Alan Turing Computing Genius And Wartime – Harry Henderson

To do this, the code breakers would seek to exploit both weak- nesses in the Enigma system and carelessness on the part of its oper- ators. Each of the millions of initial Enigma machine settings had its own internal consistency. The fact that at a given step a certain letter is encoded as a particular second letter meant that other possible let- ter matchings could not occur. It was thus possible to winnow away many possible settings.

Turing and his colleagues also refined the techniques for look- ing for “cribs”—common phrases like “nothing special to report.” Because an Enigma cannot encrypt a letter as itself, if that letter is in a crib, the crib could be matched against the ciphertext. Any position where a crib letter matched a cipher letter was a place where the crib could not have been in the plaintext. Enigma 51 A Wave (woman naval volunteer) working with a “Bombe” code-breaking machine (Na- tional Security Agency) 52 AlAn Turing Other techniques took advantage of cyclical patterns in the operation of the rotors, caused by the pawls or notches with which an outer rotor could step an inner rotor one position forward.

These patterns could be punched onto cards that could be aligned for easier comparison. The result of all these techniques (and more) was to whittle mil- lions of possible rotor settings down to a hundred thousand or so—a number that could be feasibly examined by a Bombe. In general, Turing’s mind in particular was well prepared for the mixture of intuition and systematic discipline needed for code break- ing.

After all, he had designed his mental Turing machine as a way to ✹ Bletchley Park today After the war ended, most of the equipment at Bletchley Park was quickly dismantled and the thousands of workers resumed their civil- ian careers. The history of the facility and its achievements would remain secret until the 1970s. Meanwhile, the mansion and outbuild- ings were owned by a succession of fi rms including British Telecom and various government agencies.

The facility was also used by the Government Communications Headquarters (GCHQ), for courses in cryptanalysis until 1987. At the start of the 1990s, Bletchley Park was virtually deserted, the buildings badly in need of repair. The property was being considered for demolition and redevelopment. Fortunately, Bletchley Park was designated a protected site, and in 1992, the Bletchley Park Trust was formed to rehabilitate the site as a museum, which opened the following year.

Alan Turing: Computing Genius and Wartime Code Breaker Copyright © 2011 by Harry Henderson All rights reserved. No part of this book may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval systems, without permission in writing from the publisher. For information contact: Chelsea House An imprint of Infobase Publishing 132 West 31st Street New York NY 10001 Library of Congress Cataloging-in-Publication Data Henderson, Harry, 1951– Alan Turing : computing genius and wartime code breaker / Harry Henderson.

p. cm.—(Makers of modern science) Includes bibliographical references and index. ISBN 978-0-8160-6175-4 ISBN 978-1-4381-3514-4 (e-book) 1. Turing, Alan Mathison, 1912–1954—Juvenile literature. 2. Mathematicians— Great Britain—Biography—Juvenile literature. I. Title. II. Series. QA29.T8H46. 2011 510.92—dc22 2010015798 Chelsea House books are available at special discounts when purchased in bulk quantities for businesses, associations, institutions, or sales promotions.

Please call our Special Sales Department in New York at (212) 967-8800 or (800) 322-8755. You can find Chelsea House on the World Wide Web at http://www.chelseahouse.com Excerpts included herewith have been reprinted by permission of the copyright hold- ers; the author has made every effort to contact copyright holders. The publishers will be glad to rectify, in future editions, any errors or omissions brought to their notice. Text design by Kerry Casey Composition by Keith Trego Illustrations by Sholto Ainslie Photo research by Suzanne M. Tibor Cover printed by Art Print, Taylor, Pa.

Book printed and bound by Maple Press, York, Pa. Date printed: February 2011 Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 This book is printed on acid-free paper. For Will and Thad In gratitude for many hours of universal human conversation $ Contents Preface xi Acknowledgments xv Introduction xvii 1 An Unusual Child 1 Absent Parents 2 Hazelhurst 4 Sherborne School 5 An Intrepid Journey 6 Public School Life 7 The Public School in British Culture 7 Flashes of Genius 8 The Discovery of Friendship 10 Death of a Friend 11 The “Nature of Spirit” 12 2 The Frontiers of Mathematics 14 New Intellectual Opportunities 15 Mathematical Hurdles 17 The Scope of Mathematics 19 Mathematical Logic 20 Hilbert’s Challenge 22 3 Calculating Minds 24 From Abacus to Calculator 25 Babbage, Lovelace, and Their “Difference Engine” 26 Mechanical Calculators 28 Boole’s Bridge to the Computer 29 The Turing Machine 30 The Power of Simplicity 32 A Universal Machine 34 Graduate Study at Princeton 35 4 Enigma 39 The German Enigma 41 A Fiendishly Complicated Machine 42 The First Assault on the Enigma 45 Turing and Bletchley Park 47 The Battle of the Atlantic 48 New Code-breaking Techniques 50 Bletchley Park Today 52 A Desperate Plan 56 Turing Goes Afield 57 Electronics Advances 59 The Song of Delilah 60 5 The Birth of the Computer 63 Colossus: a Forgotten Computer 66 The First Electronic Computers 68 Who Was First—Turing or von Neumann?

This is a short excerpt from the opening of “” by Unknown, quoted for review and introduction purposes. All rights belong to the copyright holders.

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