CN113656828B - Block chain privacy protection method based on lattice code and oriented to financial system transaction - Google Patents

Abstract

The invention relates to a block chain privacy protection method based on a lattice code and oriented to financial system transaction, and belongs to the technical field of block chain application. The method anonymously stores the transaction information in the global account block chain, and other nodes cannot know any useful information of the transaction except banks and users related to the transaction. The superior node can check the transaction records of the subordinate nodes, the subordinate nodes cannot directly inquire the transaction records of the superior node and other subordinate nodes, and the inquiry can be realized only when the inquiry is needed and the recovery condition of a secret sharing mechanism is required to be met. The encryption system adopted by the method is designed based on the lattice difficulty problem, and the method is still safe and usable even after the quantum computer is put into practical use. The method can effectively protect transaction data, has flexible authority management, and can effectively resist quantum attack.

Description

A blockchain privacy protection method based on lattice cryptography for financial system transactions

Technical Field

The present invention relates to a blockchain privacy protection method, and in particular to a blockchain privacy protection method based on lattice cryptography for financial system transactions, which belongs to the field of blockchain application technology.

Background Art

With the continuous development and popularization of blockchain technology, blockchain has received widespread attention from more and more governments and financial institutions. In the financial field, banks and financial institutions hope to reduce data maintenance costs and improve data security through blockchain. At the same time, since blockchain is based on a peer-to-peer network, it means that the blockchain mechanism does not process and store data from central nodes, so all transaction records must be open to all nodes, which is very detrimental to user privacy. Especially in the financial field, user data is one of the core competitiveness of enterprises, and financial institutions do not want to see user transaction information exposed on the chain.

Transaction records can reflect some sensitive knowledge and may leak the privacy of users. For example, the transaction records of users can reflect the consumption level and living conditions of users. In the blockchain, the first node to forward the transaction may be the initiating node of the transaction, which means that it is only necessary to connect to as many servers as possible and record the time of receiving transactions from different servers, so that the initiating node of the transaction can be inferred, and thus the true identity of the anonymous address can be known.

Privacy protection is generally regarded as one of the most important aspects in the field of financial security, and protecting data privacy is a key task in formulating privacy protection policies. In a bank transaction system based on a consortium chain, transaction data is equally important. Neither party wants banks outside the transaction to know the transaction data, and some upper-level banks want to manage the data of lower-level banks. For example, the upper-level node can review the lower-level node, and it can decide whether the lower-level node has the right to view the transaction data. A simple method is to encrypt all transaction data, which can hide the identity information and transaction information of both parties to the transaction. However, this method is not a feasible option in practical applications. Therefore, while ensuring privacy, some supervision measures are also needed.

At present, the overall structure of blockchain is not consistent with the overall structure of the modern financial system. Obviously, direct P2P transactions of Bitcoin and other similar digital currencies pose a huge challenge to the customer service and regulatory methods adopted by financial institutions. The financial industry is exploring a new model, that is, not directly circulating assets through peer-to-peer transactions between users, nor adopting a centralized trading system. Instead, the transactions of a large number of users are managed by a small number of entities (usually banks). Banks complete the stock transaction records of millions of users in the form of intermediaries through ledgers. Through system design and technical means, banks can ensure that they can faithfully complete the asset circulation according to the wishes of customers, but there are also many privacy protection issues. Therefore, in order to promote the long-term and healthy development of blockchain in the financial system, it is necessary to seek a balance between privacy protection and transaction supervision according to the characteristics and needs of the actual financial system.

To solve these problems, many researchers have proposed various solutions.

Among them, the hybrid currency scheme is a simple method, the principle of which is that the user first transfers funds to a third party, and then the third party transfers the funds to a designated account through multiple transfers. However, high handling fees and fund security are obvious drawbacks of this scheme.

Another method is encryption. Signature technology is widely used in the design of blockchain. In Bitcoin, elliptic curve cryptography is used to generate a public key corresponding to a private key. As the user's wallet address, the public key can distinguish different user IDs. Each user has multiple public key addresses to achieve the anonymity of transactions. In order to ensure the security authorization of transactions, the Bitcoin system digitally signs each transaction data. Both Bitcoin and Ethereum use the elliptic curve signature algorithm (ECDSA), which determines the shape of the ellipse through the parameters of secp256kl, and implements an asymmetric and efficient signature algorithm.

