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CIS/TCOM 551 Computer and Network Security Slide Set 2. Carl A. Gunter Spring 2004. Goals Availability Integrity Confidentiality Targets Hardware Software Data. Controls Physical security Limited interface Identification and authorization Encryption Analysis of costs and benefits.

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Cis tcom 551 computer and network security slide set 2

CIS/TCOM 551Computer and Network SecuritySlide Set 2

Carl A. Gunter

Spring 2004

Introduction to security










Physical security

Limited interface

Identification and authorization


Analysis of costs and benefits

Introduction to Security

Progress and risk
Progress and Risk

  • Risk = (Probability of failure) * (Size of loss)

  • Safety-critical considerations

    • Dutch port authority

    • RER train

    • Software in automobiles

    • Intelligent highways

Progress and risk cont
Progress and Risk, cont.

  • Security-critical considerations

    • Credit card purchases on the web

    • Voting on the web

    • Banking on the web

    • Mobile agents and active networks

  • Safety and security considerations

    • Military systems, eg. Star Wars

    • Actuators on public networks

Security requirements
Security Requirements

  • Banking

  • Government

  • Public Telecommunications Carriers

  • Corporate / Private Networks

  • Electronic Commerce

Ref: Computer Communications Security, W. Ford, 94.


  • Electronic Funds Transfer (EFT)

    • Prosecution of fraud problematic

    • Financial system overall at risk

  • Automated Teller Machine (ATM)

Automatic teller machines
Automatic Teller Machines

  • Goals

    • Availability: Provide automated teller operations 24x7 in convenient locations

    • Integrity: Authorized users only, transactional guarantees

    • Confidentiality: Private communication with branches or center

  • Vulnerabilities and controls

  • Risk analysis and liabilities


  • National security of course, but also

  • “Unclassified but sensitive information” must not be disclosed

    • Example: social security web page

  • Electronic signatures approved for government contractors

Public telecom carriers
Public Telecom Carriers

  • Operations, Administration, Maintenance, and Provisioning (OAM&P)

  • Availability is a key concern

  • Significant insider risks

Corporate private networks
Corporate Private Networks

  • Completely private networks are becoming a thing of the past because of telecommuting.

  • Protection of proprietary information of course, but also concerns like privacy in the health care industry.

  • Foreign government threat?

Electronic commerce
Electronic Commerce

  • Electronic Data Interchange (EDI)

  • Electronic contracts need to be binding

  • ABA Resolution: “recognize that information in electronic form, where appropriate, may be considered to satisfy legal requirements regarding a writing or signature to the same extent as information on paper or in other conventional forms, when appropriate security techniques, practices, and procedures have been adopted.”

Goals of security







Goals of Security

Ref: Pfleeger.

Safety and security
Safety and Security

  • Many things in common and some major differences.

  • Some similarities aid understanding of both.

  • System vs. Environment.

  • Accident, breach.

  • Hazard, vulnerability.

Accident and security breach
Accident and Security Breach

  • Accident

    • Loss of life

    • Injury

    • Damage to property

  • Security Breach

    • Secret is revealed

    • Service is disabled

    • Data is altered

    • Messages are fabricated

Accident definition
Accident Definition

  • An accidentis an undesired and unplanned (but not necessarily unexpected) event that results in (at least) a specified level of harm.

  • Define breach similarly.

  • A security threat is a possible form of breach

Hazards and vulnerabilities
Hazards and Vulnerabilities

  • Hazard

    • No fire alarms

    • No fire extinguishers

    • Rags close to furnace

  • Vulnerability

    • Password too short

    • Secret sent in plaintext over public network

    • Files not write protected

Hazard definition
Hazard Definition

  • A hazard is a state or set of conditions of a system that, together with other conditions in the environment of the system, will lead inevitably to an accident.

  • Define security vulnerability similarly.

Other terms
Other Terms

  • Asset: object of value.

  • Exposure: threat to an asset.

  • Attack: effort by an agent to exploit a vulnerability and create a breach.

Major threats
Major Threats

  • Interruption

  • Interception

  • Modification

  • Fabrication

Major assets
Major Assets

  • Hardware

  • Software

  • Data

Threats to hardware
Threats to Hardware

  • Interruption: crash, performance degradation

  • Interception: theft

  • Modification: tapping

  • Fabrication: spoofed devices

Threats to software code
Threats to Software Code

  • Interruption: deletion

  • Interception: theft

  • Modification

    • Trojan horse

    • Logic bomb

    • Virus

    • Back door

    • Information leak

  • Fabrication: spoofing software distribution on the web

Threats to software processes
Threats to Software Processes

  • Interruption: bad inputs

  • Interception: attacks on agents

  • Modification: of exploited data

  • Fabrication: service spoofing (man-in-the-middle)

Threats to data
Threats to Data

  • Interruption: deletion, perceived integrity violation

  • Interception: eavesdropping, snooping memory

  • Modification: alteration of important information

  • Fabrication: spoofing web pages

Principles of security
Principles of Security

  • Easiest Penetration: An intruder must be expected to use any available means of penetration.

  • Adequate Protection: Computer items must be protected only until they lose their value. They must be protected to a degree consistent with their value.

  • Effectiveness: Controls must be used to be effective. They must be efficient, easy to use, and appropriate.


  • Physical security

  • Limited interface

  • Identification and authorization

  • Encryption

Breakdown of s w controls
Breakdown of S/W Controls

  • Program controls

    • as exercised by the programmer

    • as dictated by the programming language or programming environment

  • Operating system controls

  • Development process controls

Security models
Security Models

  • Multi-layer security

  • Graham-Denning model

Ref: Pfleeger.

Military security
Military Security

  • Familiar hierarchy of sensitivities, partitioned in to compartments.


  • Each piece of information is coded with its security level and one or more compartments

Classification and clearance
Classification and Clearance

  • <rank; compartments>

  • Each piece of information, or object, o is classified by its rank and compartments. C(o) = classification of o

  • Each actor, or subject, s is given a clearance by rank and compartments. C(s) = clearance of s

  • Dominance <r;c>  <r’;c’> iff r  r’ and c is a subset of c’.

  • C(o)  C(s) if the classification of o is dominated by the clearance of s.


  • A subject s is only able to access an object o if

    • the rank of s is higher than that of o, and

    • s is cleared for all of the compartments of o.

  • The first is called a hierarchical requirement, the second a non-hierarchical requirement.

Cis tcom 551 computer and network security slide set 2


Top Secret













Graham denning model
Graham-Denning Model

Subject executing command is x.

Transferable rights are denoted r*.

Non-transferable rights are denoted r.