WO2021042736A1

WO2021042736A1 - Encryption method for application data unit in water conservancy industrial control system

Info

Publication number: WO2021042736A1
Application number: PCT/CN2020/085872
Authority: WO
Inventors: 陈宁; 高祥涛; 王美玲; 朱月; 曹晓宁; 张磊; 王培�; 陈辉; 陆明; 赵峰
Original assignee: 江苏省水文水资源勘测局
Priority date: 2019-09-06
Filing date: 2020-04-21
Publication date: 2021-03-11
Also published as: CN110557244A; CN110557244B

Abstract

Disclosed is an encryption method for an application data unit in a water conservancy industrial control system. By means of installing an encryption proxy program between an application program of the water conservancy industrial control system and a field bus communication program, transparent encryption of the application data unit is realized. In the encryption proxy program, an encryption scheme based on a domestic symmetrical encryption algorithm is used to realize the functions of control device identity verification, field bus communication data secrecy, and protocol packet integrity checking, such that an unauthorized illegal device is effectively prevented from monitoring, intercepting and tampering with data monitoring and control information on a channel of the field bus, a high resistance to man-in-the-middle attacks is provided, and security risks caused by invasion into the channel of the field bus in a water conservancy automation control system are reduced. The encryption proxy program can seamlessly access current existing water conservancy industrial control systems, and has a high device compatibility and universality.

Description

An encryption method for application data unit in water conservancy industry control system

Technical field

The invention belongs to the field of information technology, and particularly relates to an encryption method for application data units in a water conservancy industry control system.

Background technique

In the water conservancy industrial control systems currently deployed in my country, most of them use Field Bus (Field Bus) network to network the programmable logic controller (PLC) and the lower computer. The reason is that the physical layer media used in computer networks, such as STP, single-mode or multi-mode fiber, etc., cannot meet the physical properties of high weather resistance and high strength industrial application scenarios. With its excellent performance and price advantage, RS232/485 cable has more than 20 years of application history in industrial automation control systems and cannot be replaced in a short time. To replace the existing physical layer, the cost of implementing the transformation is too high, and will even be higher than the cost of the original deployment system. If wireless networking is used, the reliability and stability of the network will be reduced, and it cannot be implemented in the signal shielding scene, which has high limitations.

At present, most PLCs used in water conservancy automation control systems do not have computer network communication capabilities, and must be equipped with matching hardware interfaces. For the transformation of existing equipment, the implementation cost is also too high, and the different requirements of electrical and interface specifications between different manufacturers must be considered, and the cost-effectiveness is low. Although the Modbus TCP protocol supports transparent transmission in computer networks, its implementation is relatively simple and cannot support the security features of the network layer and transmission layer in the TCP/IP protocol. Special modifications to the network module are required, and the versatility is not strong.

Most electrical engineers only have the development experience of data communication in the field bus network. If a computer network is used to replace the field bus, there must be sufficient personnel support, which means that the relevant knowledge system, training materials, courses, practices, and processes need to be established first. Due to the long training period of electrical engineers at present, they do not yet have the personnel foundation to implement computer network transformation.

In summary, the idea of reusing relevant theories and technologies in computer networks to solve the security problems of fieldbus networks in water conservancy industrial control systems has considerable limitations under the current personnel and technical conditions.

Therefore, how to propose a low-cost and highly applicable encryption scheme for the fieldbus channel under the premise of reducing the cost of transformation, and realize the identity verification of the control equipment, the confidentiality of the fieldbus communication data, and the encryption scheme based on the domestic symmetric encryption algorithm. The protocol packet integrity check function is a subject with high research and application value.

Summary of the invention

Purpose of the invention: In view of the above problems, the present invention proposes a data unit encryption method in a water conservancy industrial control system to realize the functions of control equipment identity verification, fieldbus communication data confidentiality, and protocol packet integrity verification.

Technical solution: In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is:

An encryption method for application data units in a water conservancy industry control system includes the following steps:

S1: Install a copy of the encryption agent program on each control device connected to the fieldbus. Once the encryption agent program starts to work, it is injected into the process of the water conservancy industry control system application program and the fieldbus communication program through a hook. Write the corresponding session key and destination address code in advance in the key configuration file of the encryption agent program. The encryption function is preset in the encryption agent program to support common symmetric encryption and hash algorithms. The symmetric encryption algorithms include but are not limited to SM1, RC4, and AES; the hash algorithms include but are not limited to SM3, MD5, and SHA- 1 algorithm. The control equipment includes but is not limited to PLC, lower computer, sensor, and controller.

