A method and system for dual offline transactions of digital currency coins

Abstract

The present invention discloses a method and system for double-offline transaction of digital currency coins. The method comprises the following steps: the central bank digital currency system issues digital currency coins to the remitting user; the remitting user and the receiving terminal conduct double-offline transactions through the digital currency coins; the central bank digital currency system is used to confirm the transactions. Beneficial effects: The present invention designs digital currency equipped with private keys, enabling a method for double-offline transaction of digital currency coins; the present invention protects the identity information of the remitting party from being exposed; in the present invention, since the transactions adopt the form of digital currency coins, the operation process of the interaction between people and transaction terminals in existing digital currency transactions is avoided, and the transaction speed is extremely fast; the transaction process in the present invention supports not only double-offline transactions, but also transactions where the remitting party is online and the receiving party is offline, transactions where the remitting party is offline and the receiving party is online, and transactions where the remitting party is online and the receiving party is online.

Description

Technical Field

[0001] The present invention relates to the field of digital currency, and particularly to a method and system for double-offline transaction of digital currency coins. Background Art

[0002] The core elements of the digital currency D-RMB system of the People's Bank of China are one kind of currency, two types of libraries and three centers. One kind of currency, namely "D-RMB" (DC / EP), abbreviated as D currency, specifically refers to a string of encrypted digital strings signed by the central bank and representing a specific amount. Two types of libraries: the issuance library of D-RMB and the bank library (central bank digital currency database, commercial bank digital currency database). Digital currency in the issuance library is manifested as the central bank's digital currency fund; digital currency in the bank library is manifested as the commercial bank's inventory digital cash. Three centers: one is the registration center (recording the whole process of currency generation, circulation, counting and verification, and extinction); the other two are authentication centers, namely the CA authentication center (based on the PKI system, centrally managing the certificates of institutions and users, such as CFCA) and the IBC authentication center [i.e., the authentication center established based on identity-based cryptography (Identity-Based Cryptograph)]. Two tables can be designed in the registration center. One is the digital currency ownership registration form, recording the ownership of digital currency, and the other is the transaction record form.

[0003] The D-RMB system is a hierarchical system, jointly built by the central bank and each commercial bank. The central bank digital currency system is a computer system operated and maintained by the central bank or an institution designated by the central bank to process information about digital currency. Its main functions include being responsible for the issuance and verification monitoring of digital currency. The commercial bank digital currency system is a computer system operated and maintained by a commercial bank or an institution designated by the commercial bank to process information about digital currency. It performs various functions related to currency of existing banks, that is, bank functions, mainly including after applying for digital currency from the central bank, being responsible for directly facing the society and meeting various requirements for providing digital currency circulation services.

[0004] Patent CN201911053809 proposes an anonymous transaction method and system based on digital currency. However, there are some problems with this method and system: it can only conduct online transactions. The temporary identity of the user can only proceed with the subsequent transaction process if it is recognized by its own server. When the user cannot communicate with its own server, the payee of this method cannot use the user's temporary identity to verify the digital signature of the transaction (in the digital signature based on digital certificates, since the user needs to hide their real identity, they cannot provide a digital certificate containing their real identity, and cannot prove the association between their temporary identity and the digital certificate. Therefore, they cannot use the digital certificate to verify the digital signature of the transaction; in the digital signature based on ID cryptography, since the user needs to hide their real identity, they cannot provide their real identity, and cannot prove the association between their temporary identity and the real identity. Therefore, they cannot use the real identity to verify the digital signature of the transaction). Therefore, without receiving any identity credentials from the payer, the payee cannot recognize the legality of this transaction and complete the entire transaction process.

[0005] Based on the above analysis, the existing technologies of digital currency communication systems have the following defects:

[0006] 1. Most of the existing digital currency transaction methods based on digital certificates or user IDs expose the user's identity and transaction details;

[0007] 2. The existing anonymous digital currency transaction methods based on digital certificates or user IDs can guarantee the anonymous identity of users but cannot conduct anonymous transactions where both the payer and the payee are offline (i.e., double offline);

[0008] 3. The existing digital currency transactions require scanning codes or NFC communication, involving many operations that interact with people, resulting in slow transactions and inconvenience in certain scenarios (such as the scenario of queuing for payment in public transportation, etc.). Summary of the Invention

[0009] In view of the problems in the related technologies, the present invention proposes a double offline transaction method and system for digital currency coins to overcome the above-mentioned technical problems existing in the related technologies.

