Etextbook 978 0134444284 cryptography and network security principles and practice 7th edition

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Chapter 4 Block Ciphers and the Data Encryption Standard 100 4.1 Traditional Block Cipher Structure 101 4.2 The Data Encryption Standard 111 4.3 A DES Example 113 4.4 The Strength of DES 116 4.5 Block Cipher Design Principles 117 4.6 Key Terms, Review Questions, and Problems 119 Chapter 5 Finite Fields 123 5.1 Groups 125 5.2 Rings 127 5.3 Fields 128 5.4 Finite Fields of the Form GF(p) 129 5.5 Polynomial Arithmetic 133 5.6 Finite Fields of the Form GF(2n) 139 5.7 Key Terms, Review Questions, and Problems 151 Chapter 6 Advanced Encryption Standard 153 6.1 Finite Field Arithmetic 154 6.2 AES Structure 156 6.3 AES Transformation Functions 161 6.4 AES Key Expansion 172 6.5 An AES Example 175 6.6 AES Implementation 179 6.7 Key Terms, Review Questions, and Problems 184 8

Appendix 6A Polynomials with Coefficients in GF ( 2 ) 185 Chapter 7 Block Cipher Operation 189 7.1 Multiple Encryption and Triple DES 190 7.2 Electronic Codebook 195 7.3 Cipher Block Chaining Mode 198 7.4 Cipher Feedback Mode 200 7.5 Output Feedback Mode 202 7.6 Counter Mode 204 7.7 XTS-AES Mode for Block-Oriented Storage Devices 206 7.8 Format-Preserving Encryption 213 7.9 Key Terms, Review Questions, and Problems 227

Chapter 8 Random Bit Generation and Stream Ciphers 232 8.1 Principles of Pseudorandom Number Generation 234 8.2 Pseudorandom Number Generators 240 8.3 Pseudorandom Number Generation Using a Block Cipher 243 8.4 Stream Ciphers 249 8.5 RC4 251 8.6 True Random Number Generators 253 8.7 Key Terms, Review Questions, and Problems 262 PART Three: Asymmetric Ciphers 265 Chapter 9 Public-Key Cryptography and RSA 265 9.1 Principles of Public-Key Cryptosystems 267 9.2 The RSA Algorithm 276 9.3 Key Terms, Review Questions, and Problems 290 Chapter 10 Other Public-Key Cryptosystems 295 10.1 Diffie-Hellman Key Exchange 296 10.2 Elgamal Cryptographic System 300 10.3 Elliptic Curve Arithmetic 303 10.4 Elliptic Curve Cryptography 312 10.5 Pseudorandom Number Generation Based on an Asymmetric Cipher 316 10.6 Key Terms, Review Questions, and Problems 318 PART Four: Cryptographic Data Integrity Algorithms 321 Chapter 11 Cryptographic Hash Functions 321 11.1 Applications of Cryptographic Hash Functions 323 11.2 Two Simple Hash Functions 328 11.3 Requirements and Security 330 11.4 Hash Functions Based on Cipher Block Chaining 336 11.5 Secure Hash Algorithm (SHA) 337 11.6 SHA-3 347 11.7 Key Terms, Review Questions, and Problems 359 Chapter 12 Message Authentication Codes 363 12.1 Message Authentication Requirements 364 12.2 Message Authentication Functions 365 12.3 Requirements for Message Authentication Codes 373 12.4 Security of MACs 375 12.5 MACs Based on Hash Functions: HMAC 376 12.6 MACs Based on Block Ciphers: DAA and CMAC 381

12.7 Authenticated Encryption: CCM and GCM 384 12.8 Key Wrapping 390 12.9 Pseudorandom Number Generation Using Hash Functions and MACs 395 12.10 Key Terms, Review Questions, and Problems 398 Chapter 13 Digital Signatures 401 13.1 Digital Signatures 403 13.2 Elgamal Digital Signature Scheme 406 13.3 Schnorr Digital Signature Scheme 407 13.4 NIST Digital Signature Algorithm 408 13.5 Elliptic Curve Digital Signature Algorithm 412 13.6 RSA-PSS Digital Signature Algorithm 415 13.7 Key Terms, Review Questions, and Problems 420 PART Five: Mutual Trust 423 Chapter 14 Key Management and Distribution 423 14.1 Symmetric Key Distribution Using Symmetric Encryption 424 14.2 Symmetric Key Distribution Using Asymmetric Encryption 433 14.3 Distribution of Public Keys 436 14.4 X.509 Certificates 441 14.5 Public-Key Infrastructure 449 14.6 Key Terms, Review Questions, and Problems 451 Chapter 15 User Authentication 455 15.1 Remote User-Authentication Principles 456 15.2 Remote User-Authentication Using Symmetric Encryption 460 15.3 Kerberos 464 15.4 Remote User-Authentication Using Asymmetric Encryption 482 15.5 Federated Identity Management 484 15.6 Personal Identity Verification 490 15.7 Key Terms, Review Questions, and Problems 497 PART Six: Network And Internet Security 501 Chapter 16 Network Access Control and Cloud Security 501 16.1 Network Access Control 502 16.2 Extensible Authentication Protocol 505 16.3 IEEE 802.1X Port-Based Network Access Control 509 16.4 Cloud Computing 511 16.5 Cloud Security Risks and Countermeasures 517 16.6 Data Protection in the Cloud 519

16.7 Cloud Security as a Service 523 16.8 Addressing Cloud Computing Security Concerns 526 16.9 Key Terms, Review Questions, and Problems 527 Chapter 17 Transport-Level Security 528 17.1 Web Security Considerations 529 17.2 Transport Layer Security 531 17.3 HTTPS 548 17.4 Secure Shell (SSH) 549 17.5 Key Terms, Review Questions, and Problems 561 Chapter 18 Wireless Network Security 563 18.1 Wireless Security 564 18.2 Mobile Device Security 567 18.3 IEEE 802.11 Wireless LAN Overview 571 18.4 IEEE 802.11i Wireless LAN Security 577 18.5 Key Terms, Review Questions, and Problems 592 Chapter 19 Electronic Mail Security 594 19.1 Internet Mail Architecture 595 19.2 Email Formats 599 19.3 Email Threats and Comprehensive Email Security 607 19.4 S/MIME 609 19.5 Pretty Good Privacy 620 19.6 DNSSEC 621 19.7 DNS-Based Authentication of Named Entities 625 19.8 Sender Policy Framework 627 19.9 DomainKeys Identified Mail 630 19.10 Domain-Based Message Authentication, Reporting, and Conformance 636 19.11 Key Terms, Review Questions, and Problems 641 Chapter 20 IP Security 643 20.1 IP Security Overview 644 20.2 IP Security Policy 650 20.3 Encapsulating Security Payload 655 20.4 Combining Security Associations 663 20.5 Internet Key Exchange 666 20.6 Cryptographic Suites 674 20.7 Key Terms, Review Questions, and Problems 676

