Despite the challenges and limitations, there are some best practices and recommendations you can follow to improve the security and encryption of your PLCs. To start, conduct a risk assessment and security audit of your PLCs and their network. Identify the assets, threats, vulnerabilities, and impacts of your PLCs and their data. Then prioritize the most critical and sensitive PLCs and data and implement appropriate security and encryption controls for them. Additionally, adopt a defense-in-depth approach using multiple layers of security and encryption measures such as firewalls, VPNs, TLS, AES, or RSA to protect your PLCs from different angles. Do not rely on a single security or encryption solution or standard. Additionally, update and patch your PLCs regularly for firmware, hardware, or software updates or patches that can fix security or encryption issues or vulnerabilities. Don't forget to apply the updates or patches as soon as possible and test them before deploying them to your production environment. Finally, train and educate your staff and stakeholders on PLC security and encryption by raising awareness of its importance and providing them with guidelines on how to use and manage your PLCs securely.