Traceless block chain covert communication method based on RBF mechanism

Abstract

According to the traceless block chain covert communication method based on the RBF mechanism, a sender carries out Base64 coding on secret information, the secret information is transmitted by using the service charge rate of a transaction through the association established between a code value and the charge rate, and the information embedding amount of the transaction is improved. The sender creates the alternative transaction by using the RBF mechanism before the secret-carrying transaction is confirmed, discards the original secret-carrying transaction and finally confirms the alternative transaction, so that the effect that the secret-carrying transaction is not retained is achieved. According to the method, the receiver can obtain the sending address of the secret-carrying transaction through the derivation relationship, and the secret-carrying transaction can be quickly inquired before the secret-carrying transaction is abandoned by monitoring the sending address in real time, so that the time efficiency of communication is improved. Experimental results show that the average 1Byte information embedding and extracting time of the method is improved from the minute level to the second level compared with that of a common method, the average information embedding amount of each transaction is improved to 6 bits, and the concealment and safety are greatly improved due to the characteristic that secret-carrying transactions are not linked.

Description

Technical Field

[0001] The present invention belongs to the field of communications, and in particular relates to a traceless blockchain covert communication method based on an RBF mechanism. Background Art

[0002] Since Lampson first proposed the concept of covert communication in 1973, covert communication technology has made great progress. Covert communication refers to the transmission of hidden messages during the communication process, making it difficult for others except the participants to detect and identify. Traditional covert communication methods include steganography and encryption technology, but these methods are still easy to identify or crack. The earliest covert communication model originated from the prisoner model proposed by Simmons, which was extended to computer communication. Blockchain is a decentralized distributed ledger technology that was initially widely used in the digital currency Bitcoin. The blockchain technology associated with digital currency has the characteristics of decentralization, anonymity, strong robustness and tamper resistance, and is a natural carrier for building covert communication channels. Blockchain is a decentralized distributed database that allows participants to conduct transactions and communicate without a central control agency. This decentralized feature is consistent with the needs of covert communication, and the decentralized nature of blockchain makes it highly robust and stable. Blockchain is transparent, that is, all transaction records can be accessed and viewed by users on the network. Therefore, the transaction recipient does not need to be set as the actual information recipient, and can arbitrarily select users as the recipient of the transaction. Due to the encryption and distributed nature of blockchain, once information is written into the blockchain, it will be difficult to tamper with the information, which helps to protect the integrity of the information and ensure that the communication content has not been modified without authorization. In recent years, blockchain technology has been widely used and explored in many fields such as the Internet of Things, supply chain, and financial services. As an emerging information technology, blockchain is considered to be an important strategic frontier information technology to promote the development of a highly informationized society, and has attracted great attention from the information community. In order to meet the needs of efficient, secure, hidden, and stable transmission of information, ensure that data is not detected, and protect the personal information of data hidden transmission, data transmission based on blockchain will become a new development direction for hidden data transmission. It should be pointed out that blockchain hidden communication technology is still in its early stages and has not yet been widely used and mature solutions. At the same time, the use of blockchain for hidden communication also faces some challenges, including message capacity limitations, transmission efficiency, and security issues. Therefore, the research and development of blockchain hidden communication technology still needs further exploration and innovation.

[0003] Juha Partala proposed a relatively complete and feasible system (BLOCCE, blockchain covert channel). The BLOCCE method cleverly distributes hidden information by using the least significant bit of the address, but the information embedding rate is very low because each address only stores one binary bit of information. Song Shang et al. proposed a BLOCCE+ covert communication method based on the BLOCCE method, which was improved by embedding secret information in the low α bit of the space. She Wei et al. proposed a blockchain covert communication model for plain text information hiding. Compared with BLOCCE, this model has improved the embedding strength to a certain extent; then combined the attribute-based encryption (CP-ABE, ciphertext-policy attriute-based encryption) technology with the image steganography based on generative adversarial networks (GAN, generative adversarial networks) to propose a blockchain covert communication model that can hide sensitive documents and sender identities. Xiong Lizhi et al. proposed a blockchain network covert communication method based on transaction construction and forwarding mechanism, using the transaction forwarding mechanism to send invalid transactions to neighboring nodes, so that confidential transactions are propagated between nodes and do not exist in the blockchain ledger. Jiang Pengkun et al. proposed a covert communication method based on blockchain under the cover of normal transactions, which uses the characteristics of elliptic curves to quickly filter transactions, generate addresses by themselves, and build a negotiation-free password table to match binary bits. Although the research on covert communication based on blockchain has been deepening in recent years, there are still some problems that have not been fully solved in the existing research.

[0004] (1) The permanent storage feature of blockchain is a major challenge when using blockchain for covert communication. Although normal confidential transactions are encrypted, once they are written into the blockchain, they will still be permanently saved. Anyone can apply to view the relevant transactions, which may give attackers enough time to collect data for analysis, thereby exposing the risk of leakage of transmitted secret information. Except for the method proposed by Xiong Lizhi et al., the confidential transactions of the remaining methods based on blockchain for covert communication need to be uploaded to the chain. Although the method proposed by Xiong Lizhi et al. realizes that confidential transactions are not stored in the blockchain ledger, it requires the sender to designate the receiving node as its first-level neighbor node and send invalid transactions to the neighbor node, which is a complicated process.

