This document discusses protection and security in operating systems. It covers goals of protection like ensuring each object can only be accessed correctly by allowed processes. The principle of least privilege is introduced. Domain structure and access matrix models for protection are described. Access control matrix consists of subjects, objects, and access operations. Access control list and capability list are derivative and better forms. Security threats like intruders attempting to breach security are addressed. Categories of security violations like breach of confidentiality and methods of attacks are outlined. References from textbooks and websites on related topics are listed at the end.

1. Protection & Security
Organized By: V.A.
V.A.
CSED,TU

2. Disclaimer
This is NOT A COPYRIGHT MATERIAL
Content has been taken mainly from the following books:
Operating Systems Concepts By Silberschatz & Galvin ,
Operating systems By D M Dhamdhere,
System Programming By John J Donovan
etc…
VA.
CSED,TU

3. Protection – Goals & Principle
 Each Object has a Unique Name and can be accessed through a well-defined set
of Operations.
 Ensure that each Object is accessed correctly and only by those Processes that
are allowed to do so.
 Guiding Principle – Principle of Least Privilege
 Programs, users and systems should be given just enough privileges to
perform their tasks
VA.
CSED,TU

4. Domain Structure
 Access-right = <object-name, rights-set>
where rights-set is a subset of all valid operations that can be performed on the
object.
 Domain = Set of Access-Rights
 Domain can be realized in variety of ways: Each User, Each Process and Each
Procedure.
VA.
CSED,TU

5. Access Matrix
 View Protection as a MATRIX (access matrix)
 Rows represent Domains
 Columns represent Objects
 Access (i, j) is the Set Of Operations that a process executing in
Domaini can invoke on Objectj
VA.
CSED,TU

6. Access Control Matrix
 Access control matrix consists of triple parts such as subject, object, and access
operation.
 A SUBJECT is an Active Entity in a computer system such as User, Program,
Process and Thread.
 An OBJECT is a Passive Entity or System Resource such as File, Directory,
Database Record and Printer.
 In Access Control Matrix’s schema, the Subjects and Objects are placed in a
table. Each row represents a Subject and each column represents an Object.
 The data inside the table are Set Of Access Operations such as read, write, and
execute. The access operations are responsible for interactions between subjects
and objects.
VA.
CSED,TU

7. Access Matrix
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8. Use of Access Matrix
 If a Process in Domain Di tries to do “op” on object Oj, then “op” must be in the
ACCESS MATRIX.
 Can be Expanded to DYNAMIC PROTECTION.
 Operations to ADD, DELETE access rights.
 Special Access Rights:
 Owner of Oi
 Copy op from Oi to Oj
 Control – Di can modify Dj access rights
 Transfer – Switch from domain Di to Dj
VA.
CSED,TU

9. Access Matrix – Showing Switch
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10. Role Based Access Control
VA.
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11. Sample Access Matrix
The Derivative forms of access control matrix such as Access Control List (ACL)
and Capability List (C-list) are better applied.
VA.
CSED,TU

12. Access Control List
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13. ACL
When we look for Insurance Data we can write:
VA.
CSED,TU

14. C-List
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15. C-List
When we look for Alice’s C-list we can write:
VA.
CSED,TU

16. ACL vs CL
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17. Security
 Security must consider External Environment of the System and protect
the system resources
 Intruders (crackers) attempt to breach security
 THREAT is potential security violation
 ATTACK is attempt to breach security
 Attack can be accidental or malicious
 Easier to protect against accidental than malicious misuse
VA.
CSED,TU

18. Security Violations
 Categories
 Breach of confidentiality
 Breach of integrity
 Breach of availability
 Theft of service
 Denial of service
 Methods
 Masquerading (breach authentication)
 Replay attack
 Message modification
 Man-in-the-middle attack
 Session hijacking
VA.
CSED,TU

19. Security Attacks
VA.
CSED,TU

20. Reference List
Operating Systems Concepts By Silberschatz & Galvin,
Operating systems By D M Dhamdhere,
System Programming By John J Donovan,
www.os-book.com
www.cs.jhu.edu/~yairamir/cs418/os2/sld001.htm
http://gaia.ecs.csus.edu/~zhangd/oscal/pscheduling.html
http://www.edugrid.ac.in/iiitmk/os/os_module03.htm
http://williamstallings.com/OS/Animations.html
etc…
VA.
CSED,TU

21. Thnx…
VA.
CSED,TU