 NSTSSI Security Education Standards |
| NSTSSI Security Education Standards |
INFORMATION SYSTEMS SECURITY: A COMPREHENSIVE MODEL 1
INTRODUCTION
This Annex serves as a comprehensive model for the security
of information systems and also functions as an assessment,
systems development, and evaluation tool. The model is unique in
that it stands independent of technology. Its application is
universal and is not constrained by organizational differences.
As with all well-defined fundamental concepts, it is unnecessary
to alter the premise even as technology and human understanding
evolve.
Computers communicate. Communications systems compute. The
evolution of technology has long since eliminated any arbitrary
distinction between a computer and its communication components
or a communications network and its computing system. Some
organizations have attempted to deal with the phenomenon by
marrying these functions under common leadership. This has
resulted in hyphenated job descriptions such as Computer-
Communications Systems Staff Officer and names like Information
Technology Group. Unfortunately, these names can mask an
inappropriate or poorly executed realignment of organizational
responsibilities. Ideally, management will recognize there is a
theoretical as well as organizational impact.
The same is true for the security disciplines. Merely
combining the communications security (COMSEC) and computer
security (COMPUSEC) disciplines under an umbrella of common
management is unacceptable. Even if we address the other, albeit
less technical, aspects of information systems security such as
policy, administration, and personnel security, we still fail to
develop a comprehensive view of this evolving technology. The
reason for this becomes clear when we are reminded it's the
information that is the cornerstone of information systems
security. In this sense, any paradigm which emphasizes the
technology at the expense of information will be lacking.
_____
1. Capt John R. McCumber, Joint Staff, as extracted from
the proceedings of the 14th National Computer Security
Conference, October 1991.
THE NATURE OF INFORMATION
Defining the nature of information could be a tedious task.
To some it represents the free flowing evolution of knowledge; to
others, it is intelligence to be guarded. Add to this the
innumerable media through which the information is perceived and
we have a confusing array of contradictions. How can we present a
study of information that has universal application?
It may be best to develop a simple analogy. The chemical
compound H2O means many things to all of us. In its liquid state,
water means life-giving sustenance to a desert-dwelling Bedouin;
to a drowning victim, it is the vehicle of death. The same steam
we use to prepare vegetables could scald an unwary cook. Ice can
impede river-borne commerce on the Mississippi River or make a
drink more palatable. Science, therefore, does not deal with the
perception of the compound, but with its state.
As the compound H2O can be water, ice or steam, information
has three basic states. At any given moment, information is being
transmitted, stored, or processed. The three states exist
irrespective of the media in which information resides. This
subtle distinction ultimately allows us to encompass all
information systems technology in our model.
It is possible to look at the three states in microcosm and
say that processing is simply specialized state combinations of
storage and transfer; so, in fact, there are only two possible
states. By delving to this level of abstraction, however, we go
beyond the scope and purpose of the model. The distinction
between the three states is fundamental and necessary to
accurately apply the model. For example, cryptography can be used
to protect information while it's transferred through a computer
network and even while it is stored in magnetic media. However,
the information must be available in plaintext (at least to the
processor) in order for the computer to perform the processing
function. The processing function is a fundamental state that
requires specific security controls.
When this information is needed to make a decision, the end
user may not be aware of the number of state changes effected.
The primary concern will be certain characteristics of the
information. These characteristics are intrinsic and define the
security-relevant qualities of the information. As such, they
are the next major building block of our information systems
security model.
CRITICAL INFORMATION CHARACTERISTICS
Information systems security concerns itself with the
maintenance of three critical characteristics of information:
confidentiality (Pfleeger's "secrecy"), integrity, and
availability [PFL89]. These attributes of information
represent the full spectrum of security concerns in an automated
environment. They are applicable for any organization
irrespective of its philosophical outlook on sharing information.
CONFIDENTIALITY
Confidentiality is the heart of any security policy for an
information system. A security policy is the set of rules that,
given identified subjects and objects, determines whether a given
subject can gain access to a specific object [DOD85]. In the case
of discretionary access controls, selected users (or groups) are
controlled as to which data they may access. Confidentiality is
then the assurance that access controls are enforced.
Confidentiality is used instead of secrecy to avoid unwarranted
implications that this is solely the domain of governments.
