A method for verifying false targets of ADS-B

Abstract

The present invention discloses an ADS-B false target verification method, including: using an ADS-B message that does not clearly specify a reserved purpose as a verification message carrier, dividing the last 48 bits of the "ME" field of the reserved ADS-B message as the carrier into 4 groups, each with 12 bits, which are respectively used to verify the aircraft position, aircraft speed, aircraft identification, and four types of messages of periodic status and event-driven sent by ADS-B within a period of time, and periodically transmitting the ADS-B reserved message with the verification message. The advantages of the present invention are: low cost of use, providing an ADS-B false target verification method that is fully compatible with the current ADS-B usage specifications, responsive, and capable of dealing with multiple targets, and can effectively remove the tampered ADS-B message corresponding to the ICAO address of the aircraft using the method.

Description

Technical Field

[0001] The invention relates to the technical field of air traffic management, and in particular to an ADS-B false target verification method. Background Art

[0002] ADS-B uses a broadcast data link to enable targets (including aircraft or ground vehicles that need to be monitored, also known as monitored persons) to actively send their own identification and precise four-dimensional position data, thereby achieving passive monitoring. In the field of air traffic control, compared with traditional radar monitoring technology, ADS-B not only has timely data (data interval can reach 1 second, while traditional radar data is 4-12 seconds), accurate positioning (ADS-B uses GNSS positioning, with an accuracy of up to meters, while traditional radar has an accuracy of more than several hundred meters), but also has the advantages of low price and easy installation. Therefore, in recent years, ADS-B has been vigorously promoted by the Civil Aviation Administration.

[0003] However, since ADS-B uses a passive surveillance mode, that is, the monitor completely trusts the data sent by the target, this will lead to a serious problem, that is, criminals may illegally send false target information (completely fake target information, tampered target information or replayed previously recorded target information) to the controller's screen, making it impossible for the controller to distinguish between real targets and false targets, which may cause a fatal disaster.

[0004] Prior art related to the present invention

[0005] A Chinese invention patent discloses a method for determining whether there is a false target by measuring the target position, and the publication number is: CN102323567B. The method first reads the target representation and four-dimensional position (time, longitude and latitude, altitude) information output by the ADS-B system through the data processing center, and sends them to multiple direction-finding base stations respectively; the servo device of each direction-finding base station first points the directional antenna to the direction where the target is located, and then receives the target information from the direction with the ADS-B receiver according to the synchronization signal of the data processing center, and sends it back to the data processing center; the data processing center analyzes the results of all direction-finding base stations. If more than two direction-finding stations can receive the target information, it indicates that the target is real; if only one station or no station receives the target information, it indicates that the target is false.

[0006] Defects of prior art 1

[0007] In order to measure the target position, it is necessary to build an additional direction-finding base station, which increases the cost. When verifying whether a target is a false target, this measurement method requires the data center to first select an ADS-B target, and then send the target's identification and four-dimensional position information to each direction-finding base station. Each direction-finding base station will aim the directional antenna at the target according to the target position algorithm, and then send an antenna ready signal to the data processing center. After all stations are ready, the data processing center sends a command to start receiving to each direction-finding base station, and each direction-finding base station sends the received ADS-B information back to the data center, which determines whether the target is real or fake. There is a certainty of slow response, and this method cannot verify the tampering of information other than the target identification and four-dimensional position information.

[0008] Prior art related to the present invention

[0009] A Chinese invention patent discloses an ADS-B message authentication method based on certificateless short signatures, with the publication number: CN110177002A. This method requires the aircraft to submit its identity information to the airport before taking off. After receiving the aircraft's identity information, the airport calculates the partial private key corresponding to the identity ID and securely passes it to the aircraft. The aircraft calculates its own public key and private key based on this, keeps its own private key privately, and publishes the corresponding public key. During the flight phase, the aircraft uses the received navigation information to calculate its own position, speed and other information, and encapsulates it into the ADS-B data format. The aircraft then digitally signs the ADS-B message, and then periodically broadcasts the ADS-B information containing the signature. After receiving this ADS-B message, the surrounding aircraft or ground stations use the public key published by the aircraft to verify the legitimacy of the signature in the message. The message that passes the verification is used, and the message that fails is discarded.

