CN113689282A

CN113689282A - Block chain-based entity asset mortgage lending method

Info

Publication number: CN113689282A
Application number: CN202110847400.6A
Authority: CN
Inventors: 万志国; 刘小童
Original assignee: Zhejiang Lab
Current assignee: Zhejiang Lab
Priority date: 2021-07-27
Filing date: 2021-07-27
Publication date: 2021-11-23

Abstract

The invention provides a block chain-based entity mortgage lending method, which allows a user to use entity assets as mortgages, and a borrower directly interacts with a protocol to pay floating interest rate. The method has the advantages that the method can be used for taking the interest at any time without an early period or a so-called commission fee, the interest amount is still more or less after borrowing for a long time, the interest rate floats in real time according to the market, no black screen exists, and the fairness of the transaction is ensured. After the mortgage object changes the mortgage state, the borrower can borrow the digital currency from the platform, so that the problem of 'double flowers' is prevented; the invention adopts zero knowledge proof for proving and verifying related parameters in the transaction process, can well hide account balance, entity asset information and other relatively sensitive data of users of all parties, and the use and storage of the zero knowledge balance is verified through the zero knowledge proof, and the new zero knowledge balance is used for replacing the old zero knowledge balance, thereby protecting the personal privacy of the users.

Description

Block chain-based entity asset mortgage lending method

Technical Field

The invention relates to the field of block chain finance, in particular to a block chain-based physical asset mortgage lending method.

Background

With the continuous development of blockchain technology, the borrowing protocol based on blockchain is gradually improved, and the mortgage digital currency borrowing is a new mode in the financial field. The deca (decentralized finance) is distributed finance or decentralized finance, and compared with the traditional highly centralized finance system, the decentralized finance directly connects two transaction parties through a block chain technology to perform financial transactions, such as transfer, financing, currency exchange, loan, mortgage and the like, so that the optimization of financial service efficiency and cost is realized.

The blockchain is the bottom layer technology of digital currency, realizes the transaction record which is going to the center and can not be tampered through a distributed consensus mechanism, and can further realize complex and compulsory transaction through scripts or intelligent contracts. The block chain discloses transparent natural characteristics, so that the block chain has a plurality of limitations on the problems of privacy protection and data security, and relatively sensitive data such as account balance of each party and entity asset information can be well hidden by applying cryptography technologies such as Zero Knowledge Proof (Zero Knowledge Proof) in a block chain system, so that the personal privacy of a user is protected.

In addition, intelligent contracts can be realized by taking the block chains as the bottom layer technology. The intelligent contract is an automatic forced execution program, is not restricted by a third party, and can be executed once in sequence once the intelligent contract is triggered, so that fairness, justness and openness are ensured, and theoretically, any service can be provided for a user. The key point of decentralized finance lies in that code trust is constructed through a block chain technology and an intelligent contract, people are helped to realize decentralized transactions and point-to-point transfer, transaction programs are simplified, and transaction cost is reduced.

The existing Defi mortgage loan protocol is a financial service mainly based on digital currency, such as Compound, Aave, Dydx and other protocols, while the mortgage loan mode of physical assets, such as physical asset mortgage, automobile mortgage and the like, still adopts the traditional centralized financial loan system, the mortgage flow is complex, the cost is quite high, and the transaction fairness is difficult to guarantee. Therefore, the entity asset mortgage lending platform is designed, the role of the middle person such as a third-party organization and an intermediary is removed through the combination of the block chain technology and an intelligent contract, and meanwhile, the zero-knowledge proof technology is applied to protect the personal privacy of a user, so that the important significance and the huge application value are achieved.

Interpretation of terms:

a hash function: a one-way, collision-free function, y ═ h (x), from which y can be quickly calculated; but given x, y cannot be efficiently calculated. A typical hash function is SHA256, the output of which is 256 bits.

Digital signature: only the sender of the information can generate a digital string which can not be forged by others, and the digital string is also a valid proof for the authenticity of the transmitted information. A correctly implemented digital signature is more difficult to forge than a handwritten type. In addition, some non-repudiation digital signature schemes can provide a timestamp to ensure the validity of the signature even if the private key is compromised.

Merkel tree: a typical binary tree structure consists of a root node, a set of intermediate nodes, and a set of leaf nodes. All encrypted data in a given recording period form a Mercker tree, the first leaf node of the Mercker tree stores the Mercker accumulated root of the previous recording period, each remaining leaf node corresponds to one piece of encrypted data in the previous recording period, and each non-leaf node of the Mercker tree obtains the value of each non-leaf node by accumulating and hashing two children of each non-leaf node, and finally forms the Mercker tree.

Decentralized exchange: a smart contract that allows a user to purchase, sell, or trade cryptocurrency or digital currency. The remarkable characteristic is that the operation system is not as large as a centralized exchange, and all transactions and operations are carried out through intelligent contracts.

LToken, LToken: erc20 and Ether, and the conversion formula is LToken basic assets/current exchange rate. LToken has two roles in the loan platform, as a measure of interest and as a collateral for loans. Unlike traditional bank computing, interest rates are growing in the form of a profit. LToken is used as a metrology in loan platforms.

zk-SNARK technology: a zero knowledge proof system, the acronym zk-SNARK stands for "zero knowledge concise non-interactive proof of knowledge" that allows one party (prover) to prove a statement to the other party (verifier) that is authentic without revealing any additional information. For example, for published y, by zk-SNARK one can prove that he knows x that satisfies y ═ h (x) without leaking x.

Zero knowledge balance/amount: a hidden balance/amount represented using a hash value, consisting of: and H (addr, balance, sn), wherein addr is an account address, balance is a plaintext amount value corresponding to the cmut, sn is a serial number uniquely corresponding to the cmut, and sn publishes that the cmut has been spent. The use and deposit of a zero knowledge balance must be verified by zero knowledge proof, replacing the old zero knowledge balance with a new zero knowledge balance. Once the zero knowledge balance is updated, the serial number sn of the old balance is published.

