RU2785911C1 - System and method for protecting the transmitted data in nmea protocols (text communications protocol of navigation equipment) in vehicle control systems - Google Patents

Abstract

FIELD: communication.

SUBSTANCE: invention relates to the tools for protecting data in a vehicle control system according to the NMEA standard. The data in the navigation equipment of the vehicle (V) for sending to one or more control modules is determined, wherein the data includes a set of geographic coordinates of the navigation equipment. The data are encrypted using the AES128 block encryption algorithm in the ciphertext feedback mode (CFB mode). Based on the encrypted data, one or more messages are generated for transmission according to the NMEA standard without changing the structure and order of message fields. The encrypted data are transmitted according to the NMEA standard to one or more control modules to be decrypted by one or more control modules using the AES128 block encryption algorithm in the CFB mode.

EFFECT: higher degree of protection of the vehicle control system against unauthorised attacks.

20 cl, 9 dwg

Description

FIELD OF TECHNOLOGY

[001] This appendix concerns the National Marine Electronics Association (NMEA) protocol information field protection method, as well as the possibilities of building systems that use this method. These NMEA protocols are used in vehicle control systems.

[002] Recently, the number of cyber attacks, including attacks related to vehicles, has increased dramatically. Since existing vehicle control systems do not have means of protection against information attacks of this kind, it is not difficult for attackers to achieve what they want. Using special technical means, an attacker can easily replace information about the current coordinates of a vehicle, speed, direction of movement, coordinates of neighboring vehicles, etc. This information is used by the control system for subsequent decision making in automatic or manual mode. Incorrectly transferred data can lead to undesirable consequences, such as:

- collision with another vehicle;

- collision with civilian objects;

- failure of individual subsystems or units;

- human sacrifice;

- and others.

[003] Thus, it is obvious that there is an urgent need to develop a method for providing protection against cyber attacks of this kind. This method describes one of the options for providing this type of protection.

[004] The main purpose of the method described here is to prevent unauthorized attacks (caused by, but not limited to the substitution of transmitted data) on the vehicle control system. The implementation of the described method can be presented as a separate system or as an addition to an existing system. The structure of the system has various implementation options using software or hardware.

[005] The technology described here defines a method for protecting data transmitted over the NMEA protocols. It provides protection against unauthorized intervention and substitution of information in the data fields of this Protocol. A device identification process is also provided. The introduction of this technology serves as an addition to the extension of the NMEA protocols.

[006] The NMEA protocols define the rules for organizing data exchange between vehicle equipment (mainly, but not limited to, maritime and rail transport). The NMEA standard is designed to provide a communication channel between navigation equipment (time signal receiver) and a control center or control device(s).

BRIEF DESCRIPTION OF THE DRAWINGS

[007] FIG. 1 shows a typical topology of connected devices in the NMEA serial bus standard;

[008] FIG. 2 shows the structure of the NMEA fields;

[009] FIG. 3 shows a man-in-the-middle attack on the NMEA serial bus;

[0010] FIG. 4 shows the NMEA message format (CGA identifier);

[0011] FIG. 5 shows the formation (preparation) of a sequence of geographic coordinate data for encryption;

[0012] FIG. 6 shows a functional block diagram of the implementation of the AES128 encryption algorithm (CFB mode) into the standard NMEA protocol;

[0013] FIG. 7 shows the distribution of the ciphertext in the field packet of the standard NMEA protocol;

[0014] FIG. 8 shows a block diagram of an implementation of an AES128 block cipher algorithm (CFB mode) and a decryption method for the NMEA standard;

[0015] FIG. 9 shows a generalized block diagram of a system using the described method.

IMPLEMENTATION OF THE INVENTION

[0016] This invention relates to a method for protecting individual data fields of an NMEA message containing, among other things, information about the geographic coordinates of the vehicle (but without limitation). This data is the most important piece of information transmitted through the NMEA protocol.

[0017] According to the NMEA standard, the navigation coordinates of the vehicle can be transmitted in only two types of messages: messages of the transmitting device and internal messages.

[0018] The NMEA standard defines a range (over 50) of message options for output signal types. Each of these is defined in a message identifier field (202), namely via the SSS (message identifier) parameter. The message format for the "output" type is shown in FIG. 2.

