End-to-end group key negotiation method and device based on quadtree

Abstract

The invention discloses a quad-tree-based end-to-end group key negotiation method and device, which are applied to group communication, the connection among group users adopts a quad-tree structure, and the method comprises the following steps: a user ui sends a proposal for changing a group state, and broadcasts a proposal message to a group; other users in the group verify the received proposal message and update one of a local encryption key material and a direct path thereof, a new group key is generated, and group key update after group state update is completed; wherein group state changing comprises user joining, user leaving and user own state updating. According to the invention, on the basis of ensuring the safety of group chat communication, the performance and response speed of the group chat communication are improved, and the method can better adapt to a complex and dynamic communication environment.

Description

Technical Field

[0001] The present invention belongs to the field of communication technologies, and particularly relates to an end-to-end group key negotiation method and apparatus based on a quadtree. Background Art

[0002] With the popularization of social media and instant messaging tools, the group chat function has become an important way of daily communication. The group chat scenario involves interactions among multiple users, and information needs to be transmitted among group users. This dynamic and open communication method brings multiple information security challenges. Especially in the case of a large group size and frequent user changes, how to effectively ensure the confidentiality and integrity of information and prevent unauthorized access or tampering has become an important technical problem.

[0003] Existing point-to-point encryption protocols are mostly used in single conversation scenarios. They provide encryption protection between two parties, but often do not consider the impact of multi-user participation and dynamic changes in group chats on key management. In addition, existing protocols often have difficulty in effectively managing encryption keys in large-scale and multi-node networks, especially in the face of the dynamic joining and leaving of users in group chats. Therefore, how to ensure the security of keys and the efficiency of updates is a major challenge faced by current encryption protocols. Summary of the Invention

[0004] To solve the above problems existing in the prior art, the present invention provides an end-to-end group key negotiation method and apparatus based on a quadtree. The technical problems to be solved by the present invention are realized through the following technical solutions:

[0005] In a first aspect, an end-to-end group key negotiation method based on a quadtree provided by the present invention is applied to group communication, and the connections between group users adopt a quadtree structure. The method includes:

[0006] User u i Sends a proposal to change the group state and broadcasts the proposal message to the group;

[0007] Other users in the group verify the received proposal message, update their local encryption key materials and one of their direct paths, generate a new group key, and complete the group key update after the group state is updated;

[0008] Among them, changing the group state includes user joining, user leaving, and a user updating their own state.

[0009] In a second aspect, the present invention also provides an end-to-end group key negotiation apparatus based on a quadtree, which is applied to group communication, and the connections between group users adopt a quadtree structure. The apparatus includes:

[0010] A group state change proposal module, used for user u iPropose to change the group status and broadcast the proposal message to the group;

[0011] A group key update module, used for other users in the group to verify the received proposal message, update the local encrypted key material and one of its direct paths, generate a new group key, and complete the group key update after the group status is updated;

[0012] Among them, changing the group status includes user joining, user leaving, and user updating their own status.

[0013] Advantages of the present invention:

[0014] An end-to-end group key negotiation method and device based on a quadtree provided by the present invention solve the deficiencies of existing technical solutions in terms of performance, security, and scalability by optimizing key management, simplifying protocol implementation, improving the support efficiency for large-scale groups, and enhancing quantum resistance. By improving the existing solution, the present invention can improve its performance and response speed while ensuring the security of group chat communication, and better adapt to complex and dynamic communication environments.

[0015] The following will further elaborate on the present invention in conjunction with the accompanying drawings and embodiments. Description of the Drawings

[0016] Figure 1 is a flowchart of an end-to-end group key negotiation method based on a quadtree provided by an embodiment of the present invention;

[0017] Figure 2 is a schematic diagram of a quadtree structure provided by an embodiment of the present invention;

[0018] Figure 3 is a schematic diagram of the working mode of the quadtree structure during dynamic adjustment provided by an embodiment of the present invention. Detailed Embodiments

[0019] The following further describes the present invention in detail with specific embodiments, but the implementation manners of the present invention are not limited thereto.

[0020] In the security management of group chat, the frequent change of users (new users joining or old users leaving) leads to the need for continuous key updates. Existing encryption protocols often require a full key exchange or update when the group chat users change, which not only increases the computational and communication burden but also may cause security vulnerabilities. Existing key management methods are difficult to achieve efficient and secure key distribution in dynamic groups.

