit  123  receives, from the transmission and reception unit, the virtual currency data sent from the settlement device  200  via the network  400 . The data input/output unit  123  sends the received virtual currency data to the main control unit  121 . 
     Further, the data input/output unit  123  may receive the virtual currency data from the main control unit  121 . The data input/output unit  123 , which has received the virtual currency data, sends the virtual currency data to the transmission and reception unit, and the virtual currency data is sent from the transmission and reception unit to the settlement device  200 , for example. A transmission destination of the virtual currency data is designated by the main control unit  121  according to the input from the input device  102 , as will be described below. 
     As described above, when the main control unit  121  receives the virtual currency data from the data input/output unit  123 , the user terminal recording unit  124  receives the virtual currency data from the main control unit  121  and records it. When viewed as hardware, the user terminal recording unit  124  is configured by a part of the RAM  113 . 
     In addition, the virtual currency data recorded in the user terminal recording unit  124  may be read by the main control unit  121  at a timing to be described below. 
     The settlement device  200  will be described below. In this embodiment, the settlement device  200  also serves as a virtual currency data generating device as referred to in the present invention, but is not limited thereto. 
     The settlement device  200  is a general computer, and in this embodiment, is a general server device in more detail. Hardware configuration thereof may be equivalent to that of a settlement device in the conventional settlement system. 
     An example of the hardware configuration of the settlement device  200  is shown in  FIG. 5 . 
     The hardware includes a CPU  211 , a ROM  212 , a RAM  213 , an interface  214 , and a large-capacity recording medium that is an HDD (hard disk drive)  215  in this embodiment, and these are connected to each other by a bus  216 . 
     The CPU  211  is an arithmetic operation device that performs arithmetic operations. The CPU  211 , for example, executes a computer program recorded in the ROM  212  to execute processing to be described below. It should be noted that the computer program used herein includes at least a computer program for causing the settlement device  200  to function as a settlement device of the present invention. The computer program may be pre-installed in the settlement device  200 , or may be post-installed. The computer program may be installed in the settlement device  200  via a predetermined recording medium such as a memory card, or may be installed via the network such as the Internet. 
     The ROM  212  records the computer program and data necessary for the CPU  211  to execute processing to be described below. The computer program recorded in the ROM  212  is not limited thereto, and any other necessary computer programs may be recorded. 
     The RAM  213  provides a work area necessary for the CPU  211  to perform processing. 
     The interface  214  performs data exchange between the CPU  211 , the RAM  213 , and the like connected via the bus  216  and the outside. The interface  214  is at least connected to the transmission and reception unit. The data received by the transmission and reception unit from the network  400  is received by the interface  214 , and the data passed from the interface  214  to the transmission and reception unit is sent to the outside, for example, to the user terminal  100  by the transmission and reception unit, via the network  400 . 
     The HDD  215  is a large-capacity recording medium as described above, and records data. At least a part of the computer program or data necessary for the CPU  211  to execute processing to be described below may be recorded on the HDD  215  instead of the ROM  212 , and most of the computer program and data is more practically recorded on the HDD  215 . 
     Functional blocks as shown in  FIG. 6  are generated within the settlement device  200  when the CPU  211  executes the computer program. It should be noted that while the following functional blocks may be generated with functions of the above-described computer program alone for causing the settlement device  200  to function as the settlement device of the present invention, the following functional blocks may be generated in cooperation with the above-described computer program and the OS and other computer programs installed in the settlement device  200 . 
     A control unit  220  to be described below is generated in the settlement device  200  in relation to the functions of the present invention. A data input/output unit  221 , a main control unit  222 , a virtual currency data generating unit  223 , a basic data recording unit  224 , a decryption unit  225 , and a settlement determination unit  226  are generated in the control unit  220 . 
     The data input/output unit  221  inputs and outputs data to/from the control unit  220 . Specifically, the data input/output unit  221  receives various data to be described below, from the main control unit  222 . 
     For example, the data input/output unit  221  receives virtual currency data from the main control unit  222 . The received virtual currency data is sent to the transmission and reception unit from the data input/output unit  221 , and is sent to the user terminal  100  via the network  400 . 
     The data input/output unit  221  also receives various data to be described below, which are received by the transmission and reception unit from the user terminal  100  or the settlement terminal  300  via the network  400 , from the transmission and reception unit, and sends the received data to the main control unit  222 . For example, the data input/output unit  221  may receive virtual currency data and generation request information from the transmission and reception unit, and the data input/output unit  221 , which has received any one of the virtual currency data and the generation request information, sends any one to the main control unit  222 . 
     The main control unit  222  performs overall control within the control unit  220 . For example, the main control unit  222  is configured to perform settlement processing to be described below, and is configured to perform necessary processing by sending data to be described below to the virtual currency data generating unit  223 , decryption unit  225 , and the like. 
     As described above, the main control unit  222  may receive the virtual currency data from the data input/output unit  221 , and the main control unit  222 , which has received the virtual currency data, sends the virtual currency data to the decryption unit  225 . In this case, only the virtual currency encryption data among the data included in the virtual currency data may be sent to the decryption unit  225 . 
     As described above, the main control unit  222  may receive the generation request information from the data input/output unit  221 , and the main control unit  222 , which has received the information, sends the information to the virtual currency data generating unit  223 . 
     The main control unit  222  may also receive final determination data, which will be described below, from the settlement determination unit  226 . As will be described below, the final determination data is data indicating whether the settlement is accepted or the settlement is not accepted. Upon receiving the positive final determination data with the content of accepting the settlement which will be described below, the main control unit  222  performs settlement processing. In this embodiment, the settlement processing is a process for accepting payment of money to the settlement terminal  300  that has sent the virtual currency encryption data. The main control unit  222  retains data indicating what kind of payment has been made. For example, the main control unit  222  is configured to cause a recording medium (not shown) for each settlement terminal  300  to record information indicating how much payment is finally permitted to anybody (administrator of any settlement terminal  300 , etc.). 
     On the other hand, upon receiving the negative final determination data, which will be described below, indicating that payment is not accepted, the main control unit  222  does not perform processing for accepting the settlement. 
     As described above, the virtual currency data generating unit  223  may receive the generation request information from the main control unit  222 . Upon receiving the generation request information, the virtual currency data generating unit  223  generates virtual currency data. The virtual currency data generating unit  223  includes an encryption unit  223 A and a combination unit  223 B. A method of generating the virtual currency data using the virtual currency data generating unit  223  will be described in detail below. 
     The virtual currency data generating unit  223  uses data recorded in the basic data recording unit  224  when generating the virtual currency data. The virtual currency data generating unit  223  reads and uses necessary data among the data recorded in the basic data recording unit  224  when generating the virtual currency data. 
     The virtual currency data generating unit  223  sends the generated virtual currency data to the main control unit  222 . 
     Data necessary for generating the virtual currency data is recorded in the basic data recording unit  224 . Details of the data recorded in the basic data recording unit  224  will be described below. 
     As described above, the decryption unit  225  may receive virtual currency data (or virtual currency encryption data) from the main control unit  222 . 
     Upon receiving the virtual currency encryption data, the decryption unit  225  decrypts the received data. Details of the decryption processing will be described below. The decrypted data includes issuer information, amount information, and settlement condition information, all of which will be described in detail below. When being able to decrypt the virtual currency encryption data, the decryption unit  225  sends at least the amount information and the settlement condition information among the issuer information, the amount information, and the settlement condition information to the settlement determination unit  226 . 
     On the other hand, when not being able to decrypt the virtual currency encryption data, the decryption unit  225  notifies the settlement determination unit  226  of the purport thereof. 
     As described above, at least the amount information and the settlement condition information among the issuer information, the amount information, and the settlement condition information may be sent to the settlement determination unit  226  from the decryption unit  225 . Upon receiving these types of information, the settlement determination unit  226  performs a final determination that is a determination as to whether the settlement is accepted or not. As a result, the settlement determination unit  226  generates final determination data that is data including the content of either of acceptance of the settlement or not acceptance of the settlement. As will be described below, the settlement determination unit  226  may use the data recorded in the basic data recording unit  224  when performing such a determination. A method of generating the final determination data using the settlement determination unit  226  will be described below. 
     As described above, the settlement determination unit  226  may receive the notification that the virtual currency encryption data cannot be decrypted, from the decryption unit  225 . Upon receiving the notification, the settlement determination unit  226  generates final determination data including the content of not acceptance of the settlement. 
     In any case, when generating the final determination data, the settlement determination unit  226  sends it to the main control unit  222 . 
     The settlement terminal  300  will be described below. 
     The settlement terminal  300  plays the same role as the settlement terminal used in the settlement system using the credit card, and is a general computer. For example, it is assumed that the settlement terminal  300  is configured by a tablet. 
     The settlement terminal  300  includes a touch panel display (not shown), but an external appearance thereof is not shown because of the same as that in  FIG. 2 . As a result, the settlement terminal  300  includes a display and an input device. However, the settlement terminal  300  may alternatively include a display that is not a touch panel type and an input device including necessary input devices selected from publicly known or well-known input devices such as a numeric keypad, a keyboard, a mouse, and a trackball, in other words, may include the display and the input device separately. The description will be made below assuming that the settlement system in this embodiment includes a touch panel display. 
     In addition, the settlement terminal  300  includes a camera (not shown). The camera may be externally attached, but the settlement terminal  300 , which is a tablet, includes a publicly known built-in camera. 
     A configuration of hardware of the settlement terminal  300  is shown in  FIG. 7 . 
     The hardware includes a CPU  311 , a ROM  312 , a RAM  313 , and an interface  314 , which are interconnected by a bus  316 . 
     The CPU  311  is an arithmetic operational device that performs arithmetic operations. The CPU  311 , for example, executes a computer program recorded in the ROM  312  to execute processing to be described below. The computer program may be pre-installed in the settlement terminal  300 , or may be post-installed. The computer program may be installed in the settlement terminal  300  via a predetermined recording medium such as the memory card, or may be performed via a network such as the LAN or the Internet. 