[0010] To this end, the specific technical solutions adopted by the present invention are as follows:

[0011] According to an aspect of the present invention, a double offline transaction method for digital currency coins is provided. The method includes the following steps:

[0012] S1. Preparation stage: The central bank digital currency system issues digital currency coins to the paying user;

[0013] S2. Double offline transaction stage: The paying user and the receiving terminal conduct a double offline transaction through the digital currency coins;

[0014] S3. Online trading stage: Use the central bank digital currency system to confirm the transaction;

[0015] Among them, the steps for the central bank digital currency system to issue digital currency coins to the remitting user in S1 are as follows:

[0016] S11. The remitting user withdraws the preset currency, digital currency or online banking balance, and requests to exchange for a digital currency coin from the remitting commercial bank.

[0017] S12. The digital currency coin generates a pair of public and private keys, and sends the public key to the remitting commercial bank. At the same time, the remitting commercial bank forwards the public key to the central bank digital currency system.

[0018] S13. The central bank digital currency system generates digital currency of a specified currency value according to the public key and the currency value, and sends it to the remitting commercial bank. The remitting commercial bank stores the digital currency in the digital currency coin and cannot be withdrawn, and then the remitting commercial bank issues the digital currency coin to the remitting user.

[0019] Furthermore, the steps for the remitting user and the receiving terminal to conduct a dual-offline transaction through the digital currency coin in S2 are as follows:

[0020] S21. The digital currency coin verifies the identity information of the receiving terminal.

[0021] S22. The digital currency coin sends the transaction to the receiving terminal.

[0022] S23. The receiving terminal receives the transaction of the digital currency coin.

[0023] Furthermore, the specific steps for the digital currency coin to verify the identity information of the receiving terminal in S21 are as follows:

[0024] S211. The remitting user puts the digital currency coin into the coin slot of the receiving terminal. The digital currency coin requests to verify the identity information of the receiving terminal. The receiving terminal obtains the first timestamp, and forms the first combined information with the receiving party's identity, signs it to obtain the first signature information, and then sends the receiving party's identity, the first timestamp and the first signature information to the digital currency coin. If the signature needs to be verified with a digital certificate, the message sent to the digital currency coin also includes the digital certificate.

[0025] After the digital currency coin receives the payee's identity, the first timestamp, and the first signature information, it confirms that the first timestamp is the current time and verifies the first signature information. If the identity verification is successful, the subsequent steps are carried out. If the identity verification fails, the digital currency coin prompts a transaction failure, and the sender user retrieves the digital currency coin, and no subsequent steps are performed.

[0026] Further, the specific steps for the digital currency coin to send a transaction to the payee terminal in S22 are as follows:

[0027] The digital currency coin extracts the data structure of the digital currency coin and obtains a second timestamp, and forms a transaction by combining the second timestamp, the payee's identity, and the data structure of the digital currency coin. It signs the transaction with the private key corresponding to the digital currency coin to obtain the second signature information, and sends the transaction and the second signature information to the payee terminal in a short distance.

[0028] Further, the method of sending the transaction and the second signature information to the payee terminal in a short distance is sending in plaintext or sending after encrypting with the public key of the payee terminal. If it is encrypted and sent, the payee decrypts it with the corresponding private key after receiving it.

[0029] Further, the specific steps for the payee terminal to receive the transaction of the digital currency coin in S23 are as follows:

[0030] S231. After the payee terminal receives the transaction and the second signature information, it extracts the public key corresponding to the digital currency coin and verifies the second signature information. If the verification is successful, it verifies the data structure of the digital currency coin. If the verification is successful, it trusts the transaction. The payee terminal signs the message confirming the transaction with the private key corresponding to the payee terminal to obtain the third signature information, and then sends the message confirming the transaction and the third signature information to the digital currency coin;

[0031] S232. After the digital currency coin receives the message confirming the transaction, it marks the data structure of the digital currency coin as used but unconfirmed.