[0021] Existing secure instant messaging protocols mainly include: Transport Layer Security (TLS), Socket Secure Layer (SSL), Signal protocol, and Messaging Layer Security (MLS).

[0022] Among them, TLS and SSL protocols are mainly used for point-to-point encrypted communication to ensure the confidentiality and integrity of data during transmission and are widely used for data transmission protection in Internet applications. However, in scenarios such as group chats and large-scale concurrent users, these protocols usually face performance bottlenecks because each user needs to establish and maintain a separate encrypted session, resulting in increased communication latency and computational overhead.

[0023] The Signal protocol is an end-to-end encryption protocol specifically designed for instant messaging and has strong security. The Signal protocol uses modern encryption technologies such as forward secrecy and asymmetric encryption to ensure that only the two communicating parties can access the message content. However, the Signal protocol also has certain performance limitations when dealing with a large number of users in a group chat environment, especially when the number of users surges, and how to efficiently manage keys and sessions becomes a bottleneck.

[0024] The MLS protocol is a protocol designed specifically for secure communication involving multiple parties and aims to provide security and privacy protection for communication scenarios involving multiple parties such as instant messaging and online collaboration. The concept of the MLS protocol was first born in 2016 and was first discussed during the IETF (Internet Engineering Task Force) meeting in Berlin. The original concept was mainly based on pairwise encryption and focused on the security of one-to-one communication and group communication. This protocol improves the efficiency and security of key exchange and user management in multi-party communication by adopting an asynchronous ratchet tree structure (binary tree).

[0025] With the in-depth development of the protocol, in 2017, the University of Oxford and Facebook jointly published an academic paper on asynchronous ratchet trees. By combining the ratchet mechanism and the tree structure, asynchronous ratchet trees can efficiently update keys in a dynamic group environment, ensuring that participants can encrypt and decrypt messages without sacrificing security.

[0026] By 2021, researchers such as Alwen carried out a modular design of the MLS protocol and demonstrated its inherent security. In 2022, the Alwen team further studied and proposed the concept of the internal security of the MLS protocol, providing a more solid security guarantee for multi-party communications such as group chats. In March 2023, the MLS protocol was approved by the IETF and released as a new standard in July of the same year. The release of this standard marks the maturity of the MLS protocol in theory and practice, especially suitable for instant messaging and online collaboration scenarios that require multi-party secure communication.

[0027] The core function of the MLS protocol is group authenticated key exchange. Similar to traditional protocols such as TLS, all participants agree on a common secret value and can authenticate each other's identities. The key innovation of MLS is that it not only supports two-party communication but also multi-party authenticated key exchange, and group users can change dynamically during the protocol process, that is, the addition or withdrawal of each user will not affect the group security. This makes MLS particularly suitable for multi-person chat or cooperation scenarios, ensuring that the security and confidentiality of communications are always guaranteed even when users change.

[0028] However, despite the significant advantages of the MLS protocol in many aspects, it still faces challenges in practical applications, such as computational overhead, the depth problem of the tree structure, and the complexity of protocol implementation. First, although the protocol has been optimized in terms of performance, when the scale of group users is large, the overhead of key updates and message passing is still high. Especially when group users change frequently, the efficiency of key exchange may be affected. Second, the MLS protocol relies on a binary tree structure to manage group keys and message passing. However, as the group size increases, the depth of the tree also increases, which may lead to performance bottlenecks. In addition, the implementation complexity of the protocol is high, and processes such as key management and user authentication need to be optimized while ensuring security.

[0029] In summary, the existing TLS / SSL protocol, Signal protocol, and MLS protocol in the prior art each provide security guarantees for different communication needs, but their disadvantages mainly focus on poor scalability, high performance overhead, complex key management, and response efficiency when group users change dynamically. These disadvantages make the existing solutions face challenges in handling large-scale group chats, dynamic user management, and efficient secure communication.

[0030] In view of this, an end-to-end group key negotiation method and apparatus based on a quadtree provided by the present invention solve the deficiencies of existing technical solutions in terms of performance, security, and scalability by optimizing key management, simplifying protocol implementation, improving the support efficiency for large-scale groups, and enhancing quantum resistance. By improving the existing solution, the present invention can improve its performance and response speed while ensuring the security of group chat communication, and better adapt to complex and dynamic communication environments.