A flowing pool: a digital currency pool is established in the smart contract to facilitate transactions by providing liquidity.

And (3) fluidity investment: the method is a process for obtaining income by the fact that a DeFi product with an investment mechanism deposits or withdraws specified digital currency assets according to requirements and provides liquidity for a capital pool of the product. The benefit may be the project's native digital currency, or the governance rights it represents.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a block chain-based entity mortgage lending method, which adopts an intelligent contract technology and simultaneously applies cryptography technologies such as zero knowledge proof and the like to realize the decentralization of financial services of entity assets and has the characteristics of real-time property, non-tamper property and market interest rate. The scheme removes a centralized organization bank, and in addition, the mortgage process has no threshold and no time limitation and can be carried out anytime and anywhere, so that a large amount of intermediate cost is saved, and the efficiency is greatly improved.

In order to achieve the purpose, the invention provides the following technical scheme:

the application discloses a block chain-based entity asset mortgage lending method, which specifically comprises the following steps:

s1, the borrower applies for mortgage, the trusted entity asset register organization inquires the state of the borrower entity asset: the method comprises the steps of checking whether a borrower is a real owner of the entity asset and whether the entity asset is mortgage or not;

s2, the credible entity asset registration mechanism uses a third-party credible evaluation mechanism to evaluate the value of the price of the entity asset, and the third-party credible evaluation mechanism is used for providing price data of the entity asset when the loan is generated;

s3, the trusted entity asset registration mechanism obtains a hash value through hash operation on the plaintext information and carries out digital signature; the verifier can determine that the plaintext information is not tampered by verifying the digital signature; the plaintext information comprises physical assets and borrower information;

s4, the lender performs lending operation through the intelligent contract of the platform, wherein the lending operation comprises transfer, fund injection, fund withdrawal and deposit;

s5, the borrower determines the amount of the assets to be borrowed according to the value of the entity assets evaluated by the third-party credible evaluation institution, and borrowing operation is carried out through the intelligent contract of the platform; the borrowing operation comprises mortgage authentication, borrowing and repayment;

s6, the trusted entity asset registration mechanism executes the following operations: after the borrower borrows money, the mortgage state of the entity assets is changed into 'mortgage already'; after the borrower repays, the mortgage state of the entity assets is changed into 'not mortgaged';

s7, if the outstanding loan value of the borrower exceeds the loan capability, the liquidation is triggered, the physical assets mortgage by the borrower are auctioned according to the current market price minus the liquidation discount, the liquidation obtains the physical assets mortgage by the borrower, and the information of the related physical assets is changed by the credible physical asset register mechanism; the borrower receives the residual assets after the mortgage entity assets subtract the debt and the settlement discount;

s8, if liquidity is provided for the asset pool of the platform, the platform awards the governance digital currency with voting governance rights;

preferably, the operation of step S3 is as follows:

s31, the trusted entity asset registration mechanism obtains a hash value through hash operation on plaintext information, and the digital signature is obtained through signature on the hash value by using a private key of a signer;

s32, the sender obtains a hash value through hash operation on the digital signature and the plaintext information and sends the hash value to the verifier;

and S33, comparing the hash value obtained by the verifier by verifying the digital signature through the public key of the signer with the received hash value, and determining that the plaintext information is not tampered if the hash value is consistent with the received hash value.

Preferably, the lending operation in step S4 adopts corresponding zero-knowledge proof for proving and verifying relevant parameters in the transaction process, and hiding key information, and canceling the association relationship between each party in the transaction process, and specifically includes the following sub-steps:

s41, transferring:

s411, the lender transfers a piece of private fund for lending from the private balance of the lender and forms a private fund pool together with the private funds of other lenders;

s412, the lender generates a transfer zero knowledge proof, and the privacy balance before transfer, the transferred privacy fund and the transferred privacy balance after transfer are proved through parameters;

s413, the lender sends the public parameters and the transfer zero knowledge certificate to a blockchain system, the blockchain nodes verify the correctness of the transfer zero knowledge certificate by using the public parameters, records the transaction in the blockchain system, and updates the privacy balance of the lender;

s42, funding:

s421, creating a pseudonymous account by the lender, wherein the pseudonymous account combines all the private funds in the private fund pool into a funded Mercker tree, and leaf nodes on the funded Mercker tree correspond to different private funds;

s422, generating a funding zero-knowledge proof by the pseudonym account, and proving that the private fund for lending of the lender exists in the Mercker tree through parameters;

s423, the pseudonym account sends the public parameter and the funding zero knowledge proof to the block chain system, and the block chain node uses the public parameter to verify the correctness of the funding zero knowledge proof;

s424, transferring the plaintext fund corresponding to the private fund of the lender to the platform by the pseudonym account, recording that the pseudonym account has the corresponding number of LToken by an intelligent contract of the platform, and increasing the corresponding amount of money by the platform fund pool;

s43, withdrawing resources:

s431, calculating extractable funds by using the pseudonymous account by the lender according to the corresponding LToken recorded by the intelligent contract of the platform, generating withdrawal private funds corresponding to the extractable funds, and putting the withdrawal private funds into a private fund pool; the extractable fund is the sum of the loan principal and the interest;

s432, the pseudonymous account forms all the privacy funds in the privacy fund pool into a resource-withdrawing Mercker tree;

s433, generating a fund withdrawal zero knowledge proof by the pseudonymous account, and proving that the fund withdrawal privacy fund exists in the fund withdrawal Mercker tree through parameters;

s434, the pseudonymous account sends the public parameters and the fund withdrawal zero knowledge certificate to a blockchain system, the blockchain nodes of the blockchain nodes verify the correctness of the fund withdrawal zero knowledge certificate by using the public parameters, the transaction is recorded on the blockchain, and the platform fund pool is updated after the verification of the intelligent contract of the platform is passed;

s44, deposit:

s441, the lender generates a deposit zero knowledge proof, and the privacy balance before deposit, the retrieved privacy fund and the privacy balance after deposit are proved through parameters;

s442, the lender sends the public parameters and the deposit zero knowledge certificate to the blockchain system, the blockchain nodes of the blockchain nodes verify the correctness of the deposit zero knowledge certificate by using the public parameters, the transaction is recorded in the blockchain system, and the privacy balance of the lender is updated.

