KR102308185B1 - Method for performing smart contract based on block chain network and smart contract performing system therefor - Google Patents

Abstract

Disclosed are a method for performing a confidential smart contract using homomorphic encryption and a smart contract execution system suitable therefor.
The smart contract execution method of the present invention is
uploading, by the contract party terminal, a smart contract including a homomorphic encrypted variable to a block chain network;
a process in which nodes participating in the first distributed consensus network verify the validity of a smart contract;
when the validity of the smart contract is verified by the nodes that satisfy the quorum among the nodes participating in the first distributed consensus network, the contract execution terminal executes the contract contents of the smart contract; and
when there is a homomorphic encryption comparison operation, the contract execution terminal decrypts a homomorphic encryption comparison operation result by consensus of nodes participating in a second distributed consensus network;
a process in which the contract fulfillment terminal provides a decryption result to the contract party terminal; and
a process in which the contract party terminal terminates the smart contract when the contract fulfillment terminal with more than a quorum agrees that the appropriate contract execution has been made;
includes

Description

Method for performing smart contract based on block chain network and smart contract performing system suitable therefor

The present invention relates to a blockchain-based smart contract execution method, and more particularly, to a method for performing a confidential smart contract using homomorphic encryption and a smart contract execution system suitable therefor. .

Blockchain technology does not store transaction information in a specific institution or central server, but distributes and stores it on the network, and records and manages it jointly by all participants. The block hash and nonce are included, and if these blocks are continuously connected, a block chain is formed.

1 shows the blockchain structure.

Referring to Figure 1, each block has a timestamp, and when system participants agree, the blockchain can be updated only when new data is entered, and it has a distributed electronic cryptographic ledger or database platform that can never be deleted.

In storing digital data immutably so that the network and users can safely share it, the blockchain applies public key cryptography (a method of using different keys for encryption and decryption) to verify the owner in the ledger. Instead of a name or social security number, half of the public key pair is recorded, and only the person with the other half of the private key becomes the owner and decides on the next transaction.

Figure 2 shows the operation process of the blockchain.

Referring to Figure 2, the block chain is based on a P2P (Pear to Pear) distributed network, and forms a block of transaction information through verification and consent of network participants and distributes and stores transaction information. The core process consists of two steps:

The first stage is a process called 'mining' that collects transaction information or records without the risk of double-spending to form valid individual blocks. Find the Nonce.

When the node that first finds the correct nonce value creates a block and uploads it to the blockchain network, each node participating in the blockchain network checks whether the transmitted nonce value is correct and whether the transaction is justified. , the block is acknowledged and timestamped and accessed after the previous block.

If any information is manipulated or changed during this process, it is classified as an orphan block and destroyed by verification work. A certain incentive is given to miners who find a nonce that meets the conditions and complete a new valid block.

3 shows the block structure of a blockchain.

Here, Merkle Roots is a hash value that summarizes all transaction information in the block and is data existing in the block header.

When a valid candidate block is formed, it goes to the second stage. In this stage, the generated candidate block is delivered to all network participants, and each network participant verifies the validity of the new block received and the validity of the transaction included in the block. When validity is confirmed through the consent of more than 50% of the participants, the candidate block is connected to the previous block and chained to complete the blockchain ledger.

The reason why each miner competes in block making is because of incentives (12.5 bitcoins per valid block), so many miners around the world are consuming huge amounts of computer resources and power to mine.

The reason why such an excessively consuming mining operation is included in the process of forming the blockchain

First, it allows numerous competitors to thoroughly validate the transaction by competing and monitoring each other.

Second, it is to block arbitrary manipulation or intervention from the first step by preventing anyone from exclusively creating new blocks.

Third, through the difficult mining process, the new block formation speed is set to about 10 minutes on average, so that the collection and distribution of transactions and validation of transactions can proceed without unreasonableness.

When a transaction history is included in a block, in particular, a new block is stacked on top of the block, and the transaction history cannot be changed at all (irreversibility), and the transaction can be confirmed anywhere (publicity).

Since the concept of blockchain was first proposed, smart contract technology that can force the implementation of contract contents and recognize violations has been added. trend.

Here, ‘smart contract’ is an important function using block chain technology, and it is a program that automatically executes a transaction when certain conditions are satisfied.

4 shows the process of creating and executing a blockchain-based smart contract.

A smart contract contains smart contract code. Such a smart contract can be created using a template. A template is a reusable document that is a mixture of legal prose and smart contract code. These templates can include metadata, conditional statements, calculations, smart contract logic, signatures, IDs, and more.

