A covert communication method for collaborative groups based on the Monero blockchain network

Abstract

A collaborative group covert communication method based on the Monero blockchain network is proposed. In a blockchain-assisted collaborative location-based services (LBS) query scenario, users act as entities on the blockchain, storing data and flooding communications. Neighboring users spontaneously form collaborative groups to mutually query LBS information. A lightweight P2P key agreement scheme is proposed to generate a shared message encryption key within the group. Based on the negotiated key, the method establishes covert intra-group communication based on the Monero blockchain, concealing the communication relationship between the collaborating parties and preventing eavesdropping by malicious members. Security analysis and simulation results demonstrate that the proposed scheme achieves high security and privacy with acceptable communication and computational overhead.

Description

Technical Field

[0001] The present invention belongs to the field of blockchain, and specifically provides a collaborative group covert communication method based on the Monero blockchain network. Background Art

[0002] Location-based services (LBS) refer to value-added location-related services provided to positioning devices via the mobile internet. While widespread use of LBS has brought convenience to people's lives, it also poses a significant threat to user privacy. Collaborative location privacy protection mechanisms obscure the observation of individual users by hiding their behavior within a group. However, the effectiveness of this collaborative model presupposes that group members are honest, trustworthy, and abide by the rules of collaboration. Most existing collaborative privacy protection mechanisms implicitly assume this assumption, but this assumption is inconsistent with reality and reduces the usability of the solutions.

[0003] Blockchain, derived from Bitcoin technology, is essentially a replica state machine protocol in a Byzantine environment[1]. Blockchain networks allow participants to freely choose to join or exit, and use digital accounts instead of real-world identities to provide user anonymity. With its decentralized, auditable, and tamper-proof features, blockchain technology has the potential to address the trust issues within collaborative location privacy mechanisms. The flooding and anonymity of blockchain networks provide an ideal platform for information concealment within collaborative groups.

[0004] The above considerations drive the research of a blockchain network-assisted solution, in which some challenges remain to be overcome. Covert transmission is an effective means to solve the problem of group member eavesdropping. Covert transmission in blockchain networks mostly uses asymmetric keys negotiated in advance [2] to encrypt and decrypt the transmission content, which means that each covert communication requires the negotiation of message encryption and decryption keys in advance. In the LBS scenario with frequent interactions, this method increases the risk of communication exposure. The high computational latency of asymmetric keys is also a problem that cannot be ignored.

[0005] In the prior art, a covert channel based on a blockchain network is usually defined as a communication channel that cannot be detected due to the carrier characteristics unique to the blockchain environment. Using the blockchain transaction address as a carrier feature to make secret message transmission concealed, many covert channel construction methods have been proposed. BLOCCE[3] maps secret information to the valid bits of the blockchain transaction address. This method provides an efficient covert channel construction method, but the capacity for embedding messages is low. V-BLOCCE[4] improves [3] and has more efficient communication and message hiding capabilities, but its concealment is insufficient. Cao et al. proposed a data embedding method based on a public key chain in [5], using the transaction address generated by the public key as the message embedding carrier, which improves the concealment and transaction screening efficiency. Luo et al. in [6] combined the transaction amount matrix and the index address matrix and encoded a secret message using the transaction amount. Although the reuse of the address set reduces the transaction amount and transmission cost, it also reduces its concealment.

[0006] Different from the above methods, many researchers use the digital signature algorithm in the blockchain as a carrier feature. ChainChannels[7] replaces the random number used in the elliptic curve digital signature algorithm (ECDSA) with a secret message when constructing a covert channel, reducing time overhead. Gao et al. [2] embedded the message into the default storage parameters of the transaction and used backdoor eavesdropping to generate a special signature. The message recipient with the private key can recognize the special signature and extract the transaction content. Taking advantage of the unconditional anonymity of Monero ring signatures, Guo et al. [8] encrypted the message and embedded it into the ring signature public key set, enhancing the hiding capacity and transmission confidentiality.

