Secure communication system and method for vehicle-mounted ad hoc networks based on NTRU lattice cryptography

Abstract

The present invention belongs to the technical field of digital information transmission and relates to a secure communication system and method for an on-board ad hoc network based on an NTRU lattice cryptographic system. The system comprises a message signing module, a message encryption module, a message decryption module, an identity authentication module, and a key exchange module. The message signing module uses a private key and a random polynomial dynamically generated by a pseudo-random number generator based on the NTRU lattice cryptographic system to perform signatures. The message encryption module encrypts a message to be sent by randomly selecting a temporary polynomial and combining it with a public key of a receiver. The message decryption module decrypts received ciphertext using a private key and an inverse element of its modulus p. The identity authentication module is used for performing identity authentication. The key exchange module implements secure key exchange between communication nodes in the on-board ad hoc network through an improved Blom key distribution protocol. The system improves the security and communication efficiency of the on-board network.

Description

Technical Field

[0001] The present invention belongs to the technical field of digital information transmission, and relates to a vehicle-mounted ad hoc network security communication system and method based on the NTRU lattice cryptographic system. Background Art

[0002] With the development of vehicular ad hoc networks (VANETs), inter-vehicle communication plays a key role in intelligent transportation and autonomous driving. However, VANETs face security threats such as data tampering and identity forgery, which impact system stability and traffic safety. To ensure the authenticity and integrity of communication data, message signing and authentication technologies have become key protection measures. Currently, vehicular communication primarily relies on traditional public key infrastructure (PKI) and signature algorithms (such as RSA and DSA). However, these algorithms are computationally complex and slow, making them difficult to adapt to the in-vehicle environment.

[0003] Chinese patent CN 117614624 A discloses a "Secure Trust Method for Identity Authentication Based on Key Negotiation in the Internet of Vehicles." This method first generates a pseudo-random number, then uses elliptic curve cryptography to generate a signature, employs the Blom key distribution protocol to generate a session key, and finally authenticates the communicating entity through a three-way, two-way authentication method. This method offers advantages over the commonly used RSA signature algorithm, which is based on the large prime number factorization problem, such as shorter keys and faster computation speed. However, the industry faces challenges in further improving key generation and encryption and decryption speeds while maintaining security levels.

[0004] Furthermore, the development of quantum computing has put traditional encryption algorithms at risk of being cracked, necessitating the need for more efficient and quantum-resistant solutions. Lattice cryptography has garnered widespread attention due to its resistance to quantum attacks, particularly signature algorithms based on NTRU, which offer both efficiency and security, making them suitable for VANETs. However, existing NTRU-based schemes still suffer from computational efficiency and implementation complexity, making them difficult to meet the real-time and low-cost requirements of VANETs. Therefore, a signature scheme that combines both security and efficiency is urgently needed to enhance the communication security and performance of VANETs. Summary of the Invention

[0005] In order to solve the problems of insufficient message transmission security, low computational efficiency, and difficult privacy protection in existing vehicular ad hoc networks, the present invention provides a vehicular ad hoc network security communication system based on the NTRU lattice cryptographic system, aiming to improve the security and efficiency of message transmission in vehicular ad hoc networks. By introducing the NTRU lattice cryptographic system, an efficient message signing and verification scheme is designed to ensure the integrity of messages and the effectiveness of identity authentication, effectively deal with security threats such as identity forgery, data tampering and replay attacks in vehicular ad hoc networks, and improve the security and communication efficiency of vehicular networks.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A secure communication system for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system includes a key generation module, a message signature module, a message encryption module, a message decryption module, a message verification module, an identity authentication module, a key exchange module, and a certificate management module; the improvement made is that it also includes a pseudo-random number generator;

[0008] The key generation module uses the NTRU lattice cryptosystem to generate a public key and a private key pair for each communication node in the vehicular ad hoc network, and publishes and manages the public key through the certificate management module;

[0009] The message signature module uses the private key and the random polynomial dynamically generated by the pseudo-random number generator to sign based on the NTRU lattice cryptographic system to generate the signature polynomial , ;in, is the sender’s private key polynomial, is the message hash value, A temporary random polynomial dynamically generated by the sender, is the current timestamp, is the modulus in the NTRU encryption process, is the polynomial convolution operator symbol, Is the exclusive OR operator symbol, is the symbol for modulo operation;

[0010] The message encryption module obtains the public key of the recipient through the certificate management module and encodes the message to be sent into a number less than And the absolute value of the coefficient is at most The message polynomial m is obtained by randomly selecting a temporary polynomial The message to be sent is encrypted with the receiver's public key to form the final ciphertext. ; ;in A temporarily generated random polynomial used for randomness in encryption operations. 、 Both are moduli in the NTRU encryption process. The current timestamp is used to bind the uniqueness of each encryption to prevent replay attacks. The public key polynomial of the recipient, obtained through the certificate management module, where H represents the hash operation;

[0011] The message decryption module, the receiver uses the private key and its inverse element modulo p The received ciphertext Decrypt, restore the plaintext, and the decrypted message polynomial ;in, , , a and b are intermediate calculated values, A temporary random polynomial dynamically generated for the receiver to enhance the randomness during the decryption process. is the current timestamp, combined with a temporary random polynomial Increase the uniqueness of each decryption to prevent replay attacks;

[0012] The message verification module, the receiver obtains the sender's public key through the certificate management module, and separates the signature polynomial from the received data ; Use the sender's public key polynomial to sign the polynomial Perform polynomial convolution and modular operations to recover the hash value and random polynomial; then perform the decrypted message polynomial Perform a hash operation and compare it with the recovered hash value; at the same time, verify the validity of the random polynomial; if the hash values ​​are consistent and the random polynomial is valid, the message is considered complete and the source is legitimate, and the subsequent processing flow is entered;

[0013] The identity authentication module completes the identity authentication of the vehicle network node through a challenge-response protocol based on the NTRU lattice password to ensure the legitimacy of the identities of both communicating parties;

[0014] The key exchange module implements secure key exchange between communication nodes in a vehicle-mounted ad hoc network through an improved Blom key distribution protocol.

[0015] As a preferred embodiment of the present invention, in the key generation module, the process of generating the public key and the private key is: selecting two random polynomial and Generate a key; use the extended Euclidean algorithm to Seek the reverse, if you can't find the way out The inverse element of , then reselect the polynomial , and They are In the model and model The multiplicative inverse of ;calculate , is a temporary random polynomial, and the public key is , the private key is , the coefficients of the random polynomial of the private key are randomly selected from {-1, 0, 1} by a pseudo-random number generator;

[0016] in, and is the modulus in the NTRU encryption process, The value of is 2 to 5, which ensures the irreversibility of polynomial operations. The value of is 2048≤ q≤ 4096, and q>6p must be satisfied. represents the public key polynomial, is the symbol of the modulo operation; N is the degree of the polynomial, and its value is 509≤N ≤1277.