Hash function is also a commonly used encryption method. In Bitcoin, when a transaction begins, the user's public key address is generated by the hash value calculated by the SHA256 algorithm. When verifying transaction data, the user's public key is used to verify the signature to achieve non-repudiation of the transaction.

With the increasing rise of quantum computing, traditional signature algorithms face huge security challenges. Monero is well-known for its privacy protection. Monero uses random numbers to update the address of each transaction to ensure that observers cannot find the connection between the address and the recipient, but uses a timing analysis method to make it possible to track transactions. Zcash introduces zero-knowledge proof technology to hide transaction parameters, but its high computational overhead makes the proof process very slow.

Summary of the invention

The purpose of this invention is to address the defects and shortcomings of the existing technology, to solve the technical problem of privacy leakage risk in the transaction process of the financial system, and to creatively propose a blockchain privacy protection method based on lattice cryptography for financial system transactions.

In order to achieve the above object, the present invention adopts the following technical scheme.

First, the relevant concepts are explained.

Definition 1: Bank Intermediary Ledger System

It refers to the trading system in the modern financial system that uses the banking system for fund delivery and settlement;

Definition 2: Bank

Refers to institutions that undertake financial transaction activities. Different banks include a head office and several branches. Banks have user account lists and asset balance information;

Definition 3: Global Ledger

It refers to a system that records and stores all bank transaction information. The global ledger is composed of multiple consensus nodes and is a blockchain system that uses a secure consensus algorithm.

Definition 4: User

Refers to the object engaged in financial transaction activities, which belongs to a branch of a bank and can apply for transaction requests to the branch of the bank to which it belongs;

Definition 5: Lattice Cipher

It refers to a cryptographic system based on the lattice difficulty problem, which is a recognized cryptographic scheme that is resistant to quantum attacks;

Definition 6: Secret Sharing

It means that the secret is split in an appropriate way, and each share after the split is managed by a different participant. A single participant cannot recover the secret information. Only when specific participants participate and the number of participants reaches a certain minimum threshold, the participants can work together to recover the secret message.

Usually, secret sharing only requires a certain number of participants to work together to recover the secret message. The present invention is based on reality and adds the restriction that specific participants must participate, which is more in line with the needs of actual application scenarios.

Definition 7: Hash function

It refers to a function that can map an input of arbitrary length (also called a function preimage) into an output of fixed length (i.e., a hash value).

Hash function is one of the basic components of modern cryptography and was originally used for digital signatures. Hash function has the characteristics of one-way and anti-collision.

A blockchain privacy protection method based on lattice cryptography for financial system transactions includes the following steps:

Step 1: Initialize the entire system, including initializing the global ledger, banks, and users.

Specifically, step 1 includes the following steps:

Step 1.1: Initialize the global ledger.

Initialize the global ledger blockchain system and generate a public-private key pair for encrypting transaction information. The key is generated and managed by the highest authority owner designated by the entire system (which can be regarded as the central bank). Similar to the actual banking system, the global ledger manager can view all transaction information of its system class, while the subordinate banks can only query the transaction information of their own.

Step 1.2: Bank initialization.

The bank initializes the signature public-private key pair and the encryption-decryption public-private key pair, and initializes the respective user accounts and balance information. The signature public key is used not only for digital signatures, but also as the bank address.

Step 1.3: User initialization.

The user initializes the generation of a signature public-private key pair and an encryption-decryption public-private key pair. In addition to being used for digital signatures, the signature public key is also used as the user's personal address (i.e., username).

Step 2: Initiate a transaction. The user submits a transfer transaction request to the system.

Specifically, step 2 includes the following steps:

Step 2.1: User submits a transaction request.

The user submits the transaction request to the bank branch to which he belongs. The transaction information includes the personal address of the transfer recipient and the transfer amount. The transaction information is encrypted using the encryption key and signed using the signature key.

Step 2.2: Branch verification.

The branch receives the user's transaction request, verifies the transaction signature, and determines whether the transfer amount does not exceed the user's balance.

Step 2.3: The branch encrypts the verified transaction information using the encryption key, signs it with the signature key, and forwards it to its head office.

