ISA 62443-3-3

Abstract

<strong>Purpose and intended audience</strong> <br>The IACS community audience for this specification is intended to be asset owners, system integrators, product suppliers, service providers and, where appropriate, compliance authorities. Compliance authorities include government agencies and regulators with the legal authority to perform audits to verify compliance with governing laws and regulations. <br>System integrators, product suppliers and service providers wi ll use this document to evaluate whether their products and services can provide the functional security capability to meet the asset owner's target security level (SL-T) requirements. As with the assignment of SL-Ts, the applicability of individual control system requirements (SRs) and requirement enhancements (REs) needs to be based on an asset owner's security policies, procedures and risk assessment in the context of their specific site. Note that some SRs contain specific conditions for permissible exceptions, such as where meeting the SR will violate fundamental operational requirements of a control system (which may trigger the need for compensating countermeasures). <br>When designing a control system to meet the set of SRs associated with specific SL-Ts, it is not necessary that every component of the proposed control system support every system requirement to the level mandated in this standard. Compensating countermeasures can be employed to provide the needed functionality to other subsystems, such that the overall SL -T requirements are met at the control system level. Inclusion of compensating countermeasures during the design phase should be accompanied by comprehensive documentation so that the resulting achieved control system SL, SL-A(control system), fully reflects the intended security capabilities inherent in the design. Similarly, during certification testing and/or post -installation audits, compensating countermeasures can be utilized and documented in order to meet the overall control system SL. <br>There is insufficient detail in this document to design and build an integrated security architecture. That requires additional system-level analysis and development of derived requirements that are the subject of other documents in the ISA&#8209;62443 series (see 0.3). Note that providing specifications detailed enough to build a security architecture is not the goal of this document. The goal is to define a common, minimum set of requirements to reach progressively more stringent security levels. The actual design of an architecture that meets these requirements is the job of system integrators and product suppliers. In this task, they retain the freedom to make individual choices, thus supporting competition and innovation. Thus this standard strictly adheres to specifying functional requirements, and does not address how these functional requirements should be met.