Chapter 15. Security

Protection, as we discussed in Chapter 14, is strictly an internal problem: How do we provide controlled access to programs and data stored in a computer system? Security, on the other hand, requires not only an adequate protection system but also consideration of the external environment within which the system operates. A protection system is ineffective if user authentication is compromised or a program is run by an unauthorized user.

Computer resources must be guarded against unauthorized access, malicious destruction or alteration, and accidental introduction of inconsistency. These resources include information stored in the system (both data and code), as well as the CPU, memory, disks, tapes and networking that are the computer. In this chapter, we start by examining ways in which resources may be accidentally or purposefully misused. We then explore a key security enabler —cryptography. Finally, we look at mechanisms to guard against or detect attacks.


  • To discuss security threats and attacks.

  • To explain the fundamentals of encryption, authentication, and hashing.

  • To examine the uses of cryptography in computing.

  • To describe the various countermeasures to security attacks.

The Security Problem

In many applications, ensuring the security of the computer system is worth considerable effort. Large commercial systems containing payroll or other financial data are inviting targets to thieves. Systems that contain data pertaining to corporate operations ...

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