[0005] (2) Most of the existing Bitcoin-based covert communication methods have a small number of confidential transactions in one block. If multiple confidential transactions are to be initiated in one block, the problem of sorting confidential transaction information needs to be solved. When extracting information, the receiver needs to traverse the blockchain network to obtain newly generated transaction information, and the blockchain itself has weak real-time performance, resulting in low time efficiency of communication.

[0006] (3) Existing blockchain covert communication methods basically use the binary encoding of ciphertext, but the binary encoding of ciphertext results in low embedding strength of transactions. Transmitting one ciphertext requires transmitting 8 bits of binary information. The Bitcoin-based covert communication method generally embeds information in the OP_RETURN field or address of the transaction. Generally, the content in the OP_RETURN field of a transaction is usually very short and often empty, so storing information in the OP_RETURN field can be easily monitored by attackers, who can analyze and process the monitored information, increasing the risk of information leakage. Summary of the invention

[0007] The technical problem to be solved by the present invention is: In response to the above three problems, the present invention provides a traceless blockchain covert communication method based on the RBF mechanism.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A traceless blockchain covert communication method based on RBF mechanism, including four processes: information processing, embedding, extraction and recovery, and RBF processing;

[0010] Step 1: Information processing: Base64 encode the secret information to be transmitted;

[0011] Step 2 Embed Process: Establish a corresponding encryption rule between the code value and the transaction fee rate, that is,

[0012] transactionfees k =7+0.1*codevalue k (0≤codevalue k ≤9) (7)

[0013] transactionfees k =0.1*codevalue k (10≤codevalue k ≤63) (8)

[0014] Among them, transaction fees k Indicates the handling fee rate, codevalue k Indicates Base64 encoding base64byte k The code value of k is

[0015] Step 3: Extraction and Recovery Process: The receiver can also deduce the sending address based on the derivation relationship, that is,

[0016] pk i *PSK=pk i+1 (11)

[0017] sendaddr i = PublickeyToAddress(pk i ) (12)

[0018] After the receiver knows the sender's address, he can obtain the transaction by using a blockchain browser or calling the blockchain API. After obtaining the transaction, the handling fee rate of each transaction is the ciphertext to be transmitted. When a certain address is monitored for a long time without transactions, the monitoring is stopped, and it can be considered that the ciphertext has been received;

[0019] Step 4: RBF processing: The sender can construct a transaction T*, then broadcast T* and set the transaction fee of T* to be significantly higher than that of the confidential transaction T. Due to the high fee set, T* will eventually be confirmed and packaged into the block, while the confidential transaction T will be cleared due to the low fee and cannot be packaged into the blockchain, which is equivalent to the confidential transaction T being withdrawn.

[0020] In step 1, the information encoding process is as follows:

[0021] 1.1) Divide the information data into groups of three bytes, namely

[0022] groupbyte i =[byte 3i-2 ,byte 3i-1 ,byte 3i ] (1)

[0023] Among them, byte i Represents 1 byte, groupbyte i Represents a data group containing 3 bytes, the value of i is len indicates the number of bytes of secret information;

[0024] 1.2) Convert each byte into 8-bit binary form, i.e.

[0025] bin j =z(byte j ) (2)

[0026] groupbin i =[bin 3i-2 , bin 3i-1 , bin 3i ] (3)

[0027] Among them, z(x) means converting information x into a binary stream; binj Represents a 1-byte binary stream, the value of j is {j|j∈N * , 1≤j≤len}; groupbini represents a binary stream of 3 bytes in a data group, and the value of i is

[0028] 1.3) Divide the 24-bit binary information of a data group into groups of 6 bits, that is,

[0029] [b 4i-3 , b 4i-2 , b 4i-1 , b 4i ]=groupb i (4)

[0030] Among them, b i Represents 6 bits of binary information, groupb i with groupbin i They all represent 24 bits of binary information for a data group, but the divisions are different. The value of i is

[0031] 1.4) Convert each 6-bit binary group into the corresponding Base64 character, that is,

[0032] base64byte k =T(b k ) (5)

[0033] Among them, T(y) means converting binary information y into Base64 encoding, base64byte k Indicates a Base64 encoding, the value of k

[0034] 1.5) Connect all converted Base64 characters to form the final encoding result, that is,

[0035]

[0036] Among them, code represents the final encoding result, and the secret information of len bytes will eventually be A code.

[0037] In step 3, the steps to restore the ciphertext to secret information are as follows:

[0038] 3.1) After the recipient extracts the transaction fee rate, he first obtains the Base64-encoded code value according to the encryption rules and the known fee rate, that is,

[0039] codevalue k=(transactionfees k -7)*10(7.0≤transactionfees k ≤7.9) (13)

[0040] codevalue k =transactionfees k *10(1.0≤transactionfees k ≤6.3) (14)

[0041] Among them, k refers to the number of transactions, and the value of k is There are two cases according to the transaction fee rate. k ≤7.9, use formula (13) to calculate; when 1.0≤transactionfees k When ≤6.3, use formula (14) for calculation;

[0042] 3.2) Convert each Base64 character into its corresponding 6-bit binary, i.e.

