Implementing Email Security and Tokens: Current Standards, Tools, and Practices Sean Turner Russ Housley Wiley Publishing, Inc.
Implementing Email Security and Tokens: Current Standards, Tools, and Practices Sean Turner Russ Housley Wiley Publishing, Inc.
Implementing Email Security and Tokens: Current Standards, Tools, and Practices Published by Wiley Publishing, Inc. 10475 Crosspoint Boulevard Indianapolis, IN 46256 www.wiley.com Copyright 2008 by Wiley Publishing, Inc., Indianapolis, Indiana Published simultaneously in Canada ISBN: 978-0-470-25463-9 Manufactured in the United States of America 10987654321 No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600. Requests to the Publisher for permission should be addressed to the Legal Department, Wiley Publishing, Inc., 10475 Crosspoint Blvd., Indianapolis, IN 46256, (317) 572-3447, fax (317) 572-4355, or online at http://www.wiley.com/go/permissions. Limit of Liability/Disclaimer of Warranty: The publisher and the author make no representations or warranties with respect to the accuracy or completeness of the contents of this work and specifically disclaim all warranties, including without limitation warranties of fitness for a particular purpose. No warranty may be created or extended by sales or promotional materials. The advice and strategies contained herein may not be suitable for every situation. This work is sold with the understanding that the publisher is not engaged in rendering legal, accounting, or other professional services. If professional assistance is required, the services of a competent professional person should be sought. Neither the publisher nor the author shall be liable for damages arising herefrom. The fact that an organization or Website is referred to in this work as a citation and/or a potential source of further information does not mean that the author or the publisher endorses the information the organization or Website may provide or recommendations it may make. Further, readers should be aware that Internet Websites listed in this work may have changed or disappeared between when this work was written and when it is read. For general information on our other products and services or to obtain technical support, please contact our Customer Care Department within the U.S. at (800) 762-2974, outside the U.S. at (317) 572-3993 or fax (317) 572-4002. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books. Library of Congress Cataloging-in-Publication Data is available from publisher. Trademarks: Wiley, the Wiley logo, and related trade dress are trademarks or registered trademarks of John Wiley & Sons, Inc. and/or its affiliates in the United States and other countries, and may not be used without written permission. All other trademarks are the property of their respective owners. Wiley Publishing, Inc., is not associated with any product or vendor mentioned in this book. Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronic books.
Dedicated to all those who helped develop the Internet and those who will help develop it in the future. S.T.andR.H. Thanks for the loving support from Sue, Ryan, and Patrick. R.H. Thanks for all the support Mom and Dad. S.T.
About the Authors Sean Turner Mr. Turner is vice president and a co-founder of International Electronic Communications Analysts Inc. (www.ieca.com), a Virginia-based consulting services firm that specializes in information security, protocol design, and technical standardization for both the government and commercial sectors. His consulting efforts draw on his vast experience in secure systems analysis, architecture, design, and engineering of email, public key infrastructures, and key management systems. He assists clients with Service Oriented Architecture concepts, developing certificate policies, applying security to web services, and addressing issues of security policy and access control. He has been active in technical standards efforts in the IETF for over 12 years, and he is the author of numerous RFCs. He has been the S/MIME WG co-chair since mid-2003. Mr. Turner holds a bachelor s degree in Electrical Engineering from the Georgia Institute of Technology. He has been an IEEE member since 1995. Russ Housley Mr. Housley is owner and founder of Vigil Security, LLC (www.vigilsec.com), a very small firm that provides computer and networking security consulting. He has contributed to the development of many standards, including PKIX Part 1, Privacy-Enhanced Mail and S/MIME. He began participating in the development of Internet security specifications in 1988 as a member of the Privacy and Security Research Group. He was the chair of the IETF S/MIME WG when it was formed, passing the reigns to Sean v
vi About the Authors Turner and Blake Ramsdell when he accepted the position as IETF Security Area Director. Mr. Housley is now serving as the chair of the IETF. He is the author of more than 30 RFCs. Mr. Housley holds a bachelor s degree in Computer Science from Virginia Tech and a master s degree in Computer Science from George Mason University. He has been a member of ACM and IEEE since 1987.