[0007] Currently, many methods have been proposed to achieve covert communication using different information carriers, smart contracts, and dynamic tags. Zhang et al. proposed a covert communication model combined with smart contracts in [9], which uses parameters in the contract to map secret information sequences and calls the contract to transmit messages. This method has good tamper resistance and low complexity. Liu et al. proposed a storage covert channel for secret communication using Monero transactions as data carriers in

[10] , as well as two algorithms to resist eclipse and node crawling attacks, which improves robustness, anti-detection and anonymity. EBDL

[11] is a dynamic tag and message segmentation mechanism that can help receivers effectively extract covert messages and support large-scale covert message transmission. Summary of the Invention

[0008] Most user collaboration privacy protection mechanisms assume that collaboration group members are trustworthy and can strictly enforce collaboration rules. These assumptions are inconsistent with reality and reduce the usability of the scheme. To address the problem of untrustworthy group members, this paper proposes a covert communication method for collaborative groups based on the Monero blockchain network, enabling collaborative group members who originally lack trust to interact efficiently and securely.

[0009] In this invention, a lightweight P2P key negotiation scheme is used to generate a shared message encryption key within the group to protect the security of user data during transmission. Based on the negotiated key, a covert communication within the group based on the Monero blockchain is further constructed to conceal the communication relationship between the two collaborating parties within the group and resist eavesdropping by malicious members within the group.

[0010] Security analysis and simulation results show that this scheme achieves high security and privacy with acceptable communication and computational overhead.

[0011] Specifically, a collaborative group covert communication method based on the Monero blockchain network is proposed. In a blockchain-assisted collaborative LBS query scenario, users act as entities on the blockchain, storing data and flooding communications on the chain. Neighboring users spontaneously form a collaborative group to mutually assist in LBS information query.

[0012] First, the collaboration group members use a key agreement scheme to generate a shared session key within the group;

[0013] Then, when performing LBS information query, collaboration is carried out within the collaboration group. The collaboration process is as follows: the queryer selects a collaborator to forward his query; the collaborator interacts with the LBS in his own identity, the LBS provides the collaborator with the query results, and the collaborator returns the query results to the queryer; the collaborator and the queryer communicate using the group's covert communication method; the query forwarded by the queryer to the collaborator is a fuzzy query;

[0014] The key agreement scheme is a lightweight group key agreement method LGKA: in a collaborative group, first, a member is randomly selected as the controller of the key agreement; then, the key agreement is carried out, and the steps include:

[0015] 1.1) The controller randomly selects a random number for each member and broadcasts the random number and its corresponding hash value to other members;

[0016] 1.2) For any other member, he receives the random number sent in step 1.1) and verifies its integrity. After passing the verification, the member also selects a random number and sends it and its corresponding hash value to the controller;

[0017] 1.3) After receiving the random number and its corresponding hash value sent in step 1.2), the controller verifies the integrity of the random number. After verification, the controller generates partial key information and then returns the partial key information to the member who sent the random number in step 1.2);

[0018] 1.4) Following steps 1.2) and 1.3), all members interact with the controller. After all interactions are complete, all members in the group obtain a shared group session key.

[0019] The intra-group covert communication method uses the Monero covert channel LGKA-MCC based on LGKA for communication. A communication process includes:

[0020] 2.1) The queryer encrypts the fuzzy query using the group session key to obtain the ciphertext;

[0021] 2.2) The queryer adds a start symbol and an end symbol to the beginning and end of the ciphertext bit sequence to obtain a new sequence;

[0022] 2.3) The queryer encodes the new sequence based on the data type stored in the Monero blockchain transaction to obtain the information code;

[0023] 2.4) The queryer embeds the information code into the Monero transaction information, generating a transaction message containing hidden information;

[0024] 2.5) The queryer sends the transaction information obtained in step 2.4) through the Monero blockchain network;

[0025] 2.6) The collaborator identifies the transaction information sent in step 2.5) from the blockchain network;

[0026] 2.7) The collaborator extracts the information code from the transaction information identified in step 2.6);

[0027] 2.8) The collaborator decodes the information code to obtain the new sequence obtained in step 2.2);

[0028] 2.9) The collaborator obtains the ciphertext by removing the start and end characters;

[0029] 2.10) The collaborator decrypts the ciphertext using the group session key to obtain the fuzzy query.