[0043] b k =T -1 (base64byte k ) (15)

[0044] Among them, T -1 (x) means converting Base64 encoding x into binary information, base64byte k Indicates a Base64 encoding, the value of k is

[0045] 3.3) Put 4 b k Form a data group, namely

[0046] groupb i =[b 4i-3 , b 4i-2 , b 4i-1 , b 4i ] (16)

[0047] Among them, groupb i Represents 24 bits of binary information of a data group. The value of i is

[0048] 3.4) Divide the 24-bit binary information of a data group into 8-bit groups, that is,

[0049] [bin 3i-2 , bin 3i-1, bin 3i ]=groupbin i (17)

[0050] byte j =z -1 (bin j ) (18)

[0051] Among them, groupb i with groupbin i Both represent 24 bits of binary information for a data group, but they are divided differently; bin j Represents an 8-bit binary stream, the value of j is {j|j∈N * , 1≤j≤len}; z -1 (y) means converting binary information y into byte information;

[0052] 3.5) Byte information byte j By splicing them in order, you can get the secret information:

[0053] secret_message=byte 1 |||…||byte len (19).

[0054] The present invention adopting the above technical solution has the following technical effects:

[0055] 1) The present invention utilizes the idea of ​​Bitcoin RBF mechanism. After the sender broadcasts the confidential transaction T, it needs to wait for confirmation to be packaged into the block. Before the confidential transaction T is confirmed to be included in the block, the receiver queries the sending address to obtain the transaction fee rate of T, and then obtains the secret information m and completes the secret communication. Before the confidential transaction T is confirmed to be included in the block, the sender uses the RBF function to modify the fee of the original transaction T, which will create a new alternative transaction T*, and set the fee of T* to be higher than the fee of T. After broadcasting T*, T* can be packaged into the block. Due to the low fee, transaction T will be cleared and cannot be packaged into the blockchain. This is equivalent to the confidential transaction T being withdrawn, and T will not be at risk of being suspected over time. The use of the RBF mechanism is easy to operate and realizes that the confidential transaction is not stored in the blockchain ledger, further enhancing the concealment and security, and solving the above-mentioned problem (1).

[0056] 2) The present invention uses the idea of ​​derived addresses. In order to identify special transaction chains containing secret information, the input and output addresses or public keys of the transaction need to have a certain derivative relationship. The sender can send multiple transactions with derivative relationships in one block, and use the derivative relationship to ensure the transmission order of information. The receiver does not need to traverse the transactions or wait for transaction confirmation. He can quickly find these special transactions based on the derivative relationship and sort the information according to the derivative relationship to obtain the secret information. The use of derived addresses improves the time efficiency of communication and solves the aforementioned problem (2).

[0057] 3) The present invention changes the general basic method of information embedding, cancels the binarization of ciphertext, establishes a mapping table between Base64 encoding and transaction fee rate, and uses the handling fee rate of blockchain transactions to embed secret information. In a string encoded by Base64, each character is selected from 64 characters, so the amount of information represented by each character is 2log64 bits, and each transaction can embed 6 bits of binary information. The present invention breaks the norm and does not use the OP_RETURN field, address or transaction amount to embed information, but uses the transaction fee rate to embed secret information. The method of the present invention not only increases the amount of information embedded in the transaction, but also reduces the risk of information leakage, thereby solving the aforementioned problem (3). BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 This is a diagram of the covert communication model;

[0059] Figure 2 Get the sending address of the transaction for the sender;

[0060] Figure 3 Construct a confidential transaction graph for the sender;

[0061] Figure 4 Deducing the sending address of the encrypted transaction for the recipient;

[0062] Figure 5 To use the RBF function schematic;

[0063] Figure 6 This is the embedding time comparison experiment diagram;

[0064] Figure 7 This is an experimental diagram for embedding rate comparison. DETAILED DESCRIPTION

[0065] Bitcoin and blockchain technology are inseparable. Bitcoin is one of the first and most famous applications of blockchain technology. Bitcoin as the first application of blockchain: Bitcoin is a decentralized digital currency based on blockchain technology proposed by Satoshi Nakamoto. Satoshi Nakamoto first described the concept of blockchain in the Bitcoin white paper and used it as the underlying technology foundation of Bitcoin. Therefore, Bitcoin is regarded as the first application case of blockchain technology. Blockchain as Bitcoin's infrastructure: Bitcoin's blockchain is a public, distributed ledger that records the transaction history of Bitcoin. Blockchain links transactions together in chronological order to form an unalterable chain structure. This blockchain design enables Bitcoin to achieve decentralization, reliability and security. Bitcoin is not the only blockchain platform. Later, open source blockchain platforms such as Ethereum and Hyperledger Fabric were born. Blockchain technology can be divided into three forms: public chain, private chain, and consortium chain. Public chains (such as Bitcoin) are open, decentralized networks that anyone can participate in and verify and record transactions. A private chain is a restricted blockchain network for a specific organization or individual, with limited participants and verification mechanisms. Consortium chains (such as Fabric) can be understood as a compromise between public chains and private chains.

[0066] RBF (Replace-By-Fee) is a mechanism in the Bitcoin network that allows transaction initiators to increase transaction fees in unconfirmed transactions, thereby increasing the priority of transactions and allowing them to be packaged and confirmed more quickly. This mechanism allows transaction initiators to make adjustments to transactions that have been broadcast but not confirmed to adapt to current network congestion or to increase the priority of transactions. A user broadcasts a transaction to the Bitcoin network. If the transaction confirmation time is long, the user can create another new transaction with the same input but with adjusted transaction fees. The new transaction can increase the priority of the transaction by increasing the transaction fee or changing other parameters. In this way, the new transaction will have a higher priority and is more likely to be mined first. If the new transaction is confirmed, the old transaction will be replaced and only the new transaction will be confirmed. Note that the RBF function can only be used to modify the transaction fee before the transaction is confirmed. Once the transaction is confirmed and entered into the block, it can no longer be modified using RBF.

