Preface to Internet Cryptography by Richard E. Smith ISBN 0-201-92480-3, Addison Wesley, 1997

Contents: Who This Book is For | How This Book is Organized | Crypto Today and Tomorrow | Comments and Questions

This book is about delivering data safely across unsafe territory. The features that give the Internet its vitality also make it unsafe, like the streets of a major city. People do not walk carelessly in a vital, teeming city. Likewise, a careful person approaches the Internet with caution. Business data that crosses the public Internet can be forged, modified, or stolen. The Internet's technology and style don't fit well in the traditional mold of common carrier communications, so traditional security techniques don't fit well either.

Cryptography has emerged as the only alternative to protect Internet data, and it does the job well. Modern crypto techniques have evolved from the secret codes of decades past, brilliantly augmented with a deep knowledge of modern mathematics. New cryptographic products and technologies have been developed particularly for Internet applications. This book describes the principal techniques used in today's products, how they work, and how to use them. While we must talk about people "cracking" codes, we will spend far more time looking at system configurations and operating procedures. Configuration and operating errors have often been the bane of crypto system security. Mathematical details alone don't ensure the security of practical crypto systems. Even the most capable products can be defeated by carelessness.

Effective use of crypto systems requires a clear understanding of what your security objectives are and how they depend on important system properties. This book applies cryptographic techniques to particular Internet security goals like site protection, message secrecy, or transaction security. These goals are lined up against today's off-the-shelf products to show which are best suited to meet particular business and security objectives.

Who This Book is For

This book is intended for people who know very little about cryptography but need to make technical decisions about cryptographic security. Many people face this situation when they need to transmit business data safely over the Internet. This often includes people responsible for the data, like business analysts and managers, as well as those who must install and maintain the protections, like information systems administrators and managers. These people are the book's primary audience. Cryptographic concepts are explained using diagrams to illustrate component relationships and data flows. At every step we examine the relationship between the security measures and the vulnerabilities they address. This will guide readers in safely applying cryptographic techniques.

This book requires no prior knowledge of cryptography or related mathematics. Descriptions of low-level crypto mechanisms focus on presenting the concepts instead of the details. Programmers and product developers must look elsewhere for implementation details, and each chapter ends with a list of appropriate references. However, developers will still find a few useful insights here, like why crypto experts are so picky about mathematical arcana like random number generators ("No, it's a pseudorandom number generator!") or why their theoretically unbreakable system is vulnerable to attack.

This book also contains some general tutorial material about the Internet Protocol (IP) and its cousins, but it is best if readers already have a general familiarity with computers, networking, and the Internet. In particular, it helps if readers already understand the notion of message and packet formatting-in other words, your information must be embedded in other information for the network to deliver it correctly.

How this Book is Organized

We start with cryptographic basics, apply them to product evaluation, and then look at example deployment to achieve various business and security objectives. When we understand the risks against which various security measures might protect, we can reasonably trade off between conflicting techniques. Each chapter ends with a list of references that may provide you with deeper explanations when needed. If your particular problem cannot be solved with available products, the references can provide the technical details for implementing custom solutions.

This book is organized around a small number of basic security objectives that are addressed by a few basic Internet cryptographic technologies. The objective of extending one's internal site via the Internet is illustrated with link encryption and network encryption using the IP Security Protocol (IPSEC). The objective of transaction security is illustrated using Secure Socket Layer (SSL) as applied to the World Wide Web. Message-based security is illustrated using Pretty Good Privacy (PGP) and Privacy Enhanced Mail (PEM).

Chapter Summary

The book's contents fall roughly into three parts, starting with low-level but simple techniques and working upward to high-level, complex crypto systems.

• Introduction and traditional crypto (Chapters 1, 2, 3, and 4)
  These chapters contain general introductory material and cover traditional crypto techniques. The Introduction provides a cross-reference of security goals against the crypto techniques presented in the book. Traditional crypto includes link encryption and the handling of secret crypto keys.
• Network encryption with IPSEC protocols (Chapters 5, 6, 7, and 8)
  These chapters describe the IPSEC protocol suite that protects data passing between pairs of hosts on the Internet. These protocols were originally developed for the upcoming IP version 6, but many vendors are incorporating them into existing IP products, like routers and firewalls.
• Public key crypto and protocols for transactions (Chapters 9, 10, 11, and 12)
  These chapters describe public key crypto techniques and their application in World Wide Web and e-mail protocols. The Web security discussion centers on the SSL protocol and related client/server software. The e-mail discussion examines the techniques of PGP and PEM. Public key certificates are discussed in the final chapter.

A Typical Chapter

Most chapters follow the same general organization. A typical chapter introduces a security service and a particular cryptographic mechanism underlying that service. Chapter information is usually organized in these general sections:

• Security objectives
  This section contains a list of objectives you wish to achieve in protecting your information. The product and deployment examples in the chapter are chosen to achieve these objectives.
• Basic issues
  This section contains an overview of important problems associated with the cryptographic services and mechanisms presented in the chapter.
• Technology
  There are one or more of these sections, each presenting a technical concept underlying the products introduced. These sections always include a prioritized list of requirements for securely applying the technology.
• Product example
  There are one or more of these sections to introduce products used in the deployment examples. These sections always include a prioritized list of requirements for assessing potential product choices.
• Deployment example
  There are one or more of these examples to illustrate different ways of achieving the chapter's stated security objectives. These sections always include a prioritized list of requirements for assessing a particular deployment.
• For further information
  This section contains an annotated list of references for more in-depth information on a subject. The chapters' lists identify the author and title of the work; the bibliography at the end of this book contains the complete citation.

Crypto Today and Tomorrow

The crypto mechanisms and products appearing in this book were chosen because they illustrate what people can buy off the shelf and use today. Simple, commercially available solutions are given preference over more sophisticated techniques that require extensive vendor support or custom engineering. Naturally this limits the discussion to a fraction of what the technologies can do. However, it is risky to speculate about the behavior of nonexistent products. Countless implementation details will affect their practical effectiveness, so it's pointless to speculate about how they might best work.

This book does not try to predict which future technologies will succeed or fail as easy-to-use products. An elaborate cryptographic infrastructure for safely sharing keys among computer users worldwide has been on the drawing boards for more than a dozen years; the enabling technology and its relatively modest success in off-the-shelf products is described in Chapter 12. Likewise, the chapters on IP security focus on today's products and not on the draft standards for tomorrow. The future is left to future books.

Comments and Questions

Send comments and questions via Internet e-mail to internet-crypto@awl.com. While I tried to focus on techniques that have been used successfully, many of the techniques have not seen extensive use. I'd value any "war stories" or "been there; done that" evaluations based on personal experience.

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Richard E. Smith, smith@smat.us
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Last update: 7/25/2002

Copyright © 1997-2002, Richard E. Smith
Some material Copyright 1997, Addison Wesley Longman. All Rights Reserved