Lightweight group key agreement method for vehicular ad hoc networks

Abstract

The present application belongs to the technical field of information security, and particularly relates to a lightweight group key agreement method for a vehicle-mounted self-organizing network. The method comprises the following steps: S1, establishing system security parameters and configuring a mapping relationship between a location group and a non-orthogonal multiple access power layer; S2, a vehicle calculates a corresponding location group identifier according to its own location information, and divides the vehicle into a corresponding location group; S3, the vehicle is allocated with credential information for subsequent polynomial interpolation reconstruction; S4, the vehicle sends a group joining request, and after the network equipment authenticates the vehicle, a polynomial with a group secret as a constant term is constructed, a public auxiliary point is generated, the public auxiliary point is distributed to group vehicles in a non-orthogonal multiple access mode, the vehicle reconstructs the polynomial in combination with local credential information and the received public auxiliary point, and a group session key is generated; and S5, when the location of the vehicle changes, causing the corresponding belonging location group to change, group key update is triggered.

Description

Technical Field

[0001] This invention belongs to the field of information security technology, specifically relating to a lightweight group key negotiation method for vehicular ad hoc networks. Background Technology

[0002] As the deployment scale of vehicular ad hoc networks (VANETs) continues to expand and their intelligence level continues to improve, secure and efficient group communication between vehicles has become one of the key technologies for ensuring driving safety, improving traffic efficiency, and promoting the development of intelligent connected vehicles. However, the inherent characteristics of vehicular networks, such as high-speed node movement, frequent topology changes, and open communication environments, pose serious challenges to secure group communication.

[0003] Currently, researchers have proposed authentication and key generation schemes based on Public Key Infrastructure (PKI), Identity-Based Cryptography (IBC), and Certificateless Public Key Cryptography (CL-PKC) to address the authentication and key generation requirements in the Internet of Vehicles (IoV). PKI-based schemes achieve vehicle authentication and key generation through certificate mechanisms, but the high overhead of certificate management limits their scalability in highly dynamic vehicle environments. IBC-based schemes eliminate the dependence on certificates and support privacy protection, but they have inherent key escrow issues and rely on a trusted key generation center to form a centralized trust model. Certificateless public key cryptography can reduce the complete dependence on a single trusted institution, avoid full key escrow, and achieve conditional privacy protection and anonymous authentication. However, most existing CL-PKC-based schemes are designed for pairwise communication between two entities, and their direct application to dynamic group scenarios has significant limitations, making it difficult to support efficient multi-party group key negotiation.

[0004] In the area of ​​group key management, researchers have proposed various group key negotiation and management schemes. For example, tree-based schemes are used to generate and update group keys when members change frequently; blockchain-based and decentralized group key management schemes reduce dependence on centralized entities through distributed coordination; group signature mechanisms are used to protect the privacy of group members; and batch verification and lightweight optimization techniques are used to reduce the computational and communication overhead in the group authentication and key negotiation process.

[0005] However, the existing group key negotiation schemes mentioned above still have the following shortcomings when applied to large-scale, highly dynamic vehicular network environments:

[0006] First, the efficiency of group key generation and updating is low. To address the key update problem under conditions of frequent vehicle joining and leaving, existing technologies mainly employ tree-based, hierarchical, cloud-assisted, or blockchain-based mechanisms for group key negotiation. These methods typically rely on multi-round interactions or iterative coordination to complete group key generation and updating. As the number of vehicles and the frequency of member changes increase, this leads to high communication and computational overhead, significantly prolonging the latency of group key generation and updating, making it difficult to adapt to resource-constrained vehicular communication environments.

[0007] Second, the dynamic adaptability of the group formation process is insufficient. Existing technologies typically rely on explicit communication and frequent protocol interactions to determine group membership, failing to fully utilize the vehicle's real-time location and motion parameters (such as speed and direction of movement) for group division and key update triggering. In scenarios involving high-speed vehicle movement and frequent changes in membership, the group formation and key reconstruction processes require continuous communication coordination, leading to a surge in signaling overhead and making it difficult to balance execution efficiency and dynamic adaptability.

[0008] Third, the transmission burden during key material distribution is heavy. Existing technologies typically require multiple interactions between group members or multiple round trips with the network for distributing group key materials. As the group size increases, repeated transmission of key materials significantly consumes scarce wireless channel resources, increases transmission latency, and fails to meet the practical needs of large-scale, highly dynamic vehicular networks for low communication overhead, low computational overhead, and low latency group communication.