By compiling the smart contract, you get the bytecode (i.e. the smart contract execution program), inserting this bytecode into a block and uploading it to the blockchain. The validity of a block placed on the block chain is verified through a distributed consensus procedure within the block chain.

The smart contract executor inserts the contract execution result into the block and uploads it to the blockchain. The validity of the block placed on the block chain is also verified through the distributed consensus procedure within the block chain, and when the verification is completed, the contract is recognized as complete.

These smart contracts can be used for ownership transfer contracts, inheritance and gifting, etc. If the conditions for contract execution are specified in the smart contract, the fulfillment of the contract contents is automatically realized as soon as the conditions are satisfied. Management costs and the risk of contract default are also fundamentally excluded.

However, in order to satisfy both decentralization and integrity, the block chain discloses the specific transaction details within the block to all nodes participating in the block chain. Only when the contents are disclosed, it is possible to check whether a transaction is being made according to the contract through a distributed consensus algorithm, etc. However, due to this, it has a fundamental limitation that it is difficult to perform a transaction that guarantees confidentiality through the block chain.

1. Gentry, C. (2009, May). Fully homomorphic encryption using ideal lattices. In Stoc (Vol. 9, No. 2009, pp. 169-178). 2. Buterin, V. (2014). A next-generation smart contract and decentralized application platform. white paper.

The present invention is designed to solve the above problems, and it is based on a blockchain network that ensures confidentiality and integrity in the existing blockchain ecosystem while securing confidentiality without the need for users to build a separate private blockchain network. Its purpose is to provide a method for executing smart contracts of

Another object of the present invention is to provide a system suitable for the above method.

The blockchain network-based smart contract execution method according to the present invention that achieves the above object is

Includes a contract party terminal, a first distributed consensus network to verify the validity of a smart contract, a contract fulfillment terminal to determine the suitability of contract execution according to conditions, and a second distributed consensus network to verify the suitability of contract execution according to conditions In a method of performing a smart contract based on a blockchain network,

uploading, by the contract party terminal, a smart contract including a homomorphic encrypted variable to a block chain network;

a process in which nodes participating in the first distributed consensus network verify the validity of a smart contract;

when the validity of the smart contract is verified by the nodes satisfying the quorum among the nodes participating in the first distributed consensus network, the contract execution terminal executes the contract contents of the smart contract; and

when there is a homomorphic encryption comparison operation, the contract execution terminal decrypts a homomorphic encryption comparison operation result by consensus of nodes participating in a second distributed consensus network;

a process in which the contract fulfillment terminal provides a decryption result to the contract party terminal; and

a process in which the contract party terminal terminates the smart contract when the contract fulfillment terminal with more than a quorum agrees that the appropriate contract execution has been made;

includes

Here, the process of verifying the validity of the smart contract is a process in which nodes participating in the blockchain network verify the electronic signature of the smart contract, the leader who delivered the smart contract, and the sequence number mapped to the smart contract;

If the number of verified nodes exceeds the quorum, the process of treating the validity of the smart contract as verified;

It is characterized in that it includes.

Here, the decoding process is

calculating, by the contract fulfillment terminal, a homomorphic cryptographic comparison operation included in the smart contract; and

a process of verifying a homomorphic cryptographic comparison operation result from nodes participating in a second distributed consensus network;

It is characterized in that it includes.

Here, the nodes participating in the second distributed consensus network share the plaintext corresponding to the homomorphic encryption comparison operation result, and each node decrypts the ciphertext provided by the contract fulfillment terminal and compares it with the shared plaintext to determine whether it is consistent , propagates the judgment result to neighboring nodes, each node selects a value agreed upon by nodes with a quorum or more among the values received from the neighboring nodes, and delivers the selected value to the node (leader) that initiated the agreement,

The leader selects a value agreed upon by the nodes having a quorum or more, adopts it as a result of the agreement, and provides it to the contract fulfillment terminal.

Here, the leader is selected by the distributed consensus of the second distributed consensus network.

Here, when the leader is no longer available due to a failure, the next leader is selected in a predetermined order and approved by distributed consensus.

The blockchain-based smart contract execution system according to the present invention that achieves the above other object is

a contract party terminal for uploading a homomorphic encrypted smart contract to the block chain network;

a first distributed consensus network consisting of nodes participating in the blockchain network and for verifying the validity of a smart contract;

a contract fulfillment terminal implemented by nodes participating in the block chain network and determining suitability of contract execution according to conditions;

Consists of nodes participating in the blockchain network, and includes a second distributed consensus network to verify the suitability of contract execution according to conditions,

here,

The contract party terminal includes a template-code mapping module that converts a smart contract written in natural language into byte code, and a pre-processing module that selects and encrypts a variable to be encrypted from among the byte code,

The contract fulfillment terminal determines the contract fulfillment according to the condition, and if there is a homomorphic encryption comparison operation, it decrypts the homomorphic encryption comparison operation result by agreement with the second distributed network.