[0017] As a preferred embodiment of the present invention, the steps of identity authentication performed by the identity authentication module are:

[0018] The verifier generates a random challenge polynomial , the polynomial degree is , the coefficients are randomly selected from the sparse polynomial set L of all numbers less than N and the absolute value of the coefficients does not exceed the set threshold; at the same time, the current timestamp T is recorded to generate the challenge data , and synchronously transmit the timestamp T through the protocol and send it to the proving party;

[0019] The prover verifies the validity of the current timestamp T. If it times out, the challenge is discarded. If it is valid, the prover uses the private key f and the random polynomial dynamically generated by the pseudo-random number generator to Challenge polynomial Sign, the signature polynomial Return to the verifier;

[0020] The verifier obtains the public key of the prover from the certificate management module and uses the public key to sign the polynomial Perform the inverse operation to restore the hash value and random polynomial; then perform a hash operation on the random challenge polynomial, compare it with the restored hash value, and verify the random polynomial at the same time If the hash matches and the timestamp is valid, the authentication is successful.

[0021] As a preferred embodiment of the present invention, the key exchange module performs key exchange mainly by exchanging the public column vectors of both parties. and Implemented; when the node and When communication is required, nodes Calculate the shared secret key : ;

[0022] node Calculate the shared secret key : ;

[0023] Among them, the node The private key vector , S is a D×D symmetric matrix whose elements are randomly selected from the finite field GF(q) and satisfy the reversibility property, and q is a large prime number; is a D×D public matrix No. Column polynomial vector, public matrix The elements of are random polynomials with degree < N and coefficients in the range [-(p-1) / 2, (p-1) / 2]; For nodes The private key vector.

[0024] As a preferred embodiment of the present invention, the certificate management module is responsible for the full life cycle management of public key certificates in the VANET, including certificate generation, distribution, revocation and update.

[0025] As a preferred embodiment of the present invention, the pseudo-random number generator is a pseudo-random number generator that complies with the ANSI X9.17 standard, and the pseudo-random number generator uses a triple DES encryption method to ensure the unpredictability of the random polynomial or random number.

[0026] As a preferred embodiment of the present invention, the temporary random polynomial , a temporary random polynomial dynamically generated by the sender , a temporarily generated random polynomial , a temporary random polynomial dynamically generated by the receiver All belong to L, where L is a set of sparse polynomials whose degree is less than N and whose coefficient absolute value does not exceed the set threshold, i.e., a set of random polynomials; random polynomials The coefficients of are selected from {-1, 0, 1}.

[0027] The present invention also provides a secure communication method for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system, the method comprising the following steps:

[0028] Step 1. Generate a public and private key pair for each communication node in the VANET using the NTRU lattice cryptography system. The communication node publishes its public key to the secure communication system described above and manages it through the certificate management module, which is responsible for the distribution, revocation, and renewal of public key certificates to ensure the validity of the public key.

[0029] Step 2. When the sender needs to send a message, it uses the private key to sign the message to be sent. The random polynomial dynamically generated by the pseudo-random number generator is added to the signing process. The NTRU signature algorithm is used to complete it so that each signature is unique. The generated signature data is sent to the message encryption module together with the original message. The message encryption module requests the recipient's public key certificate from the certificate management module, encodes the message to be sent into a message polynomial that conforms to the NTRU lattice cryptosystem, and randomly selects a temporary polynomial. The public key of the recipient is used to encrypt the message to be sent, and then the signed and encrypted message is transmitted to the recipient via the VANET.

[0030] Step 3. After receiving the message, the recipient first uses the private key and its inverse element modulo p The received ciphertext Decrypt and restore the plaintext; then request the sender's public key certificate from the certificate management module, first restore the hash value and random polynomial through the signature verification operation, and then perform the decrypted message polynomial Perform hashing and compare it with the hash value obtained by the signature verification operation; at the same time, verify the validity of the random polynomial; if the hash values ​​are consistent and the random polynomial is valid, it proves that the message has not been tampered with during transmission and is indeed sent by the legitimate sender, and then proceed to step 4 to continue processing the message; if verification fails, the message is rejected;

[0031] Step 4. Identity authentication;

[0032] The receiver and sender complete identity authentication through a challenge-response method based on the NTRU lattice cipher to verify the legitimacy of the other party's identity. The verifier generates a random challenge polynomial, which the prover signs with its private key and returns. The verifier verifies the generated signature with the prover's public key to prevent replay attacks. If identity authentication succeeds, step 5 is executed; if identity authentication fails, communication is rejected.

[0033] Step 5. Perform key negotiation using the improved Blom key distribution protocol to determine the session key.

[0034] Step 6. Communication;

[0035] The receiver uses the private key to perform NTRU signing on the response message, encrypts it with the negotiated session key, and then returns the data to the sender. Upon receipt, the sender first decrypts it with the session key and then verifies the signature with the receiver's public key. After confirming that the data is valid, it parses the data.

[0036] If the communication between the sender and the receiver is stable, subsequent data exchanges are directly encrypted using the session key;

[0037] If the sender leaves the receiver's coverage area, it needs to re-authenticate and negotiate the key with the new receiver.

[0038] As a preferred embodiment of the present invention, the abnormal behavior management module monitors abnormal behavior during the communication process and executes certificate revocation or security response measures when an abnormality is found. By revoking the certificate, the device is prevented from continuing to communicate insecurely, and the certificate revocation list is dynamically updated.

[0039] As a preferred embodiment of the present invention, during identity authentication, a three-party identity authentication is used to prevent man-in-the-middle attacks. During the three-party authentication process, the on-board unit, the roadside unit and the service provider need to verify each other's certificates and confirm their identities.

[0040] As a preferred embodiment of the present invention, a pseudonym certificate issued by a pseudonym certificate authority will be attached during identity authentication. After receiving the identity authentication request, the certifying party first checks whether the pseudonym certificate is issued by a trusted pseudonym certificate authority and verifies whether the signature of the pseudonym certificate is correct to ensure its integrity; then, the validity period of the pseudonym certificate is checked to ensure that it has not expired, and at the same time, the certificate revocation list is queried or the online certificate status protocol is used to verify whether the pseudonym certificate has been revoked; if the signature of the pseudonym certificate is correct, has not expired and has not been revoked, the certifying party considers the pseudonym certificate valid and continues the next step of the identity authentication process; otherwise, the identity authentication fails.

[0041] Advantages and beneficial effects of the present invention:

[0042] (1) Currently, most VANET (vehicle network) systems use signature and encryption schemes based on elliptic curves (ECDSA) or RSA. The present invention uses signature and encryption in NTRU format. Compared with the traditional public key system, this lattice cryptography-based scheme has more advantages in resisting quantum attacks and can effectively resist the threat of quantum computing to existing encryption technology, thereby ensuring data security. At the same time, based on the optimization of the traditional NTRU algorithm, the present invention reduces the computational complexity of signature generation and verification and improves computational efficiency by improving the algorithm structure (optimizing convolution operations, reducing the number of operations, and improving the efficiency of signature generation and verification; optimizing the modular operation process, reducing computational complexity, improving computational accuracy, and ensuring that the signature process is fast and accurate). This improves the overall computational efficiency, meets the real-time and high-efficiency requirements of vehicle-mounted ad hoc networks, and is suitable for resource-constrained on-board units (OBUs). In addition, traditional VANET mainly adopts two-way authentication (OBU and RSU) or centralized CA authentication. The present invention introduces VSP (service provider) as a third party to form a three-party mutual authentication mechanism of OBU-RSU-VSP, so that RSU is not just a relay node, but can participate in identity authentication and key negotiation with VSP. This method improves the reliability of authentication and also makes communication between vehicles more secure.