Appendices 678 Appendix A Projects for Teaching Cryptography and Network Security 678 A.1 Sage Computer Algebra Projects 679 A.2 Hacking Project 680 A.3 Block Cipher Projects 681 A.4 Laboratory Exercises 681 A.5 Research Projects 681 A.6 Programming Projects 682 A.7 Practical Security Assessments 682 A.8 Firewall Projects 683 A.9 Case Studies 683 A.10 Writing Assignments 683 A.11 Reading/Report Assignments 684 A.12 Discussion Topics 684 Appendix B Sage Examples 685 B.1 Linear Algebra and Matrix Functionality 686 B.2 Chapter 2: Number Theory 687 B.3 Chapter 3: Classical Encryption 692 B.4 Chapter 4: Block Ciphers and the Data Encryption Standard 695 B.5 Chapter 5: Basic Concepts in Number Theory and Finite Fields 699 B.6 Chapter 6: Advanced Encryption Standard 706 B.7 Chapter 8: Pseudorandom Number Generation and Stream Ciphers 711 B.8 Chapter 9: Public-Key Cryptography and RSA 713 B.9 Chapter 10: Other Public-Key Cryptosystems 716 B.10 Chapter 11: Cryptographic Hash Functions 721 B.11 Chapter 13: Digital Signatures 723 References 726 Credits 735 Index 736

Online Chapters and Appendices 1 1

Online chapters, appendices, and other documents are at the Companion Website, available via the access card at

the front of this book.

PART Seven: System Security Chapter 21 Malicious Software 21.1 Types of Malicious Software (Malware) 21.2 Advanced Persistent Threat 21.3 Propagation – Infected Content – Viruses 21.4 Propagation – Vulnerability Exploit - Worms 21.5 Propagation – Social Engineering – SPAM, Trojans 21.6 Payload – System Corruption 21.7 Payload – Attack Agent – Zombie, Bots 21.8 Payload – Information Theft – Keyloggers, Phishing, Spyware 21.9 Payload – Stealthing – Backdoors, Rootkits 21.10 Countermeasures 21.11 Distributed Denial of Service Attacks 21.12 References 21.13 Key Terms, Review Questions, and Problems Chapter 22 Intruders 22.1 Intruders 22.2 Intrusion Detection 22.3 Password Management 22.4 References 22.5 Key Terms, Review Questions, and Problems Chapter 23 Firewalls 23.1 The Need for Firewalls 23.2 Firewall Characteristics and Access Policy 23.3 Types of Firewalls 23.4 Firewall Basing 23.5 Firewall Location and Configurations 23.6 References 23.7 Key Terms, Review Questions, and Problems PART Eight: Legal And Ethical Issues Chapter 24 Legal and Ethical Aspects

24.1 Cybercrime and Computer Crime 24.2 Intellectual Property 24.3 Privacy 24.4 Ethical Issues 24.5 Recommended Reading 24.6 References 24.7 Key Terms, Review Questions, and Problems 24.A Information Privacy Appendix C Sage Exercises Appendix D Standards and Standard-Setting Organizations Appendix E Basic Concepts from Linear Algebra Appendix F Measures of Secrecy and Security Appendix G Simplified DES Appendix H Evaluation Criteria for AES Appendix I Simplified AES Appendix J The Knapsack Algorithm Appendix K Proof of the Digital Signature Algorithm Appendix L TCP/IP and OSI Appendix M Java Cryptographic APIs Appendix N MD5 Hash Function Appendix O Data Compression Using ZIP Appendix P PGP Appendix Q The International Reference Alphabet Appendix R Proof of the RSA Algorithm Appendix S Data Encryption Standard Appendix T Kerberos Encryption Techniques Appendix U Mathematical Basis of the Birthday Attack Appendix V Evaluation Criteria for SHA-3 Appendix W The Complexity of Algorithms Appendix X Radix-64 Conversion Appendix Y The Base Rate Fallacy Glossary

Notation Symbol

Expression

Meaning

D, K

D(K, Y)

Symmetric decryption of ciphertext Y using secret key K

D, PR a D, PU a E, K

D ( PR a , Y ) D ( PU a , Y )

E(K, X)

E, PR a E, PU a

E ( PR a , X ) E ( PU a , X )

Asymmetric decryption of ciphertext Y using A’s private key PR a Asymmetric decryption of ciphertext Y using A’s public key PU a Symmetric encryption of plaintext X using secret key K Asymmetric encryption of plaintext X using A’s private key PR a Asymmetric encryption of plaintext X using A’s public key PU a Secret key

K PR a

Private key of user A

PU a

Public key of user A

MAC, K

MAC(K, X)

GF(p)

Message authentication code of message X using secret key K The finite field of order p, where p is prime.The field is defined as the set Z p together with the arithmetic operations modulo p.

n

GF ( 2 )

The finite field of order 2

Zn

gcd

n

Set of nonnegative integers less than n gcd(i, j)

Greatest common divisor; the largest positive integer that divides both i and j with no remainder on division.

mod

a mod m

mod, ≡

a ≡ b (mod m)

mod, ≡

a ≡b (mod m)

dlog φ

dlog a , p ( b ) ϕ ( n)

Remainder after division of a by m a mod m = b mod m a mod m ≠ b mod m

Discrete logarithm of the number b for the base a (mod p) The number of positive integers less than n and relatively prime to n.

This is Euler’s totient function.

∑

n ∑ ai

a1 + a2 + ⋯ + an

n ∏ ai

a1 × a2 × ⋯ × an

i=1

Π

i=1

|

i|j

i divides j, which means that there is no remainder when j is divided by i

|, |

|a |

∥

x∥y

≈

x ≈y

⊕

x⊕y

Absolute value of a x concatenated with y x is approximately equal to y Exclusive-OR of x and y for single-bit variables; Bitwise exclusive-OR of x and y for multiple-bit variables

⌊,⌋

⌊x ⌋

∈

x ∈S

The largest integer less than or equal to x The element x is contained in the set S.

↔

A ↔ ( a1 , a2 , … ak )

The to the sequence of integers ( a 1 , integer a2 , … A akcorresponds )

Preface What’s New in the Seventh Edition In the four years since the sixth edition of this book was published, the field has seen continued innovations and improvements. In this new edition, I try to capture these changes while maintaining a broad and comprehensive coverage of the entire field. To begin this process of revision, the sixth edition of this book was extensively reviewed by a number of professors who teach the subject and by professionals working in the field. The result is that, in many places, the narrative has been clarified and tightened, and illustrations have been improved.