Here, the nodes participating in the second distributed consensus network share the plaintext corresponding to the homomorphic encryption comparison operation result, and each node decrypts the ciphertext provided by the contract fulfillment terminal and compares it with the shared plaintext to determine whether they match and propagates the judgment result to neighboring nodes, each node selects a value agreed upon by nodes with a quorum or more among the values received from neighboring nodes, and delivers the selected value to the node (leader) that initiated the agreement,

The leader selects a value agreed upon by the nodes having a quorum or more, adopts it as a result of the agreement, and provides it to the contract fulfillment terminal.

Here, the leader is selected by the distributed consensus of the second distributed consensus network.

Here, when the leader is no longer available due to a failure, the next leader is selected in a predetermined order and approved by distributed agreement.

Here, the nodes participating in the second distributed consensus network may include a decryption module that decrypts the encrypted text by comparing the shared plain text with the encrypted text received from the contract fulfillment terminal.

Here, the contract party terminal determines that the contract is suitably completed when there is a quorum or more agreement from the contract execution terminal, and terminates the smart contract.

According to the present invention, by creating a smart contract using the homomorphic encryption, the user does not need to build a separate private blockchain network and secures confidentiality while simultaneously ensuring confidentiality and integrity in the existing blockchain ecosystem. It has the effect of making it possible.

1 shows the blockchain structure.
Figure 2 shows the operation process of the blockchain.
3 shows the block structure of a blockchain.
4 shows the process of creating and executing a blockchain-based smart contract.
5 shows the configuration of a blockchain network to which the present invention is applied.
6 shows an overview of the PBFT distributed consensus algorithm for validating encrypted smart contracts.
7 is a schematic flowchart of a smart contract execution process using homomorphic encryption according to the present invention.
8 is a flowchart showing a smart contract execution method according to the present invention.
9 shows the configuration of a blockchain-based smart contract execution system according to the present invention.
10 is a process diagram showing a smart contract execution method according to the present invention.
11 is a flowchart showing the process of verifying the validity of a smart contract in a blockchain.
12 is a flowchart illustrating a smart contract agreement process by a contract fulfillment terminal.
13 is a flowchart illustrating a smart contract implementation process by a contract fulfillment terminal.
14 shows an example of a comparison operator.

Hereinafter, the configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

5 shows the configuration of a block chain system to which the present invention is applied.

5, the blockchain system to which the present invention is applied includes a contract party terminal 10, a contract fulfillment terminal 20, a distributed consensus network for determining the validity of a smart contract (first distributed consensus network, 30), A second distributed consensus network 40 for decrypting homomorphic cryptographic operations is included.

The first distributed consensus network 30 is a network for verifying the validity of a smart contract through distributed consensus based on a blockchain network.

Here, the second distributed consensus network 40 is a distributed consensus network for verifying the suitability of contract execution according to conditions by homomorphic cryptographic comparison operation based on a block chain network. Nodes to participate in the second distributed consensus network 40 basically follow the criteria for participating in distributed consensus in the blockchain network. Usually, all participants, or nodes with high stakes, that is, nodes with relatively large number of virtual cryptocurrencies and low participation in transactions, may be selected preferentially (Ethereum method).

In case of taking the Ethereum method, verification nodes are collateralized to compensate for incorrect verification. Nodes with higher stakes are afraid of losing their mortgage, so they perform proper verification. This verification system can be set flexibly according to the request for speedy smart contract execution.

First, the contract party terminal 10 writes a smart contract, creates an encrypted smart contract including a ciphertext obtained by encrypting a variable to be encrypted using a homomorphic encryption, and uploads it to the blockchain network.

Specifically, the contract party terminal 10 creates a smart contract, compiles the created smart contract into byte code (smart contract execution statement), and encrypts variables included in the contract among the compiled byte codes using homomorphic encryption. Write an encrypted smart contract, create a block with the aptitude encrypted smart contract inserted, and upload the created block to the blockchain.

Here, the homomorphic encryption is a fourth-generation encryption following password, symmetric key encryption, and asymmetric encryption, and refers to encryption capable of arithmetic calculation in an encrypted state. In other words, it is possible to find out the ‘value calculated in the plaintext’ even through the ‘value calculated between ciphers’.