     The ROM  312  records the computer program and data necessary for the CPU  311  to execute processing to be described below, in other words, for causing the computer to function as a transmission device according to the present invention. The computer program recorded in the ROM  312  is not limited thereto, and any other necessary computer programs may be recorded. 
     The RAM  313  provides a work area necessary for the CPU  311  to perform processing. 
     The interface  314  performs data exchange between the CPU  311 , the RAM  313  and the like connected via the bus  316  and the outside. The Interface  314  is at least connected to the transmission and reception unit which is not shown. The transmission and reception unit may be connected to the network  400  to at least transmit data via the network  400 , but is configured to transmit and receive data via the network  400  in this embodiment. The data passed to the transmission and reception unit from the interface  314  is sent to the outside, for example, to the settlement device  200  by the transmission and reception unit, via the network  400 . The data output from the interface  314  and transmitted from the transmission and reception unit is mainly virtual currency data in relation to this embodiment. 
     The interface  314  is also connected to the input device provided on the touch panel display so as to accept an input from the input device. The interface  314  is connected to the touch panel display so as to send data for displaying an image to be described below, to the touch panel display. The data input from the input device to the interface  314  is, for example, data instructing the start of payment, a settlement terminal ID to be described below, and the like. 
     The interface  314  is also connected to the camera described above. Image data including an image for specifying the virtual currency data is input from the camera to the interface  314 . The virtual currency data is actually input to the interface  314  from the camera, which is slightly inaccurate. 
     The hardware may include a large-capacity recording medium, and the function at this time is as described above. 
     Functional blocks as shown in  FIG. 8  are generated within the settlement terminal  300  when the CPU  311  executes the computer program. It should be noted that the following functional blocks may be generated with functions of the above-described computer program alone for causing the settlement terminal  300  to function as the settlement terminal of the present invention, the following functional blocks may be generated in cooperation with the above-described computer program and the OS and other computer programs installed in the settlement terminal  300 . 
     A control unit  320  to be described below is generated in the settlement terminal  300  in relation to the functions of the present invention, and a main control unit  321 , a display control unit  322 , and a data input/output unit  323  are generated in the control unit  320 . 
     The control unit  320  executes information processing as will be described below. 
     The main control unit  321  performs overall control within the control unit  320 . For example, the main control unit  321  controls the display control unit  322  based on data received from the data input/output unit  323  to be detailed below. 
     The main control unit  321  is configured to receive virtual currency data from the data input/output unit  323  to be described below. The main control unit  321  of each settlement terminal  300  records a unique settlement terminal ID for each settlement terminal  300 . The main control unit  321  attaches data of the settlement terminal ID to the received virtual currency data and sends it to the data input/output unit  323 . 
     The display control unit  322  controls the images to be displayed on the above-described display of the touch panel type under control of the main control unit  321 . An image based on the data sent from the display control unit  322  is displayed on the display. The main control unit  321  sends an instruction on what image should be displayed on the display, to the display control unit  322 . 
     The data input/output unit  323  inputs and outputs data to/from the control unit  320 . 
     Specifically, the data input/output unit  323  receives the input from the input device and sends it to the main control unit  321 . An example of data input from the input device to the data input/output unit  323  is data for instructing the start of settlement. In addition, the settlement terminal ID described above may be input. Further, image data including the virtual currency data captured by the camera may be input to the data input/output unit  323 . 
     Moreover, the data input/output unit  323  outputs the data to the transmission and reception unit, which is not shown. The data output to the transmission and reception unit is the virtual currency data sent from the main control unit  321 . The settlement terminal ID is attached to the virtual currency data. The data output to the transmission and reception unit is transmitted to the settlement device  200  from the transmission and reception unit via the network  400 . 
     A method of using the settlement system as described above and an operation thereof will be described below with reference to  FIG. 9 . 
     First, as preparation for using such a system, a user ID is set in each of the user terminals  100  and a settlement terminal ID is set in each of the settlement terminals  300 . 
     The user ID is an ID unique to each of the user terminals  100  for identifying each of the user terminals  100 , and is generally an enumeration of alphabetic characters, numbers, and symbols. The same also applies to the settlement terminal ID. In order to avoid duplication of a large number of user IDs, the settlement device  200  may issue a user ID to each of the user terminals  100 . The same also applies to the settlement terminal ID. Alternatively, an individual identification number embedded in the hardware of the user terminal  100  from the time of shipment can be used as the user ID. The same also applies to the settlement terminal ID. 
     The administrator of each of the user terminal s  100  inputs the user ID for the user terminal  100  by operating the input device. Note that such an input is not necessary when the individual identification number is used as the user ID. Data of the user ID is sent from the input device to the interface  114  and sent from the interface  114  to the control unit  120 . The data input/output unit  123  of the control unit  120  receives the data and sends it to the main control unit  121 . The main control unit  121  retains the data, or records it in the main control unit  121 . 
     On the other hand, the main control unit  121  sends the user ID data to the data input/output unit  123 . The user ID data is sent from the data input/output unit  123  to the transmission and reception unit, and then sent to the settlement device  200  via the network  400 . 
     The settlement device  200  receives the user ID data at the transmission and reception unit. The user ID data is sent from the transmission and reception unit to the interface  214  and is sent from the interface  214  to the control unit  220 . The data input/output unit  221  of the control unit  220  receives the data, and sends it to the main control unit  222 . The main control unit  222  retains the data, or records it in the main control unit  222 . When all the user terminals  100  perform this processing, the main control unit  222  has a list of all the user terminals  100 . Using such a list, the settlement device  200  specifies that the virtual currency data is generated for anybody (who owns any user terminal  100 ). 
     The administrator of each of the settlement terminals  300  inputs the settlement terminal ID for the settlement terminal  300  by operating the input device. Data of the settlement terminal ID is sent from the input device to the interface  314 , and then is sent from the interface  314  to the control unit  320 . The data input/output unit  323  of the control unit  320  receives the data and sends it to the main control unit  321 . The main control unit  321  retains the data, or records it in the main control unit  321 . 
     On the other hand, the main control unit  321  sends the data of the settlement terminal ID to the data input/output unit  323 . The data of the settlement terminal ID is sent from the data input/output unit to the transmission and reception unit, and is sent to the settlement device  200  via the network  400 . 
     The settlement device  200  receives the data of the settlement terminal ID at the transmission and reception unit. The data of the settlement terminal ID is sent from the transmission and reception unit to the interface  214 , and is sent from the interface  214  to the control unit  220 . The data input/output unit  221  of the control unit  220  receives the data and sends it to the main control unit  222 . The main control unit  222  retains the data, or records it in the main control unit  222 . When all the settlement devices  200  perform this processing, the main control unit  222  has a list of all the settlement terminals  300 . Using such a list, the settlement device  200  specifies that payment (settlement) is accepted for anybody (administrator of any settlement terminal  300 ). 
     First, the virtual currency data is generated. 
     Although not limited thereto, in this embodiment, generation of the virtual currency data starts from a point where the user starts generation of generation request information (S 911 ). 
     In order to start the generation of the generation request information, for example, the user may touch an icon (not shown) displayed on the display  101 . Then, the operation content is sent from the input device  102  to the main control unit  121  via the interface  114  and the data input/output unit  123 , and the generation of the generation request information is started. 
     The generation request information is generated when the user operates the input device  102  of the user terminal  100 . The generation request information includes at least a user ID and an amount of money that the user intends to use for payment. 
     When the generation of the generation request information is started, the main control unit  121  sends an instruction to the display control unit  122  to display an image for urging the user to input the user ID or the like on the display  101 . The display control unit  122 , which has accepted this instruction, displays, on the display  101 , an image for urging the user to input the user ID and the amount of money for which the user intends to perform the payment, as shown in  FIG. 10(A) , for example. The user inputs the user ID on the right side of a field indicated as “User ID”, and inputs the amount of money for which the user intends to pay on the right side of a field indicated as “Amount of money (yen)”, respectively (S 912 ). Data on the user ID and the amount information, which is information for specifying the amount of money, input by the user is input from the input device  102  to the data input/output unit  123  via the interface  114 , and sent to the main control unit  121 . Since the user ID and the amount information, which are input by the user, are displayed on the display  101 , also including during the input, under control of the display control unit  122  controlled by the main control unit  121 , the user can input the user ID and the amount information while checking the display  101 . According to an example shown in  FIG. 10(B) , the user intends to pay 25,000 yen using this settlement system. 
     When the input of the user ID and the amount information is completed, the user clicks a button of “Decision” displayed on the display  101 . 
     When the user clicks the button of “Decision”, the user ID and the amount information are sent from the data input/output unit  123  to the main control unit  121 . The main control unit  121  collects the user ID and the amount information to use it as generation request information. 
     The generation request information may include other types of information. Although not limited thereto, in this embodiment, for example, the user can input, from the input device  102 , data (time information) indicating that the settlement period is limited to a predetermined period, by inputting the purport when the user intends to limit the settlement period to a predetermined period (for example, payment should be made due to the data only within half a year after the virtual currency data is issued, or the usable date of the virtual currency data is specified at the start and end), and data (recipient information) indicating that a recipient of payment is limited to a specific person when the user intends to limit the recipient of payment to a specific person (it is not necessarily one person. For example, it is also possible to target multiple persons being in a specific chain store, the head office and all branch offices of a corporation that operates a specific banking business, and a store that opens a certain shopping mall). These data are used when settlement condition information to be described below is generated by the settlement device  200 . Similarly to the data of the user ID, these data are input from the input device  102  to the data input/output unit  123  via the interface  114 , and is passed to the main control unit  121  from the data input/output unit  123 . When these data are input, the main control unit  121  adds the data to the user ID and the settlement terminal ID to use as generation request information. 
