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Basic Concepts of Dependability

Basic Concepts of Dependability. Jean-Claude Laprie. DeSIRE and DeFINE Workshop — Pisa, 25-27 November 2002. Dependability : ability to deliver service that can justifiably be trusted. Service delivered by a system: its behavior as it is perceived by its user(s)

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Basic Concepts of Dependability

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  1. Basic Concepts of Dependability Jean-ClaudeLaprie DeSIRE and DeFINE Workshop — Pisa, 25-27 November 2002

  2. Dependability : ability to deliver service that can justifiably be trusted Service delivered by a system: its behavior as it is perceived by its user(s) User: another system that interacts with the former Function of a system: what the system is intended to do (Functional) Specification: description of the system function Correct service: when the delivered service implements the system function Systemfailure: event that occurs when the delivered service deviates from correct service, either because the system does not comply with the specification, or because the specification did not adequately describe its function Failure modes: the ways in which a system can fail, ranked according to failure severities Dependability: ability to avoid failures that are more frequent or more severe than is acceptable to the user(s) When failures are more frequent or more severe than acceptable: dependability failure

  3. Availability Reliability Safety Confidentiality Integrity Maintainability Attributes Fault Prevention Fault Tolerance Fault Removal Fault Forecasting Dependability Means Faults Errors Failures Threats

  4. … … Faults Errors Failures Faults Failures Development faults Value failures Phase of creation or occurrence Domain Operational faults Timing failures Internal faults Consistent failures System boundaries Consistency External faults Inconsistent failures Hardware faults Dimension Controlled failures Software faults Controllability Uncontrolled failures Natural faults Phenomenological cause Minor failures Human-made faults l l l Consequences Accidental, or deliberate without malice, faults Catastrophic failures Intention Malicious faults Permanent faults Persistence Transient faults

  5. Faults Phase of creat. or occurrence developmental operational System boundaries internal internal external Dimension software hardware hardware hardware software Phenomen. cause human- made human- made natural natural natural human- made human- made acc. or non mal. del. del. mal. del. mal. acc. or non mal. del. acc. acc. acc. acc. or non mal. del. del. mal. del. mal. acc. or non mal. del. Intent per. per. per. per. per. per. tra. per. tra. tra. per. tra. per. tra. tra. Persistence softw. flaws malicious logics hardw. errata prod. def. physical deterior. physical interference attacks input mist. vir. wor. intr. Design faults Physical faults Interaction faults

  6. Importance of concept formulation Update and evolution • Agreed terminology for people exchanges and interactions • Shared understanding • Relationship dependability - security • Dependability specification • Dependability scales and classes (partial ordering, distributions) • Socio-technical systems • Risk (losses and gains) • Human faults, including malicious ones • Operation, incl. organizational drifts • Development process failures

  7. 1 A. Avizienis, J.C. Laprie, B. Randell, "Fundamental concepts of dependability", March 2001.  2 R.J. Ellison, D.A. Fischer, R.C. Linger, H.F. Lipson, T. Longstaff, N.R. Mead, "Survivable network systems: an emerging discipline", Technical Report CMU/SEI-97-TR-013, November 1997, revised May 1999. 3 F. Schneider, ed., Trust in Cyberspace, National Academy Press, 1999.

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