[0010] Defects of the Second Prior Art

[0011] This verification method uses a digital signature to verify an original ADS-B data. The digital signature and the ADS-B original data need to be packaged and sent together. According to the definition of the ADS-B message structure in the literature [1], most of the ADS-B messages currently used do not have reserved fields. In addition, the aircraft air speed type ADS-B messages, aircraft target status and condition type ADS-B messages, and aircraft operation status type ADS-B messages with reserved fields have only 2 bits, 2 bits, and 1 bit of reserved fields respectively, which cannot be filled with the digital signature generated by this verification method. Therefore, in order to implement this verification method, it is inevitable that the universal data format of ADS-B will be damaged (redefine the meaning of the field or extend the message). In the case that it cannot be guaranteed that all ADS-B receiving devices comply with this parsing mode, the ADS-B messages sent by the aircraft using this verification method cannot be recognized by aircraft that do not use this verification mechanism, which will cause incompatibility and lead to safety issues.

[0012] References

[0013] [1]RTCA, Inc. Minimum Operational Performance Standards (MOPS) for 1090MHz Extended Squitter Automatic Dependent Surveillance–Broadcast (ADS-B) and Traffic Information Services–Broadcast (TIS-B). 1150 18th Street, NW, Suite 910 Washington, DC 20036, USA. Summary of the invention

[0014] The present invention aims at the defects of the prior art and provides an ADS-B false target verification method.

[0015] In order to achieve the above invention object, the technical solution adopted by the present invention is as follows:

[0016] An ADS-B false target verification method includes: using an ADS-B message that does not explicitly specify a reserved purpose as a carrier of a verification message. An ADS-B message that does not explicitly specify a reserved purpose refers to a message in which the DF field is coded as 17 or 18, and the TYPE in the "ME" field is 19, SUBTYPE=0,5-7; TYPE=23, SUBTYPE=1-7; TYPE=24, SUBTYPE=0,2-7; TYPE=25-26; TYPE=28, SUBTYPE=0,3-7; TYPE=29, SUBTYPE=2-3; TYPE=30; TYPE=31, SUBTYPE=2-7.

[0017] The last 48 bits of the reserved ADS-B message "ME" field as a carrier are divided into 4 groups, each with 12 bits, which are used to verify the aircraft position, aircraft speed, aircraft identification, periodic status and event-driven messages sent by ADS-B within a period of time. The specific steps are as follows:

[0018] 1) Set the verification message sending period Ts to 0.5 seconds.

[0019] 2) Set the corresponding relationship between the groups and ADS-B messages. The first group is used to verify the aircraft position message, the second group is used to verify the aircraft speed message, the third group is used to verify the aircraft identification message, and the fourth group is used to verify the aircraft periodic status and event-driven messages.

[0020] 3) Calculate the check value. When sending this verification message, the ADS-B transmitter will find the message content sent between the current time and 0.5 seconds before, select the check algorithm according to the selected check algorithm encoding value, calculate the check value of the "ME" field of the message sent during this period, and fill it into the check value storage bit of each group. Groups that have not sent the corresponding type of message during this period are set to all zeros.

[0021] 4) Verification. After receiving the verification message, the ADS-B receiver will take out all ADS-B messages corresponding to the ICAO address of the verification message from now to 0.5 seconds ago for verification, and extract the verification algorithm number and check value of each group according to the above-mentioned division rules for the "ME" field of the verification message. For non-all-zero groups, the receiver selects the verification algorithm according to the verification algorithm number of each group, and uses the calculated check value of the ADS-B type message corresponding to the group to compare with the extracted check value. If the check values ​​are not equal, it means that this is a false message and it is discarded. For targets with such a verification mechanism, a special mark can be given to it on the pilot's operating panel to indicate that it is a real target that has passed verification.

[0022] Furthermore, in each group, N (0≤N≤11) bits are used to store the selectable authentication algorithm numbers, and (12-N) bits are used to store the authentication information.

[0023] Compared with the prior art, the advantages of the present invention are:

[0024] 1. Use the reserved ADS-B message as the carrier of the verification message, so there is no need to make major changes to the current ADS-B hardware and software design. Only a little software function needs to be added to achieve this verification method, and the cost of use is low.

[0025] 2. It is achieved through the flexible use of ADS-B features without the introduction of other additional systems. Therefore, it has the characteristics of ADS-B, such as quick response, wide range of action, and ability to handle multiple targets.

[0026] 3. The tampered ADS-B message corresponding to the ICAO address of the aircraft using this method can be effectively removed, and the aircraft that passes the verification can get a high-trust mark on the pilot panel, providing a basis for use in application scenarios that require high trust. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the ADS-B message structure of the present invention;

[0028] Figure 2 is a schematic diagram of grouping of the "ME" field in an embodiment of the present invention;

[0029] Figure 3 is the verification algorithm code of the default ADS-B verification message in the embodiment of the present invention;

[0030] Figure 4 It is a schematic diagram of a reserved message group without a SUBTYPE field according to an embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples.