[0043] (2) The present invention adopts the Blom key distribution protocol for key negotiation. Unlike the common Diffie-Hellman (DH) key exchange, the Blom protocol allows any two legitimate nodes to directly calculate the session key without the need for additional key exchange, which is very beneficial for highly dynamic environments such as VANET. The Blom+NTRU combination makes key negotiation more efficient and quantum-resistant.

[0044] (3) The present invention combines the NTRU signature and pseudonym certificate mechanisms, which not only supports identity authentication but also optimizes privacy protection. The pseudonym certificate is replaced regularly, so that the OBU will not be maliciously tracked during long-term communication. However, most existing VANET solutions still rely mainly on traditional pseudo-identity switching strategies for privacy protection.

[0045] (4) The pseudonym certificate in the present invention is mainly used to enhance privacy protection and prevent external attackers from inferring the vehicle's driving trajectory or identity information by tracking the vehicle's communication records over a long period of time. The pseudonym certificate is still issued by a certificate authority (such as a PCA), but it is not bound to the vehicle's real identity. Instead, it uses a pseudonym that changes regularly. The pseudonym certificate is changed every few minutes or hours, making it impossible to associate the communication records of the same vehicle over a long period of time. Even if an attacker intercepts the message sent by the OBU, it is difficult for the attacker to track the OBU over a long period of time through the public key because the pseudonym certificate is updated regularly.

[0046] (5) The Blom key distribution protocol is used for key negotiation in the present invention. The Blom key distribution protocol plays a role in secure key negotiation throughout the entire process, enabling the OBU, RSU, and VSP to dynamically calculate the shared key (session key) without leaking the key, thereby enhancing the confidentiality and anti-attack capability of the Internet of Vehicles communication.

[0047] (6) In the present invention, the entire Internet of Vehicles system performs strict authentication, signature encryption, and certificate revocation operations through multiple certificate authorities, ensuring the communication security between vehicles, roadside units, and service providers; all messages are signed and encrypted to ensure that the integrity and confidentiality of information can be maintained under malicious attacks; in addition, the certificate management and abnormal behavior management mechanisms further enhance the system's anti-attack capabilities, ensuring that all devices in the system communicate under trusted conditions.

[0048] (7) This invention employs a challenge-response mechanism and three-way authentication to enhance protection against replay attacks and support efficient identity authentication and key exchange. Compared with traditional elliptic curve cryptography and the RSA algorithm, this invention significantly improves computational efficiency and reduces bandwidth and storage requirements while maintaining the same security level, making it suitable for widespread application in vehicular ad hoc networks.

[0049] (8) The present invention uses the NTRU lattice cryptosystem to generate public and private key pairs, which significantly reduces the key length and computational complexity while ensuring security. Moreover, by using the NTRU-based signature algorithm, messages in vehicle communications can be signed and encrypted, ensuring the integrity and confidentiality of messages during transmission. In addition, the present invention adopts a pseudonym certificate mechanism to prevent the leakage of vehicle identity by randomly switching pseudonym certificates and serial numbers, further enhancing user privacy protection and avoiding the leakage of the vehicle's true identity. The pseudonym certificate mechanism is combined with the NTRU signature mechanism to further enhance privacy protection through dynamic certificate rotation.

[0050] (9) The method provided by the present invention can operate stably in a changing communication environment, effectively ensuring the security of vehicle-mounted communications and ensuring the authenticity and immutability (integrity) of information. At the same time, the optimized algorithm reduces the computing resources required for signature and verification while maintaining high security, reduces the hardware burden of the vehicle terminal, and improves the scalability and long-term stability of the system. This solution is compatible with the existing vehicle-mounted ad hoc network architecture, is easy to deploy and integrate, does not require major modifications to the system architecture, and can quickly adapt to actual application needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] By referring to the following description in conjunction with the accompanying drawings, and with a more complete understanding of the present invention, other objects and results of the present invention will become more clear and easy to understand. In the accompanying drawings:

[0052] Figure 1 This is a structural block diagram of the vehicle-mounted ad hoc network security communication system of the present invention;

[0053] Figure 2 This is a flow chart of the secure communication method for a vehicle-mounted ad hoc network according to the present invention;

[0054] Figure 3 A comparison chart of key lengths for the three signature schemes provided by the present invention;

[0055] Figure 4 This is a comparison chart of the computational efficiency of the three signature schemes provided by the present invention. DETAILED DESCRIPTION

[0056] In order to enable those skilled in the art to better understand the technical solutions and advantages of the present invention, the present application is described in detail below with reference to the accompanying drawings, but this is not intended to limit the scope of protection of the present invention.

[0057] Example 1:

[0058] like Figure 1As shown, this embodiment provides a secure communication system for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system, including a key generation module, a message signing module, a message encryption module, a message decryption module, a message verification module, an identity authentication module, a key exchange module, a pseudo-random number generator, and a certificate management module CA;

[0059] The key generation module is used to generate the public key and private key pair of the communication node in the vehicular ad hoc network. The key generation module uses the NTRU lattice cryptosystem to generate the public key and private key pair for each communication node (i.e., vehicle), and publishes and manages the public key through the certificate management module CA.

[0060] In the present invention, during the key generation process of the NTRU lattice cryptosystem, appropriate NTRU lattice parameters (such as the degree and modulus of the polynomial) are first selected according to the requirements of the vehicular ad hoc network, and public and private key pairs are generated based on these parameters.

[0061] To ensure the efficiency and security of the VANET, reduce computational overhead, and improve efficiency, this embodiment uses an optimized NTRU key generation algorithm, as follows:

[0062] Select appropriate parameters: Based on the security requirements of the vehicle communication system, the parameters of the NTRU algorithm, such as the polynomial degree and modulus, should be selected. These parameters should ensure the security of key generation while ensuring that the calculation process meets the low computing resource requirements of the vehicle network nodes.

[0063] In this embodiment, the process of generating the public key and private key is as follows: select two random polynomial and Generate a key using the extended Euclidean algorithm Seek the reverse, if you can't find the way out The inverse element of , then reselect the polynomial ; and They are In the model and model The multiplicative inverse of ;calculate , is a temporary random polynomial generated by a pseudo-random number generator, ∈L (L is a set of sparse polynomials with a degree less than N and a coefficient absolute value not exceeding a set threshold, i.e., a set of random polynomials), which is used in the public key generation process. After combining with the current timestamp T, a value for calculating the public key is generated; the public key is , the private key is ;

[0064] in, and is the modulus in the NTRU encryption process, The value of is 2 to 5, which ensures the irreversibility of polynomial operations. The value of q is 2048≤ q≤4096, and q>6p must be satisfied to prevent decryption errors. represents the public key polynomial, is the symbol for modulo operation; is the polynomial convolution operator symbol, is the XOR operator symbol, N is the polynomial degree (security parameter), and the value range is 509 ≤ N ≤ 1277. N=677 is preferred to meet the NIST post-quantum security Level 3 standard.

