INVITATION TO CYBERSECURITY 228 The higher the costs, the less likely the hacker will succeed and the more likely he will be caught. If a would-be attacker perceives that the costs will be too high to attack a target, he will choose a different, easier target. Figure 9.5 A medieval castle illustrating the defense in depth principle. This principle reminds us that implementing a single defense and then thinking everything will be fine is hubris. One defensive measure is good, but two are even better, three are better still, etc. Ideally, the layers of defense are independent of one another, so they cannot fall like dominoes. Each layer takes a different creative approach to overcome. In cybersecurity the layers include many different controls and categories of security, such as physical security, access control, network security, system security, alarm systems, and more, implemented all across the people, processes, technology, and facilities of an organization. 9.1.8 Compartmentalization “I cannot imagine any condition which would cause a ship to founder. I cannot conceive of any vital disaster happening to this vessel. Modern shipbuilding has gone beyond that.” - Captain Smith, Commander of the Titanic The Titanic was believed to be an unsinkable ship because its hull was made up of several watertight compartments (see Figure 9.6). The theory was that if the ship was ever in a collision, only the compartments directly involved in the impact would flood, and the other compartments would stay dry and provide enough buoyancy to keep the ship afloat. Tragically and ironically, on its very first voyage the Titanic struck an iceberg and sank. For various reasons, the theory did not hold up in practice. Even though it is actually a counterexample, the Titanic provides a memorable illustration of the principle of compartmentalization. The principle of compartmentalization states that access to resources should be segmented. There are two parallel benefits of compartmentalization: to limit exposure and to avoid intermingling resources that could compromise access control.
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