Beyond these refinements to improve pedagogy and user-friendliness, there have been substantive changes throughout the book. Roughly the same chapter organization has been retained, but much of the material has been revised and new material has been added. The most noteworthy changes are as follows: Fundamental security design principles: Chapter 1 includes a new section discussing the security design principles listed as fundamental by the National Centers of Academic Excellence in Information Assurance/Cyber Defense, which is jointly sponsored by the U.S. National Security Agency and the U.S. Department of Homeland Security.

Attack surfaces and attack trees: Chapter 1 includes a new section describing these two concepts, which are useful in evaluating and classifying security threats.

Number theory coverage: The material on number theory has been consolidated into a single chapter, Chapter 2. This makes for a convenient reference. The relevant portions of Chapter 2 can be assigned as needed.

Finite fields: The chapter on finite fields has been revised and expanded with additional text and new figures to enhance understanding.

Format-preserving encryption: This relatively new mode of encryption is enjoying increasing commercial success. A new section in Chapter 7 covers this method.

Conditioning and health testing for true random number generators: Chapter 8 now provides coverage of these important topics.

User authentication model: Chapter 15 includes a new description of a general model for user authentication, which helps to unify the discussion of the various approaches to user authentication.

Cloud security: The material on cloud security in Chapter 16 has been updated and expanded to reflect its importance and recent developments.

Transport Layer Security (TLS): The treatment of TLS in Chapter 17 has been updated, reorganized to improve clarity, and now includes a discussion of the new TLS version 1.3.

Email Security: Chapter 19 has been completely rewritten to provide a comprehensive and up-todate discussion of email security. It includes: — New: discussion of email threats and a comprehensive approach to email security.

— New: discussion of STARTTLS, which provides confidentiality and authentication for SMTP. — Revised: treatment of S/MIME has been updated to reflect the latest version 3.2.

— New: discussion of DNSSEC and its role in supporting email security.

— New: discussion of DNS-based Authentication of Named Entities (DANE) and the use of this approach to enhance security for certificate use in SMTP and S/MIME. — New: discussion of Sender Policy Framework (SPF), which is the standardized way for a sending domain to identify and assert the mail senders for a given domain.

— Revised: discussion of DomainKeys Identified Mail (DKIM) has been revised.

— New: discussion of Domain-based Message Authentication, Reporting, and Conformance (DMARC) allows email senders to specify policy on how their mail should be handled, the types of reports that receivers can send back, and the frequency those reports should be sent.

Objectives It is the purpose of this book to provide a practical survey of both the principles and practice of cryptography and network security. In the first part of the book, the basic issues to be addressed by a network security capability are explored by providing a tutorial and survey of cryptography and network security technology. The latter part of the book deals with the practice of network security: practical applications that have been implemented and are in use to provide network security.

The subject, and therefore this book, draws on a variety of disciplines. In particular, it is impossible to appreciate the significance of some of the techniques discussed in this book without a basic understanding of number theory and some results from probability theory. Nevertheless, an attempt has been made to make the book self-contained. The book not only presents the basic mathematical results that are needed but provides the reader with an intuitive understanding of those results. Such background material is introduced as needed. This approach helps to motivate the material that is introduced, and the author considers this preferable to simply presenting all of the mathematical material in a lump at the beginning of the book.

Support of Acm/Ieee Computer Science Curricula 2013 The book is intended for both academic and professional audiences. As a textbook, it is intended as a one-semester undergraduate course in cryptography and network security for computer science, computer engineering, and electrical engineering majors. The changes to this edition are intended to provide support of the ACM/IEEE Computer Science Curricula 2013 (CS2013). CS2013 adds Information Assurance and Security (IAS) to the curriculum recommendation as one of the Knowledge Areas in the Computer Science Body of Knowledge. The document states that IAS is now part of the curriculum recommendation because of the critical role of IAS in computer science education. CS2013 divides all course work into three categories: Core-Tier 1 (all topics should be included in the curriculum), Core-Tier-2 (all or almost all topics should be included), and elective (desirable to provide breadth and depth). In the IAS area, CS2013 recommends topics in Fundamental Concepts and Network Security in Tier 1 and Tier 2, and Cryptography topics as elective. This text covers virtually all of the topics listed by CS2013 in these three categories.

The book also serves as a basic reference volume and is suitable for self-study.

Plan of the Text The book is divided into eight parts.

Background Symmetric Ciphers Asymmetric Ciphers Cryptographic Data Integrity Algorithms Mutual Trust Network and Internet Security System Security

Legal and Ethical Issues The book includes a number of pedagogic features, including the use of the computer algebra system Sage and numerous figures and tables to clarify the discussions. Each chapter includes a list of key words, review questions, homework problems, and suggestions for further reading. The book also includes an extensive glossary, a list of frequently used acronyms, and a bibliography. In addition, a test bank is available to instructors.

Instructor Support Materials The major goal of this text is to make it as effective a teaching tool for this exciting and fast-moving subject as possible. This goal is reflected both in the structure of the book and in the supporting material. The text is accompanied by the following supplementary material that will aid the instructor: Solutions manual: Solutions to all end-of-chapter Review Questions and Problems.

Projects manual: Suggested project assignments for all of the project categories listed below.

PowerPoint slides: A set of slides covering all chapters, suitable for use in lecturing.

PDF files: Reproductions of all figures and tables from the book.

Test bank: A chapter-by-chapter set of questions with a separate file of answers.

Sample syllabuses: The text contains more material than can be conveniently covered in one semester. Accordingly, instructors are provided with several sample syllabuses that guide the use of the text within limited time. These samples are based on real-world experience by professors with the fifth edition.

All of these support materials are available at the Instructor Resource Center (IRC) for this textbook, which can be reached through the publisher’s Web site www.pearsonhighered .com/stallings or by clicking on the link labeled Pearson Resources for Instructors at this book’s Author Web site at WilliamStallings.com/Cryptography. To gain access to the IRC, please contact your local Pearson sales representative via pearsonhighered.com/­educator/replocator/requestSalesRep.page or call Pearson Faculty Services at 1-800-526-0485.

The Author Web site, at WilliamStallings.com/Cryptography (click on Instructor Resources link), includes the following: Links to Web sites for other courses being taught using this book.

Sign-up information for an Internet mailing list for instructors using this book to exchange information, suggestions, and questions with each other and with the author.

Projects and Other Student Exercises For many instructors, an important component of a cryptography or network security course is a project or set of projects by which the student gets hands-on experience to reinforce concepts from the text. This book provides an unparalleled degree of support, including a projects component in the course. The IRC not only includes guidance on how to assign and structure the projects, but also includes a set of project assignments that covers a broad range of topics from the text: Sage projects: Described in the next section.

