Vehicle-mounted CAN bus safety communication method based on attribute grouping

Abstract

The invention discloses a vehicle-mounted CAN (Controller Area Network) bus safety communication method based on attribute grouping. The method comprises the following steps: firstly, selecting a master key, a public key, a hash function and related parameters; the electronic control unit ECU registers with a gateway electronic control unit GECU; in the key generation stage, the GECU groups the ECUs and distributes key generation parameters to the ECUs in the groups, and the ECUs in the groups calculate group keys according to the key generation parameters; the ECUs in the group communicate with each other by using the group key; and in the key updating and ECU re-joining stage, the ECU can update the key without interaction. Through constructing a group key generation mechanism based on an access structure tree, group communication based on ECU function attributes is realized. And a key self-authentication mechanism is introduced, so that the interaction turns between the ECUs are reduced, and the communication load is reduced. The method is suitable for a vehicle-mounted network dynamic scene, and effectively resists attacks such as counterfeiting and replaying.

Description

Technical Field

[0001] This invention relates to the field of vehicle networking security technology, specifically to a secure communication method for in-vehicle CAN bus based on attribute grouping. Background Technology

[0002] With the rapid development of vehicle-to-everything (V2X) technology, the security of in-vehicle networks has become a focus of attention for both academia and industry. Controller Area Network (CAN bus) technology has become very popular in in-vehicle networks (IVNs) due to its widespread deployment. Research shows that CAN bus, as the core protocol for communication between electronic control units (ECUs), faces security threats such as data eavesdropping, message forgery, and replay attacks due to its open design and lack of encryption mechanisms. The traditional CAN protocol lacks authentication and encryption mechanisms, allowing attackers to tamper with critical control commands through physical interfaces or remote penetration, seriously threatening driving safety.

[0003] Despite some progress in the field of automotive CAN bus security, the following key challenges remain in practical deployment:

[0004] (1) Existing solutions rely on multiple rounds of interactive verification of key legitimacy, which can enhance security but also increase communication load. How to achieve non-interactive key self-authentication in unicast / broadcast channels while resisting man-in-the-middle attacks is a key challenge in balancing efficiency and security.

[0005] (2) Onboard ECU computing resources: Onboard ECUs have limited computing power, and traditional key updates require renegotiation or rely on central node broadcasting, which is difficult to meet real-time requirements. At the same time, ensuring forward and backward security has become a core requirement for maintaining long-term security.

[0006] Scholars have proposed numerous solutions to combat security threats, but these solutions still exhibit certain shortcomings. Some pairwise key-based secure communication mechanisms achieve point-to-point secure communication by establishing independent session keys for each pair of ECUs, but the pairwise key format significantly increases the storage load on the ECUs. Some global key-based secure communication mechanisms establish a shared session key for all ECUs. While the global key approach simplifies key management, a key leak can compromise the security of the entire vehicle network. Other solutions based on static grouping mechanisms divide ECU functions into fixed communication groups, typically employing a centralized key distribution strategy. One scholar has proposed a scheme using implicit certificates to establish authentication group keys between ECUs in the vehicle network. Further research has proposed a flexible and adaptive solution using trusted communication groups to support confidential communication between vehicle components. Although static grouping mechanisms are simple to implement, they have shortcomings in dynamic adaptability, key update efficiency, and access control.

[0007] For example, Chinese patent application CN106790053B discloses a method for secure communication of ECUs in a CAN bus. Although this technical solution optimizes key distribution, it relies on multiple rounds of interaction, resulting in a large communication load and low key update efficiency. Chinese patent application CN110086622A discloses a network security architecture design for in-vehicle networks in an intelligent connected environment. This technical solution uses complex cryptography (such as zero-knowledge proofs), which has a large computational overhead and is difficult to meet the real-time requirements of in-vehicle systems. Summary of the Invention

[0008] Purpose of the invention: The purpose of this invention is to address the shortcomings of existing technologies and provide a secure communication method for vehicle CAN bus based on attribute grouping. This invention reduces the number of interaction rounds and lowers the communication load through attribute grouping and key self-authentication mechanism. At the same time, the parallel key update based on the counter improves dynamic adaptability and effectively overcomes the above-mentioned defects.

