Introduction to Computer
Security
Introduction to Computer Security
• Books:
1. An Inroduction to Computer Security: The
NIST Handbook
2. Johannes Buchmann: Introduction to
Cryptography
3. Douglas Stinson: Cryptography Theory and
Practice
I. Outline of the semester
• Term of computer security
• Elements of computer security
• Three major security controls: Administrative
controls, Physical controls, Algorithmic
controls:
Cryptography – encryption (symmetric,
asymmetric), hash functions, digital
signatures, message authentication codes,
identification, key exchange etc.
II. Computer Security
• The protection afforded to an automated
information system in order to attain the
applicable objectives of preserving the
integrity, availability and confidentiality of
information system resources (includes
hardware, software, information/data)
II. Computer Security
• Integrity:
data integrity: Requirement that information
and programs are changed only in a specified
and authorized manner
system integrity: Requirement that a system
performs its intended function free from
unauthorized manipulation
II. Computer Security
• Availability:
Requirement intended to assure that systems
work promptly and service is not denied to
authorized users.
• Confidentiality:
Requirement that private or confidential
information not be disclosed to unauthorized
individuals.
II. Elements of Computer Security
1. Computer security supports the mission of the
organization
2. Computer security is an integral element of sound
management
3. Computer security should be cost-effective
4. Computer security responsibilities should be made explicit
5. System owners have computer security responsibilities
outside their own organizations
6. Computer security requires a comprehensive and
integrated approach
7. Computer security should be periodically reassessed
8. Computer security is constrained by societal factors
II. Computer security supports the
mission of the organization
• Computer security helps the organization’s mission by
protecting its physical and financial resources,
reputation, legal position, employees, and other
tangible and intangible assets.
• No complete security  protecting important assets
• usually security is secondary (making profit, providing
good service etc. is primary)
• Management should understand their mission and how
their information system supports it.  security
requirements are defined
• Interorganizational systems e.g.: good security of
buyers system also benefits the seller
II. Computer security is an integral
element of sound management
• Information and computer systems are often
critical assets that support the mission of an
organization. Protecting them can be as
critical as protecting other organizational
resources (e.g. money, physical assets,
employees)
• Managers should decide about the level of risk
they are willing to accept.
II. Computer security should be costeffective
• Ensure that the cost of controls does not
exceed expected benefits.
• Direct costs: purchasing, installing and
administering security systems
• Indirect costs: Security systems can sometimes
affect system performance, employee morale
or retraining requirements.
II. Computer security responsibilities
should be made explicit
• Document that states organization policy and
make explicit computer security
responsibilities
• Responsibilities may be internal to an
organization or may extend across
organizational boundaries.
II. Computer security requires a
comprehensive and integrated
approach
• Interdependencies of security controls –
Administrative, physical and algorithmic
controls work together interdependancies
e.g.: training on how to use a secure system
• Other interdependencies – system
management, legal issues, quality assurance
II. Computer security should be
periodically reassessed
• Computers and the environments they
operate in are dynamic  security
requirements are ever-changing
• Changes in the system or the environment can
create new vulnerabilities  necessary to
reassess periodically
II. Computer security is constrained by
societal factors
• Security may be limited by social issues
e.g. security vs. privacy (identification,
tracking actions)
III. Roles and Responsibilities
• Whose responsibility is it?
• Senior management
• Computer Security Management
• Program and Functional Managers/Application
owners
• Technology providers
• Supporting organizations
• Users
III. Senior management
• Senior management – ultimate responsibility
They establish the organization’s computer
security program to support the mission of the
organization.
They are responsible for setting a good
example for their employees
III. Computer Security Management
• Directs the organization’s day-to-day
management of its computer security
program
• Responsible for coordinating all securityrelated interactions among organizational
elements.
III. Program and Functional
Managers/Application owners
• Responsible for a program or function
including the supporting computer system.
• These officials are usually assisted by technical
staff.
III. Technology providers
• Managers and technicians who design and
operate computer systems.
• They are responsible for implementing technical
security on computer systems.
• Responsible for being familiar with security
technology that relates to their system.
• Responsible for analyzing technical
vulnerabilities.
• Telecommunications – providing communication
services (fax, voice, etc.)