Step 2.4: The head office verifies the transaction signature. After verification, the transaction information is encrypted with the encryption key of the receiving head office, signed with the signature key of the head office of the transaction requester, and forwarded to the receiving head office.

Step 2.5: The receiving bank verifies the transaction signature. After verification, it negotiates with the transaction requesting bank on a random number as the internal transaction voucher number and forwards the internal transaction voucher number to the relevant branches and users.

Step 2.6: The head offices of both parties submit transaction requests to the global ledger respectively. The transaction information includes the user address of the transaction requester, the user address of the transaction recipient, the transaction amount, and the internal transaction voucher number. The transaction information is encrypted using their respective encryption keys and signed using the signature key.

Step 2.7: The global ledger verifies the signatures of the transaction requests from both head offices and verifies whether the transaction information is consistent; if they are consistent, proceed to step 3, otherwise, stop the transaction.

Step 3: Transaction processing, uploading and executing the transaction.

Specifically, step 3 includes the following steps:

Step 3.1: All nodes in the global ledger blockchain network reach consensus on the transaction. The transaction information includes the user addresses of both parties to the transaction, the transaction amount, and the internal transaction voucher number. The transaction information is encrypted using an encryption key, and the hash value of the internal transaction voucher number is calculated using a hash function as the external transaction serial number. The global ledger adds the external transaction serial number and the encrypted transaction information to the blockchain.

Step 3.2: After the branches of both parties to the transaction find the transaction in the global ledger according to the external transaction sequence number, the transaction is deemed successful, and then the branch updates the corresponding user balance information;

Step 4: Transaction query.

Users can query the transaction status at any time. When querying, first submit a query request to the global ledger. The request content includes the internal transaction voucher number of the transaction. The global ledger uses a hash function to calculate the hash value of the internal transaction voucher number, and then decrypts the transaction information corresponding to the external transaction number equal to the hash value in the blockchain and sends it to the user.

Step 5: Secret sharing and recovery.

The head office distributes its own keys to its branches through secret sharing according to actual needs. When a branch wants to inquire about transactions of other branches, it will work together to recover the keys after obtaining the consent of the head office and a number of branches.

After the query is completed, the head office can change the key and re-share the secret.

Beneficial Effects

Compared with the prior art, the method of the present invention has the following beneficial effects:

1. Effectively protect transaction data. According to the method, transaction information is anonymously stored on the global ledger blockchain. Except for the banks and users involved in the transaction, other nodes cannot know any useful information about the transaction. At the same time, since the transaction data is stored on the blockchain, the transaction information is prevented from being tampered with, and the authenticity of the data is guaranteed;

2. Flexible authority management. According to the method, the upper node can view the transaction records of the lower node, but the lower node cannot directly query the transaction records of the upper node and other lower nodes. When a query is needed, the recovery conditions of the secret sharing mechanism must be met to achieve the query. The introduction of the secret sharing mechanism makes the authority configuration more flexible;

3. Ability to effectively resist quantum attacks. The encryption system used in the method is designed based on the lattice difficulty problem, which means that the method is safe before the lattice difficulty problem is solved. Since lattice cryptography is currently recognized as post-quantum cryptography, the method is still safe and usable even after quantum computers are practical.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a schematic flow diagram of the method of the present invention.

DETAILED DESCRIPTION

The specific implementation process of the method of the present invention is further described in detail below with reference to the accompanying drawings.

As shown in Figure 1, the implementation process of the privacy protection transaction method of the financial system based on blockchain using lattice cryptography is described in detail.

代表总行B_i的第j个分行，分行

拥有用户

(i总行j分行的第n个用户)。In the bank intermediary ledger system, B ₁ ,B ₂ ,···,B _m represent the head offices of different banks.

represents the jth branch of the head office _Bi ,

Owning users

(The nth user of the i head office and the j branch).

(i总行 j分行的第p个用户)向用户

(r总行s分行的第t个用户)转账的过程，包 括以下步骤：Using the privacy protection transaction method of the financial system based on blockchain, users can

(The pth user of the i head office j branch) to the user

The process of transferring money from the tth user of the r head office to the s branch includes the following steps:

Step 1: System initialization. The entire system initialization is divided into three parts: global ledger, bank, and user.