[0009] Technical solution: The present invention provides a method for secure communication of an in-vehicle CAN bus based on attribute grouping, comprising the following steps:

[0010] Step (1): System initialization. The gateway electronic control unit (GECU) generates global parameters, including the bilinear mapping group, master key MK, and public key. and broadcasts the system's common parameters (params); vehicle electronic control unit Obtain the private key and public key ;

[0011] Step (2), the registration stage, the vehicle electronic control unit (ECU) registers attribute information with the GECU, and the GECU verifies the identity of the ECU and distributes authentication parameters;

[0012] Step (3), Key Generation Stage: The gateway ECU dynamically groups ECUs based on the access structure tree, generates group key parameters, and distributes them. Each ECU verifies the group key through a key self-authentication mechanism. The specific method is as follows:

[0013] Step (3-1): GECU sets up access structure Select random number Calculate self-authentication parameters And calculate the group key generation parameters. Then generate a timestamp. Message verification code and key self-authentication message ;

[0014] Finally, GECU sends a message to all ECUs in the group. ;

[0015] ;

[0016] All ECUs within the same GECU group are grouped as follows: And the set of attributes that satisfy the attribute strategy is ; The number of attributes. , These are the ECUs within the group: Key generation parameters;

[0017] Step (3-2), the i-th Received Next, we first verify the timestamp inequality. Whether it is true and its verification The legitimacy;

[0018] If both verifications are successful, the attribute set is obtained based on the access structure. ;

[0019] Then Generate group key ,calculate And through equations To verify the correctness of the group key;

[0020] Step (4), ECU communication stage: ECUs within the group use the group key. Encrypted communication messages Obtain the ciphertext C and add a message authentication code to ensure its integrity;

[0021] Step (5), password update phase, the ECUs in the group use the master key and group counter Obtain the key update parameters, i.e. Then, the ECUs within the group perform group key updates in parallel, i.e. Finally, the group counter is obtained. ;

[0022] This indicates that the update has reached the [number]th [number]. Second-rate;

[0023] Step (6), ECU re-entry stage, new After verifying identity via GECU, the current group key and counter are obtained, and dynamic joining is completed.

[0024] Furthermore, the detailed process of the initialization phase in step (1) is as follows:

[0025] Step (1-1): Input safety parameters into GECU Generate an additive group and a multiplication group Assuming , The two generators, and Define a bilinear mapping with the same order q of large prime numbers. ;

[0026] Step (1-2): GECU selects a random number Calculate the master key MK= and public key = ,in = , Select random number As its private key = And generate a public key = ;

[0027] Steps (1-3): GECU selects hash function H: → and a key hash function (.) and publish public parameters: params { , ,e, H, h, q, , }

[0028] Furthermore, the specific process of the registration stage in step (2) is as follows:

[0029] Step (2-1): The total attribute set of the ECU in the CAN bus is each Attribute set , Calculate the hash value of all its properties: Select random number And calculate authentication parameters Generate authentication information and timestamp Next Bundle { }Sent to GECU, This is the number of attributes in the CAN bus; yes The number of attributes;

[0030] Step (2-2), GECU receives Verify the validity of the timestamp; if the verification is successful, proceed according to the verification criteria. The attribute set, calculate = Through equation To verify After verifying the legal identity, GECU selects a random number. Generate authentication information Authentication parameters and current timestamp GECU { }Send to ;

[0031] By verifying the inequality The validity of the timestamp is determined by its validity; if valid, the verification is successful. It is a time threshold parameter. GECU received the message Time;

[0032] Steps (2-3) Received Verify the validity of the timestamp; if the verification passes, then apply the equation. To verify the identity of the GECU; after successful identity verification, a random number seed is generated. Current timestamp Message verification code ( ), and put { }Sent to GECU;

[0033] This section verifies the inequality. The validity of the timestamp is verified by checking if it is true or false. If it is true, the verification passes. yes Received message The time.

[0034] Furthermore, the specific process of step (4) ECU communication stage is as follows:

[0035] Step (4-1), the sender's vehicle electronic control unit First, use the group key. Encrypted plaintext Obtain the ciphertext Then generate time And calculate the message verification code , and then Send it out;

[0036] Step (4-2), the recipient's vehicle electronic control unit Received message Afterwards, verify the freshness of the message and If all verifications pass, the legitimacy of the document is confirmed. Decrypt Obtain plaintext ;

[0037] Using inequalities This is used to verify the freshness of the message. If the inequality holds true, then the message is proven to be fresh.