[0067] Base64 encoding is an encoding method used to convert binary data into printable characters. It converts any binary data sequence into a text string consisting of 64 different characters. The Base64 character set includes uppercase letters AZ, lowercase letters az, numbers 0-9, and two special characters + and / . Base64 encoding is often used to transmit data between different systems, especially in network communications, because it can ensure that data will not be erroneous during transmission due to special characters or encoding problems. Base64 can convert any data into an easily portable string, avoiding distortion during transmission. Base64 encoding requires converting 3 8-bit bytes (3*8=24) into 4 6-bit bytes (4*6=24), and then adding two 0s in front of the 6 bits to form an 8-bit byte format. Initially, Base64 was designed to solve the problem that non-ASCII characters could not be used directly in emails. After a piece of data is encoded into an ASCII string by Base64, it can be restored to the original data at the receiving end through Base64 decoding without worrying about distortion during transmission.

[0068] The present invention provides a covert communication method for a traceless blockchain based on the RBF mechanism, including information processing, embedding, extraction and recovery, and RBF processing. The covert communication method is described in four processes. The covert communication model is as follows: Figure 1 shown.

[0069] Step 1: Information processing: The secret information to be transmitted is Base64 encoded, and the information encoding process is as follows.

[0070] 1.1) Divide the information data into groups of three bytes, namely

[0071] groupbyte i =[byte 3i-2 ,byte 3i-1 ,byte 3i ] (1)

[0072] Among them, byte i Represents 1 byte, groupbyte i Represents a data group containing 3 bytes, the value of i is len indicates the number of bytes of the secret information. If the remaining characters are less than 3 bytes, they are padded with 0 and the output characters are '=', so 1 or 2 '=' may appear at the end of the text after encoding.

[0073] 1.2) Convert each byte into 8-bit binary form, i.e.

[0074] bin j =z(byte j) (2)

[0075] groupbin i =[bin 3i-2 , bin 3i-1 , bin 3i ] (3)

[0076] Among them, z(x) means converting information x into a binary stream; bin j Represents a 1-byte binary stream, the value of j is {j|j∈N * , 1≤j≤len}; groupbin i Represents a binary stream of 3 bytes in a data group. The value of i is

[0077] 1.3) Divide the 24-bit binary information of a data group into groups of 6 bits, that is,

[0078] [b 4i-3 , b 4i-2 , b 4i-1 , b 4i ]=groupb i (4)

[0079] Among them, b i Represents 6 bits of binary information, groupb i with groupbin i They all represent 24 bits of binary information for a data group, but the divisions are different. The value of i is

[0080] 1.4) Convert each 6-bit binary group into the corresponding Base64 character, that is,

[0081] base64byte k =T(b k ) (5)

[0082] Among them, T(y) means converting binary information y into Base64 encoding, base64byte k Indicates a Base64 encoding, the value of k

[0083] 1.5) Connect all converted Base64 characters to form the final encoding result, that is,

[0084]

[0085] Where code represents the final encoding result. The secret information of len bytes will eventually be A code.

[0086] Step 2: Embedding process: Due to the use of the RBF mechanism, the original transaction and the replacement transaction only differ in the transaction fee rate, and the original transaction will be withdrawn, so using the original transaction fee rate to transmit information will be highly concealed. The Base64 encoding table is shown in Table 1.

[0087]

[0088] Table 1.

[0089] In order to use the transaction fee rate to transmit information, it is necessary to establish a certain association between the transaction fee rate and the code. The present invention establishes a corresponding encryption rule between the code value and the transaction fee rate, that is,

[0090] transactionfees k =7+0.1*codevalue k (0≤codevalue k ≤9) (7)

[0091] transactiofees k =0.1*codevalue k (10≤codevalue k ≤63) (8)

[0092] Among them, transaction fees k Indicates the handling fee rate, codevalue k Indicates Base64 encoding base64byte k The code value of k is An association is established between the code value of the Base64 encoding table and the handling fee rate, that is, the code value is expressed by the handling fee rate: the code value of 0-9 is expressed by 7.0sat / vB-7.9sat / vB, for example, the code value of F is 5 and it is expressed by 7.5sat / vB; the remaining code values ​​with two digits are all added with decimal points, for example, the code value of b is 27 and it is expressed by 2.7sat / vB.

[0093] The BLOCK method stores 1 bit of information per transaction. Sending secret information generally initiates multiple transactions, which are recorded in different blocks generated successively to ensure the order. Currently, many blockchain covert communication methods require the receiver to traverse the newly generated transaction information in the blockchain network to extract the secret information. If the sending address of the transaction has a derivative relationship, the receiver can determine the address order through the derivative relationship. It is difficult for the attacker to distinguish between special transactions and ordinary transactions, but the receiver can still quickly find these special transactions. The sender establishes the derivative relationship of the sending address as follows: Figure 2shown.

[0094] The symbols and meanings of the derived algorithm are shown in Table 2.

[0095] symbol meaning sk Private Key pk Public Key PSK Pre-shared key * Elliptic curve multiplication G Elliptic curve base point ％ Modulo Operation N Bitcoin's private key space PublickeyToAddress Convert a public key to an address

[0096] The key generation algorithm for the private key and public key of the derived chain is as follows:

[0097] sk i *PSK%N=sk i+1 (9)

[0098] sk i+1 *G=pk i+1 (10)

[0099] It should be noted that the * in the above formula refers to elliptic curve multiplication, and the % refers to the modular operation based on Bitcoin. After importing the private key into the Bitcoin wallet, the corresponding address can be obtained. The number of private keys and public keys that need to be calculated depends on the number of bytes of the secret information.

