Isa 99 00 01 security zones and conduits
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ISA 99.00.01 “Security Zones and Conduits”. The challenge to map ISA 99.00.01 to ISA 99.00.04. Presented to ISA 99 WG04 Dennis Holstein [email protected] ISA 99 WG 04 Meeting Scottsdale, AZ 25-27 June 2007. What is the challenge. ISA 99.00.01 contains Definitions and Models

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ISA 99.00.01 “Security Zones and Conduits”

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ISA 99.00.01“Security Zones and Conduits”

The challenge to map ISA 99.00.01 to ISA 99.00.04

Presented to ISA 99 WG04

Dennis Holstein

[email protected]

ISA 99 WG 04 Meeting

Scottsdale, AZ

25-27 June 2007


What is the challenge

  • ISA 99.00.01 contains Definitions and Models

    • Definitions are not the problem

    • Models are abstract – instantiation for Part 4 is the challenge

  • ISA 99.00.04 is a compliance specification

    • Compliance requires testability criteria

      • By measurement

      • By inspection and analysis

    • To be testable requirements must be prescriptive

    • But, Part 4 must not define “how to” implement the requirements – it must state “what is” required


Apply lessons learned from IEC 62443-3

  • IEC TC65WG10 approach

    • Establish a common reference model defining zones and conduits

      • Served well for analysis and contributions by independent work packages

      • Overlaps in the reference model resulted in duplication of requirements and divergent specifications

        • The challenge was to harmonize the contributions

        • The approach was to cast the requirements in the context of a security policy statement

        • This resulted in the generation of a Public Available Specification (PAS) – which is a non-binding document in Europe

    • Original 62443-3 work has been turned over to ISA 99 for their development

  • Zones and conduits used by TC65WG10 are applicable to ISA 99.00.04

    • Requirements are testable

    • ISA 99WG04 challenge is to balance the detailed prescriptive specifications

      • Technology dependent language needs to be adjusted to ensure longer life of the specification

      • Language must be cast in terms of “If required by security policy, then the capability to …. is required” – most requirements become optional


The need for foundational requirements

  • Foundational requirements can be stated that apply to any Asset Owner’s derived common reference model

    • PCSF seven foundational requirements

      • Operations centric view of requirements

      • The simplest set to understand and use

    • NIST 800-53 & INL/DHS catalog

      • A comprehensive treatment of requirements

      • A daunting task to assimilate and correlate interdependency of requirements

  • Suggested approach: two simultaneous teams

    • Start with the PCSF foundational requirements

    • Use the NIST and INL/DHS documents as a checklist to find missing requirements for Part 4


What worked well for TC65WG10

  • Common template for domains (zones & conduits)

    • Statement of cyber security issue addressed

    • Assumptions and constraints applied

      • Requirements addressed in another domain

      • Relationship to stated policy

    • Statement of requirement

      • Litmus test – it must be testable

      • Options to increase strength of protection (defense in depth)

    • Rationale or justification for requirement

      “This is important because ….”

  • Need to harmonize Part 4 statements with Parts 2 and 3 – Part 3 work needs to start


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