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PROPRIETARY MATERIAL. © 2007 The McGrawHill Companies, Inc. All rights reserved. No part of this PowerPoint slide may be displayed, reproduced or distributed in any form or by any means, without the prior written permission of the publisher, or used beyond the limited distribution to teachers and educators permitted by McGrawHill for their individual course preparation. If you are a student using this PowerPoint slide, you are using it without permission.
Security and Protection Dhamdhere: Operating Systems— Copyrightd© 2008
Security and Protection
• Security
– Guarding users’ data and programs against interference by external entities such as non-users or programs outside an OS
* Key technique: Authentication of users • Protection
– Guarding users’ data and programs against interference by internal entities such as users of the system and their programs
* Key technique: Authorization of users
Security and Protection Dhamdhere: Operating Systems— Copyrightd© 2008
Terminology used in security and protection
• Authentication
– Verifying the identity of a user
* Operating systems tend to perform authentication by knowledge
A person is the user she claims to be if she can exhibit some requisite knowledge, such as a password
• Authorization
– Verifying a user’s right to access a resource in a specific manner
Security and Protection Dhamdhere: Operating Systems— Copyrightd© 2008
Generic security and protection set-ups in an OS
• The authentication service generates an authentication token
• It is passed to the service & resource manager with each request
• Authorization service uses it to check whether user has access privileges
Security and Protection Dhamdhere: Operating Systems— Copyrightd© 2008
Policies and mechanisms of security and protection
• Security – Policy
* Whether a person can become a user of a system (implemented by system administrator)
– Mechanism
* Add or delete users, perform authentication, encrypt data • Protection
– Policy
* Which user can access a file in what manner (set by a file owner) – Mechanism
* Set or change authorization information, check whether a request conforms to a user’s privileges
Security and Protection Dhamdhere: Operating Systems— Copyrightd© 2008
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