- [Instructor] In a discretionary access control model
each resource has a clearly identified owner.
For example, a user creating a file
becomes the owner of that file.
The owner of a resource can decide at his discretion
to allow other users
or subjects access to that resource.
The owner discretion is the main characteristic
of the discretionary access control.
Now, the owner in fact,
when assigning a permission,
should comply with organization security policy.
However, the security policy compliance
is not enforced by the operating system
or any other entity.
It's actually enforced by the user itself.
So when the owner allows access to a different user,
will also set the permissions
for example, you know,
to rewrite or execute
for the other specific resource to the user.
And now, in a discretionary access model
users can be organized in groups as well.
The owner can grant access to a resource,
to the entire group,
instead of the actual individual user.
Also, a permission attributes will be assigned
to a resource for that specific group.
Now, a simple way to implement
discretionary access control
is an access control list,
which is actually associated to each object.
Now, most of modern operating systems today,
both open source and commercial operating systems,
implement a form of discretionary access control model.
In this example,
I'm showing four files in a Mac OS X system,
but this will be the same in a Linux system as well.
So as you can see, I'm the owner of all files.
And I also belong to the staff group,
and also each of the files have their own permissions.
Now, if you're not familiar with Linux permissions,
I include a link to a website that explains
them in detail here.
One of the prerequisites of this exam,
of the executive fundamentals exam,
is that you are familiar with the Linux operating system
and also, you know,
the file system, and the permissions of, you know,
of the file system.
So, I definitely urge you and suggest that you actually read
this article or this website
if you're not familiar with Linux permissions.
Now, going back to discretionary access control.
One of the drawbacks of using
a discretionary access control model,
is that the security policy is left to the discretion
of the data owner.
And then the data security administration
has actually limited access control over it.
Additionally, with the number of subjects,
so that means users, processes, programs, et cetera,
accessing a large number of objects,
maintaining the permission by respecting the need to know,
and the least privilege
becomes a complex administration task.
So, there's a concept of privilege creep,
and a privilege creep,
or otherwise known as authorization creep,
describes an issue that actually happens fairly frequently
in large organizations.
And this issue is that privileges
that are being assigned to users
are never revoked when the user does
not need them anymore,
or if they actually even,
the user actually leaves the organization.
And this definitely goes against the need to know principle,
and as well as the least privilege principle.
There are a few key concepts related
to the discretionary access control model.
The first one is
that the discretionary access controls
are controls where authorization is decided
by the owner of the object,
and also in a discretionary access control system
access permissions are associated to the object itself.
And lastly, access control is usually enforced
with access control lists.