[0038] Furthermore, the specific process of step (6), the ECU re-entry stage, is as follows:

[0039] Step (6-1), Vehicle electronic control unit to be added Select a new random number Calculate authentication parameters ,in ; Generate authentication information and timestamp ,after Bundle Send to GECU;

[0040] Step (6-2), GECU receives from After receiving the message, GECU verifies the validity of the timestamp based on... judge Does the attribute set belong to the group's attribute set, and calculate... ,verify Is it equal to If equal, then calculate. and And generate group key generation parameters Encrypt the current group counter. get Generate timestamp and message verification code , and then Send it out;

[0041] By verifying the inequality The validity of a timestamp is verified by checking whether it is valid. To receive Time;

[0042] Step (6-3) After receiving the message, verify the timestamp. and Is it equal to ; Generate an initial group key based on the access structure tree. Decryption get And generate the current key update parameters. Thus, a new group key is obtained. ;

[0043] Then verify Verify the validity of the data and generate a timestamp. and message verification code After that Send to GECU;

[0044] Step (6-4): After receiving the message, GECU verifies the timestamp. Once the timestamp verification is successful, GECU performs the verification. The validity of the verification is verified. Successful joining, the timestamp verification formula is as follows: , To receive messages The entire rejoining process incorporates a group key synchronization mechanism and can automatically obtain the current group key without interacting with other ECUs within the group, ensuring the security of dynamic joining.

[0045] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0046] (1) This invention constructs a dynamic mapping model between ECU attributes and communication permissions based on the access structure tree, realizing fine-grained division of the in-vehicle network communication domain. Through functional attribute grouping, even if a single ECU is compromised, the attacker cannot decrypt data in other groups that do not conform to its attributes, thereby reducing security risks.

[0047] (2) The present invention innovatively uses a key self-authentication algorithm, which allows ECUs within a group to independently calculate and verify the group key through pre-distributed parameters, eliminating the need for multiple rounds of interaction.

[0048] (3) The present invention has lower computation and communication overhead, and meets the safety requirements and real-time requirements of vehicle communication. Attached Figure Description

[0049] Figure 1 This is a system model diagram of the present invention;

[0050] Figure 2 This is a flowchart of the registration phase in the embodiment;

[0051] Figure 3 This is a flowchart of the key generation stage in the embodiment;

[0052] Figure 4 This is a comparison chart of communication overhead in the embodiments;

[0053] Figure 5 This is a comparison chart of bus load in the embodiments. Detailed Implementation

[0054] The technical solution of the present invention will be described in detail below, but the scope of protection of the present invention is not limited to the embodiments described.

[0055] The Controller Area Network (CAN) bus in an In-Vehicle Network (IVN) is vulnerable to security threats such as forgery and replay attacks due to the lack of authentication and encryption mechanisms. Existing group key negotiation schemes mostly use static grouping mechanisms, which are difficult to adapt to the dynamic communication scenarios of in-vehicle systems. In addition, the traditional key update process usually requires multiple rounds of interaction, increasing the communication load.

[0056] To address the aforementioned challenges, this invention proposes a secure communication method for in-vehicle CAN bus based on attribute grouping. It constructs a group key negotiation mechanism through an access structure tree to achieve group communication based on ECU functional attributes; simultaneously, it introduces a key self-authentication mechanism, enabling ECUs within the group to verify key legitimacy without interaction. Figures 2 to 3 As shown, it includes the following steps:

[0057] Step (1): System initialization. The gateway electronic control unit (GECU) generates global parameters, including the bilinear mapping group, master key MK, and public key. and broadcasts the system's common parameters (params); vehicle electronic control unit Obtain the private key and public key ;

[0058] Step (2), the registration stage, the vehicle electronic control unit (ECU) registers attribute information with the GECU, and the GECU verifies the identity of the ECU and distributes authentication parameters;

[0059] Step (3), Key Generation Stage (Key Self-Authentication Mechanism Based on Attribute Grouping, Reducing Interaction Rounds): The gateway ECU dynamically groups ECUs based on the access structure tree, generates group key parameters, and distributes them. Each ECU verifies the group key through the key self-authentication mechanism. The specific method is as follows:

[0060] Step (3-1): GECU sets up access structure Select random number Calculate self-authentication parameters And calculate the group key generation parameters. Then generate a timestamp. Message verification code and key self-authentication message ;

[0061] Finally, GECU sends a message to all ECUs in the group. ;

[0062] ;

[0063] All ECUs within the same GECU group are grouped as follows: And the set of attributes that satisfy the attribute strategy is ; The number of attributes. , These are the ECUs within the group: Key generation parameters;