[0030] In the fuzzy query information: identity is the identity of the collaborator, and queryer secret is the fuzzified queryer secret.

[0031] When a user moves out of or joins a collaboration group, the key will be updated as follows:

[0032] When an outside member wants to join the collaborative group, it first interacts with the controller through steps 1.1) and 1.2) to calculate the outside member's key update information. The controller then sends the key update information and the original group session key to the original inside and outside members, obtaining the updated group session key.

[0033] b. When a member wants to leave the collaboration group, the controller broadcasts the key update message to all members in the group except the member who wants to leave the group, and obtains the updated group session key. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a diagram of a collaborative location privacy protection framework based on the Monero blockchain;

[0035] Figure 2 It is a schematic diagram of the intra-group collaborative workflow;

[0036] Figure 3 This is a schematic diagram of the implementation method (framework) of covert transmission within a group;

[0037] Figures 4(a) and 4(b) show the impact of the collaboration group size and activity on the key agreement cost for GKA-SS, DH-based LGKA, and GKA.

[0038] Figure 4(a) shows the relationship between the negotiation time and the number of collaborative groups for the three methods;

[0039] Figure 4(b) shows the relationship between the number of queries and the probability of being attacked within 9 hours for the three methods;

[0040] Figure 5(a) and Figure 5(b) show the time cost and security comparison of the two encryption methods RSA and LGKA, where:

[0041] Figure 5(a) shows the relationship between the encryption time and the amount of data transmitted;

[0042] Figure 5(b) shows the relationship between the probability of the two messages being deciphered and time;

[0043] Figure 6(a) and Figure 6(b) show the security and time cost of LGKA-MCC, PKE-MSCCS and ordinary communication methods, where:

[0044] Figure 6(a) shows the time consumption comparison of the three communication methods;

[0045] Figure 6(b) compares the probability of being intercepted by attackers for the three communication methods. DETAILED DESCRIPTION

[0046] 1 Overview

[0047] This paper proposes a covert communication method for collaborative groups based on the Monero blockchain network. This method leverages the Monero blockchain network to establish secure intra-group interactions, enabling previously untrustworthy users to efficiently assist each other and jointly defend against external and internal attacks.

[0048] The main technical contributions include:

[0049] To combat eavesdropping and selfish behavior within the group, a lightweight P2P key negotiation method was designed to generate a shared message encryption key within the group, protecting the security of user data during transmission. Based on the negotiated key, a covert communication mechanism based on the Monero blockchain was further constructed to prevent eavesdropping by malicious group members and ensure secure and reliable message exchange within the group.

[0050] The effectiveness of the proposed scheme is objectively evaluated. Security analysis and simulations show that the proposed scheme can achieve high security and privacy levels at low communication and computational costs.

[0051] Later in the text:

[0052] The second section describes the system architecture and discusses the threat model and design goals.

[0053] The third part builds covert communication within the group.

[0054] The fourth part analyzes the design goals that can be achieved by the solution.

[0055] The fifth section uses data analysis to verify the performance of the proposed scheme.

[0056] Section 6 gives the conclusion.

[0057] 2 System Model

[0058] Consider a blockchain-assisted collaborative location-based services (LBS) query scenario. Users, as entities on the blockchain, can store data and perform flooding communications on-chain. Neighboring mobile users can spontaneously form a collaborative group to collaboratively perform LBS queries, protecting location privacy. The collaborative group elects a leader to control intra-group key negotiation and obtain a shared session key. When users leave or join the collaborative group, the key is updated. Inquiring users within the group select a collaborator to forward their queries based on a specific policy. Based on the blockchain network and pre-negotiated keys, the collaborative group uses Monero covert communication to conceal the communication relationship between collaborators and achieve secure intra-group transmission.

