WO2021042735A1

WO2021042735A1 - Session key management method in encryption device of water conservancy industrial control system

Info

Publication number: WO2021042735A1
Application number: PCT/CN2020/085870
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: CN110493257A

Abstract

Disclosed in the present invention is a session key management method in an encryption device of a water conservancy industrial control system. The method achieves the distributed credibility of all the nodes on a field bus of the water conservancy industrial control system by distributing, updating, and removing a session key for an encryption device connected to the water conservancy industrial control system. On the field bus of the water conservancy industrial control system, the encryption device is deployed between each node connected to the bus and the bus, and the session key based on a symmetric encryption algorithm is distributed for each encryption device, so that the identity authentication of the device can be realized, and thus, compared with an asymmetric encryption algorithm, the present invention has the advantages of being high in access efficiency, small in time overhead, and strong in compatibility. The present invention does not need to improve an existing bus-type network topology structure, and has high resistance to man-in-the-middle attack. In an automatic control system of the water conservancy industry, the safety risk caused because a field bus channel is subjected to invasion can be reduced, and reliable safety guarantee is provided for key infrastructures in the national economy field.

Description

A session key management method in encryption equipment of water conservancy industry control system

Technical field

The invention belongs to the field of information technology, and particularly relates to a session key management method in an encryption device of a water conservancy industrial control system.

Background technique

In our country's existing water conservancy industry control system, most of the upper computer and the lower computer use fieldbus network to realize data communication, and the communication protocol is mostly Modbus. The structure of Modbus Application Data Unit (ADU) has a high vulnerability in system security: the protocol data unit (PDU) is transmitted in plain text and lacks confidentiality; the integrity check mechanism is too simple and easy to be tampered with; There is no resistance to replay attacks. In order to address the security risks caused by the above-mentioned vulnerabilities in the fieldbus network, the secure transmission of ADU can be realized by deploying encryption equipment between the upper computer, the lower computer and other automation control equipment and the fieldbus. How to manage the keys of such encryption devices is currently a more important issue.

Due to the channel sharing characteristics of the bus-type network and the lower communication rate of the automation control equipment, a separate public key infrastructure (PKI) and certification center (CA) are established in the field bus to achieve centralized key distribution and management. It will have a greater impact on the efficiency of the system, and may even cause a decrease in availability.

Therefore, how to design a set of decentralized fieldbus channel encryption device key management method under the premise of ensuring system efficiency and availability, realize convenient and efficient key distribution, update and removal, and improve the resistance to man-in-the-middle attacks Ability to prevent unauthorized and illegal devices from monitoring, intercepting, and tampering with data monitoring and control information on the field bus channel, and reduce the security risk caused by the intrusion of the field bus channel in the industrial automation control system of the water conservancy industry. The provision of reliable security guarantees by critical infrastructure in the economic field is a subject of high academic and application value.

Summary of the invention

Purpose of the invention: In view of the above problems, the present invention proposes a session key management method in an encryption device of a water conservancy industrial control system to realize a decentralized distributed encryption device key management function.

Technical solution: In order to achieve the purpose of the present invention, the technical solution adopted by the present invention is: a session key management method in an encryption device of a water conservancy industrial control system, which includes the following steps:

S1: Set up a field bus FB of the water conservancy industrial control system, connect the encryption device between the control device and the field bus network physical interface, and initialize the encryption device. The initialization process includes the encryption device session key generation and the encryption device session secret Key pre-distribution;

S2: When the address code of the control device DD on the fieldbus FB changes, the session key of the encrypted device connected to the control device DD is updated. The update process includes generating a new session key for the encrypted device, revoking the original session key, and Encryption device session key pre-distribution;

S3: When the control device DD on the fieldbus FB temporarily or permanently disconnects the logical connection with other devices on the fieldbus FB, remove the session key in the encryption device connected to the control device DD, and move The removal process includes resetting the session key of the encryption device, and deleting the original encryption device key from every other encryption device on the fieldbus FB.

