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Unifying Safety and Security

John A Clark

Senior Lecturer in Critical Systems

University of York

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Contents

What is safety and what is security?Why do we want to unify the two?What’s the SameWhat’s DifferentHow can we make progress?

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Things that are similarBoth properties of systems Both risk based

integrity levels (e.g. SILs, assurance/confidence levels)

Certification authorities.Independent V&VProcess development standards.Subject to attack.The concepts have the same word in some languages

(Sicherheit, securite)

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Things that differNature of what we get wrong. How about (traditionally)

Safety: we get the requirements wrong.Security: we typically get the implementation wrong.

Process development standardsSecurity standards (e.g. ITSEC) place heavy emphasis on top

level correctness (with greater informality in refinement). Essentially get the model and top level spec right.

Safety standards seem more keen to propagate rigour (formality) through refinement levels.

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Things that cause problems‘People are our greatest asset…’People are our worst nightmare

Human factors issues with safety widely appreciatedBut with security comes malice

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Some things of Interest in SecurityConfidentialityIntegrityAvailabilityAccountability