[0100] The present invention determines the order of encrypted transactions based on the derivative relationship between the sending addresses and stores the encrypted information based on the transaction fee rate. Taking the transmission of Base64 encoding F and b as an example, the transaction and ciphertext transmission of the blockchain are as follows: Figure 3 shown.

[0101] Step 3: Extraction and Recovery Process: Since the sending address has a derivative relationship, the receiver only needs to know the pre-shared key PSK and the public key of sending address 1 to get the sending address of each transaction below. Figure 4 shown.

[0102] The receiver can also deduce the sending address based on the derivation relationship, that is,

[0103] pk i *PSK=pk i+1 (11)

[0104] sendaddr i = PublickeyToAddress(pk i ) (12)

[0105] After the receiver knows the sender's address, he can use the blockchain browser or call the blockchain API to obtain the transaction. After obtaining the transaction, the handling fee rate of each transaction is the ciphertext to be transmitted. When a certain address is monitored for a long time without transactions, stop monitoring, and it can be considered that the ciphertext has been received. The steps to restore the ciphertext to secret information are as follows.

[0106] 3.1) After the recipient extracts the transaction fee rate, he first obtains the Base64-encoded code value according to the encryption rules and the known fee rate, that is,

[0107] codevalue k =(transactionfees k -7)*10(7.0≤tramsactionfees k ≤7.9) (13)

[0108] codevalue k =transactionfees k *10(1.0≤transactionfees k ≤6.3) (14)

[0109] Among them, k refers to the number of transactions, and the value of k is There are two cases according to the transaction fee rate. k ≤7.9, use formula (13) to calculate; when 1.0≤transactionfees k When ≤6.3, use formula (14) for calculation.

[0110] 3.2) Convert each Base64 character into its corresponding 6-bit binary, i.e.

[0111] b k =T -1 (base64byte k ) (15)

[0112] Among them, T -1 (x) means converting Base64 encoding x into binary information, base64byte k Indicates a Base64 encoding, the value of k is

[0113] 3.3) Put 4 b k Form a data group, namely

[0114] groupb i =[b 4i-3 , b 4i-2 , b 4i-1 , b 4i ] (16)

[0115] Among them, groupb i Represents 24 bits of binary information of a data group. The value of i is

[0116] 3.4) Divide the 24-bit binary information of a data group into 8-bit groups, that is,

[0117] [bin 3i-2 , bin 3i-1 , bin 3i ]=groupbin i (17)

[0118] byte j =z -1 (bin j ) (18)

[0119] Among them, groupb i with groupbin i Both represent 24 bits of binary information for a data group, but they are divided differently; bin j Represents an 8-bit binary stream, the value of j is {j|j∈N * , 1≤j≤≤len}; z -1 (y) means converting binary information y into byte information.

[0120] 3.5) Byte information byte j The secret information can be obtained by splicing them in order.

[0121] secret_message=byte 1 |||…||byte len (19)

[0122] Step 4 : RBF processing process:After the sender broadcasts the confidential transaction T, the confidential transaction T needs to wait for confirmation to be packaged into the block. Before the confidential transaction T waits for confirmation to be packaged into the block, the receiver queries the relevant information of the confidential transaction T and obtains the handling fee rate of the transaction T. If the transaction T is confirmed, it will not be possible to perform RBF processing on it. Therefore, it is necessary to set the handling fee rate of the transaction T to be low so that the transaction T will not be confirmed too quickly. During the period when the transaction T is waiting for confirmation to be packaged into the block, the sender constructs and creates another new transaction T* with the same input but adjusted transaction fees. According to this method, the sender can construct transaction T*, then broadcast T*, and set the transaction fee of T* to be significantly higher than that of the confidential transaction T. Since T* and T share the same transaction input, there will be a conflict. If these two transactions are not packaged on the blockchain, the transaction with a higher handling fee will be packaged to maximize the benefits. T* will eventually be confirmed and packaged into the block due to the high handling fee set, while the confidential transaction T will be cleared due to the low handling fee and cannot be packaged into the blockchain, which is equivalent to the confidential transaction T being withdrawn. Since the confidential transaction T is not recorded in the blockchain, the risk of being tracked is reduced, thereby further improving security. The RBF construction process is as follows: Figure 5 shown.

[0123] Simulation experiment and performance analysis:

[0124] The present invention conducts simulation experiments and analyzes the proposed covert communication method in combination with the experimental results. The hardware platform used in the experiment is a PC, the processor is a 13th Gen Intel(R) Core(TM) i7-13700H@2.40GHz, and the memory is 16.0GB.

[0125] The simulation experiment uses the Bitcoin test network to simulate the blockchain network under the Windows system, uses Python to implement the algorithm for deriving addresses, and simulates the entire covert communication process in the Electrum wallet. The private keys obtained by the derivation algorithm are imported into the blockchain network in sequence to create accounts. The previous and next accounts have a derivative relationship. The information of each account is shown in Table 3.

[0126]

[0127]

[0128] Table 3 Derived experimental data information.

