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Chapter 1

Introduction. Chapter 1. Chapter Overview. Overview of Operating Systems Secure Operating Systems Basic Concepts in Information Security Design of a Secure Operating System Threats to a Secure Operating System Define the problem (roughly). What is an Operating System?.

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Chapter 1

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  1. Introduction Chapter 1

  2. Chapter Overview • Overview of Operating Systems • Secure Operating Systems • Basic Concepts in Information Security • Design of a Secure Operating System • Threats to a Secure Operating System • Define the problem (roughly)

  3. What is an Operating System? • Provides/controls access to the various hardware resources in the system. • Runs and administers processes. • Tasks: • Mechanisms that enable high performance (efficient use) of computer systems. • Fair process administration. • Control access to resources to provide security.

  4. Figure of an Operating System

  5. Why is security an issue? • Processes share data and interact in other ways: • The output of one process is often used by other processes. • Processes can share information, often across computers or networks. • Sometimes the shared information is bad-intentioned and wants to share other information which should not be shared. • The challenge is to develop operating systems which can share information without allowing this behavior.

  6. The state of Security in Operating Systems • Formal security models and mechanisms have been defined, but they do not completely apply to practical systems. • Two kinds of operating systems: • Constrained, very secure systems • General purpose systems with a low level of security assurance. • Recent advances are improving both kinds of operating systems.

  7. What is a Secure Operating System? • A Secure Operating System provides security mechanisms that ensure that the system's security goals are enforced despite the threats faced by the system. • It is an ideal, because it is impossible to write a bug-free program. • It is an oxymoron in the sense that an OS is too complicated to be secure.

  8. Security Goals • Define the operations that can be executed by a system while still preventing unauthorized operations. • Should be defined at a high abstraction level. • Should be implementable and demonstrable.

  9. Basic Concepts in Information Security • Confidentiality: Keeping data from being given to forbidden parties. • Integrity: Keeping data from being modified except by authorized parties • Availability: Making it possible for data to be accessed by those who are supposed to access it.

  10. Basic Parties and concepts in Operating Systems Security • Subjects: Programs/processes (acting on a user's behalf) • Objects: files, sockets and other system resources. • Operations: What the subjects can do on the objects (e.g. read, write, append, update, execute, etc.)

  11. The Security Quandary • Security goals should be defined so they can be verified: functional goals are insufficient. • Confidentiality and integrity goals are so restrictive that they prevent function in favor of security. • New technology, for example virtual machine technology, may bridge the gap. • Also, general purpose OS's may now be capable of expressing and enforcing security goals.

  12. The Trust Model • A system's Trust Model consists of the software and data upon which the system depends for system security. • For an OS, it is called its “Trusted Computing Base” (TCB) • Ideally, the TCB should be minimal. • In a monolithic OS there are no boundaries, so the TCB is the whole OS! • Some programs outside the OS may have to be in the TCB also.

  13. Requirements of the TCB • The TCB must mediate all security-sensitive operations • The TCB and its data must be verifiably correct. • It must be possible to verify that the TCB cannot be altered by processes outside it.

  14. Assumed Threats • Powerful attacker. • Can inject operations from the network and may be in control of some of the software in the system. • Attacker is actively trying to violate security.

  15. The Task of The Secure OS developer • Protect the TCB from the threats mentioned in the previous slide. • That way, can maintain security by limiting interactions of processes with data in the system. • Protecting the TCB is more difficult because it interacts with many untrusted processes. • Countermeasures for each threat are needed.

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