[0019] The geographic coordinates of the vehicle for "transmitter messages" are transmitted along with the following SSS message identifiers (202):

- [WEIGHT] direction and distance to the next waypoint;

- [BWR] direction and distance to the next waypoint;

- [GGA] fixed data of the global positioning system;

- [GLL] geographic location;

- [RMA] recommended minimum navigation information;

- [RMB] recommended minimum navigation information;

- [RMC] recommended minimum navigation information;

- [WPL] location of the next waypoint;

- other.

[0020] The geographic coordinates of the vehicle for some established "internal messages" are transmitted along with the following message identifiers:

- $PGRMFPosition fix sentence (fixed position message);

- $PGRMISensor Initialization Information (sensor initialization information);

- and others.

[0021] The navigational coordinates of the vessel are determined by two parameters: latitude and longitude.

[0022] The latitude value for "transmitter messages"/"internal messages" is in one of the fields of the data packet (204) in FIG. 2. For each of the SSS message identifiers (202), a specific field has a designated place in the overall message field sequence (according to the NMEA standard).

[0023] The latitude value has the following representation format - VVVV.VVVV, (BB - degrees; BB.VVVV - integer degrees and minutes; a - N/S north/south).

[0024] The longitude value for "transmitter messages"/"internal messages" is in one of the fields of the data packet (204) of FIG. 2. For each of the SSS message identifiers (202), a specific field has a designated place in the overall message field sequence (according to the NMEA standard).

[0025] The longitude value has the following representation format - LLLLL.LLLL (LLL - degrees; LL.LLLL - integer degrees and minutes; a - E/W east/west).

[0026] FIG. 4 shows a description of a message with type identifier GGA (Global Positioning System Fixed Data). Therein, the data packets represented by field 204 have the following purposes: field observation time (204.1); latitude (204.2+204.3); longitude (204.4+204.5); observation quality indicator (204.6); the number of satellites used may differ from their number in the field of view (204.7); the value of the horizontal geometric factor (ratio of change in navigational coordinate to change in distance) (204.8); altitude above mean sea level (204.9); the unit of height is meters (204.10); excess of geoid over ellipsoid WGS-84 (204.11); the unit of measure is meters (204.12); differential adjustment time (204.13); differentiating station identifier (204.14);

[0027] The information to be protected consists of two components: BBBB.BBBB, a+LLLLL.LLLL, a (latitude + longitude).

[0028] As one of the ways to protect this data, it is proposed to use the AES block cipher algorithm with an encryption key length of 128 (AES128). However, to use this method, the following conditions must be met - the length of each block must be equal to the length of the encryption key (key), namely 128 bits.

[0029] FIG. 5 shows the method for generating received data sequences (211) used for encryption. Data packets 204.2, 204.3, 204.4, 204.5 contain initial information for compiling such a data sequence. The total length of the sequence (211) is 76 bits.

[0030] There are several ways to solve the problem of a different length of the encryption key (128 bits) and message block (76 bits) when using the block cipher algorithm. The proposed method considers the use of AES128 in CFB mode (ciphertext feedback mode).

[0031] To use the AES128 encryption algorithm, all devices must have the same encryption key. Therefore, this information must be transmitted to devices before they start working. The methods and channels for transmitting the encryption key may differ and are determined by the organization.

[0032] In CFB mode, you must additionally use the Initialization Vector parameter/initialization vector (IV). This parameter, like the encrypted key, must be identical on all devices.

[0033] In the proposed method, the IV parameter is used as a device identification factor. The same IV can be used both on a permanent basis and on each new communication session. Methods may differ and are determined by the organization.

Based on the measures described above, the NMEA protocol provides the following:

- protection (encryption) of data fields; and

- Identification of devices within the NMEA Protocol.