Homomorphic encryption is a mathematical algorithm that can perform arithmetic operations in an undecrypted state (with a password attached). It can be widely used in a way that can be proved by

Using this, the present invention encrypts information (an important variable in the summary of the present invention) that you do not want to be disclosed to the outside in the process of creating a smart contract with a homomorphic encryption. Although it is not disclosed to the outside, the integrity can be verified through the value calculated between the ciphertexts. This is because, as mentioned earlier, the value calculated in the plaintext can be found from the value calculated between the ciphertexts.

For example, we want to prove that while there is a balance of 10,000 won in account A, and 2,000 won is transferred to account B with a balance of 0, 8,000 won remains in A and a balance of 2,000 won is generated in B.

Assuming that the initial balances of A and B are I(A) and I(B), the transfer amount is Y, and the balance after the transaction of A and B is B(A) and B(Y), respectively, the encrypted arithmetic below Suppose we have equations (1) and (2).

I(A) - Y = B(A) -- (1)

Y + I(B) = B(B) -- (2)

The fact that the integrity of the final balance can be verified in encrypted arithmetic expressions such as (1) and (2).

For reference, the following equations show homomorphic encryption procedures for various operations.

1) Homomorphic encryption procedure for addition expression:

2) Homomorphic Encryption Procedure for Multiplication Expressions

3) Homomorphic Encryption Procedure for Subtraction Expressions

4) homomorphic encryption procedure for division

5) Homomorphic ciphers and procedures for comparison operations

The nodes participating in the first distributed consensus network 30 verify the validity of the smart contract.

6 shows an overview of the consensus algorithm of the first distributed consensus network for verifying the validity of a smart contract.

PBFT (Practical Byzantine Fault Tolerance) is a consensus algorithm developed so that all nodes participating in the distributed system can successfully reach consensus when the distributed system is an asynchronous system in which Byzantine nodes that do not perform the promised behavior can exist. am. In the PBFT consensus algorithm, there is a special node called a primary or a leader. This node is responsible for distributing client requests to other nodes.

The agreement is carried out as follows.

1) The leader collects requests from clients and propagates them to other nodes.

2) After receiving the message from the leader, the nodes verify that the message was received from the leader and then propagate it to all nodes once again.

3) Every node chooses the same message (more than a quorum) that it receives the most from other nodes.

After the process of 1) 2) 3), all nodes have the same request (smart contract) agreed upon by a quorum or more.

When the validity of the smart contract is verified by the nodes that satisfy the quorum among the nodes participating in the first distributed consensus network, the contract execution terminal executes the contract contents according to the smart contract and evaluates whether the smart contract is suitable.

The contract fulfillment terminal evaluates the suitability of contract execution according to the conditions by evaluating the conditions for implementing the smart contract. In addition, when all conditions included in the smart contract are fulfilled, the suitability of contract execution according to the conditions is determined by the homomorphic cryptographic comparison operation. If a plurality of nodes constitute the second distributed consensus network for decrypting the homomorphic cryptographic comparison operation, and the nodes exceeding the quorum verify that the contract execution has been properly completed, the corresponding smart contract is treated as appropriately completed.

According to the system shown in FIG. 5, by creating a smart contract using homomorphic encryption, the user does not need to build a separate private blockchain network, and secures confidentiality while maintaining confidentiality and integrity in the existing blockchain ecosystem. At the same time, it is effective to perform a guaranteed smart contract.

7 is a schematic flowchart of a smart contract execution process using homomorphic encryption according to the present invention.

Referring to FIG. 7 , in step s702, the contract party terminal creates a smart contract. At this time, the information to be encrypted is encrypted using a homomorphic encryption function and inserted into the byte code.

For example, when transferring 2,000 won from the current balance of 10,000 won is in the contract, the result of taking 10,000 and 2,000 as variables using the homomorphic cryptographic function H(), that is, the result of H(10000) and H(2000) It is replaced with the result value (that is, isomorphic encrypted ciphertext), and in the smart contract, it is specified that H(10000) - H(2000) is the homomorphic encryption value of 8,000 plaintext. Here, the operation statement specifying that H(10000) - H(2000) becomes the homomorphic encryption value of the plaintext 8,000 corresponds to the homomorphic encryption comparison operation in the summary of the present invention. (H(10000) - H(2000) itself is a ‘homomorphic encryption operation’, and ‘-H(2000) = 8000’ corresponds to a ‘homomorphic encryption comparison operation’.)

If it is determined that the contract has been properly performed as a result of decryption from the contract fulfillment terminals having a quorum or more, the contract party terminal terminates the smart contract.

