CSEN 1001

Computer and Network SecurityAmr El MougyAmr Osman

Course Details• Instructor:

Amr El MougyEmail: amr.elmougy@guc.edu.egOffice hours: Mon 12:00-1:00

Thursday 3:00-4:00

Office: C7.312

• Assessment:

Assignments5% Quizz

es10%

Class Work

5%

Project20%

Mid-term20%

Final40%

•TA:Amr OsmanEmail: amr.salaheldin@guc.edu.egOffice: C7.220

Course Details• Text book and some lecture slides:

Authors: William Stallings and Lawrie BrownTitle: Computer Security, Principles and PracticePublisher: Pearson Education, Inc., 2008

• Note: These slides are not meant to be comprehensive lecture notes! They are only remarks and pointers. The material presented here is not sufficient for studying for the course. Your main sources for studying are the text and your own lecture notes

Course Details• Security concepts• Cryptographic tools• User authentication• Access control• Security attacks• Prevention systems• Software Security• Cryptographic algorithms• Internet security• Management issues

Lecture (1)

Introduction and Key Security Concepts

Definitions• The US-based National Institute for Standards and Technology (NIST)

defines computer security as follows:

[Computer security is] the protection afforded to an automated information system in order to attain the applicable objectives of preserving integrity, availability, and confidentiality of information system resources (includes hardware, software, firmware, information/data, and telecommunications)

Definition (Computer Security)

Key Security Concepts

CIA Triad

ConfidentialityConfidentiality covers two concepts:

Data confidentiality: Assures that private or confidential information is not made available or disclosed to unauthorized individuals

Privacy: Assures that individuals control or influence what information related to them may be collected and stored and by whom and to whom that information may be disclosed

IntegrityIntegrity as a security goal also covers two related concepts:

Data integrity: Assures that information and programs are changed only in a specified and authorized manner

System integrity: Assures that a system performs its intended function in an unimpaired manner, free from deliberate or inadvertent unauthorized manipulation of the system

Availability

Availability ensures that a system works promptly and service is not denied to authorized users. A loss of availability is the disruption of access to or use of information or an information system

Further ConsiderationsSome additional aspects are often mentioned:

Authenticity:• The property of being genuine and able to be verified• Confidence in the validity of a transmission, verifiability of a message originator, inputs

arriving from trusted sources• Verifiability of a user’s identity

Accountability:• Actions can be uniquely traced to their originator• Essential for nonrepudiation, deterrence, fault isolation, intrusion detection, after

action recovery, legal action• Truly secure systems are not achievable, so security breaches must be traceable

DAD Triad• The complement of CIA

Denial

AlternationDi

sclo

sure

Unauthorized individuals gain access to confidential information

Data is modified or destroyed through some unauthorized mechanism

Authorized users can not gain access to a system for legitimate purposes

DAD activities may be malicious or accidental

Levels of Security Breaches

Low

Moderate

High

• Limited adverse effect• System performs its primary functions• Minor damages to assets and individuals

• Serious adverse effect• System performs its primary functions

with lower efficiency• Significant damage to assets and

individuals (no loss of life)

• Catastrophic adverse effect• System unable to perform its

primary functions• Major damage to assets and

individuals

Layered Security AspectsSecurity considerations include:Physical securityOperating system security

Windows, Mac OS, Unix/Linux (Sun OS, Solaris, Open BSD, . . . )Application layer security

Browser, e-mail client, . . .Communication security

• Encryption• Firewalls• Intrusion detection systems

Computer Security Challenges1. not simple2. must consider potential attacks3. procedures used counter-intuitive4. involve algorithms and secret info5. must decide where to deploy mechanisms6. battle of wits between attacker / admin7. not perceived on benefit until fails8. requires regular monitoring9. too often an after-thought10. regarded as impediment to using system

Security Vocabulary System resource: (Asset)

Data, services, capabilities (processing power, communication bandwidth), equipment, etc.Adversary:

An entity that attacks or is a threat to a systemAttack:

An assault from an intelligent threat; an intelligent act manifesting a deliberate attempt to breach securityVulnerability:

A flaw or weakness that could be exploited to violate a system’s securityThreat:

A potential to violate security; a possible danger that might exploit a vulnerabilityRisk:

Probability of a particular threat exploiting a particular vulnerabilitySecurity policy:

A set of rules and practices that regulate how a system provides security for their assetsCountermeasure:

An action or device to reduce a threat/vulnerability/attack by eliminating or preventing it or by minimizing adverse effects

Security Vocabulary

Countermeasures

Owners

Vulnerabilities

Threat Agents

Threats

Risk

Assetsto

to

value

wish to minimize

imposeto reduce

that may possesthat may be

reduced by

may be aware of

Wish to abuse and/or may damage

give rise to

that exploit

leading to

that increase

ExampleThe water flowing to the right is a threat to the man (he might catch a cold)Example: The existence of a particular virus

The crack in the wall is a vulnerabilityExample: Open ports on a computerVulnerability + Threat = Risk! Vulnerability ThreatRisk

Vulnerabilities and AttacksSystem resource vulnerabilities may• be corrupted (loss of integrity)• become leaky (loss of confidentiality)• become unavailable (loss of availability)