Hacking project: Exercise designed to illuminate the key issues in intrusion detection and prevention.

Block cipher projects: A lab that explores the operation of the AES encryption algorithm by tracing its execution, computing one round by hand, and then exploring the various block cipher modes of use. The lab also covers DES. In both cases, an online Java applet is used (or can be downloaded) to execute AES or DES. Lab exercises: A series of projects that involve programming and experimenting with concepts

from the book.

Research projects: A series of research assignments that instruct the student to research a particular topic on the Internet and write a report.

Programming projects: A series of programming projects that cover a broad range of topics and that can be implemented in any suitable language on any platform.

Practical security assessments: A set of exercises to examine current infrastructure and practices of an existing organization.

Firewall projects: A portable network firewall visualization simulator, together with exercises for teaching the fundamentals of firewalls.

Case studies: A set of real-world case studies, including learning objectives, case description, and a series of case discussion questions.

Writing assignments: A set of suggested writing assignments, organized by chapter.

Reading/report assignments: A list of papers in the literature—one for each chapter—that can be assigned for the student to read and then write a short report.

This diverse set of projects and other student exercises enables the instructor to use the book as one component in a rich and varied learning experience and to tailor a course plan to meet the specific needs of the instructor and students. See Appendix A in this book for details.

The Sage Computer Algebra System One of the most important features of this book is the use of Sage for cryptographic examples and homework assignments. Sage is an open-source, multiplatform, freeware package that implements a very powerful, flexible, and easily learned mathematics and computer algebra system. Unlike competing systems (such as Mathematica, Maple, and MATLAB), there are no licensing agreements or fees involved. Thus, Sage can be made available on computers and networks at school, and students can individually download the software to their own personal computers for use at home.

Another advantage of using Sage is that students learn a powerful, flexible tool that can be used for virtually any mathematical application, not just cryptography.

The use of Sage can make a significant difference to the teaching of the mathematics of cryptographic algorithms. This book provides a large number of examples of the use of Sage covering many cryptographic concepts in Appendix B, which is included in this book.

Appendix C lists exercises in each of these topic areas to enable the student to gain hands-on experience with cryptographic algorithms. This appendix is available to instructors at the IRC for this book. Appendix C includes a section on how to download and get started with Sage, a section on programming with Sage, and exercises that can be assigned to students in the following categories: Chapter 2—Number Theory and Finite Fields: Euclidean and extended Euclidean algorithms, 4 polynomial arithmetic, GF ( 2 ) , Euler’s Totient function, Miller–Rabin, factoring, modular exponentiation, discrete logarithm, and Chinese remainder theorem.

Chapter 3—Classical Encryption: Affine ciphers and the Hill cipher.

Chapter 4—Block Ciphers and the Data Encryption Standard: Exercises based on SDES. Chapter 6—Advanced Encryption Standard: Exercises based on SAES. Chapter 8—Pseudorandom Number Generation and Stream Ciphers: Blum Blum Shub, linear congruential generator, and ANSI X9.17 PRNG. Chapter 9—Public-Key Cryptography and RSA: RSA encrypt/decrypt and signing.

Chapter 10—Other Public-Key Cryptosystems: Diffie–Hellman, elliptic curve.

Chapter 11—Cryptographic Hash Functions: Number-theoretic hash function.

Chapter 13—Digital Signatures: DSA.

Online Documents for Students

For this new edition, a tremendous amount of original supporting material for students has been made available online, at two Web locations. The Author Web site, at WilliamStallings.com/ Cryptography (click on Student Resources link), includes a list of relevant links organized by chapter and an errata sheet for the book.

Purchasing this textbook new also grants the reader six months of access to the Companion Website, which includes the following materials: Online chapters: To limit the size and cost of the book, four chapters of the book are provided in PDF format. This includes three chapters on computer security and one on legal and ethical issues. The chapters are listed in this book’s table of contents.

Online appendices: There are numerous interesting topics that support material found in the text but whose inclusion is not warranted in the printed text. A total of 20 online appendices cover these topics for the interested student. The appendices are listed in this book’s table of contents.

Homework problems and solutions: To aid the student in understanding the material, a separate set of homework problems with solutions are available.

Key papers: A number of papers from the professional literature, many hard to find, are provided for further reading.

Supporting documents: A variety of other useful documents are referenced in the text and provided online.

Sage code: The Sage code from the examples in Appendix B is useful in case the student wants to play around with the examples.

To access the Companion Website, follow the instructions for “digital resources for students” found in the front of this book.

Acknowledgments This new edition has benefited from review by a number of people who gave generously of their time and expertise. The following professors reviewed all or a large part of the manuscript: Hossein Beyzavi (Marymount University), Donald F. Costello (University of Nebraska–Lincoln), James Haralambides (Barry University), Anand Seetharam (California State University at Monterey Bay), Marius C. Silaghi (Florida Institute of Technology), Shambhu Upadhyaya (University at Buffalo), Zhengping Wu (California State University at San Bernardino), Liangliang Xiao (Frostburg State University), Seong-Moo (Sam) Yoo (The University of Alabama in Huntsville), and Hong Zhang (Armstrong State University).

Thanks also to the people who provided detailed technical reviews of one or more chapters: Dino M. Amaral, Chris Andrew, Prof. (Dr). C. Annamalai, Andrew Bain, Riccardo Bernardini, Olivier Blazy, Zervopoulou Christina, Maria Christofi, Dhananjoy Dey, Mario Emmanuel, Mike Fikuart, Alexander Fries, Pierpaolo Giacomin, Pedro R. M. Inácio, Daniela Tamy Iwassa, Krzysztof Janowski, Sergey Katsev, Adnan Kilic, Rob Knox, Mina Pourdashty, Yuri Poeluev, Pritesh Prajapati, Venkatesh Ramamoorthy, Andrea Razzini, Rami Rosen, Javier Scodelaro, Jamshid Shokrollahi, Oscar So, and David Tillemans.

In addition, I was fortunate to have reviews of individual topics by “subject-area gurus,” including Jesse Walker of Intel (Intel’s Digital Random Number Generator), Russ Housley of Vigil Security (key wrapping), Joan Daemen (AES), Edward F. Schaefer of Santa Clara University (Simplified AES), Tim Mathews, formerly of RSA Laboratories (S/MIME), Alfred Menezes of the University of Waterloo (elliptic curve cryptography), William Sutton, Editor/Publisher of The Cryptogram (classical encryption), Avi Rubin of Johns Hopkins University (number theory), Michael Markowitz of Information Security Corporation (SHA and DSS), Don Davis of IBM Internet Security Systems (Kerberos), Steve Kent of

BBN Technologies (X.509), and Phil Zimmerman (PGP).