Preferably, the lending operation in step S5 adopts corresponding zero-knowledge proof for proving and verifying relevant parameters in the transaction process, and hiding key information, and canceling the association relationship between each party in the transaction process, and specifically includes the following sub-steps:

s51, mortgage authentication:

s511, the trusted entity asset registration mechanism checks the state of the entity asset of the borrower, generates an asset state zero-knowledge proof, and proves that the asset state of the borrower is not mortgage through the parameters;

s512, a trusted entity asset registration mechanism registers and signs entity assets;

s513, the trusted entity asset registration mechanism carries out value evaluation on the assets to generate a value evaluation zero knowledge proof, and the current market value of the assets is proved through parameters without revealing the specific conditions of the assets;

s514, the trusted entity asset registration mechanism carries out value signature on the value evaluation of the asset;

s52, borrowing:

s521, the borrower creates a pseudonymous account, the pseudonymous account determines the borrowing amount according to the value of the credible entity asset registration mechanism on the entity asset evaluation and the platform mortgage coefficient, private funds corresponding to the borrowing amount are generated, and the borrower forms the borrowing Mercker tree by the private funds and the private funds transferred by other lenders;

s522, generating a borrowing zero-knowledge proof by the pseudonymous account, and proving that the privacy fund exists in the borrowed Mercker tree through parameters;

s523, the pseudonym account sends the public parameters, the borrowing zero knowledge proof, the registration signature and the value signature to the block chain system, the block chain nodes verify the correctness of the borrowing zero knowledge proof by using the public parameters, the transaction is recorded in the block chain system, the platform transfers the borrowing to the pseudonym account, and the platform general ledger is updated;

s524, the borrower extracts the corresponding private fund on the borrowed Merck tree to an account, generates an extracted zero knowledge proof, and proves the original zero knowledge amount, the borrowed zero knowledge amount and the operated zero knowledge balance through parameters;

s525, the borrower sends the public parameters and the extracted zero knowledge certificate to the blockchain system, the blockchain nodes verify the correctness of the extracted zero knowledge certificate by using the public parameters, records the transaction in the blockchain system, and updates the zero knowledge balance of the borrower;

s53, repayment:

s531, the borrower uses the pseudonymous account to deduct the corresponding private fund to be returned from the private balance, wherein the private fund to be returned is the sum of the debit principal and interest of the pseudonymous account recorded by the platform;

s532, the borrower generates a repayment zero knowledge proof, and the original privacy balance, the privacy fund to be restored transferred into the privacy fund pool and the operated privacy balance are proved through parameters;

s533, the borrower sends the public parameter and the repayment zero knowledge certificate to the blockchain system, the blockchain nodes verify the correctness of the repayment zero knowledge certificate by using the public parameter, records the transaction in the blockchain system, and updates the privacy balance of the borrower;

s534, the pseudonymous account forms all the privacy funds in the privacy fund pool into a Mercker tree, generates a zero-knowledge ending certificate, and verifies that the privacy funds exist in the Mercker tree after being withdrawn through parameters;

and S535, the pseudonym account sends the public parameter and the ending zero knowledge certificate to the blockchain system, the blockchain node verifies the correctness of the ending zero knowledge certificate by using the public parameter, so that the pseudonym account returns the fund to the platform, the platform deletes the borrowing item corresponding to the pseudonym account, and the repayment operation is completed.

The invention has the beneficial effects that:

1. the invention allows a user to use physical assets as mortgages, and borrowers interact directly with the agreement to pay floating interest rates. The method has the advantages that the method can be used for taking the interest at any time, the early charge is avoided, the handling fee is avoided, the interest is more or less after being borrowed for a long time, the interest rate floats in real time according to the market, no black screen is provided, and the fairness of the transaction is ensured.

2. After the mortgage object changes the mortgage state, the borrower can borrow the digital currency from the platform, so that the problem of 'double flowers' is prevented.

3. The invention realizes decentralization through the block chain technology and the intelligent contract, does not need a third party transaction platform, and has simple transaction process and low transaction cost.

4. According to the invention, the user and entity asset information is subjected to Hash processing to generate corresponding signatures, so that the privacy of borrowers and mortgages in the mortgage process is well protected, and the information cannot be tampered in the transmission process and cannot be revealed to a third party.

5. The invention adopts zero knowledge proof for proving and verifying related parameters in the transaction process, can well hide account balance, entity asset information and other relatively sensitive data of users of all parties, and the use and storage of the zero knowledge balance is verified through the zero knowledge proof, and the new zero knowledge balance is used for replacing the old zero knowledge balance, thereby protecting the personal privacy of the users.

6. The interest of the loan is put in real time, the loan is paid in real time, and the one-to-one loan matching problem does not exist.

7. The clearing mechanism of the invention can avoid the unrelieved borrowing money and ensure the rights and interests of lenders. Once the bad account is found through the monitoring contract, the clearing program is triggered, the clearing person starts clearing immediately, the platform is prevented from being debt and bad account, the repayment capability of the system is maintained, meanwhile, the clearing person obtains the benefit of the clearing person, and the platform operates normally and stably.

8. The governing digital currency has the characteristics of no pre-digging and no pre-selling, and the only way for obtaining the governing digital currency is to provide liquidity for the asset pool to obtain the governing digital currency, so the distribution is fair, the governing digital currency belongs to chips controlled by communities, and the enthusiasm and the participation degree of the communities are ensured.

The features and advantages of the present invention will be described in detail by embodiments in conjunction with the accompanying drawings.

