Lesson plan

Object-capability model

The object-capability model is a computer security model. A capability describes a transferable right to perform one (or more) operations on a given object. It can be obtained by the following combination: :* An unforgeable reference (in the sense of object references or protected pointers) that can be sent in messages. :* A message that specifies the operation to be performed. The security model relies on not being able to forge references. :* Objects can interact only by sending messages on references. :* A reference can be obtained by: ::# Initial conditions: In the initial state of the computational world being described, object A may already have a reference to object B. ::# Parenthood: If A creates B, at that moment A obtains the only reference to the newly created B. ::# Endowment: If A creates B, B is born with that subset of A's references with which A chose to endow it. ::# Introduction: If A has references to both B and C, A can send to B a message containing a reference to C. B can retain that reference for subsequent use. In the object-capability model, all computation is performed following the above rules.…

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Article summary

The object-capability model is a computer security model. A capability describes a transferable right to perform one (or more) operations on a given object. It can be obtained by the following combination: :* An unforgeable reference (in the sense of object references or protected pointers) that can be sent in messages. :* A message that specifies the operation to be performed. The security model relies on not being able to forge references. :* Objects can interact only by sending messages on references. :* A reference can be obtained by: ::# Initial conditions: In the initial state of the computational world being described, object A may already have a reference to object B. ::# Parenthood: If A creates B, at that moment A obtains the only reference to the newly created B. ::# Endowment: If A creates B, B is born with that subset of A's references with which A chose to endow it. ::# Introduction: If A has references to both B and C, A can send to B a message containing a reference to C. B can retain that reference for subsequent use. In the object-capability model, all computation is performed following the above rules.…

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Discussion questions

  1. Summarise the article in your own words. Which single claim would you verify first, and why?
  2. Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
  3. If two sources disagreed about one of these facts, what would you need in order to trust one over the other?

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