Further, the encryption device is initialized in step S1; the method is as follows:

Use the built-in symmetric encryption module of the encryption device to generate a session key PK, the corresponding symmetric encryption algorithm includes but not limited to DES, AES, SM1; set the address code of the control device connected to the encryption device as DADR;

Use PK and DADR as a two-tuple and write them into the memory of the encrypted device, which includes but not limited to NAND Flash and eMMC; use PK and DADR as a two-tuple and export them to the mobile device MD for pre-allocation For stage use, the form of MD of the mobile device includes but not limited to mobile hard disk, U disk, SD card;

After the session key generation of all encryption devices on the fieldbus FB is completed, the pre-distribution operation is performed on each encryption device. After the pre-distribution is completed, the initialization process ends.

Further, perform pre-allocation operations on each encryption device on the fieldbus FB; the method is as follows:

If the control device connected to the encryption device is the master device (Master), export all the encryption devices connected to other slave devices (Slave) on the fieldbus FB to the two-tuple PK and DADR of the mobile device MD, and write them to the master device respectively In the storage of the connected encryption device;

If the control device connected to the encryption device is a slave device (Slave), export the only encryption device connected to the master device (Master) on the fieldbus FB to the two-tuple PK, DADR of the mobile device MD, and write it to connect with the slave device Of the encrypted device’s memory.

Further, in step S2, when the address code of the control device DD on the field bus FB changes, update the session key of the encrypted device connected to the control device DD; suppose the original address code of the control device DD is DADR, and for its connection The encryption device of, the update method is as follows:

S2.1: Use the built-in symmetric encryption module of the encryption device to regenerate a session key PK_NEW of the encryption device. The corresponding symmetric encryption algorithm includes but not limited to DES, AES, SM1; set the new address code of the control device DD Is DADR_NEW;

Write PK_NEW and DADR_NEW as a two-tuple into the storage of the encrypted device and overwrite the original two-tuple PK and DADR of the encrypted device; use PK_NEW and DADR_NEW as a two-tuple to export to the mobile device MD, and Overwrite the original two-tuple PK and DADR of the encrypted device stored in the MD for use in the pre-allocation phase. The form of the mobile device MD includes but not limited to mobile hard disk, U disk, SD card;

S2.2: After completing the generation of the new session key of the encryption device, perform the operation of revoking the original session key of the encryption device on each other encryption device on the fieldbus FB. If the memory of the other encryption device on the fieldbus FB is If there is the original two-tuple PK and DADR of the encryption device that have been written, delete the two-tuple;

S2.3: After all other encryption devices revoke the original session key of the encryption device, perform a pre-distribution operation on the encryption device;

If the control device DD whose address code connected to the encryption device changes is the master device (Master), export the encryption device to the two-tuple PK_NEW and DADR_NEW of the mobile device MD, and write them to all other slaves connected to the fieldbus FB. In the storage of the encrypted device of the device (Slave);

If the control device DD whose address code changes to the encrypted device is a slave device (Slave), export the encrypted device to the two-tuple PK_NEW, DADR_NEW of the mobile device MD, and write it to the only connected master device on the field bus FB (Master) in the storage of the encryption device;

S2.4: After the pre-allocation of step S2.3 is completed, the update process ends.

Further, in step S3, when the control device DD on the field bus FB temporarily or permanently disconnects the logical connection with other devices on the field bus FB, the session key in the encryption device connected to the control device DD is moved. Except; suppose the original address code of the control device DD is DADR, for the encrypted device connected to it, the removal method is as follows:

S3.1: If there are two-tuples PK and DADR that have been written in the memory of the encryption device, delete the two-tuples and reset the memory of the encryption device to the original state;

S3.2: After resetting the encrypted device, perform the operation of revoking the original session key of the encrypted device on each other encrypted device on the fieldbus FB; if the encrypted device has been written in the memory of the other encrypted device The original two-tuple PK, DADR of, delete the two-tuple;

S3.3: After all other encryption devices revoke the original session key of the encryption device, the removal process ends.