All organizations have a requirement to protect certain
information. Even owners of a clearinghouse operation or
electronic bulletin need the ability to prevent unwanted access
to supervisory functions within their system. It's also
important to note the definition of data, which must be
protected with confidentiality controls, is broadening throughout
government [OTA87]. Actual information labeling and need-to-know
imperatives are aspects of the system security policy that are
enforced to meet confidentiality objectives. The issue of
military versus civilian security controls is one which need not
impact the development of a comprehensive representation of
information systems security principles.
INTEGRITY
Integrity is perhaps the most complex and misunderstood
characteristic of information. We seem to have a better
foundation in the development of confidentiality controls than
those which can help ensure data integrity. Pfleeger defines
integrity as "assets" (which) can only be modified by authorized
parties" [PFL89]. Such a definition unnecessarily confines the
concept to one of access control.
A much broader definition is used here. Data integrity is a
matter of degree (as is the concept of "trust" as applied to
trusted systems) that has to be defined as a quality of the
matter of degree (as is the concept of "trust" as applied to
trusted systems) that has to be defined as a quality of the
information and not as who does/does not have access to it.
Integrity is that quality of information that identifies how
closely the data represent reality. How closely does your resume
reflect "you?" Does the credit report accurately reflect the
individual's historical record of financial transactions? The
definition of integrity must include the broad scope of accuracy,
relevancy, and completeness.
Data integrity calls for a comprehensive set of aids to
promote accuracy and completeness as well as security. This is
not to say that too much information can't be a problem. Data
redundancy and unnecessary records present a variety of
challenges to system implementors and administrators. The users
must define their needs in terms of the information necessary to
perform certain functions. Information systems security
functions help ensure this information is robust and (to the
degree necessary) reflects the reality it is meant to represent.
AVAILABILITY
Availability is a coequal characteristic with confiden-
tiality and integrity. This vital aspect of security ensures the
information is provided to authorized users when it's requested
or needed. Often it's viewed as a less technical requirement that
is satisfied by redundancies within the information system such
as back-up power, spare data channels, and parallel data bases.
This perception, however, ignores one of the most valuable
aspects of our model that this characteristic provides.
Availability is the check-and-balance constraint on our model.
Because security and utility often conflict, the science of
information systems security is also a study of subtle
compromises.
As well as ensuring system reliability, availability acts as a
metric for determining the extent of information systems security
breaches [DOJ88]. Ultimately, when information systems
security preventive measures fail, remedial action may be
necessary. This remedial activity normally involves support from
law enforcement or legal departments. In order to pursue formal
action against people who abuse information systems resources,
the ability to prove an adverse impact often hinges
on the issue of denying someone the availability of information
resources. Although violations of information confidentiality
and integrity can be potentially more disastrous, denial of
service criteria tend to be easier to quantify and thus create a
tangible foundation for taking action against violators [CHR90].
The triad of critical information characteristics covers all
aspects of security-relevant activity within the information
system. By building a matrix with the information states
(transmission, storage, processing) positioned along the
horizontal axis and the critical information (confidentiality,
integrity, availability) characteristics aligned down the
vertical, we have the foundation for the model.
SECURITY MEASURES
We've now outlined a matrix that provides us with the
theoretical basis for our model. What it lacks at this stage is a
view of the measures we employ to ensure the critical information
characteristics are maintained while information resides in or
moves between states. It's possible, at this point, to perceive
the chart as a checklist. At a very high level of abstraction,
one could assess the security posture of a system by using this
approach. For example, you may single out systems information
confidentiality during transmission or any intersection area for
scrutiny.
The two-dimensional matrix also has another less obvious
utility. We can map various security technologies into the nine
boxes. Using our example from above, we note it is necessary
to protect the confidentiality of the information during its
transmission state. We can then determine which security
technologies help ensure confidentiality during transmission of
the information. In this case, cryptography would be considered a
primary security technology. We can then place various
cryptographic techniques and products within a subset in this
category. Then we repeat the process with other major types of
technology that can be placed within these spaces. The procedure
is repeated for all nine blocks on our grid. Thus we form the
first of three layers which will become the third dimension of our
model--security measures.