Specifically, the steps include:

Step 1.1: Global ledger initialization. Initialize the global ledger blockchain system and generate a public-private key pair {Lepk, Lesk} for encrypting transaction information. The key is generated and managed by the highest authority owner designated by the entire system (which can be regarded as the central bank). Similar to the actual banking system, the global ledger manager can view all transaction information of its system class, and the subordinate banks can only query the transaction information of their own;

和加解密公私钥对

并初始化各 自所属用户账户

和余额信息

其中，签名公钥除用于数字签名外，还 作为银行地址。Step 1.2: Bank initialization. The head office of the bank initializes and generates its own signature public-private key pair {Bsignpk _i ,Bsignsk _i } and encryption-decryption public-private key pair {Bepk _i ,Besk _i }. Each branch initializes and generates its own signature public-private key pair

And encryption and decryption public and private key pairs

And initialize their respective user accounts

and balance information

Among them, the signature public key is used not only for digital signature, but also as a bank address.

和加解密公私钥对

其中，签名公钥除用于数字签名外，还作为 用户个人地址(即用户名)。Step 1.3: User initialization, user initialization generates signature public and private key pairs

And encryption and decryption public and private key pairs

Among them, the signature public key is not only used for digital signature, but also serves as the user's personal address (ie, user name).

In the above steps, the key is generated using the lattice password encryption method.

需向用户

转 账V元。Step 2: Initiate a transaction. The user submits a transfer transaction request to the system.

Need to provide users

Transfer V Yuan.

Specifically, the steps include:

提交交易请求Trequest。Step 2.1: User

Submit a transaction request Trequest.

将交易请求Trequest提交所属银行分行

交易信息包括转账接收 方用户个人地址

转账金额v。交易信息使用加密密钥

加密，并 用签名密钥

签名：user

Submit the transaction request Trequest to the bank branch to which it belongs

Transaction information includes the transfer recipient's personal address

Transfer amount v. Transaction information uses encryption key

Encrypted with a signing key

sign:

表示用秘钥

加密

表示用

加密v。in,

Indicates using a secret key

encryption

Indicates

Encryption v.

Step 2.2: The branch verifies the transaction request.

接收用户交易请求Trequest后验证交易签名，判断转账金额v是否不 超过用户余额

其中“？”表示判断，如果不超过， 则执行步骤2.3，否则终止交易。Branches

After receiving the user's transaction request Trequest, verify the transaction signature to determine whether the transfer amount v does not exceed the user's balance

The “?” indicates judgment. If it does not exceed, execute step 2.3, otherwise terminate the transaction.

将验证后的交易信息使用加密密钥

加密，用签名密 钥

签名，并将交易Trequest′转发其总行B_i：Step 2.3: Branch

Use the encryption key to encrypt the verified transaction information

Encrypted with signing key

Sign and forward the transaction Trequest′ to its head office _Bi :

表示用

加密

表示用

加密v。in,

Indicates

encryption

Indicates

Encryption v.

Step 2.4: The head office verifies the transaction signature of Trequest′. After verification, the transaction information is encrypted with the encryption key Bepk _r of the receiving head office, signed with the signature key Bsignpk _i of the transaction requesting head office _Bi , and the transaction Ti _,r is forwarded to the receiving head office B _r :

)。Step 2.5: The receiving bank B _r verifies the signature of the transaction Ti _,r . After the verification is passed, it negotiates with the transaction requesting bank B _i on the random number r as the internal transaction voucher number Txidinner, and forwards the internal transaction voucher number to the relevant branches and users (i.e.

).

交易接收方用户地址

交易 金额v、内部交易凭证号Txidinner。交易信息使用各自加密密钥Bepk_i和Bepk_r加 密，并用签名密钥Bsignpk_i和Bsignpk_r签名：Step 2.6: The head offices of both parties, _Bi and _Br, submit transaction requests _Ti,r ′ and T _r,i ′ to the global ledger L respectively. The transaction information includes the user address of the transaction requester.