     The generation request information is sent from the main control unit  121  to the data input/output unit  123 , and is sent from the data input/output unit  123  to the transmission and reception unit. The generation request information is sent from the transmission and reception unit to the settlement device  200  via the network  400  (S 913 ). 
     As in the case hereinafter, all communications performed via the network  400  in this embodiment may be encryption communications. Techniques used for encryption and decryption in this case can be publicly known or well-known. 
     The settlement device  200  accepts the data of the generation request information at the transmission and reception unit (S 921 ). The transmission and reception unit sends the data of the generation request information to the data input/output unit  221 , and the data input/output unit  221  sends the data to the main control unit  222 . 
     Although not necessarily limited to this, the main control unit  222  in this embodiment performs credit determination, which is determination as to whether virtual currency data may be generated with respect to the user terminal  100  specified by the user ID (S 922 ). Such determination may be performed in the same manner as a procedure generally called credit determination. As will be described below, if there is no particular problem, the settlement device  200  issues virtual currency data to the user terminal  100 , but since the virtual currency data is data having a monetary value, determination as to whether such data may be issued to the user, who has sent the generation request information, is performed. 
     For example, the main control unit  222  can communicate with a deposit account database for each user in which the balance of the amount of money deposited from each user is recorded in association with the user ID of each user, and may determine that the credit of the user is accepted when the balance is larger than the amount of money specified by the amount information, which is transmitted in a state of being included in the generation request information from the user. The main control unit  222  can communicate with each bank having a bank account designated by each user, and may determine that the credit of the user is accepted when the balance of the bank account designated by the user is larger than the amount of money specified by the amount information, which is transmitted in a state of being included in the generation request information from the user. Alternatively, when the user terminal  100  sends the generation request information to the settlement device  200 , the settlement device  200  may urge the user, who operates the user terminal  100  that has sent the generation request information, to pay the amount of money specified by the amount information transmitted in a state of being included in the generation request information; and when it is checked that the user has paid the amount of money to the administrator of the settlement device  200  with a credit card from the user terminal  100 , for example, the main control unit  222  of the settlement device  200  may determine that the credit of the user is accepted. Alternatively, as in the credit determination in the payment with the credit card, when the amount of money specified by the amount information transmitted in a state of being included in the generation request information from the user is within a credit limit which is determined in advance depending on the user&#39;s occupation, annual income, own house, etc., the main control unit  222  may determine that the credit of the user is accepted. 
     In any case, the main control unit  222  sends the amount information, which is included in the generation request information sent from the user, when the credit of the user is accepted and the data necessary for generating the settlement condition information if existing to the virtual currency data generating unit  223 . 
     The virtual currency data generating unit  223 , which has received the amount information and the like, generates virtual currency data (S 923 ). 
     The virtual currency data includes at least issuer information, amount information, and settlement condition information all of that are in encrypted condition. Further, as described above, the virtual currency data generating unit  223  uses the data recorded in the basic data recording unit  224  when generating the virtual currency data. In order to describe a method of generating the virtual currency data, first, the data recorded in the basic data recording unit  224  will be described. 
     The data recorded in the basic data recording unit  224  in this embodiment is information that can be issuer information and settlement condition information. As will be described below, the issuer information may include the data not recorded in the basic data recording unit  224 , and the same also applies to the settlement condition information. 
     The issuer information is generally information indicating circumstances of issue including the issuer of the virtual currency data. The information capable of being the issuer information is, for example, issuer information, which is information for specifying the settlement device  200  being an issuer of the virtual currency data, and is, for example, an IP address of the settlement device  200 . Note that a sender of the generation request information can be an issuer, and, in this case, the issuer information is an IP address of the user terminal  100 . Another example of information that can be issuer information is authentication information that is issued by a person who has the authority to guarantee authenticity of the virtual currency data, for example, a government organization and is information for guaranteeing the authenticity of the virtual currency data. Still another example of information that can be issuer information is serial number information that is information unique to each virtual currency data for distinguishing the virtual currency data from other virtual currency data. The issuer information may include another information, or may include data that is not recorded in the basic data recording unit  224  as will be described below. Of these, what is essential is only information for specifying the issuer of the virtual currency data (in this embodiment, it is assumed to be settlement device  200 .). Further, information other than the authentication information and the serial number information may be recorded in the basic data recording unit  224 , as information that can be the issuer information. 
     The serial number information described above will be complementally described. The serial number information is information on the serial number. For example, banknotes issued by the Japanese government (or the Bank of Japan) are recorded with serial numbers that are enumerated by numbers and alphabets. Similarly, in order to distinguish between the previously issued virtual currency data and the newly issued virtual currency data, each virtual currency data may include serial number information in an encrypted state. The serial number information is, for example, a serial number of a multi-digit number starting from 1 (for example, 1,000-digit number) represented in hexadecimal notation as in the serial number printed on banknotes issued by the Japanese government. The basic data recording unit  224  is recorded with, as the serial number information, the serial number information next to the serial number information included in the virtual currency data issued immediately before. The serial number information is rewritten as will be described below. 
     The settlement condition information is information that becomes a condition for causing the settlement device  200 , which has received the virtual currency data, to accept the settlement as will be described below. The settlement condition determined by the settlement condition information may be determined by the user terminal  100  or the settlement device  200 . The settlement condition information determined by the settlement device  200  is recorded in the basic data recording unit  224 . 
     For example, as described above, recipient information or time information is recorded in the basic data recording unit  224 , as information that can be the settlement condition information. However, if the settlement condition information set by the settlement device  200  is difficult for the user to use the virtual currency data for payment, the use of the virtual currency data becomes difficult, so that it is important to set the settlement condition information that will be beneficial for the user. The settlement condition information may also be information for changing the amount of money specified by the amount information. Specifically, the settlement condition information can be information for gradually reducing the amount of money specified by the amount information with the passage of time or reducing the amount of money specified by the amount information in a step-by-step manner with the passage of time. The settlement condition information can be information that the amount of money specified by the amount information is increased by 10% when being on payment to a recipient belonging to a certain store or a certain corporate group, or a recipient who has an address in a certain region, in other words, a recipient having a certain attribute, for example, within a designated period. The final example includes a case in which a user can use the virtual currency data like a coupon. 
     The basic data recording unit  224  is also recorded with data required when the settlement device  200  performs settlement determination to be described below. Since the data is used by the settlement determination unit  226  rather than by the virtual currency data generating unit  223 , the data is not necessarily recorded in the basic data recording unit  224  as much as possible. Although not limited thereto, in this embodiment, the settlement terminal ID for each settlement terminal  300 , the position (for example, its latitude and longitude) where each settlement terminal  300  exists, and the attribute (indicating which corporate group it is included to or which shopping mall it is resident in, for example) of each settlement terminal  300  are recorded as shown in  FIG. 11 . 
     The virtual currency data generating unit  223 , which has received the amount information or the like, reads the information that can be the issuer information and the settlement condition information recorded in the basic data recording unit  224  when generating the virtual currency data. Data (see  FIG. 12(A) ) obtained by combination of the issuer information, the amount information, and the settlement condition information (although not necessarily in this order) is generated. 
     The issuer information in this embodiment includes information for specifying the settlement device  200  that is the issuer of the virtual currency data, authentication information, serial number information, and timing information, but is not limited thereto. When reading the serial number information, the virtual currency data generating unit  223  overwrites the serial number information recorded in the basic data recording unit  224  with “+1”. Thus, the serial number information is always kept up-to-date. In addition, the timing information indicates a time at which the virtual currency data generating unit  223  generates such virtual currency data (for example, a time at which the virtual currency data generating unit  223  receives the amount information or the like) in units of seconds, for example. In order to make this, the virtual currency data generating unit  223  always receives date and time information from a clock (not shown) included in the settlement device  200 . 
     In this embodiment, the amount information is information for specifying the amount of money of 25,000 yen as described above. Naturally, the amount of money is not limited to 25,000 yen, and the unit of money is not limited to yen. Furthermore, the unit of money need not be the same as the legal currency. 
     In this embodiment, the settlement condition information is included in the generation request information sent from the user terminal  100 , and indicates various conditions specified by the data necessary for generating the settlement condition information sent from the main control unit  222  to the virtual currency data generating unit  223  and the data necessary for generating the settlement condition information recorded in the basic data recording unit  224 . 
     Then, data shown in  FIG. 12(A)  is encrypted by the encryption unit  223 A in the virtual currency data generating unit  223  and converted into virtual currency encryption data. The encryption method may be publicly known or well-known, but it is necessary to able to perform decryption by at least an appropriate method in this embodiment. 
     The virtual currency data generating unit  223  sequentially generates virtual currency data according to a large number of requests from a large number of users. For the sake of description, it is assumed that the encrypted portion of the data structure is subjected to shading. Although not limited thereto, in this embodiment, the encryption method executed in the process of generating the virtual currency data is also applied to a case of generating any virtual currency data. In this embodiment, the encryption method is applied even in the case of generating any virtual currency data by making the algorithm and key used to encryption unchanged. 
     By the way, as described above, in this embodiment, the data to be encrypted includes serial number information and timing information on the premise that the content is changed. In particular, there is no same serial number information. Therefore, there is also no same virtual currency encryption data. The virtual currency encryption data is formed by alphabetic characters, numbers, symbols, or a combination of two or more thereof, and is enumerated by characters having a certain number of characters (for example, 1,000-digit number) or more (or the number of digits). 