Drawings

FIG. 1 is a schematic diagram illustrating a general flow of a block chain-based physical asset mortgage lending method according to an embodiment of the invention;

FIG. 2 is a schematic view showing the operation of the lender in making and withdrawing a deposit;

FIG. 3 is a diagram of a relationship demonstrated by lender transfer operations

FIG. 4 is a diagram of the relationship demonstrated by the lender funding operation

FIG. 5 is a diagram of the relationship demonstrated by the lender funding operation

FIG. 6 is a diagram of the relationship demonstrated by the lender's deposit operation

FIG. 7 is a schematic view of a flow chart of a mortgage loan operation of a borrower;

FIG. 8 is a diagram of a relationship certified by physical mortgage certification of a borrower;

FIGS. 9 and 10 are graphs illustrating relationships demonstrated by the borrower borrowing operation;

FIGS. 11 and 12 are graphs illustrating relationships demonstrated by the borrower payment operation;

FIG. 13 is a flow diagram of a clearing mechanism;

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood, however, that the description herein of specific embodiments is only intended to illustrate the invention and not to limit the scope of the invention. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present invention.

The block chain-based entity asset mortgage lending method comprises the following steps:

step one, a borrower applies for mortgage, and a trusted entity asset registration mechanism inquires the status of entity assets through middleware (interface API): and checking whether the borrower is the real owner of the physical asset and whether the physical asset is mortgage.

And step two, the credible entity asset registration mechanism uses a third-party credible evaluation mechanism to evaluate the value of the entity asset price and provides entity asset price data when the loan is generated.

And step three, the trusted entity asset registration mechanism obtains a hash value and signs the hash value by performing hash operation on the entity asset and borrower information (plaintext) by adopting a digital signature technology. The verifier can determine that the plaintext information has not been tampered by verifying the digital signature.

And step four, before lending, the lender needs to take out the lending fund from the account balance of the lender and transfer the lending fund to the intelligent contract. The lender can withdraw money at any time with his own interest, and the lender will receive his original deposit and interest, which is accumulated from the reserve.

And step five, the borrower determines the amount of the assets to be borrowed according to the entity asset value evaluated by the evaluation mechanism and calls the intelligent contract borrowing. After the borrower excessively mortises the physical materials, the borrower can borrow from the platform. The borrower can repay at any time, and the total repayment quantity is determined according to the interest rate and time of the borrowed money during repayment.

Step six, the trusted entity asset registration mechanism executes subsequent mortgage operation, changes the mortgage state of the entity asset, marks the mortgage state as 'mortgage already', and prevents the lender from mortgage for multiple times on different platforms; after the borrower completes the repayment, the trusted entity asset register organization changes the entity asset mortgage state into 'uncanceled'.

And step seven, if the outstanding loan value of an account exceeds the loan capability, clearing is triggered, the entity assets are auctioned according to the current market price minus the clearing discount, the clearing person acquires the mortgage entity assets of the borrower, the debt of the borrower is paid, and the credible entity asset registration mechanism changes the information of the related entity assets.

Step eight, in the platform, if liquidity is provided for the asset pool, the platform awards the governing digital currency. The governing digital currency has a voting governing right, and community governing can be carried out by voting through governing the digital currency when the profit rate parameters of different currencies of the platform are adjusted.

In the fourth to fifth steps, each step adopts corresponding zero-knowledge proof for proving and verifying relevant parameters in the transaction process, hiding key information and canceling the association relation of each transaction party in the operation process.

In the scheme, the specific operation of the third step is as follows:

and (3) obtaining a hash value by performing hash operation on the entity asset and the borrower information by adopting a digital signature technology, and signing the hash value by using a private key of a signer. The sender sends the digital signature to the verifier together with the hash value calculated by the same hash algorithm on the plaintext. Any verifier can verify the hash value obtained by the digital signature through the public key of the signer to be compared with the received hash value, and if the hash value is consistent with the received hash value, the plaintext information can be determined not to be tampered.

In the scheme, the specific operation of the step four is as follows:

the lender can enjoy the interest and income of lending by using the money market of the property stored in the platform intelligent contract as the bottom property, the loan demand is automatically processed by the platform intelligent contract, and the lender and the borrower do not need to negotiate interest, borrowing time, mortgage property and the like.

The scheme utilizes zero-knowledge proof and a pseudonymous account to protect the identity information of the lender. The lender transfers a piece of private fund for lending from the private balance of the lender to a private fund pool through transfer operation, and a pseudonymous account is created, and the pseudonymous account firstly combines the private fund with the private fund transferred by other lenders to form a Mercury tree; secondly, constructing a zero-knowledge proof to ensure that the privacy fund really exists on the Mercker tree, and transferring the corresponding plaintext fund to the platform to be recorded in the intelligent contract; finally, the platform will give the pseudonymous account a corresponding number of LToken's that will be used for lender withdrawal and interest calculation. When withdrawing the fund, the platform calculates interest according to the quantity of the LToken held by the lender, and then transfers the interest to the pseudonymous account. The pseudonymous account converts the plaintext fund into corresponding privacy fund and puts the privacy fund into a privacy fund pool. The lender firstly combines the private funds with the private funds transferred by other lenders to form a Mercker tree; secondly, zero knowledge proof is utilized to ensure that the private funds exist on the Mercker tree and the private funds are deposited into the account through a deposit operation. It is noted that each lender's lending operation uses a different pseudonymous account, thereby protecting the lender's privacy. The detailed process of each operation is as follows:

(1) transferring accounts: lenders deducting privacy funds cmt from privacy balances_sThe private capital Pool is formed by the private capital Pool and other lenders_zk。

The lender generates a zero knowledge proof pi_costThe following was demonstrated:

original privacy balance cmt_U＝H(addr_U，balance_U，sn_U，r_U)；

Wherein addr_UTo keep privateFund cmt_UThe account address of the holder; balance_UIs cmt_UThe corresponding plaintext amount; sn_UIs cmt_UUnique corresponding serial number, in cmt_UDisclosed after spending, prevention of double flowers; r is_UIs a private random number;