TECHNOLOGY
The technology layer will be the primary focus of the third
dimension. We will see that it provides the basis for the other
two layers. For our purposes, we can define technology as any
physical device or technique implemented in physical form that is
specifically used to help ensure the critical information
characteristics are maintained through any of the information
states. Technology can be implemented in hardware, firmware, or
software. It could be a biometric device, cryptographic module,
or security-enhanced operating system. When we think of a thing,
which could be used to protect the critical characteristics of
information, we are thinking of technology.
Usually organizations are built around functional
responsibilities. The advent of computer technology created
the perception that a group needed to be established to
accommodate the new machines that would process, store, and
transmit much of our vital information. In other words, the
organization was adapted to suit the evolving technology. Is this
wrong? Not necessarily; however, it is possible to create the
impression that technology exists for technology's sake.
Telecommunications and computer systems are simply media for
information. The media need to be adapted to preserve certain
critical characteristics with the adaptation and use of the
information media (technology). Adaptation is a design problem,
but use and application concerns bring us to the next layer.
POLICY AND PRACTICE
The second layer of the third dimension is that of policy and
practice. It's the recognition of the fact that information
systems security is not just a product that will be available at
some future date. Because of our technology focus, it's easy to
begin to think of security solutions as devices or add-on packages
for existing information systems. We are guilty of waiting for
technology to solve that which is not solely a technological
problem. Having an enforceable (and enforced) policy can aid
immeasurably in protecting information.
A study has shown 75% of federal agencies don't have a policy
for the protection of information on PC-based information systems
[OTA87]. Why, if it is so effective, is policy such a neglected
security measure? It may be due in part to the evolving social
and moral ethic with regard to our use of
information systems. The proliferation of unauthorized software
duplication is just another symptom of this problem. Even though
software companies have policies and licensing caveats on
their products, sanctions and remedies allowed by law are
difficult if not impossible to enforce. No major lawsuit
involving an individual violator has come before our courts, and
it appears many people don't see the harm or loss involved.
Although there are limits established by law, it seems we as
"society" accept a less stringent standard.
Closely associated with the matter of policy is that of
practice. A practice is a procedure we employ to enhance our
security posture. For example, we may have a policy that states
that passwords must be kept confidential and may only be used by
the uniquely-authenticated user. A practice, which helps ensure
this policy is followed, would be committing the password to
memory rather than writing it somewhere.
The first two layers of the third dimension represent the
design and application of a security-enhanced information
system. The last building block of our model represents the
understanding necessary to protect information. Although an
integral aspect of the preceding two layers, it must be
considered individually as it is capable of standing alone as a
significant security measure.
EDUCATION, TRAINING, AND AWARENESS
The final layer of our third dimension is that of education,
training, and awareness. As you will see, were the model laid on
its back like a box, the whole model would rest on this layer.
This phenomenon is intentional. Education, training,
and awareness may be our most prominent security measures, for
only by understanding the threats and vulnerabilities
associated with our proliferating use of automated information
systems can we begin to attempt to deal effectively with other
control measures.
Technology and policy must rely heavily on education,
training, and awareness from numerous perspectives. Our
upcoming engineers and scientists must understand the principles
of information security if we expect them to consider the
protection of information in the systems they design.
Currently, nearly all university graduates in computer science
have no formal introduction to information security as part of
their education [HIG89].
Those who are responsible for promulgating policy and regu-
latory guidance must place bounds on the dissemination of infor-
mation. They must ensure information resources are distributed
selectively and securely. The issue is ultimately
one of awareness. Ultimate responsibility for its protection
rests with those individuals and groups that create and use this
information; those who use it to make critical decisions must rely
on its confidentiality, integrity, and availability.
Education, training and awareness promises to be the most
effective security measure in the near term.
Which information requires protection is often debated in
government circles. One historic problem is the clash of
society's right to know and an individual's right to privacy.
It's important to realize that these are not bipolar concepts.
There is a long continuum that runs between the beliefs that
information is a free flowing exchange of knowledge and that it is
intelligence that must be kept secret. From a governmental or
business perspective, it must be assumed that all information is
intelligence. The question is not should information be
protected, but how do we intend to protect the confiden-tiality,
integrity, and availability of it within legal and moral
constraints?
THE MODEL
OVERVIEW
The completed model is depicted below. There are nine
distinct boxes, each three layers deep. All aspects of
information systems security can be viewed within the framework
of the model. For example, we may cite a cryptographic module as
technology that protects information in its transmission state.