     When the encryption unit  223 A generates the virtual currency encryption data, the virtual currency encryption data is sent to the combination unit  223 B. The combination unit  223 B combines a predetermined one of issuer information, amount information, and settlement condition information (These are encrypted in the virtual currency encryption data.) included in the virtual currency encryption data with the virtual currency encryption data in plaintext. Virtual currency data is obtained by combining the above-described data with the virtual currency encryption data. Information added to the virtual currency encryption data may be a part or all of the issuer information, the amount information, and the settlement condition information, but is the serial number information, the amount information, and the recipient information in this embodiment as shown, e.g., in  FIG. 12(B) . The content of the serial number information, the amount information, and the recipient information in plaintext can be grasped not only by the settlement device  200  but also by the user terminal  100  or the settlement terminal  300  without any special processing (because of being readable, the content is understood by reading). When a malicious third party obtains the virtual currency data, the malicious third party can also read the plaintext data, but cannot grasp all the contents of the data that is encrypted and included in the virtual currency encryption data, so that the malicious third party is difficult to misuse the virtual currency data. For example, when the malicious third party requests the settlement device  200  to make a settlement via the settlement terminal  300  as will be described below under conditions against the encrypted settlement condition information attached to the virtual currency encryption data, the malicious third party follows the specification of the settlement device  200  or the settlement terminal  300 , but may leave a history of requesting the settlement device  200  or the settlement terminal  300  to make the settlement under wrong conditions. Such a history is a powerful evidence for identifying the malicious third party, and is a powerful force that prevents the malicious third party from misusing the virtual currency data. 
     The generated virtual currency data is sent from the virtual currency data generating unit  223  to the main control unit  222 . The main control unit  222  instructs the user terminal  100 , which is specified by the user terminal ID attached to the generation request information serving as an application for generating the virtual currency data, to return the virtual currency data, and sends the virtual currency data to the data input/output unit  221 . The virtual currency data is further sent to the transmission and reception unit and sent to the user terminal  100  specified by the user terminal ID, via the network  400  (S 924 ). 
     The transmission and reception unit of the user terminal  100  receives the sent virtual currency data (S 914 ). The received virtual currency data is sent from the data input/output unit  123  to the main control unit  121 . 
     The virtual currency data can be used in this state. That is, the user, an owner of the user terminal  100 , can pay to a third party using the virtual currency data. The user performs an operation for preserving the virtual currency data using the input device  102 . Then, the operation content of the purport is sent from the input device  102  to the main control unit  121  via the interface and the data input/output unit  123 . The virtual currency data is sent from the main control unit  121  to the user terminal recording unit  124 , and is recorded in the user terminal recording unit  124  that is a part of the RAM  113  when viewed as hardware. The same user can naturally store a plurality of virtual currency data in his/her user terminal  100 . In this case, the plurality of virtual currency data is recorded in the user terminal recording unit  124 . 
     The user can use the virtual currency data preserved in the user terminal  100  for payment at any time. When the user wants to use the virtual currency data, the user operates the input device  102  of the user terminal  100  to input the purport. Such an input is input to the main control unit  121  via the interface  114  and the data input/output unit  123 . Upon receiving the input, the main control unit  121  reads, for example, all the virtual currency data from the user terminal recording unit  124 , and, based on the data, instructs the display control unit  122  to display the image as shown in  FIG. 13 . 
     As shown in  FIG. 13 , the plurality of virtual currency data is displayed on the display  101  so that one of them can be selected. The displays including the amount of money surrounded by a square frame correspond to the virtual currency data, respectively. As described above, the data of the virtual currency data is recorded with the encrypted virtual currency encryption data and the respective plaintext serial number information, amount information, and recipient information. Since the user terminal  100  can read plaintext information, the user terminal  100  can display information based on the information described in plaintext on the display  101 , as an image corresponding to each virtual currency data. In this embodiment, although not limited thereto, the amount of money specified by the amount information and the information on the recipient who can receive payment based on the recipient information are displayed on the display  101 . The virtual currency data, which is not displayed based on the recipient information, has no restriction on the recipient. Note that the image displayed on the display  101  can include all of the data described in plaintext, and, for example, may include serial number information. 
     The user operates the input device  102 , which is one of functions of the display  101 , to select virtual currency data used for payment. Such an input is input to the main control unit  121  as described above. Then, the display on the display  101  is switched as shown in  FIG. 14 . Under the control of the main control unit  121 , the display control unit  122  displays on the display  101  a display corresponding to the virtual currency data, and more specifically, a display obtained by converting the virtual currency data into a two-dimensional barcode. Information included in such a two-dimensional barcode needs to correspond to the virtual currency encryption data at a minimum, but, in this embodiment, is assumed to correspond to the entire virtual currency encryption data. 
     The user is a counterpart who makes payment, and delivers the virtual currency data from the user terminal  100  to the settlement terminal  300  managed by a clerk of a store, for example (S 915 ). 
     The virtual currency data is delivered by capturing the image of the two-dimensional barcode displayed on the display  101  of the user terminal  100  with a camera provided in the settlement terminal  300 . The captured image data is sent from the camera of the settlement terminal  300  to the data input/output unit  323  via the interface  314  and then sent from the data input/output unit  323  to the main control unit  321 . The main control unit  321  generates virtual currency encryption data from the two-dimensional barcode reflected in the image data. Thereby, the virtual currency data is delivered from the user terminal  100  to the settlement terminal  300  (S 931 ). 
     The virtual currency data is delivered from the user terminal  100  to the settlement terminal  300  by reading of the two-dimensional barcode in this embodiment, but the virtual currency data may be delivered using not only the two-dimensional barcode but also a one-dimensional barcode or another identifier. Furthermore, the virtual currency data is not required to be delivered from the user terminal  100  to the settlement terminal  300  by reading of such an identifier, and may be delivered by Bluetooth (trademark) or another communication. In an extreme case, the virtual currency data may be delivered in a manner that the user verbally tells to the administrator or the like of the settlement terminal  300  or the virtual currency data is displayed on the display  101  and shown to the administrator or the like of the settlement terminal  300 . In this case, the administrator or the like of the settlement terminal  300  may input the virtual currency data to the settlement terminal  300  by manually inputting the data using the input device, for example. 
     In any case, the main control unit  321  temporarily records the virtual currency data, for example, at least until payment due to the virtual currency data is completed. Such recording is performed on the RAM  313  as hardware. As described above, the settlement terminal  300  can read serial number information, amount information, and recipient information described in plaintext in the virtual currency data. Accordingly, the main control unit  321  can cause the display control unit  322  to display the information (shown in  FIG. 14 ), which is specified by these types of information, on the display. For example, the administrator or the like of the settlement terminal  300  can check the amount of payment to be expected by displaying the amount of money specified by the amount information, and can know whether the administrator is a person who can receive the payment by the information specified by the recipient information. When the payment is inappropriate, the administrator or the like of the settlement terminal  300  may receive other virtual currency data from the user. 
     When the virtual currency data received from the user is appropriate, the administrator or the like of the settlement terminal  300  operates the input device of the settlement terminal  300  to perform an operation for sending the virtual currency data to the settlement device  200 . 
     When such an operation is performed, the operation content is sent from the input device to the main control unit  321  via the data input/output unit  323 . When the operation content is input, the main control unit  321  sends data, which is obtained by imparting the settlement terminal ID to the virtual currency data, to the data input/output unit  323 . The data input/output unit  323  sends the data to the transmission and reception unit, and the transmission and reception unit sends the data to the settlement device  200  via the network  400  (S 932 ). At this time, at least virtual currency encryption data needs to be sent to the settlement device  200  together with the settlement terminal ID, but in this embodiment, the entire virtual currency data is sent to the settlement device  200  together with the settlement terminal ID. 
     The settlement device  200  receives the data of the settlement terminal ID and the virtual currency data at the transmission and reception unit (S 925 ). These data are sent to the main control unit  222  via the interface  214  and the data input/output unit  221 . 
     The main control unit  222 , which has received such data, sends the data of the settlement terminal ID and the virtual currency data to the decryption unit  225 . At this time, at least the virtual currency encryption data needs to be sent to the decryption unit  225  together with the settlement terminal ID, but the entire virtual currency data is sent to the decryption unit  225  together with the settlement terminal ID in this embodiment. 
     The decryption unit  225  decrypts the virtual currency encryption data (S 926 ). As described above, since the encryption unit  223 A performs the same encryption processing on all the virtual currency encryption data, the decryption unit  225  also performs the same decryption processing corresponding to the encryption processing. When the virtual currency encryption data is decrypted, the encrypted issuer information, amount information, and settlement condition information are returned in the form of plaintext. The decryption unit  225  sends the issuer information, the amount information, and the settlement condition information to the settlement determination unit  226  together with the data of the settlement terminal ID. 
     In this embodiment, due to the fact that the virtual currency encryption data can be decrypted by the decryption unit  225 , it is possible to temporarily determine that the virtual currency encryption data and the virtual currency data including the virtual currency encryption data are authentic. When the decryption of the virtual currency encryption data cannot be performed, information indicating the purport thereof is sent to the settlement determination unit  226  from the decryption unit  225 . 
     The settlement determination unit  226  receives the issuer information, the amount information, the settlement condition information, and the settlement terminal ID, or information indicating that the decryption of the virtual currency encryption data cannot be performed, from the decryption unit  225 . 
     Upon receiving the issuer information, the amount information, the settlement condition information, and the settlement terminal ID among the information, the settlement determination unit  226  executes a final determination (S 927 ). In a case of executing the final determination, the settlement determination unit  226  reads necessary data from the basic data recording unit  224 . 
     As described above, the issuer information includes the information for specifying the settlement device  200  that is the issuer of the virtual currency data. Since the same data is recorded in the basic data recording unit  224 , the settlement determination unit  226  reads the data from the basic data recording unit  224 , and compares with both data. When both data coincide with each other, the settlement determination unit  226  determines that the virtual currency encryption data is authentic. 
     As described above, the issuer information may include the authentication information that is issued by a person who has the authority to guarantee authenticity of the virtual currency data, for example, a government organization. When such data is used for authentication, since data for authentication also exists in the basic data recording unit  224 , the settlement determination unit  226  reads the data from the basic data recording unit  224 , and compares both data for authentication with each other. When both data for authentication coincide with each other, the settlement determination unit  226  determines that the virtual currency encryption data is authentic. 