[0059] Assume that there are two types of malicious entities in the network, namely: untrusted LBS and malicious members.

[0060] Untrusted LBS, which infers user privacy based on user background knowledge;

[0061] Malicious members monitor group communications and steal private information.

[0062] 2.1 Solution Description

[0063] like Figure 1 As shown, the symbols and operations involved in the framework of the proposed scheme are defined as follows:

[0064] U represents the set of members of a collaboration group.

[0065] o = {u, s} is the original query information of u, where u represents the identity of the query initiator and s is the secret of the queryer (such as u's location or preferences).

[0066] o′ = {u′, s′} is the LBS query submitted by the collaborator and is observable to all users in the network. u′ represents the collaborator’s identity and s′ is the obfuscated queryer’s secret.

[0067] by Figure 1 Taking the four-person collaboration group shown in the figure as an example, the intra-group collaboration process based on covert communication includes:

[0068] ① Query u wishes to conceal his or her identity and location. When performing an LBS query, u selects a collaborator u′, generates a disguised secret s′, and then forwards the fuzzy query o′ = {u′, s′} to u′ via covert communication.

[0069] ② After collaborator u′ receives the fuzzy query o′ sent by u, it interacts with the LBS under its own identity to cover up u.

[0070] ③LBS provides query results for u′ based on o′. Malicious LBS managers may speculate the identity and secrets of u.

[0071] ④u′ transmits the LBS feedback result back to u through covert communication to interfere with the monitoring of malicious members in the group.

[0072] 2.2 Threat Model

[0073] Speculation attack: The attacker uses statistics or machine learning methods to infer the identity of the queryer based on the user's prior leaks. and secrets

[0074] Correlation Analysis: The attacker monitors the on-chain communication between the two collaborating parties and identifies the identities of u and u′ through traffic analysis and transaction correlation.

[0075] 2.3 Design Goals

[0076] It is difficult for an attacker to associate the identity of the queryer by observing LBS requests, nor can they obtain the identity of the queryer by intercepting and analyzing group communications.

[0077] User privacy;

[0078] Malicious members in the group cannot detect the existence of collaborative communication and cannot steal collaborative information.

[0079] 3 Collaborative Security Framework

[0080] To ensure the security and confidentiality of intra-group interactions, this paper proposes a lightweight P2P key negotiation scheme to generate a shared message encryption key within the group, protecting the security of user data during transmission. Based on the negotiated key, this paper further constructs covert intra-group communication based on the Monero blockchain, concealing the communication relationship between collaborating parties within the group and preventing eavesdropping by malicious members within the group.

[0081] 3.1 Workflow

[0082] Based on the blockchain network, the workflow of the collaboration between the queryer u and the collaborator u′ is as follows: Figure 2 shown.

[0083] 1) In-group key agreement

[0084] Collaboration group members use a lightweight method to negotiate a key within the group. The negotiated encryption key can support covert communication within the group for a period of time.

[0085] 2) Collaboration based on covert communication

[0086] To protect the confidentiality of the transmitted data, the queryer u and the collaborator u′ will use covert communication to complete the information transmission in two processes, including: 1) u forwards o′ to u′; 2) u′ sends the query result fed back by LBS back to u.

[0087] 3.2 Intra-group key round-robin negotiation

[0088] Group key agreement (GKA) enables group members to negotiate a shared session key in a public, untrusted network environment. Based on the constant round negotiation interaction framework

[13] , this paper constructs a lightweight group key agreement method (LGKA) by integrating hash functions with the DH key calculation method

[12] . The purpose is to adapt to the dynamic nature of collaborative groups and low-latency LBS queries.