[0032] Further, the specific steps for using the central bank digital currency system to confirm a transaction in S3 are as follows:

[0033] S31. The payee terminal sends the transaction to the central bank digital currency system;

[0034] S32. The central bank digital currency system confirms the transaction message.

[0035] Further, the specific steps for the payee terminal to send a transaction to the central bank digital currency system in S31 are as follows:

[0036] The receiving terminal encrypts the confirmed transaction with the public key corresponding to the receiving party's commercial bank to obtain the first ciphertext, signs the first ciphertext to obtain the fourth signature information, and at the same time sends the first ciphertext and the fourth signature information to the receiving party's commercial bank. The receiving party's commercial bank verifies the fourth signature information. If the verification passes, it decrypts to obtain the transaction, encrypts the transaction with the public key corresponding to the central bank digital currency system to obtain the second ciphertext, signs the second ciphertext to obtain the fifth signature information, and sends the second ciphertext and the fifth signature information to the central bank digital currency system.

[0037] Further, the specific steps for the central bank digital currency system to confirm the transaction message in S32 are as follows:

[0038] S321. After receiving the second ciphertext and the fifth signature information, the central bank digital currency system verifies the fifth signature information. If the verification passes, it decrypts to obtain the transaction. The central bank digital currency system records the transaction and generates a central bank confirmation message. At the same time, it encrypts the transaction and the central bank confirmation message to obtain the third ciphertext, signs the third ciphertext to obtain the sixth signature information, and sends the third ciphertext and the sixth signature information to the remitting party's commercial bank. The remitting party's commercial bank decrypts to obtain the transaction and the central bank confirmation message after verifying the sixth signature information and records the transaction.

[0039] S322. The central bank digital currency system generates a data structure for a new digital currency coin, that is, changes the encrypted information of the owner of the digital currency in the data structure of the digital currency coin from the remitting user to the receiving terminal, includes the data structure of the new digital currency coin in the new central bank confirmation message, encrypts the new central bank confirmation message to obtain the fourth ciphertext at the same time, signs the fourth ciphertext with the private key corresponding to the central bank to obtain the seventh signature information, and sends the fourth ciphertext and the seventh signature information to the receiving party's commercial bank together.

[0040] S323. After verifying the seventh signature information, the receiving party's commercial bank decrypts to obtain the new central bank confirmation message, encrypts and signs the new central bank confirmation message to obtain the eighth signature information and the fifth ciphertext at the same time, and sends the eighth signature information and the fifth ciphertext to the receiving terminal. After verifying the eighth signature information, the receiving terminal decrypts to obtain the new central bank confirmation message, encrypts and signs the new central bank confirmation message to obtain the ninth signature information and the sixth ciphertext at the same time, and sends the ninth signature information and the sixth ciphertext to the digital currency coin.

[0041] S324. After verifying the ninth signature information, the digital currency coin decrypts to obtain the new central bank confirmation message and stores it. After the transaction is completed, the digital currency coin belongs to the receiving terminal.

[0042] According to another aspect of the present invention, a digital currency coin dual-offline transaction system is provided. The system includes a central bank digital currency system, a commercial bank digital currency system, and users, and the users hold corresponding user terminals;

[0043] The user terminal includes a remitting user and a receiving terminal. The receiving terminal is equipped with a digital currency coin transaction machine, and the digital currency coin transaction machine can communicate closely with the digital currency coin; the commercial bank digital currency system includes a remitting commercial bank and a receiving commercial bank. The remitting commercial bank corresponds to the remitting user, and the receiving commercial bank corresponds to the receiving terminal;

[0044] Among them, the central bank digital currency system is used to generate and issue digital currency, and conduct ownership registration of digital currency; the commercial bank digital currency system is used to perform banking functions for digital currency; users are the main body of digital currency use, and users can conduct digital currency transactions by holding terminals; the digital currency coin is a hardware security module, and inside is a key card or an RFID card,

[0045] and the digital currency coin includes a digital currency coin ID, a face value, a random number, encrypted information of the owner of the digital currency, and a central bank signature.

