Protection and Security in Operating Systems

Protection and
Security in OS
V.V.SUBRAHMANYAM
SOCIS, IGNOU
DATE: 28-10-07
TIME: 16-30 TO 17-00

Introduction
 Interference in resource utilization is a
very serious threat in an OS
 The nature of the threat depends on the
nature of a resource and the manner in
which it is used.
 In this session, we discuss threats to
information stored in files because they
are the most common, and also the
most complex, threats.

Protection and Security
 OS use two sets of techniques to
counter threats to information namely:
Protection
Security

Protection
 It involves guarding a user’s data and
programs against interference by other
authorized users of the system.

Security
 It involves guarding of a user’s data
and programs against interference by
external entities, e.g. unauthorized
persons.

Facets to protection of information
 There are two facets to protection of
information
Secrecy: Implies that only authorized users
should be able to access information.
Privacy: Implies that information should be
used only for the purpose(s) for which it is
intended and shared.
OS focuses on guaranteeing secrecy of
information , and leaves the issue of privacy
to the users and their processes.

Security and Protection: Policies and Mechanisms
Security Policy Specify whether a person can
become a user of the system.
This function is performed by
the system administrator
Mechanisms 1. Add or delete users
2. Verify whether a person
is an authorized user.
Protection Policy Specify whether a user can
access a specific file. The
owner of a file performs this
function while creating it.
Mechanisms 1. Set or change
protection information
for a file.
2. Check whether a file
can be accessed by a
user.

Security Attributes
 Security is traditionally defined by the
three attributes namely:
Confidentiality: It is the prevention of
unauthorized modification of information or
resources.
Integrity: It is the prevention of unauthorized
Availability: It is the prevention of
unauthorized withholding of information or
resources.

Security Threats
 Direct: This is any direct attack on your
specific systems, whether from outside
hackers or from disgruntled insiders.
 Indirect: This is general random attack,
most commonly computer viruses,
computer worms or Trojan horses.

Reasons for taking Security measures
 To prevent loss of data
 To prevent corruption of data
 To prevent compromise of data
 TO prevent theft of data
 To prevent sabotage

Authentication
 Goal of Authentication: Reasonable
assurance that anyone who attempts
to access a system or a network is a
legitimate user.
 3 Mechanisms:
Password
Physical token or an artifact
Biometric measure

Security Models
 Security models can be discretionary or
mandatory.
Discretionary: Holders of right can be
allowed to transfer them at their discretion.
Mandatory: Only designated roles are
allowed to grant rights and users cannot
transfer them.

Security policy Vs. Security Model
 Security Policy: Outlines several high
level points: how the data is accessed, the
amount of security required and what are
the steps when these requirements are
not met.
 Security Model: The mechanism to
support the security policy. This involves
in the design of the security system.

Access Matrix Model
 Consists three principal components:
A set of passive objects (files, terminals,
devices and other entities)
A set of active subjects, which may be
manipulate the objects
A set of rules governing the manipulation
of objects by subjects.

The access matrix is a rectangular array
with one row per subject and one column
per object.
Objects
Subjects
File 1 File 2 File 3
User 1 r,w r r,w,x
User 2 r r r,w,x
User 3 r,w,x r,w r,w,x

Role Based Access Control
 Enforces access controls depending upon
a user role(s).
 Roles represent specific organization
duties and are commonly mapped to job
title. Ex: Administrator, Developer etc.
 Role definitions and associated access
rights must be based upon a thorough
understanding of an organization’s
security policy.

Take-Grant Model
 This model use graphs to model access
control.
 The graph structure can be represented as an
adjacency matrix and labels on the arcs can
be coded as different values in the matrix.
 Nodes in the graph are of two types, one
corresponding to subjects and the other to
objects.
 The possible access rights are read( r),
write(w), take(t) and grant(g).

Multilevel Models
 This type of models corresponds to the
multilevel policies where data is classified
into sensitivity levels and users have
access according to their clearances.
 Also known as Data Flow Models.

Contd…
 The Bell-La Padula model, intended to
contral leakage of information between
levels.
 The Biba Model, which controls the
integrity.
 The Lattice Model, which generalizes the
partially ordered levels of the previous
models using the concept of mathematical
lattices.

Protection and Security in Operating Systems

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