S2: After the control device is turned on, the encryption agent program is started through the script. The encryption agent program starts to work, and is injected into the water conservancy industrial control system application program and the process of the fieldbus communication program through a hook, and initializes the key configuration file of the encryption agent program; if the initialization process is completed, go to step S3 ; If the initialization process is terminated, no subsequent operations are performed; the initialization process is as follows:

(2-1) Find all the stored destination address codes in the key configuration file and the corresponding session key records;

(2-2) Store at least one destination address code and the corresponding session key in the key configuration file; determine whether the number of session key records is greater than or equal to 1, if the number of session key records is greater than or equal to 1, The initialization process is complete; otherwise, the initialization process is terminated and no subsequent operations are performed.

S3: After the initialization of the encryption agent's key configuration file is completed, the monitoring process begins; the monitoring process includes two parts: First, the serial communication application data unit for all incoming encryption agent programs on the interface of the fieldbus communication program ADU monitors; second, monitors all serial communication application data units ADUs of incoming encrypted agent programs on the interface of the water conservancy industrial control system application program; the steps are as follows:

(3-1) On the interface of the fieldbus communication program, monitor all the serial communication application data units ADU passed into the encryption agent program;

(3-1-1) When the encryption agent program receives the incoming serial communication application data unit ADU from the interface of the fieldbus communication program, it sends an interrupt request to the encryption function. The encryption function responds to the interrupt and enters the interrupt processing process. The check code CRC at the end of the application data unit ADU is used to check the rest of the data in the unit except the CRC. The check algorithm uses the internal preset hash algorithm in the encryption function. , Including but not limited to SM3, MD5, SHA-1 algorithms.

(3-1-2) If the verification fails, the encryption function is interrupted and returned, and there is no response to the application data unit ADU. If the verification is successful, the encryption function uses the destination address code ADDR of the ADU header of the application data unit to find the session key PK corresponding to the destination address code ADDR in the key management module. ADDR is hexadecimal (HEX) data greater than or equal to 1 byte.

(3-1-3) If the session key PK does not exist, the encryption function is interrupted and returned, and no response is made to the application data unit ADU; if the session key PK exists, the session key PK is used, and the symmetric encryption is built in the encryption function The algorithm decrypts the ciphertext CK located in the header of the protocol data unit (Protocol Data Unit, PDU) in the application data unit ADU, and obtains the data plaintext PD. Symmetric encryption algorithms include but are not limited to SM1, RC4, and AES algorithms.

(3-1-4) The data plaintext PD is used as the new protocol data unit PDU2. The destination address code ADDR is appended to the header of PDU2, and the check code CRC2 of PDU2 is calculated and appended to the end of PDU2 as a new application data unit ADU2. The verification algorithm uses the internally preset hash algorithm in the encryption function, including but not limited to SM3, MD5, and SHA-1 algorithms.

(3-1-5) Send ADU2 through the interface of the water conservancy industry control system application program.

(3-2) Monitor all serial communication application data units ADU passed into the encrypted agent program on the interface of the water conservancy industrial control system application program;

(3-2-1) When the encryption agent program receives the incoming serial communication application data unit ADU from the interface of the water conservancy industry control system application program, it sends an interrupt request to the encryption function. The encryption function responds to the interrupt and enters the interrupt processing process. The check code CRC at the end of the application data unit ADU is used to check the rest of the data in the unit except the CRC. The check algorithm uses the internal preset hash algorithm in the encryption function. , Including but not limited to SM3, MD5, SHA-1 algorithms.

(3-2-2) If the verification fails, the encryption function is interrupted and returned, and there is no response to the application data unit ADU. If the verification is successful, the encryption function uses the destination address code ADDR of the ADU header of the application data unit to find the session key PK corresponding to the destination address code ADDR in the key management module. Among them, ADDR is hexadecimal (HEX) data greater than or equal to 1 byte.

(3-2-3) If the session key PK does not exist, the encryption function is interrupted and returned, and no response is made to the application data unit ADU; if the session key PK exists, the protocol data unit PDU in the application data unit ADU is used as the data Plain text PD.