[0089] In a collaborative group U, LGKA randomly selects a member as the controller for key negotiation. Taking member u as the controller as an example, the key negotiation process is as follows:

[0090] 1) For each member i∈U\{u}, u randomly selects a random number a for him i and will (g is a generator of a mathematical group G) broadcast to i;

[0091] Here we introduce the discrete mathematics knowledge in the DH key agreement. Before the two parties exchange keys, they will select two public numbers g and p, where p is a prime number and g is a root of p. ai Calculated by member i, it can be understood as the intermediate information used for key generation with member i's attributes;

[0092] 2) When member i receives He will verify After verification, he will select a random number b i and will Send to u;

[0093] 3) u receives the message sent by i Post-verification After verification, u generates partial key information Then send this information to i;

[0094] Here, g ajbj It can be understood as the information used by each member in U except the controller and i for key generation.

[0095] Other members of U perform the same steps as i to interact with u. After all interactions are completed, the members of the group can calculate a shared group session key

[0096]

[0097] When member m wants to join the collaboration group, he needs to interact with u through steps 1) and 2) so that both parties can calculate the key update information. After the interaction is completed, u will update the information The original key k is sent to the original group members and m respectively. The group session key is updated to

[0098]

[0099] When a member m wants to leave the collaboration group, u will update the message Broadcast to all members of U except m. The group session key is updated to

[0100]

[0101] LGKA is suitable for low-latency LBS scenarios. Even if the group negotiation process is attacked and the session key is no longer secure, LGKA's game model can still stably protect the privacy of group members, eliminating the need for users to worry about privacy leaks.

[0102] 3.3 Covert Transmission within a Group

[0103] Public key encryption (PKE)

[14] is often used to encrypt and decrypt transmitted messages. Before each communication, both parties need to negotiate PKE-related information, which increases the risk of communication exposure. In addition, the asymmetric keys used by PKE can lead to long encryption and decryption delays, making it difficult to adapt to collaborative scenarios with frequent interactions.

[0104] To address the above issues, a Monero covert channel (LGKA-MCC) based on LGKA was constructed by combining LGKA and the covert communication method in the literature

[10] to achieve secure message interaction and reduce the computational burden of mobile devices. The PKE encryption scheme was replaced by a symmetric encryption scheme based on LGKA to reduce the message encryption and decryption time. Assume that the inquirer u intends to transmit a secret message s′ of length l to the collaborator u′. Figure 3 As shown in Figure 1, a covert communication process includes:

[0105] ①u uses the key k (agreed in advance within the group) to encrypt s′ to obtain the binary sequence ciphertext C, that is, C = k(s′);

[0106] ②u adds the start character C at the beginning and end of the bit sequence of C start and the end character C end , get C start +C+C end ;

[0107] ③u calculates C based on the storage data type in the Monero blockchain transaction start +C+C end Encode and obtain information code I;

[0108] ④u embeds the information code I into the Monero transaction information to generate the transaction information M containing the hidden information;

[0109] ⑤u sends a transaction message M containing hidden information through the Monero blockchain network;

[0110] ⑥u′ identifies the transaction information M carrying hidden information from the blockchain network;

[0111] ⑦u′ extracts the information code I from M;

[0112] ⑧u′ decodes I according to the data type of the information carrier and obtains C start +C+C end ;

[0113] ⑨u′ is obtained by removing C start and C end Obtain ciphertext C;

[0114] ⑩u′ decrypts C with k and obtains the secret message s′=k(C).

[0115] 4 Security and Privacy Analysis

[0116] This section uses theoretical methods to analyze whether the proposed scheme can achieve the design goals.

[0117] Since the observable o′=(u′,s′) is blurred and anonymized, it is difficult for the attacker to infer the true identity and secret information of the query u based on o′.

[0118] Covert communication within the group prevents malicious members from eavesdropping and tampering. Attackers cannot distinguish special transactions carrying secret information among numerous blockchain transactions, and therefore cannot associate user identities by monitoring the interaction information within the group.