Nikhil Bhargava (IIT Delhi) developed the set of online homework problems and solutions. Dan Shumow of Microsoft and the University of Washington developed all of the Sage examples and assignments in Appendices B and C. Professor Sreekanth Malladi of Dakota State University developed the hacking exercises. Lawrie Brown of the Australian Defence Force Academy provided the AES/DES block cipher projects and the security assessment assignments.

Sanjay Rao and Ruben Torres of Purdue University developed the laboratory exercises that appear in the IRC. The following people contributed project assignments that appear in the instructor’s supplement: Henning Schulzrinne (Columbia University); Cetin Kaya Koc (Oregon State University); and David Balenson (Trusted Information Systems and George Washington University). Kim McLaughlin developed the test bank.

Finally, I thank the many people responsible for the publication of this book, all of whom did their usual excellent job. This includes the staff at Pearson, particularly my editor Tracy Johnson, program manager Carole Snyder, and production manager Bob Engelhardt. Thanks also to the marketing and sales staffs at Pearson, without whose efforts this book would not be in front of you.

About the Author Dr. William Stallings has authored 18 titles, and counting revised editions, over 40 books on computer security, computer networking, and computer architecture. His writings have appeared in numerous publications, including the Proceedings of the IEEE, ACM Computing Reviews, and Cryptologia.

He has 13 times received the award for the best Computer Science textbook of the year from the Text and Academic Authors Association.

In over 30 years in the field, he has been a technical contributor, technical manager, and an executive with several high-technology firms. He has designed and implemented both TCP/IP-based and OSIbased protocol suites on a variety of computers and operating systems, ranging from microcomputers to mainframes. As a consultant, he has advised government agencies, computer and software vendors, and major users on the design, selection, and use of networking software and products.

He created and maintains the Computer Science Student Resource Site at ComputerScienceStudent.com. This site provides documents and links on a variety of subjects of general interest to computer science students (and professionals). He is a member of the editorial board of Cryptologia, a scholarly journal devoted to all aspects of cryptology.

Dr. Stallings holds a PhD from MIT in computer science and a BS from Notre Dame in electrical engineering.

Part One: Background Chapter 1 Computer and Network Security Concepts 1.1 Computer Security Concepts A Definition of Computer Security Examples The Challenges of Computer Security 1.2 The OSI Security Architecture 1.3 Security Attacks Passive Attacks Active Attacks 1.4 Security Services Authentication Access Control Data Confidentiality Data Integrity Nonrepudiation Availability Service 1.5 Security Mechanisms 1.6 Fundamental Security Design Principles 1.7 Attack Surfaces and Attack Trees Attack Surfaces Attack Trees 1.8 A Model for Network Security 1.9 Standards 1.10 Key Terms, Review Questions, and Problems

Learning Objectives After studying this chapter, you should be able to: Describe the key security requirements of confidentiality, integrity, and availability.

Describe the X.800 security architecture for OSI. Discuss the types of security threats and attacks that must be dealt with and give examples of the types of threats and attacks that apply to different categories of computer and network assets.

Explain the fundamental security design principles.

Discuss the use of attack surfaces and attack trees.

List and briefly describe key organizations involved in cryptography standards.

This book focuses on two broad areas: cryptographic algorithms and protocols, which have a broad range of applications; and network and Internet security, which rely heavily on cryptographic techniques.

Cryptographic algorithms and protocols can be grouped into four main areas: Symmetric encryption: Used to conceal the contents of blocks or streams of data of any size, including messages, files, encryption keys, and passwords.

Asymmetric encryption: Used to conceal small blocks of data, such as encryption keys and hash function values, which are used in digital signatures.

Data integrity algorithms: Used to protect blocks of data, such as messages, from alteration.

Authentication protocols: These are schemes based on the use of cryptographic algorithms designed to authenticate the identity of entities.

The field of network and Internet security consists of measures to deter, prevent, detect, and correct security violations that involve the transmission of information. That is a broad statement that covers a host of possibilities. To give you a feel for the areas covered in this book, consider the following examples of security violations: 1. User A transmits a file to user B. The file contains sensitive information

(e.g., payroll records) that is to be protected from disclosure. User C, who is not authorized to read the file, is able to monitor the transmission and capture a copy of the file during its transmission.

2. A network manager, D, transmits a message to a computer, E, under its management. The message instructs computer E to update an authorization file to include the identities of a number of new users who are to be given access to that computer. User F intercepts the message, alters its contents to add or delete entries, and then forwards the message to computer E, which accepts the message as coming from manager D and updates its authorization file accordingly.

3. Rather than intercept a message, user F constructs its own message with the desired entries and transmits that message to computer E as if it had come from manager D. Computer E accepts the message as coming from manager D and updates its authorization file accordingly.

4. An employee is fired without warning. The personnel manager sends a message to a server system to invalidate the employee’s account. When the invalidation is accomplished, the server is to post a notice to the employee’s file as confirmation of the action. The employee is able to intercept the message and delay it long enough to make a final access to the server to retrieve sensitive information. The message is then forwarded, the action taken, and the confirmation posted. The employee’s action may go unnoticed for some considerable time.

5. A message is sent from a customer to a stockbroker with instructions for various transactions. Subsequently, the investments lose value and the customer denies sending the message.

Although this list by no means exhausts the possible types of network security violations, it illustrates the range of concerns of network security.

1.1 Computer Security Concepts A Definition of Computer Security The NIST Computer Security Handbook [NIST95] defines the term computer security as follows:

COMPUTER SECURITY: The protection afforded to an automated information system in order to attain the applicable objectives of preserving the integrity, availability, and confidentiality of information system resources (includes hardware, software, firmware, information/data, and telecommunications).

This definition introduces three key objectives that are at the heart of computer security: Confidentiality: This term covers two related concepts: Data1 confidentiality: Assures that private or confidential information is not made available or disclosed to unauthorized individuals.

1

RFC 4949 defines information as “facts and ideas, which can be represented (encoded) as various forms of

data,” and data as “information in a specific physical representation, usually a sequence of symbols that have meaning; especially a representation of information that can be processed or produced by a computer.” Security literature typically does not make much of a distinction, nor does this book.

Privacy: Assures that individuals control or influence what information related to them may be collected and stored and by whom and to whom that information may be disclosed.

Integrity: This term covers two related concepts: Data integrity: Assures that information (both stored and in transmitted packets) and programs are changed only in a specified and authorized manner.

System integrity: Assures that a system performs its intended function in an unimpaired manner, free from deliberate or inadvertent unauthorized manipulation of the system.