[0009] In summary, existing group key negotiation technologies for vehicular ad hoc networks still have significant shortcomings in terms of dynamic group communication support, communication and computation efficiency, transmission latency, and dynamic adaptability, making it difficult to simultaneously meet the requirements of scalability, high efficiency, and low latency in large-scale, highly dynamic vehicle environments. Therefore, there is an urgent need to provide a lightweight group key negotiation scheme that can adapt to frequent changes in vehicle occupants, reduce communication and computational overhead, and decrease the latency of group key generation and update. Summary of the Invention

[0010] This invention aims to overcome the technical bottlenecks of existing group key negotiation schemes in large-scale, highly dynamic vehicular ad hoc networks, such as high communication and computing overhead, low group formation efficiency, and long delays in key generation and update. It provides a lightweight group key negotiation method for vehicular ad hoc networks that can adapt to frequent changes in vehicle members, reduce communication and computing overhead, and reduce the delay in group key generation and update.

[0011] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0012] A lightweight group key negotiation method for vehicular ad hoc networks includes the following steps;

[0013] S1, Initialization Phase:

[0014] Establish system security parameters and configure the mapping relationship between location groups and non-orthogonal multiple access power layers;

[0015] S2, Position Mapping Stage:

[0016] The vehicle calculates the corresponding location group identifier locally based on its own location information and assigns the vehicle to the corresponding location group;

[0017] S3, Entity Registration Phase:

[0018] Assign credential information to the vehicle for subsequent polynomial interpolation reconstruction;

[0019] S4, Authentication and Group Key Negotiation Phase:

[0020] When a vehicle sends a group join request, the network device authenticates the vehicle and constructs a polynomial with the group secret as a constant term and generates a common auxiliary point. The common auxiliary point is then distributed to the group vehicles using a non-orthogonal multiple access method. The vehicle reconstructs the polynomial by combining its local credential information and the received common auxiliary point and generates a group session key.

[0021] S5, Group Member Management and Key Update Phase:

[0022] When a vehicle's location changes, causing a change in its corresponding location group, a group key update is triggered.

[0023] Preferably, during the initialization phase, the trusted organization selects an elliptic curve and base points to form an additive cyclic group, selects the system master private key and calculates the system public key, selects a cryptographic hash function and a pseudo-random function, sets the location group division interval and the mapping relationship between the location group identifier and the non-orthogonal multiple access power layer, and publishes the system public key and each function as public parameters.

[0024] Preferably, in the location mapping stage, the vehicle obtains its own geographic coordinates and the reference point coordinates of the service roadside unit, calculates the Euclidean distance between the vehicle's own geographic coordinates and the reference point coordinates, maps the Euclidean distance to the corresponding location group level according to the preset location group division interval, and generates the location group identifier in combination with the area identifier of the service roadside unit.

[0025] Preferably, during the entity registration phase, the trusted institution generates a long-term fog node certificate based on the system master private key and the fog node identity; the trusted institution generates a long-term vehicle certificate based on the system master private key and the vehicle's real identity, and generates the vehicle's lateral interpolation coordinates based on the vehicle identity and the vehicle's long-term certificate. The vehicle's longitudinal interpolation coordinates are dynamically generated during each key negotiation process based on the vehicle's long-term certificate and the current session timestamp; the roadside unit registers with its affiliated fog node and obtains an area identifier.

[0026] Preferably, during the authentication and group key negotiation phase, when a vehicle generates a group join request, a temporary private key is randomly selected and a temporary public key is calculated. The vehicle's real identity is hidden as an anonymous pseudo-identity using the system public key. The location group identifier corresponding to the current location is calculated, and an authentication code is generated based on the anonymous pseudo-identity and the location group identifier. The group join request includes at least the anonymous pseudo-identity, the temporary public key, the location group identifier, the current timestamp, and the authentication code.

[0027] Preferably, the network device includes fog nodes and sub-trusted institutions; after receiving a request, the fog nodes aggregate vehicle requests according to location group identifiers and send them to the sub-trusted institutions; the sub-trusted institutions recover the vehicle's true identity from the anonymous pseudo-identity based on the system master private key, obtain the vehicle's long-term certificate based on the recovered vehicle's true identity, recalculate the authentication code and compare it with the authentication code in the request to verify the validity of the vehicle's identity; after successful verification, vehicles with the same location group identifier are grouped into an authentication group.

