WO2019109598A1 - 基于随机加密周期的VANETs位置隐私保护的系统及方法 - Google Patents

基于随机加密周期的VANETs位置隐私保护的系统及方法 Download PDF

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Publication number
WO2019109598A1
WO2019109598A1 PCT/CN2018/087564 CN2018087564W WO2019109598A1 WO 2019109598 A1 WO2019109598 A1 WO 2019109598A1 CN 2018087564 W CN2018087564 W CN 2018087564W WO 2019109598 A1 WO2019109598 A1 WO 2019109598A1
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Prior art keywords
vehicle
vehicle node
key
ticket
roadside unit
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PCT/CN2018/087564
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English (en)
French (fr)
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高天寒
辛欣
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东北大学
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Publication of WO2019109598A1 publication Critical patent/WO2019109598A1/zh

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0861—Generation of secret information including derivation or calculation of cryptographic keys or passwords
    • H04L9/0869—Generation of secret information including derivation or calculation of cryptographic keys or passwords involving random numbers or seeds
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L63/00—Network architectures or network communication protocols for network security
    • H04L63/04—Network architectures or network communication protocols for network security for providing a confidential data exchange among entities communicating through data packet networks
    • H04L63/0407—Network architectures or network communication protocols for network security for providing a confidential data exchange among entities communicating through data packet networks wherein the identity of one or more communicating identities is hidden
    • H04L63/0414—Network architectures or network communication protocols for network security for providing a confidential data exchange among entities communicating through data packet networks wherein the identity of one or more communicating identities is hidden during transmission, i.e. party's identity is protected against eavesdropping, e.g. by using temporary identifiers, but is known to the other party or parties involved in the communication
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L63/00—Network architectures or network communication protocols for network security
    • H04L63/04—Network architectures or network communication protocols for network security for providing a confidential data exchange among entities communicating through data packet networks
    • H04L63/0428—Network architectures or network communication protocols for network security for providing a confidential data exchange among entities communicating through data packet networks wherein the data content is protected, e.g. by encrypting or encapsulating the payload
    • H04L63/0442—Network architectures or network communication protocols for network security for providing a confidential data exchange among entities communicating through data packet networks wherein the data content is protected, e.g. by encrypting or encapsulating the payload wherein the sending and receiving network entities apply asymmetric encryption, i.e. different keys for encryption and decryption
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0838—Key agreement, i.e. key establishment technique in which a shared key is derived by parties as a function of information contributed by, or associated with, each of these
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0861—Generation of secret information including derivation or calculation of cryptographic keys or passwords
    • H04L9/0866—Generation of secret information including derivation or calculation of cryptographic keys or passwords involving user or device identifiers, e.g. serial number, physical or biometrical information, DNA, hand-signature or measurable physical characteristics

Definitions

  • the invention belongs to the technical field of network security, and in particular relates to a system and method for VANETs location privacy protection based on a random encryption period.
  • Vehicle self-organizing network uses vehicles as the basic information unit, and uses wireless access technology to connect road entities such as vehicles and roadside infrastructure with the transportation network to form an intelligent network system, which allows vehicles to communicate with other vehicles during high-speed travel ( Vehicle-to-vehicle (V2V for short) or vehicle-to-infrastructure (V2I).
  • V2V Vehicle-to-vehicle
  • V2I vehicle-to-infrastructure
  • DSRC dedicated short-distance communication technology
  • OBU on-board unit
  • the vehicle ad hoc network can also provide users with peer-to-peer (P2P) services, value-added services such as Internet access services, to achieve coordinated driving between vehicles, traffic decision support, traffic intelligent dispatch, traffic charging services, real-time Traffic information release, wireless value-added information services and other functions.
  • P2P peer-to-peer
  • value-added services such as Internet access services
  • VANETs play an important role in traffic safety and traffic efficiency improvement, but because they need to broadcast safety information periodically, external eavesdroppers can easily obtain the trajectory of the vehicle nodes based on the acquired location, pseudonym information, and the subsequent travel. The route is predicted, which causes the leakage of the vehicle location privacy, which greatly jeopardizes the privacy of the vehicle node. Therefore, the protection of vehicle node privacy must be realized in VANETs. Privacy protection is primarily concerned with protecting the driver's true identity and location information. No external eavesdropper should acquire the true identity of the driver or track specific vehicles.
  • Replacing a pseudonym is a way to protect the privacy of the vehicle's location.
  • the establishment of the Mix zone is a common solution for replacing pseudonyms in VANETs. Multiple vehicles change the pseudonym in one area at the same time to confuse the association between old and new pseudonyms.
  • the vehicle nodes can only change the pseudonym in a fixed area, which often brings great inconvenience to the vehicle node. If the vehicle node cannot change the pseudonym in the Mix zone area in time, it will not be very good. Protect your privacy.
  • the location privacy protection scheme based on the random encryption cycle can establish an encrypted Mix zone area at any time, which greatly enhances the privacy intensity.
  • the negotiation and update of the group key requires a large overhead.
  • the present invention provides a system and method for VANETs location privacy protection based on a random encryption period.
  • a method for VANETs location privacy protection based on a random encryption cycle comprising:
  • each vehicle node After entering the VANETs, each vehicle node registers with the third-party trust institution TA, and obtains the ticket issued by the third-party trust organization TA for the vehicle node and the first signature obtained by signing the ticket, the ticket is trusted by the third-party trust institution.
  • TA selects the private key generated by the vehicle node calculated by the random number;
  • the vehicle unit OBU generates a plurality of tokens by cooperation with a legal roadside unit of the ticket; and selects one token to generate a pseudonym and a corresponding private key;
  • the random encryption period is turned on, and the vehicle node that receives the pseudonym of the request is about to expire to replace the pseudonym;
  • the roadside unit RSU periodically changes the group key. If there is a vehicle node that is revoked in the current encryption group, the roadside unit RSU generates a new group key, and sends the new group key to the encryption group with the negotiated shared key. The remaining legal vehicle nodes.
  • the vehicle unit OBU registers with the third-party trust organization TA, including:
  • the vehicle node submits its own real identity ID to the third party trust institution TA through the vehicle unit OBU;
  • the third-party trust authority TA selects a random number to calculate the private key S a of the vehicle node;
  • the third-party trust authority TA signs the ticket with its own private key to obtain the first signature
  • the public key is mapped into the vehicle node ID and the true identity of a trusted third party agency TA database, the vehicle node v a public key, the first signature, the private key S a vehicle node node into a vehicle onboard unit OBU.
  • the vehicle node generates a plurality of tokens by cooperation with a legal roadside unit of the ticket, including:
  • the vehicle unit OBU of the vehicle node generates a symmetric key used as a shared key with the roadside unit RSU, combines the symmetric key with the ticket and the first signature to generate a first message, and the vehicle unit OBU generates a signature for the first message a second signature, the vehicle unit OBU encrypts the first message with the public key of the roadside unit RSU to generate a second message, and sends the second message and the second signature to the roadside unit;
  • the roadside unit decrypts the second message, the roadside unit calculates the token of the legal vehicle node of the ticket, and generates a third signature including the private key of the roadside unit, the token and its effective time, and selects the current group key, and uses the order.
  • the card and its valid time, the third signature, the group key, the random number, the certificate of the roadside unit RSU, generate a third message, store the token and the ticket in the database, and encrypt the third message with the shared key to generate the fourth
  • the message is sent to the vehicle node;
  • the vehicle unit OBU of the vehicle node decrypts the fourth message and verifies the third signature. If the third signature is legal, the third message is stored, otherwise the third message is discarded.
  • the second signature is verified by the ticket in the second message, and the first signature is verified by the public key of the third-party trust authority TA to verify whether the ticket is legal: If the signature and the second signature are both legal, the ticket is legal. Otherwise, the ticket is illegal, and the roadside unit refuses to cooperate with the vehicle node.
  • the random encryption period is turned on, and the vehicle node that receives the pseudonym of the request is about to expire to replace the pseudonym, including:
  • the vehicle unit OBU of the vehicle node v a broadcasts a request message for turning on the random encryption period to the neighboring vehicle node under the same roadside unit RSU and encrypts it with a group key, which contains the pseudonym and turns on the random encryption period.
  • Request and random encryption duration
  • the vehicle unit OBU of the remaining legal vehicle nodes that received the request message decrypts the request message with the current group key, and encrypts any message sent by itself with the group key within the random encryption duration, and starts a random encryption cycle.
  • the set of vehicle nodes v a and the remaining legitimate vehicle nodes that receive the request message are defined as an encrypted group;
  • the remaining legitimate vehicle nodes in the encryption group whose pseudonyms are about to expire are selected to cooperate with the vehicle node v a and return a response to the vehicle node v a ;
  • Cooperative vehicle nodes change the pseudonym together, as well as the trajectory or speed
  • the vehicle node v a Before the end of the random encryption duration, it is judged whether the cooperative vehicle node in the encryption group satisfies the condition for terminating the random encryption period. If yes, the random encryption period is ended. If not, the vehicle node v a broadcasts another open random encryption period. Request a message to open a new random encryption cycle to protect your location privacy;
  • the vehicle node in the encryption group whose pseudonym is about to expire is replaced with a pseudonym and a response is returned to the vehicle node v a , the vehicle node v a sends a termination request, and the remaining vehicle nodes that receive the termination request stop encrypting.
  • the condition for terminating the random encryption period includes:
  • the roadside unit RSU periodically changes the group key. If there is a vehicle node that is revoked in the current encryption group, the roadside unit RSU generates a new group key, and sends the new group key to the encryption with the negotiated shared key.
  • the remaining legal vehicle nodes in the group including:
  • the roadside unit RSU periodically changes the group key: when there is no vehicle node in the area of the roadside unit RSU, if a new vehicle node seeks the group key, the roadside unit RSU generates a new group key and issues it For its vehicle unit OBU, the previous group key is invalidated;
  • the pseudonym of the illegal neighboring vehicle node is submitted to the roadside unit RSU, and the roadside unit RSU finds the corresponding ticket by the pseudonym, and submits the ticket to the third party trust center TA, and the third party trusts
  • the central TA detects the true identity of the vehicle node based on the ticket and performs an undo operation on the illegal vehicle node; then the third party trust center TA sends the cancelled vehicle node ticket to all roadside units RSU, and then the roadside unit RSU Broadcast to all vehicle nodes;
  • All roadside units that have issued a group key to the revoked vehicle node detect whether the current group key has been updated. If the current group key has not been updated, the group key needs to be revoked and the rest The legal vehicle node issues a new group key; the roadside unit RSU generates a new group key, encrypts it with the shared key previously negotiated with the vehicle unit OBU, and sends it to the legitimate vehicle node to complete the group key update.
  • a system for VANETs location privacy protection based on a random encryption cycle comprising:
  • the third-party trust institution TA accepts the registration of each vehicle node after entering the VANETs, issues a ticket for the vehicle node and a first signature obtained by signing the ticket, the ticket is selected by the third-party trust institution TA to select the vehicle calculated by the random number The private key of the node is generated;
  • Vehicle unit OBU for the vehicle node to register with the third-party trust institution TA after entering the VANETs, generate multiple tokens by cooperation with the legal roadside unit of the ticket; and select one token to generate the pseudonym and the corresponding private key; the vehicle node When the pseudonym is about to expire and no other vehicle node requests to open the random encryption period, the random encryption period is turned on, and the pseudonym is replaced by the vehicle node that is about to expire after receiving the request;
  • Roadside unit RSU periodically change the group key. If there is a vehicle node that is revoked in the current encryption group, the roadside unit RSU generates a new group key and sends the new group key to the encryption group with the negotiated shared key. The remaining legal vehicle nodes within.
  • the present invention applies a location privacy protection scheme based on a random encryption period to a location privacy protection of a vehicle node in VANETs, and uses a random encryption period scheme.
  • the vehicle node does not need to change the pseudonym in the fixed area, but can be randomly selected according to requirements.
  • the encryption period is opened and the neighboring nodes cooperate with each other, which effectively improves the privacy protection strength of the vehicle nodes; and the RSU is used to issue and manage the group key, which effectively reduces the loss caused by the intermediate key generation and the group key update. , greatly improving the performance of the system.
  • FIG. 1 is a schematic diagram of a VANETs location privacy protection system architecture and a trust model based on a random encryption period according to an embodiment of the present invention
  • FIG. 2 is a schematic diagram of an encryption group according to an embodiment of the present invention.
  • FIG. 3 is a flowchart of pseudonym generation according to an embodiment of the present invention.
  • the present embodiment is to apply a system and method for VANETs location privacy protection based on a random encryption period to a mobile vehicle node mobile communication process, because the random encryption period can be opened at any time and any place, effectively protecting the vehicle node during the movement process. Location privacy.
  • the VANETs location privacy protection system based on the random encryption period shown in FIG. 1 includes: a third-party trust authority TA, a plurality of roadside units RSU, and a plurality of mobile vehicle units OBU.
  • the third-party trust authority TA is connected to the roadside unit RSU through the network, and the vehicle unit OBU is connected to the roadside unit RSU.
  • the vehicle unit OBU communicates with the third party trust authority TA via the roadside unit RSU.
  • the third-party trust authority TA is completely trusted by default, and the roadside unit RSU is also trusted by default.
  • the vehicle unit OBU is not trusted with each other, and the vehicle unit OBU trusts the roadside unit RSU in one direction.
  • the architecture of the entire system is divided into three layers:
  • the first layer is the Trusted Authority (TA).
  • the third-party trust organization TA is completely trusted by default. It is generally controlled by the government management department. At the same time, the third-party trust organization TA acts as PKG (Public Key Generation) and accepts each. After the vehicle node enters the VANETs, the vehicle node issues a ticket generated according to the real identity ID of the vehicle unit OBU and a first signature obtained by signing the ticket, the ticket being calculated by the third-party trust authority TA selecting the random number.
  • the second layer is the roadside unit RSU, and the roadside unit RSU is also trusted by default.
  • the roadside unit RSU is an infrastructure built on the roadside, and is responsible for network access of the vehicle unit OBU and the third party trust organization TA and the vehicle unit OBU;
  • the group key is changed periodically. If there is a vehicle node that is revoked in the current encryption group, the roadside unit RSU generates a new group key, and sends the new group key to the remaining legal vehicle nodes in the encryption group by using the negotiated shared key. .
  • the third layer is the vehicle unit OBU, which is a communication unit mounted on the vehicle node, and switches between different roadside units RSU as the vehicle node moves, and is responsible for the relationship between the vehicle node and the roadside unit RSU or other vehicle nodes. Communication; messages can be issued to other mobile vehicle units OBU, and different vehicle units OBU can communicate directly in the range of neighbors (300 m), and use the opportunity routing method to communicate outside the range of the neighbors.
  • the vehicle unit OBU periodically issues a safety message containing information such as the kana, current speed, position and road condition of the vehicle node corresponding to the vehicle unit OBU.
  • the vehicle unit OBU registers with the third-party trust institution TA after entering the VANETs, generates a plurality of tokens by cooperation with the legal roadside unit of the ticket; and selects one token to generate the pseudonym and the corresponding private key; the vehicle node
  • the pseudonym is about to expire and no other vehicle node requests to turn on the random encryption cycle
  • the random encryption cycle is turned on, and the pseudonym is replaced with the vehicle node that the pseudonym that received the request is about to expire.
  • the external eavesdropper cannot obtain all the information in the current group, and the two pseudonyms before and after the replacement of the vehicle unit OBU cannot be associated, thereby protecting the security privacy of the system.
  • the random encryption cycle scheme proposed by Wasef A, Shen X et al. and the identity authentication scheme proposed by Misra S and Verma M are used to enhance the practicability of the scheme to replace the pseudonym in the non-fixed area, and the vehicle is ensured.
  • the strength of the node's privacy protection also reduces the computational overhead and communication overhead of the solution.
  • the above system performs a method for VANETs location privacy protection based on a random encryption period, including:
  • Step 1 After entering the VANETs, each vehicle node registers with the third-party trust institution TA, and obtains the ticket issued by the third-party trust organization TA for the vehicle node and the first signature obtained by signing the ticket.
  • the three-party trust authority TA selects a private key generated by the vehicle node calculated by a random number.
  • the vehicle unit OBU registers with the third-party trust organization TA, including:
  • the vehicle node v a submits its own real identity ID, ie ID a , to the third party trust institution TA through the vehicle unit OBU;
  • Third-party trust authority TA chooses a random number
  • G 1 is an additive group, and P is a generator in G 1 ;
  • the third-party trust authority TA signs the ticket ⁇ a with its own private key S TA to obtain the first signature SIG( ⁇ a , S TA );
  • mapping of the public key of the vehicle node v a and the real identity ID ⁇ ⁇ a , ID a > is stored in the database of the third-party trust authority TA, and the public key of the vehicle node v a is the ticket ⁇ a and the first signature SIG ( ⁇ a , S TA ), the private key S a of the vehicle node v a , that is, ⁇ a , SIG( ⁇ a , S TA ), Sa a > stored in the onboard unit OBU of the vehicle node v a .
  • Step 2 vehicle unit OBU node v a vehicle by ⁇ a valid ticket and the roadside units cooperate to generate a plurality of tokens R i; and select a token Generating a pseudonym and using the random number obtained from the roadside unit R i Generate the corresponding private key;
  • the vehicle node generates a plurality of tokens by cooperation with a legal roadside unit of the ticket, including:
  • Step 2-3 The vehicle unit OBU of the vehicle node v a decrypts the fourth message C' and verifies the third signature If the third signature is legal, the third message M is stored, otherwise the third message M is discarded.
  • the process of generating pseudonyms and corresponding private keys includes:
  • Step 2-4 Randomly select the token And corresponding random numbers
  • Step 2-5 Calculate As the token of the vehicle node v a The corresponding private key, using the selected token And its effective time, the token Listen to the corresponding third signature
  • Step 3 When the pseudonym of the vehicle node is about to expire and no other vehicle node requests to open the random encryption period, the random encryption period is started, and the vehicle node that has received the pseudonym of the request is about to expire to replace the pseudonym;
  • Step 3-1 The vehicle unit OBU of the vehicle node v a broadcasts a request message for turning on the random encryption period to the neighboring vehicle node under the same roadside unit RSU when the pseudonym is about to expire. And encrypted with a group key, the request message msg contains a pseudonym Request request REP and random encryption duration T REP for random encryption cycle;
  • Step 3-2 The vehicle unit OBU of the remaining legal vehicle nodes receiving the request message msg decrypts the request message with the current group key, and performs any message sent by itself with the group key in the random encryption duration T REP . Encrypting, starting a random encryption period, defining a set of vehicle nodes v a and the remaining legitimate vehicle nodes that receive the request message as an encryption group, as shown in FIG. 2;
  • Step 3-3 The remaining legal vehicle nodes in the encryption group whose pseudonyms are about to expire are selected to cooperate with the vehicle node v a and return a response to the vehicle node v a ;
  • Step 3-4 The cooperative vehicle nodes change the pseudonym together with the driving trajectory or speed; the cooperative vehicle node can replace the pseudonym together to confuse the attacker and achieve the purpose of protecting the location privacy;
  • Step 3-5 Before the end of the random encryption duration T REP , determine whether the cooperative vehicle node in the encryption group satisfies the condition for terminating the random encryption period. If yes, the random encryption period is ended. If not, the vehicle node v a broadcasts. Another request message that initiates a random encryption cycle is used to enable a new random encryption cycle to protect its location privacy.
  • the vehicle node in the encryption group whose pseudonym is about to expire is replaced with a pseudonym and a response is returned to the vehicle node v a , the vehicle node v a sends a termination request, and the remaining vehicle nodes that receive the termination request stop encrypting.
  • the condition for terminating the random encryption period includes:
  • the eavesdropper does not have the current group key, the information in the security message cannot be obtained, and the location and pseudonym of the vehicle node cannot be obtained. After a period of time, because the vehicle node has changed the trajectory or speed of the vehicle, the external attacker cannot associate the pseudonym after the replacement of the vehicle node with the previous pseudonym according to the previous prediction, and the trajectory of the vehicle node cannot be learned.
  • the purpose of protecting location privacy For the members of the group, since all the members of the legal group have the current group key, they can decrypt the security information and obtain the current road condition information, and do not affect the normal traffic of the members in the group.
  • the random encryption period can be turned on at any time and at any place, which improves the location privacy intensity better than the Mix zone in the previous fixed area.
  • Step 4 The roadside unit RSU periodically changes the group key. If there is a vehicle node that is revoked in the current encryption group, the roadside unit RSU generates a new group key, and sends the new group key to the negotiated shared key. Encrypt the remaining legal vehicle nodes in the group
  • Step 4-1 The roadside unit RSU periodically changes the group key: when there is no vehicle node in the area of the roadside unit RSU, if a new vehicle node seeks the group key, the roadside unit RSU generates a new group secret. Key and issue it to its vehicle unit OBU, the previous group key is invalid;
  • Step 4-2 If the vehicle node finds that the neighboring vehicle node has an illegal behavior, the pseudonym of the illegal neighboring vehicle node is submitted to the roadside unit RSU, and the roadside unit RSU finds the corresponding ticket by the pseudonym, and submits the ticket to the third party trust center.
  • the third-party trust center TA detects the true identity of the vehicle node according to the ticket, and performs an undo operation on the illegal vehicle node; then the third-party trust center TA sends the cancelled vehicle node ticket to all roadside units RSU, and then Broadcast to all vehicle nodes by the roadside unit RSU;
  • Step 4-3 All roadside units that have issued a group key to the revoked vehicle node detect whether the current group key has been updated. If the current group key has not been updated, the group key needs to be Cancel and issue a new group key k' g to the remaining legal vehicle nodes; the roadside unit RSU generates a new group key, which is encrypted with the shared key previously negotiated with the vehicle unit OBU and sent to the legal vehicle node respectively. The update of the group key is completed; the revoked vehicle unit OBU is unable to seek a new group key from the roadside unit RSU or other legitimate vehicle unit OBU because of its identity.

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  • Computer Networks & Wireless Communication (AREA)
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Abstract

本发明提供一种基于随机加密周期的VANETs位置隐私保护的系统及方法，每个车辆节点在进入VANETs后其车辆单元向第三方信任机构注册，得到第三方信任机构颁发的票据及对该票据签名得到的第一签名；车辆单元通过与票据合法的路边单元合作生成多个令牌并选择一个令牌生成假名及相应的私钥；车辆节点的假名即将过期且无其他车辆节点请求开启随机加密周期时，开启随机加密周期，接收到该请求的假名即将过期的车辆节点合作更换假名；路边单元定期更改组密钥，若当前加密组中存在被撤销的车辆节点，路边单元生成新的组密钥，并将新的组密钥发送给加密组内其余合法车辆节点。本发明有效提高车辆节点的隐私保护强度，减少中间密钥生成和组密钥更新所产生的损耗。

Description

基于随机加密周期的VANETs位置隐私保护的系统及方法 技术领域
本发明属于网络安全技术领域，特别涉及一种基于随机加密周期的VANETs位置隐私保护的系统及方法。
背景技术
近年来，移动自组织网络的应用日益广泛，作为移动自组织网络在智能交通领域的应用，车辆自组织网络因其巨大的潜力而逐渐成为研究的热点。车辆自组织网络以车辆为基本信息单元，利用无线接入技术等将车辆、路边基础设施等道路实体与交通网络连接，形成智能网络体系，它允许车辆在高速行进过程中与其他车辆通信(vehicle-to-vehicle，简称V2V)或与路边基础设施直接通信(vehicle-to-infrastructure，简称V2I)。根据专用短距离通信技术(DSRC)，任意配备车载单元(OBU)的车辆会定时广播位置，当前时间，方向，速度，交通事件等常规交通信息，为用户提供实时路况信息和邻居车辆节点的信息等用以规避交通风险，对事故现场进行预警，提前预防潜在的交通隐患，解决行车安全问题。车辆自组网还可以为用户提供点对点(Peer to Peer，P2P)的服务，对Internet的访问服务等增值业务，以实现车辆间协同安全驾驶、交通决策支持、交通智能调度、交通收费服务、实时交通信息发布、无线增值信息服务等功能。
VANETs在交通安全和交通效率的提高方面发挥着重要作用，但因其需要定时广播安全信息，外部窃听者极易根据获取到的位置，假名信息获得车辆节点的运动轨迹，并对其之后的行进路线进行预测，这造成了车辆位置隐私的泄露，极大地危害了车辆节点的隐私安全。因此在VANETs中必须要实现对车辆节点隐私的保护。隐私保护主要与保护驾驶员的真实身份和位置信息有关。任何外部窃听者都不应该获取驾驶员的真实身份，也不能对特定的车辆进行追踪。
更换假名是对车辆位置隐私保护的一种方法。建立Mix zone是VANETs中更换假名的一种常见方案，多个车辆在一个区域内同时更换假名，以混淆新旧假名的关联。但在常规Mix zone方案中车辆节点往往只能在固定的区域内更换假名，这往往给车辆节点带来了极大地不便，若是车辆节点不能及时在Mix zone区域内更换假名，便不能很好的保护自己的隐私。基于随机加密周期的位置隐私保护方案能随时建立加密的Mix zone区域，大大提升了隐私强度。但组密钥的协商和更新需要较大的开销。
发明内容
针对现有技术存在的不足，本发明提供一种基于随机加密周期的VANETs位置隐私保护 的系统及方法。
本发明的技术方案如下：
基于随机加密周期的VANETs位置隐私保护的方法，包括：
每个车辆节点在进入VANETs后其车辆单元OBU向第三方信任机构TA注册，得到第三方信任机构TA为车辆节点颁发的票据及对该票据签名得到的第一签名，该票据由第三方信任机构TA选择随机数所计算出的车辆节点的私钥生成；
车辆单元OBU通过与票据合法的路边单元合作生成多个令牌；并从中选择一个令牌生成假名及相应的私钥；
车辆节点的假名即将过期且无其他车辆节点请求开启随机加密周期时，开启随机加密周期，接收到该请求的假名即将过期的车辆节点合作更换假名；
路边单元RSU定期更改组密钥，若当前加密组中存在被撤销的车辆节点，路边单元RSU生成新的组密钥，并用协商的共享密钥将新的组密钥发送给加密组内其余合法车辆节点。
所述每个车辆节点在进入VANETs后其车辆单元OBU向第三方信任机构TA注册，具体包括：
车辆节点通过车辆单元OBU向第三方信任机构TA提交自己的真实身份ID；
第三方信任机构TA选择一个随机数计算车辆节点的私钥S a；
第三方信任机构TA为车辆节点颁发票据δ a并将该票据作为车辆节点的公钥；δ a＝S aP∈G 1；G 1是一个加法群，P是G 1内的一个生成元；
第三方信任机构TA用自己的私钥对票据签名得到第一签名；
将车辆节点的公钥和真实身份ID的映射存入第三方信任机构TA的数据库中，将车辆节点v a的公钥、第一签名、车辆节点的私钥S a存入车辆节点的车载单元OBU中。
所述车辆节点通过与票据合法的路边单元合作生成多个令牌，包括：
车辆节点的车辆单元OBU生成用作与路边单元RSU之间的共享密钥的对称密钥，将对称密钥与票据以及第一签名组合生成第一消息，车辆单元OBU对第一消息签名生成第二签名，车辆单元OBU将第一消息用路边单元RSU的公钥加密生成第二消息，将第二消息和第二签名发送给路边单元；
路边单元解密第二消息，路边单元计算票据合法的车辆节点的令牌，并生成包含路边单元的私钥、令牌及其有效时间的第三签名，选择当前组密钥，利用令牌及其有效时间、第三签名、组密钥、随机数、路边单元RSU的证书，生成第三消息，将令牌和票据存入数据库中， 用共享密钥加密第三消息生成第四消息发送给车辆节点；
车辆节点的车辆单元OBU解密第四消息并验证第三签名，若第三签名合法，则存储第三消息，否则将第三消息丢弃。
所述路边单元计算票据合法的车辆节点的令牌之前，用第二消息中的票据验证第二签名，用第三方信任机构TA的公钥验证第一签名，来验证票据是否合法：若第一签名、第二签名均合法，则票据合法，否则，票据不合法，路边单元拒绝与车辆节点合作。
所述车辆节点的假名即将过期且无其他车辆节点请求开启随机加密周期时，开启随机加密周期，接收到该请求的假名即将过期的车辆节点合作更换假名，包括：
车辆节点v a的车辆单元OBU在假名即将过期时，向相同路边单元RSU下的邻居车辆节点广播开启随机加密周期的请求消息并用组密钥加密，该请求消息中包含假名、开启随机加密周期的请求及随机加密时长；
接收到该请求消息的其余合法车辆节点的车辆单元OBU用当前组密钥解密该请求消息，并在随机加密时长内用组密钥对自己发出的任意一条消息进行加密，启动随机加密周期，将车辆节点v a与这些接收到该请求消息的其余合法车辆节点的集合定义为一个加密组；
加密组中假名即将过期的其余合法车辆节点选择与车辆节点v a合作并向车辆节点v a返回应答；
合作的车辆节点一起更改假名，以及行驶轨迹或速度；
在随机加密时长结束前，判断加密组中合作的车辆节点是否满足终止随机加密周期的条件，如满足，则结束随机加密周期，如不满足，则车辆节点v a广播另一个开启随机加密周期的请求消息来开启新的随机加密周期以保障自己的位置隐私得到保护；
随机加密周期结束时加密组内假名即将到期的车辆节点更换假名并给车辆节点v a返回一个应答，车辆节点v a则发送终止请求，其余收到终止请求的车辆节点停止加密。
所述终止随机加密周期的条件，包括：
①加密组中更改假名的车辆节点的数量≥2；
②更改假名的车辆节点已改变自己的速度或轨迹。
所述路边单元RSU定期更改组密钥，若当前加密组中存在被撤销的车辆节点，路边单元RSU生成新的组密钥，并用协商的共享密钥将新的组密钥发送给加密组内其余合法车辆节点，包括：
路边单元RSU定期更改组密钥：当该路边单元RSU的区域内不存在车辆节点后，若有 新的车辆节点寻求组密钥，路边单元RSU生成新的组密钥并将其颁发给其车辆单元OBU，之前的组密钥作废；
车辆节点若发现邻居车辆节点存在非法行为，将非法邻居车辆节点的假名提交给路边单元RSU，路边单元RSU由假名查找出对应票据，并将票据提交给第三方信任中心TA，第三方信任中心TA根据票据查出车辆节点的真实身份，并对非法的车辆节点进行撤销操作；随后第三方信任中心TA将被撤销的车辆节点的票据发送给全部路边单元RSU，再由路边单元RSU广播给全部车辆节点；
所有向被撤销的车辆节点颁发过组密钥的路边单元检测当前的组密钥是否已经进行过更新，若当前组密钥未进行过更新，则此组密钥需要被撤销，并向其余的合法车辆节点颁发新的组密钥；路边单元RSU生成新的组密钥，用之前与车辆单元OBU协商的共享密钥加密，分别发送给合法的车辆节点，完成组密钥的更新。
一种基于随机加密周期的VANETs位置隐私保护的系统，包括：
第三方信任机构TA：接受每个车辆节点在进入VANETs后的注册，为车辆节点颁发票据及对该票据签名得到的第一签名，该票据由第三方信任机构TA选择随机数所计算出的车辆节点的私钥生成；
车辆单元OBU：为车辆节点在进入VANETs后向第三方信任机构TA注册，通过与票据合法的路边单元合作生成多个令牌；并从中选择一个令牌生成假名及相应的私钥；车辆节点的假名即将过期且无其他车辆节点请求开启随机加密周期时，开启随机加密周期，与接收到该请求的假名即将过期的车辆节点合作更换假名；
路边单元RSU：定期更改组密钥，若当前加密组中存在被撤销的车辆节点，路边单元RSU生成新的组密钥，并用协商的共享密钥将新的组密钥发送给加密组内其余合法车辆节点。
有益效果：
本发明将基于随机加密周期的位置隐私保护方案，应用在VANETs中车辆节点的位置隐私保护中，使用了随机加密周期方案，车辆节点不需要在固定区域内更改假名，而是可以根据需求随机的开启加密周期与周边节点相互配合，有效地提高了车辆节点的隐私保护强度；并且使用了RSU对组密钥进行颁发与管理，有效地减少了中间密钥生成和组密钥更新所产生的损耗，极大地提高了系统的性能。
附图说明
图1为本发明具体实施方式的基于随机加密周期的VANETs位置隐私保护系统架构及信任模型图；
图2为本发明具体实施方式的加密组示意图；
图3为本发明具体实施方式的假名生成流程图。
具体实施方式
下面结合附图对本发明的具体实施方式做详细说明。
本实施方式是将基于随机加密周期的VANETs位置隐私保护的系统及方法应用于移动车辆节点移动通信过程中，因为随机加密周期可以在任何时间任何地点开启，有效保护了车辆节点在移动过程中的位置隐私。
如图1所示的基于随机加密周期的VANETs位置隐私保护系统，包括：第三方信任机构TA、若干个路边单元RSU及若干个移动的车辆单元OBU。
第三方信任机构TA通过网络与路边单元RSU连接，车辆单元OBU与路边单元RSU相连。车辆单元OBU与第三方信任机构TA通过路边单元RSU进行通信。第三方信任机构TA默认完全可信，路边单元RSU也默认可信，车辆单元OBU之间互不可信，车辆单元OBU单向信任路边单元RSU。
整个系统的架构分为三层：
第一层为第三方信任机构TA(TrustedAuthority，TA)，第三方信任机构TA默认完全可信，一般由政府管理部门控制，同时，第三方信任机构TA作为PKG(Public Key Generation)，接受每个车辆节点在进入VANETs后的注册，为车辆节点颁发根据车辆单元OBU的真实身份ID生成的票据及对该票据签名得到的第一签名，该票据由第三方信任机构TA选择随机数所计算出的车辆节点的私钥生成；系统中仅第三方信任机构TA能够获悉车辆节点的真实身份ID，也只有三方信任机构TA能对系统中的车辆单元OBU进行撤销操作。
第二层为路边单元RSU，路边单元RSU同样默认可信，路边单元RSU是建立在路边的基础设施，负责车辆单元OBU与第三方信任机构TA以及车辆单元OBU的网络接入；定期更改组密钥，若当前加密组中存在被撤销的车辆节点，路边单元RSU生成新的组密钥，并用协商的共享密钥将新的组密钥发送给加密组内其余合法车辆节点。
第三层为车辆单元OBU，是装载在车辆节点上的通信单元，随车辆节点移动过程中在不同的路边单元RSU之间切换移动，负责车辆节点与路边单元RSU或其它车辆节点间的通信；可以向其他移动的车辆单元OBU发布消息，不同车辆单元OBU在邻居范围内(300m)能够直接通信，邻居范围外使用机会路由方式进行通信。车辆单元OBU会定期发布安全消息，包含了车辆单元OBU所对应的车辆节点的假名、当前速度、位置和路况等信息。车辆单元OBU为车辆节点在进入VANETs后向第三方信任机构TA注册，通过与票据合法的路边单元合作生成多个令牌；并从中选择一个令牌生成假名及相应的私钥；车辆节点的假名即将过期且无其他车辆节点请求开启随机加密周期时，开启随机加密周期，与接收到该请求的假名即将过 期的车辆节点合作更换假名。在加密时期的有效时间内，外部窃听者无法获得当前组内的全部信息，也就无法将车辆单元OBU更换的前后两个假名进行关联，保护了系统的安全隐私。
为方便后续描述，给出如表1所示的标识及说明。
表1相关标识及说明
Figure PCTCN2018087564-appb-000001
在本实施方式中运用Wasef A、Shen X等人提出的随机加密周期方案和Misra S、Verma M等人提出的身份认证方案，增强了方案在非固定区域内更换假名的实用性，确保了车辆节点的隐私保护的强度，同时也降低了方案的计算开销和通信开销。
上述系统进行基于随机加密周期的VANETs位置隐私保护的方法，包括：
步骤1：每个车辆节点在进入VANETs后其车辆单元OBU向第三方信任机构TA注册，得到第三方信任机构TA为车辆节点颁发的票据及对该票据签名得到的第一签名，该票据由 第三方信任机构TA选择一个随机数所计算出的车辆节点的私钥生成。
所述每个车辆节点在进入VANETs后其车辆单元OBU向第三方信任机构TA注册，具体包括：
车辆节点v a通过车辆单元OBU向第三方信任机构TA提交自己的真实身份ID，即ID a；
第三方信任机构TA选择一个随机数
Figure PCTCN2018087564-appb-000002
计算车辆节点v a的私钥S a＝H 2(ID a，rnd)∈{0，1} n，其中H 2表示哈希函数，{0，1} n是一个乘法群。
第三方信任机构TA为车辆节点v a颁发票据δ a＝S aP∈G 1，将该票据作为车辆节点v a的公钥；G 1是一个加法群，P是G 1内的一个生成元；
第三方信任机构TA用自己的私钥S TA对票据δ a签名，得到第一签名SIG(δ a，S TA)；
将车辆节点v a的公钥和真实身份ID的映射<δ a，ID a>存入第三方信任机构TA的数据库中，将车辆节点v a的公钥即票据δ a、第一签名SIG(δ a，S TA)、车辆节点v a的私钥S a，即<δ a，SIG(δ a，S TA)，S a>存入车辆节点v a的车载单元OBU中。
步骤2：车辆节点v a的车辆单元OBU通过δ a与票据合法的路边单元R i合作生成多个令牌；并从中选择一个令牌
Figure PCTCN2018087564-appb-000003
生成假名及利用从路边单元R i处获取的随机数
Figure PCTCN2018087564-appb-000004
生成相应的私钥；
所述车辆节点通过与票据合法的路边单元合作生成多个令牌，包括：
步骤2-1：车辆节点v a的车辆单元OBU生成用作与路边单元RSU之间的共享密钥的对称密钥k a，将对称密钥k a与票据δ a以及第一签名SIG(δ a，S TA)组合生成第一消息Δ a＝<k a，δ a，SIG(δ a，S TA)>，车辆单元OBU对第一消息Δ a签名生成第二签名SIG(Δ a；S a)，车辆单元OBU将第一消息Δ a用路边单元R i的公钥加密生成第二消息C，将第二消息C和第二签名SIG(Δ a；S a)发送给路边单元R i；
步骤2-2：路边单元R i用私钥
Figure PCTCN2018087564-appb-000005
解密第二消息C，用第二消息C中的票据δ a验证第二签名SIG(Δ a；S a)，用第三方信任机构TA的公钥P TA验证第一签名SIG(δ a，S TA)，来验证票据δ a是否合法：若第一签名SIG(δ a，S TA)、第二签名SIG(Δ a；S a)均合法，则票据δ a合法，否则，票据δ a不合法，路边单元R i拒绝与车辆节点v a合作；路边单元R i选择随机数
Figure PCTCN2018087564-appb-000006
计算票据合法的车辆节点的令牌T (a，i)＝γ (a，i)δ a，并生成包含路边单元R i的私钥
Figure PCTCN2018087564-appb-000007
令牌T (a，i)及其有效时间t (a，i)的第三签名
Figure PCTCN2018087564-appb-000008
选择当前组密钥k g，利用令牌T (a，i) 及其有效时间t (a，i)、第三签名
Figure PCTCN2018087564-appb-000009
组密钥k g、随机数γ (a，i)、路边单元路边单元R i从第三方信任机构TA处获取的证书
Figure PCTCN2018087564-appb-000010
生成第三消息
Figure PCTCN2018087564-appb-000011
将令牌T (a，i)和票据δ a之间的映射存入数据库中，用共享密钥k a加密第三消息M生成第四消息C′发送给车辆节点v a；
步骤2-3：车辆节点v a的车辆单元OBU解密第四消息C′并验证第三签名
Figure PCTCN2018087564-appb-000012
若第三签名合法，则存储第三消息M，否则将第三消息M丢弃。
生成假名及相应的私钥的过程包括：
步骤2-4：随机选取令牌
Figure PCTCN2018087564-appb-000013
和对应随机数
Figure PCTCN2018087564-appb-000014
步骤2-5：计算
Figure PCTCN2018087564-appb-000015
作为车辆节点v a的令牌
Figure PCTCN2018087564-appb-000016
所对应的私钥，利用选取的令牌
Figure PCTCN2018087564-appb-000017
及其有效时间、该令牌
Figure PCTCN2018087564-appb-000018
听对应的第三签名
Figure PCTCN2018087564-appb-000019
车辆节点v a从第三方信任机构TA处获取的证书
Figure PCTCN2018087564-appb-000020
生成车辆节点v a的假名
Figure PCTCN2018087564-appb-000021
Figure PCTCN2018087564-appb-000022
颁发的令牌
Figure PCTCN2018087564-appb-000023
作为车辆节点v a的公钥。
以上为如图3所示的假名生成过程，假名生成后，车辆节点为了自己的位置隐私，常常需要更换假名来混淆外部攻击者。
步骤3：车辆节点的假名即将过期且无其他车辆节点请求开启随机加密周期时，开启随机加密周期，接收到该请求的假名即将过期的车辆节点合作更换假名；
步骤3-1：车辆节点v a的车辆单元OBU在假名即将过期时，向相同路边单元RSU下的邻居车辆节点广播开启随机加密周期的请求消息
Figure PCTCN2018087564-appb-000024
并用组密钥加密，该请求消息msg中包含假名
Figure PCTCN2018087564-appb-000025
开启随机加密周期的请求request REP及随机加密时长T REP；
步骤3-2：接收到该请求消息msg的其余合法车辆节点的车辆单元OBU用当前组密钥解密该请求消息，并在随机加密时长T REP内用组密钥对自己发出的任意一条消息进行加密，启动随机加密周期，将车辆节点v a与这些接收到该请求消息的其余合法车辆节点的集合定义为一个加密组，如图2所示；
步骤3-3：加密组中假名即将过期的其余合法车辆节点选择与车辆节点v a合作并向车辆节点v a返回应答；
步骤3-4：合作的车辆节点一起更改假名，以及行驶轨迹或速度；合作的车辆节点一起更换假名可以混淆攻击者，达到保护位置隐私的目的；
步骤3-5：在随机加密时长T REP结束前，判断加密组中合作的车辆节点是否满足终止随机加密周期的条件，如满足，则结束随机加密周期，如不满足，则车辆节点v a广播另一个开启随机加密周期的请求消息来开启新的随机加密周期以保障自己的位置隐私得到保护；
随机加密周期结束时加密组内假名即将到期的车辆节点更换假名并给车辆节点v a返回一个应答，车辆节点v a则发送终止请求，其余收到终止请求的车辆节点停止加密。
所述终止随机加密周期的条件，包括：
①加密组中更改假名的车辆节点的数量≥2；
②更改假名的车辆节点已改变自己的速度或轨迹。
在外部攻击者角度来看，组内全部成员均使用组密钥对信息加密，窃听者因为没有当前组密钥，所以无法获知安全消息内的信息，也就无法获得车辆结点的位置和假名，在一段时间后，因为车辆节点已经更换了运动轨迹或速度，外部攻击者无法根据之前的预判将车辆节点更换后的假名与之前假名进行关联，也就无法获悉车辆节点的运动轨迹，达到了保护位置隐私的目的。但对于组内成员来说，因为全部合法的组内成员均拥有当前组密钥，故其可以解密安全信息，获得当前路况信息，并不影响组内成员的正常交通。对于车辆结点来说，随机加密周期可以在任意时间，任意地点进行开启，相较于以前固定区域的Mix zone来说，更好的提高了位置隐私强度。
步骤4：路边单元RSU定期更改组密钥，若当前加密组中存在被撤销的车辆节点，路边单元RSU生成新的组密钥，并用协商的共享密钥将新的组密钥发送给加密组内其余合法车辆节点
步骤4-1：路边单元RSU定期更改组密钥：当该路边单元RSU的区域内不存在车辆节点后，若有新的车辆节点寻求组密钥，路边单元RSU生成新的组密钥并将其颁发给其车辆单元OBU，之前的组密钥作废；
步骤4-2：车辆节点若发现邻居车辆节点存在非法行为，将非法邻居车辆节点的假名提交给路边单元RSU，路边单元RSU由假名查找出对应票据，并将票据提交给第三方信任中心TA，第三方信任中心TA根据票据查出车辆节点的真实身份，并对非法的车辆节点进行撤销操作；随后第三方信任中心TA将被撤销的车辆节点的票据发送给全部路边单元RSU，再由路边单元RSU广播给全部车辆节点；
步骤4-3：所有向被撤销的车辆节点颁发过组密钥的路边单元检测当前的组密钥是否已经 进行过更新，若当前组密钥未进行过更新，则此组密钥需要被撤销，并向其余的合法车辆节点颁发新的组密钥k′ g；路边单元RSU生成新的组密钥，用之前与车辆单元OBU协商的共享密钥加密，分别发送给合法的车辆节点，完成组密钥的更新；被撤销的车辆单元OBU因为身份被公布，故其无法向路边单元RSU或者其他合法的车辆单元OBU寻求新的组密钥。

Claims (8)

  1. 基于随机加密周期的VANETs位置隐私保护的方法，其特征在于，包括：
    每个车辆节点在进入VANETs后其车辆单元OBU向第三方信任机构TA注册，得到第三方信任机构TA为车辆节点颁发的票据及对该票据签名得到的第一签名，该票据由第三方信任机构TA选择随机数所计算出的车辆节点的私钥生成；
    车辆单元OBU通过与票据合法的路边单元合作生成多个令牌；并从中选择一个令牌生成假名及相应的私钥；
    车辆节点的假名即将过期且无其他车辆节点请求开启随机加密周期时，开启随机加密周期，接收到该请求的假名即将过期的车辆节点合作更换假名；
    路边单元RSU定期更改组密钥，若当前加密组中存在被撤销的车辆节点，路边单元RSU生成新的组密钥，并用协商的共享密钥将新的组密钥发送给加密组内其余合法车辆节点。
  2. 根据权利要求1所述的方法，其特征在于，所述每个车辆节点在进入VANETs后其车辆单元OBU向第三方信任机构TA注册，具体包括：
    车辆节点通过车辆单元OBU向第三方信任机构TA提交自己的真实身份ID；
    第三方信任机构TA选择一个随机数计算车辆节点的私钥S a；
    第三方信任机构TA为车辆节点颁发票据δ a并将该票据作为车辆节点的公钥；δ a＝S aP∈G 1；G 1是一个加法群，P是G 1内的一个生成元；
    第三方信任机构TA用自己的私钥对票据签名得到第一签名；
    将车辆节点的公钥和真实身份ID的映射存入第三方信任机构TA的数据库中，将车辆节点v a的公钥、第一签名、车辆节点的私钥S a存入车辆节点的车载单元OBU中。
  3. 根据权利要求1所述的方法，其特征在于，所述车辆节点通过与票据合法的路边单元合作生成多个令牌，包括：
    车辆节点的车辆单元OBU生成用作与路边单元RSU之间的共享密钥的对称密钥，将对称密钥与票据以及第一签名组合生成第一消息，车辆单元OBU对第一消息签名生成第二签名，车辆单元OBU将第一消息用路边单元RSU的公钥加密生成第二消息，将第二消息和第二签名发送给路边单元；
    路边单元解密第二消息，路边单元计算票据合法的车辆节点的令牌，并生成包含路边单元的私钥、令牌及其有效时间的第三签名，选择当前组密钥，利用令牌及其有效时间、第三签名、组密钥、随机数、路边单元RSU的证书，生成第三消息，将令牌和票据存入数据库中， 用共享密钥加密第三消息生成第四消息发送给车辆节点；
    车辆节点的车辆单元OBU解密第四消息并验证第三签名，若第三签名合法，则存储第三消息，否则将第三消息丢弃。
  4. 根据权利要求3所述的方法，其特征在于，所述路边单元计算票据合法的车辆节点的令牌之前，用第二消息中的票据验证第二签名，用第三方信任机构TA的公钥验证第一签名，来验证票据是否合法：若第一签名、第二签名均合法，则票据合法，否则，票据不合法，路边单元拒绝与车辆节点合作。
  5. 根据权利要求1所述的方法，其特征在于，所述车辆节点的假名即将过期且无其他车辆节点请求开启随机加密周期时，开启随机加密周期，接收到该请求的假名即将过期的车辆节点合作更换假名，包括：
    车辆节点v a的车辆单元OBU在假名即将过期时，向相同路边单元RSU下的邻居车辆节点广播开启随机加密周期的请求消息并用组密钥加密，该请求消息中包含假名、开启随机加密周期的请求及随机加密时长；
    接收到该请求消息的其余合法车辆节点的车辆单元OBU用当前组密钥解密该请求消息，并在随机加密时长内用组密钥对自己发出的任意一条消息进行加密，启动随机加密周期，将车辆节点v a与这些接收到该请求消息的其余合法车辆节点的集合定义为一个加密组；
    加密组中假名即将过期的其余合法车辆节点选择与车辆节点v a合作并向车辆节点v a返回应答；
    合作的车辆节点一起更改假名，以及行驶轨迹或速度；
    在随机加密时长结束前，判断加密组中合作的车辆节点是否满足终止随机加密周期的条件，如满足，则结束随机加密周期，如不满足，则车辆节点v a广播另一个开启随机加密周期的请求消息来开启新的随机加密周期以保障自己的位置隐私得到保护；
    随机加密周期结束时加密组内假名即将到期的车辆节点更换假名并给车辆节点v a返回一个应答，车辆节点v a则发送终止请求，其余收到终止请求的车辆节点停止加密。
  6. 根据权利要求5所述的方法，其特征在于，所述终止随机加密周期的条件，包括：
    ①加密组中更改假名的车辆节点的数量≥2；
    ②更改假名的车辆节点已改变自己的速度或轨迹。
  7. 根据权利要求1所述的方法，其特征在于，所述路边单元RSU定期更改组密钥，若当前加密组中存在被撤销的车辆节点，路边单元RSU生成新的组密钥，并用协商的共享密钥将新的组密钥发送给加密组内其余合法车辆节点，包括：
    路边单元RSU定期更改组密钥：当该路边单元RSU的区域内不存在车辆节点后，若有新的车辆节点寻求组密钥，路边单元RSU生成新的组密钥并将其颁发给其车辆单元OBU，之前的组密钥作废；
    车辆节点若发现邻居车辆节点存在非法行为，将非法邻居车辆节点的假名提交给路边单元RSU，路边单元RSU由假名查找出对应票据，并将票据提交给第三方信任中心TA，第三方信任中心TA根据票据查出车辆节点的真实身份，并对非法的车辆节点进行撤销操作；随后第三方信任中心TA将被撤销的车辆节点的票据发送给全部路边单元RSU，再由路边单元RSU广播给全部车辆节点；
    所有向被撤销的车辆节点颁发过组密钥的路边单元检测当前的组密钥是否已经进行过更新，若当前组密钥未进行过更新，则此组密钥需要被撤销，并向其余的合法车辆节点颁发新的组密钥；路边单元RSU生成新的组密钥，用之前与车辆单元OBU协商的共享密钥加密，分别发送给合法的车辆节点，完成组密钥的更新。
  8. 一种基于随机加密周期的VANETs位置隐私保护的系统，其特征在于，包括：
    第三方信任机构TA：接受每个车辆节点在进入VANETs后的注册，为车辆节点颁发票据及对该票据签名得到的第一签名，该票据由第三方信任机构TA选择随机数所计算出的车辆节点的私钥生成；
    车辆单元OBU：为车辆节点在进入VANETs后向第三方信任机构TA注册，通过与票据合法的路边单元合作生成多个令牌；并从中选择一个令牌生成假名及相应的私钥；车辆节点的假名即将过期且无其他车辆节点请求开启随机加密周期时，开启随机加密周期，与接收到该请求的假名即将过期的车辆节点合作更换假名；
    路边单元RSU：定期更改组密钥，若当前加密组中存在被撤销的车辆节点，路边单元RSU生成新的组密钥，并用协商的共享密钥将新的组密钥发送给加密组内其余合法车辆节点。
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