Let the cryptographic value after contract execution be the value of H (8000), for example Y.

In process s704, the user uploads the encrypted smart contract to the blockchain network.

In process s706, the contract execution terminal inside the blockchain network implements the corresponding smart contract.

8 is a flowchart showing a method of performing a smart contract according to the present invention.

First, the contract party terminal creates a smart contract (s802).

The contract party terminal converts the smart contract written in natural language into byte code (smart contract execution statement). (s804)

Variables inside the bytecode are encrypted by homomorphic encryption. (s806)

Validate the smart contract (s808)

When the validity of the smart contract is verified, the contract execution terminal executes the verified smart contract (s810).

If there is a homomorphic cryptographic comparison operation, the contract fulfillment terminal performs the homomorphic cryptographic comparison operation and decrypts the homomorphic cryptographic comparison operation result using a distributed consensus network (s812, s814).

The contract fulfillment terminal delivers the smart contract execution result to the contract party terminal. (s816)

If the same result of more than a quorum is selected, the contract party terminal terminates the smart contract (s818).

In FIG. 8 , the homomorphic cryptographic comparison operation is a process of performing the homomorphic cryptographic comparison operation by the ciphertext included in the smart contract in order to determine whether the contents of the smart contract are legitimate.

A homomorphic cryptographic comparison operation is performed by an operation statement of less than, greater than, less than, equal to, greater than or equal to, equal to, or the like. This homomorphic cipher comparison operation is to evaluate the mathematical suitability of the homomorphic ciphertext.

The homomorphic cryptographic comparison operation checks whether the value obtained through the ciphertext operation is the same as the value after contract execution specified in the smart contract.

For example, Z == Y, that is, the Z value obtained through direct ciphertext operation and the value of the ciphertext in the contract, that is, Y, the result value of H(8000), is verified through a homogeneous encryption comparison operation.

The result of the homomorphic cryptographic comparison operation is also a ciphertext.

Whether the result value of the homomorphic cryptographic comparison operation is correct (True) or incorrect (False) can be checked in a specific server through the established asymmetric cryptosystem.

However, in the present invention, in order to maintain the decentralized nature of the block chain, the neighboring nodes perform a comparison between the computation result between ciphertexts and the ciphertext value to be compared contractually, and the result of the comparison is determined in plaintext by distributed consensus (Distributed Consensus). ) to make a decision. In the present invention, a PBFT algorithm may be applied.

Specifically, what the comparison result is in plaintext is shared by each node participating in the distributed consensus network to verify the suitability of contract completion. Each node selects a value accepted by a quorum or more among the values received from neighboring nodes, and transmits the consensus to the node (leader).

The node that initiates the consensus process is called the leader. This leader is selected according to a set order. When selected, approval also follows distributed consensus, and it is assumed that the leader who is finally approved through consensus performs its role stably. When a leader is no longer available due to a disability, the next leader is selected and approved by distributed consensus.

9 shows the configuration of a smart contract execution system according to the present invention.

Referring to FIG. 9 , the smart contract execution system according to the present invention includes a contract party terminal 20 , a first distributed consensus network 30 , and a second distributed consensus network 40 . The contract party terminal 10 includes a contract code mapping module 12 and a smart contract preprocessing module 14 .

The first distributed consensus network 30 includes a consensus module 32 and a contract fulfillment module 20 .

The second distributed consensus network 40 for homomorphic cryptographic comparison operation evaluation includes a plurality of nodes, and each node includes a decryption module 42 . In the same way as the consensus module 32 inside the first distributed consensus network 30 performs, each node under the first distributed consensus network 40 for homomorphic cryptographic comparison evaluation evaluates each homomorphic cryptographic comparison evaluation. The result is decrypted and delivered to the node of the blockchain network that requested the evaluation of homomorphic cryptographic comparison evaluation. Nodes in the blockchain network will adopt the same answer with more than a quorum as a result of consensus.

10 is a process diagram showing a smart contract execution process by the smart contract execution system according to the present invention.

The contract party terminal includes a template-code mapping module and a smart contract pre-processing module.

Referring to FIG. 10 , first, the contract party terminal 10 selects a desired contract template and then creates a smart contract (s1002). The contract party terminal 10 may be two or more in terms of the contents of the contract, but only a representative contract party terminal will be described here in order to simplify the description.

The contract party terminal 10 writes the contract contents according to the contract form composed of UI widgets, such as a text form.

Next, the contract party terminal 10 compiles the smart contract content written in natural language into byte code using the template-code mapping module 12 (s1004). The template-code mapping module 12 includes a contract template and a code template (not shown).

