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This chapter is from the book

This chapter is from the book

1.6 Operational Issues

Any useful policy and mechanism must balance the benefits of the protection against the cost of designing, implementing, and using the mechanism. This balance can be determined by analyzing the risks of a security breach and the likelihood of it occurring. Such an analysis is, to a degree, subjective, because in very few situations can risks be rigorously quantified. Complicating the analysis are the constraints that laws, customs, and society in general place on the acceptability of security procedures and mechanisms; indeed, as these factors change, so do security mechanisms and, possibly, security policies.

1.6.1 Cost-Benefit Analysis

Like any factor in a complex system, the benefits of computer security are weighed against their total cost (including the additional costs incurred if the system is compromised). If the data or resources cost less, or are of less value, than their protection, adding security mechanisms and procedures is not cost-effective because the data or resources can be reconstructed more cheaply than the protections themselves. Unfortunately, this is rarely the case.


A database provides salary information to a second system that prints checks. If the data in the database is altered, the company could suffer grievous financial loss; hence, even a cursory cost-benefit analysis would show that the strongest possible integrity mechanisms should protect the data in the database.

Now suppose the company has several branch offices, and every day the database downloads a copy of the data to each branch office. The branch offices use the data to recommend salaries for new employees. However, the main office makes the final decision using the original database (not one of the copies). In this case, guarding the integrity of the copies is not particularly important, because branch offices cannot make any financial decisions based on the data in their copies. Hence, the company cannot suffer any financial loss.

Both of these situations are extreme situations in which the analysis is clear-cut. As an example of a situation in which the analysis is less clear, consider the need for confidentiality of the salaries in the database. The officers of the company must decide the financial cost to the company should the salaries be disclosed, including potential loss from lawsuits (if any); changes in policies, procedures, and personnel; and the effect on future business. These are all business-related judgments, and determining their value is part of what company officers are paid to do.

Overlapping benefits are also a consideration. Suppose the integrity protection mechanism can be augmented very quickly and cheaply to provide confidentiality. Then the cost of providing confidentiality is much lower. This shows that evaluating the cost of a particular security service depends on the mechanism chosen to implement it and on the mechanisms chosen to implement other security services. The cost-benefit analysis should take into account as many mechanisms as possible. Adding security mechanisms to an existing system is often more expensive (and, incidentally, less effective) than designing them into the system in the first place.

1.6.2 Risk Analysis

To determine whether an asset should be protected, and to what level, requires analysis of the potential threats against that asset and the likelihood that they will materialize. The level of protection is a function of the probability of an attack occurring and the effects of the attack should it succeed. If an attack is unlikely, protecting against it has a lower priority than protecting against a likely one. If the unlikely attack would cause long delays in the company's production of widgets but the likely attack would be only a nuisance, then more effort should be put into preventing the unlikely attack. The situations between these extreme cases are far more subjective.

Let's revisit our company with the salary database that transmits salary information over a network to a second computer that prints employees' checks. The data is stored on the database system and then moved over the network to the second system. Hence, the risk of unauthorized changes in the data occurs in three places: on the database system, on the network, and on the printing system. If the network is a local (company-wide) one and no wide area networks are accessible, the threat of attackers entering the systems is confined to untrustworthy internal personnel. If, however, the network is connected to the Internet, the risk of geographically distant attackers attempting to intrude is substantial enough to warrant consideration.

This example illustrates some finer points of risk analysis. First, risk is a function of environment. Attackers from a foreign country are not a threat to the company when the computer is not connected to the Internet. If foreign attackers wanted to break into the system, they would need physically to enter the company (and would cease to be "foreign" because they would then be "local"). But if the computer is connected to the Internet, foreign attackers become a threat because they can attack over the Internet. An additional, less tangible issue is the faith in the company. If the company is not able to meet its payroll because it does not know whom it is to pay, the company will lose the faith of its employees. It may be unable to hire anyone, because the people hired would not be sure they would get paid. Investors would not fund the company because of the likelihood of lawsuits by unpaid employees. The risk arises from the environments in which the company functions.

Second, the risks change with time. If a company's network is not connected to the Internet, there seems to be no risk of attacks from other hosts on the Internet. However, despite any policies to the contrary, someone could connect a modem to one of the company computers and connect to the Internet through the modem. Should this happen, any risk analysis predicated on isolation from the Internet would no longer be accurate. Although policies can forbid the connection of such a modem and procedures can be put in place to make such connection difficult, unless the responsible parties can guarantee that no such modem will ever be installed, the risks can change.

Third, many risks are quite remote but still exist. In the modem example, the company has sought to minimize the risk of an Internet connection. Hence, this risk is "acceptable" but not nonexistent. As a practical matter, one does not worry about acceptable risks; instead, one worries that the risk will become unacceptable.

Finally, the problem of "analysis paralysis" refers to making risk analyses with no effort to act on those analyses. To change the example slightly, suppose the company performs a risk analysis. The executives decide that they are not sure if all risks have been found, so they order a second study to verify the first. They reconcile the studies then wait for some time to act on these analyses. At that point, the security officers raise the objection that the conditions in the workplace are no longer those that held when the original risk analyses were done. The analysis is repeated. But the company cannot decide how to ameliorate the risks, so it waits until a plan of action can be developed, and the process continues. The point is that the company is paralyzed and cannot act on the risks it faces.

1.6.3 Laws and Customs

Laws restrict the availability and use of technology and affect procedural controls. Hence, any policy and any selection of mechanisms must take into account legal considerations.


Until the year 2000, the United States controlled the export of cryptographic hardware and software (considered munitions under United States law). If a U.S. software company worked with a computer manufacturer in London, the U.S. company could not send cryptographic software to the manufacturer. The U.S. company first would have to obtain a license to export the software from the United States. Any security policy that depended on the London manufacturer using that cryptographic software would need to take this into account.


Suppose the law makes it illegal to read a user's file without the user's permission. An attacker breaks into the system and begins to download users' files. If the system administrators notice this and observe what the attacker is reading, they will be reading the victim's files without his permission and therefore will be violat

Complicating this issue are situations involving the laws of multiple jurisdictions—especially foreign ones.


In the 1990s, the laws involving the use of cryptography in France were very different from those in the United States. The laws of France required companies sending enciphered data out of the country to register their cryptographic keys with the government. Security procedures involving the transmission of enciphered data from a company in the United States to a branch office in France had to take these differences into account.


If a policy called for prosecution of attackers and intruders came from Russia to a system in the United States, prosecution would involve asking the United States authorities to extradite the alleged attackers from Russia. This undoubtedly would involve court testimony from company personnel involved in handling the intrusion, possibly trips to Russia, and more court time once the extradition was completed. The cost of prosecuting the attackers might be considerably higher than the company would be willing (or able) to pay.

Laws are not the only constraints on policies and selection of mechanisms. Society distinguishes between legal and acceptable practices. It may be legal for a company to require all its employees to provide DNA samples for authentication purposes, but it is not socially acceptable. Requiring the use of social security numbers as passwords is legal (unless the computer is one owned by the U.S. government) but also unacceptable. These practices provide security but at an unacceptable cost, and they encourage users to evade or otherwise overcome the security mechanisms.

The issue that laws and customs raise is the issue of psychological acceptability. A security mechanism that would put users and administrators at legal risk would place a burden on these people that few would be willing to bear; thus, such a mechanism would not be used. An unused mechanism is worse than a nonexistent one, because it gives a false impression that a security service is available. Hence, users may rely on that service to protect their data, when in reality their data is unprotected.

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