Ambient authority
From Erights
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Definition
A subject may have several different permissions.
Ambient authority is authority that can be used without having to identify which specific permission is intended.
In an ambient authority system when a subject requests an action (typically by naming an object and an operation on that object), the action is allowed if the subject has any permission that would allow the action.
Notes
In contrast, in a designated authority system, a subject explicitly identifies a subset (usually one) of its permissions, and the action is allowed only if permitted by that subset of permissions.
In an ambient authority system, a subject making a request does not specify which permission to use -- the subject does not identify which permission is claimed to justify allowing the request. Instead, the system looks through all of the subject's permissions and allows the request if any of the subject's permissions would justify allowing the request.
In an ambient authority system, a subject may have many permissions, and there is often no way for the subject to single one of these out. As a result, in these systems, developers may not think of the subject as having multiple different permissions at once; instead, developers might just associate the union of all those permissions with the subject, and call them the permissions of the subject.
Examples of ambient authority
All UNIX processes run by some user have ambient authority to manipulate all files owned by that user.
All UNIX processes have ambient authority to listen to TCP or UDP ports 1024--65535.
All UNIX processes have ambient authority to send any signal to any other UNIX process.
Acknowledgement
The term ambient authority was coined by Dean Tribble and Mark S. Miller.