[0065] In this embodiment, the private key is a random polynomial generated based on the NTRU lattice cryptosystem, whose coefficients are randomly selected from {-1, 0, 1} by a pseudo-random number generator that complies with the ANSI X9.17 standard, and its reversibility under modulo p and modulo q is verified by the extended Euclidean algorithm to ensure quantum security. When communicating with other nodes, the generated private key is used to sign the message, and the public key is used to verify the signature. In this way, nodes can authenticate each other, ensure the legitimacy of each other's identity, and prevent identity forgery.

[0066] The message signing module is used to ensure the integrity and non-tampering of the message during transmission. The sender uses its own private key and a random polynomial dynamically generated by a pseudo-random number generator based on the NTRU lattice cryptosystem to sign and generate a signature polynomial;

[0067] Specifically, the NTRU parameters are first initialized: the polynomial degree N-1 is selected (the value range is a prime number that meets the post-quantum security standard, 509 to 1277 is recommended), the modulus p (a small prime number in the range of 2 to 5) and q (a large prime number that satisfies q>6p, in the range of 2048 to 4096); the private key is a randomly generated polynomial whose coefficients are selected from {-1, 0, 1} and verified by the reversibility of the modulo p and q.

[0068] Signature generation phase: Hash the signed message to generate a message digest Finally, a temporary random polynomial is dynamically generated by a pseudo-random number generator that complies with the ANSIX9.17 standard (using triple DES encryption to protect the seed), and a unique signature polynomial is generated through NTRU polynomial convolution and modular operations. , ,in, is the sender’s private key polynomial, is the message hash value, A temporary random polynomial dynamically generated by the sender, ∈L, is the current timestamp, The modulus used in the NTRU encryption process; check Is the coefficient range within If not, make model adjustments.

[0069] This embodiment can ensure that each signature is unpredictable due to the dynamic change of the random polynomial, and the signature data is bound to the original message and then transmitted to the message encryption module.

[0070] The message encryption module obtains the public key of the recipient through the certificate management module CA, encodes the message to be sent into a message polynomial that conforms to the NTRU lattice cryptosystem, and randomly selects a temporarily generated random polynomial. The message to be sent containing the signature data is encrypted in combination with the recipient's public key to form the final ciphertext;

[0071] Specifically, the original message is converted into a message with a number less than The polynomial m (the value range is a prime number that meets the post-quantum security standard, usually 509 to 1277) has a coefficient range of [-(p-1) / 2, (p-1) / 2], that is, the absolute value of the coefficient does not exceed (p-1) / 2, p is a small modulus, ranging from 2 to 5; when encrypting, a random polynomial is selected from the random polynomial set L (The coefficient is selected from {-1, 0, 1}), L is the number of times less than N, and the absolute value of the coefficient does not exceed the set threshold (usually k sparse is 1 or 2); then, combined with the receiver's public key polynomial h (a polynomial of degree N-1), the polynomial convolution operation (symbol ) and modular operation to generate ciphertext ; where q is a large modulus (ranging from 2048 to 4096), q>6p, Represents hash operation, is the current timestamp, ∈L, Represents the encoded message polynomial, ciphertext The coefficients are adjusted to the range of [-q / 2, q / 2).

[0072] In this embodiment, the generated ciphertext is transmitted through the vehicle network, and the recipient can decrypt and verify it based on his or her own private key. The entire process relies on lightweight polynomial operations, which significantly reduces the computational overhead compared to traditional solutions that rely on elliptic curve scalar multiplication. At the same time, through dynamic parameter selection and quantum-resistant design, a balance between security and efficiency is ensured.

[0073] The message decryption module, the recipient uses his own private key and its inverse element modulo p The received ciphertext Decrypt and restore the plaintext;

[0074] Specifically, the receiver receives the ciphertext Then, use the private key f (the coefficients are randomly generated from {-1, 0, 1} and verified by the reversibility of modulo p and q) and its inverse element modulo p Decrypt and calculate the intermediate results , and adjust the coefficient to the range of (-q / 2, q / 2); perform a modulo p operation on a, and get ; Through the inverse element Recover the plaintext, decrypted message polynomial ; Where M is the decrypted message polynomial, a and b are intermediate calculated values, A temporary random polynomial dynamically generated for the receiver, ∈L, enhances the randomness during decryption, is the current timestamp, combined with a random polynomial Increase the uniqueness of each decryption to prevent replay attacks;

[0075] The message verification module, the receiver obtains the sender's public key through the certificate management module CA, and uses the sender's public key to perform integrity check on the decrypted data; first restore the hash value and random polynomial through the signature verification operation, and then perform the decrypted message polynomial on the decrypted message. Perform hashing and compare it with the hash value obtained by the signature verification operation; at the same time, verify the validity of the random polynomial; if the hash values ​​are consistent and the random polynomial is valid, it proves that the message has not been tampered with during transmission and was indeed sent by the legitimate sender, confirming the integrity of the message;

[0076] Specifically, the receiver obtains the sender's public key through the certificate management module and decrypts the message polynomial Perform integrity check to verify the validity of the signature data to ensure that the message has not been tampered with and the source is legitimate. The implementation steps are as follows:

[0077] Public key acquisition and parameter initialization: Obtain the sender's public key polynomial from the certificate management module (The degree of the polynomial is ;in, To meet the post-quantum security standard, the prime number range is ), confirm the NTRU parameter range, small module Value range: Large modulus Value range: , and satisfies .

[0078] Signature data extraction and preprocessing: Separate the signature polynomial from the received data ;

[0079] Signature verification operation: using the sender's public key polynomial Signature polynomial Perform polynomial convolution and modular operations to recover the hash value and random polynomial: , Represents a polynomial convolution operation (modular multiplication and accumulation of coefficients), which splits the result into the recovered hash value and random polynomials .

[0080] Integrity comparison and random polynomial verification:

[0081] Hash consistency verification: polynomial of the decrypted message Perform hash operation (algorithm consistent with the sender, such as SM3 / SHA-256) to generate a local hash value , and the restored Strict comparison.

[0082] Random polynomial validity verification:

[0083] Checking random polynomials Is the generation of ANSI X9.17 compliant (based on current timestamp and seed update mechanism)?

[0084] verify Checks whether the current timestamp is within the valid window (such as ±1 second) to prevent replay attacks.

[0085] Verification result processing: If and If the hash value does not match or the random polynomial times out, the message is determined to be tampered with or illegally sent, triggering the exception management module (such as recording logs and notifying the Certificate Revocation Authority (PCA)).

[0086] The identity authentication module completes the identity authentication of the vehicle network node through the Challenge-Response Protocol based on the NTRU lattice password, ensuring the legitimacy of the identities of the communicating parties, that is, the communicating parties are authorized devices, and preventing attacks by forged identities;

[0087] Specifically, the identity authentication module verifies the legitimacy of the onboard network nodes (such as the vehicle-side OBU and roadside unit RSU) through a challenge-response protocol based on the NTRU lattice cipher, ensuring that both communicating parties are authorized devices and resisting spoofing attacks. The implementation steps are as follows:

[0088] Challenge generation (Verifier → Prover): Verifier (verifier, such as RSU): generates a random challenge polynomial ; The degree of the polynomial is (N is a safety parameter, the value range is ); coefficients from the set L (sparse polynomial, coefficient absolute value ≤ k, usually k sparse = 1 or 2); append the current timestamp T (accuracy to milliseconds) to generate challenge data And synchronously transmit the timestamp T through the protocol and send it to Prover.