[0031] Please refer to Figure 1 , Figure 1 which is a flowchart of an end-to-end group key negotiation method based on a quadtree provided by an embodiment of the present invention. An end-to-end group key negotiation method based on a quadtree provided by the present invention is applied to group communication. The connections between group users adopt a quadtree structure. The method includes:

[0032] S101. User u i issues a proposal to change the group state and broadcasts the proposal message to the group.

[0033] Among them, changing the group state includes user joining, user leaving, and user updating their own state.

[0034] Specifically, in this embodiment, before user u i issues a proposal to change the group state and broadcasts the proposal message to the group, it further includes:

[0035] One or more initial users create their initial states, and its expression is:

[0036] γ i ← init(u i );

[0037] Among them, init(·) represents the operation of initializing the user state, which is an operation for initializing a user state. When each user joins the encryption group, they need to generate or set their initial state, which contains the user's encryption information and key material and is used for subsequent encryption and verification operations in the entire protocol. Through the init(·) operation, each user generates their own initial encryption state and prepares to enter the subsequent steps in the protocol;

[0038] The initial users create a group according to their initial states. The group includes the users in list G, G = (u i ) i∈[1,n] , and send a welcome message W to all users in the group. The welcome message W includes the necessary information for joining the group, and its expression is:

[0039] (γ′ i , W): = creat-group(γi , G);

[0040] Among them, creat-group(·) represents the operation of initializing the group state. Specifically, it creates a new encrypted group and initializes the states of group members. This operation involves creating a new encrypted group containing multiple users and generating and sending the required initial information for the members of this group, γ i ' represents the state after the initial user is updated.

[0041] In this embodiment, user u i proposes to change the group state through operation a ∈ A, which is a set of authorized actions of CGKA; among them,

[0042] Add represents the operation of adding user u j , that is, user u i proposes to add user u j to the group; Remove represents deleting user u j , that is, user u i proposes to delete user u j from the group; Update represents that user u i updates the local encrypted key material and generates an updated state.

[0043] Then user u i sends an encrypted ciphertext to the branch node, the branch node sends the encrypted ciphertext to the root node, and the root node broadcasts the topic message. The content of the broadcast proposal message includes:

[0044] (γ′ i , P) ← propose(γ i , a[, u j );

[0045] Among them, propose(·) represents the operation for the user to propose a state change. Through this operation, the user proposes a change to the encrypted group state, usually requesting to add or remove group members, or update the encryption key, etc. γ i represents the current state of user u i , γ′ i represents the updated state of user u i , a[, u j represents that user u i proposes a proposal to change the group state through action a ∈ A, and P represents the proposal message.

[0046] It should be noted that this embodiment works based on the Continuous Group Key Agreement (CGKA).

[0047] S102. Other users in the group verify the received proposal message, update one of their local encrypted key materials and its direct path, generate a new group key, and complete the group key update after the group status is updated.

[0048] Specifically, in this embodiment, when other users in the group receive the broadcast proposal message, they verify the proposal message to avoid malicious proposals. After passing the verification, other users in the group update one of their local encrypted key materials and its direct path, and generate a new group key k.

[0049] Further, the root node broadcasts an update message to the group users, and its content includes:

[0050] (γ i ', k, C[, W]) ← commit(γ i , P);

[0051] Among them, γ′ i represents the updated group status of user u i , k represents the new group key, C[, W] represents broadcasting a commit message C or a welcome message W, and commit(·) represents the operation of verifying and confirming after receiving proposals from other users. This operation processes all proposals and updates the group's encrypted key and status according to the verification results.

[0052] It should be noted that the new path key is distributed to existing users through tree path encryption to ensure backward secrecy. Each user updates their local view to ensure a consistent understanding of the new key and the tree structure.

[0053] Further, in the case of a user leaving or a user updating their local status, the group users update their local status according to the received update message, and calculate the group key after the group status is updated to complete the confirmation after the group status is updated; among them, the expression of the group key after the group status is updated is:

[0054] (γ′ i , k): = process(γ i , m ∈ {C});

[0055] Among them, process(·) represents an operation of the cryptographic group key agreement (CGKA), which is used to process the commit message C to ensure that when users receive confirmations from other members or new members join, they update their status and synchronize the group's encrypted information. In this way, it helps users maintain consistency and key synchronization in the cryptographic group.

