Application of security metrics to instrument systems that use distributed processing

Modern sensors are often integrated into microprocessor chips or into packages with embedded processors to provide “smart sensor” capabilities or to function in networks (e.g., wireless sensor networks) to make complex measurements and to distribute the processing load by performing initial data analysis tasks close to the point of measurement. These systems have many of the operating characteristics of distributed control systems (DCSs), including attendant advantages and vulnerabilities. Important desirable features of DCSs include use of network communications, access to file servers and services supported by modern operating systems. Cyber security, however, is a significant area of vulnerability requiring attention. The International Society for Automation (ISA) has and is developing standards (ISA99) to address all aspects of cyber security for industrial automation. One of these aspects deals with development of security metrics that can be used to determine compliance with the security standards and can also serve as a basis for an effort to monitor in real time those processes that have potential associated security risks and to provide warning of the occurrence of possible security incidents. Security metrics developed for ISA99 are described and some ways to use them to protect instrument systems are proposed.