[0089] Response generation (Prover → Verifier): Prover (prover, such as OBU) verifies the validity of the current timestamp T (such as time window ±1 second). If the timeout is exceeded, the challenge is discarded; if valid, the private key f (coefficients are selected from {-1, 0, 1}, satisfying the modulus and Reversibility) for challenging polynomials Sign and generate signature polynomial ;in, To challenge the polynomial Perform hash operations; A dynamic random polynomial generated by a pseudo-random number generator that complies with the ANSI X9.17 PRNG standard. ∈L; Sign With the current timestamp Combined into response data , return to Verifier.

[0090] Verifier: Obtain the Prover public key polynomial from the certificate management module , using the public key polynomial h Signature polynomial Perform the inverse operation to restore the hash value and random polynomial: ; Calculate local hash , and the restored Strict comparison; verification of random polynomials Timestamp validity (process and challenges in If the hashes are consistent and the timestamp is valid, the authentication is successful; otherwise, it is determined to be an illegal node, an alarm is triggered, and the session is terminated.

[0091] In this embodiment, the identity authentication module can prevent man-in-the-middle attacks and protect the security of the system through multi-party identity authentication (e.g., OBU, RSU, VSP);

[0092] The key exchange module implements secure key exchange between communication nodes in a VANET based on the Blom protocol, ensuring key security and confidentiality during communication. During the key exchange process, both parties exchange keys to ensure that subsequent communication encryption is protected. This key exchange protocol design improves efficiency and security, ensuring secure information transmission regardless of network environment.

[0093] Specifically, the key exchange module (based on the Blom protocol) implements secure key exchange between communication nodes (such as OBUs and RSUs) in a vehicle-mounted ad hoc network (VANET) through an improved Blom key distribution protocol. This ensures that the generation and distribution of dynamic session keys between nodes meet the requirements of quantum attack resistance and lightweight computing. The implementation steps are as follows:

[0094] 1. System initialization:

[0095] Parameter definition:

[0096] Safety threshold k security (The maximum number of anti-capture nodes is in the range of 50≤k security ≤200);

[0097] Finite field GF(q), where q is a large prime number (consistent with NTRU parameters, 2048≤q≤4096);

[0098] Public matrix dimension D (value is k security +1, that is, D=k security +1).

[0099] Matrix generation:

[0100] Generate a D×D symmetric matrix S, whose elements are randomly selected from GF(q) and satisfy the reversibility;

[0101] Generate a D×D public matrix G, whose elements are random polynomials (degree < N, coefficient range [-(p-1) / 2, (p-1) / 2], compatible with NTRU parameters).

[0102] 2. Private Key Vector Distribution

[0103] Node registration:

[0104] Each node (such as OBU) is assigned a unique identity (such as vehicle MAC address or digital certificate);

[0105] For nodes Calculate the private key vector : ;in, is a matrix No. Column polynomial vector.

[0106] Private key vector storage:

[0107] node Secure storage (polynomial vector of length D), destroy the matrix S to prevent leakage.

[0108] 3. Dynamic key negotiation

[0109] Session key generation:

[0110] When the node and When communication is needed, both parties exchange public column vectors and ;

[0111] node Calculate the shared secret key :

[0112] node Calculate the shared secret key :

[0113] Guaranteed by matrix symmetry = , as the session key.

[0114] In this embodiment, the matrix operations of the Blom protocol are combined with NTRU polynomial convolution. The elements of the public matrix G are NTRU-compatible polynomials (with coefficients in the range [-(p-1) / 2, (p-1) / 2]). This utilizes the lattice cryptographic properties of NTRU to resist quantum computing attacks. Furthermore, this module can be designed with a dynamic update mechanism, allowing the public matrix G to be updated periodically (e.g., every 24 hours) to prevent the risk of long-term key exposure.

[0115] The certificate management module (CA) is responsible for the full lifecycle management of public key certificates in the VANET (vehicle-mounted ad hoc network), including certificate generation, distribution, revocation, and renewal. It combines the NTRU lattice cryptography system to resist quantum computing attacks and ensure the legitimacy of node identities and the security of communication links. The implementation steps are as follows:

[0116] 1. System initialization and parameter configuration

[0117] NTRU parameter definition:

[0118] Polynomial degree N (a prime number that meets the post-quantum security standard, with a value range of );

[0119] Small module , large modulus .

[0120] Certificate Template:

[0121] Use lightweight X.509 certificate format extension, embed NTRU public key polynomial h (format is coefficient list, range );

[0122] The certificate fields contain:

[0123] Node ID (such as vehicle MAC address or VIN number);

[0124] Public key polynomial ;

[0125] Validity period (dynamically adjusted, 24 hours by default);

[0126] Authority signature (NTRU-based certificate authority private key generate).

[0127] 2. Certificate Generation and Distribution

[0128] Node registration:

[0129] New Node i (such as OBU / RSU) Generate NTRU key pair ;

[0130] Submit a registration request to the Certificate Authority (CA), including and .

[0131] Certificate issuance:

[0132] After CA verifies the legitimacy of the node identity, use the private key Sign the certificate content and generate a certificate file : Signature polynomial ;in is the hash operation (hash function), A replay-resistant random polynomial generated by a pseudo-random number generator compliant with the ANSI X9.17 standard. ∈L.

[0133] Will Distributed to nodes and all network side units (RSU).

[0134] 3. Certificate Revocation List (CRL) Management

[0135] Revocation trigger conditions:

[0136] The number of times a node's private key is leaked, its identity is abnormal, or session key negotiation fails exceeds the threshold.

[0137] CRL generation and broadcasting:

[0138] CA regularly generates a revocation list (CRL), which contains the ID of the revoked certificate and the current revocation timestamp. The CRL format is a polynomial code (coefficient range ), broadcast to the entire network through RSU, with an update cycle of ≤5 minutes; the NTRU signature of the CA is attached during broadcast to ensure the integrity of the list.

[0139] 4. Certificate renewal and collaborative certification

[0140] Periodic updates:

[0141] Before the certificate expires, the CA automatically generates a new certificate , pushed to the node through RSU; the node verifies the CA signature of the new certificate and replaces the old certificate without the need for re-registration.

[0142] In this embodiment, in the challenge-response protocol, the verifier (such as RSU) obtains the other party's public key polynomial through the certificate management module. , and check Is it in the latest CRL? If the certificate is valid and the signature verification passes, the identity is considered legitimate.

[0143] Furthermore, in this embodiment, the pseudo-random number generator is a pseudo-random number generator that complies with the ANSI X9.17 standard. The ANSI X9.17 pseudo-random number generator uses triple DES encryption to ensure the unpredictability of the random polynomial or random number, thereby improving the security of the random polynomial or random number.