What many information system developers fail to appreciate is
that for every technology control there is a policy (sometimes
referred to as doctrine) that dictates the constraints on the
application of that technology. It may also specify
parameters that delimit the control's use and may even cite
degrees of effectiveness for different applications. Doctrine
(policy) is an integral yet distinct aspect of the technology.
The third layer--education, training, and awareness then
functions as a catalyst for proper application and use of the
technology based on the policy (practice) application.
Not every security measure begins with a specific tech- nol-
ogy. A simple policy or practice often goes a long way in the
protection of information assets. This policy or practice is then
effected by communicating it to employees through the education,
training and awareness level alone. This last layer is ultimately
involved in all aspects of the information systems security
model. The model helps us understand the comprehensive nature of
information security.
USE OF THE MODEL
The model has several significant applications. Initially,
the two-dimensional matrix is used to identify information states
and system vulnerabilities. Then, the three layers of security
measures can be employed to minimize these vulnera-bilities based
on a knowledge of the threat to the information asset. Let's take
a brief look at these applications.
A developer would begin using the model by defining the
various information states within the system. When an
information state is identified, one then works down the vertical
path to address all three critical information characteristics
identifying the vulnerabilities. Once vulnerabilities are noted
in this fashion, it becomes a simple matter of working down
through the three layers of security measures. If a specific
technology is available, the designer knows that policy and
practice, as well as education, training, and awareness will be
logical follow-on aspects of that control. If a technology cannot
be identified, then policy/practice must be viewed as the next
likely avenue. If none of the first two layers can satisfactorily
counter the vulnerability then, as a minimum, an awareness of the
weakness becomes important and fulfills the dictates of the model
at the third layer.
Another important application is realized when the model is
used as an evaluation tool. As in the design and development
application, the evaluator first identifies the different
information states within the system. These states can be
identified separately from a specific technology. A valuable
aspect of the model is the designer need not consider the medium.
After identifying all the states, an evaluator or auditor can
perform a comprehensive review much the same way the systems
designer used the model during the development phase. For each
vulnerability discovered, the same model is used to determine
appropriate security measures. It is important to note that a
vulnerability may be left unsecured (at an awareness level in the
third layer) if the designer or evaluator determines no threat to
that vulnerability exists. Although no security practitioner
should be satisfied with glaring vulnerabilities, a careful study
of potential threats to the information may disclose that the cost
of the security measure is more than the loss should the
vulnerability be exploited. This is one of the subtle compromises
alluded to earlier.
The model can also be used to develop comprehensive
information systems security policy and guidance necessary for
any organization. With an accurate understanding of the relation
of policy to technology and education, training, and awareness,
you can ensure your regulations address the entire spectrum of
information security. It's of particular importance that
corporate and government regulations not be bound by
technology. Use of this model allows management to structure its
policy outside the technology arena.
The model functions well in determining requirements for
education, training, and awareness. Since this is the last layer,
it plays a vital role in the application of all the security
measures. Even if a designer, evaluator, or user determines to
ignore a vulnerability (perhaps because of a lack of threat), then
the simple acknowledgement of this vulnera-bility resides in the
last layer as "awareness." Ultimately, all technology, policies,
and practices must be translated to the appropriate audience
through education, training, and awareness. This translation is
the vehicle that makes all security measures effective. For a
more complete understanding of the nuances of education,
training, and awareness see [MAC89].
The 27 individual "cubes" created by the model can be
extracted and examined individually. This key aspect can be
useful in categorizing and analyzing countermeasures. It's also
a tool for defining organizational responsibility for information
security. By considering all 27 such "cubes", the analyst is
assured of a complete perspective of all available security
measures. This model connotes a true "systems" viewpoint.
CONCLUSION
The information systems security model acknowledges
information, not technology, as the basis for our security
efforts. The actual medium is transparent in the model. This
eliminates unnecessary distinctions between Communications
Security (COMSEC), Computer Security (COMPUSEC), Technical
Security (TECHSEC), and other technology-defined security
sciences. As a result, we can model the security relevant
processes of information throughout an entire information system-
-automated or not.
This model responds to the need for a theoretical foundation
for modeling the information systems security sciences. The pro-
cess begins now by acknowledging the central element in all our
efforts--information. Only when we build on this foundation
will we accurately address the needs of information systems secu-
rity in the next decade and beyond.