it_600_module10_overview.pdf - Relationship to Previous...

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IT 600 Module Ten 1 Relationship to Previous Concepts Operating systems act as a layer of abstraction between applications and hardware. They are also, from a security perspective, the gateway between those applications and the outside world (e.g., users logging on to a console, network applications sending packets from other servers, internet users.). Most applications rely on system calls to ensure applications are protected, file system access is controlled, and network communications are secure (Tanenbaum & Bos, 2015). Without a hard outer shell, the application layer would be vulnerable. Hardware too must be security aware in the context of operating systems. Microprocessors, reviewed in Module One, must ensure Ring 2 microprocessor instructions do not indirectly invoke Ring 0 instructions intended for protected mode operation only (Tanenbaum & Bos, 2015). Memory management units (MMUs), reviewed in Module Four, must enforce page protection mechanisms and protection faults must result when an application attempts to access memory regions it is not permitted to touch. Operating System Security Evaluation One of the first protections an operating system user encounters is the log-on prompt. The log-on prompt ensures only those with proper authorization can access the local console. The log-on prompt requires a user to enter a valid user name and password prior to accessing the services of the operating system. Behind the scenes, there is much more to operating system security than logging on. The United States Department of Defense (Dod) established a system to evaluate the level of protection offered by a commercial operating system called Trusted Computer System Evaluation Criteria (TCSEC) (Russinovich & Solomon, 2009). Although TCSEC is 20 years old and has been supplanted by the Common Criteria (covered in next paragraph), it is still a good example of the kind of criteria used to evaluate an operating syste m’s security. The rating levels used to evaluate operating systems included the following: Rating Description A1 Verified Design B3 Security Domains B2 Structured Protection
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