Seminar: Advanced Topics in Software and Systems

EngineeringPresenter: Sabbir Ahmmed

MotivationBasic Concepts and Taxonomy of Dependable and Secure

Computing

Motivation

Motivation

Motivation

● Main definitions relating to dependability○ reliability○ availability○ safety○ integrity○ maintainability

● additional definitions ○ threats to dependability and security ○ e.g faults, errors, failures

● means for their achievement○ fault prevention, fault tolerance○ fault removal, fault forecasting etc

Introduction

"Basic Concepts and Taxonomy of Dependable and Secure Computing" by A. Avizienis, J.C. Laprie, B. Randell, C. Landwehr● 2525 citations● 360 citations● 315 citations

Introduction

This paper aims to give precise definitions of● dependability and security● computing and communications systems● focus on concepts

Introduction

This paper does not address the● measures of dependability and security● documenting state-of-the-art● implementations issues● confidentiality

Basic Concepts

● Basic set of definitions● Entire range of computing and

communications systems○ individual logic gates○ networks of computers○ computer based systems

Basic Concepts

● System function● Behaviour

○ described by a sequence of states○ total states

■ computation■ communication■ stored information■ interconnection■ physical connection

● Structure● Service

Basic Concepts

Threats to dependability and Security● Failures

○ also known as service failure○ a transition from correct service to incorrect

service○ service outage and service restoration

● Errors○ when at least one external state of the system

deviates from correct service state● Faults

○ hypothesized cause of an error○ could be internal or external○ could be active or dormant

Basic Concepts

[Mordechai Ben-Ari, Weizmann Institute of Science] (1999) The bug that destroyed a rocket

Basic Concepts

Software Hall of Shame

Basic Concepts

Software Growth

Picture Credit: Dr. Werner J.A. Dahm, Director, Security & Defense Systems Initiative, Arizona State University

Basic Concepts

● Degraded mode/partial failures○ slow service ○ limited service○ emergency service

Basic Concepts

Dependability○ ability to deliver a service that can justifiably be

trusted○ ability to avoid service failures○ encompasses the following attributes

■ availability■ reliability ■ safety■ integrity■ maintainability

Basic Concepts

Security○ is a composite of the attributes

■ confidentiality■ integrity■ availability

Basic Concepts

Means to attain dependability and security● Fault prevention● Fault tolerance● Fault removal● Fault forecasting

Threats to dependability

System life cycle● Development phase

○ physical world○ human developers○ development tools○ production and test facilities

● Use phase○ users○ administrators○ the infrastructure○ intruders○ ....

Threats to dependability

Forms of maintenance

Threats to dependability

A Taxonomy of Faults○ development fault○ physical faults○ interaction faults

FaultsThe elementary fault classes

31 likely combinations/256 possible combinations

● Natural Faults○ internal○ external

● Human-made Faults○ omission faults○ commission faults

Faults

Faults

Faults

Classification of Human-made faults

● Non- malicious Faults○ accidental○ incompetence

Faults

● Malicious faults○ malicious logic faults

■ logic bomb■ Trojan horse■ trapdoor■ virus■ worm■ zombie

○ intrusion attempts

Faults

Single vs MultipleIndependent vs Related

Failures

Service failure modes

Failures modes With respect to failure domain

Failures

Development failures and principal causesAAS example ($ 1.5 billion)● Complete development failure

○ budget failure○ schedule failure

● Partial development failure○ overruns (example F-35)○ downgrading (example F-35)

Dependability and security failuresAAS example (outage limit)

Errors

● Detected errors● Latent errors

● Multiple related errors● Single errors

Error propagation

Chain of threats

The way forward

Means to attain dependability

● Fault Prevention● Fault Tolerance● Fault Removal

○ during development■ verification■ diagnosis■ correction

○ during use

Fault tolerance techniques

Fault tolerance techniques

Fault removal (Verification)

Fault removal (Testing)

Conclusion