     Similarly, the serial number information, the timing information, the amount information, the information included in the settlement condition information and the like may be used to determine the authenticity of the virtual currency encryption data, but when it can be determined that the virtual currency data is authentic depending on the determination of the authenticity of the virtual currency encryption data, the settlement determination unit  226  subsequently determines whether the condition specified by the settlement condition information is satisfied. However, since the confirmation that the virtual currency encryption data is authentic is actually performed by the fact that the virtual currency encryption data can be decrypted by the decryption unit  225 , the confirmation of the authenticity of the virtual currency encryption data may be omitted herein. 
     The determination as to whether the condition specified by the settlement condition information is satisfied is performed as follows, for example. 
     As described above, the settlement condition information may include the recipient information. The recipient information is information for restricting a person who can receive payment depending on the attribute of the recipient or the address of the recipient. The settlement determination unit  226  reads information, from the basic data recording unit  224 , on the attribute or the like associated with the settlement terminal ID received from the decryption unit  225 , and determines whether the attribute or the like associated with the settlement terminal ID satisfies the condition of a person who can receive payment specified by the recipient information included in the settlement condition information. When such a condition is satisfied, the settlement determination unit  226  temporarily determines that the condition specified by the settlement condition information is satisfied. 
     The settlement condition information may include the time information as described above. The time information is information for specifying a time when payment from the user to the administrator of the settlement terminal  300  is accepted. The time information may be described by an absolute date and time, for example, from 0:0 on Jul. 1, 2017 to 0:0 on Jul. 30, 2017, depending on the date and time. In such a case, the settlement determination unit  226  may receive information related to the date and time from a clock (not shown) provided in the settlement device  200 , and may determine whether the determination time satisfies a condition specified by the time information. When such a condition is satisfied, the settlement determination unit  226  temporarily determines that the condition specified by the settlement condition information is satisfied. On the other hand, the time information may be relatively determined based on a generation time of the virtual currency data, for example, payment is accepted within three months after the virtual currency data is generated or only within 10 days from one week after the virtual currency data is generated. In such a case, the settlement determination unit  226  is required to include the timing information in the decrypted issuer information, but may determine, based on the generation time of the virtual currency data specified by the timing information, whether the above-described condition is satisfied. When such a condition is satisfied, the settlement determination unit  226  temporarily determines that the condition specified by the settlement condition information is satisfied. 
     The settlement condition information also determines as to a case of information for changing the amount of money specified by the amount information using the same method whether the condition specified by the settlement condition information is satisfied. 
     Note that the settlement condition information is not limited to the above, and can include events that is determined in some cases after the virtual currency data is issued from the settlement device  200 , for example, payment is accepted only when the weather of the day at a certain place is sunny; payment is accepted only when a specific soccer team wins a specific game; and payment is accepted only when an average stock price in a certain stock market exceeds a certain price. In such a case, the settlement device  200  may search for information necessary for determining whether the settlement condition information is satisfied from an external device via the network  400 , and may supply the information to the settlement determination unit  226 . 
     In any case, when the settlement determination unit  226  determines that the settlement condition information (all of them in a plurality of cases) is satisfied, the settlement determination unit  226  generates final determination data indicating positive information that payment of the amount of money specified by the amount information is accepted. When the settlement condition information is information for changing the amount of money specified by the amount information, the payment amount to be accepted is the amount of money after the change. 
     On the other hand, in cases where: the settlement determination unit  226  receives, from the decryption unit  225 , the information indicating that the decryption of the virtual currency encryption data cannot be performed; the determination is not performed that the virtual currency encryption data is authentic; and the settlement determination unit  226  is not determined that settlement condition information (all of them in a plurality of cases) is satisfied, the settlement determination unit  226  generates final determination data indicating negative information that payment of the amount of money specified by the amount information is not accepted. 
     In any case, the generated final determination data is sent from the settlement determination unit  226  to the main control unit  222 . 
     The main control unit  222  receives the final determination data and performs the following processing. 
     When the final determination data is positive, the main control unit  222  executes a process of paying the amount of money specified by the final determination data to the administrator of the settlement terminal  300 . The settlement processing is a process of accepting the payment of the money to the settlement terminal  300  that has sent the virtual currency encryption data. In this embodiment, the main control unit  222  retains data indicating what kind of settlement has been made. For example, the main control unit  222  is configured to cause a recording medium (not shown) for each settlement terminal  300  to record information indicating how much payment is finally permitted to who (administrator or the like of which settlement terminal  300 ). These data is sent, for example, to the bank where the bank account specified by the administrator of the settlement terminal  300  exists, and as a result, payment is made to the administrator of the settlement terminal  300  from, for example, the administrator (or, from the bank account or the like specified by the user using the virtual currency data) of the settlement device  200 . 
     When the final determination data is positive, the main control unit  222  generates positive determination result data that is data including at least information on the fact that payment has been made and the amount of money. 
     On the other hand, when the final determination data is negative, the main control unit  222  does not perform the settlement processing. Further, the main control unit  222  generates negative determination result data that is data including at least information that payment has not been made. 
     In any case, the determination result data is sent from the main control unit  222  to the transmission and reception unit via the data input/output unit  221  and is transmitted to the settlement terminal  300  via the network  400  (S 928 ). 
     The determination result data is received by the transmission and reception unit of the settlement terminal  300  (S 933 ). 
     The determination result data received by the transmission and reception unit is sent to the main control unit  321  as in the previous cases. 
     The main control unit  321  instructs the display control unit  322  to display on the display according to the determination result data. As a result, the display control unit  322  causes the display to display according to the determination result data (S 934 ). Although not shown, the display will include, for example, the fact that the payment is accepted and the amount of money in the case where the determination result data is positive, and include the fact that the settlement is not accepted in the case where the determination result data is negative. In the latter case, the determination result data includes the information for specifying the reason why the settlement is not accepted, and thus the reason why the settlement is not accepted is desirably displayed on the display. 
     The determination result data can also be transmitted to the user terminal  100 , and the image based on the determination result data can be displayed on the display  101  even in the user terminal  100 . 
     Thus, the payment processing using the virtual currency data from the user to the administrator of the settlement terminal  300  is completed. 
     In the above description, the recipient of payment due to the virtual currency data using a certain user terminal  100  is only the administrator or the like of the settlement terminal  300 . However, a recipient of payment due to the virtual currency data using a certain user terminal  100  can be a user of another user terminal  100 . 
     In this case, the user terminal  100  owned by the user who receives the payment may have the same functional blocks as those of the settlement terminal  300  by installing the same computer program as that installed in the settlement terminal  300 . This is possible when the user terminal  100  is a smartphone including a computer. In addition, although the settlement terminal  300  is equipped with the camera as hardware, the user terminal  100  has a camera in common sense when being a smartphone, and thus the user terminal  100  also satisfies the conditions. In this case, the basic data recording unit  224  of the settlement device  200  will be required to be recorded with the data, which are equivalent to various data recorded in association with the settlement terminal ID of each settlement terminal  300 , in association with the user ID of each user terminal  100  within a range necessary for the settlement determination unit  226  to determine satisfiability of the settlement condition information when the settlement determination unit  226  determines whether the payment to each user can be performed. 
     In this embodiment, the virtual currency data is delivered from the user terminal  100  to the settlement terminal  300  without using the network  400 . However, regardless of whether such a delivery is a delivery of the virtual currency data from the user terminal  100  to the settlement terminal  300  or a delivery of the virtual currency data between the user terminals  100 , such a delivery may be realized by transmission/reception of the virtual currency data via the network  400  (in some cases, transmission/reception via the settlement device  200  to prevent double transfer of the virtual currency data). 
     In this embodiment, the settlement device  200  has both the function of issuing the virtual currency data and sending it to the outside and the function of receiving the virtual currency data and determining whether the settlement is permitted, but a virtual currency data issuing device and a virtual currency data settlement device can also be separated from each other, which have these functions, respectively. 
     In this case, both the former and the latter can be the same as the settlement device  200  already described as the hardware configuration; and regarding the functional block, the former may have a functional block having a function necessary until the virtual currency data is sent to the user terminal  100 , and the latter may have a functional block having a function necessary after that. 
     Modification Example 1 
     A settlement system according to Modification Example 1 is almost the same as the settlement system according to the first embodiment. In particular, the configuration of the user terminal  100  and the settlement terminal  300  and the process executed therein are no different from those in the first embodiment. Furthermore, the data structure of the virtual currency data is the same as that in the first embodiment. 
     The configuration of the settlement device  200  and the process executed therein are different from those in the first embodiment. Nevertheless, the configuration of the settlement device  200  according to Modification Example 1 and the process executed therein are mostly the same as those in the first embodiment. 
     In the settlement system of the first embodiment, the encryption method used by the encryption unit  223 A to generate the virtual currency encryption data included in each of the multiple virtual currency data is identically applied to all the cases of generating the virtual currency encryption data. On the other hand, in this modification example, a plurality of encryption methods are executed to obtain virtual currency encryption data. 
     Then, if the decryption unit  225  cannot known which of the plurality of encryption methods is used to encrypt the virtual currency encryption data when trying to decrypt a certain virtual currency encryption data, the decryption unit cannot perform the decryption processing. What makes this problem possible is the difference between the settlement device  200  of Modification Example 1 and the settlement device  200  of the first embodiment. 
     In this embodiment, the encryption performed by the encryption unit  223 A is different for each virtual currency encryption data, but is not limited thereto. Therefore, the decryption processing performed for each virtual currency encryption data by the decryption unit  225  is also different. There are three types of methods for changing the encryption and decryption methods: changing an algorithm, changing a key, and changing both of the algorithm and the key. All of three types can be adopted, but the method for changing the key is adopted in this embodiment. 