[0046] The beneficial effects of the present invention are as follows:

[0047] 1. The present invention designs digital currency with a private key, and can realize a digital currency coin dual-offline transaction method;

[0048] 2. The present invention protects the identity information of the remitting party and prevents it from being exposed;

[0049] 3. In the transaction of the present invention, because the form of digital currency coin is adopted, the operation process of the interaction between people and the transaction terminal in the existing digital currency transaction is avoided, and the transaction speed is extremely fast.

[0050] 4. The transaction process in the present invention supports not only dual-offline transactions, but also transactions where the remitting party is online and the receiving party is offline, transactions where the remitting party is offline and the receiving party is online, and transactions where the remitting party is online and the receiving party is online, that is, this process supports all types of transactions. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is a flowchart of the dual-offline transaction of digital currency coins in the embodiment of the present invention;

[0052] Figure 2 It is a basic structure diagram of the central bank digital currency system in the embodiment of the present invention;

[0053] Figure 3 It is a structure diagram of the data structure of the digital currency coin HM in the embodiment of the present invention. Detailed implementation manners

[0054] To further illustrate each embodiment, the present invention provides accompanying drawings. These drawings are part of the disclosure of the present invention, mainly used to illustrate the embodiments, and can cooperate with the relevant descriptions in the specification to explain the operation principle of the embodiments. With reference to these contents, those of ordinary skill in the art should be able to understand other possible implementation manners and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are usually used to represent similar components.

[0055] According to an embodiment of the present invention, a method and system for double-offline transaction of digital currency coins are provided.

[0056] Now, with reference to the accompanying drawings and specific implementation manners, the present invention will be further described. According to an embodiment of the present invention, as Figure 1 shown, a method for double-offline transaction of digital currency coins is provided, and the method includes the following steps:

[0057] S1. Preparation stage: The central bank digital currency system issues digital currency coins to the remitting user;

[0058] Among them, the central bank digital currency system issuing digital currency coins to the remitting user in S1 includes the following steps:

[0059] PT (remitting user) withdraws a certain amount of currency, digital currency or online banking balance, and requests to exchange for a digital currency coin from PS (remitting party commercial bank); the digital currency coin generates a set of public and private keys PK HM / SK HM , sends the public key PK HM to PS, PS forwards PK HM to SS (central bank digital currency system), SS generates a digital currency of a specified currency value according to the public key and the currency value and sends it to PS, PS stores the digital currency in HM (digital currency coin) and cannot be withdrawn, and then PS issues HM to PT.

[0060] S2. Double-offline transaction stage: The remitting user and the receiving terminal conduct a double-offline transaction through the digital currency coin;

[0061] Among them, the double-offline transaction between the remitting user and the receiving terminal through the digital currency coin in S2 specifically includes the following steps:

[0062] HM sends a transaction:

[0063] The PT puts the HM into the coin slot of the CT (collection terminal), and the HM requests to verify the identity information of the CT. The CT obtains the current timestamp T1 (the first timestamp), combines it with its own identity IDCT to form IDCT||T1 (the first combined information), signs it to get SIG CT (the first signature information), and then sends IDCT||T1||SIG CT to the HM. If a digital certificate is required for signature verification, the message also includes the digital certificate.

[0064] After receiving IDCT||T1||SIG CT , the HM confirms that the timestamp T1 is the current time and verifies the signature SIG CT (for example, verify it according to the digital certificate and mathematical signature of the CT using RSA and ECC algorithms, or verify it according to the ID and mathematical signature of the CT using the theory of ID-based cryptography). If the identity verification is successful, proceed to the subsequent steps; if the identity verification fails, the HM prompts that the transaction fails, the PT retrieves the HM, and no subsequent steps are taken.

[0065] The HM takes out the HMD (data structure of the digital currency coin), obtains the current timestamp T2 (the second timestamp), and combines T2, the payee identity IDCT, and the HMD to form TX (the transaction), that is, TX = {T2||IDCT||HMD}. Sign TX with the private key SK HM corresponding to the HM to get TXS (the second signature information), and send TX||TXS to the CT at close range (send it in plain text or encrypt it with the public key of the CT, and if it is encrypted, the CT decrypts it with the corresponding private key after receiving it).