[0129] In this experiment, the secret information that the sender wants to transmit is set to "zzu", and its Base64 encoding is "enp1". enp1 has a total of 4 codes, and 4 derived addresses are required to construct 4 secret transactions to transmit e, n, p, and 1 in sequence. During the transmission process, the sending address of the transaction is the imported derived address, and the receiving address can be selected arbitrarily without directly selecting the recipient's address. The transfer amount can be customized. According to the Base64 code value table and the established encryption rules, the handling fee rates of the above 4 transactions are set to 3.0sat / vB, 3.9sat / vB, 4.1sat / vB, and 5.3sat / vB, respectively, so as to cleverly use the transaction fee to transmit hidden information.

[0130] Each time a confidential transaction T is broadcast, the RBF function needs to be used, that is, to create another alternative transaction T* with the same input but adjusted transaction fees. T* will eventually be confirmed and packaged into the block due to the high handling fee set, while the confidential transaction T will be cleared due to the low handling fee and cannot be packaged into the blockchain. Therefore, in addition to creating 4 confidential transactions, RBF is also required to create 4 corresponding alternative transactions. The confidential transaction has the same sending address, receiving address, and transfer amount as the corresponding alternative transaction, but their handling fee rates are different. The handling fee rate of the alternative transaction is significantly higher than the handling fee rate of the confidential transaction. The transaction-related information is shown in Tables 4 and 5.

[0131] Confidential transaction ID Fee Rate 1 c5613a06739045b40439e87f8e67a2091e32fca4c49e7654f51e74223f30f4f7 3.0sat / vB 2 ed8785b332e90a158c31224a427eb2a4128cdb7cf4ed5388bca9408c1eaf98ce 3.9sat / vB 3 9ed66d81f8eb67e10a55d0779536dbbfe184283f40d7489d77362b151e679646 4.1sat / vB 4 76f0919ee2dc9e29c24f486ec4328631dc4d6c5c4ef993005fc29a7fced15e19 5.3sat / vB

[0132] Table 4 contains confidential transaction information.

[0133] Alternative Transaction ID Fee Rate 1 60126b06b40b76e926f69010ee638c4152af38ed588c9fb3599a11289134f223 20.1sat / vB 2 fbb75772873feded5c2f9760a0d70cc0d78b7eaabaa580623788dc2ec662b62f 18.1sat / vB 3 0511343117d77bd816afb8e4643de634e7f72d4b3331963534de73e4bb5e7049 18.7sat / vB 4 c512a278b968860c38917b6ac30765a1dbd3a7473fd78bc7f8bb78d74f4eb878 17.3sat / vB

[0134] Table 5 Alternative transaction information.

[0135] The receiver can obtain the sending address of the confidential transaction in turn according to the pre-shared key PSK and the public key of the sending address 1, and monitor the transactions sent by the sending address. The transaction fee rate is the hidden information to be transmitted. When no transaction is monitored for a period of time, the transaction is considered terminated. Transaction fees higher than 6.3sat / byte are alternative transactions, and transaction fees between 0 and 6.3sat / byte are confidential transactions. There is no need to worry about the confusion between confidential transactions and alternative transactions during monitoring. Subsequently, the alternative transaction will be confirmed after broadcasting, and the confidential transaction will be cleared and can no longer be queried.

[0136] The receiver will get the handling fee rates of the four transactions from the four encrypted transactions monitored as 3.0sat / vB, 3.9sat / vB, 4.1sat / vB, and 5.3sat / vB. Then according to the encryption rules, the code values ​​of the secret information are 30, 39, 41, and 53 respectively. By comparing the Base64 encoding table, the Base64 encoding of the secret information is "enp1". Finally, Base64 decoding is performed to obtain the secret information "zzu".

[0137] The present invention mainly analyzes the covert communication method through experiments from three aspects: embedding strength, time efficiency and security.

[0138] 1) Safety analysis

[0139] The openness, transparency and transaction traceability of blockchain are challenges faced by using blockchain for covert communication. The essence of blockchain is an unalterable distributed database, in which data is recorded in a chain structure, and each block contains the hash value of the previous block. This structure ensures the traceability and unalterability of data. At present, most of the confidential transactions of the covert communication methods based on blockchain are on the chain. The method of the present invention uses the RBF function of Bitcoin, and the confidential transactions will be withdrawn and regarded as invalid transactions. The confidential transactions will not be on the chain in the end.

[0140] Since the data on the blockchain is publicly available, anyone can view and analyze the transactions and information on the blockchain. This limits the confidentiality of covert communications because there is a risk that they may be discovered by others. Transactions on the blockchain are immutable, which means that once a transaction is recorded, it will exist permanently on the blockchain. This may allow the history of covert communications conducted through transactions to be traced, thereby reducing the confidentiality of the communication. The method of the present invention does not upload confidential transactions to the blockchain, which can solve the problems of limited confidentiality and transaction traceability in covert communications using blockchain, greatly improving confidentiality and security.

[0141] The anti-detection property of secret information refers to the consistency of the secret information and the carrier information in statistical characteristics, that is, the degree to which the information is not easily detected or discovered. The relative entropy D(P||Q) is an important indicator of anti-detection property. The smaller the relative entropy, the higher the consistency and the stronger the anti-detection ability. P represents the probability distribution of the carrier information after the secret information is embedded, and Q represents the probability distribution of the carrier information before the secret information is embedded. The formula of relative entropy D(P||Q) is as follows:

[0142]

[0143] The carrier used by the BLOCCE method is the transaction address, which does not change arbitrarily before and after embedding, and the relative entropy D(P||Q) takes a value of 0. Based on the space method, the carrier information changes before and after embedding, and the relative entropy D(P||Q) takes a value of 0.00341. The carrier used by the method of the present invention is the transaction fee rate, which does not change before and after embedding, and the relative entropy D(P||Q) takes a value of 0. Although the relative entropy values ​​of the BLOCCE method and the method of the present invention are both 0, the encrypted transactions of the method of the present invention will eventually be regarded as invalid transactions and discarded, and will not be retained on the chain, so the anti-detection ability of the method of the present invention is stronger than that of the BLOCCE method. The comparison of the relative entropy of the methods is shown in Table 6.