Transaction recipient user address

Transaction amount v, internal transaction voucher number Txidinner. Transaction information is encrypted using the respective encryption keys Bepk _i and Bepk _r , and signed using the signature keys Bsignpk _i and Bsignpk _r :

表示用Bepk_i加密

和Txidinner，Encrypt(Bepk_i,v)表示用Bepk_i加密v。in,

Indicates encryption _with Bepki

And Txidinner, Encrypt(Bepk _i ,v) means encrypting v with Bepk _i .

Step 2.7: The global ledger L verifies the signatures of the transaction requests from both head offices and verifies whether the transaction information is consistent.

Among them, “?” indicates judgment.

The encryption process in the above steps is implemented using a lattice cipher encryption method.

Step 3: Transaction processing, uploading and executing the transaction.

和

交易金额v、交易内部凭证号Txidinner。交 易信息使用加密密钥Lepk加密，使用哈希函数计算交易内部凭证号的哈希值作 为外部交易序号Txid。全局账本将外部交易序号和加密后的交易信息添加在区块 链上：Step 3.1: All nodes in the global ledger L blockchain network reach consensus on transaction T. The transaction information includes the user addresses of both parties to the transaction.

and

Transaction amount v, transaction internal voucher number Txidinner. The transaction information is encrypted using the encryption key Lepk, and the hash value of the transaction internal voucher number is calculated using a hash function as the external transaction serial number Txid. The global ledger adds the external transaction serial number and encrypted transaction information to the blockchain:

表示用Lepk加密

v和Txidinner。in,

Indicates encryption with Lepk

v and Txidinner.

The encryption process involved in this step is implemented using a lattice cipher encryption method.

和

根据外部交易序号在全局账本中查询到交易 后，视为交易成功。随后，分行更新对应用户余额

和

Step 3.2: Transaction Banking

and

After the transaction is found in the global ledger according to the external transaction serial number, the transaction is deemed successful. Subsequently, the branch updates the corresponding user balance

and

Step 4: Transaction query. Users can query the transaction status at any time. When querying, they first submit a query request u _query to the global ledger. The request content includes the internal transaction voucher number Txidinner of the queried transaction. The global ledger L uses a hash function to calculate the hash value of the internal transaction voucher number, and then decrypts the transaction T corresponding to the external transaction number Txid in the blockchain that is equal to the hash value and sends it to the user.

The decryption process in this step is implemented using the lattice cipher decryption method.

Step 5: Secret sharing and recovery. The head office can distribute its own keys to its branches through secret sharing according to actual needs. When a branch wants to query transactions of other branches, it can jointly recover the keys after obtaining the consent of the head office and a number of branches. After the query is completed, the head office can replace the key and re-share the secret.

In the above steps, the grid password encryption method used is as follows:

The parameters are set as follows:

γ is the length of the public key of the global decryption party W, γ _i is the length of the public key of the encryption party W _i (i=1,2···,n); η is the length of the private key of W, η _i is the length of the private key of W _i ; ρ is the interference length of W, ρ _i is the interference length of W _i ; λ is the security parameter. τ represents the number of integers contained in the public key of W, and τ _i identifies the number of integers contained in the public key of W _i .

Let γ=O(λ ⁶ ), γ _i =O(λ ⁶ ), η=O(λ ⁵ ), η _i =O(λ ⁵ ), ρ=λ, ρ _i =λ, τ=λ+γ, τ _i =λ+γ.

The key generation method is:

$表示随机选取， Z表示整数集；w_i随机排列pk＝<x₀,x₁,···,x_τ>，得到

表示pk经过随机排列变换后的序列，

表示变换后的第τ个数。然后，w_i随机选 择数q_i,0,q_i,1,···,q_i,τ和γ_i,0,γ_i,1,···,γ_i,τ，q_i,τ表示w_i随机选择的q_i,0,q_i,1,···,q_i,τ中的第τ 个数，γ_i,τ表示w_i随机选择的γ_i,0,γ_i,1,···,γ_i,τ的第τ个数，其中，

并计算

x_i,0是x_i,j中最大值，最后重新计算

将pk_i＝< x_i,0,x_i,1,···,x_i,τ>作为w_i的公钥。The encryption system consists of a global decryption party W and multiple encryption parties _Wi (i=1,2···,n). W generates a public key pk=< _x0 , _x1 ,···, _xτ > and randomly selects a random number w as a private key sk, w∈[ ^{2η- 1,2η} ). _Wi randomly selects a random number _w as its private key sk _i .