[0119] Since the covert communication within the group cannot be perceived, malicious members in the group are even less able to perceive the existence of secret information during the covert transmission process, preventing malicious members from stealing collaborative private information.

[0120] 5. Analysis of information interaction performance within the group

[0121] This section verifies the performance of the proposed intra-group key agreement scheme, encryption scheme, and intra-group covert communication in terms of time overhead and security through simulation.

[0122] 5.1 Intra-group key negotiation performance

[0123] This section discusses the time consumption and security of intra-group key agreement under different group sizes and interaction frequencies. GKA-SS

[13] and DH-based GKA

[12] are selected as benchmark methods. Signature verification is omitted in GKA-SS to facilitate comparison with the proposed LGKA. Five collaborative groups of different sizes were constructed, and the time consumption data generated by three key agreement schemes within 9 hours were collected. As shown in Figure 4(a), the negotiation time (including group interaction time and key calculation time) of the three constant round schemes all showed a slowly increasing trend. Compared with GKA-SS, LGKA significantly reduced the negotiation time by simplifying the key calculation.

[0124] Figure 4(b) shows the impact of intra-group interaction frequency on the security of group key agreement when the group size is 15. The probability of attack is positively correlated with the frequency of intra-group interactions. Compared to DH-based GKA, LGKA significantly reduces the likelihood of key interception due to its introduction of a hash function and tighter negotiation. While ensuring security, LGKA simplifies key calculation, meeting the requirements of LBS applications.

[0125] 5.2 Encryption Scheme Performance

[0126] This simulation tests the effect of the amount of data transmitted on the time required to encrypt a message in a collaborative group of 15 people. An asymmetric encryption scheme based on RSA

[15] is selected for comparison with a symmetric encryption scheme based on LGKA. As shown in Figure 5(a), the encryption time of both schemes is proportional to the amount of data transmitted. Symmetric encryption generally involves only simple bit operations, while asymmetric encryption and decryption are much more complex. Therefore, the encryption time of the LGKA-based scheme is much lower than that of the RSA-based scheme.

[0127] Considering a collaborative group that includes an attacker, the security of this encryption scheme was analyzed. As shown in Figure 5(b), over a period of 9 hours, the probability of a message being decrypted increases over time under both encryption schemes. Asymmetric cryptographic algorithms are typically based on difficult mathematical problems and involve complex calculations, making it difficult for attackers to decrypt the message in a short period of time. Therefore, RSA-based asymmetric encryption is less susceptible to decryption than LGKA-based symmetric encryption. While the RSA-based scheme offers high security, its high encryption time makes it unsuitable for scenarios with frequent collaborative interactions. The LGKA-based encryption scheme balances real-time performance with security, significantly reducing encryption latency at the expense of a small reduction in security.

[0128] 5.3 Intra-group Covert Communication Performance

[0129] The performance of LGKA-MCC is verified in terms of the total time spent on a single communication (including channel establishment time and message transmission delay) and security when the team size is set to 15 people. PKE-based MSCCS

[10] and ordinary communication are selected as benchmark methods.

[0130] In Figure 6(a), when running Monero covert communication, the time consumed by group members constructing special Monero transactions is slightly higher than the time consumed by normal communication, but within an acceptable range. LGKA-MCC uses lightweight symmetric encryption, and the time required for message encryption and decryption is lower than that of PKE-MSCCS. LGKA-MCC provides excellent communication security protection at a low time cost.

[0131] A 15-person collaborative group was constructed. An attacker, hidden within the group, used traffic analysis and message eavesdropping to identify special communications carrying secret information and intercept communication flows and transaction data on the blockchain network. The number of times the collaborative group was intercepted by the attacker using different communication methods was continuously counted, for example, over a 9-hour period. As shown in Figure 6(b), intra-group transmissions using normal communication were intercepted most frequently. When Monero covert communication was running, special Monero transactions carrying secret information were intermixed with normal transactions within the blockchain network. Because it is difficult for an attacker to identify and distinguish special Monero transactions, the probability of interception of Monero covert communication was much lower than that of normal communication. Compared to PKE-MSCCS, LGKA-MCC reduces the number of pre-transmission negotiations between the communicating parties, further reducing the risk of communication exposure.