[0144] Example 2:

[0145] like Figure 2 As shown, this embodiment provides a secure communication method for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system, the method comprising the following steps:

[0146] Step 1. Generate a public key and private key pair for each communication node in the VANET using the NTRU lattice cryptosystem. The communication node publishes its public key to the secure communication system of Example 1 and manages it through the certificate management module (CA). The certificate management module (CA) is responsible for the distribution, revocation, and renewal of public key certificates to ensure the validity of the public key.

[0147] In this embodiment, the public key certificate is mainly used for identity authentication to ensure the true identity of the communication entity. It is issued by the certificate management module CA and binds the true identity of the communication entity (such as the VIN code, which is the unique identification information of the vehicle) with the public key to ensure the credibility of the public key. The communication entities include the on-board unit (OBU), the roadside unit (RSU), and the service provider (VSP).

[0148] Step 2. When the sender needs to send a message, it uses its own private key to sign the message to be sent. The random polynomial generated by the pseudo-random number generator (ANSI X9.17 PRNG) is added to the signing process, and the NTRU signature algorithm is used to complete it, so that each signature is unique (even for the same message, since some random factors are added in the signing process, the signature value generated each time will be different). The generated signature data is sent to the message encryption module together with the original message. The message encryption module requests the recipient's public key certificate from the CA, encodes the message to be sent into a message polynomial that conforms to the NTRU lattice cryptosystem, and randomly selects a temporary polynomial. The public key of the recipient is used to encrypt the message to be sent, and then the signed and encrypted message is transmitted to the recipient through the vehicle-mounted ad hoc network.

[0149] For example, when an onboard unit (OBU) enters a certain area, it needs to request traffic signal status and road conditions ahead from a nearby roadside unit (RSU). The OBU first generates a request message containing information such as location, speed, direction, and current timestamp, and uses the NTRU signature algorithm for integrity protection. It also encrypts the message with the RSU's public key to ensure communication security. The OBU then sends the encrypted message to the RSU.

[0150] In this embodiment, the OBU and RSU obtain each other's public key by exchanging public key certificates during communication, thereby performing encryption and signature verification.

[0151] Step 3. After receiving the message, the recipient first uses his own private key and its inverse element modulo p The received ciphertext Decrypt and restore the plaintext; then request the sender's public key certificate from the CA, first restore the hash value and random polynomial through the signature verification operation, and then perform the decrypted message polynomial Perform hashing and compare it with the hash value obtained by the signature verification operation; at the same time, verify the validity of the random polynomial; if the hash values ​​are consistent and the random polynomial is valid, it proves that the message has not been tampered with during transmission and is indeed sent by the legitimate sender, and then proceed to step 4 to continue processing the message; if verification fails, the message is rejected;

[0152] For example, when the RSU receives a message, it first decrypts the message using its own private key and verifies the signature using the OBU's public key, while also checking whether the OBU's public key certificate is valid. If the verification passes, the RSU processes the OBU's request, such as querying the current traffic light status, and encapsulates the result into a response message.

[0153] Step 4. Identity Authentication:

[0154] The receiver and sender complete identity authentication through a challenge-response method based on the NTRU lattice cipher to verify the legitimacy of the other party's identity and prevent identity forgery attacks. The authenticator (such as the RSU) generates a random challenge polynomial. The authenticated party (such as the OBU, also known as the prover) needs to sign the random challenge polynomial with its own private key and return it. The generated signature authenticator (also known as the verifier) ​​will verify it with the authenticated party's public key to prevent replay attacks. If the identity authentication passes, step 5 is executed; if the identity authentication fails, communication is rejected.

[0155] In this embodiment, when the OBU sends an identity authentication request, it will be accompanied by a pseudonym certificate issued by a pseudonym certificate authority (PCA, used to issue pseudonym certificates for on-board units and roadside units to prevent user privacy leakage). After receiving the identity authentication request, the RSU or VSP first checks whether the pseudonym certificate is issued by a trusted PCA and verifies whether the signature of the pseudonym certificate is correct (the signature of the pseudonym certificate is verified using the public key of the PCA in the pseudonym certificate. If the verification is successful, it means that the pseudonym certificate is issued by a trusted PCA and has not been tampered with) to ensure its integrity; then, the validity period of the pseudonym certificate is checked to ensure that it has not expired, and the certificate revocation list (CRL) is queried or the online certificate status protocol (OCSP) is used to verify whether the pseudonym certificate has been revoked; if the signature of the pseudonym certificate is correct, has not expired, and has not been revoked, the RSU or VSP considers the pseudonym certificate valid and continues the next step of the identity authentication process; for example, verifying the signed message sent by the OBU; otherwise, the identity authentication fails, the RSU or VSP will refuse to communicate further with the OBU, and notify the certificate management module CA Or the abnormal behavior management module MA will process it; finally, the verification result will be fed back to the OBU; if the identity authentication is passed, it will enter the subsequent key negotiation and secure communication stage, thereby ensuring that the communication devices in the Internet of Vehicles have legal identities and can interact securely.

[0156] It should be noted that identity authentication will only occur during the first communication, and subsequent communication will no longer require identity authentication.

[0157] Step 5. Key negotiation is performed using the improved Blom key distribution protocol to determine the session key:

[0158] Specifically, when the node and When communication is needed, both parties exchange public column vectors and That's it;

[0159] node Calculate the shared secret key : ;node The private key vector ;in, is a D×D public matrix No. Column polynomial vector, public matrix The elements of are random polynomials with degree < N and coefficients in the range [-(p-1) / 2, (p-1) / 2]; S is a D×D symmetric matrix whose elements are randomly selected from GF(q) and satisfy reversibility. q is a large prime number, 2048≤q≤4096;

[0160] node Calculate the shared secret key : ;

[0161] Guaranteed by matrix symmetry = , as the session key;

[0162] The matrix operation of the Blom protocol is combined with the NTRU polynomial convolution to ensure that both parties (OBU and RSU) can securely negotiate a shared session key without directly sharing the key (encrypting public information to ensure that both parties can calculate the same key), avoiding the security risks of direct key exchange.

[0163] Step 6. Communication:

[0164] The receiver (e.g., RUS) uses its own private key to perform NTRU signing on the response message, encrypts it with the session key (shared key) previously negotiated with the OBU, and then returns the data to the sender (e.g., OBU). Upon receipt, the sender (e.g., OBU) first decrypts it with the session key and then verifies the signature with the receiver's (e.g., RSU) public key to ensure the data has not been tampered with. After confirming the data is valid, the OBU analyzes the traffic signal status and adjusts its driving strategy based on its own speed.

[0165] If the communication between the OBU and RSU is stable, subsequent data exchanges can be directly encrypted using the session key, such as the OBU sending regular location updates and the RSU reporting congestion on the road ahead;

[0166] If the OBU leaves the coverage area of ​​the RSU, it must re-authenticate and negotiate keys with the new RSU to ensure communication security. Throughout the entire process, the NTRU signature ensures message non-repudiation, the certificate management module (CA) is responsible for identity authentication, and the session key ensures the confidentiality of subsequent communications.