[0064] Step (3-2), the i-th Received Next, we first verify the timestamp inequality. Whether it is true and its verification The legitimacy;

[0065] If both verifications are successful, the attribute set is obtained based on the access structure. ;

[0066] Then Generate group key ,calculate And through equations To verify the correctness of the group key;

[0067] Step (4), ECU communication stage: ECUs within the group use the group key. Encrypted communication messages Obtain the ciphertext C and add a message authentication code to ensure its integrity;

[0068] Step (5), password update stage (implements parallel key update, improving dynamic adaptability), the ECUs within the group use the master key and group counter Obtain the key update parameters, i.e. Then, the ECUs within the group perform group key updates in parallel, i.e. Finally, the group counter is obtained. ;

[0069] This indicates that the update has reached the [number]th [number]. Second-rate;

[0070] Step (6), ECU re-entry stage, new After verifying identity via GECU, the current group key and counter are obtained, and dynamic joining is completed.

[0071] The above technical solution aims to achieve real-time data transmission and collaborative operation between multiple ECUs, such as... Figure 1 As shown, multiple ECUs are connected via a shared two-wire bus, forming a decentralized network that allows each control unit to independently send and receive information. This structure consists of a GECU and ECUs. The GECU is the central component of the vehicle's electronic and electrical architecture, responsible for cross-network protocol conversion and data routing, supporting real-time data exchange, ensuring functional coordination and resource optimization scheduling between onboard subsystems, and guaranteeing the reliability of the vehicle's functions and network. The ECUs are responsible for managing different vehicle functions, such as engine control, transmission control, body control, ABS system, and infotainment system. Each ECU exchanges data with other ECUs via the CAN bus, sharing information and executing commands in real time.

[0072] The detailed process of step (1) initialization in this embodiment is as follows:

[0073] Step (1-1): Input safety parameters into GECU Generate an additive group and a multiplication group Assuming , The two generators, and Define a bilinear mapping with the same order q of large prime numbers. ;

[0074] Step (1-2): GECU selects a random number Calculate the master key MK= and public key = ,in = , Select random number As its private key = And generate a public key = ;

[0075] Steps (1-3): GECU selects hash function H: → and a key hash function (.) and publish public parameters: params { , ,e, H, h, q, , }

[0076] The specific process of step (2) registration stage in this embodiment is as follows:

[0077] Step (2-1): The total attribute set of the ECU in the CAN bus is each Attribute set , Calculate the hash value of all its properties: Select random number And calculate authentication parameters Generate authentication information and timestamp Next Bundle { }Sent to GECU, This is the number of attributes in the CAN bus; yes The number of attributes;

[0078] Step (2-2), GECU receives Verify the validity of the timestamp; if the verification is successful, proceed according to the verification criteria. The attribute set, calculate = Through equation To verify After verifying the legal identity, GECU selects a random number. Generate authentication information Authentication parameters and current timestamp GECU { }Send to ;

[0079] By verifying the inequality The validity of the timestamp is determined by its validity; if valid, the verification is successful. It is a time threshold parameter. GECU received the message Time;

[0080] Steps (2-3) Received Verify the validity of the timestamp; if the verification passes, then apply the equation. To verify the identity of the GECU; after successful identity verification, a random number seed is generated. Current timestamp Message verification code ( ), and put { }Sent to GECU;

[0081] This section verifies the inequality. The validity of the timestamp is verified by checking if it is true or false. If it is true, the verification passes. yes Received message The time.

[0082] The specific process of step (4) of the ECU communication stage in this embodiment is as follows:

[0083] Step (4-1), the sender's vehicle electronic control unit First, use the group key. Encrypted plaintext Obtain the ciphertext Then generate time And calculate the message verification code , and then Send it out;

[0084] Step (4-2), the recipient's vehicle electronic control unit Received message Afterwards, verify the freshness of the message and If all verifications pass, the legitimacy of the document is confirmed. Decrypt Obtain plaintext ;

[0085] Using inequalities This is used to verify the freshness of the message. If the inequality holds true, then the message is proven to be fresh.