[0132] 6 Conclusion

[0133] We propose a privacy-preserving framework for collaborative groups based on the Monero blockchain. This framework includes a lightweight key agreement scheme and Monero-based intra-group covert communication. This approach protects user data while concealing the communication relationships between collaborating parties, enabling efficient collaboration among members who lack trust. Security analysis demonstrates that the proposed intra-group covert communication scheme achieves high security at low communication and computational costs.

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Claims

1. A cooperative group covert communication method based on the Monero blockchain network, characterized in that In a blockchain-assisted collaborative LBS query scenario, users act as entities on the blockchain, performing data storage and flooding communication on the chain; adjacent users spontaneously form a collaborative group to mutually assist in LBS information query; First, the collaboration group members use a key agreement scheme to generate a shared session key within the group; Then, when performing LBS information query, collaboration is carried out within the collaboration group. The collaboration process is as follows: the queryer selects a collaborator to forward his query; the collaborator interacts with the LBS in his own identity, the LBS provides the collaborator with the query results, and the collaborator returns the query results to the queryer; the collaborator and the queryer communicate using the group's covert communication method; the query forwarded by the queryer to the collaborator is a fuzzy query; The key agreement scheme is a lightweight group key agreement method LGKA: in a collaborative group, first, a group member is randomly selected as the controller of the key agreement; Then, key negotiation is performed, including the following steps: 1.1) The controller randomly selects a random number for each member and broadcasts the random number and its corresponding hash value to other members; 1.2) For any other member, he receives the random number sent in step 1.1) and verifies its integrity. After passing the verification, the member also selects a random number and sends it and its corresponding hash value to the controller; 1.3) After receiving the random number and its corresponding hash value sent in step 1.2), the controller verifies the integrity of the random number. After verification, the controller generates partial key information and then returns the partial key information to the member who sent the random number in step 1.2); 1.4) Following steps 1.2) and 1.3), all members interact with the controller. After all interactions are complete, all members in the group obtain a shared group session key. The intra-group covert communication method uses the Monero covert channel LGKA-MCC based on LGKA for communication. A communication process includes: 2.1) The queryer encrypts the fuzzy query using the group session key to obtain the ciphertext; 2.2) The queryer adds a start symbol and an end symbol to the beginning and end of the ciphertext bit sequence to obtain a new sequence; 2.3) The queryer encodes the new sequence based on the data type stored in the Monero blockchain transaction to obtain the information code; 2.4) The queryer embeds the information code into the Monero transaction information, generating a transaction message containing hidden information; 2.5) The queryer sends the transaction information obtained in step 2.4) through the Monero blockchain network; 2.6) The collaborator identifies the transaction information sent in step 2.5) from the blockchain network; 2.7) The collaborator extracts the information code from the transaction information identified in step 2.6); 2.8) The collaborator decodes the information code to obtain the new sequence obtained in step 2.2); 2.9) The collaborator obtains the ciphertext by removing the start and end characters; 2.10) The collaborator decrypts the ciphertext using the group session key to obtain the fuzzy query.

2. The covert communication method for collaborative groups based on the Monero blockchain network according to claim 1 is characterized in that In the fuzzy query information: identity is the identity of the collaborator, and queryer secret is the fuzzified queryer secret.

3. The covert communication method for collaborative groups based on the Monero blockchain network according to claim 1 or 2, characterized in that The collaboration process within the collaboration group includes: 1) When a queryer u wants to hide his identity and location, he needs to perform an LBS query. He selects a collaborator u′ and disguises his secret s as a fuzzy secret s′, obtaining a fuzzy query o′={u′,s′}. He then forwards the fuzzy query o′={u′,s′} to u′ via LGKA-MCC covert communication. 2) After collaborator u′ receives the fuzzy query o′ sent by u, it interacts with the LBS under its own identity to cover u; 3) LBS provides query results for u′ based on o′; 4) u′ transmits the query result feedback back to u through LGKA-MCC.