(3-2-4) Use the session key PK to encrypt the data plaintext PD through the built-in symmetric encryption algorithm to obtain the ciphertext CK. Symmetric encryption algorithms include but are not limited to SM1, RC4, and AES algorithms.

(3-2-5) Use the cipher text CK as the new protocol data unit PDU2. The destination address code ADDR is appended to the header of PDU2, the check code CRC2 of PDU2 is calculated and appended to the end of PDU2 as a new application data unit ADU2. The check algorithm uses the internally preset hash algorithm in the encryption function, including but not limited to SM3, MD5, SHA-1 algorithm.

(3-2-6) Send ADU2 through the interface of the fieldbus communication program.

S4: After the encryption agent program starts to execute the monitoring process, the monitoring process is terminated if and only when the control device is turned off. Otherwise, the monitoring process is always performed. After the control device is turned off, and only when the control device is turned on again, the encryption agent program is started through the script, and the encryption agent program re-executes the initialization process described in step S2 and the monitoring process described in step S3.

Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

The invention installs an encryption agent program between the application program of the upper computer, lower computer and other control equipment of the water conservancy industrial control system and the field bus communication program, and uses a symmetric encryption algorithm to realize the transparency of the protocol data unit (PDU) Encryption provides control equipment authentication, fieldbus communication data confidentiality, and protocol packet integrity verification functions, which can effectively prevent unauthorized and illegal equipment from monitoring, intercepting, and tampering with data monitoring and control information on the fieldbus channel. The man-in-the-middle attack has high resistance and reduces the security risk caused by the intrusion of the field bus channel in the water conservancy industrial control system. Compared with the link layer plaintext data transmission method adopted in the existing fieldbus, it can provide reliable safety guarantee for the water conservancy industrial control system as a key infrastructure in the national economy. The invention has higher compatibility and versatility, does not need to change the field bus network topology and the physical layer transmission media, and can realize the low-cost transformation of the existing water conservancy industrial control system.

Description of the drawings

Figure 1 is a schematic diagram of an encryption agent program module;

Figure 2 is the data structure of the communication packet from the fieldbus communication program interface to the application program interface during the monitoring process;

Figure 3 is the communication packet data structure from the application program interface to the fieldbus communication program interface during the monitoring process;

Figure 4 is a flowchart of the initialization process;

Figure 5 is a flow chart of the monitoring process of the fieldbus communication program interface;

Figure 6 is a flowchart of the application program interface monitoring process.

detailed description

The technical solution of the present invention will be further described below in conjunction with the drawings and embodiments.

Suppose that in a water industry control system, there are control devices D1, D2, and D3 respectively on the same field bus, where D1 is the upper computer, set to master mode, and the address is 0x01; D2, D3 are lower computers, set to slave mode, The addresses are 0x02 and 0x03 respectively.

The method for encrypting application data units in a water conservancy industry control system according to the present invention includes the following steps:

S1: Use the configuration file in advance to write the key to the key configuration file of the encryption agent copy G1, G2, G3 according to the following rules:

In G1, write the session key of address 0x01 and D1 of D1; write the session key of address 0x02 and D2 of D2; write the session key of address 0x03 and D3 of D3.

In G2, write the address 0x02 of D2 and the session key of D2; write the address 0x01 of D1 and the session key of D1.

In G3, write the address 0x03 of D3 and the session key of D3; write the address 0x01 of D1 and the session key of D1.

Install the copies G1, G2, and G3 of the encryption agent program on the devices D1, D2, and D3, respectively.

S2: After D1, D2, and D3 are turned on, run G1, G2, and G3 through scripts. After G1, G2, and G3 are started, they are injected into the process of the water conservancy industrial control system application program and the fieldbus communication program on D1, D2, and D2 through hooks respectively, and the initialization process of the key configuration file is started. The process is shown in Figure 4. The initialization process is as follows:

Find all the stored destination address codes in the key configuration file and the corresponding session key records; determine whether the number of session key records is greater than or equal to 1, if the number of session key records is greater than or equal to 1, the initialization process Complete; otherwise, the initialization process is terminated and no subsequent operations are performed.

Since the session key written in the above step S1 meets the requirements of the initialization process, the initialization process is completed, and G1, G2, and G3 start to perform the monitoring process.