Availability: Assures that systems work promptly and service is not denied to authorized users.

These three concepts form what is often referred to as the CIA triad. The three concepts embody the fundamental security objectives for both data and for information and computing services. For example, the NIST standard FIPS 199 (Standards for Security Categorization of Federal Information and Information Systems) lists confidentiality, integrity, and availability as the three security objectives for information and for information systems. FIPS 199 provides a useful characterization of these three objectives in terms of requirements and the definition of a loss of security in each category: Confidentiality: Preserving authorized restrictions on information access and disclosure, including means for protecting personal privacy and proprietary information. A loss of confidentiality is the unauthorized disclosure of information.

Integrity: Guarding against improper information modification or destruction, including ensuring information nonrepudiation and authenticity. A loss of integrity is the unauthorized modification or destruction of information.

Availability: Ensuring timely and reliable access to and use of information. A loss of availability is the disruption of access to or use of information or an information system.

Although the use of the CIA triad to define security objectives is well established, some in the security field feel that additional concepts are needed to present a complete picture (Figure 1.1). Two of the most commonly mentioned are as follows:

Figure 1.1 Essential Network and Computer Security Requirements Authenticity: The property of being genuine and being able to be verified and trusted; confidence in the validity of a transmission, a message, or message originator. This means verifying that users are who they say they are and that each input arriving at the system came from a trusted source.

Accountability: The security goal that generates the requirement for actions of an entity to be traced uniquely to that entity. This supports nonrepudiation, deterrence, fault isolation, intrusion detection and prevention, and after-action recovery and legal action. Because truly secure systems are not yet an achievable goal, we must be able to trace a security breach to a responsible party.

Systems must keep records of their activities to permit later forensic analysis to trace security breaches or to aid in transaction disputes.

Examples We now provide some examples of applications that illustrate the requirements just enumerated.2 For these examples, we use three levels of impact on organizations or individuals should there be a breach of security (i.e., a loss of confidentiality, integrity, or availability). These levels are defined

in FIPS PUB 199: 2

These examples are taken from a security policy document published by the Information Technology Security

and Privacy Office at Purdue University.

Low: The loss could be expected to have a limited adverse effect on organizational operations, organizational assets, or individuals. A limited adverse effect means that, for example, the loss of confidentiality, integrity, or availability might (i) cause a degradation in mission capability to an extent and duration that the organization is able to perform its primary functions, but the effectiveness of the functions is noticeably reduced; (ii) result in minor damage to organizational assets; (iii) result in minor financial loss; or (iv) result in minor harm to individuals.

Moderate: The loss could be expected to have a serious adverse effect on organizational operations, organizational assets, or individuals. A serious adverse effect means that, for example, the loss might (i) cause a significant degradation in mission capability to an extent and duration that the organization is able to perform its primary functions, but the effectiveness of the functions is significantly reduced; (ii) result in significant damage to organizational assets; (iii) result in significant financial loss; or (iv) result in significant harm to individuals that does not involve loss of life or serious, life-threatening injuries.

High: The loss could be expected to have a severe or catastrophic adverse effect on organizational operations, organizational assets, or individuals. A ­severe or catastrophic adverse effect means that, for example, the loss might (i) cause a severe degradation in or loss of mission capability to an extent and duration that the organization is not able to perform one or more of its primary functions; (ii) result in major damage to organizational assets; (iii) result in major financial loss; or (iv) result in severe or catastrophic harm to individuals involving loss of life or serious, life-threatening injuries.

Confidentiality Student grade information is an asset whose confidentiality is considered to be highly important by students. In the United States, the release of such information is regulated by the Family Educational Rights and Privacy Act (FERPA). Grade information should only be available to students, their parents, and employees that require the information to do their job. Student enrollment information may have a moderate confidentiality rating. While still covered by FERPA, this information is seen by more people on a daily basis, is less likely to be targeted than grade information, and results in less damage if disclosed. Directory information, such as lists of students or faculty or departmental lists, may be assigned a low confidentiality rating or indeed no rating. This information is typically freely available to the public and published on a school’s Web site.

Integrity Several aspects of integrity are illustrated by the example of a hospital patient’s allergy information stored in a database. The doctor should be able to trust that the information is correct and current.

Now suppose that an employee (e.g., a nurse) who is authorized to view and update this information deliberately falsifies the data to cause harm to the hospital. The database needs to be restored to a trusted basis quickly, and it should be possible to trace the error back to the person responsible.

Patient allergy information is an example of an asset with a high requirement for integrity. Inaccurate information could result in serious harm or death to a patient and expose the hospital to massive liability.

An example of an asset that may be assigned a moderate level of integrity requirement is a Web site

that offers a forum to registered users to discuss some specific topic. Either a registered user or a hacker could falsify some entries or deface the Web site. If the forum exists only for the enjoyment of the users, brings in little or no advertising revenue, and is not used for something important such as research, then potential damage is not severe. The Web master may experience some data, financial, and time loss.

An example of a low integrity requirement is an anonymous online poll. Many Web sites, such as news organizations, offer these polls to their users with very few safeguards. However, the inaccuracy and unscientific nature of such polls is well understood.

Availability The more critical a component or service, the higher is the level of availability required. Consider a system that provides authentication services for critical systems, applications, and devices. An interruption of service results in the inability for customers to access computing resources and staff to access the resources they need to perform critical tasks. The loss of the service translates into a large financial loss in lost employee productivity and potential customer loss.

An example of an asset that would typically be rated as having a moderate availability requirement is a public Web site for a university; the Web site provides information for current and prospective students and donors. Such a site is not a critical component of the university’s information system, but its unavailability will cause some embarrassment.

An online telephone directory lookup application would be classified as a low availability requirement.

Although the temporary loss of the application may be an annoyance, there are other ways to access the information, such as a hardcopy directory or the operator.

The Challenges of Computer Security Computer and network security is both fascinating and complex. Some of the ­reasons follow: 1. Security is not as simple as it might first appear to the novice. The requirements seem to be

straightforward; indeed, most of the major requirements for security services can be given selfexplanatory, one-word labels: confidentiality, authentication, nonrepudiation, or integrity. But the mechanisms used to meet those requirements can be quite complex, and understanding them may involve rather subtle reasoning.

2. In developing a particular security mechanism or algorithm, one must always consider potential attacks on those security features. In many cases, successful attacks are designed by looking at the problem in a completely different way, therefore exploiting an unexpected weakness in the mechanism.

3. Because of point 2, the procedures used to provide particular services are often counterintuitive.

Typically, a security mechanism is complex, and it is not obvious from the statement of a particular requirement that such elaborate measures are needed. It is only when the various aspects of the threat are considered that elaborate security mechanisms make sense.