[0066] The collection terminal CT receives the transaction:

[0067] After receiving the message, the CT gets TX||TXS. The CT takes out the public key PK HM corresponding to the HM, verifies the signature TXS, and after successful verification, verifies the HMD, such as verifying the central bank signature and verifying whether the currency value is equal to the transaction amount. If the verification is successful, trust the transaction. The CT signs the message RET CT with its own private key to get SIG' CT (the third signature information), and then sends RET_CT||SIG' CT to the HM.

[0068] After the HM confirms the message, it marks the HMD as used but unconfirmed and cannot be used for another transaction

[0069] S3. Online transaction stage: Use the central bank digital currency system to confirm the transaction.

[0070] Among them, using the central bank digital currency system to confirm transactions specifically includes the following steps:

[0071] The payee CT sends a transaction:

[0072] CT encrypts the previously confirmed transaction TX with the public key of CS to obtain a ciphertext (the first ciphertext), then signs the ciphertext and sends the ciphertext and the signature (the fourth signature information) to CS (the payee's commercial bank). CS verifies the signature, decrypts to obtain TX upon successful verification, encrypts TX with the public key of SS, then signs the ciphertext (the second ciphertext) (the fifth signature information) and sends the ciphertext and the signature to SS.

[0073] The central bank SS sends a confirmation message:

[0074] After receiving the message, SS verifies the signature and decrypts to obtain TX upon successful verification. SS records TX, generates a confirmation message RET SS (Central bank confirmation message), encrypts TX and RET SS to obtain a ciphertext (the third ciphertext), signs the ciphertext (the sixth signature information) and sends the ciphertext and the signature together to PS. After PS verifies the signature, it decrypts to obtain TX and RET SS , and records TX.

[0075] SS generates a new data structure HMD' of HM, mainly changing the information of the digital currency owner in EM included in the original HMD from PT to CT, that is, changing IDPS||{IDPT}EMR in EM to IDCS||{IDCT}EMR. Include HMD' in the new confirmation message RET' SS inside, encrypt RET' SS to obtain a ciphertext (the fourth ciphertext), sign the ciphertext with the private key (the seventh signature information) and send the ciphertext and the signature together to CS.

[0076] After CS verifies the signature, it decrypts to obtain the confirmation message RET' SS , and similarly encrypts (the fifth ciphertext) and signs (the eighth signature information) RET' SS and sends it to CT. After CT verifies the signature, it decrypts to obtain the confirmation message RET' SS , and similarly encrypts and signs RET' SS and sends it to HM.

[0077] After HM verifies the signature, it decrypts to obtain RET' SS , extracts HMD' from it and stores it. After the transaction is completed, HM belongs to CT.

[0078] According to another aspect of the present invention, a digital currency coin dual-offline trading system is provided. As Figure 2 shown, taking the operation example of central bank digital currency, the basic structure of the digital currency system mainly includes the central bank digital currency system, commercial bank digital currency systems (which can be multiple commercial bank digital currency systems in practice), and users. Among them, the central bank digital currency system is used to generate and issue digital currency, and conduct ownership registration of digital currency; the commercial bank digital currency system is used to perform banking functions for digital currency; users are the main body of digital currency use. In the present invention, users hold terminals to conduct digital currency transactions.

[0079] The system of the present invention includes the central bank (i.e., the central bank digital currency system) SS, the remitting user PT and the corresponding commercial bank of PT (i.e., the commercial bank digital currency system) PS, the receiving terminal CT and the corresponding commercial bank CS of CT. Their corresponding IDs are IDSS, IDPT, IDPS, IDCT, and IDCS respectively. The digital currency coin is a hardware security module, inside which is a key card or an RFID card, and the key information therein cannot be taken out. CT has a digital currency coin trading machine and can communicate with the digital currency coin at a short distance.

[0080] The data structure of the digital currency coin HM is called HMD, as Figure 3 shown: including IDHM, currency value, random number PMR, encrypted information EM of the owner of the digital currency, and central bank signature. Among them, the random number EMR is encrypted with the central bank public key PK_SS to obtain {EMR}PK_SS, the IDPT is encrypted with EMR and combined with IDPS to obtain IDPS||{IDPT}EMR, and then it is combined with {EMR}PK_SS to be EM, that is, EM = {EMR}PK_SS||IDPS||{IDPT}EMR.