[0034] FIG. 1 shows a typical topology of NMEA devices connecting to each other. Navigation device (101), time signal receiver can be any device that supports the NMEA standard in terms of messaging, and is also capable of operating in one or more satellite navigation systems (GPS, GLONASS, DORIS, BeiDou, Galileo, etc.). ). The control modules (102, 103, 104) receiving information from the time signal receiver device can be any device or system, for example: navigation equipment, satellite dishes, laser radars (lidars), radars, radar stations, automated ship traffic systems and etc.). A person skilled in the art will understand that different devices or centers can be used as modules. The number of such devices is determined by the system topology and the technical characteristics of the communication interface. Switching of all devices participating in data exchange according to the NMEA standard is carried out through communication lines (111, 112, 113, 114).

[0035] As a communication interface, an asynchronous serial interface RS-422/485 or a CAN interface is used to combine a device for receiving a time signal or a navigation device (101) and control modules (102, 103, 104).

[0036] NMEA protocols describe the format of the transmitted messages, as well as the exchange rate. These parameters have different values for different standards (NMEA-0183, NMEA-2000) written directly in the standards themselves.

[0037] The NMEA standard is a text Protocol (in ASCII format). The message can be of three types:

- Messages of the transmitting device;

- Messages - requests;

- Internal messages.

[0038] FIG. 2 shows the generalized structure of the fields of the output signals. Messages start with the symbol "$" (201) and end with the symbol "*" (205). The message is identified by a header (202), where tt is the navigation system ID; sss - message identifier. Next, depending on the message identifier, a data packet (204) is transmitted, the number of which depends on the message type. All data fields are separated by the symbol "," (203). The "hh" (206) message is the result of the 8-bit XOR sum of all characters (including ",") in the sequence between "$" and "*", shortened to two uppercase ASCII characters for a 16-bit byte representation ( 0-9, A-F). "CR" (207) - carriage return and "LR" (208) carriage return fields serve as indication of the end of the message transmission.

[0039] In modern vehicles, especially in maritime and rail transport, the NMEA serial data standard is widely used for transmitting ship management and control data (including geographic coordinates). These serial networks are often "linked" at several points to higher level ship control networks, including GPS, satellite terminal, ECDIS, etc.

[0040] These serial networks (based on NMEA) are used not only to transmit geographic coordinates, but also to control the operation of individual components such as steering mechanism, engines, ballast pumps, etc.

[0041] In particular, due to the fact that the first versions of the NMEA standard were published in the 90s of the XX century, this standard is not able to fully guarantee the security of transmitted data.

[0042] However, subsequent versions of this standard (including the new generation of the NMEA-2000 standard) have not solved the above problems. The main disadvantages of the NMEA standard are the lack of identification, encryption or verification of all messages. All data is transmitted in text format as ASCII characters. This allows an attacker to freely modify data while connected to a serial network (for example, in a man-in-the-middle attack). For example, the use of GPS spoofing (connection imitation) leads to the "injection" of subtle errors that slowly but surely deviate the ship or other vehicle from the course. Incorrect information about the position of the vehicle can lead to such consequences as:

♦ Vehicle accident;

♦ Collision with other vehicles;

• Damage to infrastructure;

• Human sacrifice.

[0043] In an attack, attackers modify (but not limited to spoofing) information about the position and speed of the vehicle, that is, the data that a control system, such as a port dispatcher, receives and transmits, in order to avoid collision with other ships. An attack on a GPS signal or connection to a control system can cause navigational problems up to a vehicle collision, which always results in serious damage and sometimes loss of life.

[0044] The reason for such attacks is a vulnerability in the NMEA standard software. The set of measures that allow protecting a vehicle, reporting an attack and eliminating it, is related to the information security of vehicles (primarily, among other things, with modern ships and rail transport).

[0045] FIG. Figure 3 shows one possible attack (using man-in-the-middle technology) on the NMEA serial data bus. We are looking at the case where an attacker has connected to your device (121). Thus, he can, at his own discretion, change the NMEA data fields in the messages sent by the navigation device (101), while remaining unnoticed by other modules (102, 103, 104).

[0046] There are several ways to protect against the attacks shown: protection at the software level and/or protection at the hardware level.

[0047] The method presented in this invention provides protection of NMEA data fields based on encryption/decryption without changing the structure and sequence of fields.

