Talk:Access control matrix

This article is within the scope of WikiProject Computer security, a collaborative effort to improve the coverage of computer security on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.Computer securityWikipedia:WikiProject Computer securityTemplate:WikiProject Computer securityComputer security

???

This article has not yet received a rating on Wikipedia's content assessment scale.

???

This article has not yet received a rating on the project's importance scale.

This article is supported by WikiProject Computing.

Things you can help WikiProject Computer security with:

Article alerts are available, updated by AAlertBot. More information...

Review importance and quality of existing articles
Identify categories related to Computer Security
Tag related articles
Identify articles for creation (see also: Article requests)
Identify articles for improvement
Create the Project Navigation Box including lists of adopted articles, requested articles, reviewed articles, etc.
Find editors who have shown interest in this subject and ask them to take a look here.

Computing Unassessed

	This article is within the scope of WikiProject Computing, a collaborative effort to improve the coverage of computers, computing, and information technology on Wikipedia. If you would like to participate, please visit the project page, where you can join the discussion and see a list of open tasks.ComputingWikipedia:WikiProject ComputingTemplate:WikiProject ComputingComputing
???	This article has not yet received a rating on Wikipedia's content assessment scale.
???	This article has not yet received a rating on the project's importance scale.

"Most general description of OS protection mechanism"

Removed:

"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)[reply]