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

The invention realizes the decentralized distributed management of the key of the field bus channel encryption device through the method of offline distribution, update and removal of the symmetric session key. In the fieldbus network of the existing water conservancy industrial control system, there is no need to establish a separate public key infrastructure (Public Key Infrastructure) and a certification center (Certificate Authority) to realize the identity authentication of the control equipment, which has strong equipment compatibility . The invention is compatible with the existing bus-type topology network, does not need to modify the field bus physical layer and the link layer, and can effectively prevent unauthorized and illegal devices from monitoring, intercepting, tampering and other man-in-the-middle attacks on the field bus channel. Compared with the asymmetric encryption scheme, the symmetric encryption scheme adopted in the session key of the present invention has the characteristics of high access efficiency and low time overhead, and therefore has a higher competitive advantage in terms of equipment cost and node processing delay. On the premise of saving computing resources, it reduces the security risk of the fieldbus channel in the industrial control system of the water conservancy industry, and provides a reliable security guarantee for the critical infrastructure in the national economy.

Description of the drawings

Figure 1 is a hierarchical structure diagram of the method of the present invention;

Figure 2 is an initialization flowchart of the present invention;

Figure 3 is an update flow chart of the present invention;

Figure 4 is a removal flow chart of the present invention.

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 conservancy industrial control system, there are control devices D1, D2, and D3 on a field bus FB, 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 control devices D1, D2, and D3 are directly connected to the field bus FB, and no encryption device is deployed between the field bus FB.

The session key management method in the encryption device of the water conservancy industrial control system described in this embodiment, as shown in FIG. 1, includes the following steps:

S1: Deploy the new encryption devices ND1, ND2, and ND3 between the control devices D1, D2, D3 and the fieldbus FB respectively, and perform the following operations on ND1, ND2, and ND3 in turn:

Use the built-in symmetric encryption module of ND1 to generate a session key PK1, and its corresponding symmetric encryption algorithm is SM1. The address code DADR1 of the control device D1 connected to ND1 is 0x01, and PK1 and DADR1 are used as a two-tuple and written into the memory of ND1, which is NAND Flash. PK1 and DADR1 are exported as a two-tuple to the mobile device MD, and the mobile device MD is in the form of a U disk.

Use the built-in symmetric encryption module of ND2 to generate a session key PK2, and its corresponding symmetric encryption algorithm is SM1. The address code DADR2 of the control device D2 connected to ND2 is 0x02, and PK2 and DADR2 are used as a two-tuple and written into the memory of ND2, which is NAND Flash. Export PK2 and DADR2 as a two-tuple to the mobile device MD.

Use the built-in symmetric encryption module of ND3 to generate a session key PK3, and its corresponding symmetric encryption algorithm is SM1. The address code DADR3 of the control device D3 connected to ND3 is 0x03, and PK3 and DADR3 are used as a two-tuple and written into the memory of ND3, which is NAND Flash. Export PK3 and DADR3 as a two-tuple to the mobile device MD.

The control device D1 connected to ND1 is the master device (Master), and all the encryption devices ND2, ND3 connected to the other slave devices (Slave) D2 and D3 on the fieldbus FB are exported to the two-tuples PK2, DADR2 and PK3 of the mobile device MD , DADR3, respectively write into the memory of ND1.

The control device D2 connected to ND2 is a slave device (Slave), which exports the only encryption device ND1 connected to the master device (Master) D1 on the fieldbus FB to the binary group PK1, DADR1 of the mobile device MD, and writes it to the memory of ND2 in.

The control device D3 connected to ND3 is the slave device (Slave), which exports the only encryption device ND1 connected to the master device (Master) D1 on the fieldbus FB to the binary group PK1, DADR1 of the mobile device MD, and writes it to the memory of ND3 in.

At this point, the initialization process is over, and their own session keys are written in the memories of ND1, ND2, and ND3. Among them, the addresses of ND2 and ND3 and the session key are written into the memory of ND1, and the addresses and the session key of ND1 are written into the memory of ND2 and ND3. Therefore, ND1 can perform data communication with ND2 and ND3 respectively, and data communication cannot be performed between ND2 and ND3 due to the lack of the other party's session key, thus realizing communication data isolation between slave devices. The initialization process is shown in Figure 2.