4. Having designed various security mechanisms, it is necessary to decide where to use them.

This is true both in terms of physical placement (e.g., at what points in a network are certain security mechanisms needed) and in a logical sense (e.g., at what layer or layers of an architecture such as TCP/IP [Transmission Control Protocol/Internet Protocol] should mechanisms be placed).

5. Security mechanisms typically involve more than a particular algorithm or protocol. They also require that participants be in possession of some secret information (e.g., an encryption key), which raises questions about the creation, distribution, and protection of that secret information.

There also may be a reliance on communications protocols whose behavior may complicate the

task of developing the security mechanism. For example, if the proper functioning of the security mechanism requires setting time limits on the transit time of a message from sender to receiver, then any protocol or network that introduces variable, unpredictable delays may render such time limits meaningless.

6. Computer and network security is essentially a battle of wits between a perpetrator who tries to find holes and the designer or administrator who tries to close them. The great advantage that the attacker has is that he or she need only find a single weakness, while the designer must find and eliminate all weaknesses to achieve perfect security.

7. There is a natural tendency on the part of users and system managers to perceive little benefit from security investment until a security failure occurs.

8. Security requires regular, even constant, monitoring, and this is difficult in today’s short-term, overloaded environment.

9. Security is still too often an afterthought to be incorporated into a system after the design is complete rather than being an integral part of the design process.

10. Many users and even security administrators view strong security as an impediment to efficient and user-friendly operation of an information system or use of information.

The difficulties just enumerated will be encountered in numerous ways as we examine the various security threats and mechanisms throughout this book.

1.2 The OSI Security Architecture To assess effectively the security needs of an organization and to evaluate and choose various security products and policies, the manager responsible for security needs some systematic way of defining the requirements for security and characterizing the approaches to satisfying those requirements. This is difficult enough in a centralized data processing environment; with the use of local and wide area networks, the problems are compounded.

ITU-T3 Recommendation X.800, Security Architecture for OSI, defines such a systematic approach.4 The OSI security architecture is useful to managers as a way of organizing the task of providing security. Furthermore, because this architecture was developed as an international standard, computer and communications vendors have developed security features for their products and services that relate to this structured definition of services and mechanisms.

3

The International Telecommunication Union (ITU) Telecommunication Standardization Sector (ITU-T) is a United

Nations-sponsored agency that develops standards, called Recommendations, relating to telecommunications and to open systems interconnection (OSI).

4

The OSI security architecture was developed in the context of the OSI protocol architecture, which is described in

Appendix L. However, for our purposes in this chapter, an understanding of the OSI protocol architecture is not required.

For our purposes, the OSI security architecture provides a useful, if abstract, overview of many of the concepts that this book deals with. The OSI security architecture focuses on security attacks, mechanisms, and services. These can be defined briefly as Security attack: Any action that compromises the security of information owned by an organization.

Security mechanism: A process (or a device incorporating such a process) that is designed to detect, prevent, or recover from a security attack.

Security service: A processing or communication service that enhances the security of the data processing systems and the information transfers of an organization. The services are intended to counter security attacks, and they make use of one or more security mechanisms to provide the service.

In the literature, the terms threat and attack are commonly used to mean more or less the same thing.

Table 1.1 provides definitions taken from RFC 4949, Internet Security Glossary.

Table 1.1

Threats and Attacks (RFC 4949)

Threat A potential for violation of security, which exists when there is a circumstance, capability, action, or event that could breach security and cause harm. That is, a threat is a possible danger that might exploit a vulnerability.

Attack

An assault on system security that derives from an intelligent threat; that is, an intelligent act that is a deliberate attempt (especially in the sense of a method or technique) to evade security services and violate the security policy of a system.

1.3 Security Attacks A useful means of classifying security attacks, used both in X.800 and RFC 4949, is in terms of passive attacks and active attacks (Figure 1.2). A passive attack attempts to learn or make use of information from the system but does not affect system resources. An active attack attempts to alter system resources or affect their operation.

Passive Attacks Passive attacks (Figure 1.2a) are in the nature of eavesdropping on, or monitoring of, transmissions.

The goal of the opponent is to obtain information that is being transmitted. Two types of passive attacks are the release of message contents and traffic analysis.

The release of message contents is easily understood. A telephone conversation, an electronic mail message, and a transferred file may contain sensitive or confidential information. We would like to prevent an opponent from learning the contents of these transmissions.

A second type of passive attack, traffic analysis, is subtler. Suppose that we had a way of masking the contents of messages or other information traffic so that opponents, even if they captured the message, could not extract the information from the message. The common technique for masking contents is encryption. If we had encryption protection in place, an opponent might still be able to observe the pattern of these messages. The opponent could determine the location and identity of communicating hosts and could observe the frequency and length of messages being exchanged.

This information might be useful in guessing the nature of the communication that was taking place.

Passive attacks are very difficult to detect, because they do not involve any alteration of the data.

Typically, the message traffic is sent and received in an apparently normal fashion, and neither the sender nor receiver is aware that a third party has read the messages or observed the traffic pattern.

However, it is feasible to prevent the success of these attacks, usually by means of encryption. Thus, the emphasis in dealing with passive attacks is on prevention rather than detection.

Active Attacks Active attacks (Figure 1.2b) involve some modification of the data stream or the creation of a false stream and can be subdivided into four categories: masquerade, replay, modification of messages, and denial of service.

Figure 1.2

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DANCE ON STILTS AT THE GIRLS’ UNYAGO, NIUCHI

Newala, too, suffers from the distance of its water-supply—at least the Newala of to-day does; there was once another Newala in a lovely valley at the foot of the plateau. I visited it and found scarcely a trace of houses, only a Christian cemetery, with the graves of several missionaries and their converts, remaining as a monument of its former glories. But the surroundings are wonderfully beautiful. A thick grove of splendid mango-trees closes in the weather-worn crosses and headstones; behind them, combining the useful and the agreeable, is a whole plantation of lemon-trees covered with ripe fruit; not the small African kind, but a much larger and also juicier imported variety, which drops into the hands of the passing traveller, without calling for any exertion on his part. Old Newala is now under the jurisdiction of the native pastor, Daudi, at Chingulungulu, who, as I am on very friendly terms with him, allows me, as a matter of course, the use of this lemon-grove during my stay at Newala.

