A concept from security (not ICS-specific): ensuring that a party in a communication cannot deny the authenticity of their signature on a document or a message that they originated. In OT, this might come into play with logging and forensics: ensuring actions (like a command to change a setpoint) are traceable to a user and cannot be refuted. Digital signatures and audit logs contribute to non-repudiation. It’s less talked about than confidentiality, integrity, availability in ICS, but it’s one of those classic infosec principles.
