Serious Cryptography: A Practical Introduction to Modern Encryption

314 Pages·2017·5.394 MB·English

by  Jean-Philippe Aumasson

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A Practical Introduction
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🔑 Key concepts in cryptography, such as About the Author a
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computational security, attacker models, ti
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and forward secrecy Jean-Philippe Aumasson is Principal Research a
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Engineer at Kudelski Security, an international I
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cybersecurity company based in Switzerland. t
protocol behind HTTPS secure websites He has authored more than 40 research a rticles ro
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Jean-Philippe Aumasson
Foreword by Matthew D. Green

serious cryptography

s e r i o u s
C r y p t o g r a p h y
a practical introduction
to Modern encryption
by Jean-Philippe Aumasson
San Francisco
SERIOUS CRYPTOGRAPHY. Copyright © 2018 by Jean-Philippe Aumasson.
All rights reserved. No part of this work may be reproduced or transmitted in any form or by any means,
electronic or mechanical, including photocopying, recording, or by any information storage or retrieval
system, without the prior written permission of the copyright owner and the publisher.
Printed in USA
Seventh printing
25 24 23 22 21 7 8 9 10 11
ISBN-10: 1-59327-826-8
ISBN-13: 978-1-59327-826-7
Publisher: William Pollock
Production Editor: Laurel Chun
Cover Illustration: Jonny Thomas
Interior Design: Octopod Studios
Developmental Editors: William Pollock, Jan Cash, and Annie Choi
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Brief Contents
Foreword by Matthew D. Green ........................................xv
Preface.........................................................xvii
Abbreviations .................................................... xxi
Chapter 1: Encryption ............................................... 1
Chapter 2: Randomness ............................................. 21
Chapter 3: Cryptographic Security...................................... 39
Chapter 4: Block Ciphers ............................................ 53
Chapter 5: Stream Ciphers ........................................... 77
Chapter 6: Hash Functions .......................................... 105
Chapter 7: Keyed Hashing .......................................... 127
Chapter 8: Authenticated Encryption ................................... 145
Chapter 9: Hard Problems .......................................... 163
Chapter 10: RSA................................................. 181
Chapter 11: Diffie–Hellman.......................................... 201
Chapter 12: Elliptic Curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 217
Chapter 13: TLS.................................................. 235
Chapter 14: Quantum and Post-Quantum ................................ 251
Index ......................................................... 271

Contents in De tail
Foreword by Matthew d. green xv
preFace xvii
This Book’s Approach...............................................xviii
Who This Book Is For . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .xviii
How This Book Is Organized.......................................... xix
Fundamentals.............................................. xix
Symmetric Crypto ........................................... xix
Asymmetric Crypto .......................................... xix
Applications................................................xx
Acknowledgments ..................................................xx
abbreviations xxi
1
encryption 1
The Basics........................................................ 2
Classical Ciphers................................................... 2
The Caesar Cipher ........................................... 2
The Vigenère Cipher.......................................... 3
How Ciphers Work ................................................. 4
The Permutation ............................................. 4
The Mode of Operation........................................ 5
Why Classical Ciphers Are Insecure ............................... 6
Perfect Encryption: The One-Time Pad..................................... 7
Encrypting with the One-Time Pad................................. 7
Why Is the One-Time Pad Secure?................................. 8
Encryption Security.................................................. 9
Attack Models ............................................. 10
Security Goals ............................................. 12
Security Notions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Asymmetric Encryption .............................................. 15
When Ciphers Do More Than Encryption ................................. 16
Authenticated Encryption ...................................... 16
Format-Preserving Encryption ................................... 16
Fully Homomorphic Encryption .................................. 17
Searchable Encryption........................................ 17
Tweakable Encryption ........................................ 17
How Things Can Go Wrong.......................................... 18
Weak Cipher.............................................. 18
Wrong Model ............................................. 19
Further Reading................................................... 19
2
randoMness 21
Random or Non-Random?............................................ 22
Randomness as a Probability Distribution ................................. 22
Entropy: A Measure of Uncertainty...................................... 23
Random Number Generators (RNGs) and
Pseudorandom Number Generators (PRNGs) ........................... 24
How PRNGs Work .......................................... 25
Security Concerns........................................... 26
The PRNG Fortuna .......................................... 26
Cryptographic vs. Non-Cryptographic PRNGs ....................... 27
The Uselessness of Statistical Tests................................ 29
Real-World PRNGs................................................. 29
Generating Random Bits in Unix-Based Systems ...................... 30
The CryptGenRandom() Function in Windows........................ 33
A Hardware-Based PRNG: RDRAND in Intel Microprocessors............. 34
How Things Can Go Wrong.......................................... 35
Poor Entropy Sources......................................... 35
Insufficient Entropy at Boot Time ................................. 35
Non-cryptographic PRNG ..................................... 36
Sampling Bug with Strong Randomness............................ 37
Further Reading................................................... 38
3
cryptographic security 39
Defining the Impossible.............................................. 40
Security in Theory: Informational Security........................... 40
Security in Practice: Computational Security......................... 40
Quantifying Security................................................ 42
Measuring Security in Bits ..................................... 42
Full Attack Cost............................................. 43
Choosing and Evaluating Security Levels ........................... 44
Achieving Security................................................. 46
Provable Security ........................................... 46
Heuristic Security ........................................... 48
Generating Keys .................................................. 49
Generating Symmetric Keys .................................... 49
Generating Asymmetric Keys ................................... 49
Protecting Keys............................................. 50
How Things Can Go Wrong.......................................... 51
Incorrect Security Proof ....................................... 52
Short Keys for Legacy Support .................................. 52
Further Reading................................................... 52
4
bLock ciphers 53
What Is a Block Cipher?............................................. 54
Security Goals ............................................. 54
Block Size ................................................ 54
The Codebook Attack ........................................ 55
viii Contents in Detail