② transfer to Pool_zkAmount of cmt_s＝H(addr_s，balance_s，sn_s，r_s)；

Wherein addr_sIs a pseudonymous account address, balance_sFor lending amounts, sn_sIs cmt_sUniquely corresponding serial number r_sIs a private random number;

operated privacy balance cmt_U′＝H(addr_U，balance_U′，sn_U′，r_U′)；

Wherein balance_U′Is cmt_U′Corresponding plaintext balance, sn_U′Is cmt_U′Uniquely corresponding serial number r_U′Is a private random number;

④balance_U≥balance_s，balance_U-balance_s＝balance_U′。

the above relationship is shown in FIG. 3, where the disclosed parameter is sn_U，cmt_U，cmt_s，cmt_U′，addr_U(ii) a The private parameter is balance_U，r_U，balance_s，sn_s，r_s，balance_U′，sn_U′，r_U′addr_s。

Lender will disclose the parameters and pi_costSending to the block chain system, the block chain node verifies pi by using public parameters_costFor correctness, the transaction is recorded in the blockchain system, and the privacy balance of the lender is updated to cmt_U′。

(2) And (3) funding: the lender creates a pseudonymous account that will Pool private funds Pool_zkWherein all privacy capital in the set constitute a Merck tree, wherein the leaf nodes correspond to different privacy capital, andwill cmt_sCorresponding plain text amount balance_sAnd turning to the platform to complete the loan operation.

Pseudonym account generation zero knowledge proof pi_commitThe following was demonstrated:

①cmt_s＝H(addr_s，balance_s，sn_s，r_s)；

zero knowledge amount cmt_sPresent at RT_cmtIn the mercker tree of roots.

The above relationship is shown in FIG. 4, where the disclosed parameter is sn_s，RT_cmt，balance_s，addr_s(ii) a Secret parameter is cmt_s，r_s。

The pseudonymous account will disclose the parameters with pi_commitSending to the block chain system, the block chain node verifies pi by using public parameters_commitThe correctness of the operation. The verifier can only know the balance of the plaintext amount_sCorresponding privacy Fund cmt_sExisting in the Mercker Tree, without knowing the cmt_sWhich leaf node on the Merck Tree, the cmt, corresponds_sDue to sn_sFails to work. So that the pseudonymous account will balance_sAnd turning to a platform, recording that the pseudonym identity has the corresponding number of LToken by the intelligent contract, and increasing the corresponding amount of money in a platform fund pool.

(3) Withdrawing resources: when the lender wants to withdraw the funds from the platform fund pool, the payor uses the pseudonym account to calculate the withdrawable funds refund according to the corresponding LToken recorded by the intelligent contract and generates the privacy funds cmt corresponding to the refund_s′Where refund is the sum of the principal and interest being credited. Lender will keep private capital Pool_zk′All the privacy funds in (a) constitute a merkel tree.

Pseudonym account generation zero knowledge proof pi_redeemThe following was demonstrated:

①cmt_s′＝H(addr_U，refund，sn_s′，r_s′)；

the above relationship is shown in FIG. 5, where the public parameter is cmt_s′Refund; secret parameter is sn_s′，r_s′，addr_U。

The pseudonymous account will disclose the parameters with pi_redeemSending to the block chain system, the block chain node verifies pi by using public parameters_redeemThe transaction is recorded on the blockchain, and the platform fund sum is updated after the intelligent contract verification is passed.

(4) Depositing: the lender draws the private funds into its private account and updates the private balance.

Lender zero-making knowledge proof pi_refundThe following was demonstrated:

original privacy balance cmt_U′＝H(addr_U，balance_U′，sn_U′，r_U′)；

② amount to be retrieved cmt_s′＝H(addr_U，refund，sn_s′，r_s′)；

Operated privacy balance cmt_U″＝H(addr_U，balance_U″，sn_U″，r_U″)；

④balance_U′+refund＝balance_U″；

⑤cmt_s′Present at RT_cmt' in the Mercker tree which is the root;

the above relationship is shown in fig. 6, where the disclosed parameters are: cmt_U′，addr_U，sn_U′，sn_s′，cmt_U″， RT_cmt'; the secret parameters are: balance_U′，r_U′，cmt_s′，refund，r_s′，balance_U″，sn_U″，r_U″。

Lender will disclose the parameters and pi_refundSending to the block chain system, the block chain node verifies pi by using public parameters_refundFor correctness, records transactions in a blockchain system, cmt_s′Due to sn_s′Invalidation of disclosure, update of the lender's privacy balance to cmt_U″The process ends.

In the scheme, the concrete operation of the step five is as follows:

the borrower may over-mortgage the physical assets and borrow from the platform. The borrower can pay at any time, and the total payment amount is determined according to the interest rate and time of the loan during payment, wherein the loan interest rate is related to the market utilization rate, and the loan interest rate is updated in time along with the change of the market utilization rate. The interest of the borrowed money during repayment is distributed to all lenders according to the ratio of the lending assets. Meanwhile, the platform provides a reserve fund as the platform benefit according to the reserve factor for the interest benefit of each loan.