     Even in the settlement device  200  of Modification Example 1, as described in the first embodiment, a control unit  220  serving as a functional block is generated therein by execution of a computer program. As shown in  FIG. 15 , functional blocks generated in the control unit  220  in Modification Example 1 are substantially the same as those in the first embodiment, and the functions carried out by the same functional blocks are the same as those in the first embodiment except for the encryption unit  223 A and the decryption unit  225 . The functional blocks generated in the control unit  200  in Modification Example 1 include a key generating unit  227 , which is different from the first embodiment. 
     The key generating unit  227  generates a key used for encryption or decryption, and provides the key to the encryption unit  223 A and the decryption unit  225 . A method of generating the key and a timing for providing the key to the encryption unit  223 A and the decryption unit  225  will be described. 
     A timing at which the key generating unit  227  supplies the key to the encryption unit  223 A is a timing at which the encryption unit  223 A performs the encryption processing. As described above, when the data shown in  FIG. 12(A) , that is, the plaintext data including the issuer information, the amount information, and the settlement condition information is generated, the encryption unit  223 A transmits data for requesting the key generating unit  227  to generate a key. Upon receiving the data, the key generating unit  227  generates a key and sends data of the generated key to the encryption unit  223 A. The encryption unit  223 A obtains virtual currency encryption data by encrypting the data shown in  FIG. 12(A)  using an invariant algorithm and the provided key. 
     For example, the key generating unit  227  generates a key as follows. The key is generated as a “solution” in the following description, and is generated as an enumeration of at least one of alphabetic characters, numbers, and symbols. The solution can be, for example, a pseudo-random number sequence which is always the same under a certain condition and has initial value dependency. An example of the solution is a publicly known and well-known one-time password generation method in which one-time passwords are continuously generated from a certain initial value. 
     In order to generate the solution in this embodiment, a method of substituting a past solution into a predetermined function using a certain initial value (which may be two or more initial values) and thereby sequentially creating a new solution may be executed each time the solution is required. Thereby, the solution, which is the above “value”, can be continuously generated. Such a solution becomes a pseudo-random number having initial value dependency. 
     Examples of the function used for creating the above-described “solution” include the following (a) to (c). Each of the following (a) to (c) is an expression for creating X N  that is the N-th “solution”. Moreover, P, Q, R, and S are natural numbers. 
       ( X   N )=( X   N-1 ) P +( X   N-2 ) Q   (a)
 
       ( X   N )=( X   N-1 ) P   (b)
 
       ( X   N )=( X   N-1 ) P ( X   N-2 ) Q ( X   N-3 ) R ( X   N-4 ) S   (c)
 
     The expression (a) generates a new “solution” using past two “solutions” to add them raised to the P-th power and the Q-th power, respectively. It should be noted that, precisely, when the past two “values” are used and the values raised to the P-th power and the Q-th power are added, the number of digits increases, and thus the new “solution” is actually generated by extracting the appropriate number of digits from the beginning of an obtained value, extracting the appropriate number of digits from the end of the value, or extracting the appropriate number of digits from an appropriate portion of the value or the like. 
     The expression (b) has a new “solution” using one past “solution” to arrange the number of digits of the value raised to the P-th power as described above. 
     The expression (c) has a new “solution” using four past “solutions” to take the product of them raised to the P-th power, the Q-th power, the R-th power, and the S-th power, respectively, and then arranging the number of digits as described above. 
     The above-described (a) to (c) are an example of an algorithm for generating the solution, and a change can be added to the algorithm when the solution is generated, for example, a change can also be added in which the above-described (a) to (c) are used in rotation or the like. 
     If the solution is generated by such a method, a first solution generated based on a certain initial value is always the same, a second solution generated is also always the same, and similarly an N-th solution generated is also always the same. This is the initial value dependency. 
     Using the solution generated as described above as a key, the encryption unit  223 A encrypts the data shown in  FIG. 12(A) , and generates virtual currency encryption data. As in the case of the first embodiment, a combination unit  232 B adds several plaintext data to the virtual currency encryption data, and thus virtual currency data is generated. 
     Such virtual currency data is sent from the settlement device  200  to the user terminal  100  as in the case of the first embodiment. 
     A method of using the virtual currency data is the same as in the first embodiment. The virtual currency data is delivered from the user terminal  100  to the settlement terminal  300  and is sent from the settlement terminal  300  to the settlement device  200  together with a settlement terminal ID. 
     The virtual currency data is sent from the main control unit  222  to the decryption unit  225  together with the settlement terminal ID as in the case of the first embodiment. 
     Here, as in the case of the first embodiment, the decryption unit  225  decrypts virtual currency encryption data. However, for this purpose, the decryption unit  225  needs to obtain the key used when the encryption unit  223 A encrypts the virtual currency encryption data. Therefore, the decryption unit  225 , which has received the virtual currency data, sends data for requesting the key generating unit  227  to generate key data. Then, the decryption unit  225  attaches serial number information, which is included in the virtual currency data in a plaintext state, to the data. 
     As described above, the serial number information of this embodiment is a serial number of a multi-digit number starting from 1 represented in hexadecimal notation. In other words, the number specified by such serial number information indicates what number key is generated to be used in a case of encrypting the virtual currency encryption data to be decrypted. Therefore, the key generating unit  227  continuously performs arithmetic operations to obtain the number-th solution specified by the serial number information using mathematical expressions (a) to (c). As a result, the key generating unit  227  can generate the same solution as the key used in a case of encrypting the virtual currency encryption data to which the serial number information is attached. Then, the key generating unit  227  sends the key, which is the generated solution, to the decryption unit  225 . 
     Thus, the decryption unit  225  can perform the decryption processing using the key used when the encryption unit  223 A encrypts the virtual currency encryption data. That is, in Modification Example 1, the serial number information also serves as the encryption condition information as referred to in the present invention. 
     Note that the encryption condition information included in the virtual currency data may be in plaintext, or may be in an encrypted state. However, in a case of encryption of the encryption condition information, the encryption method is identically applied to the encryption condition information included all of the virtual currency data in practice. The reason is because, if the encryption condition information included in each virtual currency data is encrypted by different methods (for example, different keys), a decryption condition (encryption condition when the encrypted encryption condition information is encrypted) is required in a case of decrypting each type of encryption condition information. In the settlement device  200 , although not limited to this, the main control unit  222  encrypts the encryption condition information when the virtual currency data is generated and issued, and the main control unit  222  decrypts the encryption condition information when the settlement is performed. When the encryption method and the decryption method are the same, it is naturally possible for the same main control unit  222  to perform the encryption and the decryption. In Modification Example 1, the serial number information also serves as the encryption condition information, and when the serial number information is necessary to be kept in plaintext, it is necessary to prepare encryption condition information other than the serial number information as will be described below. Then, it is possible to keep the serial number information included in the virtual currency data in plaintext and to encrypt the encryption condition information included in the virtual currency data. 
     Subsequent processes are the same as those in the first embodiment. 
     In Modification Example 1, the serial number information is used as the encryption condition information as referred to in the present invention. That is, the serial number information, which is a part of the issuer information, is also used as the encryption condition information. 
     Alternatively, for example, the serial number information is not used as the encryption condition information (in this case, the serial number information need not be a serial number.), and information different from the serial number information can be included in the virtual currency data in a plaintext state or in an encrypted state. The data is data serial number data indicating what number key is generated by the key generating unit  227  to be used when the virtual currency encryption data is generated. 
     In addition, the combination unit  223 B adds the key itself used when the encryption unit  223 A performs the encryption processing to the virtual currency encryption data encrypted by the key, and thus the encryption condition information can also be included in the virtual currency data. Since such virtual currency data is attached with a key that can be used to decrypt the virtual currency encryption data included in the virtual currency data, there is a risk that the virtual currency encryption data is decrypted by a malicious third party. However, unless the algorithm used for encryption and decryption is known to the third party, the malicious third party cannot decrypt the virtual currency encryption data, and thus tentative safety can be maintained. When the encryption condition information is the key itself, the decryption unit  225  can perform decryption using the key, and thus the decryption unit  225  needs not to receive the key from the key generating unit  227  when performing the decryption processing. 
     Note that the encryption condition information does not depend on the above description. For example, the solution is determined by the date and time when the above-described solution is generated. In other words, when the key generating unit  227  uses an algorithm, which can always reproduce the solution later if a certain date is specified, to generate the solution, the encryption condition information can be information for specifying the date and time when the solution used by the encryption unit  223 A is generated by the key generating unit  227 . When the decryption unit  225  notifies the key generating unit  227  of the date and time, the key generating unit  227  can generate the same solution as the key used for the encryption by the encryption unit  223 A, and thus the decryption unit  225  receives the same key as the key used for the encryption by the encryption unit  223 A, from the key generating unit  227 . 
     Second Embodiment 
     A settlement system according to a second embodiment is almost the same as the settlement system according to the first embodiment. In particular, configurations of the user terminal  100  and the settlement terminal  300  and processes executed by it are no different from those in the first embodiment. Further, a data structure of virtual currency data is also basically the same as that in the first embodiment. The virtual currency data used in the settlement system according to the second embodiment also includes virtual currency encryption data, which is encrypted data, as in the case of the first embodiment, but, as will be described below, encryption processing performed on the virtual currency encryption data need not to include decryption, unlike the case of the first embodiment. For example, the encryption processing performed on the data shown in  FIG. 12(A)  to obtain virtual currency encryption data can be conversion such as taking a hash value. 
     The difference between the second embodiment and the first embodiment is a configuration of the settlement device  200  and a process executed by it. Nevertheless, the configuration of the settlement device  200  according to the second embodiment and the process executed by it are mostly the same as those in the case of the first embodiment. 
     Even in the settlement device  200  according to the second embodiment, as described in the first embodiment, a control unit  220  serving as a functional block is generated therein by execution of a computer program. As shown in  FIG. 16 , functional blocks generated in the control unit  200  of the second embodiment are substantially the same as those in the first embodiment, and the functions carried out by the same functional blocks are the same as those in the first embodiment except for some functions of the virtual currency data generating unit  223 . In addition, the functional blocks generated in the control unit  200  in the second embodiment include a second authentication unit  228  and a virtual currency data recording unit  228 A that are not included in the first embodiment, instead of the decryption unit  225  that is included in the first embodiment. This is a main difference between the first embodiment and the second embodiment. 