[0081] In summary, the present invention designs a digital currency equipped with a private key, which can realize a digital currency coin dual-offline trading method; the present invention protects the identity information of the remitting party and prevents it from being exposed; the transaction in the present invention adopts the form of digital currency coin, avoiding the operation process of the interaction between people and transaction terminals in the existing digital currency transactions, and the transaction speed is extremely fast. The transaction process in the present invention supports not only dual-offline transactions, but also transactions where the remitting party is online and the receiving party is offline, transactions where the remitting party is offline and the receiving party is online, and transactions where the remitting party is online and the receiving party is online, that is, this process supports all types of transactions.

[0082] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in this specification.

[0083] The above-described embodiments merely represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A method for dual-offline transactions of digital currency coins, characterized in that, The method includes the following steps: S1. Preparation stage: The central bank digital currency system issues digital currency coins to the remitting user; S2. Dual-offline transaction stage: A dual-offline transaction is conducted between the remitting user and the receiving terminal through digital currency coins; S3. Online transaction stage: The central bank digital currency system is used to confirm the transaction; Among them, the central bank digital currency system issuing digital currency coins to the remitting user in S1 includes the following steps: S11. The remitting user withdraws the preset currency, digital currency or online banking balance, and requests to exchange for a digital currency coin from the remitting commercial bank; S12. The digital currency coin generates a pair of public and private keys, and sends the public key to the remitting commercial bank, and at the same time, the remitting commercial bank forwards the public key to the central bank digital currency system; S13. The central bank digital currency system generates digital currency of a specified currency value according to the public key and the currency value and sends it to the remitting commercial bank. The remitting commercial bank stores the digital currency in the digital currency coin and cannot be withdrawn. The remitting commercial bank then issues the digital currency coin to the remitting user; The central bank digital currency system confirming the transaction in S3 includes the following steps: S31. The receiving terminal sends the transaction to the central bank digital currency system; S32. The central bank digital currency system confirms the transaction message; The receiving terminal sending the transaction to the central bank digital currency system in S31 specifically includes the following steps: The receiving terminal encrypts the confirmed transaction with the public key corresponding to the receiving commercial bank to obtain the first ciphertext, signs the first ciphertext to obtain the fourth signature information, and at the same time sends the first ciphertext and the fourth signature information to the receiving commercial bank. The receiving commercial bank verifies the fourth signature information. If the verification passes, it decrypts to obtain the transaction, encrypts the transaction with the public key corresponding to the central bank digital currency system to obtain the second ciphertext, signs the second ciphertext to obtain the fifth signature information, and sends the second ciphertext and the fifth signature information to the central bank digital currency system; The central bank digital currency system confirming the transaction message in S32 specifically includes the following steps: S321. After receiving the second ciphertext and the fifth signature information, the central bank digital currency system verifies the fifth signature information. If the verification passes, it decrypts to obtain the transaction. The central bank digital currency system records the transaction and generates a central bank confirmation message. At the same time, it encrypts the transaction and the central bank confirmation message to obtain the third ciphertext, signs the third ciphertext to obtain the sixth signature information, and sends the third ciphertext and the sixth signature information together to the remitting commercial bank. The remitting commercial bank decrypts to obtain the transaction and the central bank confirmation message after verifying the sixth signature information and records the transaction; S322. The central bank digital currency system generates the data structure of a new digital currency coin, that is, encrypts the information of the owner of the digital currency in the data structure of the digital currency coin to change it from the remitting user to the receiving terminal, includes the data structure of the new digital currency coin in the new central bank confirmation message, and encrypts the new central bank confirmation message to obtain the fourth ciphertext. Signs the fourth ciphertext with the private key corresponding to the central bank to obtain the seventh signature information, and sends the fourth ciphertext and the seventh signature information to the receiving commercial bank together; S323. After verifying the seventh signature information, the receiving commercial bank decrypts it to obtain the new central bank confirmation message, encrypts and signs the new central bank confirmation message in the same way to obtain the eighth signature information and the fifth ciphertext, and sends the eighth signature information and the fifth ciphertext to the receiving terminal. After verifying the eighth signature information, the receiving terminal decrypts it to obtain the new central bank confirmation message, encrypts and signs the new central bank confirmation message in the same way to obtain the ninth signature information and the sixth ciphertext, and sends the ninth signature information and the sixth ciphertext to the digital currency coin; S324. After verifying the ninth signature information, the digital currency coin decrypts it to obtain the new central bank confirmation message and stores it. After the transaction is completed, the digital currency coin belongs to the receiving terminal.

