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Computer Security

Introduction

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Introduction

What is the goal of Computer Security?

A first definition: To prevent or detect unauthorized actions by users

of the system.

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Introduction

How do we achieve Computer Security: 1. Security principles/concepts: explore general

principles/concepts that can be used as a guide to design secure information processing systems.

2. Security mechanisms: explore some of the security mechanisms that can be used to secure information processing systems.

3. Physical/Organizational security: consider physical & organizational security measures (policies)

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Security

Security is about protecting assets.This involves:• Prevention• Detection • Reaction (recover/restore assets)

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Computer Security

1. Confidentiality: prevent unauthorized disclosure of information.

2. Integrity: prevent unauthorized modification of information.

3. Availability: prevent unauthorized withholding of information.

Additionally:Authenticity, accountability, reliability, safety, dependability, survivability . . .

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Computer Security

Even at this general level there is disagreement on the precise definitions of some of the required security aspects.References:• TCSEC or Orange book – US Dept of Defense, Trusted

Computer System Evaluation Criteria.• ITSEC – European Trusted Computer System Product Criteria.• CTCPEC – Canadian Trusted Computer System Product

Criteria

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Confidentiality

Historically, security is closely linked to secrecy. Security involved a few organizations dealing mainlywith classified data.However, nowadays security extends far beyond confidentiality.Confidentiality involves:• privacy: protection of private data,• secrecy: protection of organizational data.

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Integrity

“Making sure that everything is as it is supposed to be.”For Computer Security this means: Preventing unauthorized writing or modifications.

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Availability

For Computer Systems this means that:Services are accessible and useable (without undue Delay) whenever needed by an authorized entity.

For this we need fault-tolerance.Faults may be accidental or malicious (Byzantine).Denial of Service attacks are an example of malicious attacks.

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Relationship between Confidentiality Integrity and Availability

Integrity

Confidentiality

Secure

Availability

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Accountability

Actions affecting security must be traceable to the responsible party.For this, • Audit information must be kept and protected,• Access control is needed.

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Other security requirements

• Reliability – deals with accidental damage,• Safety – deals with the impact of the environment

on system failure• Dependability – reliance can be justifiably placed on

the system• Survivability – deals with the recovery of the system

after massive failure.

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Computer Security

If I must give a definition…. (again)Computer Security deals with the prevention and

detection of unauthorized actions by users of the

System.

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Fundamental dilemma of Computer Security

Functionality or Assurance: which one?

• Security mechanisms need additional computational resources.

• Security policies interfere with working patterns, and can be very inconvenient.

• Managing security requires additional effort and costs.

• Ideally there should be a tradeoff.

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Principles of Computer Security-- fundamental design parameters

Application Software

| |User ---------------------------|-------------------- Resource (subject) | (object) | Hardware

The dimensions of Computer Security

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Principles of Computer Security

Integrity = compliance with a given set of rules.Integrity = compliance with a given set of rules.

Rules:• Internal consistency of data items• Authorized operations on data items• Access control

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1st Design decision

Should protection focus on data, operations or users?

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Layers of an IT system• Application – users run application programs tailored to meet

specific requirements• Services – application programs make use of services provided

by a software packages like a Database Management System (DBMS) or an Object Reference Broker (ORB).

• OS – The software packages run on top of the OS which controls access to resources

• OS kernel – the OS may have a kernel that mediates every access to the processor or memory

• Hardware – (processor & memory) physically stores and manipulates data.

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2nd Design decision

In which layer should security be placed?

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The onion model of protection mechanisms

Hardware

OS Kernel

OS

Services

Application

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Complexity vs Assurance

3rd Design decision

Should security focus on simplicity or security?

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Centralized vs Decentralized

4th Design decision

Should security control tasks be given to a central entity of left to individual components?

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The layer belowPhysical and organizational security mechanisms define a security perimeter or boundary.Attackers may try to bypass this boundary.

Computer Security

Physical and organizational security measures protection boundary

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The layer below

Access to the layer below is controlled through physical and organizational security measures.• Parts of the system that can malfunction without

compromising the protection mechanisms lie beyond the perimeter.

• Parts that can be used to disable the protection mechanisms lie within the perimeter.

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5th Design decision

How to prevent the attacker from accessing the layer below the protection boundary?

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Vulnerabilities

• Hardware: Interruption (DOS), Modification, Interception (Theft), Fabrication (Substitution)

• Software: Interruption (Deletion), Modification, Interception, Fabrication

• Data: Interruption (Loss), Modification, Interception, Fabrication

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Hardware

Hardware is more visible, so it is more easy to add/remove/change devices, intercept traffic, flood with traffic and generally control their functionality.

Attacks: physical damage

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Software• Interruption (Deletion): surprisingly easy!• Modification:

– Logic bombs –failure when certain conditions are met)– Trojan horses –a program that overtly does one thing while

covertly does another– Viruses –a specific Trojan horse that can be used to spread its

“infection”.– Trapdoors –a program that has a specific entry point– Information leaks in programs –code that makes information

accessible to unauthorized users• Interception (Theft): unauthorized copying

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Data

Hardware security is usually the concern of a relatively small number of staff. Software extends to programmers and analysts who create an modify programs.However data can be readily interpreted by the general public. Because of its visibility data attacks are much more widespread.

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Data

• Data Confidentiality: wiretapping, planting bugs, sifting though trash receptacles, monitoring electromagnetic radiation, bribing, inferring, requesting …

• Data Integrity: a higher level of sophistication is needed.– Salami attacks –shave off a little from many accounts to

form a valuable result– Replay attacks

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Computer Criminals

• Amateurs – Normal people who observe a weakness in a security system – Disgruntled over some negative work situation– Have committed most of computer crimes to date

• Crackers– Often high school or university students: cracking is seen as the

ultimate victimless crime– Attack for curiosity, self-satisfaction and personal gain– No common profile or motivation

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Computer Criminals

• Career criminals– Understand the targets of computer crime– Usually begin as computer professionals who later

engage in computer crime finding the prospects and payoff good.

– Electronic spies and information brokers who recognize – That trading in companies secrets can be lucrative.