[0028] Preferably, during the authentication and group key negotiation phase, when the network device constructs the polynomial, the polynomial simultaneously passes through the point corresponding to the group secret and the private interpolation point of each vehicle in the group; the common auxiliary point is selected from multiple points on the polynomial that are different from the private interpolation points of each vehicle, and the number of the common auxiliary points is determined according to the number of group members.

[0029] Preferably, during the authentication and group key negotiation phase, the sub-trusted institution is also used to generate vehicle authentication codes for each vehicle and message authentication codes for fog nodes; after the fog node verifies the message authentication code, it extracts broadcast materials and sends them to the roadside unit; the roadside unit, based on the non-orthogonal multiple access power layer corresponding to the location group identifier, superimposes the broadcast materials of multiple groups in the power domain and then broadcasts them uniformly.

[0030] Preferably, during the authentication and group key negotiation phase, the vehicle determines the corresponding decoding layer based on the location group identifier, extracts the common auxiliary point of the group to which it belongs from the broadcast signal through serial interference elimination, combines the locally stored private interpolation point with the common auxiliary point, reconstructs the polynomial through Lagrange interpolation to extract the constant term of the polynomial, and generates the group session key based on the constant term.

[0031] Preferably, during the group member management and key update phase, the network device estimates the time when the vehicle leaves the current location group based on the vehicle's current location, direction of movement, and speed, and uses the time when the vehicle leaves the current location group as the basis for triggering the key update; when a vehicle joins or leaves the group, the network device regenerates the polynomial, selects the constant term of the polynomial, and updates the common auxiliary point, so that the group session keys before and after the update are independent of each other.

[0032] Compared with the prior art, the beneficial effects of this invention are: (1) In terms of security: by dynamically binding the vehicle long-term certificate, current timestamp and private interpolation point, unauthenticated vehicles cannot obtain the complete interpolation information required to reconstruct the polynomial, thereby ensuring the confidentiality of the group session key; by updating the polynomial constant term in each session, the group keys generated by different sessions are made independent of each other, ensuring forward confidentiality and backward confidentiality in the case of dynamic vehicle joining and leaving; by using dynamic anonymous identity and identity recovery mechanism, while protecting the real identity of the vehicle and the non-associative nature of communication, the authorized agency retains the ability to trace the identity of abnormal vehicles; in addition, the location group, non-orthogonal multiple access power layer and vehicle cryptographic certificate are bound together, so that the group session key can only be obtained by valid vehicles that simultaneously meet the geographical location requirements and identity authentication requirements; (2) In terms of system efficiency: by broadcasting the public auxiliary point once, multiple rounds of interaction and iterative coordination between group members are avoided; location mapping is used to reduce the additional signaling overhead in the group formation process, and the parallel distribution of multiple vehicle group key materials is achieved by superimposing the power domain of non-orthogonal multiple access. Experimental results show that when the group size is 100 vehicles, the communication overhead is reduced by 9.07% to 49.83%; compared with some comparative schemes, the total computation overhead is reduced by 71.47%, and the network side computation overhead is reduced by about 92.88%; when the vehicle speed reaches 40m / s, the group key generation delay is reduced by 90.8%; (3) In terms of applicability: the present invention can support the dynamic joining and leaving of vehicles, and can timely form groups and update keys according to the real-time location, direction of movement and motion parameters of vehicles. It is suitable for vehicle network environments with high-speed vehicle movement, frequent changes in members and dense distribution of multiple vehicles; while ensuring the security of group communication, it achieves lower communication overhead, computation overhead and transmission delay, and improves the scalability and practical deployment capability of the group key negotiation scheme in large-scale, highly dynamic vehicle self-organizing networks. Attached Figure Description

[0033] Figure 1 This is a flowchart of a lightweight group key negotiation method for vehicular ad hoc networks according to the present invention; Figure 2 A comparative diagram of the communication overhead of the present invention and the prior art under different vehicle numbers, provided for an embodiment of the present invention; Figure 3 This is a schematic diagram comparing the group key generation delay of the present invention and the prior art under different vehicle speed conditions, provided as an embodiment of the present invention. Detailed Implementation

[0034] To more clearly illustrate the embodiments of the present invention, specific implementation methods will be described below with reference to the accompanying drawings. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings and other implementation methods can be obtained based on these drawings without any creative effort.