[0167] Furthermore, in this embodiment, during identity authentication, multi-party identity authentication (e.g., OBU, RSU, VSP) is used to prevent man-in-the-middle attacks and protect system security. In this three-party authentication process, the onboard unit (OBU), roadside unit (RSU), and service provider (VSP) need to verify each other's identities.

[0168] OBU and RSU: OBU first sends an identity authentication request to RSU, and RSU verifies OBU's certificate and confirms its identity;

[0169] RSU and VSP: RSU makes an identity authentication request through VSP, and VSP verifies the RSU's certificate and confirms its identity;

[0170] OBU and VSP: Under the guidance of RSU, OBU sends an identity authentication request to VSP, and VSP verifies OBU's certificate again to ensure the validity of OBU's identity.

[0171] The present invention introduces the VSP (service provider) as a third party to form a three-party mutual authentication mechanism of OBU-RSU-VSP, so that the RSU is not just a relay node, but can participate in identity authentication and key negotiation with the VSP; this approach improves the reliability of authentication and also makes communication between vehicles more secure.

[0172] This paper uses the NTRU-Blom hybrid architecture, combining lattice cryptography with a lightweight key distribution protocol to address the quantum resistance flaws of the traditional Blom protocol. This method employs a dynamic security design, with random polynomial generation strictly adhering to the ANSI X9.17 standard and bound to the current timestamp (with a ±1-second window) to ensure the uniqueness and replay resistance of each communication. Key management uses dynamic session keys (updated with each communication) and short-term certificates (mandatory updates every 24 hours) to significantly reduce the risk of key leakage. The certificate revocation list (CRL) is updated every 5 minutes through sharded broadcasting, with a network-wide synchronization delay of less than 1 second. The entire link is bound to the current timestamp, random polynomial, and hash, achieving a dynamic association between message signing, identity authentication, and certificate issuance, surpassing existing technologies in quantum resistance, real-time performance, dynamic scalability, and resource efficiency.

[0173] This paper conducts a comprehensive comparative analysis of the elliptic curve cryptosystem (LD1), the NTRU lattice cryptosystem (LD2), and the commonly used RSA signature algorithm based on the large prime number factorization problem (Scheme 3), focusing on the three aspects of security, computational overhead, and communication overhead. In terms of security, this scheme compares the key lengths of the three signature schemes (in bits). The results are as follows: Figure 3 As shown. Figure 3 The four sets of data show that, in terms of security strength, the NTRU scheme with a 347-bit key length is comparable to the 224-bit LD1 and 2048-bit RSA schemes, reflecting the differences in key lengths between different signature algorithms. In terms of computational overhead, the NTRU scheme has the advantages of shorter key and ciphertext lengths, resulting in faster computational speed. Compared to RSA and elliptic curve signature schemes, it can perform encryption and decryption operations more efficiently. Furthermore, due to its lower storage space requirements and smaller transmission bandwidth, the NTRU scheme reduces the requirements for system hardware resources, making it more suitable for applications with lower processor speed and network bandwidth requirements.

[0174] The computational efficiency of the above three signature schemes is as follows: Figure 4 As shown. Figure 4 The data shows that there are significant differences in the computational efficiency of the three signature schemes. In LD1, based on the elliptic curve cryptosystem, 160 rational point scalar multiplication operations are required for encryption and decryption. In contrast, LD2 based on the NTRU algorithm only involves addition, multiplication, and modular operations of small integers. Therefore, in the encryption and decryption processes, LD2 performs one convolution operation and two convolution operations, respectively. As for scheme three, it relies on the large prime number problem and requires 17 and 1000 modular multiplication operations for encryption and decryption, respectively. This shows that at the same security level, the computational speed of LD2 is significantly faster than the other two public key systems. The computational overhead of the three schemes is shown in Table 1.

[0175] Table 1 Computational overhead of three solutions

[0176] plan Key Generation (ms) Encryption (ms) Decryption (ms) Total time (ms) Option 3 4.07 248.21 4.012 256.29 LD1 0.27 9.119 10.472 9.389 LD2 0.014 0.829 0.952 1.795

[0177] Overall, LD2 outperforms LD1 in both key generation and encryption / decryption speeds, running approximately 5.23 times faster than LD1 and 142.84 times faster than Scheme 3. This demonstrates that LD2 not only achieves the same security standards but also offers significant advantages in computational efficiency, making it particularly suitable for scenarios requiring efficient processing.

[0178] By optimizing the NTRU signature algorithm, the present invention effectively reduces computational overhead, improves the efficiency of signature generation and verification, meets the real-time and high-efficiency requirements of vehicle-mounted ad hoc networks, and can operate stably in complex network environments.

[0179] The above description of the present invention using specific examples is intended only to facilitate understanding of the present invention and is not intended to limit the present invention. A person skilled in the art of the present invention may make several simple deductions, modifications, or substitutions based on the principles of the present invention. Therefore, the scope of protection of the present invention shall be subject to the scope of protection of the claims.

Claims

1. A secure communication system for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system, comprising a key generation module, a message signing module, a message encryption module, a message decryption module, a message verification module, an identity authentication module, a key exchange module, and a certificate management module; characterized in that: Also includes a pseudo-random number generator; The key generation module uses the NTRU lattice cryptosystem to generate a public key and a private key pair for each communication node in the vehicular ad hoc network, and publishes and manages the public key through the certificate management module; The message signature module uses the private key and the random polynomial dynamically generated by the pseudo-random number generator to sign based on the NTRU lattice cryptographic system to generate the signature polynomial , ;in, is the sender’s private key polynomial, is the message hash value, A temporary random polynomial dynamically generated by the sender, is the current timestamp, is the modulus in the NTRU encryption process, is the polynomial convolution operator symbol, Is the exclusive OR operator symbol, is the symbol for modulo operation; The message encryption module obtains the public key of the recipient through the certificate management module and encodes the message to be sent into a number less than And the absolute value of the coefficient is at most The message polynomial m is obtained by randomly selecting a temporary polynomial The message to be sent is encrypted with the receiver's public key to form the final ciphertext. ; ;in A temporarily generated random polynomial used for randomness in encryption operations. 、 Both are moduli in the NTRU encryption process. is the current timestamp, is the recipient's public key polynomial, and H represents the hash operation; The message decryption module, the receiver uses the private key and its inverse element modulo p The received ciphertext Decrypt, restore the plaintext, and the decrypted message polynomial ;in, , , a and b are intermediate calculated values, A temporary random polynomial dynamically generated for the receiver; The message verification module, the receiver obtains the sender's public key through the certificate management module, and separates the signature polynomial from the received data ; Use the sender's public key polynomial to sign the polynomial Perform polynomial convolution and modular operations to recover the hash value and random polynomial; then perform the decrypted message polynomial Perform a hash operation and compare it with the recovered hash value; at the same time, verify the validity of the random polynomial; if the hash values ​​are consistent and the random polynomial is valid, the message is considered complete and the source is legitimate, and the subsequent processing flow is entered; The identity authentication module completes the identity authentication of the vehicle network node through a challenge-response protocol based on the NTRU lattice password to ensure the legitimacy of the identities of both communicating parties; The key exchange module implements secure key exchange between communication nodes in a vehicle-mounted ad hoc network through an improved Blom key distribution protocol.