S2: When the control device D2 on the fieldbus FB needs to be replaced due to a fault, the address code of the new device D2 after the replacement is changed from 0x02 to 0x04. For the ND2 that has been deployed between D2 and FB, perform the following operations in sequence:

Use the built-in symmetric encryption module of ND2 to regenerate a session key PK4, and its corresponding symmetric encryption algorithm is SM1. The new address code DADR4 of the new device D2 connected to ND2 is 0x04, and PK4 and DADR4 are written as a two-tuple into the memory of ND2, and the original two-tuple PK2 and DADR2 are overwritten. Export PK4 and DADR4 as a two-tuple to the mobile device MD, and overwrite the original two-tuple PK2 and DADR2 stored in the MD.

Then, search for the original two-tuple PK2 and DADR2 of ND2 in the memory of ND1 and ND3 in turn. Since the two-tuple has been written in the memory of ND1, it is necessary to perform the operation of revoking the original key of ND2, and change the original key of ND2 in the memory of ND1. The two-tuple is deleted.

Finally, perform the pre-allocation operation. Since the control device D2 is a slave device (Slave), the two tuples PK4 and DADR4 exported to the mobile device MD are written into the memory of the encryption device ND1, which is the only encryption device connected to the master device (Master) D1 on the field bus FB.

At this point, the update process ends. The PK2 of the original device D2 is removed from the memory of the encryption device ND2. Even if the original device D2 is connected to the field bus FB through the encryption device ND2, it cannot communicate with the master device D1. The new device D2 can communicate with the main device D1 normally. The update process is shown in Figure 3.

S3: When the control device D3 on the fieldbus FB is scrapped, it needs to permanently disconnect the logical connection with D1 and D2. For the encryption device ND3 that has been deployed between D3 and FB, perform the following operations in sequence:

Since there are two-tuples PK3 and DADR3 that have been written in the memory of ND3, first delete the two-tuples, and then reset the memory of ND3 to the state before the initialization process.

The original two-tuples PK3 and DADR3 of the ND3 that have been written in the memory of the encryption device ND1 connected to the master device D1 are deleted, and the two-tuples are deleted.

At this point, the removal process ends. PK3 does not exist in ND1, ND2, and ND3, and D3 cannot communicate with D1. At this time, even if the scrapped D3 is obtained by a malicious attacker, the D1 and D2 on the fieldbus FB cannot be attacked after accessing the encryption device ND3. If it is necessary to connect a new control device to the encryption device ND3 and access the field bus FB, the encryption devices ND1, ND2, and ND3 need to be initialized again. The removal process is shown in Figure 4.

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

A session key management method in an encryption device of a water conservancy industry control system, characterized in that: the method includes the following steps:

S1: For a field bus of a water conservancy industrial control system, connect an encryption device between the control device and the network physical interface of the field bus to initialize the encryption device; the initialization process includes encryption device session key generation and encryption device session key preprocessing distribution;

S2: When the address code of the control device on the field bus of the water conservancy industrial control system changes, update the session key of the encrypted device connected to the control device; the update process includes generating a new session key for the encrypted device and revoking the original session Pre-distribution of the key and the session key of the encryption device;

S3: When the control device on the field bus of the water conservancy industrial control system temporarily or permanently disconnects the logical connection with other devices on the field bus, remove the session key in the encrypted device connected to the control device; The removal process includes resetting the session key of the encryption device and deleting the original session key of the encryption device from every other encryption device on the fieldbus.
The session key management method in the encryption device of the water conservancy industry control system according to claim 1, wherein the encryption device is initialized in step S1; the method is as follows:

Use the built-in symmetric encryption module of the encryption device to generate a session key PK; set the address code of the control device connected to the encryption device as DADR;