[0035] like Figure 1 As shown, this invention provides a lightweight group key negotiation method for vehicular ad hoc networks. The invention mainly comprises a complete workflow consisting of five stages: initialization stage, location mapping stage, entity registration stage, authentication and group key negotiation stage, and group member management and key update stage. The detailed process of each stage is as follows:

[0036] Step 1, Initialization Phase: Establish system security parameters and configure the mapping relationship between location groups and non-orthogonal multiple access power layers. The specific process is as follows:

[0037] 1-1, The Trusted Organization (TA) selects a non-singular elliptic curve defined on a finite field. On the elliptic curve, select an order of... The base point This forms an addition cyclic group. Trusted institution TA from model set of nonzero invertible integers Randomly select the system master private key And calculate the system public key. ,in, Based on The order. The system master private key. The cryptographic hash functions are stored within the trusted platform modules of the Trusted Authority (TA) and its sub-TAs and are not publicly disclosed. The Trusted Authority (TA) further selects six independent cryptographic hash functions. to Pseudo-random functions Location group division interval And the mapping function between location group identifiers and non-orthogonal multiple access power layers. .in, Indicates the first The identifier of a location group This represents the non-orthogonal multiple access power domain layer corresponding to the location group, used to determine the power allocation coefficients corresponding to that location group. And serial interference elimination decoding order. The system discloses elliptic curve parameters, system public key, various cryptographic hash functions, position mapping parameters, and power layer mapping function.

[0038] Step 2, Location Mapping Stage: The vehicle calculates its corresponding location group identifier locally based on its own location information and is then assigned to the appropriate location group. The specific process is as follows:

[0039] 2-1, Vehicle From its service roadside unit Get the area identifier And based on its own geographical coordinates and the coordinates of the roadside unit reference points Calculate the Euclidean distance between the vehicle and the reference point of the service roadside unit. Vehicles are divided into intervals according to preset location groups. Locally computed location group identifier Vehicles within the same distance range and served by the same roadside unit receive the same location group identifier. This allows vehicles to be associated with the same location group. Vehicles can determine their group locally based on their current location without additional signaling interaction. Simultaneously, the system uses a preset mapping function. Location group identifier Mapping to the corresponding non-orthogonal multiple access power layer and decoding order enables the binding between vehicle location groups and physical layer transmission resources.

[0040] Step 3, Entity Registration Phase: Assign credential information to vehicles for subsequent polynomial interpolation reconstruction.

[0041] In this phase, the trusted authority (TA) uses the system's master private key and a cryptographic hash function to complete identity registration and related parameter allocation for fog nodes, vehicles, and roadside units, thereby establishing a trusted identity foundation for subsequent anonymous authentication, location group formation, and group key negotiation. The registration process for each entity is completed through a secure channel to ensure the confidentiality and integrity of registration information during transmission. The specific process is as follows:

[0042] 3-1, Fog Node Registration: Fog Node Select a unique identifier It then sends this information to the Trusted Authority (TA) via a secure channel. The TA calculates the fog node's long-term credential based on the system's master private key. Subsequently, the trusted agency TA will Return to fog node and key-value pairs Write to the first hash table The first hash table is synchronized to the corresponding sub-TA (Trusted Authority), and the fog node will hold the long-term credentials. Stored in secure hardware.

[0043] 3-2, Vehicle Registration: Vehicle Select a unique real identity identifier It is then sent to the Trusted Authority (TA) via a secure channel. The TA calculates the vehicle's long-term certificate. Based on the vehicle's identity and long-term certificate, a unique lateral interpolation coordinate is generated. Trusted institution TA will The data is returned to the vehicle, which stores it in the Trusted Platform module. Simultaneously, the Trusted Authority (TA) stores the key-value pair. Write to the first hash table The first hash table is then synchronized to the corresponding sub-Trusted Authority (sub-TA). The vehicle's longitudinal interpolation coordinates are not pre-allocated during registration, but are dynamically generated based on the vehicle's long-term credentials and the current timestamp during each group key negotiation, thus binding the vehicle's private interpolation points to the vehicle credentials and the current session.

[0044] 3-3, Roadside Unit Registration: Roadside Unit To the fog node Register and obtain a regional identifier In subsequent stages, the roadside unit receives group key materials and non-orthogonal multiple access power allocation information, and is responsible for superimposing, encoding, and broadcasting the key materials of multiple groups.

