Security Design Solutions for IoT Applications Driven by PLC Function Block Diagrams
A few days ago, a friend involved in factory automation rushed to me, saying that their temperature control system inexplicably activated in the middle of the night, nearly causing a safety incident. After investigation, it was found that their newly launched remote monitoring system had security vulnerabilities and was hacked. This made me realize that as PLC control systems increasingly connect to the internet, security issues have become a critical aspect that cannot be ignored.
The security risks of PLC systems in the IoT environment are far greater than imagined. The traditional design of PLC systems was intended to operate in a closed environment. Once connected to the internet, it is like installing a lock on the front door of a house but forgetting to close the windows, leading to various security risks. According to statistics, over 60% of industrial control systems have suffered from cyberattacks, most of which were due to a lack of basic security measures.
The PLC function block diagram, as the core of industrial control programs, also needs to be re-evaluated from a security perspective. Function blocks are essentially encapsulated functional modules, such as temperature PID control and motor drive, which are like applications on our computers, each serving its purpose. However, in the IoT environment, these function blocks require an additional “security shell” for protection.
The most common security vulnerabilities come from the communication layer. Imagine your PLC system as the central hub of your smart home, needing to communicate with various sensors and actuators. If this communication is not encrypted, it is like shouting private information for everyone to hear. The solution is simple:integrate a communication encryption module into the function blocks, ensuring that all data entering and leaving the PLC must be encrypted. I prefer using the AES-256 encryption algorithm, which acts like a bulletproof vest for data; even if intercepted, it cannot be cracked.
Another issue is lax authentication. Many engineers, for convenience, use simple passwords or even no password for remote access to PLC systems, which is like hanging the house key directly on the door. Once, while assisting in troubleshooting a system failure, I found that the client used “12345” as their password, which was easily breached by hackers, resulting in a three-day production line shutdown. The correct approach is to incorporatemulti-factor authentication mechanisms into the function block design, which not only verifies the password but also checks the login location, device characteristics, and other multiple pieces of information, greatly enhancing security.
Data integrity is also a critical issue. In IoT applications, PLCs collect data from sensors and transmit it to the upper computer or cloud platform. If the data is tampered with, it can lead to erroneous decisions. This is as serious as a doctor receiving incorrect temperature data leading to a misdiagnosis. I recommend implementing a data verification mechanism in the function blocks, using hash algorithms to sign the data and ensure its integrity.
In practical applications, I designed a security solution for a chemical plant’s temperature control system. First, all communications between function blocks use encrypted channels; second, remote access must go through a VPN and use dynamic passwords; third, a data anomaly monitoring mechanism is set up to immediately alert and cut off remote control permissions when data shows abnormal fluctuations. This system has successfully withstood multiple attack attempts over the past two years.
A common oversight during the debugging phase is not modifying default configurations. Many PLCs and network devices come with default passwords and open ports, which is as dangerous as moving into a new house without changing the locks. My experience is to create a “security configuration checklist” that must be confirmed item by item before going live, including whether the default password has been changed, whether unnecessary communication ports have been closed, and whether logging and auditing features have been enabled.
Regular security audits are an effective means of discovering potential issues. Just as regular health check-ups can detect health risks early, conducting security scans on PLC systems can timely identify and patch vulnerabilities. I recommend performing a comprehensive security assessment at least quarterly to check for new vulnerabilities and whether firmware or security policies need updating.
In security design, the “principle of least privilege” should also be considered, where each function block is only granted the minimum permissions necessary to complete its tasks. Just like access cards in a company, the finance department’s card cannot open the technical department’s door. This way, even if a function block is compromised, hackers cannot gain control over the entire system.
Finally, do not forget to establish an emergency response plan. No matter how robust the security measures are, vulnerabilities may still arise, and the key is to respond quickly when issues are detected. A good emergency plan should include: methods for quickly cutting off network connections, backup plans for system recovery, and contact processes with relevant departments.
In the IoT era, PLC security design is no longer optional but a necessity. By integrating security thinking into the function block design phase, we can build industrial control systems that are both intelligent and secure. Remember, security is not a one-time task but a continuous process that requires ongoing learning of new security knowledge and technologies, racing against cybersecurity threats. The next time you design a PLC function block, ask yourself: if this system connects to the internet, what security measures have I implemented?
