Chapter 1: Introduction
• Components of computer security
• Threats
• Policies and mechanisms
• The role of trust
• Assurance
• Operational Issues
• Human Issues
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 1
Basic Components
• Confidentiality
– Keeping data and resources hidden
• Integrity
– Data integrity (integrity)
– Origin integrity (authentication)
• Availability
– Enabling access to data and
resources
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 2
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Basic Components Confidentiality
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 3
Basic Components - Integrity
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 4
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Basic Components Availability
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 5
Classes of Threats
• Disclosure
– Snooping
• Deception
– Modification, spoofing, repudiation of origin,
denial of receipt
• Disruption
– Modification
• Usurpation
– Modification, spoofing, delay, denial of
service
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
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Classes of Threats - Disclosure
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 7
Classes of Threats - Deception
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 8
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Classes of Threats - Disruption
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 9
Classes of Threats - Usurpation
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 10
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Policies and Mechanisms
• Policy says what is, and is not,
allowed
– This defines “security” for the
site/system/etc.
• Mechanisms enforce policies
• Composition of policies
– If policies conflict, discrepancies may
create security vulnerabilities
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 11
Policies – An Example
• A university disallows cheating: copying
another student's homework assignment.
• A computer science class requires the
students to do their homework on the
department's computer.
• One student notices that a second student
has not read protected the file containing
her homework and copies it. Has either
student (or have both students) breached
security?
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 12
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Policy may be expressed in …
– natural language;
– mathematics;
– policy languages.
• What are pros and cons of the above
ways of expressing policies?
Imprecise vs. Easy to Understand
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 13
Policy may be expressed in
Mathematics – An example
A simple finite-state machine. In this example,
the authorized states are s1 and s2.
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 14
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Policies - Consistencies
• The composition problem requires checking for
inconsistencies among policies.
• For example, one policy allows students and
faculty access to all data, and the other allows
only faculty access to all the data, then they
must be resolved (e.g., partition the data so
that students and faculty can access some
data, and only faculty access the other data).
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 15
Mechanisms may be …
• technical, in which controls in the computer
enforce the policy;
example?
For example, the requirement that a user supply a password to
authenticate herself before using the computer
• procedural, in which controls outside the
system enforce the policy;
example?
For example, give a zero to both students
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 16
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Goals of Security
• Prevention
– Prevent attackers from violating security
policy
• Detection
– Detect attackers’ violation of security policy
• Recovery
– Stop attack, assess and repair damage
– Continue to function correctly even if attack
succeeds
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 17
Goals of Security - Prevention
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 18
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Goals of Security - Detection
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 19
Goals of Security - Recovery
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 20
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Trust and Assumptions
• Underlie all aspects of security
• Policies
– Unambiguously partition system states
– Correctly capture security requirements
• Mechanisms
– Assumed to enforce policy
– Support policies work correctly
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 21
Trust and Assumptions (Cont.)
• Example: a bank’s policy may state that
officers of the bank are authorized to
shift money among accounts. If a bank
officer puts $10,000 in his account, has
the bank’s security been violated?
Based on the policy statement – no.
In the “real world” – yes.
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 22
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Types of Mechanisms
secure
precise
set of reachable states
broad
set of secure states
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 23
Assurance
• Specification
– Requirements analysis
– Statement of desired functionality
• Design
– How system will meet specification
• Implementation
– Programs/systems that carry out
design
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
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Operational Issues
• Cost-Benefit Analysis
– Is it cheaper to prevent or recover?
• Risk Analysis
– Should we protect something?
– How much should we protect this thing?
• Laws and Customs
– Are desired security measures illegal?
– Will people do them?
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 25
Laws and Customs – an Example
• The United States controls the export of
cryptographic hardware and software
(considered munitions under United
States law).
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 26
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Human Issues
• Organizational Problems
– Power and responsibility
– Financial benefits
• People problems
– Outsiders and insiders
– Social engineering
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 27
Human Issues - Examples
• If concluding a stock trade takes two minutes
without security controls and three minutes
with security controls, adding those controls
results in a 50% loss of productivity.
• Untrained personnel: one operator did not
realize that the contents of backup tapes
needed to be verified before the tapes were
stored. When attackers deleted several critical
system files, she discovered that none of the
backup tapes could be read.
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 28
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Tying Together
Threats
Policy
Specification
Design
Implementation
Operation
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 29
Key Points
• Policy defines security, and
mechanisms enforce security
– Confidentiality
– Integrity
– Availability
• Trust and knowing assumptions
• Importance of assurance
• The human factor
Introduction to Computer Security
Auburn University
Computer Science and Software Engineering
Slide 30
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