S3: When D1 sends a serial communication application data unit ADU to D2, set the destination address of the ADU to be 0x02, the encryption agent copy G1 generates an interrupt, and its encryption function responds to the interrupt and starts the interrupt processing process, as shown in Figure 6. . Since the session key of D2 is written in G1, the original ADU sent by D1 is processed by G1 and becomes an encrypted ADU, which enters the field bus through the interface of the field bus communication program. The communication packet data structure is shown in Figure 3. .

When the encryption agent copy G2 receives the above-mentioned encrypted ADU sent by G1, G2 generates an interrupt, and its encryption function responds to the interrupt and begins to enter the interrupt processing process, as shown in Figure 5. Because the session key of D2 is written in G2, the ADU sent by G1 is processed by G2 and then restored to plaintext, and transmitted to D2 through the interface of the water conservancy industrial control system application program. The communication packet data structure is shown in Figure 2. At this time, D2 receives the serial communication application data unit ADU sent by D1, can perform related operations, and can feed data back to D1.

Since the ADU destination address returned by the slave device to the master in the Modbus protocol is always the device address, the returned packet destination address is 0x02, the encryption agent copy G2 generates an interrupt, and its encryption function responds to the interrupt and begins to enter the interrupt processing process, as shown in the figure 6 shown. Since the session key of D2 is written in G2, the original ADU sent by D2 is processed by G2 and becomes an encrypted ADU, which enters the field bus through the interface of the field bus communication program. The communication packet data structure is shown in Figure 4. .

When the encryption agent copy G1 receives the above-mentioned encrypted ADU sent by G2, G1 generates an interrupt, and the encryption function of G1 responds to the interrupt and begins to enter the interrupt processing process, as shown in Figure 5. Because the session key of D2 is written in G1, the ADU sent by G2 is processed by G1 and restored to plaintext, and transmitted to D1 through the interface of the water conservancy industrial control system application program. The communication packet data structure is shown in Figure 2.

Suppose that the malicious attacker sends the malicious device D4 directly to the interface of the fieldbus communication program without using the encryption agent program, and the address of D4 is 0x04. The attacker knows that the address of the master device D1 is 0x01, and tries to send a malicious packet P to D1. In the Modbus protocol, the ADU destination address returned by the slave device to the master is always the device address, and the destination address of P is 0x04. After G1 receives P, it checks whether the address 0x04 and its corresponding session key exist in the key configuration file. Since the address and session key do not exist, G1 discards P and the attack fails.

The malicious attacker copies the encrypted proxy program copy G3 from D3, and then copies it to D4 and runs it, trying to access the encrypted proxy program copy G3 on D4 through the water conservancy industrial control system application program interface, and send a malicious packet PP to D1. Because the addresses of D3 and D4 are different, G3 cannot find D4's address 0x04 and its corresponding session key in the key configuration file. G3 discards the PP and the attack fails.

The embodiments are only to illustrate the technical ideas of the present invention, and cannot be used to limit the scope of protection of the present invention. Any changes made on the basis of the technical solutions based on the technical ideas proposed by the present invention fall into the protection scope of the present invention. .

Claims

An encryption method for application data units in a water conservancy industry control system is characterized in that the method includes the following steps:

S1: Install a copy of the encryption agent program on each control device connected to the field bus, and write the corresponding session key and destination address code in advance in the key configuration file of the encryption agent program; The encryption function is preset in the encryption agent program to support symmetric encryption and hashing algorithms;

S2: After the control device is turned on, the encryption agent program is started through the script; the encryption agent program starts to work, and is injected into the process of the water conservancy industrial control system application program and the fieldbus communication program through the hook, and configures the key configuration file of the encryption agent program Perform initialization; if the initialization process is completed, go to step S3; if the initialization process is terminated, do not perform subsequent operations;

S3: After the key configuration file of the encryption agent is initialized, the monitoring process is started;

S4: After the encryption agent starts to perform the monitoring process, the monitoring process is terminated if and only when the control device is turned off; otherwise, the monitoring process is always performed; after the control device is turned off, and only when the control device is turned on again, it is started by a script The encryption agent program re-executes the initialization process described in step S2 and the monitoring process described in step S3.
The method for encrypting application data units in a water conservancy industry control system according to claim 1, wherein the initialization process in step S2 is as follows:

