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School of Computer Science & Engineering
University of New South Wales
 Advanced Operating Systems 
 COMP9242 2002/S2 

Access matrix implementation: Capabilities

Represent row-wise: capabilities

• Capability list associated with agent.
• Each capability confers a certain right to its holder.
  • Propagation: copy capabilities between agents (how?)
  • Restriction: lesser rights require new (``derived'') capabilities
  • Revocation: requires invalidation of capabilities from all agents
  • Amplification: special invocation capability.
  • Accessibility: requires inspection of all capability lists (how?)
  • Protection domain: explicit in capability list.
• Can have negative rights, to:
  • reduce ``window of vulnerability'',
  • simplify management of groups of capabilities.
• Successful commercial system: IBM System/38 et fils[Sol97]
• Popular among research distributed OS.