     The description will be made with respect to functions of the virtual currency data generating unit  223 , the second authentication unit  228 , and the virtual currency data recording unit  228 A in the settlement device  200  of the second embodiment and processes executed by the former two units. 
     First, the description will be made with respect to the virtual currency data generating unit  223 . The function of the virtual currency data generating unit  223  of the second embodiment and the process executed performed by it are almost the same as those in the first embodiment. The virtual currency data generating unit  223  includes an encryption unit  223 A and a combination unit  223 B as in the case of the first embodiment. The function of the combination unit  223 B and the process performed by it are the same as those in the first embodiment. 
     The function of the encryption unit  223 A of the second embodiment and the process performed by it are basically the same as those in the first embodiment, but the encryption processing performed by the encryption unit  223 A of the second embodiment may include decryption later, or may not include decryption. 
     As in the case of the first embodiment, the encryption unit  223 A encrypts the data shown in  FIG. 12(A)  to generate virtual currency encryption data. As in the case of the first embodiment, such virtual currency encryption data is sent to the combination unit  223 B, the combination unit  223 B adds the plaintext data described in the first embodiment to the virtual currency encryption data, and thus virtual currency data is generated. The virtual currency data generating unit  223  of the first embodiment sends the virtual currency data to the main control unit  222  in order for the settlement device  200  to perform a process of sending the virtual currency data from the settlement device  200  to the user terminal  100 , but the virtual currency data generating unit  223  of the second embodiment is configured to send the virtual currency data to the virtual currency data recording unit  228 A as well as the main control unit  222 . In this embodiment, the virtual currency data generating unit  223  sends not only the virtual currency data but also plaintext issuer information, plaintext amount information, and plaintext settlement condition information which are data shown in  FIG. 12(A)  and serving as the origin of the virtual currency encryption data included in the virtual currency data, to the virtual currency data recording unit  228 A. 
     The received virtual currency data is recorded in the virtual currency data recording unit  228 A in association with the received plaintext issuer information, amount information, and settlement condition information which serve as the origin of the virtual currency encryption data included in the virtual currency data. Since such a process is repeatedly performed, the virtual currency data recording unit  228 A is typically recorded with a plurality of sets of data formed by, in pairs, the virtual currency data with the plaintext issuer information, amount information, and settlement condition information which serve as the origin of the virtual currency encryption data included in the virtual currency data. 
     The virtual currency data sent to the main control unit  222  is sent from the settlement device  200  to the user terminal  100  as in the case of the first embodiment. 
     A method of using such virtual currency data is the same as that in the first embodiment, and the virtual currency data is delivered from the user terminal  100  to the settlement terminal  300  and is sent from the settlement terminal  300  to the settlement device  200  together with a settlement terminal ID. 
     The virtual currency data is sent from the main control unit  222  to the second authentication unit  228  together with the settlement terminal ID as in the case of the first embodiment. 
     The second authentication unit  228  has a function of confirming whether the received virtual currency data is authentic, or more specifically, whether the virtual currency encryption data included in the received virtual currency data is authentic. This confirmation is actually performed, in the first embodiment, by the fact that the virtual currency encryption data can be decrypted by the decryption unit  225 , but the second authentication unit  228  performs the confirmation with a different method. 
     The second authentication unit  228 , which has received the virtual currency data from the main control unit  222 , searches for the data recorded in the virtual currency data recording unit  228 A, determines that the virtual currency encryption data received from the main control unit  222  is authentic when the same virtual currency data as the virtual currency data received from the main control unit  222  is recorded in the virtual currency data recording unit  228 A, and determines that the virtual currency encryption data received from the main control unit  222  is not authentic when the same virtual currency data as the virtual currency data received from the main control unit  222  is not recorded in the virtual currency data recording unit  228 A. In a case of using such a determination method, it is preferable to perform an appropriate way, for example, to increase the number of characters (the number of digits) of the virtual currency data so as to avoid duplication in a large number of pieces of virtual currency data generated by a large number of requests from a large number of user terminals  100 . Out of the virtual currency data recorded in the virtual currency data recording unit  228 A, the data read from the second authentication unit  228  is preferably erased from the virtual currency data recording unit  228 A after the payment to the administrator of the settlement terminal  300  using the corresponding virtual currency data is completed, for example. 
     When determining that the virtual currency data received from the main control unit  222  is authentic, the second authentication unit  228  reads the issuer information, the amount information, and the settlement condition information which are recorded in the virtual currency data recording unit  228 A in a state of being associated with the same virtual currency data as the virtual currency data received from the main control unit  222 . In this state, the second authentication unit  228  has the issuer information, the amount information, and the settlement condition information. These types of the issuer information, the amount information, and the settlement condition information are data serving as the origin of the virtual currency encryption data when the second authentication unit  228  encrypts the virtual currency encryption data included in the virtual currency data received from the main control unit  222 . That is, the state in which the second authentication unit  228  has the issuer information, the amount information, and settlement conditions is the same as the state in which the decryption unit  225  decrypts the virtual currency encryption data included in the virtual currency data received from the main control unit  222  in the first embodiment. 
     That is, all subsequent processes can be made the same as those in the first embodiment, and thus these processes are applied to the second embodiment. According to the first embodiment, the decryption unit  225  sends the issuer information, the plaintext amount information, and the plaintext settlement condition information that are all returned to plaintext to the settlement determination unit  226  together with the data of the settlement terminal ID, but according to the second embodiment, the second authentication unit  228  sends all of the plaintext issuer information, the plaintext amount information, and the plaintext settlement condition information to the settlement determination unit  226  together with the data of the settlement terminal ID. On the other hand, according to the first embodiment, when the virtual currency encryption data cannot be decrypted, the information indicating the purport thereof is sent from the decryption unit  225  to the settlement determination unit  226 , but according to the second embodiment, when the same virtual currency data as the virtual currency data sent from the main control unit  222  to the second authentication unit  228  does not exist in the virtual currency data recording unit  228 A, the information, which has the same meaning as the information indicating that the decryption cannot be performed in the first embodiment and indicates that the same virtual currency data does not exist in the virtual currency data recording unit  228 A, is sent to the settlement determination unit  226 . 
     The subsequent description will not be made. 
     In the description of the second embodiment, the second authentication unit  228  determines the authenticity of the virtual currency encryption data out of the virtual currency data sent from the main control unit  222  depending on whether the same virtual currency data as the virtual currency data sent from the main control unit  222  exists in the virtual currency data recording unit  228 A. 
     However, such a determination can be made only with respect to the virtual currency encryption data without depending on the entire virtual currency data. Therefore, the main control unit  222  may send only the virtual currency encryption data instead of the entire virtual currency data to the second authentication unit  228  together with the settlement terminal ID. In this case, the virtual currency data generating unit  223  records the virtual currency encryption data instead of the virtual currency data in the virtual currency data recording unit  228 A in association with the plaintext issuer information, the plaintext amount information, and the plaintext settlement condition information. Then, the second authentication unit  228  determines the authenticity of the virtual currency encryption data out of the virtual currency data sent from the main control unit  222  depending on whether the same virtual currency encryption data as the virtual currency encryption data sent from the main control unit  222  exists in the virtual currency data recording unit  228 A. 
     Third Embodiment 
     A settlement system according to a third embodiment is almost the same as the settlement system according to the first embodiment. In particular, configurations of the user terminal  100  and the settlement terminal  300  and processes executed by it are no different from those in the first embodiment. Further, a data structure of virtual currency data is also basically the same as that in the first embodiment. The virtual currency data used in the settlement system according to the third embodiment also includes virtual currency encryption data, which is encrypted data, as in the case of the first embodiment, but, as will be described below, encryption processing performed on the virtual currency encryption data need not to include decryption, unlike the case of the first embodiment. For example, the encryption processing performed on the data shown in  FIG. 12(A)  to obtain virtual currency encryption data can be conversion such as taking a hash value as in the case of the second embodiment. 
     The difference between the third embodiment and the first embodiment is a configuration of the settlement device  200  and a process executed by it. Nevertheless, the configuration of the settlement device  200  according to the third embodiment and the process executed by it are mostly the same as those in the case of the first embodiment. 
     Even in the settlement device  200  according to the third embodiment, as described in the first embodiment, a control unit  220  serving as a functional block is generated therein by execution of a computer program. As shown in  FIG. 17 , functional blocks generated in the control unit  200  of the third embodiment are substantially the same as those in the first embodiment, and the functions carried out by the same functional blocks are the same as those in the first embodiment except for some functions of the virtual currency data generating unit  223 . In addition, the functional blocks generated in the control unit  200  in the third embodiment include a third authentication unit  229  and a plaintext data recording unit  229 A that are not included in the first embodiment, instead of the decryption unit  225  that is included in the first embodiment. 
     The description will be made with respect to functions of the virtual currency data generating unit  223 , the third authentication unit  229 , and the plaintext data recording unit  229 A in the settlement device  200  of the third embodiment and processes executed by the former two units. 
     First, the description will be made with respect to the virtual currency data generating unit  223 . The function of the virtual currency data generating unit  223  of the third embodiment and the process executed performed by it are almost the same as those in the first embodiment. The virtual currency data generating unit  223  includes an encryption unit  223 A and a combination unit  223 B as in the case of the first embodiment. The function of the combination unit  223 B and the process performed by it are the same as those in the first embodiment. 
