The PLC programs in automation control systems often encapsulate years of technological accumulation and core algorithms of enterprises. As industrial competition intensifies, protecting PLC programs from illegal copying and theft has become an important issue in the field of industrial automation. This article introduces a Siemens PLC program encryption solution practically applied at the Aerospace Research Institute, building a security protection system from multiple hardware and software levels.
1
Basic Principles of Encryption
The essence of PLC program encryption is to restrict access to program blocks and obfuscate the code. Siemens S7 series PLCs provide two basic protection mechanisms: Know-how protection and access levels. Know-how protection restricts the viewing and modification permissions of program blocks through passwords, while access levels control the operational permissions of different users.
Imagine the safe we use every day; Know-how protection is like the password lock of the safe, where only those who know the password can open and view its contents. Access levels are like the access control system in an office, where different levels of employee cards can enter different areas. The combination of these two mechanisms forms the basic protection network for the program.
2
Hardware Encryption Solution
Implement hardware-level protection by installing a CP encryption module on the PLC rack:
-
The CP module has a built-in encryption chip that stores authorization information.
-
The program must be verified through the CP module before it can run.
-
Even if the program is copied, it cannot be used without the corresponding CP module.
-
The CP module supports remote authorization management and expiration settings.
Notes:
-
The CP module requires separate power supply; power failure will cause authorization to become invalid. It is recommended to configure a UPS power supply.
-
The encryption module needs regular authorization updates; it is recommended to check once every quarter.
-
Record the serial number of the encryption module upon initial installation for future technical support.
3
Software Encryption Implementation
//Program block encryption exampleFUNCTION_BLOCK FB100VAR Auth_Code : DWORD; //Authorization code Run_Enable : BOOL; //Run enable Error_Count : INT; //Error count System_Time : DATE_AND_TIME; //System timeEND_VAR//Check authorizationIF Auth_Code <> 16#A5B4C3D2 THEN Error_Count := Error_Count + 1; //Lock system after three consecutive verification failures IF Error_Count >= 3 THEN Run_Enable := FALSE; //Record exception time System_Time := DTL#2024-02-17-00:00:00; RETURN; END_IF;END_IF;//Program protection after verificationREGION KNOW_HOW_PROTECTED Run_Enable := TRUE; //Core algorithm code ...END_REGION4
Multi-Factor Authentication Mechanism
Using a multi-layer protection strategy is like building a wall, with each layer providing different protections:
-
Overall project password protection
-
Set project access password
-
Restrict program upload and download permissions
-
Disable online program comparison function
-
Core program block Know-how protection
-
Encrypt core algorithm FB/FC
-
Set independent access passwords
-
Prohibit exporting program blocks
-
CP module hardware encryption
-
Bind hardware serial number
-
Set authorization expiration date
-
Remote management of authorization status
-
Software authorization code verification
-
Dynamic authorization code generation
-
Error count limitation
-
Exception record tracking
-
Online monitoring restrictions
-
Shield key variable monitoring
-
Limit forced variable functionality
-
Disable program status display
5
Practical Application Case
A certain model of aircraft engine test bench control system adopts this solution:
-
Encapsulate core algorithms such as engine parameter calculation and performance evaluation in encrypted program blocks.
-
The running interface only displays basic process parameters and hides core data.
-
System maintenance requires manufacturer authorization and a dedicated key.
-
It has been running stably for three years, during which it has resisted multiple attempts of illegal access.
Once, a certain company attempted to crack the program using decryption software, but due to the existence of the multi-layer protection mechanism, they could only obtain the basic framework code, while the core algorithm remained secure. This case illustrates that a single encryption method is easily cracked; a multi-layered protection strategy is the way to go.
6
Common Issues and Solutions
-
Forgot Password:
-
Create a password management file, kept by a dedicated person.
-
Set up a password recovery mechanism with multiple validations.
-
Reserve an emergency access channel, but it requires manufacturer authorization.
-
Program Abnormalities:
-
Retain basic diagnostic functions for troubleshooting.
-
Set up a fault alarm mechanism to monitor system status in real-time.
-
Provide remote technical support for rapid issue response.
-
Authorization Expiry:
-
Regularly check authorization status and update in advance.
-
Backup authorization files to prevent accidental loss.
-
Establish an emergency response process to ensure production continuity.
7
Practical Recommendations
-
Implement tiered encryption for programs, with core algorithms receiving focused protection while general functions are appropriately open.
-
Regularly update encryption algorithms and keys to prevent security risks from long-term use.
-
Establish a complete password management system, including updates, handovers, and backups.
-
Ensure to backup programs before encryption and store them in a secure environment.
-
Reserve necessary debugging interfaces while ensuring security and maintainability.
Practical Exercises:
-
Set up a Siemens S7-1500 system with a CP encryption module.
-
Write a simple encrypted program block to implement authorization verification functionality.
-
Test different levels of program protection schemes to evaluate their security.
-
Simulate common fault scenarios to practice issue diagnosis and handling processes.
-
Familiarize yourself with the configuration and authorization management operations of the encryption module.