Capability

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Definition

A capability is a token that identifies an object and provides its holder with the permission to operate on the object it identifies. Capabilities must either be totally unforgeable or infeasible to forge.

Examples

Some examples of unforgeable capabilities:

  • Designations of objects in the E language. Those who hold these capabilities have the permission to invoke any method supported by the designated object.
  • Designations of functions and procedures in Emily. Those who hold these capabilities have the permission to call designated functions or procedures.

Some examples of capabilities that are infeasible to forge:

  • Designations of remote objects in E, such as captp://*orwqphzlugjwqj2wozz7tmg47ime466j@74.125.87.147:55189/oa6vn5whhapylswhzesdlqh5ppmjkcrq. Those who hold these capabilities have the permission to invoke any method supported by the designated object.
  • Password capabilities
    • Private URLs where having the URL is necessary and sufficient to use the resource. Common examples are:
      • "Confirm your e-mail address" links for website account registrations and mailing list subscriptions.
      • Shared private documents such as in Google Docs, Google Maps, Picasa albums, Doodle schedulers.

XXX What exactly do we mean by password capabilities here, such that a captp URL is not one?

See also

XXX improve this section

See What is a Capability, Anyway? for a partisan explanation of what capabilities actually are.

See also Overview: Capability Computation

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