2. The method for dual-offline transaction of digital currency coins according to claim 1, wherein The double-offline transaction between the remitting user and the receiving terminal in S2 includes the following steps: S21. The digital currency coin verifies the identity information of the receiving terminal; S22. The digital currency coin sends a transaction to the receiving terminal; S23. The receiving terminal receives the transaction of the digital currency coin.

3. The digital currency coin dual-offline trading method according to claim 2, wherein The specific steps for the digital currency coin to verify the identity information of the receiving terminal in S21 are as follows: S211. The remitting user puts the digital currency coin into the coin slot of the receiving terminal. The digital currency coin requests to verify the identity information of the receiving terminal. The receiving terminal obtains the first timestamp, forms the first combined information with the receiving party's identity, signs it to obtain the first signature information, and then sends the receiving party's identity, the first timestamp, and the first signature information to the digital currency coin. If a digital certificate is required for signature verification, the message sent to the digital currency coin also carries the digital certificate; S212. After receiving the receiving party's identity, the first timestamp, and the first signature information, the digital currency coin confirms that the first timestamp is the current time and verifies the first signature information. If the identity verification is successful, the subsequent steps are carried out. If the identity verification fails, the digital currency coin prompts that the transaction fails, and the remitting user retrieves the digital currency coin and no subsequent steps are carried out.

4. The digital currency coin dual-offline trading method according to claim 2, wherein, The specific steps for the digital currency coin to send a transaction to the receiving terminal in S22 are as follows: The digital currency coin extracts the data structure of the digital currency coin and obtains the second timestamp, forms a transaction with the second timestamp, the receiving party's identity, and the data structure of the digital currency coin, signs the transaction with the private key corresponding to the digital currency coin to obtain the second signature information, and sends the transaction and the second signature information to the receiving terminal in a short distance.

5. The method for dual-offline transaction of digital currency coins according to claim 4, wherein, The way to send the transaction and the second signature information to the receiving terminal in close proximity is to send it in plain text or to encrypt it with the public key of the receiving terminal. If it is encrypted and sent, the recipient decrypts it with the corresponding private key after receiving it.

6. The method for double off-line transactions of digital currency coins according to claim 2, wherein The specific steps for the receiving terminal to receive the digital currency coin transaction in S23 are as follows: S231. After the receiving terminal receives the transaction and the second signature information, it extracts the public key corresponding to the digital currency coin and verifies the second signature information. If the verification is successful, it verifies the data structure of the digital currency coin. If the verification is successful, it trusts the transaction. The receiving terminal signs the message confirming the transaction with the private key corresponding to the receiving terminal to obtain the third signature information, and then sends the message confirming the transaction and the third signature information to the digital currency coin. S232. After the digital currency coin receives the message confirming the transaction, it marks the data structure of the digital currency coin as used but unconfirmed.

7. A digital currency coin dual-offline trading system for implementing the method steps of the digital currency coin dual-offline trading described in claims 1-6, characterized in that, The system includes a central bank digital currency system, a commercial bank digital currency system, and users, and the users hold corresponding user terminals. The user terminal includes a remitting user and a receiving terminal. The receiving terminal is equipped with a digital currency coin transaction machine, and the digital currency coin transaction machine can communicate with the digital currency coin in close proximity. The commercial bank digital currency system includes a remitting commercial bank and a receiving commercial bank. The remitting commercial bank corresponds to the remitting user, and the receiving commercial bank corresponds to the receiving terminal. Among them, the central bank digital currency system is used to generate and issue digital currency and register the ownership of digital currency. The commercial bank digital currency system is used to perform banking functions for digital currency; users are the main body of digital currency use, and users can conduct digital currency transactions by holding terminals; the digital currency coin is a hardware security module, and inside is a key card or an RFID card. And the digital currency coin includes a digital currency coin ID, a currency value, a random number, encrypted information of the owner of the digital currency, and a central bank signature.

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