CN102215077B

CN102215077B - Automatic dependence surveillance-broadcast (ADS-B) accurate target location encryption method

Info

Publication number: CN102215077B
Application number: CN201110157125A
Authority: CN
Inventors: 冯子亮; 潘卫军; 王洋; 侯明正; 蒲亮
Original assignee: Sichuan University
Current assignee: Sichuan University
Priority date: 2011-06-13
Filing date: 2011-06-13
Publication date: 2012-10-03
Anticipated expiration: 2031-06-13
Also published as: CN102215077A

Abstract

The invention discloses an automatic dependence surveillance-broadcast (ADS-B) accurate target location encryption method, which belongs to a method for encrypting a target location in an air traffic system. The ADS-B accurate target location encryption method comprises the following steps of: splitting and processing data in an original ADS-B data packet into a low-accuracy data part and a high-accuracy part, encrypting the high-accuracy data part, encapsulating the two data parts into an ADS-B downlink data packet, and transmitting the ADS-B downlink data packet by using an ADS-B communication channel; after ADS-B receiving equipment receives the data, directly decoding the low-accuracy data part and determining an approximate target location by using an ordinary receiver; and decrypting the high-accuracy data part, and recovering a high-accuracy location from the decrypted high-accuracy data part and the low-accuracy data part by using an authorized receiver, wherein the encryption and decryption adopt a symmetric key encryption algorithm, and a legal receiver directly acquires a password from a civil aviation telegram system network. In the method, the original target location data is split into the two parts, the accuracy of a broadcast part is reduced, and only the legal receiver can decrypt the high-accuracy target location data, so the security of the data is improved.

Description

A kind of ADS-B target exact position method of encrypting

Technical field

The present invention relates to the air traffic control field.Be to utilize the modern encryption technology specifically; Encrypt target location to broadcasting in Automatic dependent surveillance broadcast (the ADS-B:Automatic Dependence Surveillance-Broadcast) system; Thereby the data of avoiding the ADS-B system to send are received by illegal, improve its Information Security.

Background technology

Field of traffic control aloft; ADS-B is a kind of surveillance technology of cheapness; It is through the data chainning of broadcast mode; Make by observer's (comprise the target that needs such as airborne vehicle or surface car are kept watch on, be also referred to as target) and initiatively send data such as self identification and accurate four-dimensional position, thereby realize PASSIVE SURVEILLANCE.Compare with the traditional radar surveillance technology; ADS-B not only data in time (data break can reach 1 second; And traditional radar data is 4-12 second), accurate positioning (ADS-B uses the GPS positioning accuracy can reach meter level, and the precision of traditional radar is more than the hundreds of meter level); And have low price, advantages such as simple are installed, thereby received great attention.

But because the ADS-B employing is the active broadcast position technique; And frequency, modulation system and the data of broadcasting are various etc. all to be disclosed; This means that anyone can buy and make corresponding receiver devices, receives these high-precision target locations in real time; In case yet the lawless person can obtain these information, maybe the safety to airborne vehicle be caused catastrophic consequence.

Make the authorized receiver just can receive complete positional information; But can not encrypt fully again and need be received, thereby tell the own position of airborne vehicle on every side to avoid the initial purpose of midair crash through broadcasting because this will have influence on ADS-B again by common recipient.

Summary of the invention

The purpose of this invention is to provide a kind of ADS-B target exact position method of encrypting, to strengthen the fail safe of ADS-B system monitoring target data.

The objective of the invention is to realize like this: the high accuracy target position data in the original ADS-B packet at first is divided into low precision and two parts of high accuracy, and wherein the data of low precision nibble are not encrypted, and the high accuracy partial data is encrypted; These two parts data are packaged into the ADS-B downlink data, will be sent by the ADS-B communication port at last.

In the ADS-B data that ground or other ADS-B receiving equipment are received; The low precision nibble data of unencrypted can be by common recipient's direct decoding; Thereby can confirm the rough position of ADS-B target; But error is bigger, thereby reaches position concealment effect and the purpose of impact position broadcasting not of part; The authorized receiver then can decipher the high accuracy partial data and low precision nibble data can restore original high precision position together, thereby makes the authorized receiver unaffected.

Above-mentioned encryption and decryption algorithm uses symmetric key encryption algorithm; The distribution of symmetric key and transmission can adopt the network of civil aviaton's telegraphy to carry out; Legitimate receiver can directly obtain password at this network; Because this network is the network system of a sealing, it is safe using this network system to transmit key.

The invention has the beneficial effects as follows:

1, original high-precision AD S-B target position data is divided into two parts, the data precision of broadcast segment is reduced, thereby reduced the risk of attacking to the ADS-B target;

2, legitimate receiver can obtain key through the earth telegraphy system, thereby decrypts high-precision target data, thereby has improved the safety of ADS-B target.

The present invention adopts the modern encryption technology; High accuracy in the positional information responsive in the ADS-B packet is partly encrypted; Have only the authorized receiver to decipher this part, common recipient then can only obtain low precision position information, is guaranteeing the ADS-B impregnable while of original function like this; Strengthen the fail safe of ADS-B system monitoring target data, thereby improved the fail safe of whole ADS-B system.

Description of drawings

Fig. 1 is an overview flow chart of the present invention.

Fig. 2 is that original high-precision longitude and latitude position of the present invention is split as low precision nibble and high accuracy part sketch map.

Fig. 3 is high accuracy part encryption flow figure.

Fig. 4 is the transmission flow sketch map of ADS-B downlink data packet.

Fig. 5 is the structure sketch map of the downlink data packet of ADS-B newtype.