Detailed Description of the Preferred Embodiment of the Invention

[0048] FIG. 6 shows a block diagram of the AES128 block cipher (CFB mode). The length of the ciphertext is 76 bits. The encryption key (301) is 128 bits long, as is the Initialization Vector (302). At the beginning of the algorithm, the initialization vector (302) is encrypted using the AES128 block cipher. The encryption takes place in a Block cipher encryption (303) using an encryption key (301). The result of encryption is a sequence of 128 bits (304). Then, the first 76 bits of information are extracted from the received sequence, and an additional operation modulo two XOR (305) is performed. The input data after adding the operation module two to the previously obtained sequence is entered into the required prepared field (211). As a result of operation (305), the ciphertext (304) is 76 bits long.

[0049] Upon receipt of the ciphertext, an NMEA message packet is generated.

[0050] FIG. 7 shows the distribution of ciphertext in the fields of a standard NMEA protocol message packet (eg CGA). The resulting ciphertext (304) is 76 bits long, which corresponds to the number of ASCII characters (19 at 4 bits per character). In FIG. 7, every 4 bits of information are numbered from A1 to A19. As previously shown in FIG. 5, the bits numbered A1 through A19 are strictly encapsulated in a standard NMEA message packet.

[0051] The generated final packet is sent over the communication channel to available receivers. Upon receipt of this packet by the receiver, the reverse process of decapsulation and decryption is performed.

[0052] FIG. 8 shows a functional block diagram of the AES-128 algorithm (CFB mode) used to decrypt a 76 bit message. The encryption key (301) is 128 bits long, as is the initialization vector (302). At the beginning of the algorithm, the initialization vector (302) is encrypted using the AES128 algorithm. The encryption takes place in the encryption block (303) using the encryption key (301). The result of encryption is a sequence of 128 bits (304). Then, the first 76 bits of information are extracted from the received sequence, and an additional operation is performed - module 2 XOR (305) is performed. The input data after the operation of module 2 in addition to the previously received sequence becomes the received ciphertext (304). The result of operation (211) is the navigation coordinates, which can then be used by the receiver to the destination.

[0053] FIG. 9 shows a generalized block diagram of a system that implements the specified method of protecting data transmitted in the NMEA standard. To implement the algorithms described above, the encryption/decryption units (401, 402) are built into the time signal receiver or navigation device (101), as well as into the control device (102). These modules allow you to implement the AES-128 block cipher algorithm (CFB mode).

Claims (31)

