COMPUTER SECURITY CONCEPTS

A Definition of Computer Security


COMPUTER SECURITY
The protection afforded to an automated information system in order to attain the
applicable objectives of preserving the integrity, availability, and confidentiality of
information system resources (includes hardware, software, firmware, information/
data, and telecommunications).




This definition introduces three key objectives that are at the heart of computer
security.
• Confidentiality: This term covers two related concepts:
Data2 confidentiality: Assures that private or confidential information is not
made available or disclosed to unauthorized individuals.
Privacy: Assures that individuals control or influence what information
related to them may be collected and stored and by whom and to whom that
information may be disclosed.
• Integrity: This term covers two related concepts:
Data integrity: Assures that information and programs are changed only in
a specified and authorized manner.
System integrity: Assures that a system performs its intended function in an
unimpaired manner, free from deliberate or inadvertent unauthorized
manipulation of the system.
• Availability: Assures that systems work promptly and service is not denied to
authorized users.



These three concepts form what is often referred to as the CIA triad (Figure 1.1).
The three concepts embody the fundamental security objectives for both data and
for information and computing services. For example, the NIST Standards for Security
Categorization of Federal Information and Information Systems (FIPS 199) lists
confidentiality, integrity, and availability as the three security objectives for information
and for information systems.

Confidentiality: Preserving authorized restrictions on information access

and disclosure, including means for protecting personal privacy and proprietary

information. A loss of confidentiality is the unauthorized disclosure of

information.

• Integrity: Guarding against improper information modification or destruction,

including ensuring information nonrepudiation and authenticity.

A loss of integrity is the unauthorized modification or destruction of

information.

• Availability: Ensuring timely and reliable access to and use of information.A loss

of availability is the disruption of access to or use of information or an information

system.

Examples

We now provide some examples of applications that illustrate the requirements just

enumerated. For these examples, we use three levels of impact on organizations or

individuals should there be a breach of security (i.e., a loss of confidentiality,

integrity, or availability).These levels are defined in FIPS 199:

• Low: The loss could be expected to have a limited adverse effect on organizational

operations, organizational assets, or individuals. A limited adverse effect

means that, for example, the loss of confidentiality, integrity, or availability

might (i) cause a degradation in mission capability to an extent and duration

that the organization is able to perform its primary functions, but the effectiveness

of the functions is noticeably reduced; (ii) result in minor damage to

organizational assets; (iii) result in minor financial loss; or (iv) result in minor

harm to individuals.

Moderate: The loss could be expected to have a serious adverse effect on

organizational operations, organizational assets, or individuals. A serious

adverse effect means that, for example, the loss might (i) cause a significant

degradation in mission capability to an extent and duration that the organization

is able to perform its primary functions, but the effectiveness of the

functions is significantly reduced; (ii) result in significant damage to organizational

assets; (iii) result in significant financial loss; or (iv) result in significant

harm to individuals that does not involve loss of life or serious,

life-threatening injuries.

• High: The loss could be expected to have a severe or catastrophic adverse

effect on organizational operations, organizational assets, or individuals. A

severe or catastrophic adverse effect means that, for example, the loss might

(i) cause a severe degradation in or loss of mission capability to an extent and

duration that the organization is not able to perform one or more of its primary

functions; (ii) result in major damage to organizational assets; (iii) result

in major financial loss; or (iv) result in severe or catastrophic harm to individuals

involving loss of life or serious, life-threatening injuries.

The Challenges of Computer Security

Computer and network security is both fascinating and complex. Some of the reasons

include:

1. Security is not as simple as it might first appear to the novice. The requirements

seem to be straightforward; indeed, most of the major requirements for

security services can be given self-explanatory, one-word labels: confidentiality,

authentication, nonrepudiation, integrity. But the mechanisms used to

meet those requirements can be quite complex, and understanding them may

involve rather subtle reasoning.

2. In developing a particular security mechanism or algorithm, one must always

consider potential attacks on those security features. In many cases, successful

attacks are designed by looking at the problem in a completely different way,

therefore exploiting an unexpected weakness in the mechanism.

3. Because of point 2, the procedures used to provide particular services are often

counterintuitive.Typically, a security mechanism is complex, and it is not obvious

from the statement of a particular requirement that such elaborate measures are

needed. It is only when the various aspects of the threat are considered that elaborate

security mechanisms make sense.

4. Having designed various security mechanisms, it is necessary to decide where to

use them.This is true both in terms of physical placement (e.g., at what points in

a network are certain security mechanisms needed) and in a logical sense [e.g., at

what layer or layers of an architecture such as TCP/IP (Transmission Control

Protocol/Internet Protocol) should mechanisms be placed).

5. Security mechanisms typically involve more than a particular algorithm or

protocol. They also require that participants be in possession of some secret

information (e.g., an encryption key), which raises questions about the creation,

distribution, and protection of that secret information. There also may

be a reliance on communications protocols whose behavior may complicate

the task of developing the security mechanism. For example, if the proper

functioning of the security mechanism requires setting time limits on the

transit time of a message from sender to receiver, then any protocol or network

that introduces variable, unpredictable delays may render such time

limits meaningless.

6. Computer and network security is essentially a battle of wits between a perpetrator

who tries to find holes and the designer or administrator who tries to close

them.The great advantage that the attacker has is that he or she need only find a

single weakness, while the designer must find and eliminate all weaknesses to

achieve perfect security.

7. There is a natural tendency on the part of users and system managers to perceive

little benefit from security investment until a security failure occurs.

8. Security requires regular, even constant, monitoring, and this is difficult in today’s

short-term, overloaded environment.

9. Security is still too often an afterthought to be incorporated into a system

after the design is complete rather than being an integral part of the design

process.

10. Many users (and even security administrators) view strong security as an

impediment to efficient and user-friendly operation of an information system

or use of information.