$ represents random selection, Z represents a set of integers; w _i randomly arranges pk = <x ₀ ,x ₁ ,···,x _τ >, and obtains

represents the sequence after pk is randomly permuted and transformed.

represents the τth number after transformation. Then, w _i randomly selects numbers q _i,0 ,q _i,1 ,···,q _i,τ and γ _i,0 ,γ _i,1 ,···,γ _i,τ , q _i,τ represents the τth number among q _i,0 ,q _i,1 ,···,q _i,τ randomly selected by wi _, and γ _i,τ represents the τth number among γ _i,0 ,γ _i,1 ,···,γ _i,τ randomly selected by _wi , where

And calculate

x _i,0 is the maximum value among x _i,j , and is recalculated at the end

Let pk _i = < x _i,0 , x _i,1 ,···, x _i,τ > be the public key of _wi .

The encryption method is:

和随机数t_i,

对明文m_i∈{0,1}进行加密，输出密文

s_i表示集合{1,2，···,τ_i}中随机选择的某个数。w _i randomly selects

and random number t _i ,

Encrypt the plaintext m _i ∈ {0,1} and output the ciphertext

s _i represents a number randomly selected from the set {1, 2, ···, τ _i }.

The decryption method is:

即可解密。或者，W使用sk＝w计算m_i←[[c_i]_sk]₂也可解密。 _Wi is calculated using sk _i = _wi

Alternatively, W can use sk = w to calculate m _i ← [[c _i ] _sk ] ₂ , which can also be decrypted.

It can be seen from the above encryption method that W can arbitrarily decrypt the ciphertext of _Wi , while each _Wi can only decrypt its own ciphertext and cannot decrypt the ciphertext of other _Wi and W. Using this property, the encryption and decryption keys designed in the method of the present invention can be generated step by step by this encryption method, so that the upper-level node can decrypt the transaction information of the lower-level node, while the lower-level node cannot decrypt the transaction information of the upper-level node and other nodes at the same level.

In step 5, the secret sharing and recovery method used is as follows:

Preparation stage:

F _q is a finite field over prime numbers q, U _i represents the i-th participant, Share _i represents the secret share obtained by U _i , Share _i ∈F _q .

share is the secret that participant U wants to share, random is the random number generated by participant U, and participant U randomly generates an n-1 order polynomial:

f(x)≡share+random+a ₁ x+…+a _n-1 x ^n-1 (modq) (8)

Wherein, a ₁ and a _n-1 represent the coefficients of the 1st-order term x and the n-1th-order term x _n-1 in f(x), respectively, mod represents the modulus operation, and the modulus is q. x ^n-1 represents the n-1th-order term of f(x).

Secret sharing phase:

Participant U randomly selects _yi , calculates _z = f( _y ), and sends ( _z , _yi ) to _{U. Zi} represents the value of f( _y ), and _yi represents the value _yi of x randomly selected by U for _U.

Secret recovery phase:

When k ≥ n, n sub-secret owners recover share+random:

Where _yi represents the value _yi given by _U to randomly select x. k represents the number of sub-secret owners who participate in recovering the secret.

At this point, U needs to provide random to further restore the share.

It can be seen from the above secret sharing scheme that if the sub-secret owner wants to recover the secret, it requires the joint cooperation of the participant U and k≥n sub-secret owners. Using this property, the secret sharing recovery in the method described in the present invention can distribute the head office key to its branches through secret sharing according to actual needs. When a branch wants to inquire about transactions of other branches, it can jointly recover the key after obtaining the consent of the head office and a number of branches.