[0045] Step 4, Authentication and Group Key Negotiation Phase: The vehicle sends a group join request. After the network device authenticates the vehicle, it constructs a polynomial with the group secret as a constant term and generates a common auxiliary point. The common auxiliary point is distributed to the group vehicles through a non-orthogonal multiple access method. The vehicle combines its local credential information and the received common auxiliary point to reconstruct the polynomial and generate a group session key.

[0046] In this stage, the vehicle Fog nodes Trusted sub-organizations and roadside units Collaboratively complete vehicle request generation, request aggregation, identity authentication, location group formation, and group key material generation and distribution. For vehicles with the same location group identifier... For valid vehicles, the sub-trusted institution constructs the corresponding group polynomial and generates common auxiliary interpolation points. The roadside unit uses a non-orthogonal multiple access method to uniformly broadcast key materials. Vehicles use their local private interpolation points and the received common auxiliary points to generate a consistent group session key. The specific process is as follows:

[0047] 4-1, Vehicle Random selection And calculate the temporary public key. The vehicle uses the system's public key to generate an anonymous pseudo-identity. The vehicle calculates its location group identifier based on its current location and the service roadside unit area identifier. and get the current timestamp Subsequently, the vehicle calculates the authentication code. And send a group join request to the fog node. ;

[0048] 4-2, the roadside unit forwards requests from vehicles within its coverage area to the fog node. The fog node first checks the freshness of each vehicle's timestamp and then determines the request based on the location group identifier. Vehicles are grouped. Fog nodes establish a second hash table. Identified by location group The key is used to store the anonymous pseudo-identity, location coordinates, and direction of movement for the corresponding vehicle. Subsequently, the fog nodes calculate the aggregated authentication code. And generate an aggregation request message. ,in, This indicates the number of valid vehicle requests within the current aggregation period. Fog nodes aggregate request messages. Send to the sub-trusted authority (sub-TA);

[0049] 4-3. After receiving the aggregation request message, the sub-TA checks the timestamp. The freshness, and based on the fog node identity identifier From the first hash table Obtain long-term certificates The system recalculates the aggregate authentication code and verifies message integrity. Upon successful verification, the sub-trusted authority restores the vehicle's true identity using the system's master private key. The sub-trusted institution, based on the recovered data... Query the first hash table Obtain a long-term vehicle certificate and lateral interpolation coordinates Recalculate the vehicle authentication code And determine whether it satisfies Upon successful verification, the sub-trusted organization will have the same location group identifier. Valid vehicle composition certification group and through a third hash table Record the anonymous pseudo-identities, long-term credentials, and lateral interpolation coordinates of group members.

[0050] 4-4, for those containing Certification group of valid vehicles The trusted sub-organization randomly selects the group secret. and order The trusted sub-institution determines the time based on the current session timestamp. Dynamically generate longitudinal interpolated coordinates for each vehicle. This yields the vehicle's private interpolation point. A sub-trusted organization constructs a polynomial of degree The polynomial is made to pass through the group secret point simultaneously. Private interpolation points for all vehicles in the group Subsequently, the sub-trusted mechanism from the polynomial Select above A set of public auxiliary points is formed by identifying public auxiliary points that do not coincide with the vehicle's private x-coordinate. The statement is disclosed separately. One public auxiliary point is insufficient to determine The effective vehicle needs to combine its local private interpolation points with its public auxiliary point set to obtain the polynomial required for recovery. Interpolation points.

[0051] 4-5, The trusted sub-agency calculates an authentication code for each vehicle within the group. And calculate the message authentication code for fog nodes. This generates a key material distribution message. Fog node verification timestamp and verification code After successful verification, the fog node extracts the broadcast material. And will synchronize messages Send to the roadside unit. The roadside unit determines the location based on the group identifier. Match the appropriate power coefficient to each vehicle group. The broadcast materials from multiple groups are superimposed in the power domain to form a non-orthogonal multiple access downlink signal: .