Fig. 6 is a high precision position data computation flow chart.

Fig. 7 is the transmission of password and obtains schematic flow sheet.

Embodiment

Fig. 1 explanation, the high accuracy target position data in the down-transmitting data of aircraft A at first is divided into high accuracy and two parts of low precision by mode shown in Figure 2; High accuracy partly uses mode shown in Figure 3 to encrypt the formation ciphertext; High accuracy part, low precision nibble and other data necessary are sent from ADS-B information sendaisle by mode shown in Figure 4, are split as the high accuracy part of hanging down precision nibble and encryption at ground base station or other ADS-B receiving equipments; Domestic consumer obtains low precision target location by mode shown in Figure 4; Authorized user obtains the high accuracy target location by mode shown in Figure 6.

Fig. 2 explanation, the longitude of the WGS84 form of general gps system output representes that with 24 latitude is used 23 bit representations usually usually, can represent that 0 spends to the longitude of 360 degree, and-90 degree (south latitude) is to the latitude of 90 degree (north latitude).Its least unit is 2.1457672 * 10 ^-5Degree, near the under the line precision of expression like this is approximately 2.39 meters.We use 12 bit representations with the low precision nibble of longitude, and the low precision nibble of latitude is used 11 bit representations, and both least unit are all reduced to 0.08789 degree, under the line near the distance represented of the longitude and latitude of this precision be approximately 9.8 kilometers.Add the back represent that after high-precision 12, the distance of expression then can reach 2.39 meters.

Fig. 3 explanation, 24 high accuracy datas by the high accuracy part of 12 longitudes and 12 s' latitude high accuracy partly constitutes can use symmetric cryptosystem to encrypt.According to the demand of AES, 128 aes algorithm is output as 128, and the 3DES algorithm is output as 64, and the RC4 algorithm is output as 24.Three kinds of algorithms have the different security rank, and the input of the output of preceding two kinds of algorithms with respect to 24, and expansion is in various degree all arranged.

Fig. 5 explanation, in the ADS-B of UAT pattern system, the valid data length of each bag is 34 bytes (272), comprises a long HDR of 32 (having contained necessary informations such as airborne vehicle (target) sign, bag type), the back is with concrete data.Wherein, bag type 0-10 defines, and 11-31 is undefined, and therefore, we have defined Class1 1 again, and are as shown in Figure 5.Wherein, encryption type is represented the type of back ciphertext.0 represents AES-128, and 1 represents 3DES, and 2 represent RC4.Ciphertext length after the encryption depends on AES.

Fig. 6 explanation, authorized user obtains password by mode shown in Figure 7; Authorized user is being received low accuracy data bag, and after receiving the high accuracy data bag Class1 1 of encryption; High accuracy data in the authorized user decrypted packet Class1 1; Reduce high accuracy longitude and latitude data in the former bag; Authorized user finally can obtain high-precision target longitude and latitude position.

Fig. 7 explanation, authorized user can obtain password through civil aviaton's telegraph network.Its flow process is: at first report the remarks item in (FPL) in the AFTN plan of navigating, increase " KEY/ " field; Taking off preceding half an hour, original base will send the FPL newspaper, generate password this moment at random, and by 4 one group, be expressed as character visible with hexadecimal code, and will be as shown in the table.

Coding	The expression character	Coding	The expression character
				0000	0	1000	8
0001	1	1001	9
				0010	3	1010	A
0011	3	1011	B
				0100	4	1100	C
0101	5	1101	D
				0110	6	1110	E
0111	7	1111	F

After FPL is received on relevant airport, search machine tail number and flight number earlier, just store password, then new password more as not finding.

Claims

1. ADS-B target exact position method of encrypting is characterized in that: may further comprise the steps:

A) data in the original ADS-B packet at first are split as low precision nibble and high accuracy part, wherein, hang down the precision nibble data and do not encrypt, and the high accuracy partial data is encrypted;

B) above-mentioned low precision nibble data and encryption back high accuracy partial data are packaged into the ADS-B downlink data packet, and send by the ADS-B communication port;

C) in the ADS-B data that ground or other ADS-B receiving equipment are received, the low precision nibble data of unencrypted are by common recipient's direct decoding, thus the rough position of definite ADS-B target; The authorized receiver deciphers the high accuracy partial data, and restores original high precision position together with low precision nibble data;

Symmetric key encryption algorithm is adopted in above-mentioned encryption and decryption, and the distribution of symmetric key and transmission adopt the network of civil aviaton's telegraphy to carry out, and legitimate receiver directly obtains password at this network;

Data in the said original ADS-B packet are the WGS84 form, and its fractionation mode is following:

A1) with the low precision nibble of longitude in the data with preceding 12 bit representations, the low precision nibble of latitude is with preceding 11 bit representations, thereby forms low precision nibble data;

A2) high accuracy of longitude in the data is partly used back 12 bit representations, the high accuracy of latitude is partly used back 12 bit representations, thereby forms the high accuracy partial data; Said symmetric key encryption algorithm is aes algorithm, 3DES algorithm or RC4 algorithm;

The 5th byte is an encryption type in the said ADS-B downlink data packet: 0 represents AES, and 1 represents 3DES, and 2 represent RC4.

2. a kind of ADS-B target according to claim 1 exact position method of encrypting, it is characterized in that: said ADS-B downlink data packet send mode is following:

When sending packet, at first will be behind the longitude and latitude packet wherein 12 be kept at other places, clear 0 in this bag, also transmission of composition data bag then; Behind the back 12 bit encryption group bags with back 12 and the latitude of the original longitude of preserving, send from the ADS-B communication channel.