[0032] The ADS-B message in the present invention specifically refers to the ADS-B 1090MHz ES message. These ADS-B messages can be divided into four categories: aircraft position message, aircraft speed message, aircraft identification message, and periodic status and event-driven message. They are composed of 112 bits of data. The meaning and space of each field are as follows: Figure 1 shown.

[0033] The present invention uses the ADS-B message for which the reserved purpose is not explicitly specified in the document [1], and divides the 48 bits in the "ME" field except the first byte (used to store the type and possible subtype) into 4 groups, each with 12 bits, such as Figure 2 As shown, they are used to verify the four types of messages sent by ADS-B within a period of time: aircraft position, aircraft speed, aircraft identification, and periodic status and event-driven.

[0034] ADS-B messages that do not explicitly specify a reserved purpose are carriers of verification information, which means that the DF field is encoded as 17 or 18, and TYPE=19 in the "ME" field, SUBTYPE=0,5-7; TYPE=23, SUBTYPE=1-7; TYPE=24, SUBTYPE=0,2-7; TYPE=25-26; TYPE=28, SUBTYPE=0,3-7; TYPE=29, SUBTYPE=2-3; TYPE=30; TYPE=31, SUBTYPE=2-7.

[0035] The verification method adopted by the present invention needs to be described from two aspects: ADS-B transmitter and ADS-B receiver.

[0036] 1. ADS-B transmitter:

[0037] like Figure 2 As shown in FIG. 1 , the last 48 bits in the "ME" field of the ADS-B message as the carrier of the verification message will be equally divided into 4 groups, each with 12 bits. The first group is used to verify the aircraft position message, the second group is used to verify the aircraft speed message, the third group is used to verify the aircraft identification message, and the fourth group is used to verify the aircraft periodic status and event-driven message.

[0038] Reference [1] stipulates that the transmission rate of ADS-B shall not exceed an average of 2 aircraft position messages, 2 aircraft speed messages, 0.2 aircraft identification messages, and 2 aircraft periodic status and event-driven messages per second in any uniform interval of 60 seconds. Moreover, these messages are sent at random time intervals, and this random time interval is evenly distributed on a special time interval (quantified by a time length of no more than 15ms). That is, the maximum transmission frequency of ADS-B messages is aircraft position message, aircraft speed message, aircraft periodic status and event-driven message (1 message / 0.5 seconds), and aircraft identification message (1 message / 5 seconds). The present invention sets the ADS-B message carrying the verification message to be sent at a period of 0.5 seconds, which can well ensure that in the interval between sending two ADS-B messages for verification, at most only one aircraft position message, aircraft speed message, aircraft identification message, and periodic status and event-driven message is sent, so that in the ADS-B message carrying the verification message, the four groups of the "ME" field can correspond one-to-one to the four types of ADS-B messages.

[0039] Regarding the method of generating verification information, in order to ensure flexibility in design, in the four 12-bit groups in the "ME" field, N (0≤N≤11) bits are used in each group to store the optional verification algorithm number, and (12-N) bits are used to store the verification information. The present invention defines the ADS-B message with TYPE of 19 and SUBTYPE of 0 in the "ME" field as the default verification message type, and specifies N=2 for this verification type ADS-B message. It can be foreseen that when sending a verification message, there is a situation in which one or more of the above four messages (aircraft position message, aircraft speed message, aircraft identification message, and periodic status and event-driven message) are not sent and do not need to be verified within a cycle. For this situation, the present invention sets the group corresponding to the information that does not need to be verified to all zeros by default. Therefore, in order to distinguish it from the situation where the group is set to all zeros, zero is not used to arrange the verification algorithm serial number. Under this idea, N=2 in the default verification message type means that there are three verification algorithms to choose from, such as Figure 3 shown.

[0040] When generating the check value, the N value of each group can be randomly selected. The N value is used to indicate the algorithm number for generating the check value. According to the check value algorithm, the aircraft position message, aircraft speed message, aircraft identification message, and the "ME" field of the periodic status and event-driven message sent in the current verification cycle (i.e., 0.5 seconds before sending this ADS-B verification message) are filled with the check value calculated by the check algorithm into the space for storing the check value in the corresponding group. For the group that does not send the ADS-B message type in the current verification cycle, it can be filled with all zeros.

[0041] For reserved ADS-B messages that do not specify a SUBTYPE, the last 3 bits of the "ME" field may be used to encode the size of the N value, such as Figure 4 shown.