1. A system for protecting data transmitted in a vehicle control system according to the NMEA standard, including: navigation equipment of the vehicle (V) and one or more control modules connected by means of communication with the navigation equipment of the vehicle according to the NMEA standard; and an encryption/decryption unit built into the navigation equipment of the vehicle, an encryption/decryption unit built into each one or more control modules, wherein the encryption/decryption of data transmitted between the navigation equipment of the vehicle and one or more control modules is carried out using the AES128 block cipher algorithm in the feedback mode from the ciphertext (Cipher Feedback Mode, CFB mode), and based on the encrypted data, one or more messages are generated for transmission according to the NMEA standard without changing the structure and sequence of the message fields. 2. The system according to claim 1, in which the data includes a set of geographical coordinates of the navigation equipment of the vehicle to be sent to one or more control modules, the encryption/decryption block in the navigation equipment of the vehicle contains instructions for encrypting a set of geographic coordinates using the AES128 block cipher algorithm in CFB mode, and the encryption/decryption unit in each one or more control modules includes instructions for encrypting a set of geographic coordinates received from the navigation equipment of the vehicle to determine its location; and the system applies to geographic coordinates and the entire NMEA protocol data stream. 3. The system according to claim 2, in which a set of geographical coordinates of the navigation equipment of the vehicle is sent with one of the following message identifiers: direction and distance to the next waypoint (BEC), direction and distance to the next waypoint (BWR), fixed data in the system global positioning (GGA), geographic position (GLL), recommended minimum navigation information (RMA), recommended minimum navigation information (RMB), recommended minimum navigation information (RMC), next waypoint location (WPL), fixed position message $PGRMFPosition and information about $PGRMISensor sensor initialization. 4. The system according to claim 2, in which the set of geographical coordinates of the navigation equipment of the vehicle includes a latitude parameter and a longitude parameter, in which latitude and longitude parameters are given in the following format, respectively: BBBB.BBBB, a (BB is degrees; BB.BBBB is whole degrees and minutes; a is North/South) and LLLLL. LLLL, a (LLL is degrees; LL.LLLL is whole degrees and minutes; a is East/West). 5. The system of claim 2, wherein the encryption/decryption unit in the navigation equipment of the vehicle also includes instructions for encrypting the first initialization vector using the first encryption key and determining the ciphertext to be sent to the control module, wherein the ciphertext is based on the encrypted first initialization vector and a set of geographical coordinates of the navigation equipment of the vehicle. 6. The system of claim 5, wherein the encryption/decryption unit in each one or more control modules also contains instructions for obtaining the ciphertext, encrypting the second initialization vector using the second encryption key, and locating the vehicle navigation equipment based on the encrypted second initialization vector and ciphertext. 7. The system of claim 6, wherein the first initialization vector and the second initialization vector are the same. 8. The system of claim. 7, in which the first initialization vector and the second initialization vector are entered by the user in manual or automatic mode. 9. The system of claim. 6, in which the first encryption key and the second encryption key are the same; and in which the first encryption key and the second encryption key can be entered manually or automatically. 10. A method for protecting data in a vehicle control system according to the NMEA standard, including: determining data in the navigation equipment of the vehicle (TC) to send to one or more control modules, wherein the data includes a set of geographic coordinates of the navigation equipment; data encryption using the AES128 block cipher algorithm in ciphertext feedback mode (CFB mode); generating, based on the encrypted data, one or more messages for transmission according to the NMEA standard without changing the structure and sequence of the message fields; and sending encrypted data according to the NMEA standard to one or more control modules for decryption by one or more control modules using the AES128 block cipher algorithm in CFB mode; and the method applies to geographic coordinates and the entire NMEA protocol data stream. 11. The method according to claim 10, in which the definition of data includes the definition of a set of geographical coordinates of the navigation equipment of the vehicle, and in which the set of geographical coordinates includes a latitude parameter and a longitude parameter in the following format, respectively: BBBB.BBBB, and (BB - degrees; BB .BBBB is whole degrees and minutes; a is North/South) and LLLLL.LLLL, a (LLL is degrees; LL.LLLL is whole degrees and minutes; a is East/West). 12. The method of claim 11, wherein sending the encrypted information data includes sending a set of geographic coordinates with one of the following message identifiers: direction and distance to the next waypoint (BEC), direction and distance to the next waypoint (BWR), fixed data in Global Positioning System (GGA), Geographical Position (GLL), Recommended Minimum Navigation Information (RMA), Recommended Minimum Navigation Information (RMB), Recommended Minimum Navigation Information (RMC), Next Waypoint Location (WPL), Fixed Position Message $PGRMFPosition and initialization information for the $PGRMISensor sensor. 13. The method of claim. 10, in which data encryption includes encrypting the first initialization vector using the first encryption key and determining the ciphertext based on the encrypted first initialization vector and data to send to one or more control modules, and in which sending the encrypted data includes sending a specific ciphertext to one or more control modules for decryption. 14. The method of claim 13, further comprising receiving the ciphertext by the one or more control modules, encrypting the second initialization vector using the second encryption key, and determining data from the vehicle navigation equipment based on the encrypted second initialization vector and the ciphertext. 15. The method of claim 14, wherein the first initialization vector and the second initialization vector are the same. 16. The method of claim 15, wherein the first initialization vector and the second initialization vector are entered manually or automatically by the user. 17. The method according to p. 14, in which the first encryption key and the second encryption key are the same; and where the first encryption key and the second encryption key can be entered manually and automatically. 18. The method of claim 13, wherein determining the ciphertext includes performing an XOR sum between a predetermined number of bits of the encrypted first initialization vector and data to be sent to one or more control modules. 19. The method of claim 14, wherein determining the data includes performing an XOR between a predetermined number of bits of the encrypted second initialization vector and the ciphertext. 20. The method of claim 14, wherein the navigation equipment and one or more control modules each include an encryption/decryption unit, including instructions for executing the AES128 block cipher algorithm in CFB mode.

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