[0056] Alternatively, for the case of a user joining, the group adds the user. The group users update their local status according to the received update message and calculate the group key after the group status is updated to complete the confirmation after the group status is updated; where the expression of the group key after the group status is updated is:

[0057] (γ′ i ,k):=process(γ i ,m∈{W});

[0058] where process(·) represents an operation of the encryption group key protocol for processing the welcome message W.

[0059] It should be noted that for the case of a user joining, the key distribution is completed through node encryption (HPKE) on the path. The path key is encrypted by the public key of the root node of the tree and distributed to ensure the security of the tree's encrypted path key distribution.

[0060] It should also be noted that in this embodiment, symmetric encryption (AEAD) and key encapsulation mechanism (KEM) are used to generate a shared key for protecting communication. When a user leaves or joins, the tree nodes are updated and synchronized to all users to maintain the forward and backward secrecy of the key.

[0061] Please refer to Figure 2 , Figure 2 which is a schematic diagram of the quadtree structure provided by the embodiment of the present invention. Considering that in a large-scale group chat system or other distributed communication scenarios, the number of users is huge and widely distributed, the traditional message passing method often faces problems of delay and bandwidth bottlenecks. To solve this problem, this embodiment adopts a quadtree structure to optimize the communication system. A quadtree is a space partitioning data structure with adaptive characteristics that can automatically adjust the branch depth and structure according to the node density in different regions.

[0062] As Figure 2 shown, the quadtree structure includes a root node, branch nodes, and leaf nodes. The root node is the top node of the quadtree, representing the initial area of the entire system, and all user nodes or device nodes are distributed based on this. Each layer under the root node divides the area into four sub-regions, and each sub-region corresponds to a branch node. Through this recursive space partitioning, the system can efficiently deliver information to users or devices within a specified area. At the bottom layer of the quadtree, the leaf nodes represent specific users or devices, and each leaf node corresponds to a communication node, and the ultimate goal of message passing is these nodes.

[0063] Among them, the root node is used to broadcast proposal messages and update information.

[0064] Four nodes are connected under the root node. If other nodes are further connected under this node, this node is a branch node; if no other nodes are connected under this node, this node is a leaf node. The branch node is used to transmit proposals for changing the group state, and the leaf node represents a group user and is used to send proposals for changing the group state or receive messages to change the local state.

[0065] Through the hierarchical management of the quadtree, when the system needs to transmit a message, it only starts from the leaf node where the target user is located and quickly transmits the information upward through the tree structure, avoiding irrelevant nodes, thereby significantly reducing unnecessary communication and latency. This dynamic adjustment method based on spatial partitioning enables the communication to always be efficient and low-latency regardless of the number of users or devices in the system.

[0066] Please refer to Figure 3 , Figure 3 which is a schematic diagram of the working mode of the quadtree structure provided by the embodiment of the present invention during dynamic adjustment, further showing the working mode of the quadtree structure during dynamic adjustment. When the number and distribution of the user group change, the structure of the quadtree will be automatically adjusted. For example, when the number of users in a certain area increases sharply, the quadtree will automatically further divide the space in this area to adapt to the new user needs and ensure that the efficiency and quality of message transmission are not affected.

[0067] In this embodiment, for the case of user joining, the new user calculates the path with the least load through the lightest child node algorithm and joins the leaf node on this path to keep the communication cost of the quadtree optimal. At the same time, the other leaf nodes on the branch node corresponding to this leaf node update their paths to reduce communication latency, and clear the nodes on the path of the new user to ensure that the new user does not share the existing group keys.

[0068] In addition, if the capacity of the quadtree is insufficient, new levels will be automatically expanded to ensure depth balance. The newly expanded levels will contain empty nodes for allocation when future users join.

[0069] In this embodiment, for the case of user leaving or the user updating the local state, the nodes on the path of the leaving user are cleared, and all relevant path keys are also invalidated to ensure that the leaving user cannot continue to access the group content. At the same time, the remaining group users re-plan the path and are assigned to the optimal leaf node. By gradually updating the path nodes, redundant communication is reduced. The nodes of the leaving user may be merged by a new subtree to maintain the communication efficiency of the tree; or,

[0070] Within a preset period, the group users re-plan the path to find the leaf node at the optimal position; among them, the leaf node at the optimal position includes the leaf node with the minimum path load.