[0042] To implement this verification mechanism, the ADS-B transmitter needs to retain the sent ADS-B messages for a period of time. This transmitter characteristic can be defined as: the ADS-B transmitter needs to timestamp the sent ADS-B messages and save them for at least 0.5 seconds.

[0043] 2. Receiver:

[0044] The ADS-B receiver needs to store the received ADS-B for a period of time. This receiver characteristic can be defined as: the ADS-B receiver needs to timestamp the received ADS-B message and store it for at least 1 second.

[0045] During verification, after receiving the verification message, the ADS-B receiver will take out all ADS-B messages corresponding to the ICAO address of the verification message from now to 0.5 seconds ago for verification, and extract the verification algorithm number and check value of each group according to the above-mentioned division rules for the "ME" field of the verification message. For non-all-zero groups, the receiver selects the verification algorithm according to the verification algorithm number of each group, and compares the calculated check value of the ADS-B type message corresponding to the group with the extracted check value. If the check values ​​are not equal, it means that this is a false message and it is discarded. For targets with this verification mechanism, a special mark can be given to it on the pilot's operating panel to indicate that it is a real target that has passed verification.

[0046] After selecting the verification message carrier, specifying the verification message sending cycle and the generation and verification method of the check value, the impact of adding this verification mechanism on the current ADS-B system can be evaluated. Because the reserved ADS-B message is selected as the carrier of the verification message, the verification information will not destroy the standardized ADS-B data format. ADS-B receiving devices that have not yet used this verification mechanism only need to discard these verification messages after receiving them, which will not affect their reception of normal ADS-B messages. In addition, sending this verification message at a cycle of 0.5 seconds is only equivalent to increasing the number of aircraft in the airspace by 0.3226 times (when all aircraft in the airspace use this verification method), and will not cause excessive occupation of the 1090MHz bandwidth in the airspace.

[0047] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the implementation methods of the present invention, and should be understood that the protection scope of the present invention is not limited to such special statements and embodiments. Those skilled in the art can make various other specific variations and combinations that do not deviate from the essence of the present invention based on the technical revelations disclosed by the present invention, and these variations and combinations are still within the protection scope of the present invention.

Claims

1. An ADS-B false target verification method, characterized in that: include: Using ADS-B messages without a clear reserved purpose as a carrier for verification messages; An ADS-B message that does not explicitly specify a reserved purpose is one in which the DF field is coded 17 or 18, and the TYPE in the "ME" field is 19, SUBTYPE=0,5-7; TYPE=23, SUBTYPE=1-7; TYPE=24, SUBTYPE=0,2-7; TYPE=25-26; TYPE=28, SUBTYPE=0,3-7; TYPE=29, SUBTYPE=2-3; TYPE=30; TYPE=31, SUBTYPE=2-7; The last 48 bits of the reserved ADS-B message "ME" field as a carrier are divided into 4 groups, each with 12 bits, which are used to verify the aircraft position, aircraft speed, aircraft identification, periodic status and event-driven messages sent by ADS-B within a period of time. The specific steps are as follows: 1) Set the verification message sending period Ts to 0.5 seconds; 2) Set the corresponding relationship between the groups and ADS-B messages; the first group is used to verify the aircraft position message, the second group is used to verify the aircraft speed message, the third group is used to verify the aircraft identification message, and the fourth group is used to verify the aircraft periodic status and event-driven messages; 3) Calculate the check value; when sending such a verification message, the ADS-B transmitter will find the message content sent between the current time and 0.5 seconds before, select the check algorithm according to the selected check algorithm code value, calculate the check value of the "ME" field of the message sent during this period, and fill it into the check value storage bit of each group; the group that has not sent the corresponding type of message during this period is set to all zeros; 4) Verification; After receiving the verification message, the ADS-B receiver takes out all ADS-B messages corresponding to the ICAO address of the verification message from now to 0.5 seconds ago for verification, and extracts the verification algorithm number and check value of each group according to the division rule of the "ME" field of the verification message; for non-all-zero groups, the receiver selects the verification algorithm according to the verification algorithm number of each group, and uses the calculated check value of the ADS-B type message corresponding to the group to compare with the extracted check value; If the verification values ​​are not equal, it means that this is a false message and is discarded; for targets with such a verification mechanism, a special mark is given to it on the pilot's operating panel to indicate that it is a real target that has passed verification.

2. The ADS-B false target verification method according to claim 1, characterized in that: In each group, N (0≤N≤11) bits are used to store the optional authentication algorithm numbers, and (12-N) bits are used to store the authentication information.

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