2. A secure communication system for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system according to claim 1, characterized in that: In the key generation module, the process of generating the public key and private key is: select two random polynomial and Generate a key; use the extended Euclidean algorithm to Seek the reverse, if you can't find the way out The inverse element of , then reselect the polynomial , and They are In the model and model The multiplicative inverse of ;calculate , is a temporary random polynomial, and the public key is , the private key is , the coefficients of the random polynomial of the private key are randomly selected from {-1, 0, 1} by a pseudo-random number generator; in, and is the modulus in the NTRU encryption process, The value range is 2 to 5. The value of is 2048≤ q≤4096, and q>6p must be satisfied. N is the degree of the polynomial and the value is 509≤N ≤1277.

3. The secure communication system for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system according to claim 1, characterized in that: The steps of identity authentication performed by the identity authentication module are as follows: The verifier generates a random challenge polynomial , the polynomial degree is , the coefficients are randomly selected from the sparse polynomial set L of all times less than N and the absolute value of the coefficients does not exceed the set threshold; add the current timestamp T to generate the challenge data , and synchronously transmit the timestamp T through the protocol and send it to the proving party; The prover verifies the validity of the current timestamp T. If it times out, the challenge is discarded. If it is valid, the prover uses the private key f and the random polynomial dynamically generated by the pseudo-random number generator to Challenge polynomial Sign, the signature polynomial Return to the verifier; The verifier obtains the public key of the prover from the certificate management module and uses the public key to sign the polynomial Perform the inverse operation to restore the hash value and random polynomial; then perform the hash operation on the random challenge polynomial, compare it with the restored hash value, and verify the random polynomial at the same time Timestamp validity; If the hash matches and the timestamp is valid, the authentication is successful.

4. The secure communication system for a vehicle-mounted ad hoc network based on the NTRU lattice cryptography system according to claim 1, characterized in that: The key exchange module performs key exchange mainly by exchanging the public column vectors of both parties. and Implemented; when the node and When communication is required, nodes Calculate the shared secret key : ; node Calculate the shared secret key : ; Among them, the node The private key vector , S is a D×D symmetric matrix whose elements are randomly selected from the finite field GF(q) and satisfy the reversibility property, and q is a large prime number; is a D×D public matrix No. Column polynomial vector, public matrix The elements of are random polynomials with degree < N and coefficients in the range [-(p-1) / 2, (p-1) / 2]; For nodes The private key vector.

5. The secure communication system for a vehicle-mounted ad hoc network based on the NTRU lattice cryptography system according to claim 1, characterized in that: The certificate management module is responsible for the full life cycle management of public key certificates in the vehicle-mounted ad hoc network, including certificate generation, distribution, revocation and update; the pseudo-random number generator is a pseudo-random number generator that complies with the ANSI X9.17 standard, and the pseudo-random number generator uses triple DES encryption to ensure the unpredictability of random polynomials or random numbers.

6. The secure communication system for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system according to claim 2, characterized in that: Temporary random polynomial , a temporary random polynomial dynamically generated by the sender , a temporarily generated random polynomial , a temporary random polynomial dynamically generated by the receiver All belong to L, where L is a set of sparse polynomials whose degree is less than N and whose coefficient absolute value does not exceed the set threshold, i.e., a set of random polynomials; random polynomials The coefficients of are selected from {-1, 0, 1}.

7. A secure communication method for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system, characterized in that: The method comprises the following steps: Step 1. Generate a public key and private key pair for each communication node in the vehicular ad hoc network using the NTRU lattice cryptographic system. The communication node publishes its public key to the vehicular ad hoc network secure communication system based on the NTRU lattice cryptographic system as described in any one of claims 1 to 6, and manages it through a certificate management module. The certificate management module is responsible for the distribution, revocation, and update of public key certificates to ensure the validity of the public key. Step 2. When the sender needs to send a message, it uses the private key to sign the message to be sent. The random polynomial dynamically generated by the pseudo-random number generator is added to the signing process. The NTRU signature algorithm is used to complete it so that each signature is unique. The generated signature data is sent to the message encryption module together with the original message. The message encryption module requests the recipient's public key certificate from the certificate management module, encodes the message to be sent into a message polynomial that conforms to the NTRU lattice cryptosystem, and randomly selects a temporary polynomial. The public key of the recipient is used to encrypt the message to be sent, and then the signed and encrypted message is transmitted to the recipient via the VANET. Step 3. After receiving the message, the recipient first uses the private key and its inverse element modulo p The received ciphertext Decrypt and restore the plaintext; then request the sender's public key certificate from the certificate management module, first restore the hash value and random polynomial through the signature verification operation, and then perform the decrypted message polynomial Perform hashing and compare it with the hash value obtained by the signature verification operation; at the same time, verify the validity of the random polynomial; if the hash values ​​are consistent and the random polynomial is valid, it proves that the message has not been tampered with during transmission and is indeed sent by the legitimate sender, and then proceed to step 4 to continue processing the message; if verification fails, the message is rejected; Step 4. Identity authentication; The receiver and sender complete identity authentication through a challenge-response method based on the NTRU lattice cipher to verify the legitimacy of the other party's identity. The verifier generates a random challenge polynomial, which the prover signs with its private key and returns. The verifier verifies the generated signature using the prover's public key. If the identity authentication succeeds, step 5 is executed. If the identity authentication fails, communication is rejected. Step 5. Perform key negotiation using the improved Blom key distribution protocol to determine the session key. Step 6. Communication; The receiver uses the private key to perform NTRU signing on the response message, encrypts it with the negotiated session key, and then returns the data to the sender. Upon receipt, the sender first decrypts it with the session key and then verifies the signature with the receiver's public key. After confirming that the data is valid, it parses the data. If the communication between the sender and the receiver is stable, subsequent data exchanges are directly encrypted using the session key; If the sender leaves the receiver's coverage area, it needs to re-authenticate and negotiate the key with the new receiver.

8. The secure communication method for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system according to claim 7, characterized in that: The abnormal behavior management module monitors abnormal behavior during the communication process and performs certificate revocation or security response measures when an abnormality is found, while dynamically updating the certificate revocation list.

9. The secure communication method for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system according to claim 8, characterized in that: During identity authentication, three-party identity authentication is used to prevent man-in-the-middle attacks. During the three-party authentication process, the on-board unit, roadside unit, and service provider need to verify each other's certificates and confirm their identities.

10. A secure communication method for a vehicle-mounted ad hoc network based on the NTRU lattice cryptographic system according to claim 9, characterized in that: During identity authentication, a pseudonym certificate issued by a pseudonym certificate authority will be attached. After receiving the identity authentication request, the certifying party will first check whether the pseudonym certificate is issued by a trusted pseudonym certificate authority and verify whether the signature of the pseudonym certificate is correct to ensure its integrity; Then, check the validity period of the pseudonym certificate to ensure it has not expired, and query the certificate revocation list or use the online certificate status protocol to verify whether the pseudonym certificate has been revoked; If the signature of the pseudonym certificate is correct, has not expired, and has not been revoked, the certifying party considers the pseudonym certificate valid and proceeds to the next step of the identity authentication process; otherwise, the identity authentication fails.

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