Claims (2)

1. A block chain privacy protection method based on lattice codes facing financial system transaction firstly explains related concepts:

definition 1: bank intermediary account book system

The system refers to a transaction system for carrying out fund delivery settlement by utilizing a bank system in a modern financial system;

definition 2: bank

The financial transaction system is characterized in that the financial transaction system is an organization for undertaking financial transaction activities, different banks comprise a main bank and a plurality of branch banks, and the banks have account lists and asset balance information of users;

wherein,

represents a head office of a different bank>

Represents a total row +>

Is based on the fifth->

Each branch is divided into rows and is divided into rows>

Having a user pick>

，

To representiHead officejGo in different rowsnA user;

definition 3: global account book

The system is used for recording and storing all bank transaction information, and the global account book is a block chain system which consists of a plurality of consensus nodes and adopts a safe consensus algorithm;

definition 4: user' s

The system is characterized in that an object engaged in financial transaction activities belongs to a branch of a certain bank and can apply for a transaction request to the branch of the bank;

definition 5: lattice code

The method is characterized by comprising the following steps of (1) establishing a cryptosystem based on the lattice difficulty problem;

definition 6: secret sharing

The secret is split, each split share is managed by different participants, a single participant cannot recover secret information, and only when a specific participant participates and the number of the participants reaches a certain minimum threshold value, the participants cooperate together to recover the secret information;

definition 7: hash function

The function is a function capable of mapping an input with any length into an output with a fixed length;

the method is characterized by comprising the following steps:

step 1: initializing the whole system, including initializing a global account book, a bank and a user, comprising the following steps:

step 1.1: initializing a global account book;

initializing global account book blockchain system and generating public and private key pair

The key is generated and managed by the highest authority owner appointed by the whole system; similar to an actual bank system, the global account book manager can check all transaction information of the system class, and lower-level banks can only inquire the transaction information of the lower-level banks;

step 1.2: initializing a bank;

each head office initializes to generate a signature public and private key pair

And public and private key pair for encryption and decryption

Row initialization generates respective signed public and private key pairs { (R { })>

And a public and private key pair for encryption and decryption { (R) }>

And initializing user accounts which belong to the user accounts>

And balance information->

The public signature key is used for digital signature and also used as a bank address;

step 1.3: initializing a user;

user initialized generating signature public and private key pair

Male and female key pair for encryption and decryption

Wherein the public signature key is used for digital signatureAlso as a user's personal address;

in step 1, a secret key is generated using a lattice code, the method being as follows:

the parameter setting comprises the following steps:

is->

Length of the public key of (4), and>

is encrypted square>

The public key length of (c);

Is->

Length of the private key of (4)>

Is->

The length of the private key of (c);

Is

Is greater than or equal to>

Is->

The interference length of (2);

Is a safety parameter;

represents->

An integer number contained in the public key>

Identification>

The integer number contained in the public key;

order to

，

，

，

，

，

，

，

；

The key generation method comprises the following steps:

the encryption system consists of a global decryptor

And a plurality of encryption sides>

Make up and/or are present>

Generating public keys

Selecting a random number->

As private key->

，

,

Randomly selecting a random number->

As its private key->

，

,

)，

Indicates a random selection>

Representing a set of integers;

Is randomly arranged->

Get->

，

Represents->

The sequences after random permutation and transformation are true>

Indicates the changed ^ th->

The number of the cells; then, is taken up or taken off>

Randomly selecting a number->

And &>

，

Represents->

Randomly selected>

Is greater than or equal to>

Number and/or unit>

Represents->

Selected randomly->

Is based on the fifth->

Number, wherein>

,

And calculates->

+

,

，

Is->

Medium maximum, and finally recalculated>

Will >>

=

As->

The public key of (2); step 2: initiating a transaction, the user submitting a transfer transaction request to the system, the user @>

Needs to be picked up and picked up by the user>

Transfer box>

A cell, comprising the steps of:

step 2.1: user' s

Submit a transaction request pick>

；

User' s

Will transaction request->

Submit the affiliated bank branch->

The transaction information includes the transfer recipient user's personal address->

And transfer amount->

Transaction information is encrypted using an encryption key>

Encrypting and using a signing key

Signing;

wherein,

representing key->

Encrypted->

，

Means for>

Encrypted->

；

Step 2.2: verifying by lines;

is divided into rows

Receiving a user transaction request->

Verifying the transaction signature and determining the transfer amount>

Whether or not the user balance is not exceeded>

；

Step 2.3: is divided into rows

Using an encryption key to ^ the authenticated transaction information>

Encryption, using a signing key

Sign and combine the transaction>

Forward its row in>

：

Wherein,

means for>

Encrypted->

，

Means for>

Encrypted->

；

Step 2.4: head office verification

The transaction is signed and verified, and then the encryption key is encrypted by the receiver's bank>