Attacks are threats carried out and may be• passive• active• insider• outsider

Typical ThreatsHacker• Anyone who attempts to penetrate the security of an information

system, regardless of intent• Early definition included anyone very proficient in computer useMalicious insider• Someone from within the organization that attempts to go beyond

the rights and permissions that they legitimately hold• Security professionals and system administrators are particularly

dangerous

Typical ThreatsMalicious code objectVirus:

A program that attaches itself to a program or file so it can spread from one computer to another, leaving infections as it travels

Worm: A program that takes advantage of file or information transport features on your system, which allows it to travel unaided. The biggest danger with a worm is its capability to replicate itself on your system (e.g., sending itself to all of the e-mail list in your computer)

Trojan horse: A program that at first glance will appear to be useful software but will actually do damage once installed or run on your computer. It usually appears that is coming from a trusted source

CountermeasuresMeans used to deal with security attacks• prevent• detect• recover

May result in new vulnerabilitiesWill have residual vulnerabilityGoal is to minimize risk given constraints

Threat Consequences

Unauthorized Disclosure

• Exposure• Interception• Inference• Intrusion

Deception

• Masquerade• Falsification• Repudiation

Disruption

• Incapacitation• Corruption• Obstruction

Usurpation

• Misappropriation• Misuses

Attacks on Communication Networks

We distinguish:Passive attacks

• Attempts to learn or make use of information from the system but does not affect system resources• Eavesdropping or monitoring of transmissions

Active attacks• Attempts to alter system resources or affect their operation.

Passive AttacksRelease of message contents / snoopingTraffic analysis / spoofingPassive attacks are hard to detect!

Active Attacks

Masquerade: One entity pretends to be a different entity

Replay attack: Passive capture of a data unit and its subsequent retransmission to produce an unauthorized effect

Active AttacksModification attack: Some

portion of a legitimate message is altered or messages are reordered to produce an unauthorized effect

Denial of service: Prevents or inhibits the normal use or management of communications facilities

Security Functional Requirements

Technical measures:• Access control; identification & authentication; system & communication

protection; system & information integrityManagement controls and procedures: • Awareness & training; audit & accountability; certification, accreditation, &

security assessments; contingency planning; maintenance; physical & environmental protection; planning; personnel security; risk assessment; systems & services acquisition

Overlapping technical and management:• Configuration management; incident response; media protection

threat + vulnerability = riskRisk analysis, assessment, and management are

required

Risk AnalysisActions involved in risk analysis:

• Determine which assets are most valuable• Identify risks to assets• Determine the likelihood of each risk occurring• Take action to manage the risk

Security professionals formalize the risk analysis process

Step 1: Asset ValuationStep 1 in risk analysis process: Asset valuation

• Identify the information assets in the organization-Hardware, software, and information/data

•Assign value to those assets using a valuation method

Asset Valuation MethodsReplacement cost valuation

• Replacement cost (also called current cost accounting or CCA) values assets based on what it would cost to replace them if they were acquired today

• For example, if Utility Company were placing this same plant today, the materials would cost $530,000 and the installation would cost $56,000. The replacement cost value is $586,000

Original cost valuation• Original cost (also called historic cost accounting or HCA) values assets based on what the company

actually spent for the assets when they were acquired• Example: In 1990, Utility Company spent $500,000 to purchase the materials for its fixed lines and

$50,000 to install them. The original cost value of these assets is $550,000 before depreciationDepreciated valuation

• Uses the original cost less an allowance for value deterioration (original value – how much drop in its price since purchased)

Qualitative valuation• Assigns priorities to assets without using dollar values

Step 2: Risk Assessment Qualitative Assessment

Quantitative Assessment

Focuses on analyzing intangible properties of an asset rather than financial value

Prioritizes risks to aid in the assignment of security resources

Relatively easy to conduct

Assigns dollar values to each risk based on measures such as: asset value (AV).

Assesses the exposure factor (EF), i.e., the expected portion (%) that can be destroyed by a given risk

Assesses the annualized rate of occurrence (ARO), i.e., the number of times you expect the risk to occur.

Determines the single loss expectancy (SLE), amount of damage each time the risk occur (SLE = AV × EF)

Evaluates the annualized loss expectancy (ALE), i.e., the amount of damage each year from a given risk (ALE = ARO × SLE)

Step 3: Managing RisksRisk avoidance

• Used when a risk overwhelms the benefits gained from having a particular mechanism available

• Avoid any possibility of risk by disabling the mechanism that is vulnerable• Disabling e-mail is an example of risk avoidance

Risk mitigation• Used when a threat poses a great risk to a system• Takes preventative measures to reduce the risk• A firewall is an example of risk mitigation

Risk acceptance• Useful when risk or potential damage is small• Do nothing to prevent or avoid the risk

Risk transference• Ensure that someone else is liable if damage occurs• Buy insurance for example

Security TradeoffsSecurity can be seen as a tradeoff between risks and benefits Cost of implementing the security mechanism vs. the amount

of damage it may preventTradeoff considerations:• user convenience• business goals• expenses

X.800 Security Architecture• X.800, Security Architecture for OSI• Systematic way of defining requirements for security and

characterizing approaches to satisfying them• Defines:• Security attacks - compromise security • Security mechanism - act to detect, prevent, recover from attack• Security service - counter security attacks

Security Taxonomy