[0071] In summary, the end-to-end group key negotiation method based on quad-tree provided by the present invention has the following

[0072] Beneficial effects:

[0073] First, it improves the group chat communication efficiency: In the case of large-scale user dynamic changes in the traditional group chat system, the communication efficiency is low, usually requiring a long message transmission path or high network bandwidth. By introducing the ratchet tree design of the quad-tree structure, the present invention effectively reduces the number of hops of message transmission in group chat, optimizes the node distribution, and significantly reduces the message transmission delay. This tree structure is more suitable for processing a large number of nodes compared to the traditional binary tree, thus improving the communication efficiency, especially in the case of high concurrency and large groups.

[0074] Second, it reduces the computational complexity and communication overhead: Existing group chat systems face problems of high computational complexity and large network bandwidth consumption when dealing with encryption and key updates, especially when the number of group users increases, these problems become more serious. The present invention realizes a more efficient key update and message encryption process by optimizing the tree structure, reduces the amount of calculation and communication overhead, effectively improves the processing speed of the system, and enables the system to still operate efficiently in a large-scale group chat environment.

[0075] Third, the optimized dynamic tree structure adjustment mechanism: The tree structure in the prior art is usually fixed and cannot be flexibly adjusted according to the change of the group chat scale, resulting in low resource utilization in group chats of different scales and possible unnecessary calculation and communication waste. The dynamic tree structure adjustment mechanism proposed by the present invention can dynamically adjust the depth and node distribution of the tree according to the change of the group chat scale, enabling the system to optimize resource allocation according to actual needs. This flexible mechanism greatly improves the adaptability of the system to group chats of different scales and maximizes the utilization efficiency of resources.

[0076] Fourth, it resists the threat of quantum computing: With the development of quantum computing, existing encryption technologies are at risk of being cracked, which poses a threat to the data security of group chat systems. The present invention integrates a quantum-resistant encryption algorithm to ensure that the system can resist quantum computing attacks and protect the communication data security in group chat. The application of this technology ensures the long-term security of the system, not only solves the vulnerability problem of existing encryption technologies to quantum computing, but also enhances the security of the system in the future technical environment.

[0077] Fifth, the scalability and adaptability of the system are improved: Traditional group chat systems usually have bottlenecks in scalability. As the number of group chat users increases, the performance and response speed of the system may decline sharply, even leading to system crashes. The technical solution of the present invention enables the system to make a smooth transition during user expansion by adopting a quadtree structure, optimized key management, and quantum-resistant encryption algorithms. The dynamic adjustment of the tree structure and the optimization of encryption calculations effectively avoid performance bottlenecks, thereby enhancing the scalability and adaptability of the system in large-scale group chats.

[0078] Based on the same inventive concept, the present invention also provides an end-to-end group key negotiation device based on a quadtree for implementing the end-to-end group key negotiation method based on a quadtree provided in the above embodiments of the present invention. For the embodiments of the method, please refer to the above, and details will not be repeated here; the device is applied to group communication, and the connections between group users adopt a quadtree structure. The device includes:

[0079] A group status change proposal module for user u i to issue a proposal to change the group status and broadcast the proposal message to the group;

[0080] A group key update module for other users in the group to verify the received proposal message, update one of their local encrypted key materials and its direct path, generate a new group key, and complete the group key update after the group status is updated;

[0081] wherein, changing the group status includes user joining, user leaving, and user updating their own status.

[0082] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant is intended to cover non-exclusive inclusion, so that an article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed. Without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the article or device including the said element. "Connection" or "connected" and other similar words are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The orientation or positional relationship indicated by "up", "down", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present invention.

[0083] In the description of this specification, the descriptions referring to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples", etc. mean that the specific features or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0084] The above content is a further detailed description of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is only limited to these descriptions. For those of ordinary skill in the technical field to which the present invention pertains, without departing from the concept of the present invention, several simple deductions or substitutions can be made, and all should be regarded as belonging to the protection scope of the present invention.

Claims

1. A quadtree-based end-to-end group key agreement method, characterized in that: Applied to group communication, the connection between group users adopts a quadtree structure, and the method includes: User i Issue a proposal to change the group state and broadcast the proposal message to the group; Other users in the group verify the received proposal message, and update the local encryption key material and one of its direct paths to generate a new group key, completing the group key update after the group status is updated; The changing of group status includes user joining, user leaving and user updating their own status.

