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Chapter: Cryptography and Network Security Principles and Practice : Overview

The Challenges of Computer Security

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

The Challenges of Computer Security


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


1.         Security is not as simple as it might first appear to the novice. The require-ments seem to be straightforward; indeed, most of the major requirements for security services can be given self-explanatory, one-word labels: confi-dentiality, authentication, nonrepudiation, or 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.


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 compli-cate 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 imped-iment to efficient and user-friendly operation of an information system or use of information.


The difficulties just enumerated will be encountered in numerous ways as we examine the various security threats and mechanisms throughout this book.





To assess effectively the security needs of an organization and to evaluate and choose various security products and policies, the manager responsible for security needs some systematic way of defining the requirements for security and characterizing the approaches to satisfying those requirements. This is difficult enough in a centralized data processing environment; with the use of local and wide area networks, the problems are compounded.

ITU-T3 Recommendation X.800, Security Architecture for OSI, defines such a systematic approach.4 The OSI security architecture is useful to managers as a way of organizing the task of providing security. Furthermore, because this architecture was developed as an international standard, computer and communications vendors have developed security features for their products and services that relate to this structured definition of services and mechanisms.


For our purposes, the OSI security architecture provides a useful, if abstract, overview of many of the concepts that this book deals with. The OSI security archi-tecture focuses on security attacks, mechanisms, and services. These can be defined briefly as


             Security attack: Any action that compromises the security of information owned by an organization.


             Security mechanism: A process (or a device incorporating such a process) that is designed to detect, prevent, or recover from a security attack.


             Security service: A processing or communication service that enhances the security of the data processing systems and the information transfers of an organization. The services are intended to counter security attacks, and they make use of one or more security mechanisms to provide the service.


In the literature, the terms threat and attack are commonly used to mean more or less the same thing. Table 1.1 provides definitions taken from RFC 2828, Internet Security Glossary.

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