The scheme utilizes zero-knowledge proof and a pseudonymous account to protect the identity information of the borrower. Firstly, the borrower submits an application for mortgage of the real object under the real name, the trusted asset registration mechanism checks the state of the real object of the borrower and carries out signature, and meanwhile, the trusted asset evaluation mechanism carries out value evaluation on the real object and carries out signature on the hash value of corresponding content. Secondly, the borrower uses the pseudonymous account to determine the own borrowing amount according to the evaluated asset value and the mortgage coefficient, and generates zero knowledge to prove that the legality of the borrowing amount is ensured. On the basis, the pseudonymous account makes a borrowing application to the platform by using the borrowing amount and corresponding zero knowledge proof. After the debit amount is obtained, the corresponding privacy fund is generated by the pseudonymous account and is stored in the privacy fund pool. The borrower firstly combines the private fund and the private fund transferred by other lenders into a Mercker tree; secondly, zero knowledge proof is utilized to ensure that the privacy fund exists on the Mercker tree and is deposited into the account of the user. And during repayment, the borrower calculates the amount of the interest to be returned according to the current loan interest rate and loan time, generates corresponding private funds, and returns the funds to the platform through the pseudonymous account. The detailed process of each operation is as follows:

mortgage authentication:

the trusted authority adopts the zero-knowledge proof of the trusted physical assets to respectively prove the state and the current market value of the assets of the borrower, and sends the generated hash values of the two signatures to the pseudonymous account of the borrower, and the following relation is shown in fig. 8.

Firstly, a trusted asset registration mechanism checks the asset state of a borrower, generates a zero knowledge proof and proves that the borrower really has an asset state of non-mortgage:

h₁＝H(pk_u，estate_id，state_ideither as "not mortgage")

Wherein, pk_uIs a pseudonymous account for use by the borrower, estate_idIs an asset that borrower u mortises.

The trusted asset registration authority signs the asset: sigma₁＝Sign(sk_auth1，h₁)。

And thirdly, the trusted asset evaluation organization evaluates the value of the asset, generates a zero-knowledge proof, and proves the current market value of the asset without revealing the specific conditions of the asset:

h₂＝H(pk_u，estate_id，value)

where value is the price of the asset being evaluated.

Fourthly, the trusted asset assessment organization signs the asset value: sigma₂＝Sign(sk_auth2，h₂)。

(II) borrowing:

(1) the pseudonymous account determines the loan amount of the loan according to the value evaluated by the credible asset evaluation organization and the mortgage coefficient k of the platform, and generates the privacy fund cmt corresponding to the loan_t(ii) a The borrower combines all the private funds in the private fund pool into a Mercker tree.

Pseudonym account generation zero knowledge proof pi_mortgageThe following was demonstrated:

1, lan < value k; wherein k is a mortgage coefficient;

②cmt_t＝H(addr_B，loan，sn_t，r_t) (ii) a Wherein addr_BIs the account address of the borrower.

The above relationship is shown in fig. 9, where the disclosed parameters are: loan, k, cmt_t(ii) a The secret parameters are: addr_B， sn_t，r_t。

The borrower will disclose the parameters and pi_mortgage、σ₁、σ₂Sent to the block chain system, the block chain node verifies pi by using public parameter verification_mortgageAnd the correctness of the transaction is that the transaction is recorded in a block chain system, the platform transfers the loan to the pseudonymous account, and the platform general ledger is updated.

(2) And the borrower extracts the corresponding privacy fund on the Mercker tree to the account and updates the privacy balance.

The borrower generates a zero knowledge proof pi_borrowThe following was demonstrated:

original zero knowledge balance cmt_b＝H(addr_B，v_b，sn_b，r_b)；

② zero knowledge amount cmt of borrowing_t＝H(addr_B，loan，sn_t，r_t)；

③ zero knowledge balance cmt after operation_b′＝H(addr_B，v_b′，sn_b′，r_b′)；

④v_b′＝loan+v_b

⑤cmt_tPresent at RT_bIn the mercker tree of roots;

the above relationship is shown in fig. 10, where the parameters disclosed are: cmt_b，addr_B，sn_b，sn_t，cmt_b′，RT_b(ii) a The secret parameters are: v. of_b，r_b，cmt_t，addr_B，loan，r_t，v_b′，sn_b′，r_b′；

The borrower will disclose the parameters and pi_borrowSending to the block chain system, the block chain node verifies pi by using public parameters_borrowFor correctness, records transactions in a blockchain system, cmt_tDue to sn_tIs invalidated, the borrower's zero knowledge balance is updated to cmt_b′。

(III) repayment:

(1) the borrower deducts the privacy fund cmt corresponding to the fund debt to be returned from the privacy balance_t′Where debt is the pseudonymous account debit principal recorded by the platform andsum of interest, cmt_t′And the private funds and other lenders form a private fund pool together.

The borrower generates a zero knowledge proof pi_backThe following was demonstrated:

original privacy balance cmt_b′＝H(addr_B，v_b′，sn_b′，r_b′)；

Amount cmt transferred to private fund pool_t′＝H(pk_u，debt，sn_t′，r_t′)；

Wherein, pk_uIs a pseudonymous account of the borrower;

operated privacy balance cmt_b″＝H(addr_B，v_b″，sn_b″，r_b″)；

④v_b′≥debt，v_b′-debt＝v_b″。

The above relationship is shown in fig. 11, where the parameters disclosed are: cmt_b′，addr_B，sn_b′，cmt_t′，cmt_b″(ii) a The parameter of privacy is v_b′，r_b′，pk_u，debt，sn_t′，r_t′，v_b″，sn_b″，r_b″。

The borrower will disclose the parameters and pi_backSending to the block chain system, the block chain node verifies pi by using public parameters_backThe transaction is recorded in the blockchain system, and the privacy balance of the borrower is updated to cmt_b″。

(2) The pseudonym account combines all the private funds in the private fund pool into a Merck tree and combines the cmt_t′And transferring the corresponding plaintext amount debt to the platform to finish the operation.

Pseudonym account generation zero knowledge proof pi_finishThe following was demonstrated:

①cmt_t′＝H(pk_u，debt，sn_t′，r_t′)；

zero knowledge amount cmt_t′Exist inRT_b′In the mercker tree of roots.

The above relationship is shown in FIG. 12, where the disclosed parameter is pk_u，debt，sn_t′，RT_b′(ii) a Secret parameter is cmt_t′， r_t′。

The pseudonymous account will disclose the parameters with pi_finishSending to the block chain system, the block chain node verifies pi by using public parameters_finishThe correctness of the operation. And the pseudonymous account returns debt to the platform, the platform deletes the borrowing item corresponding to the pseudonymous account, and the repayment operation is completed.