The contract party terminal 10 converts a smart contract written in natural language into a formal smart contract using a contract template, selects a code template (compiler) corresponding to the contract template, and converts the contract content into byte code.

In this way, the smart contract written between the contracting parties is converted into byte code through the ‘template-code mapping module’. In this process, if the contract template and the corresponding pre-written code template are matched one-to-one, automation is possible.

Before the written code is uploaded to the blockchain network, the variable to be encrypted is encrypted through a pre-processing process to insert it into the code so that the variable to be encrypted is not visible. In the preprocessing process, the variable to be encrypted is encrypted using the homomorphic encryption (s1006).

The process is as follows.

program 1; Code without preprocessing

program 2; Code with all preprocessing done

program 3; preprocessor execution code

a) The preprocessor module (Preprocessor, 14) finds the part to be encrypted (plaintext) inside the smart contract. (The encryptFromPlain function is used in line 1 of program 1)

The plaintext to be encrypted is automatically converted from the document contract into a smart contract through the ‘template-code module’. During the conversion process, keywords inside the contract are extracted according to a predetermined procedure and filled into the unfinished smart contract template. In this process, all keywords to be filled in the unfinished smart contract template are subject to encryption.

b) The preprocessing module 14 extracts the plaintext found in a) and fills it in the template of program 2.

c) The preprocessing module 14 stores the cipher by executing the completed template code (program 3).

d) Change the plaintext encryption part in the smart contract code (program 1) to the method of calling the cipher generated and stored in c).

In the preprocessing of the preprocessing module 14, it is basically assumed that only one homomorphic encryption is used, but if desired, it is possible to apply a different encryption technique to each encryption variable.

Referring back to FIG. 9 , the consensus module 32 of the first distributed consensus network 30 verifies the validity of the smart contract (s1008).

If the validity of the smart contract is verified by the nodes satisfying the quorum among the nodes participating in the first distributed consensus network 30, the contract execution terminal 20 executes the smart contract (s1008, s1010).

11 is a flowchart showing a process of verifying the validity of a smart contract.

Referring to FIG. 11 , nodes participating in the distributed network for contract validation receive the smart contract uploaded by the contract party terminal (s1102). Nodes participating in the distributed network for contract validation are basically block chains. Nodes participating in the network.

The node verifies the digital signature of the received smart contract, the leader who delivered the smart contract, and the sequence number mapped to the smart contract (s1104).

Here, the node refers to a node that initiates the distributed consensus process, derives the consensus result, and delivers it to the requester.

The sequence number is the unique information of the smart contract obtained by combining the header information of the block.

If the verification is successful, the verification fact is transmitted to all other blockchain nodes. (s1106, s1108)

The node receives the fact that other nodes have verified the transaction (s1110).

The leader determines whether verification of a quorum or more has been collected (s1112).

When the verification of more than a quorum is collected, the leader notifies the terminal of the contracting party of the block chain that the agreement has been successful. (s1114)

Referring back to FIG. 10 , when the validity of the smart contract is verified by the consensus module, the contract fulfillment terminal executes the smart contract according to the smart contract (s1010).

If there is a homomorphic encryption comparison operation in the process of the contract execution terminal implementing the smart contract, it is decrypted by the second distributed consensus network.

The nodes participating in the second distributed consensus network 40 have a decryption module 42 .

12 is a flowchart illustrating a process of verifying completion suitability of a smart contract by a contract fulfillment terminal.

When the agreement on the smart contract is terminated, the contract fulfillment module 20 starts the execution of the smart contract (s1202), and checks whether homomorphic cryptographic comparison evaluation exists, that is, homomorphic cryptographic operation exists (s1204) .

Here, the contract fulfillment module is a module that confirms whether the contract is fulfilled according to the conditions through verification of the encrypted text. This module is loaded on all nodes participating in contract fulfillment verification, and implementation is verified according to the distributed consensus process programmed in these modules (distributed consensus algorithm).

If homomorphic encryption exists, the operation between homomorphic encryptions is performed (s1206), and it is determined whether the operation performed immediately before is homomorphic encryption comparison evaluation (s1208).

To determine whether the operation performed immediately before in s1208 was homomorphic encryption comparison evaluation, whether the result is a comparison evaluation operation requiring decryption when the homomorphic encryption operation is performed, or general arithmetic operations that do not require decryption (+, -, *, /) is what we want to determine. In the case of performing an arithmetic operation, there is no need to use the second distributed sum network, so the rest of the code is executed. A process of requesting the network to decrypt is necessary.