[0086] The specific process of step (6) ECU re-entry stage in this embodiment is as follows:

[0087] Step (6-1), Vehicle electronic control unit to be added Select a new random number Calculate authentication parameters ,in ; Generate authentication information and timestamp ,after Bundle Send to GECU;

[0088] Step (6-2), GECU receives from After receiving the message, GECU verifies the validity of the timestamp based on... judge Does the attribute set belong to the group's attribute set, and calculate... ,verify Is it equal to If equal, then calculate. and And generate group key generation parameters Encrypt the current group counter. get Generate timestamp and message verification code , and then Send it out;

[0089] By verifying the inequality The validity of a timestamp is verified by checking whether it is valid. To receive Time;

[0090] Step (6-3) After receiving the message, verify the timestamp. and Is it equal to ; Generate an initial group key based on the access structure tree. Decryption get And generate the current key update parameters. Thus, a new group key is obtained. ;

[0091] Then verify Verify the validity of the data and generate a timestamp. and message verification code After that Send to GECU;

[0092] Step (6-4): After receiving the message, GECU verifies the timestamp. Once the timestamp verification is successful, GECU performs the verification. The validity of the verification is verified. Successful joining, the timestamp verification formula is as follows: , To receive messages The entire rejoining process incorporates a group key synchronization mechanism and can automatically obtain the current group key without interacting with other ECUs within the group, ensuring the security of dynamic joining.

[0093] This embodiment uses a Raspberry Pi 5 to simulate a GECU with strong computing power, and an STM32H743VIT6 development board to simulate an ECU with weak computing power. In terms of CPU frequency, the Raspberry Pi is set to 2.4GHz and the STM32H743VIT6 is set to 400MHz. This embodiment achieves CAN bus communication test at a baud rate of 500 kb / s, which meets the strict reliability requirements of the automotive environment.

[0094] In this embodiment, the computation time of the cryptographic algorithm was measured 2000 times on a hardware platform using the widely accepted Miracl cryptography library. The results are shown in Table 1.

[0095] Table 1

[0096] cryptographic operations STM32H743VIT6 (milliseconds) Raspberry Pi 5 (milliseconds) AES-CBC-256 (encryption / decryption) 0.233 / 0.228 0.009 / 0.008 RSA-512 (encryption / decryption) 2.341 / 38.051 0.057 / 0.934 RSA-512 signature generation / verification 37.618 / 2.323 0.941 / 0.059 Encoding / Decoding 0.447 / 0.142 0.012 / 0.004 SHA256 0.034 0.002 HMAC (SHA256) 0.136 0.005 Key derivation function 0.428 0.017 Ate pairing 79.328 3.136 Scalar multiplication 18.928 0.414 Dot addition 0.157 0.003 Reverse Model 6.874 0.006 multiplication 0.004 0.001 Exponentiation 2.091 0.051

[0097] A comparison of the computational overhead of the technical solution of this invention in practical application with the communication overhead of other solutions yields the following results: Figure 4 As shown, the present invention has significant advantages. A comparison of the baud rates of the technical solution of the present invention under different environments yields the following results: Figure 5 As shown, the technical solution of the present invention is feasible for practical deployment in modern high-speed vehicle networks.

[0098] In summary, this invention achieves group communication based on ECU functional attributes by constructing a group key generation mechanism based on an access structure tree; it also introduces a key self-authentication mechanism to reduce the number of interaction rounds between ECUs and lower the communication load. This invention is applicable to dynamic scenarios in vehicle networks and effectively resists attacks such as spoofing and replay attacks.

Claims

1. A method for secure communication on an in-vehicle CAN bus based on attribute grouping, characterized in that, Includes the following steps: Step (1): System initialization. The gateway electronic control unit (GECU) generates global parameters, including the bilinear mapping group, master key MK, and public key. and broadcasts the system's common parameters (params); vehicle electronic control unit Obtain the private key and public key ; Step (2), the registration stage, the vehicle electronic control unit (ECU) registers attribute information with the GECU, and the GECU verifies the identity of the ECU and distributes authentication parameters; Step (3), Key Generation Stage: The gateway ECU dynamically groups ECUs based on the access structure tree, generates group key parameters, and distributes them. Each ECU verifies the group key through a key self-authentication mechanism. The specific method is as follows: Step (3-1): GECU sets up access structure Select random number Calculate self-authentication parameters And calculate the group key generation parameters. Then generate a timestamp. Message verification code and key self-authentication message ; Finally, GECU sends a message to all ECUs in the group. ; ； All ECUs within the same GECU group are grouped as follows: And the set of attributes that satisfy the attribute strategy is ; The number of attributes. , These are the ECUs within the group: Key generation parameters; Step (3-2), the i-th Received Next, we first verify the timestamp inequality. Whether it is true and its verification The legitimacy; If both verifications are successful, the attribute set is obtained based on the access structure. ; Then Generate group key ,calculate And through equations To verify the correctness of the group key; Step (4), ECU communication stage: ECUs within the group use the group key. Encrypted communication messages Obtain the ciphertext C and add a message authentication code to ensure its integrity; Step (5), password update phase, the ECUs in the group use the master key and group counter Obtain the key update parameters, i.e. Then, the ECUs within the group perform group key updates in parallel, i.e. Finally, the group counter is obtained. ; This indicates that the update has reached the [number]th [number]. Second-rate; Step (6), ECU re-entry stage, new After verifying identity via GECU, the current group key and counter are obtained, and dynamic joining is completed.