In the above scheme, the specific operation of the seventh step is as follows:

as shown in fig. 13, the actual clearing process is the process of making a payment by the clearing person instead of the borrower, and the process is basically the same as the process of making a payment by the borrower, except that the borrower becomes the clearing person.

If the outstanding debit value of an account exceeds its debit capability, a clearing process is triggered. The transfer of the caller's property to the borrower's collateral is done by calling a liquidation function at a price slightly above market. The borrower pays the liquidation penalty, the liquidator triggers a liquidation program to immediately start liquidation, and the entity assets are auctioned according to the current market price minus the liquidation discount, the partial price is rewarded by the liquidator, and extra collateral is provided for the liquidator so as to encourage the liquidator to liquidate actively.

The liquidator repays the debt of the borrower, acquires the physical assets of the borrower and changes the assets owners. The borrower's physical assets are auctioned and the platform liability crisis is removed, while the borrower receives the remaining assets after the physical assets minus the liability and clearing the discount, which is also the reason for the excess mortgage loan. Therefore, the borrower repays the platform loan, the platform is prevented from being debt and bad account, and the repayment capability of the system is maintained. Meanwhile, the clearing person obtains 3% -5% of the single income, the clearing person obtains the income, and the platform operates normally.

In the above scheme, the specific operation of step eight is as follows:

in this platform, if liquidity is provided for the pool of assets, the platform will award governance digital currency. The only way to obtain governance digital currency is through liquidity investment generation. The process of generating governance digital currency is also a process of obtaining revenue by providing liquidity to the platform capital pool. At present, the popular mode of liquidity investment is to deposit stable currency or other digital currency and then generate governing digital currency. The governing digital currency has a voting governing right, and community governing can be carried out by voting through the governing digital currency when the profit rate parameters of different products of the platform are adjusted.

In the scheme, the concrete operation of the step five is as follows:

The scheme utilizes zero-knowledge proof and a pseudonymous account to protect the identity information of the borrower.

Firstly, the borrower submits an application for mortgage of the real object under the real name, the trusted asset registration mechanism checks the state of the real object of the borrower and carries out signature, and meanwhile, the trusted asset evaluation mechanism carries out value evaluation on the real object and carries out signature on the hash value of corresponding content.

Secondly, the borrower uses the pseudonymous account to determine the own borrowing amount according to the evaluated asset value and the mortgage coefficient, and generates zero knowledge to prove that the legality of the borrowing amount is ensured.

On the basis, the pseudonymous account makes a borrowing application to the platform by using the borrowing amount and corresponding zero knowledge proof. After the debit amount is obtained, the corresponding privacy fund is generated by the pseudonymous account and is stored in the privacy fund pool. The borrower firstly combines the private fund and the private fund transferred by other lenders into a Mercker tree; secondly, zero knowledge proof is utilized to ensure that the privacy fund exists on the Mercker tree and is deposited into the account of the user. And during repayment, the borrower calculates the amount of the interest to be returned according to the current loan interest rate and loan time, generates corresponding private funds, and returns the funds to the platform through the pseudonymous account. The detailed process of each operation is as follows:

(IV) mortgage authentication:

Checking the asset state of the borrower by the trusted asset registration mechanism to generate a zero knowledge proof to prove that the borrower really has an asset state of non-mortgage:

h₁＝H(pk_u，estate_id，state_iaeither as "not mortgage")

Sixth, the trusted asset registration authority signs the asset: sigma₁＝Sign(sk_auth1，h₁)。

The credible asset evaluation mechanism carries out value evaluation on the asset, generates zero knowledge proof, proves the current market value of the asset and does not reveal the specific conditions of the asset:

h₂＝H(pk_u，estate_id，value)

where value is the price of the asset being evaluated.

Signing the asset value by a trusted asset evaluation organization: sigma₂＝Sign(sk_auth2，h₂)。

(V) borrowing:

(3) the pseudonymous account determines the loan amount of the loan according to the value evaluated by the credible asset evaluation organization and the mortgage coefficient k of the platform, and generates the privacy fund cmt corresponding to the loan_t(ii) a The borrower combines all the private funds in the private fund pool into a Mercker tree.

③ loan is less than value x k; wherein k is a mortgage coefficient;

④cmt_t＝H(addr_B，loan，sn_t，r_t) (ii) a Wherein addr_BIs the account address of the borrower.

(4) And the borrower extracts the corresponding privacy fund on the Mercker tree to the account and updates the privacy balance.

original zero knowledge balance cmt_b＝H(addr_B，v_b，sn_b，r_b)；

Seventhly, borrowing zero knowledge amount cmt_t＝H(addr_B，loan，sn_t，r_t)；

Zero-knowledge balance cmt after operation_b′＝H(addr_B，v_b′，sn_b′，r_b′)；

⑨v_b′＝loan+v_b

⑩cmt_tPresent at RT_bIn the mercker tree of roots;

(VI) repayment:

(3) the borrower deducts the privacy fund cmt corresponding to the fund debt to be returned from the privacy balance_t′Wherein debt is the sum of the pseudonymous account debit principal and interest recorded by the platform, cmt_t′And the private funds and other lenders form a private fund pool together.

original privacy balance cmt_b′＝H(addr_B，v_b′，sn_b′，r_b′)；

Wherein, pk_uIs a pseudonymous account of the borrower;

seventhly, the privacy balance cmt after operation_b″＝H(addr_B，v_b″，sn_b″，r_b″)；

⑧v_b′≥debt，v_b′-debt＝v_b″。

The borrower will disclose the parameters and pi_backSending to a blockchain system, using disclosure of blockchain nodesParameter verification pi_backThe transaction is recorded in the blockchain system, and the privacy balance of the borrower is updated to cmt_b″。

(4) The pseudonym account combines all the private funds in the private fund pool into a Merck tree and combines the cmt_t′And transferring the corresponding plaintext amount debt to the platform to finish the operation.