• Help desk – recognize security incidents and refer
the caller to the appropriate person or
organization for a response
III. Supporting organizations
• Audit – Auditors are responsible for examining
systems whether the system is meeting stated
security requirements.
• Quality assurance – Responsible for improving
the products and services, how computer
security can be used to improve the quality.
• Training office – Responsible for training users,
operators, managers in computer security.
• Risk Management – Responsible for studying
all types of risks including computer securityrelated risks.
III. Users
• Users of information
Individuals who use information provided by the
computer system. They may read computerprepared reports etc.
• Users of systems
Individuals who directly use computer systems,
responsible for following security procedures,
reporting security problems, attending security
training.
IV. Threats
• Threats range from errors harming database
integrity to fires destroying entire computer
centers
• Threats from the actions of trusted
employees, outside hackers, careless data
entry clerks etc.
• Attack confidentiality, integrity of data or
availability of a system
IV. Threats
• Knowledge of threat environment is necessary
for system manager to implement the most
cost-effective security measures.
• It might be more cost-effective to simply
tolerate the expected losses  risk analysis
IV. Errors and omissions
• Threat to data and system integrity
• Made by users who create and edit data 
training can help
• Large percentage of threats
• Contribute directly or indirectly to security
problems
IV. Errors and omissions
• Directly: data entry error or programming
error that crashes a system
• Indirectly: errors create vulnerabilities
• Errors in programming are called bugs
• Installation and maintenance errors security
vulnerabilities
IV. Fraud and theft
• Automating traditional methods of fraud and
theft
• E.g.: financial systems are at risk, systems that
control access to any resource (inventory
systems etc.)
• Insiders (former employees also) are in a
better position, outsiders
• Hardware and software are vulnerable to theft
IV. Employee sabotage
• Employees know what actions might cause
the most damage
• Employee sabotage is believed to be much
smaller than the instances of theft, but the
cost of such incidents can be quite high.
IV. Loss of physical and Infrastructure
support
• Includes power failures, loss of
communication, water leaks, lack of
transportation service, fire, flood etc.
• Loss of infrastructure often results in
unexpected ways
IV. Malicious hackers/crackers
• A hacker breaks into computers and computer
networks, either for profit or motivated by the
challenge.
• Black hat (crackers) hackers: for malicious reasons such
as vandalism, credit card fraud, identity theft, piracy, or
other types of illegal activity
• White hat hackers: for non-malicious reasons, for
instance testing their own security system
• Grey hat hackers: combination of a Black Hat and a
White Hat Hacker (repair the system for a small fee)
IV. Malicious hackers/crackers
• Losses due to hacker attacks are significantly
smaller than losses due to insider theft and
sabotage, the hacker problem is widespread and
serious.
• Receive more attention: hacker threat is a more
recently encountered threat, organizations do not
know the purpose of a hacker (browse, steal,
damage, etc.)  no limitations, hackers’ identity
is unknown (case of painter and burglar)
IV. Industrial espionage
• Gathering proprietary data from private
companies or the government for the purpose of
aiding another company.
• Goal is to improve their competitive advantage .
• Since information is processed and stored on
computer systems, computer security can help.
(employees may sell information)
• E.g.: pricing information, product development,
customer lists, sales data, cost data, strategic
plans
IV. Malicious code
• Virus: A code segment that replicates by
attaching copies of itself to existing executables.
The new copy of the virus is executed when a
user executes the new host program.
• Trojan horse: A program that performs a desired
task, but that also includes unexpected functions.
They steals information, harm the system and do
not replicate themselves.
IV. Malicious code
• Worm: A self-replicating program that is selfcontained and does not require a host
program. The program creates a copy of itself
and causes it to execute, no user intervention
is required. Sometimes just consume
bandwith.
IV. Threats to personal privacy
• Electronic information about individuals by
governments, credit bureaus, private
companies, etc. have created a threat to
individual privacy.
• Often referred to „Big Brother”.
• Federal and state employees have sold
personal information collected by the
government. (1992, USA)
V. Administrative controls – Risk
management
• Risk is the possibility of something adverse
happening.
• Risk management is the process of assessing
risk, taking steps to reduce risk to an
acceptable level and maintaining that level of
risk.