Use PK and DADR as a two-tuple and write them into the storage of the encrypted device; use PK and DADR as a two-tuple and export them to the mobile device MD;

After the session key generation of all encryption devices on the field bus is completed, the pre-distribution operation is performed on each encryption device. After the pre-distribution is completed, the initialization process ends.
The session key management method in the encryption device of the water conservancy industrial control system according to claim 2, wherein the pre-distribution operation is performed on each encryption device separately, and the method is as follows:

If the control device connected to the encryption device is the master device (Master), export all the encryption devices connected to other slave devices (Slave) on the field bus to the two-tuple PK and DADR of the mobile device MD, and write them to the master device respectively. In the storage of the connected encryption device;

If the control device connected to the encryption device is a slave device (Slave), export the only encryption device connected to the master device (Master) on the fieldbus to the two-tuple PK, DADR of the mobile device MD, and write it to connect with the slave device Of the encrypted device’s memory.
The session key management method in the encryption equipment of the water conservancy industry control system according to claim 3, characterized in that: in step S2, when the address code of the control equipment on the field bus changes, encrypt the control equipment connected to it. The device key is updated; suppose the original address code of the control device is DADR. For the encrypted device connected to it, the update method is as follows:

S2.1: Use the built-in symmetric encryption module of the encryption device to regenerate a session key PK_NEW of the encryption device; set the new address code of the control device as DADR_NEW;

Write PK_NEW and DADR_NEW as a two-tuple into the storage of the encrypted device and overwrite the original two-tuple PK and DADR of the encrypted device; use PK_NEW and DADR_NEW as a two-tuple to export to the mobile device MD, and Overwrite the original two-tuple PK and DADR of the encryption device stored in the MD;

S2.2: After completing the generation of the new session key of the encryption device, perform the operation of revoking the original session key of the encryption device on each other encryption device on the field bus. If there are already existing session keys in the memory of the other encryption device on the field bus. The written original two-tuple PK and DADR of the encryption device, delete the two-tuple;

S2.3: After all other encryption devices revoke the original session key of the encryption device, perform a pre-distribution operation on the encryption device;

If the control device whose address code is changed to the encrypted device is the master device (Master), export the encrypted device to the two tuples PK_NEW and DADR_NEW of the mobile device MD, and write them into all other slave devices connected to the field bus ( Slave) in the storage of the encrypted device;

If the control device whose address code changes to the encrypted device is a slave device (Slave), export the encrypted device to the two-tuple PK_NEW, DADR_NEW of the mobile device MD, and write it to the only connected master device (Master) on the field bus. ) In the storage of the encrypted device;

S2.4: After the pre-allocation of step S2.3 is completed, the update process ends.
The session key management method in the encryption equipment of the water conservancy industry control system according to claim 2 or 3 or 4, characterized in that: in step S3, when the control equipment on the field bus is temporarily or permanently disconnected from the field For the logical connection of other devices on the bus, remove the session key in the encrypted device connected to the control device; suppose the original address code of the control device is DADR. For the encrypted device connected to it, the removal method is as follows:

S3.1: If there are two-tuples PK and DADR that have been written in the memory of the encryption device, delete the two-tuples and reset the memory of the encryption device to the original state;

S3.2: After resetting the encryption device, perform the operation of revoking the original session key of the encryption device on each other encryption device on the field bus; if there is an encrypted device written in the memory of the other encryption device The original two-tuple PK, DADR, delete the two-tuple;

S3.3: After all other encryption devices revoke the original session key of the encryption device, the removal process ends.
A session key management method in an encryption device of a water conservancy industry control system according to claim 2 or 4, characterized in that: a symmetric encryption module built into the encryption device is used to generate a session key PK, and its corresponding symmetric encryption algorithm Including but not limited to DES, AES, SM1.
According to claim 2 or 4, a session key management method in an encryption device of a water conservancy industry control system, characterized in that: the memory of the encryption device includes but is not limited to NAND Flash, eMMC; the form of the MD of the mobile device includes but is not limited to Mobile hard disk, U disk, SD card.