①cmt_t′＝H(pk_u，debt，sn_t′，r_t′)；

zero knowledge amount cmt_t′Present at RT_b′In the mercker tree of roots.

In the above scheme, the specific operation of the seventh step is as follows:

In the above scheme, the specific operation of step eight is as follows:

Example (b):

in this embodiment, there are three entities, namely, lender A, borrower B, and clearinghouse C. The borrower has physical assets and is used as a mortgage guarantee on the platform to obtain the assets; the lender deposits the asset into the money market funding pool of the platform for interest while providing liquidity for accrual digital monetary awards, as shown in figure 1. All processes are finished in a mode that a user serves as a block chain node and sends a transaction through the block chain node in a block chain system, the transaction is identified and packaged through other block chain nodes, block synchronization is finished, and zero knowledge proof generation and verification are integrated in the transaction process. By way of example with the DAI with the highest annual interest rate in the loan at present, the operation steps of each entity side are as follows:

when the lender A puts the DAI into the intelligent contract, the intelligent contract generates extra cDAI to the lender, and the lender is automatically put and interest is generated. The lender can use the cDAI to change back the original DAI and the interest of the added DAI at any time, as shown in FIG. 2. Assuming that the exchange rate of DAI and cDAI is 0.025(1/40), the exchange rate gets larger and larger as time and interest rate increase. If the lender A then places 1,000 DAIs into the intelligent contract, 40,000 cDAIs are obtained based on the exchange rate. After a period of time, if a decides to cash out the loan, then the exchange rate of DAI and cDAI increases to 0.0275, whereupon a redeems the previously held 40,000cDAI back to 40,000 x 0.0275 ═ 1,100 DAI.

Calculating the annual interest rate of the borrower and the lender: the annual interest rate of borrowing is the basic interest rate + (usage rate x added interest rate). If the basic interest rate is 5%, the added interest rate is 12%, and the usage rate is 62.13%, the borrowing annual interest rate of the borrower B is 5% + (12% × 0.6213) ═ 12.4556%, that is, the annual interest rate of the borrower B required to pay interest is 12.46%. Similarly, the loan annual rate is 12.46% of the borrowing annual rate × the usage rate (1-reserve interest rate), the usage rate is 62.13% of the borrowing annual rate, and the reserve interest rate is 5%. The annual loan rate for a is calculated to be 12.46% x 62.13% x (1-5%) to 12.46% x 0.6213 x 0.95 to 7.3543281%. The annual rate at which lender a will receive interest is 7.35%.

The borrower B can mortgage the physical assets in excess and borrow from the platform, the borrower applies for mortgage material objects first, the amount of borrowing of the borrower is determined according to the evaluated asset value and the mortgage coefficient, then the transaction is sent to the intelligent contract for borrowing operation, after the platform borrows the borrowed funds meeting the specification, the borrower performs deposit operation, the borrower deposits the borrowed funds into the privacy account of the borrower, and interest is paid according to the interest rate, as shown in FIG. 7. To prevent the borrower from paying no interest, the borrower excessively mortises the physical assets, and the amount of the loanable assets is the mortgage material value x the mortgage coefficient. If the outstanding loan value of the borrower B exceeds the borrowing capacity, a clearing program is triggered and the intelligent contract automatically auctions the mortgage physical assets of the borrower B. The liquidant C repays the debt of the borrower B and acquires the physical assets of the borrower B. The borrower B also receives the remaining assets from the price of the physical assets minus the debt and clearing discount as shown in fig. 11.

The specific excess mortgage and clearing process comprises the following steps: assuming that borrower B wants to mortgage physical assets to borrow DAI, if the physical asset has a market value of 600 RMB (corresponding to 928,200USD), then B mortgages the asset corresponding to USD. If the mortgage rate is 0.75, then B is able to borrow the largest asset that B can actually borrow 928,200x0.75 to 696,150USD, and thus B borrows 680,000DAI (assuming that the current market price is 1DAI to 1 USD). Suppose that after a period of time, B needs to pay back the interest of 20,000DAI, and 20,000+680,000 to 70,000DAI has exceeded the maximum amount of money that B can borrow, but B has no action to pay back. The mortgage physical property will then be liquidated and auctioned at a lower than market price because of the total B need to refund 700,000 DAIs. If the Liquidation incorporated is 1.1, then B's 928,200USD entity assets will be impounded, liquidiser C takes B's entity assets at the price of 928,200DAI ÷ 1.1 ═ 843,818DAI, changes the entity asset owner, and then liquidiser C helps borrower B pay 700,000DAI liabilities and gives B843,818 DAI-700,000 DAI ═ 143,818DAI of the remaining additional assets. Note that: this proportional Liquidation input is to reward the clearing person, providing the clearing person with additional collateral to encourage the clearing person to clear bad accounts. Thus, after the liquidation is over, the borrower B is deducted from the physical assets (928,200USD), and after the liquidator C refunds the DAI debt of 700,000USD for B, B proceeds to the assets of hand 143,818DAI, and C obtains the liquidation profit of 928,200 DAI-843,818 DAI 84,382DAI and the mortgage physical assets of the borrower B, at which point the liquidation is over.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents or improvements made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A block chain based physical asset mortgage lending method is characterized by comprising the following steps:

s8, if liquidity is provided for the asset pool of the platform, the platform awards governance digital currency with voting governance

2. The method as claimed in claim 1, wherein the step S3 is specifically performed as follows:

3. The method of claim 1, wherein the step of lending the block chain-based physical asset

The loan operation in S4 adopts a corresponding zero-knowledge proof for proving and verifying relevant parameters in the transaction process, and hiding key information, and canceling an association relationship of each party of the transaction in the operation process, specifically including the following sub-steps: