WO2021244589A1 - 智能钥匙、防中继攻击方法及系统 - Google Patents
智能钥匙、防中继攻击方法及系统 Download PDFInfo
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- WO2021244589A1 WO2021244589A1 PCT/CN2021/098014 CN2021098014W WO2021244589A1 WO 2021244589 A1 WO2021244589 A1 WO 2021244589A1 CN 2021098014 W CN2021098014 W CN 2021098014W WO 2021244589 A1 WO2021244589 A1 WO 2021244589A1
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B60—VEHICLES IN GENERAL
- B60R—VEHICLES, VEHICLE FITTINGS, OR VEHICLE PARTS, NOT OTHERWISE PROVIDED FOR
- B60R25/00—Fittings or systems for preventing or indicating unauthorised use or theft of vehicles
- B60R25/20—Means to switch the anti-theft system on or off
- B60R25/24—Means to switch the anti-theft system on or off using electronic identifiers containing a code not memorised by the user
- B60R25/248—Electronic key extraction prevention
Definitions
- the present invention relates to the technical field of wireless control, in particular to an intelligent key, a method and system for preventing relay attacks.
- the existing smart key system PEPS Passive Entry & Passive Start
- keyless system and keyless start system is mainly composed of in-vehicle communication and control systems and the smart key RFID (Radio Frequency Identification) carried by users for legal identification. Also known as radio frequency identification, SmartKey or Fob composition.
- RFID Radio Frequency Identification
- SmartKey Radio Frequency Identification
- the user When the user carries the smart key into the detection range of the vehicle, the user only needs to directly pull the outer opening handle on the door or press the unlock button on the door handle, and the vehicle will actively identify and verify the legitimacy of the smart key. If the authentication is passed, the vehicle When the user enters the car, he only needs to press the start button, and the vehicle will actively identify and authenticate the smart key inside the vehicle.
- the vehicle will release the engine anti-theft and other anti-theft devices, such as electronic With steering shaft lock, the user can directly start or power on the vehicle.
- the advantage of a vehicle equipped with a smart key system is that it eliminates the cumbersome operation of finding and operating keys when the user uses the vehicle, and improves the convenience of using the vehicle.
- the smart key system has become the standard configuration of mid-to-high-end cars, and there is a trend of popularization in mid- and low-end cars.
- the smart key system has experienced 10 years of development, and the technology has matured and been widely used.
- the RFID device of the smart key system the smart key has existed in diversified forms, such as card-type smart key, pendant smart key, watch smart key, remote control smart key, and Bluetooth-based key car key.
- the existing conventional keyless start system mainly uses the wireless signal interaction between the smart key and the car to realize the control of the vehicle.
- the wireless signal for example, LF-RF (low frequency-radio frequency) signal, BLE (Bluetooth) signal or Zigbee Bee) signal and so on.
- LF-RF low frequency-radio frequency
- BLE Bluetooth
- Zigbee Bee Zigbee Bee
- the purpose of the present invention is to provide a smart key, an anti-relay attack method and system, so as to solve the problem that the existing PEPS system is susceptible to relay attacks.
- an anti-relay attack method for a keyless start system including:
- the vehicle end agrees on the communication key with the key end by way of key agreement
- the vehicle terminal After establishing a wireless connection with the key terminal, the vehicle terminal sends a control code in cipher text to the key terminal to trigger the key terminal to use the communication key to perform the control code in the cipher text. Parse to obtain the plaintext of the control code, and use the plaintext to control the strength of the transmitted wireless signal;
- the vehicle terminal performs code restoration on the identified signal strength, and judges whether the restored code is consistent with the plaintext, if it is, it maintains the connection with the key terminal, if not, it disconnects the connection with the key terminal.
- control code is composed of a series of identifiers representing different transmit power change values of the wireless signal.
- control code includes three identifiers, and the transmit power change values indicated by the three identifiers differ by 20 dB in sequence.
- control code is sent at a set time interval.
- the anti-relay attack method further includes: the vehicle side sets a delay judgment window time, when the time interval for identifying different signal strengths exceeds the delay judgment In the window time, the connection with the key terminal is disconnected.
- the present invention also provides an intelligent key used in a keyless start system, including:
- the first key module is used to agree on a communication key with the vehicle in a key agreement manner
- the control code receiving module is configured to receive the control code in cipher text form from the vehicle end after establishing a wireless connection with the vehicle end;
- the control code analysis module is configured to analyze the control code in ciphertext form by using the communication key to obtain the plaintext of the control code;
- the first control module is configured to use the plaintext to control the intensity of the transmitted wireless signal.
- the present invention also provides an anti-relay attack system, which is set on the vehicle side and is used for a keyless start system, including:
- the second key module is used to agree on a communication key with the key terminal in a key agreement manner
- the control code sending module is used to send a control code in cipher text to the key end after establishing a wireless connection with the key end to trigger the key end to parse the control code in the cipher text form to obtain the control Coded plaintext, and using the plaintext to control the strength of the transmitted wireless signal;
- the second control module is used to restore the code size of the identified signal strength, and determine whether the restored code is consistent with the plaintext, if yes, keep the connection with the key end, if not, disconnect the The connection of the key end.
- control code is composed of a series of identifiers indicating different transmit power change values of the wireless signal.
- control code includes three identifiers, and the transmit power change values indicated by the three identifiers differ by 20 dB in sequence.
- the second control module is further configured to set a delay judgment window time, and when the time interval for identifying different signal strengths exceeds the delay judgment window time, Disconnect the connection with the key end.
- the key end and the vehicle end agree on a communication key by means of key negotiation, so that a wireless connection is established between the key end and the vehicle end.
- the key end receives the control code in the cipher text form from the vehicle end, it can use the communication key to analyze the control code in the cipher text form to obtain the plain text of the control code, and Use the plaintext to control the strength of the transmitted wireless signal, and then encode and restore the identified signal strength through the vehicle terminal, and determine whether the restored code is consistent with the plaintext, and if so, keep it consistent with the plaintext.
- connection of the key end if not, disconnect the connection with the key end, so as to achieve the purpose of preventing the attack of the relay station. Since the vehicle end communicates with the key end normally, the strength of the wireless signal transmitted by the vehicle end and the strength of the received wireless signal are basically linear. Therefore, when the strength of the identified wireless signal is coded and restored, under normal circumstances, The vehicle can restore the intensity change characteristics consistent with the plaintext. If it is inconsistent, it means that there is a relay station attack, so the connection is disconnected. In this way, the transmission power change control and detection are performed based on the transmitted code information to achieve the relay attack Recognition.
- FIG. 1 is a schematic diagram of a PEPS system provided by an embodiment of the present invention in a normal situation
- FIG. 2 is a schematic diagram of a situation where the PEPS system provided by an embodiment of the present invention is attacked by a relay station;
- FIG. 3 is a flowchart of a wireless signal sending method provided by an embodiment of the present invention.
- FIG. 4 is a block diagram of the smart key provided by an embodiment of the present invention.
- FIG. 5 is a flowchart of a method for preventing relay attacks provided by an embodiment of the present invention.
- FIG. 6 is a flowchart of an anti-relay attack system provided by an embodiment of the present invention.
- FIG. 7 is a schematic diagram of the linear relationship between the strength of the wireless signal received by the vehicle end and the strength of the wireless signal transmitted by the key end in an embodiment of the present invention
- 01-Key section 02-Vehicle end; 03-Relay station; 04-Relay station;
- 21-Second key module 22-Control code sending module; 23-Second control module.
- the key terminal 01 and the vehicle terminal 02 can interact with the vehicle terminal 02 through wireless control signals to realize the vehicle control function.
- the working logic of the PEPS system is generally as follows: the PEPS module on the vehicle end wirelessly broadcasts in real time, and when scanned by the key end, it sends identity authentication information to the key end. If the authentication is passed, the connection is established; if the authentication fails, then Disconnect.
- the attacker implements a remote attack by setting up relay station 03 and relay station 04.
- the wireless control signal of the key terminal 01 is sent to the vehicle terminal 02 after being routed by the relay station 03 and the relay station 04, and the control function of the vehicle terminal 02 can also be realized.
- the communication distance can usually reach 100 meters or even longer, and the wireless control signal sent from the key terminal 01 to the vehicle terminal 02 does not require any tampering.
- remote control can be achieved.
- the purpose of vehicle end 02. Therefore, the attacker can control the vehicle terminal 02 without the driver's perception through the attack of the relay station, which is a huge threat and low security.
- the inventor further found that when the user carries the key close to the vehicle, as the distance between the key terminal 01 and the vehicle terminal 02 decreases, when the distance is reduced to a certain distance (generally 15m), the wireless transmission from the vehicle terminal 02 The strength of the signal and the strength of the received wireless signal exhibit linear characteristics.
- an embodiment of the present invention provides a wireless signal sending method, and the wireless signal sending method includes the following steps:
- an embodiment of the present invention also provides a smart key, and the smart key includes:
- the first key module 11 is used to agree on a communication key with the vehicle in a key agreement manner
- the control code receiving module 12 is configured to receive the control code in cipher text form from the vehicle end after establishing a wireless connection with the vehicle end;
- the control code analysis module 13 is configured to use the communication key to analyze the control code in ciphertext form to obtain the plaintext of the control code;
- the first control module 14 is configured to use the plaintext to control the intensity of the transmitted wireless signal.
- the key side/smart key may be a smart phone or a wearable device.
- the wireless signal is one of a Bluetooth signal, a radio frequency signal and a Zigbee signal.
- the present invention also provides an anti-relay attack method, which includes the following steps:
- the vehicle terminal After establishing a wireless connection with the key terminal, the vehicle terminal sends a control code in cipher text to the key terminal to trigger the key terminal to use the communication key to control the cipher text. Parsing the code to obtain the plaintext of the control code, and using the plaintext to control the intensity of the transmitted wireless signal;
- S23 The vehicle terminal performs code restoration on the identified signal strength, and judges whether the restored code is consistent with the plain text, if yes, keep the connection with the key terminal, if not, disconnect the connection with the key terminal. connect.
- control code is composed of a series of identifiers representing different transmission power variation values of the wireless signal.
- the identification can be a number, a letter, a symbol, etc.
- each identifier is uniformly reduced or increased by a certain value, and each of the identifiers is sent at a set interval.
- controllable gears of the wireless signal transmission power of the key end can be divided into 3 levels, each with a difference of 20dB, that is, the control code
- the three identifiers are included, and the transmit power change values indicated by the three identifiers differ by 20 dB in sequence.
- the anti-relay attack method further includes: the vehicle end sets a delay judgment window time, and when the time interval between identifying different signal strengths exceeds the delay judgment window time, disconnecting from the key end connect.
- an embodiment of the present invention also provides an anti-relay attack system, the anti-relay attack system is provided on the vehicle side, and the anti-relay attack system includes:
- the second key module 21 is used to agree on a communication key with the key terminal in a key agreement manner
- the control code sending module 22 is configured to send a control code in cipher text to the key end after establishing a wireless connection with the key end, so as to trigger the key end to parse the control code in the cipher text form to obtain the Control the coded plaintext, and use the plaintext to control the strength of the transmitted wireless signal;
- the second control module 23 is used to restore the code size of the identified signal strength and determine whether the restored code is consistent with the plaintext. The connection of the key end.
- the second control module 23 is also configured to set a delay judgment window time, and disconnect the connection with the key terminal when the time interval between identifying different signal strengths exceeds the delay judgment window time.
- the attacker will only perform data forwarding, and will not perform wireless signal strength monitoring and forwarding. Even if the attacker wants to monitor and forward wireless signal strength, due to the delay characteristics of wireless signal judgment, the translation characteristics of wireless signal changes, First, the attacker will be required to filter and identify the wireless signal changes at the key end. This will inevitably cause a delay in the wireless signal change. Therefore, when the vehicle end determines the window time according to the calibration setting delay, it can eliminate the attacker's translation of the wireless signal change. action.
- the wireless connection is one of a Bluetooth connection, a radio frequency connection, and a Zigbee connection.
- the wireless signal transmission power controllable gear of the key can be divided into 3 levels, each with a difference of 20dB, to accommodate the abnormal deviation caused by conventional human interference and interfere with the attack recognition.
- 1 represents a reduction of 20dB transmission
- 2 represents a reduction of 40dB transmission
- 3 represents a reduction of 60dB transmission.
- the wireless signal strength received by the vehicle end and the wireless signal transmitted by the key end vehicle end basically exhibit linear characteristics. Therefore, the identified signal strength can be coded and restored based on the linear characteristics. Under normal circumstances, the vehicle end can restore the intensity change characteristics of 31231. Also, because the vehicle side knows the value of RCC1, and then according to the actual measured value of the received intensity change, it can be determined whether there is a relay attack.
- anti-relay attack method and system provided by the embodiments of the present invention
- active coding defense can be performed.
- a typical defense scenario is when the smart key is in motion and the attacker is close to the owner.
- the common motion sensor anti-relay will fail, but the method provided by the present invention can still identify the attack state, so as to achieve the purpose of anti-relay attack.
- the smart key, anti-relay attack method and system provided in this embodiment solve the problem that the existing PEPS system is vulnerable to relay attacks.
- the PEPS system is an application in vehicle keyless start, but it should be understood that the PEPS system can also be applied in other aspects, for example, it can be applied to an access control system.
- the PEPS system can also be applied in other aspects, for example, it can be applied to an access control system.
- the corresponding vehicle end is the access control end. If it is applied to an access control system, the possibility of relay attacks can also be reduced when the smart key, anti-relay attack method and system provided by the present invention are used.
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Abstract
一种智能钥匙、防中继攻击方法及系统，首先，钥匙端（01）与车辆端（02）以密钥协商的方式约定通讯密钥，从而在钥匙端（01）与车辆端（02）建立无线连接后，钥匙端（01）在接收到来自车辆端（02）的密文形式的控制编码时，能够利用通讯密钥对密文形式的控制编码进行解析以得到控制编码的明文，并利用明文对发送的无线信号的强度进行控制，而后，通过车辆端（02）对识别的信号强度进行编码还原，并判断还原得到的编码是否与明文一致，若是，则保持与钥匙端（01）的连接，若否，则断开与钥匙端（01）的连接，以达到阻止中继站攻击的目的。
Description
本发明涉及无线控制技术领域，特别涉及一种智能钥匙、防中继攻击方法及系统。
现有智能钥匙系统PEPS(Passive Entry&Passive Start)，又称无钥匙系统、无钥匙启动系统，主要由车载通讯及控制系统和用户随身携带的用于合法身份识别的智能钥匙RFID(Radio Frequency Identification)，又称射频识别、Smart Key或Fob组成。当用户携带智能钥匙进入车辆的探测范围时，用户只需要直接拉动车门上的外开启手柄或者按动门把手上的开锁按钮，车辆便主动识别和认证智能钥匙的合法性，如认证通过，车辆就解除防盗并车辆车门；当用户进入车内时，只需要按下启动按钮，车辆便主动识别和认证处于车辆内部的智能钥匙，如认证通过，车辆就解除发动机防盗和其他防盗设备，如电子转向轴锁，用户可以直接启动或给车辆上电。车辆配备智能钥匙系统的好处是免去了用户使用车辆时找钥匙、操作钥匙的繁琐操作，提高车辆使用的便利性。目前智能钥匙系统已成为中高档轿车的标准配置，而且有向中低档车型普及的趋势。智能钥匙系统已经历10年的发展，技术已经成熟并得到广泛应用。智能钥匙作为智能钥匙系统的RFID设备，已经以多样化的形式存在，如卡片式智能钥匙、挂坠智能钥匙、手表智能钥匙、遥控智能钥匙以及基于蓝牙的钥匙汽车钥匙。
现有常规无钥匙启动系统主要利用智能钥匙和汽车之间的无线信号交互来实现车辆的控制，所述无线信号例如，LF-RF(低频-射频)信号、BLE(蓝牙)信号或Zigbee(紫蜂)信号等。然而，此类无线通讯信号均容易遭受中继站的攻击，从而导致安全性低的问题。基于收发点通信时间片的定位方式可以有效抵御中继攻击，但目前官方蓝牙协议暂尚未支持，因此，尤其是对于基于蓝牙的PEPS(BLE-PEPS)系统来说，其容易遭受中继攻击，从而导致被盗风险增加。
发明内容
本发明的目的在于提供一种智能钥匙、防中继攻击方法及系统，以解决现有PEPS系统容易遭受中继攻击的问题。
为解决上述问题，本发明提供一种防中继攻击方法，用于无钥匙启动系统，包括：
车辆端以密钥协商的方式与钥匙端约定通讯密钥；
所述车辆端在与所述钥匙端建立无线连接后，以密文形式向所述钥匙端发送控制编码，以触发所述钥匙端利用所述通讯密钥对密文形式的所述控制编码进行解析以得到所述控制编码的明文，并利用所述明文对发送的无线信号的强度进行控制；
所述车辆端对识别的信号强度进行编码还原，并判断还原得到的编码是否与所述明文一致，若是，则保持与所述钥匙端的连接，若否，则断开与所述钥匙端的连接。
可选的，在所述的防中继攻击方法中，所述控制编码由一串表示无线信号不同发射功率变化值的标识组成。
可选的，在所述的防中继攻击方法中，所述控制编码包括三个所述标识，三个所述标识表示的发射功率变化值依次相差20dB。
可选的，在所述的防中继攻击方法中，所述控制编码按设定时间间隔进行发送。
可选的，在所述的防中继攻击方法中，所述防中继攻击方法还包括：所述车辆端设定延迟判断窗口时间，当识别到不同信号强度的时间间隔超过所述延迟判断窗口时间，则断开与所述钥匙端的连接。
本发明还提供一种智能钥匙，用于无钥匙启动系统，包括：
第一密钥模块，用于以密钥协商的方式与车辆端约定通讯密钥；
控制编码接收模块，用于与所述车辆端建立无线连接后，接收来自所述车辆端的密文形式的控制编码；
控制编码解析模块，用于利用所述通讯密钥对密文形式的所述控制编码 进行解析以得到所述控制编码的明文；
第一控制模块，用于利用所述明文对发送的无线信号的强度进行控制。
本发明还提供一种防中继攻击系统，设于车辆端，用于无钥匙启动系统，包括：
第二密钥模块，用于以密钥协商的方式与钥匙端约定通讯密钥；
控制编码发送模块，用于与钥匙端建立无线连接后，以密文形式向所述钥匙端发送控制编码，以触发所述钥匙端对密文形式的所述控制编码进行解析以得到所述控制编码的明文，并利用所述明文对发送的无线信号的强度进行控制；
第二控制模块，用于对识别的信号强度进行编码大小还原，并判断还原得到的编码是否与所述明文一致，若是，则保持与所述钥匙端的连接，若否，则断开与所述钥匙端的连接。
可选的，在所述的防中继攻击系统中，所述控制编码由一串表示无线信号不同发射功率变化值的标识组成。
可选的，在所述的防中继攻击系统中，所述控制编码包括三个所述标识，三个所述标识表示的发射功率变化值依次相差20dB。
可选的，在所述的防中继攻击系统中，所述第二控制模块还用于设定延迟判断窗口时间，并在识别到不同信号强度的时间间隔超过所述延迟判断窗口时间时，断开与所述钥匙端的连接。
在本发明提供的智能钥匙、防中继攻击方法及系统中，首先，钥匙端与车辆端以密钥协商的方式约定通讯密钥，从而在所述钥匙端在与所述车辆端建立无线连接后，所述钥匙端在接收到来自所述车辆端的密文形式的控制编码时，能够利用所述通讯密钥对密文形式的所述控制编码进行解析以得到所述控制编码的明文，并利用所述明文对发送的无线信号的强度进行控制，而后，通过所述车辆端对识别的信号强度进行编码还原，并判断还原得到的编码是否与所述明文一致，若是，则保持与所述钥匙端的连接，若否，则断开与所述钥匙端的连接，以达到阻止中继站攻击的目的。由于车辆端与钥匙端正常通信时，车辆端发射的无线信号的强度和接收的无线信号的强度基本呈 线性特征，因此，当对识别到的无线信号的强度进行编码还原时，正常情况下，车辆可以还原出与所述明文一致的强度变化特性，如若不一致，则说明存在中继站攻击，因此断开连接，如此，便基于所传递的编码信息进行发射功率变化控制和检测，达到对中继攻击的识别。
图1为本发明实施例提供的PEPS系统处于正常情况下的示意图；
图2为本发明实施例提供的PEPS系统受到中继站攻击情况下的示意图；
图3为本发明实施例提供的无线信号发送方法的流程图；
图4为本发明实施例提供的智能钥匙的组成框图；
图5为本发明实施例提供的防中继攻击方法的流程图；
图6为本发明实施例提供的防中继攻击系统的流程图；
图7为本发明实施例中车辆端接收的无线信号强度与钥匙端发射的无线信号强度的线性关系示意图；
其中，各附图标记说明如下：
01-钥匙段；02-车辆端；03-中继站；04-中继站；
11-第一密钥模块；12-控制编码接收模块；13-控制编码解析模块；14-第一控制模块；
21-第二密钥模块；22-控制编码发送模块；23-第二控制模块。
以下结合附图和具体实施例对本发明提出的智能钥匙、防中继攻击方法及系统作进一步详细说明。根据下面说明，本发明的优点和特征将更清楚。需说明的是，附图均采用非常简化的形式且均使用非精准的比例，仅用以方便、明晰地辅助说明本发明实施例的目的。此外，附图所展示的结构往往是实际结构的一部分。特别的，各附图需要展示的侧重点不同，有时会采用不同的比例。
如图1所示，对于PEPS系统而言，正常情况下，钥匙端01可以和车辆 端02通过无线控制信号的交互，来实现车辆控制功能。
具体而言，PEPS系统的工作逻辑一般如下：车辆端的PEPS模块实时无线广播，当被钥匙端扫描到后，向钥匙端发送身份认证信息，若认证通过，则建立连接，若认证不通过，则断开连接。
发明人发现，钥匙端01和车辆端02之间的无线信号具有可以截取和复制的可能性，所以容易遭受中继站的攻击，从而导致安全性低的问题。如图2所示，攻击者通过架设中继站03和中继站04来实现远程攻击。具体的，钥匙端01的无线控制信号经过中继站03和中继站04的路由之后，发送给车辆端02，亦可实现对车辆端02的控制功能。此种情况下的通讯距离通常可以达到百米甚至更长，而且钥匙端01发送给车辆端02的无线控制信号，不需进行任何篡改，只要通过两个中继站的信号路由，即可实现远程控制车辆端02的目的。因此攻击者通过中继站的攻击，可以在驾驶员完全无感知的情况下，实现对车辆端02的操控，威胁巨大，安全性低。
发明人进一步发现，当用户携带钥匙靠近车辆时，随着钥匙端01和车辆端02之间距离的减小，当减小到一定距离(一般为15m)范围内时，车辆端02发射的无线信号的强度和接收的无线信号的强度呈现线性特征。
基于上述发现，本发明实施例提供一种无线信号发送方法，所述无线信号发送方法包括如下步骤：
S11，钥匙端以密钥协商的方式与车辆端约定通讯密钥；
S12，所述钥匙端在与所述车辆端建立无线连接后，在接收到来自所述车辆端的密文形式的控制编码时，利用所述通讯密钥对密文形式的所述控制编码进行解析以得到所述控制编码的明文，并利用所述明文对发送的无线信号的强度进行控制。
对应于所述钥匙端，本发明实施例还提供一种智能钥匙，所述智能钥匙包括：
第一密钥模块11，用于以密钥协商的方式与车辆端约定通讯密钥；
控制编码接收模块12，用于与所述车辆端建立无线连接后，接收来自所述车辆端的密文形式的控制编码；
控制编码解析模块13，用于利用所述通讯密钥对密文形式的所述控制编码进行解析以得到所述控制编码的明文；
第一控制模块14，用于利用所述明文对发送的无线信号的强度进行控制。
本实施例中，所述钥匙侧/智能钥匙可为智能手机或可穿戴设备等。所述无线信号为蓝牙信号、射频信号和紫蜂信号中的一种。
另外，本发明还提供一种防中继攻击方法，所述防中继攻击方法包括如下步骤：
S21，车辆端以密钥协商的方式与钥匙端约定通讯密钥；
S22，所述车辆端在与所述钥匙端建立无线连接后，以密文形式向所述钥匙端发送控制编码，以触发所述钥匙端利用所述通讯密钥对密文形式的所述控制编码进行解析以得到所述控制编码的明文，并利用所述明文对发送的无线信号的强度进行控制；
S23，所述车辆端对识别的信号强度进行编码还原，并判断还原得到的编码是否与所述明文一致，若是，则保持与所述钥匙端的连接，若否，则断开与所述钥匙端的连接。
其中，所述控制编码由一串表示无线信号不同发射功率变化值的标识组成。所述标识可为数字，也可为字母、符号等。本实施例中，考虑到车辆对编码还原的难易程度，较佳的，各个标识统一为按某一数值降低或增加，且各所述标识按设定间隔进行发送。进一步的，为了容纳常规的人体干扰造成的异常偏差对攻击识别造成干扰，可将钥匙端的无线信号发送功率可控档位划分为3个等级，每个等级相差20dB，亦即，所述控制编码包括三个所述标识，三个所述标识表示的发射功率变化值依次相差20dB。
较佳的，所述防中继攻击方法还包括：所述车辆端设定延迟判断窗口时间，当识别到不同信号强度的时间间隔超过所述延迟判断窗口时间，则断开与所述钥匙端的连接。
相应的，本发明实施例还提供一种防中继攻击系统，所述防中继攻击系统设于车辆端，所述防中继攻击系统包括：
第二密钥模块21，用于以密钥协商的方式与钥匙端约定通讯密钥；
控制编码发送模块22，用于与钥匙端建立无线连接后，以密文形式向所述钥匙端发送控制编码，以触发所述钥匙端对密文形式的所述控制编码进行解析以得到所述控制编码的明文，并利用所述明文对发送的无线信号的强度进行控制；
第二控制模块23，用于对识别的信号强度进行编码大小还原，并判断还原得到的编码是否与所述明文一致，若是，则保持与所述钥匙端的连接，若否，则断开与所述钥匙端的连接。
较佳的，所述第二控制模块23还用于设定延迟判断窗口时间，并在识别到不同信号强度的时间间隔超过所述延迟判断窗口时间时，断开与所述钥匙端的连接。
通常，攻击者常规只会进行数据的转发，不会进行无线信号强度的监测和转发，即使攻击者想进行无线信号强度的监测和转发，由于无线信号判断的延迟特性，转译无线信号变化特性，首先会要求攻击者也对钥匙端的无线信号变化进行滤波识别，这样必然会造成无线信号变化的延时，故当车辆端根据标定设定延迟判断窗口时间时，可以消除攻击者转译无线信号变化的动作。
在本发明实施例提供的防中继攻击方法及系统中，所述无线连接为蓝牙连接、射频连接和紫蜂连接中的一种。
为了描述的方便，描述以上智能设备和防中继攻击系统时以功能分为各种模块分别描述。当然，在实施本发明时可以把各模块的功能在同一个或多个软件和/或硬件中实现。
以下进行举例说明。
例如，可将钥匙端的无线信号发送功率可控档位划分为3个等级，每个等级相差20dB，以容纳常规的人体干扰造成的异常偏差对攻击识别造成干扰。其中，1代表降低20dB发送，2代表降低40dB发送，3代表降低60dB发送。如若对控制编码RCC1进行解密之后，得到RCC1＝31231，则代表钥匙端在进行无线信号的发送时，进行5次变功率动作，控制序列是降低60dB发送并持 续CXms，随后降低20dB发送并持续CXms，随后降低40dB发送并持续CXms，随后降低60dB发送并持续CXms，随后降低20dB发送并持续CXms，其中，功率切换间隔时间CX可以进行配置。
如图7所示，车辆端接收的无线信号强度与所述钥匙端车辆端发射的无线信号基本呈现线性特性，因此，可基于该线性特性，对识别到的信号强度进行编码还原。正常情况下，车辆端可以还原出31231的强度变化特性。又因为车辆端已知RCC1的值，再根据接收到的强度的变化实测值，可以得出是否存在中继攻击的判断。
即，使用了本发明实施例提供的智能钥匙、防中继攻击方法及系统后，可以进行主动的编码防御，比较典型的防御场景是智能钥匙在运动且攻击者距离车主也比较近的情况下，常见的运动传感器防中继会失效，但本发明所提供的方法仍然可以识别出攻击状态，从而达到防中继攻击的目的。
综上所述，本实施例提供的智能钥匙、防中继攻击方法及系统解决了现有PEPS系统容易遭受中继攻击的问题。
需要说明的是，在本发明的描述中，PEPS系统为在车载无钥匙启动方面的应用，但需理解PEPS系统也可以应用在其它方面，例如可应用在门禁系统，当应用在门禁系统时，相应的车辆端即为门禁端，若应用在门禁系统，采用本发明提供的智能钥匙、防中继攻击方法及系统时同样可以降低中继攻击的可能性。
上述描述仅是对本发明较佳实施例的描述，并非对本发明范围的任何限定，本发明领域的普通技术人员根据上述揭示内容做的任何变更、修饰，均属于权利要求书的保护范围。
Claims (10)
- 一种防中继攻击方法，用于无钥匙启动系统，其特征在于，包括：车辆端以密钥协商的方式与钥匙端约定通讯密钥；所述车辆端在与所述钥匙端建立无线连接后，以密文形式向所述钥匙端发送控制编码，以触发所述钥匙端利用所述通讯密钥对密文形式的所述控制编码进行解析以得到所述控制编码的明文，并利用所述明文对发送的无线信号的强度进行控制；所述车辆端对识别的信号强度进行编码还原，并判断还原得到的编码是否与所述明文一致，若是，则保持与所述钥匙端的连接，若否，则断开与所述钥匙端的连接。
- 如权利要求1所述的防中继攻击方法，其特征在于，所述控制编码由一串表示无线信号不同发射功率变化值的标识组成。
- 如权利要求2所述的防中继攻击方法，其特征在于，所述控制编码包括三个所述标识，三个所述标识表示的发射功率变化值依次相差20dB。
- 如权利要求2或3所述的防中继攻击方法，其特征在于，各所述标识按设定时间间隔进行发送。
- 如权利要求1所述的防中继攻击方法，其特征在于，所述防中继攻击方法还包括：所述车辆端设定延迟判断窗口时间，当识别到不同信号强度的时间间隔超过所述延迟判断窗口时间，则断开与所述钥匙端的连接。
- 一种智能钥匙，用于无钥匙启动系统，其特征在于，包括：第一密钥模块，用于以密钥协商的方式与车辆端约定通讯密钥；控制编码接收模块，用于与所述车辆端建立无线连接后，接收来自所述车辆端的密文形式的控制编码；控制编码解析模块，用于利用所述通讯密钥对密文形式的所述控制编码进行解析以得到所述控制编码的明文；第一控制模块，用于利用所述明文对发送的无线信号的强度进行控制。
- 一种防中继攻击系统，设于车辆端，用于无钥匙启动系统，其特征在 于，包括：第二密钥模块，用于以密钥协商的方式与钥匙端约定通讯密钥；控制编码发送模块，用于与钥匙端建立无线连接后，以密文形式向所述钥匙端发送控制编码，以触发所述钥匙端对密文形式的所述控制编码进行解析以得到所述控制编码的明文，并利用所述明文对发送的无线信号的强度进行控制；第二控制模块，用于对识别的信号强度进行编码大小还原，并判断还原得到的编码是否与所述明文一致，若是，则保持与所述钥匙端的连接，若否，则断开与所述钥匙端的连接。
- 如权利要求7所述的防中继攻击系统，其特征在于，所述控制编码由一串表示无线信号不同发射功率变化值的标识组成。
- 如权利要求8所述的防中继攻击方法，其特征在于，所述控制编码包括三个所述标识，三个所述标识表示的发射功率变化值依次相差20dB。
- 如权利要求7所述的防中继攻击系统，其特征在于，所述第二控制模块还用于设定延迟判断窗口时间，并在识别到不同信号强度的时间间隔超过所述延迟判断窗口时间时，断开与所述钥匙端的连接。
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