[0144] method Relative entropy D(P||Q) BLOCCE 0 Based on the space method 0.00341 Method of the present invention 0

[0145] Table 6 Comparison of relative entropy of covert communication methods.

[0146] Generally, the sending address of most methods is fixed, but the receiving address is not fixed. The transaction recipient is not necessarily the same as the actual secret information recipient. The random selection of the receiving address can protect the identity security of the recipient due to the characteristics of the blockchain. The general method uses the same sending address to send covert messages. Frequently sending messages with the same address in the same time period may increase the traceability of the message. The sending address of the present invention is not fixed, and changing the sending address of the transaction can further enhance security. The address comparison of the covert communication method is shown in Table 7.

[0147] method Shipping Address Receiving Address BLOCCE fixed Not fixed Based on the space method fixed Not fixed Method of the present invention Not fixed Not fixed

[0148] Table 7 Comparison of transaction addresses of covert communication methods.

[0149] 2) Time efficiency

[0150] The transmission time is mainly divided into embedding time and extraction time. If the average transmission of 8-bit secret content is taken as an example, the transmission time of the following method is analyzed. The method of the present invention first encodes the ciphertext to be transmitted by Base64 and converts it into a transaction fee rate. It is also necessary to run python to generate the public key and address with a derivative relationship that we need. A single information embedding can be completed within 30 seconds. The receiver needs to monitor the derived address to obtain transaction information. The time for extracting information is mainly reflected in calling the blockchain API or using a blockchain browser query to obtain secret information. The obtained transaction fee rate is converted into a code and Base64 decoded to obtain the secret information. A single information extraction can also be completed within 30 seconds. The transmission of "zzu", that is, 24-bit content, can be completed within 3 minutes, so the average transmission of 8-bit content can be regarded as completed within 1 minute.

[0151] The BLOCCE method takes about 10 minutes to transmit 1 bit of secret content, and it takes more than 1 hour to transmit 8 bits of secret content on average. The information embedding strength of each transaction in the method based on the space method is low, and the time to transmit 24 bits of secret information is more than 5 minutes, and the average transmission of 8 bits of secret content is also more than 1 minute. The double steganography method uses the interplanetary file system and image steganography, and the time to transmit 8 bits of secret content is at the minute level. Comparison of embedding time of covert communication methods Figure 6 The average time comparison of 1 Byte information embedding and extraction by the methods is shown in Table 8.

[0152] method Embedding time Extraction time BLOCCE >1h About 2s Based on the space method About 1 minute About 1 minute Method of the present invention About 25 seconds About 30 seconds

[0153] Table 8 Comparison of information embedding and extraction time of covert communication methods.

[0154] 3) Embedding strength

[0155] The BLOCCE method uses the least significant bit of the address space to transmit secret information, and each transaction can transmit 1 bit of secret information. The BLOCCE+ method improves the BLOCCE method and uses the low α bits of the address space to transmit secret information. Each transaction can transmit α bits of secret information, but in actual operation, the time overhead of hash function calculation will increase sharply with the increase of α, seriously reducing the efficiency of the system. Therefore, α is usually taken as a small value. The space method cleverly uses spaces to embed secret information into the text content. Each transaction can generally transmit 2 bits of secret information. The double steganography method combines blockchain with interstellar file system technology, which solves the problem of large file transmission in blockchain and greatly improves the embedding strength. The comparison of plaintext information embedding rate is as follows: Figure 7 shown.

[0156] The communication method proposed by the present invention is based on Base64 encoding. It is necessary to construct 4 encrypted transactions to transmit 3 bytes, that is, the embedding strength of each transaction is 6 bits. Base64 encoding is a method of representing binary data based on 64 printable characters. Since 2 to the sixth power is equal to 64, every 6 bits is a unit corresponding to a certain printable character. 3 bytes have 24 bits, corresponding to 4 Base64 units, that is, 3 bytes can be represented by 4 printable characters. If the remaining characters are less than 3 bytes, they are filled with 0, and the output characters use =.

[0157] A comprehensive comparison of blockchain-based covert communication methods is shown in Table 9.

[0158] method Embedding strength Transfer time Is it on the chain? BLOCCE 1 Hourly yes BLOCCE+ α(smaller) ------ yes Based on the space method 2 Minute level yes Double Steganography -------- Minute level yes Method of the present invention 6 Seconds no

[0159] Table 9 Comprehensive comparison of covert communication methods.