[0052] 4-6, the vehicle receives the superimposed signal. Then, according to the mapping function The non-orthogonal multiple access (NOMA) decoding layer corresponding to the group is determined, and the broadcast material of this group is extracted using serial interference cancellation technology. Vehicle inspection timestamp The freshness, and calculated based on its own long-term vouchers. .like If the authentication code exists in the received set, the vehicle calculates the longitudinal interpolated coordinates corresponding to this session based on the current timestamp. The vehicle will use a local private interpolation point. With public auxiliary point set Combined, the polynomial is recovered by Lagrange interpolation. and obtain its constant term. The group session key is calculated as follows: Therefore, vehicles that have been authenticated within the same location group can generate the same group session key, while entities that do not possess valid long-term credentials and private interpolation points cannot recover the group secret based on the set of public auxiliary points.

[0053] Step 5, Group Member Management and Key Update Phase: When a vehicle's location changes, causing a change in the corresponding location group, the group key update is triggered.

[0054] In this phase, the system manages vehicle joining and leaving operations based on vehicle location changes and group member status, and updates the corresponding location group status and group key materials. The specific process is as follows:

[0055] 5-1 Vehicle Joining: When a vehicle joins a new location group, it submits its identity and location information to the sub-trusted authority via roadside units and fog nodes. After completing vehicle identity authentication, the sub-trusted authority determines the vehicle's location based on its location group identifier. Add it to the third hash table The corresponding authentication group Subsequently, the sub-trusted organization updates the group member status, reselects the group secret, and constructs a new set of polynomials and common auxiliary points. The updated group key material is sent to group members via fog nodes and roadside units, enabling newly joined vehicles to generate the latest group session key.

[0056] 5-2, Vehicle Departure: Fog Nodes use the second hash table The system stores vehicle positions, directions of movement, and preset maximum speeds to estimate the earliest time each vehicle can leave the current group, and notifies roadside units to periodically check the real-time status of vehicles. Once it confirms a vehicle has left the current group, the fog node generates a member update set and sends it to the sub-trusted organization. The sub-trusted organization then uses a third hash table... Verify the identity of the group members whose vehicles are to be removed, and remove the vehicles confirmed to be leaving from the group. Delete and regenerate the group secret, group polynomial, and set of common auxiliary points. The updated key material is distributed to the remaining valid vehicles through fog nodes and roadside units, ensuring that the group session key used after changes in vehicle members is independent of the group session key before the update, thereby guaranteeing forward and backward confidentiality under dynamic vehicle joining and leaving conditions.

[0057] Based on the technical solution of this invention, the following case scenario illustrates the implementation process of this invention in practical applications. The specific application implementation scheme is as follows:

[0058] Theoretical analysis and simulation experiments were conducted to address the communication overhead and group key generation latency of this invention. Performance tests of basic cryptographic operations and related computations were performed on a computer equipped with an Intel(R) Core(TM) i7-14650HX@2.20GHz processor and 16GB of memory, using the Windows 11 operating system. To obtain a stable average execution time and reduce statistical bias, basic operations such as elliptic curve scalar multiplication, secure hash functions, pseudo-random functions, and the construction and evaluation of Lagrange polynomials were all repeated 10,000 times.

[0059] In the group key generation latency test, a vehicle-mounted ad hoc network scenario was constructed using the NS-3 network simulator, with 30 vehicles configured. The Gauss-Markov motion model was used to simulate vehicle movement, with vehicle speeds ranging from 10 m / s to 40 m / s. The underlying wireless communication adopted the IEEE 802.11p standard. The experiment compared this invention with existing group key negotiation schemes to evaluate the group key generation latency at different vehicle speeds.

