Page 645 - (ISC)² CISSP Certified Information Systems Security Professional Official Study Guide

well-defined, specific interfaces to provide necessary security. All

inbound requests from outer (less-sensitive) layers are subject to
stringent authentication and authorization checks before they’re
allowed to proceed (or denied, if they fail such checks). Using layering
for security is similar to using security domains and lattice-based
security models in that security and access controls over certain
subjects and objects are associated with specific layers and privileges
and that access increases as you move from outer to inner layers.

In fact, separate layers can communicate only with one another
through specific interfaces designed to maintain a system’s security
and integrity. Even though less secure outer layers depend on services
and data from more secure inner layers, they know only how to
interface with those layers and are not privy to those inner layers’
internal structure, characteristics, or other details. So that layer
integrity is maintained, inner layers neither know about nor depend
on outer layers. No matter what kind of security relationship may exist

between any pair of layers, neither can tamper with the other (so that
each layer is protected from tampering by any other layer). Finally,
outer layers cannot violate or override any security policy enforced by
an inner layer.

Abstraction

Abstraction is one of the fundamental principles behind the field
known as object-oriented programming. It is the “black-box” doctrine

that says that users of an object (or operating system component)
don’t necessarily need to know the details of how the object works;
they need to know just the proper syntax for using the object and the
type of data that will be returned as a result (that is, how to send input
and receive output). This is very much what’s involved in mediated
access to data or services, such as when user mode applications use

system calls to request administrator mode services or data (and
where such requests may be granted or denied depending on the
requester’s credentials and permissions) rather than obtaining direct,
unmediated access.

Another way in which abstraction applies to security is in the
introduction of object groups, sometimes called classes, where access