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1.1.1 Mandatory Access Control (MAC)
Mandatory Access Control (MAC)
is military-strength access control. In the absence of a permission
that specifically allows you access, you are not getting in. Every thing
in the system is an object and every object gets a classification label,
which usually represents the sensitivity of the object, such as top
secret or confidential. Individual users, called
subjects, are also assigned a privilege level, called a clearance.
To determine whether or not a given individual can access a certain
object, the objects classification level and the users clearance
level are compared. There is an established hierarchy to the labels
(or levels), such that anyone authorized to see top secret
information can also view secret and general access
information since those are less sensitive, but someone authorized only
to view general access information cant necessarily
see the more sensitive top secret information.
Labels may be used to define projects as well. This means that while you may have a top-secret clearance, you are not automatically granted access to a secret project if that particular project is not assigned to your area.
The Bell-LaPadula formal model
of access control uses mandatory access control. It is based on
several properties, including:
- star property (or * property), also called
the containment level, which states that an untrustworthy user can only
write (append information) to objects whose security level is greater
than or equal to their own (to make sure that someone with a high clearance
level doesnt accidentally share sensitive information with someone
having a lower clearance level i.e., it prevents information
- simple property, which states that a user
can read data only if its security level is as sensitive as, or less
sensitive than, their clearance level (think about a 4-star general
being entitled to see more data than a 1-star general)
- tranquility property, which states that
the security level of an object cannot be changed while it is in use
by the computer system (this sidesteps the problem of what to do with
users actively using an object who are no longer permitted access when
the objects security level changes)
The Bell-LaPadula model describes a mandatory access control model that is used by the military. It determines whether an access is permissible by comparing an objects (or data items) assigned hierarchical classification level and the subjects clearance level. If the users clearance level is at least as high as the classification level of the object, the access control rule permits the access. Otherwise, access is denied.
Figure 3: MAC uses both hierarchical classification and the subjects clearance level.
Another MAC-based model
is the Lattice-based access control model. It shares with the Bell-LaPadula
model the idea that objects and users are each given a hierarchical
security level label, and that you determine whether or not a user has
access to an object, by comparing their labels. As with Bell-LaPadula,
if the users clearance level is at or above the classification
level of the object, access is permitted.
Bell-LaPadula and Lattice
Sometimes the terms Bell-LaPadula model and Lattice-based model are used interchangeably, but the original version of the Lattice-based model did not include the Bell-LaPadulas requirement that a user is not permitted to write into a document with a lower security level than the users security level. Thus, technically, it did not prevent disclosure of higher-level information to lower-level users as well as does the Bell-LaPadula model.
MAC & Lattice
Another MAC model is Lattice-based48 access control, sometimes also referred to as the Bell-LaPadula model.
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