• Computer security risk management
addresses risks which arise from an
organization’s use of information technology.
V. Administrative controls – Risk
management
• E.g.: To maximize the return on their investments,
businesses must often decide between aggressive
(but high-risk) and slow-growth (but more
secure) investment plans. These decisions require
analysis of risk.  Management decides
• There is always risk. (from trusted employees or
fire etc.)
• Risk management is made up of three activities:
risk assessment, risk mitigation and uncertainty
analysis
V. Administrative controls – Risk
management – Risk assessment
• Risk assessment: Process of analyzing and
interpreting risk
Basic activities:
• determining the assessment’s scope and
methodology
• Collecting and analyzing data
• Interpreting the risk analysis results
V. Administrative controls – Risk
management – Risk mitigation
Selecting safeguards
• Method of selecting safeguards: what if
analysis to test what difference each makes
with regard to cost, effectiveness and other
factors
• E.g.: what if passwords are strengthened?
Personnel may be required to change
passwords more frequently. There are no
direct monetary expenditure, but staff and
administrative overhead is increased.
V. Administrative controls – Risk
management – Uncertainty analysis
• Risk management often must rely on
speculation, best guesses, incomplete data,
and many unproven assumptions.
• Sources of uncertainty: lack of confidence or
precision in the risk management model or
lack of sufficient information to determine
the exact value of the elements of the risk
model
VI. Computer Support and Operations
(Regulations)
• This includes both system administration and
tasks external to the system that support its
operation (e.g., maintaining documentation).
It does not include system planning or design.
• Support and operations are routine activities
that enable computer systems to function
correctly. (e.g. fixing software or hardware
problems, maintaining software)
VI. Computer Support and Operations
• User Support:
– through a Help Desk
– which problems are security-related
– they may not be aware of the "whole picture„
• Software Support:
– controlling what software is used on a system ( must
not load any)
– ensure the software has not been modified without
proper authorization (This can be done with a
combination of logical and physical access controls.)
VI. Computer Support and Operations
• Configuration Management:
– process of keeping track of changes to the system and,
if needed, approving them
– the security goal is to know what changes occur, not
to prevent security from being changed
• Backups:
– Support and operations personnel and sometimes
users back up software and data
– Frequency of backups will depend upon how often
data changes and how important those changes are.
– Finally, backups should be stored securely
VI. Computer Support and Operations
• Logging:
– to support accountability
– Control numbers (or other tracking data), the
times and dates of transfers, names and
signatures of individuals involved, and other
relevant information
• Integrity Verification:
– no modification
– error detection and correction, cryptographicbased technologies
VII. Physical and environmental
security
• Physical Access Protection:
– Media can be stolen, destroyed, replaced with a look-alike
copy, or lost.
– Physical access controls, which can limit these problems,
include locked doors, desks, file cabinets, or safes.
• Environmental Protection:
– media should be protected against heat, liquids, dust etc.
• Disposition
– The process of removing information from media is called
sanitization.
– e.g.: overwriting, destruction by shredding or burning
VII. Physical and environmental
security
• refers to measures taken to protect systems, buildings, and related
supporting infrastructure against threats associated with their
physical environment
• three areas:
– the building, other structure, or vehicle housing the system and network
components; determine the level of such physical threats as fire, roof
leaks, or unauthorized access
– facility's general geographic operating location determines the
characteristics of natural threats, which include earthquakes and
flooding; man-made threats such as burglary or damaging nearby
activities, including toxic chemical spills, explosions, fires, and
electromagnetic interference
– system's operation usually depends on supporting facilities such as
electric power, heating and air conditioning, and telecommunications.
VII. Physical and environmental
security
• Interception of Data
– Direct Observation - terminal and workstation
display screens
– Interception of Data Transmissions - access to data
transmission lines
– Electromagnetic Interception - Systems routinely
radiate electromagnetic energy that can be
detected with special-purpose radio receivers.
(TEMPEST attack)
Algorithmic Control – Identification,
Entity authentication
• Identification is the means by which a user
provides a claimed identity to the system.
• Entity authentication is the means of
establishing the validity of this claim.
– something the individual knows (e.g.: password,
PIN)
– something the individual possesses (e.g.: smart
card, token)
– something the individual is (e.g.: biometric)