(2-1) Find all the stored destination address codes in the key configuration file and the corresponding session key records;

(2-2) Determine whether the session key record is greater than or equal to 1. If the session key record is greater than or equal to 1, the initialization process is completed; otherwise, the initialization process is terminated and no subsequent operations are performed.
The method for applying data unit encryption in a water conservancy industry control system according to claim 1, wherein the monitoring process in step S3 includes two parts: one is to encrypt all incoming data on the interface of the fieldbus communication program The serial communication application data unit ADU of the agent program monitors; secondly, the serial communication application data unit ADU of all incoming encrypted agent programs is monitored on the interface of the water conservancy industrial control system application program.
The method for applying data unit encryption in a water conservancy industry control system according to claim 3, characterized in that: monitoring all serial communication application data units ADUs passed into the encryption agent program on the interface of the field bus communication program; step as follows:

(3-1-1) When the encryption agent program receives the incoming serial communication application data unit ADU from the interface of the fieldbus communication program, it sends an interrupt request to the encryption function; the encryption function responds to the interrupt, enters the interrupt processing process, and uses the application The check code CRC at the end of the data unit ADU checks the rest of the data in the unit except the CRC, and the check algorithm uses the internally preset hash algorithm in the encryption function;

(3-1-2) If the verification fails, the encryption function interrupts and returns, and no response is made to the application data unit ADU; if the verification is successful, the encryption function encodes ADDR through the destination address of the application data unit ADU header, in the key management module Find the session key PK corresponding to the destination address code ADDR; ADDR is hexadecimal data greater than or equal to 1 byte;

(3-1-3) If the session key PK does not exist, the encryption function is interrupted and returned, and no response is made to the application data unit ADU; if the session key PK exists, the session key PK is used, and the symmetric encryption is built in the encryption function Algorithm to decrypt the ciphertext CK of the protocol data unit PDU in the application data unit ADU to obtain the data plaintext PD;

(3-1-4) The data plaintext PD is used as the new protocol data unit PDU2; the destination address code ADDR is appended to the header of PDU2, the check code CRC2 of PDU2 is calculated and appended to the end of PDU2 as the new application data unit ADU2; The verification algorithm uses the internally preset hash algorithm in the encryption function;

(3-1-5) Send ADU2 through the interface of the water conservancy industry control system application program.
A method for fieldbus channel encryption in a water conservancy industry control system according to claim 3, characterized in that: all incoming serial communication application data units ADU of the encryption agent program are monitored on the interface of the water conservancy industry control system application program ;Proceed as follows:

(3-2-1) When the encryption agent program receives the incoming serial communication application data unit ADU from the interface of the water conservancy industry control system application program, it sends an interrupt request to the encryption function; the encryption function responds to the interrupt and enters the interrupt processing process, Use the check code CRC at the end of the application data unit ADU to check the rest of the data in the unit except the CRC, and the check algorithm uses the internally preset hash algorithm in the encryption function;

(3-2-2) If the verification fails, the encryption function interrupts and returns, and no response is made to the application data unit ADU; if the verification is successful, the encryption function encodes ADDR through the destination address of the application data unit ADU header, in the key management module Find the session key PK corresponding to the destination address code ADDR in the ADDR; where ADDR is hexadecimal data greater than or equal to 1 byte;

(3-2-3) If the session key PK does not exist, the encryption function is interrupted and returned, and no response is made to the application data unit ADU; if the session key PK exists, the protocol data unit PDU in the application data unit ADU is used as the data Plaintext PD;

(3-2-4) Use the session key PK to encrypt the data plaintext PD through the built-in symmetric encryption algorithm to obtain the ciphertext CK;

(3-2-5) The ciphertext CK is used as the new protocol data unit PDU2; the destination address code ADDR is appended to the header of PDU2, the check code CRC2 of PDU2 is calculated and appended to the end of PDU2, as the new application data unit ADU2, The verification algorithm uses the internally preset hash algorithm in the encryption function;

(3-2-6) Send ADU2 through the interface of the fieldbus communication program.
The method for fieldbus channel encryption in a water conservancy industry control system according to any one of claims 1-5, wherein the symmetric encryption algorithm includes but is not limited to SM1, RC4, and AES; and the hash algorithm includes But not limited to SM3, MD5, SHA-1 algorithms.