[0160] The present invention proposes a blockchain covert communication method based on the Bitcoin RBF mechanism, which solves the problems of low embedding strength, low time efficiency, insufficient security and concealment to a certain extent. The proposed model uses Base64 encoding and transaction fees to establish mapping transmission information, which improves the embedding strength of the transaction. In addition, the address with a derivative relationship is used as the transaction sending address, so that the receiver can quickly extract the confidential information, which improves the time efficiency. The method of the present invention introduces the Bitcoin RBF mechanism, so that the confidential transaction is not stored in the blockchain account book, and the information transmission is more concealed and secure. The experimental results show that the method of the present invention has good embedding strength and time efficiency, and the confidential transaction is not on the chain, which can achieve a concealed communication without retention, can effectively resist attacks and analysis and detection, and has sufficient security and concealment. Since the RBF mechanism is a transaction fee strategy based on Bitcoin, future work will explore a covert communication method based on the alliance chain that does not retain confidential transactions on the chain.

Claims

1. A traceless blockchain covert communication method based on RBF mechanism, characterized by: It includes four processes: information processing, embedding, extraction and recovery, and RBF processing; Step 1: Information processing: Base64 encode the secret information to be transmitted; Step 2: Embedding process: Establish a corresponding encryption rule between the code value and the transaction fee rate, that is, transactionfees k =7+0.1*codevalue k (0≤codevalue k ≤9) (7) transactionfees k =0.1*codevalue k (10≤codevalue k ≤63) (8) Among them, transaction fees k Indicates the handling fee rate, codevalue k Indicates Base64 encoding base64byte k The code value of k is Step 3: Extraction and Recovery Process: The receiver can also deduce the sending address based on the derivation relationship, that is, pk i *PSK=pk i+1 (11) sendaddr i =PublickeyToAddress(pk i ) (12) After the receiver knows the sender's address, he can obtain the transaction by using a blockchain browser or calling the blockchain API. After obtaining the transaction, the handling fee rate of each transaction is the ciphertext to be transmitted. When a certain address is monitored for a long time without transactions, the monitoring is stopped, and it can be considered that the ciphertext has been received; Step 4: RBF processing: The sender can construct a transaction T*, then broadcast T* and set the transaction fee of T* to be significantly higher than that of the confidential transaction T. Due to the high fee set, T* will eventually be confirmed and packaged into the block, while the confidential transaction T will be cleared due to the low fee and cannot be packaged into the blockchain, which is equivalent to the confidential transaction T being withdrawn.

2. According to claim 1, a traceless blockchain covert communication method based on RBF mechanism is characterized in that: In step 1, the information encoding process is as follows: 1.1) Divide the information data into groups of three bytes, namely groupbyte i =[byte 3i-2 ,byte 3i-1 ,byte 3i ] (1) Among them, byte i Represents 1 byte, groupbyte i Represents a data group containing 3 bytes, the value of i is len indicates the number of bytes of secret information; 1.2) Convert each byte into 8-bit binary form, i.e. bin j =z(byte j ) (2) groupbin i =[bin 3i-2 ,I am 3i-1 ,I am 3i ] (3) Among them, z(x) means converting information x into a binary stream; bin j Represents a 1-byte binary stream, the value of j is {j|j∈N * , 1≤j≤len}; groupbin i Represents a binary stream of 3 bytes in a data group. The value of i is 1.3) Divide the 24-bit binary information of a data group into groups of 6 bits, that is, [b 4i-3 ,b 4i-2 ,b 4i-1 ,b 4i ] (4) Among them, b i Represents 6 bits of binary information, groupb i with groupbin i They all represent 24 bits of binary information for a data group, but the divisions are different. The value of i is 1.4) Convert each 6-bit binary group into the corresponding Base64 character, that is, base64byte k =T(b k ) (5) Among them, T(y) means converting binary information y into Base64 encoding, base64byte k Indicates a Base64 encoding, the value of k 1.5) Connect all converted Base64 characters to form the final encoding result, that is, Among them, code represents the final encoding result, and the secret information of len bytes will eventually be A code.

3. According to claim 1, a traceless blockchain covert communication method based on RBF mechanism is characterized in that: In step 3, the steps to restore the ciphertext to secret information are as follows: 3.1) After the recipient extracts the transaction fee rate, he first obtains the Base64-encoded code value according to the encryption rules and the known fee rate, that is, codevalue k =(transactionfeesk-7)*10(7.0≤transanctionfees k ≤7.9) (13) codevalue k =transactionfees k *10(1.0≤transactionfees k ≤6.3) (14) Among them, k refers to the number of transactions, and the value of k is There are two cases according to the transaction fee rate. k ≤7.9, use formula (13) to calculate; when 1.0≤transactionfees k When ≤6.3, use formula (14) for calculation; 3.2) Convert each Base64 character into its corresponding 6-bit binary, i.e. b k =T -1 (base64byte k ) (15) Among them, T -1 (x) means converting Base64 encoding x into binary information, base64byte k Indicates a Base64 encoding, the value of k is 3.3) Put 4 b k Form a data group, namely groupb i =[b 4i-3 ,b 4i-2 ,b 4i-1 ,b 4i ] (16) Among them, groupb i Represents 24 bits of binary information of a data group. The value of i is 3.4) Divide the 24-bit binary information of a data group into 8-bit groups, that is, [thousand 3i-2 ,thousand 3i-1 ,thousand 3i ]=grouppupbin i (17) byte j =from -1 (bin j ) (18) Among them, groupb i with groupbin i Both represent 24 bits of binary information for a data group, but they are divided differently; bin j Represents an 8-bit binary stream, the value of j is {j|j∈N * , 1≤j≤len}; z -1 (y) means converting binary information y into byte information; 3.5) Byte information byte j By splicing them in order, you can get the secret information: secret_message=byte1|||…||byte len (19)。

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