If the operation performed immediately before was a comparison operation, the decryption result is verified by mutual cooperation with a distributed network for homomorphic encryption comparison evaluation (s1210).

s1202 (Start Smart Contract Implementation) means that you are already executing the smart contract line by line. Therefore, in the case of only plaintext codes or homomorphic cryptographic arithmetic operations (+, -, *, /), the contract execution module alone has the ability to execute a smart contract. Therefore, all contracts can be executed in step s1202 without the need to express the expression 'execute the rest of the code'.

On the other hand, if the homomorphic cryptographic comparison operation is inserted inside the smart contract, the contract fulfillment module alone has no ability to execute the smart contract. Therefore, in order to clearly express the need to use the second distributed agreement network, the contract fulfillment module is temporarily stopped, and the comparison operation is delegated to the second distributed agreement network. After the second distributed agreement network is finished, the contract is executed again The module is executed.

Homomorphic cipher comparison operation is an operation that compares and evaluates whether the values of two isomorphic encrypted ciphers are the same, different, larger, smaller, etc. For example, when there is a comparative evaluation statement A < B, if A is actually less than B, this expression has a true value as a Boolean value. Otherwise, it will have a false value. However, since even the result of homomorphic encryption comparison evaluation is confidential by homomorphic encryption, it is necessary to check what this boolean value is through decryption.

Nodes equipped with the contract fulfillment module 20 can directly return the result of the homomorphic cryptographic comparison operation and determine the actual Boolean value through the decryption key. Check the boolean value of the homomorphic cryptographic comparison expression through the distributed consensus process and check whether the implementation is correct.

The case where the rest of the code execution process is not performed is the case of a general smart contract in which homomorphic encryption is not used.

If homomorphic encryption is used but not homomorphic encryption comparison evaluation, condition evaluation is not performed, but the rest of the code execution process is performed. This will be described in detail below.

There are two cases where the comparison operation is not.

When encryption is performed without computation for the purpose of purely maintaining confidentiality.

When using arithmetic operation (arithmetic operation).

Since case 1 of the above two cases is self-evident, case 2 will be described.

No. 2 is that the condition evaluation process is not performed because the decoding process is not required. For example, if it is specified in the smart contract to obtain the sum of certain numbers, it is possible to obtain the sum without a decryption procedure by the homomorphic encryption system. Therefore, there is no need to go through the decoding module for conditional operation evaluation.

Condition evaluation and the rest of the code are performed (s1212).

Executing the rest of the code means executing the program after the schematic flowchart, and even executing the smart contract being implemented.

Referring back to FIG. 10 , the contract party terminal 10 checks whether the smart contract is completed (s1014).

13 is a flowchart illustrating a smart contract completion confirmation process of a contract party terminal.

Referring to FIG. 13 , the contract party terminal 10 waits for reception of the smart contract result from the contract fulfillment terminal 20 ( s1302 ).

The smart contract result is received (s1304), and it is determined whether there is an identical result more than a quorum (s1306).

If there is more than a quorum of the same result, the agreement is completed and terminated (s1308).

Completion of the agreement means that the contract has been properly executed.

14 shows an example of a comparison arithmetic circuit.

Since the NAND gate is a universal gate, it is possible to configure an arbitrary comparison operation circuit.

The terms or words used in the present specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventor may properly define the concept of the term in order to best describe his invention. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that there is.

Therefore, the embodiments described in this specification and the configurations shown in the drawings are only the most preferred embodiment of the present invention, and do not represent all of the technical spirit of the present invention. It should be understood that there may be equivalents and variations.

10...Terminal of contracting party 20...Terminal of contract fulfillment
30...First Distributed Consensus Network 40...Second Distributed Consensus Network

Claims (12)

