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Foundations of Computer Security
David Salomon
Foundations of
Computer Security
With 45 Figures
Professor David Salomon (emeritus)
Computer Science Department
California State University
Northridge, CA 91330-8281
email: david.salomon@csun.edu
British Library Cataloguing in Publication Data
A catalogue record for this book is available from the British Library
Library of Congress Control Number: 2005932091
ISBN-10: 1-84628-193-8
e-ISBN 1-84628-193-8
ISBN-13: 978-1-84628-193-8
Printed on acid-free paper
© Springer-Verlag London Limited 2006
Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under
the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any
form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic repro-
duction in accordance with the terms of licences issued by the Copyright Licensing Agency. Enquiries concerning
reproduction outside those terms should be sent to the publishers.
The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific state-
ment, that such names are exempt from the relevant laws and regulations and therefore free for general use.
The publisher makes no representation, express or implied, with regard to the accuracy of the information contained
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Printed in the United States of America
Springer Science+Business Media
Dedicated to the many anonymous users and experts who serve with
zeal and dedication in the unending war of computer security.
There isn’t an author who doesn’t take their [sic] books personally.
—Muriel Spark,
A Far Cry From Kensington
entle Reader. Your interest in this book is understandable. Computer security
has become one of the most important areas in the entire discipline of computing.
Computers today are used not only in the home and o
ce, but in a multitude of crucial
and sensitive applications. Computers control long distance telephone conversations,
the flow of information on the Internet, the distribution of electrical power to cities,
and they monitor the operations of nuclear power plants and the performance of space
satellites, to name just a few important applications.
We have become used to these small, quiet machines that permeate our lives and
we take them for granted, but from time to time, when they don’t perform their tasks,
we immediately become aware that something has gone terribly wrong. Considering
the complexity of today’s computers and their functions, and considering especially the
physical hazards that abound in the world, it is a wonder that our computers function
at all, yet we expect them to be reliable and we entrust them with more and more
delicate, sensitive, and complex assignments.
It is easy to disrupt a computer. Just brush your elbow accidentally against your
desk and you may spill your cup of coffee on your computer. A power loss lasting a
fraction of a second may lead to a head crash of the hard disk, resulting in a complete
loss of the disk and all its data. Carelessness on the part of operators or administrators
in a large computations center can cause a costly loss of data or even physical damage
to expensive equipment. Yet all these dangers (and there are many more like them)
pale in comparison with the many types of intentional criminal damage that we have
come to expect and that we collectively associate with the field of computer security.
A term closely related to computer security is computer crime. A computer crime
is an incident of computer security in which a law is broken. Traditionally, computer
crime has had a low profile. After all, in a computer crime there are no smoking guns,
no blood-stained victims, and no getaway cars. Often, such a crime is solved just by
sheer accident. In contrast, computer security is a high-visibility discipline because it
involves most of us.
Experience has shown that the more sophisticated a civilization is, the more vul-
nerable it is to natural or man-made disruptions. A tree that fell on power lines in
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