4. The Monero blockchain network-based collaborative group covert communication method according to claim 1, characterized in that When a user moves out of or joins a collaboration group, the key will be updated as follows: When an outside member wants to join the collaborative group, it first interacts with the controller through steps 1.1) and 1.2) to calculate the outside member's key update information. The controller then sends the key update information and the original group session key to the original inside and outside members, obtaining the updated group session key. b. When a member wants to leave the collaboration group, the controller broadcasts the key update message to all members in the group except the member who wants to leave the group, and obtains the updated group session key.

5. The cooperative group covert communication method based on the Monero blockchain network according to claim 1 or 4, characterized in that In the key agreement scheme: Firstly, based on the constant round negotiation interaction framework, a lightweight group key agreement method LGKA is constructed by integrating the hash function and the DH key calculation method. In a collaborative group U, LGKA randomly selects a member as the controller of key negotiation. Let member u be the controller. The key negotiation process includes: 1.1) For each member i∈U\{u}, u randomly selects a random number a for member i i , and Broadcast to i; 1.2) When member i receives Verify first After verification, member i selects a random number b i and will Send to u; 1.3) u receives the message sent by i After that, verify integrity; after verification, u generates partial key information Then send this information to i; 1.4) Other members of U and i execute steps 1.1) to 1.3) simultaneously to interact with u; after all interactions are completed, the members of the group derive a shared group session key. g is a generator of a mathematical group; For member i, g ai is calculated by u, with member i attributes, and used to generate g aibi Intermediate information of g bi is calculated by i, with member i attributes, and is used to generate g aibi Intermediate information of g aibi is the intermediate information calculated by u and with the attribute i for generating the key k; For any member j in the group, g ajbj is the intermediate information computed by u and attributed to member j for generating the key k; And in the style In, g ajbj It only represents the intermediate information calculated by u and used by each member of U except u and i to generate the key k. The formula is the intermediate information g ajbj The product of .

6. The cooperative group covert communication method based on the Monero blockchain network according to claim 5 is characterized by When a user moves out of or joins a collaboration group: a. When member m wants to join the collaboration group, he needs to interact with u through steps 1.1) and 1.2) so that both parties can calculate the key update information. g ambm is the intermediate information used for key generation calculated by u and with the attributes of member m; After the interaction is completed, u will update the information The original key k is sent to the original group members and m respectively, and the group session key is updated to b. When a member m wants to leave the collaboration group, u will update the message Broadcast to all members of U except m, and the group session key is updated to 7. The cooperative group covert communication method based on the Monero blockchain network according to claim 1 is characterized in that The intra-group covert communication method uses the Monero covert channel LGKA-MCC based on LGKA for intra-group covert communication. Assume that the queryer u intends to transmit a secret message s′ of length l to the collaborator u′. A covert communication process includes: 2.1) u encrypts s′ using the group session key k to obtain the binary sequence ciphertext C, i.e., C = k(s′); 2.2) u adds a start character C at the beginning and end of the bit sequence of C start and the end character C end , and get C start +C+C end ; 2.3) u calculates C based on the storage data type in the Monero blockchain transaction start +C+C end Encode and obtain information code I; 2.4) u embeds the information code I into the Monero transaction information, generating a transaction message M containing the hidden information; 2.5) u sends a transaction message M containing hidden information through the Monero blockchain network; 2.6) u′ identifies the transaction information M carrying hidden information from the blockchain network; 2.7) u′ extracts the information code I from M; 2.8) u′ decodes I according to the data type of the information carrier and obtains C start +C+C end ; 2.9) u′ is obtained by removing C start and C end Obtain ciphertext C; 2.10) u′ decrypts C using k and obtains the secret message s′=k(C).

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