Credits Executive Editor Carol Long Development Editor Julie M. Smith Production Editor Angela Smith Copy Editor Foxxe Editorial Services Editorial Manager Mary Beth Wakefield Production Manager Tim Tate Vice President and Executive Group Publisher Richard Swadley Vice President and Executive Publisher Joseph B. Wikert Project Coordinator, Cover Lynsey Stanford Proofreader Sossity Smith Indexer Johnna VanHoose Dinse vii
Contents Acknowledgments xv Part I Email and Security Background Chapter 1 Introduction 3 How This Book Is Organized 3 Part I: Email and Security Background 4 Part II: PKI Basics 4 Part III: Secure Email 4 Part IV: Tokens 4 Part V: Case Studies 5 Part VI: Expectations for the Future 5 Appendices 5 WhoShouldReadThisBook 5 Chapter 2 Understanding Email 7 History and Evolution 8 Internet Email 11 Wow! Email Is Just Like Snail Mail 11 Process 11 Formats 12 Commands 16 Mail Transfer System Architecture 19 Emailing 21 Email Client 21 Webmail 22 Chapter 3 Security Fundamentals 23 Who Wants to Read Your Email? 24 Governments 24 Businesses 26 ix
x Contents Criminals 27 Hackers 27 Reporters and Bloggers 28 Friends and Family Members 28 Where They Can Read Your Email 28 How They Can Read Your Email 29 Eavesdrop 29 Masquerade 29 What Else Can They Do to the MTS? 30 How You Can Stop Them 30 Security Services 31 Fundamental Services 31 Derivative Services 32 Cryptographic Mechanisms 33 Encryption 33 Digital Signatures 33 One-Way Hash Functions 34 Basic Security Tools 34 Access Control Lists 34 Fake Traffic 34 Logs 34 Nonces 35 Signed Receipts 35 Sequence Numbering 35 Time 35 More Attacks 35 Chapter 4 Cryptography Primer 37 Symmetric Cryptography 38 Types 38 Algorithms 39 Modes 39 Symmetric Key Management 40 Symmetric Integrity Functions 42 Asymmetric Cryptography 45 Public Key Encryption 45 Digital Signatures 47 Asymmetric Key Management 51 Part II PKI Basics Chapter 5 Understanding Public Key Infrastructure 55 Trust 56 PKI Architectures 57 Single CA 57 Trust Lists 58 Hierarchical PKI 59
Contents xi Mesh PKI 61 Cross-Certified PKIs 62 Bridge CAs 64 X.509 Public Key Certificates 66 Tamper-Evident Envelope 66 Basic Certificate Contents 67 Certificate Extensions 68 Subject Type Extensions 69 Name Extensions 69 Key Attributes 70 Policy 71 Additional Information 72 X.509 Certificate Revocation Lists 73 Signed Certificate List 73 CRL Extensions 75 CRL Entry Extensions 77 PKI Components and Users 78 Infrastructure Users 78 Subscribers 79 Replying Parties 79 Infrastructure Components 79 Certification Authorities 80 Registration Authority 83 Repository 84 Archive 84 Part III Secure Email Chapter 6 Protecting Email Message Contents 87 Evolution 87 Privacy Enhanced Mail 88 Pretty Good Privacy 89 MIME Object Security Services 90 Message Security Protocol 91 Public-Key Cryptography Standard #7 91 Secure Multipurpose Internet Mail Extensions 91 Protecting Email Content 92 Concepts 93 CMS Content Types 93 Encapsulating 93 Version Numbers 95 Attributes 95 MIME Layer 95 Protecting CMS Content Types 96 Signed Data 96 Enveloped Data 98 Encrypted Data 102
xii Contents Digest Data 102 Authenticated Data 103 Authenticated-Enveloped Data 104 Non-Protecting Content Types 104 Data 105 Compressed Data 105 Receipt Syntax 105 Content Collection 106 Content with Attributes 107 Attributes 107 Content Type 108 Message Digest 109 Signing Time 110 Counter Signatures 110 S/MIME Capabilities 111 Encryption Key Preference 111 Signed Receipts 112 Content Hints 115 Content Reference 116 Signing Certificates 116 Security Labels 117 Equivalent Labels 118 Secure Mail Lists 118 Algorithms 120 Generating an S/MIME Message 122 Chapter 7 Protecting Email Passwords, Headers, and Commands 125 Password Scramble 126 Connection Security 127 Transport Layer Security 128 Handshake Protocol 129 Record Protocol 132 IPsec 133 Security Associations 134 Authentication Header 136 Encapsulating Security Payload 137 Internet Key Exchange (IKE) 139 Part IV Tokens Chapter 8 Tokens and Hardware Security Modules 143 Evaluation Criteria 144 Tokens 148 PC Cards 149 Smart Cards 151 Looking under the Hood 153 Operating Systems and Smart Cards 154
Contents xiii Choosing Smart Cards 154 USB Tokens 155 Software Tokens 156 ibutton Tokens 156 Embedded Tokens 157 Hardware Security Modules 158 Network-Attached Multi-User Hardware Security Modules 159 Application Program Interfaces 160 Part V Case Studies Chapter 9 Signatures and Authentication for Everyone 165 SAFE Architecture 166 Cryptographic Algorithms 166 PKI Architecture 167 Certificate Policies 169 Certificate, CRL, and OCSP Profiles 169 Tokens and Cryptographic Modules 173 Applications 174 Successes and Shortcomings 175 Lessons Learned 176 Chapter 10 Chapter 11 Department of Defense Public Key Infrastructure, Medium Grade Service, and Common Access Card 181 Architectures 182 Cryptographic Algorithms 182 PKI Architecture 183 DEERS/RAPIDS Architecture 184 Certificate Policies 186 Certificate and CRL Profiles 188 Certificate Status Responders 190 Repositories 191 CAC and Cryptographic Modules 193 Applications 194 Success and Shortcomings 196 Lessons Learned 197 National Institute of Standards and Technology Personal Identity Verification 201 PIV Architecture 203 Cryptographic Algorithms 203 Architecture 205 Certificate Policies 206 Certificate, CRL, and OCSP Profiles 209 Cards and Cryptographic Modules 215 Applications 218 Lessons Learned 220