     In the first embodiment, the virtual currency data generating unit  223  first generates the data which has the data structure as shown in  FIG. 12(A)  and includes the issuer information, the amount information, and the settlement condition information. As in the first embodiment, such data is encrypted by the encryption unit  223 A and converted into virtual currency encryption data. The function of the encryption unit  223 A of the third embodiment and the process performed by it are basically the same as those in the first embodiment, but the encryption processing performed by the encryption unit  223 A of the third embodiment may include decryption later, or may not include decryption. As in the case of the first embodiment, the virtual currency encryption data is sent to the combination unit  223 B, the combination unit  223 B adds the plaintext data described in the first embodiment to the virtual currency encryption data, and thus virtual currency data is generated. The virtual currency data generating unit  223  of the first embodiment sends the virtual currency data to the main control unit  222  in order for the settlement device  200  to perform a process of sending the virtual currency data from the settlement device  200  to the user terminal  100 , but the same applies to third embodiment. 
     On the other hand, according to the third embodiment, the data shown in  FIG. 12(A)  is sent from the virtual currency data generating unit  223  to the plaintext data recording unit  229 A and recorded in the plaintext data recording unit  229 A. Since such a process is repeatedly performed, the plaintext data recording unit  229 A is typically recorded with a large number of pieces of data formed by the issuer information, the amount information, and the settlement condition information which are associated with each other. 
     The virtual currency data sent to the main control unit  222  is sent from the settlement device  200  to the user terminal  100  as in the case of the first embodiment. 
     A method of using such virtual currency data is the same as that in the first embodiment, and the virtual currency data is delivered from the user terminal  100  to the settlement terminal  300  and is sent from the settlement terminal  300  to the settlement device  200  together with a settlement terminal ID. 
     The virtual currency data is sent from the main control unit  222  to the third authentication unit  229  together with the settlement terminal ID as in the case of the first embodiment. 
     The third authentication unit  229  has a function of confirming whether the received virtual currency data is authentic, or more specifically, whether the virtual currency encryption data included in the received virtual currency data is authentic. This confirmation is actually performed, in the first embodiment, by the fact that the virtual currency encryption data can be decrypted by the decryption unit  225 , but the third authentication unit  229  performs the confirmation with a different method. 
     The third authentication unit  229 , which has received the virtual currency data from the main control unit  222 , first extracts the serial number information included in the virtual currency data in a form of plaintext. Then, when the issuer information including the serial number information is searched from the data recorded in the plaintext data recording unit  229 A and such issuer information is found, the issuer information and the amount information and the settlement condition information associated with the issuer information are read from the plaintext data recording unit  229 A. 
     When the serial number information included in the virtual currency data received from the main control unit  222  cannot be found from the data recorded in the plaintext data recording unit  229 A, the main control unit  222  does not perform reading of the issuer information and the like. 
     When the issuer information and the like are read, the third authentication unit  229  sends the plaintext issuer information, amount information, and settlement condition information read from the plaintext data recording unit  229 A, to the virtual currency data generating unit  223 , and requests the encryption unit  223 A to encrypt these types of information. The encryption unit  223 A encrypts the requested information and converts it into virtual currency encryption data. The virtual currency encryption data newly created by the virtual currency data generating unit  223  is sent from the virtual currency data generating unit  223  to the third authentication unit  229 . 
     Then, the third authentication unit  229  compares the virtual currency encryption data included in the virtual currency data sent from the main control unit  222  with the virtual currency encryption data newly created by the virtual currency data generating unit  223  in response to the request of the third authentication unit  229 . The third authentication unit  229  determines that the virtual currency encryption data received from the main control unit  222  is authentic when both data coincide with each other as a result of comparison, and determines that the virtual currency encryption data received from the main control unit  222  is not authentic when both data do not coincide with each other. Even when the serial number information included in the virtual currency data received from the main control unit  222  is not found from the data recorded in the plaintext data recording unit  229 A, the third authentication unit  229  determines that the virtual currency encryption data received from the main control unit  222  is not authentic. As in the case of the first embodiment, the encryption of the encryption unit  223 A is always performed by the same method in the third embodiment. If there no falsification of the virtual currency encryption data, which is sent from the main control unit  222 , by a malicious third party, since the virtual currency encryption data included in the virtual currency data sent from the main control unit  222  coincides with the virtual currency encryption data newly created by the virtual currency data generating unit  223  in response to the request of the third authentication unit  229 , the authenticity of the virtual currency encryption data included in the virtual currency data sent from the main control unit  222  can be determined depending on whether the two pieces of virtual currency encryption data coincide with each other. In the case of such a determination, out of the issuer information, the amount information, the settlement condition information associated with each other and recorded in the plaintext data recording unit  229 A, the information read from the third authentication unit  229  is preferably erased from the plaintext data recording unit  229 A after the payment to the administrator or the like of the settlement terminal  300  using the corresponding virtual currency data is completed, for example. 
     When the third authentication unit  229  determines that the virtual currency data received from the main control unit  222  is authentic, the third authentication unit  229  is in a state of having the issuer information, the amount information, and the settlement condition information which are read from the plaintext data recording unit  229 A and associated with each other. These types of the issuer information, the amount information, and the settlement condition information are data serving as the origin of the virtual currency encryption data when the third authentication unit  229  encrypts the virtual currency encryption data included in the virtual currency data received from the main control unit  222 . That is, the state in which the third authentication unit  229  has the issuer information, the amount information, and settlement conditions is the same as the state in which the decryption unit  225  decrypts the virtual currency encryption data included in the virtual currency data received from the main control unit  222  in the first embodiment. 
     That is, as in the case of the second embodiment, all subsequent processes can be made the same as those in the first embodiment, and thus these processes are applied to the third embodiment. As in the case of the first embodiment, according to the third embodiment, the third authentication unit  229  sends all of the plaintext issuer information, the plaintext amount information, and the plaintext settlement condition information to the settlement determination unit  226  together with the data of the settlement terminal ID. On the other hand, according to the first embodiment, when the virtual currency encryption data cannot be decrypted, the information indicating the purport thereof is sent from the decryption unit  225  to the settlement determination unit  226 , but according to the third embodiment, when it is determined that the virtual currency encryption data included in the virtual currency data sent from the main control unit  222  to the third authentication unit  229  is not authentic, the information, which has the same meaning as the information indicating that the decryption cannot be performed in the first embodiment and indicates the determination that the virtual currency encryption data included in the virtual currency data sent from the main control unit  222  is not authentic, is sent to the settlement determination unit  226 . 
     The subsequent description will not be made. 
     In the third embodiment, the same issuer information, amount information, and settlement condition information as the issuer information, amount information, and settlement condition information serving as the origin of the virtual currency encryption data included in the virtual currency data provided to the user terminal  100  are re-encrypted, and the authenticity of the virtual currency encryption data included in the virtual currency data provided to the user terminal  100  is determined depending on whether the virtual currency encryption data obtained by re-encryption coincides with the virtual currency encryption data included in the virtual currency data provided to the user terminal  100 . 
     In order to make this possible, the virtual currency encryption data, which is a determination target of the authenticity and included in the virtual currency data sent from the settlement terminal  300 , needs to be decided from the issuer information, the amount information, and the settlement condition information that are recorded in the plaintext data recording unit  229 A of the settlement terminal  300  and associated with each other. In the above example, this can be made by using the serial number information as a query, but is not necessarily realized by the serial number information. Each virtual currency data includes identification information that is obtained by encrypting a set of issuer information, amount information, and settlement condition information or respective types of information and is in one-to-one correspondence with the virtual currency encryption data included in the virtual currency data and provided to the user terminal  100 , the identification information is recorded in the plaintext data recording unit  229 A in association with the issuer information, the amount information, and the settlement condition information which are associated with each other, and thus such identification information can be used as a search query. 
     Modification Example 2 
     A settlement system according to Modification Example 2 is almost the same as the settlement system according to the third embodiment. The relation between the settlement system of Modification Example 2 and the settlement system of the third embodiment is the same as the relation between the settlement system of Modification Example 1 and the settlement system of the first embodiment. 
     In the settlement system of the first embodiment, the encryption method using the encryption unit  223 A to generate the virtual currency encryption data included in each of the multiple virtual currency data is identically applied to all the cases of generating the virtual currency encryption data. On the other hand, in Modification Example 1, a plurality of encryption methods are executed to obtain virtual currency encryption data. 
     Similarly, in the settlement system of the third embodiment, the encryption method using the encryption unit  223 A to generate the virtual currency encryption data included in each of the multiple virtual currency data is identically applied to all the cases of generating the virtual currency encryption data. On the other hand, in Modification Example 2, a plurality of encryption methods are executed to obtain virtual currency encryption data. 
     Then, when the encryption unit  223 A in Modification Example 2 performs re-encryption of the issuer information, the amount information, and the condition information recorded in the plaintext data recording unit  229 A, which will be described below, as in Modification Example 1, if the encryption unit  223 A cannot know which of the plurality of encryption methods is used to encrypt the virtual currency encryption data for which authenticity is to be determined by the third authentication unit  229 , decryption processing cannot be performed. In order to perform the decryption processing, a key generating unit  227  is also provided in a settlement device  200  of Modification Example 2 as in the settlement device  200  of the Modification Example 1 ( FIG. 18 ). 
     In Modification Example 2, the encryption unit  223 A is configured to receive a key necessary for encryption from a key generating unit  227  even in a case of creating the virtual currency encryption data included in the virtual currency data provided to the user terminal  100  by encryption of the data formed by the issuer information, the amount information, and the settlement condition information shown in  FIG. 12(A)  and even in a case of creating the virtual currency encryption data used by the third authentication unit  229  to determine the authenticity of the virtual currency encryption data included in the virtual currency data sent from the settlement terminal  300  to the settlement device  200  by encryption of the data formed by the issuer information, the amount information, and the settlement condition information provided from the third authentication unit  229 . 
     In order to enable the key generating unit  227  to generate the key used in both cases, for example, the serial number information may be used as the encryption condition information as in the case of Modification Example 1. Alternatively, as described in Modification Example 1, information other than the serial number information can be used as the encryption condition information. As described in Modification Example 1, the encryption condition information may also be encrypted in plaintext.