2. The vehicle CAN bus secure communication method based on attribute grouping according to claim 1, characterized in that: The detailed process of the initialization phase in step (1) is as follows: Step (1-1): Input safety parameters into GECU Generate an additive group and a multiplication group Assuming , The two generators, and Define a bilinear mapping with the same order q of large prime numbers. ; Step (1-2): GECU selects a random number Calculate the master key MK= and public key = ,in = , Select random number As its private key = And generate a public key = ; Steps (1-3): GECU selects hash function H: → and a key hash function (.) and publish public parameters: params { , ,e, H, h, q, , } 3. The vehicle CAN bus secure communication method based on attribute grouping according to claim 1, characterized in that: The specific process of the registration stage in step (2) is as follows: Step (2-1): The total attribute set of the ECU in the CAN bus is each Attribute set , Calculate the hash value of all its properties: Select random number And calculate authentication parameters Generate authentication information and timestamp Next Bundle { }Sent to GECU, This is the number of attributes in the CAN bus; yes The number of attributes; Step (2-2), GECU receives Verify the validity of the timestamp; if the verification is successful, proceed according to the verification criteria. The attribute set, calculate = Through equation To verify After verifying the legal identity, GECU selects a random number. Generate authentication information Authentication parameters and current timestamp GECU { }Send to ; By verifying the inequality The validity of the timestamp is determined by its validity; if valid, the verification is successful. It is a time threshold parameter. GECU received the message Time; Steps (2-3) Received Verify the validity of the timestamp; if the verification passes, then apply the equation. To verify the identity of the GECU; after successful identity verification, a random number seed is generated. Current timestamp Message verification code ( ), and put { }Sent to GECU; This section verifies the inequality. The validity of the timestamp is verified by checking if it is true or false. If it is true, the verification passes. yes Received message The time.

4. The vehicle CAN bus secure communication method based on attribute grouping according to claim 1, characterized in that: The specific process of step (4) ECU communication stage is as follows: Step (4-1), the sender's vehicle electronic control unit First, use the group key. Encrypted plaintext Obtain the ciphertext Then generate time And calculate the message verification code , and then Send it out; Step (4-2), the recipient's vehicle electronic control unit Received message Afterwards, verify the freshness of the message and If all verifications pass, the legitimacy of the document is confirmed. Decrypt Obtain plaintext ; Using inequalities This is used to verify the freshness of the message. If the inequality holds true, then the message is proven to be fresh.

5. The vehicle CAN bus secure communication method based on attribute grouping according to claim 1, characterized in that: The specific process of step (6) ECU re-entry stage is as follows: Step (6-1), Vehicle electronic control unit to be added Select a new random number Calculate authentication parameters ,in ; Generate authentication information and timestamp ,after Bundle Send to GECU; Step (6-2), GECU receives from After receiving the message, GECU verifies the validity of the timestamp based on... judge Does the attribute set belong to the group's attribute set, and calculate... ,verify Is it equal to If equal, then calculate. and And generate group key generation parameters Encrypt the current group counter. get Generate timestamp and message verification code , and then Send it out; By verifying the inequality The validity of a timestamp is verified by checking whether it is valid. To receive Time; Step (6-3) After receiving the message, verify the timestamp. and Is it equal to ; Generate an initial group key based on the access structure tree. Decryption get And generate the current key update parameters. Thus, a new group key is obtained. ; Then verify Verify the validity of the data and generate a timestamp. and message verification code After that Send to GECU; Step (6-4): After receiving the message, GECU verifies the timestamp. Once the timestamp verification is successful, GECU performs the verification. The validity of the verification is verified. Successful joining, the timestamp verification formula is as follows: , To receive messages The time.

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