[0060] Through theoretical analysis and simulation experiments, Figure 2 This paper presents a comparison of the communication overhead of the present invention with several other schemes, including a cloud-assisted authentication key negotiation scheme, a lightweight conditional privacy-preserving authentication key negotiation scheme based on multiple trusted institutions and fog computing, a blockchain-assisted conditional anonymity authentication and adaptive tree-structured group key negotiation scheme, and a physically secure privacy-preserving key negotiation scheme based on physically non-cloning functions, under different vehicle numbers. The experimental results show that the communication overhead of each scheme increases with the number of vehicles, while the present invention exhibits lower communication overhead across different vehicle scales. When the number of vehicles is 100, the present invention reduces communication overhead by 9.07% to 49.83% compared to the aforementioned comparative schemes. This is because the present invention uses aggregated requests and group broadcasts to transmit key negotiation materials, and enables vehicles to generate group session keys using local private interpolation points and public auxiliary points obtained from a single broadcast, reducing iterative interactions and redundant information transmissions among group members. Figure 3This paper presents a comparison of the group key generation latency of the present invention with that of cloud-assisted authentication key negotiation schemes, blockchain-assisted conditional anonymity authentication, and adaptive tree-structured group key negotiation schemes at different vehicle speeds. Experimental results show that the present invention exhibits lower communication latency during the group key generation stage, and its latency remains relatively stable as vehicle speed increases. At a vehicle speed of 40 m / s, the group key generation latency of the present invention is reduced by 90.8%, indicating that the method can adapt to the dynamic network environment of high-speed vehicle movement. The present invention utilizes a location mapping mechanism, enabling vehicles to determine their group locally based on their real-time location, reducing the additional signaling interactions required for group formation; it employs a polynomial-based group key negotiation mechanism, allowing eligible vehicles to generate group session keys using local private interpolation points and public auxiliary points, avoiding multi-round iterative coordination among group members; and it uses a non-orthogonal multiple access assisted transmission method to superimpose the key materials of multiple vehicle groups in the power domain and broadcast them uniformly, improving the transmission efficiency of key materials.

[0061] By comparing with existing technologies, it can be seen that the present invention can reduce the communication overhead and group key generation latency during the group key negotiation process while supporting dynamic vehicle joining and leaving. It is suitable for vehicle-mounted ad hoc network environments with high-speed vehicle movement, frequent changes in group members, and dense vehicle distribution.

[0062] The innovative aspects of this invention are as follows:

[0063] 1. A lightweight group key negotiation mechanism based on polynomials is constructed. This mechanism sets the group secret as a constant term of the polynomial and dynamically generates private interpolation points for each vehicle using a pseudo-random function, based on the vehicle's long-term credentials, interpolated x-coordinates, and the current timestamp. Group vehicles only need to use their locally stored private interpolation points and a public auxiliary point obtained from a single broadcast to recover the polynomial constant term and generate the group session key through Lagrange interpolation. This mechanism avoids iterative interactions between group members, reducing computational and communication overhead in the group key generation process.

[0064] 2. A location-mapping-based group formation and key update mechanism is proposed. This mechanism maps vehicle locations to corresponding group identifiers based on the distance between the vehicle and the serving roadside unit, enabling vehicles to determine their spatial group locally based on their real-time location without additional signaling handshakes. Simultaneously, the earliest time a vehicle can leave the current group is estimated based on its current location, direction of movement, and motion parameters, and this time is used as the trigger for group key updates. This reduces the communication burden caused by explicit group coordination and frequent updates, and supports timely key updates in cases of dynamic vehicle joining and leaving.

[0065] 3. A non-orthogonal multiple access (NMO)-assisted group key material distribution method is proposed. This method determines the corresponding NMO power layer and decoding order based on the location group identifier. Roadside units superimpose the key auxiliary materials from multiple vehicle groups in the power domain and broadcast them uniformly. Vehicles determine their decoding layer based on their own group identifier, extract the key material of their respective group through serial interference cancellation, and generate the group session key by combining local private interpolation points. This method improves the parallel distribution efficiency of multi-group key materials in dense vehicle environments. Experimental results show that even at vehicle speeds of 40 m / s, the proposed scheme still reduces the group key generation latency by 90.8%.

[0066] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A lightweight group key negotiation method for vehicular ad hoc networks, characterized in that, Includes the following steps; S1, Initialization Phase: Establish system security parameters and configure the mapping relationship between location groups and non-orthogonal multiple access power layers; S2, Position Mapping Stage: The vehicle calculates the corresponding location group identifier locally based on its own location information and assigns the vehicle to the corresponding location group; S3, Entity Registration Phase: Assign credential information to the vehicle for subsequent polynomial interpolation reconstruction; During the entity registration phase, the trusted institution generates a long-term fog node credential based on the system master private key and the fog node identity. The trusted institution generates a long-term vehicle certificate based on the system master private key and the vehicle's real identity, and generates the vehicle's lateral interpolation coordinates based on the vehicle's identity and the long-term vehicle certificate. The vehicle's longitudinal interpolation coordinates are dynamically generated during each key negotiation process based on the long-term vehicle certificate and the current session timestamp. The roadside unit registers with its respective fog node and obtains an area identifier. S4, Authentication and Group Key Negotiation Phase: When a vehicle sends a group join request, the network device authenticates the vehicle and constructs a polynomial with the group secret as a constant term and generates a common auxiliary point. The common auxiliary point is then distributed to the group vehicles using a non-orthogonal multiple access method. The vehicle reconstructs the polynomial by combining its local credential information and the received common auxiliary point and generates a group session key. S5, Group Member Management and Key Update Phase: When a vehicle's location changes, causing a change in its corresponding location group, a group key update is triggered.