Includes a contract party terminal, a first distributed consensus network to verify the validity of a smart contract, a contract fulfillment terminal to determine the suitability of contract execution according to conditions, and a second distributed consensus network to verify the suitability of contract execution according to conditions In a method of performing a smart contract based on a blockchain network,
uploading, by the contract party terminal, a smart contract including homomorphic encrypted variables, which is information not to be disclosed to the outside in the process of creating a smart contract, to a block chain network;
a process in which nodes participating in the first distributed consensus network verify the validity of a smart contract;
when the validity of the smart contract is verified by the nodes that satisfy the quorum among the nodes participating in the first distributed consensus network, the contract execution terminal executes the contract contents of the smart contract; and
When there is a homomorphic cryptographic comparison operation performed by an operation statement of less than, greater than, less than, equal to, greater than, or equal to, in the contract content of the smart contract, the contract execution terminal performs the second distributed agreement A process of decrypting a homomorphic encryption comparison operation result by consensus of nodes participating in the network;
a process in which the contract fulfillment terminal provides a decryption result to the contract party terminal; and
When the contract fulfillment terminal with a quorum or more agrees that the appropriate contract has been performed, the contract party terminal terminates the smart contract;
The homomorphic cryptographic comparison operation is
A method of performing a smart contract, comprising the step of checking whether the value obtained through ciphertext operation is the same as the value after contract execution specified in the smart contract. According to claim 1,
The process of verifying the validity of the smart contract is a process in which nodes participating in the blockchain network verify the electronic signature of the smart contract, the leader who delivered the smart contract, and the sequence number mapped to the smart contract;
If the number of verified nodes exceeds the quorum, the process of treating the validity of the smart contract as verified;
A method of performing a smart contract, comprising: According to claim 1,
The decryption process is
calculating, by the contract fulfillment terminal, a homomorphic cryptographic comparison operation included in the smart contract; and
a process of verifying a homomorphic cryptographic comparison operation result from nodes participating in a second distributed consensus network;
A method of performing a smart contract, comprising: 4. The method of claim 3,
Nodes participating in the second distributed consensus network share the plaintext corresponding to the homomorphic encryption comparison operation result, and each node decrypts the ciphertext provided by the contract fulfillment terminal and compares it with the shared plaintext to determine whether or not they match The result is propagated to the neighboring nodes, and each node selects the value agreed by the nodes with a quorum or more among the values received from the neighboring nodes, and delivers the selected value to the node (leader) that initiated the consensus,
The smart contract execution method, characterized in that the leader selects a value agreed upon by nodes with a quorum or more, adopts it as a result of the agreement, and provides it to the contract fulfillment terminal. 5. The method of claim 4,
The smart contract execution method, characterized in that the leader is selected by the distributed consensus of the second distributed consensus network. 6. The method of claim 5,
When the leader is no longer available due to a failure, the next leader is selected in a predetermined order and is approved by distributed consensus. a contract party terminal for uploading a smart contract including homomorphic encrypted variables, which is information that is not intended to be disclosed to the outside in the process of creating a smart contract, to a block chain network;
a first distributed consensus network consisting of nodes participating in the blockchain network and for verifying the validity of a smart contract;
a contract fulfillment terminal implemented by nodes participating in the block chain network and determining suitability of contract execution according to conditions;
Consists of nodes participating in the blockchain network, and includes a second distributed consensus network to verify the suitability of contract execution according to conditions,
The contract party terminal,
It includes a template-code mapping module that converts a smart contract written in natural language into bytecode, and a preprocessing module that selects a variable to be encrypted from among the bytecode and encrypts it,
The contract fulfillment terminal,
Judging the contract execution according to the conditions, and if there is a homomorphic cryptographic comparison operation performed by an operation statement of less than, greater than, less than, equal to, greater than, equal to, or equal to, in the contract contents of the smart contract, Decrypts the homomorphic cryptographic comparison operation result by agreement with the second distributed consensus network,
The homomorphic cryptographic comparison operation is
A blockchain-based smart contract execution system including the process of checking whether the value obtained through the ciphertext operation is the same as the value after contract execution specified in the smart contract. 8. The method of claim 7,
The nodes participating in the second distributed consensus network share the plaintext corresponding to the homomorphic encryption comparison operation result, and each node decodes the ciphertext provided by the contract fulfillment terminal and compares it with the shared plaintext to determine whether it is consistent, The decision result is propagated to the neighboring nodes, and each node selects a value agreed by the nodes with a quorum or more among the values received from the neighboring nodes, and delivers the selected value to the node (leader) that initiated the consensus,
The leader selects a value agreed upon by nodes with a quorum or more, adopts it as a result of the consensus, and provides it to the contract fulfillment terminal. 9. The method of claim 8,
The blockchain-based smart contract execution system, characterized in that the leader is selected by the distributed consensus of the second distributed consensus network. 10. The method of claim 9,
When the leader is no longer available due to a failure, the next leader is selected in a predetermined order and approved by distributed consensus. 8. The method of claim 7,
Nodes participating in the second distributed consensus network include a decryption module that decrypts the encrypted text by comparing the shared plain text with the encrypted text received from the contract fulfillment terminal. 8. The method of claim 7,
The block chain-based smart contract execution system, wherein the contract party terminal determines that the contract is properly completed and terminates the smart contract when there is a quorum or more agreement from the contract execution terminal.

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