Talk:Access Control Matrix

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"Most general description of OS protection mechanism"[edit]


"It is the most general description of operating system protection mechanism [reference to Landwehr 1981]"

The access matrix model is not the most general possible description of a system's protection state, and doesn't try to be a description of any protection mechanisms at all.

Presumably the reference is to this sentence from Landwehr's paper:

"The access matrix model, described in detail below, was developed in the early 1970s as a generalized description of operating system protection mechanisms."

First, "generalized" is certainly not the same thing as "most general".

Second, Landwehr's statement is wrong, or at least misleading. The access matrix is an abstraction of the instantaneous direct permissions that subjects have to objects. This does not capture all of the protection state; for instance, in a capability system, the access matrix shows whether each subject holds a capability to each object, but not which variable(s) those capabilities are held in. Therefore, two system states can have exactly the same access matrix, but one of those states can be secure while the other is insecure (according to some criteria). Critically, the access matrix also does not capture how permissions can change.

David-Sarah Hopwood (talk) 20:12, 31 January 2009 (UTC)


The example talks about two processes, but in the matrix those things are refered to as assets, which makes the paragraph confusing. —Preceding unsigned comment added by (talk) 16:02, 24 September 2010 (UTC)