2. The lightweight group key negotiation method for vehicular ad hoc networks according to claim 1, characterized in that, In the initialization phase, the trusted institution selects an elliptic curve and base points to form an additive cyclic group, selects the system master private key and calculates the system public key, selects a cryptographic hash function and a pseudo-random function, and sets the mapping relationship between the location group division interval and the location group identifier and the non-orthogonal multiple access power layer, and publishes the system public key and each function as public parameters.

3. The lightweight group key negotiation method for vehicular ad hoc networks according to claim 2, characterized in that, In the location mapping stage, the vehicle obtains its own geographic coordinates and the reference point coordinates of the service roadside unit, calculates the Euclidean distance between the vehicle's own geographic coordinates and the reference point coordinates, maps the Euclidean distance to the corresponding location group level according to the preset location group division interval, and generates the location group identifier in combination with the area identifier of the service roadside unit.

4. The lightweight group key negotiation method for vehicular ad hoc networks according to claim 1, characterized in that, During the authentication and group key negotiation phase, when a vehicle generates a group join request, it randomly selects a temporary private key and calculates a temporary public key. It uses the system public key to hide the vehicle's real identity as an anonymous pseudo-identity, calculates the location group identifier corresponding to the current location, and generates an authentication code based on the anonymous pseudo-identity and the location group identifier. The group join request includes at least the anonymous pseudo-identity, the temporary public key, the location group identifier, the current timestamp, and the authentication code.

5. The lightweight group key negotiation method for vehicular ad hoc networks according to claim 4, characterized in that, The network device includes fog nodes and sub-trusted institutions; after receiving a request, the fog node aggregates the vehicle requests according to the location group identifier and then sends them to the sub-trusted institution; The sub-trusted institution recovers the vehicle's true identity from the anonymous pseudo-identity based on the system master private key, obtains the vehicle's long-term certificate based on the recovered true identity, recalculates the authentication code, and compares it with the authentication code in the request to verify the validity of the vehicle's identity. Once verified, vehicles with the same location group identifier will be grouped into a certification group.

6. The lightweight group key negotiation method for vehicular ad hoc networks according to claim 5, characterized in that, During the authentication and group key negotiation phase, when the network device constructs the polynomial, the polynomial simultaneously passes through the point corresponding to the group secret and the private interpolation point of each vehicle in the group; the common auxiliary point is selected from multiple points on the polynomial that are different from the private interpolation points of each vehicle, and the number of the common auxiliary points is determined according to the number of group members.

7. The lightweight group key negotiation method for vehicular ad hoc networks according to claim 6, characterized in that, During the authentication and group key negotiation phase, the sub-trusted institution is also used to generate vehicle authentication codes for each vehicle and message authentication codes for fog nodes; after the fog node verifies the message authentication code, it extracts broadcast material and sends it to the roadside unit. The roadside unit, based on the non-orthogonal multiple access power layer corresponding to the location group identifier, superimposes the broadcast materials of multiple groups in the power domain and then broadcasts them uniformly.

8. The lightweight group key negotiation method for vehicular ad hoc networks according to claim 7, characterized in that, During the authentication and group key negotiation phase, the vehicle determines the corresponding decoding layer based on the location group identifier. After extracting the common auxiliary point of the group to which it belongs from the broadcast signal through serial interference elimination, the vehicle combines the locally stored private interpolation point with the common auxiliary point, reconstructs the polynomial through Lagrange interpolation, extracts the constant term of the polynomial, and generates the group session key based on the constant term.

9. The lightweight group key negotiation method for vehicular ad hoc networks according to claim 8, characterized in that, During the group member management and key update phase, the network device estimates the time when a vehicle leaves the current location group based on its current location, direction of movement, and speed, and uses the time when the vehicle leaves the current location group as the basis for triggering key updates. When a vehicle joins or leaves the group, the network device regenerates the polynomial, selects the constant term of the polynomial, and updates the common auxiliary point, so that the group session keys before and after the update are independent of each other.

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