Encrypting the transaction information, based on the transaction requester's chief line>

Signature key->

Signs and puts the transaction->

Forward receiver column>

：

Step 2.5: receiver head office

Validating transaction>

Signature, and after passing the verification, the transaction requester's chief line>

Co-negotiating a random number->

As an internal transaction credential number &>

And forwards the internal transaction voucher number to the relevant branch and the user, i.e. &>

；

Step 2.6: two-party head office

Respectively to a global credit>

Submitting a transaction request +>

And &>

The transaction information includes the address of the user of the transaction requester>

Subscriber address of the transaction receiver>

The transaction amount pickand place>

Internal transaction voucher number->

Transaction information is encrypted using a respective encryption key>

And &>

Encrypting and using a signing key

And &>

Signature:

wherein,

for indicating

，

Means for>

Encrypted->

；

Step 2.7: global account book

The signature is verified for the transaction request of the head office of both parties and the transaction information is verified

Whether the two are consistent;

and step 3: transaction processing, linking and executing transactions, comprising the steps of:

step 3.1: global account book

Node pairs in a block chain network having transaction on/off>

Making a consensus, the transaction information including the address of the user of both parties of the transaction>

And &>

The transaction amount pickand place>

Transaction internal voucher number->

Transaction information is encrypted using an encryption key>

Encryption, using a hash function to calculate a hash of the transaction's internal credential number as the external transaction sequence number->

The global account book adds the external transaction sequence number and the encrypted transaction information to the blockchain: />

，

Wherein,

means for>

Encryption

；

Step 3.2: both sides of the transaction branch

And &>

After the transaction is inquired in the global account book according to the external transaction sequence number, the transaction is considered to be successful, and then the corresponding user balance is updated in different banks and based on the fact that the user balance is on or off>

And &>

；

And 2, encrypting by using a lattice code in the steps 3, wherein the method comprises the following steps:

is selected at random>

And a random number->

,

For clear text->

Encrypt and output the encrypted text->

Indicates that the collection is->

A certain number selected randomly;

and 4, step 4: transaction inquiry, user can inquire transaction condition at any time, and when inquiring, firstly, it submits inquiry request to global account book

The request content contains the internal transaction voucher number @' of the queried transaction>

Global ledger->

Calculating a hash value of the internal transaction credential number using a hash function, and then concatenating the external transaction sequence numbers in the block chain equal to the hash value

The corresponding transaction->

Decrypting and sending to the user;

in the decryption process in the step 4, the lattice code is used for decryption, and the method comprises the following steps:

use>

Calculate->

Or

Use>

Calculate->

；

And 5: secret sharing and recovery;

the head office distributes the own secret key to the affiliated branch lines through secret sharing according to actual requirements; when the branch lines need to inquire other branch line transactions, after the agreement of the head line and a plurality of branch lines is solicited, the key is recovered by cooperation together;

the secret sharing and recovering method used in step 5 is as follows:

a preparation stage:

is a prime numberqUpper finite field, is greater than or equal to>

Represents a fifth->

Is involved in>

Represents->

The resulting share of the secret is shared with,

；/>

is the party participating in>

Secret that wants to be shared, based on the number of times that the user has selected>

Is the party participating in>

Generated random numbers, parties involved

Is randomly generated>

Order polynomial:

wherein,

、

respectively denote->

Sub-term->

And &>

Is greater than or equal to>

Representing a modulo operation with a modulus ofq；

Represents->

Is/are>

A secondary term;

secret sharing stage:

participant side

Random selection>

Calculate->

Will >>

Is sent to>

Represents->

，

Represents->

Give/pick>

Selected randomly->

Value->

；

Secret recovery phase:

when in use

When, is greater or less>

Sub-secret owner recovers>

：

Wherein,

represents->

Give/pick>

Is selected at random>

Value->

Represents the number of child secret owners that are involved in recovering the secret;

at this time, it is necessary to

Providing +>

Can be further restored>

。

2. The financial system transaction-oriented block chain privacy protection method based on the lattice code as claimed in claim 1, wherein after the query is completed, the head office changes the key and performs secret sharing again.

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