2. The quadtree-based end-to-end group key agreement method according to claim 1, characterized in that: In user u i Before proposing to change the group state and broadcasting the proposal message to the group, it also includes: One or more initial users create their initial state, which is expressed as: c i ←init(u i ); Among them, init(·) represents the operation of initializing the user state; The initial user creates a group according to its initial state, and the group includes the users in the list G, G = (u i ) i∈[1,n] , and sends a welcome message W to all users in the group. The welcome message W includes the necessary information for joining the group, and its expression is: (c' i ,W):=creat-group(γ i ,G); Among them, creat-group(·) represents the operation of initializing the group state, γ' i Indicates the status after the initial user update.

3. The quadtree-based end-to-end group key agreement method according to claim 1, characterized in that: The expression of the broadcast proposal message is: (c' i ,P)←propose(c i ,a[,u j ]); Among them, propose(·) represents user u i Propose a state change operation, γ i Represents user u i The current state, γ' i Represents user u i The updated state, a[,u j ] indicates user u i A proposal to change the group state is made through action a∈A, and P represents the proposal message.

4. The quadtree-based end-to-end group key agreement method according to claim 1, characterized in that: The group key update after completing the group status update includes: Broadcast update message to the group, the expression is: (c' i ,k,C[,W])←commit(γ i ,P); Among them, γ' i Represents user u i In the updated state, k represents the new group key, C[,W] represents broadcasting a commit message C or a welcome message W, and commit(·) represents the operation of verifying and confirming after receiving proposals from other users.

5. The quadtree-based end-to-end group key agreement method according to claim 4, characterized in that: The group key update after completing the group status update includes: In the case where the user leaves or updates the local status, the group user updates the local status according to the received update message and calculates the group key after the group status is updated to complete the confirmation after the group status is updated; wherein, the expression of the group key after the group status is updated is: (γ’ i ,k):=process(γi,m∈{C}); Wherein, process(·) represents an operation of the encryption group key protocol, which is used to process the submission message C.

6. The quadtree-based end-to-end group key agreement method according to claim 4, characterized in that: The group key update after completing the group status update includes: In the case of user joining, a new user is added to the group. The group user updates the local state according to the received update message and calculates the group key after the group state is updated to complete the confirmation after the group state is updated; wherein, the expression of the group key after the group state is updated is: (γ’ i ,k):=process(γi,m∈{W}); Wherein, process(·) represents an operation of the encryption group key protocol, which is used to welcome the message W.

7. The quadtree-based end-to-end group key agreement method according to claim 1, characterized in that: The quadtree structure includes a root node, branch nodes and leaf nodes, wherein: The root node is used to broadcast proposal messages and update information; The root node is connected to four nodes. If the node is connected to other nodes, the node is a branch node. If the node is not connected to other nodes, the node is a leaf node. The branch node is used to transmit a proposal to change the group status. The leaf node represents a group user and is used to issue a proposal to change the group status or receive a message to change the local status.

8. The quadtree-based end-to-end group key agreement method according to claim 7, characterized in that: The group key update after completing the group status update includes: When a new user joins, the new user calculates the path with the least load through the lightest child node algorithm and joins the leaf node on the path; at the same time, the other leaf nodes on the branch node corresponding to the leaf node update their paths and clear the nodes on the new user's path to ensure that the new user does not share the existing group key.

9. The quadtree-based end-to-end group key agreement method according to claim 7, characterized in that: The group key update after completing the group status update includes: When a user leaves or updates their local status, the nodes on the path of the user who left are cleared to ensure that the user who left cannot continue to access the group content. At the same time, the remaining group users re-plan their paths and assign them to the optimal leaf nodes. Or, Within a preset period, the group users re-plan the path to find the leaf node at the optimal position; wherein the leaf node at the optimal position includes the leaf node with the smallest path load.

10. A quadtree-based end-to-end group key agreement device, characterized in that: Applied to group communication, the connection between group users adopts a quadtree structure, and the device includes: Group state change proposal module for user u i Issue a proposal to change the group state and broadcast the proposal message to the group; A group key update module, used for other users in the group to verify the received proposal message, and update the local encryption key material and one of its direct paths, generate a new group key, and complete the group key update after the group status is updated; The changing of group status includes user joining, user leaving and user updating their own status.

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