FEET MUTILATED BY THE RAVAGES OF THE “JIGGER” (Sarcopsylla penetrans)

The water-supply of New Newala is in the bottom of the valley, some 1,600 feet lower down. The way is not only long and fatiguing, but the water, when we get it, is thoroughly bad. We are suffering not only from this, but from the fact that the arrangements at Newala are nothing short of luxurious. We have a separate kitchen—a hut built against the boma palisade on the right of the baraza, the interior of which is not visible from our usual position. Our two cooks were not long in finding this out, and they consequently do—or rather neglect to do—what they please. In any case they do not seem to be very particular about the boiling of our drinking-water—at least I can attribute to no other cause certain attacks of a dysenteric nature, from which both Knudsen and I have suffered for some time. If a man like Omari has to be left unwatched for a moment, he is capable of anything. Besides this complaint, we are inconvenienced by the state of our nails, which have become as hard as glass, and crack on the slightest provocation, and I have the additional infliction of pimples all over me. As if all this were not enough, we have also, for the last week been waging war against the jigger, who has found his Eldorado in the hot sand of the Makonde plateau. Our men are seen all day long—whenever their chronic colds and the dysentery likewise raging among them permit—occupied in removing this scourge of Africa from their feet and trying to prevent the disastrous consequences of its presence. It is quite common to see natives of this place with one or two toes missing; many have lost all their toes,

or even the whole front part of the foot, so that a well-formed leg ends in a shapeless stump. These ravages are caused by the female of Sarcopsylla penetrans, which bores its way under the skin and there develops an egg-sac the size of a pea. In all books on the subject, it is stated that one’s attention is called to the presence of this parasite by an intolerable itching. This agrees very well with my experience, so far as the softer parts of the sole, the spaces between and under the toes, and the side of the foot are concerned, but if the creature penetrates through the harder parts of the heel or ball of the foot, it may escape even the most careful search till it has reached maturity.

Then there is no time to be lost, if the horrible ulceration, of which we see cases by the dozen every day, is to be prevented. It is much easier, by the way, to discover the insect on the white skin of a European than on that of a native, on which the dark speck scarcely shows. The four or five jiggers which, in spite of the fact that I constantly wore high laced boots, chose my feet to settle in, were taken out for me by the all-accomplished Knudsen, after which I thought it advisable to wash out the cavities with corrosive sublimate. The natives have a different sort of disinfectant—they fill the hole with scraped roots. In a tiny Makua village on the slope of the plateau south of Newala, we saw an old woman who had filled all the spaces under her toe-nails with powdered roots by way of prophylactic treatment. What will be the result, if any, who can say?

The rest of the many trifling ills which trouble our existence are really more comic than serious. In the absence of anything else to smoke, Knudsen and I at last opened a box of cigars procured from the Indian store-keeper at Lindi, and tried them, with the most distressing results. Whether they contain opium or some other narcotic, neither of us can say, but after the tenth puff we were both “off,” three-quarters stupefied and unspeakably wretched. Slowly we recovered—and what happened next? Half-an-hour later we were once more smoking these poisonous concoctions—so insatiable is the craving for tobacco in the tropics.

Even my present attacks of fever scarcely deserve to be taken seriously. I have had no less than three here at Newala, all of which have run their course in an incredibly short time. In the early afternoon, I am busy with my old natives, asking questions and making notes. The strong midday coffee has stimulated my spirits to

an extraordinary degree, the brain is active and vigorous, and work progresses rapidly, while a pleasant warmth pervades the whole body. Suddenly this gives place to a violent chill, forcing me to put on my overcoat, though it is only half-past three and the afternoon sun is at its hottest. Now the brain no longer works with such acuteness and logical precision; more especially does it fail me in trying to establish the syntax of the difficult Makua language on which I have ventured, as if I had not enough to do without it. Under the circumstances it seems advisable to take my temperature, and I do so, to save trouble, without leaving my seat, and while going on with my work. On examination, I find it to be 101·48°. My tutors are abruptly dismissed and my bed set up in the baraza; a few minutes later I am in it and treating myself internally with hot water and lemon-juice.

Three hours later, the thermometer marks nearly 104°, and I make them carry me back into the tent, bed and all, as I am now perspiring heavily, and exposure to the cold wind just beginning to blow might mean a fatal chill. I lie still for a little while, and then find, to my great relief, that the temperature is not rising, but rather falling. This is about 7.30 p.m. At 8 p.m. I find, to my unbounded astonishment, that it has fallen below 98·6°, and I feel perfectly well. I read for an hour or two, and could very well enjoy a smoke, if I had the wherewithal—Indian cigars being out of the question.

Having no medical training, I am at a loss to account for this state of things. It is impossible that these transitory attacks of high fever should be malarial; it seems more probable that they are due to a kind of sunstroke. On consulting my note-book, I become more and more inclined to think this is the case, for these attacks regularly follow extreme fatigue and long exposure to strong sunshine. They at least have the advantage of being only short interruptions to my work, as on the following morning I am always quite fresh and fit.

My treasure of a cook is suffering from an enormous hydrocele which makes it difficult for him to get up, and Moritz is obliged to keep in the dark on account of his inflamed eyes. Knudsen’s cook, a raw boy from somewhere in the bush, knows still less of cooking than Omari; consequently Nils Knudsen himself has been promoted to the vacant post. Finding that we had come to the end of our supplies, he began by sending to Chingulungulu for the four sucking-pigs which we had

bought from Matola and temporarily left in his charge; and when they came up, neatly packed in a large crate, he callously slaughtered the biggest of them. The first joint we were thoughtless enough to entrust for roasting to Knudsen’s mshenzi cook, and it was consequently uneatable; but we made the rest of the animal into a jelly which we ate with great relish after weeks of underfeeding, consuming incredible helpings of it at both midday and evening meals. The only drawback is a certain want of variety in the tinned vegetables. Dr. Jäger, to whom the Geographical Commission entrusted the provisioning of the expeditions—mine as well as his own—because he had more time on his hands than the rest of us, seems to have laid in a huge stock of Teltow turnips,[46] an article of food which is all very well for occasional use, but which quickly palls when set before one every day; and we seem to have no other tins left. There is no help for it—we must put up with the turnips; but I am certain that, once I am home again, I shall not touch them for ten years to come.

Amid all these minor evils, which, after all, go to make up the genuine flavour of Africa, there is at least one cheering touch: Knudsen has, with the dexterity of a skilled mechanic, repaired my 9 × 12 cm. camera, at least so far that I can use it with a little care.

How, in the absence of finger-nails, he was able to accomplish such a ticklish piece of work, having no tool but a clumsy screw-driver for taking to pieces and putting together again the complicated mechanism of the instantaneous shutter, is still a mystery to me; but he did it successfully. The loss of his finger-nails shows him in a light contrasting curiously enough with the intelligence evinced by the above operation; though, after all, it is scarcely surprising after his ten years’ residence in the bush. One day, at Lindi, he had occasion to wash a dog, which must have been in need of very thorough cleansing, for the bottle handed to our friend for the purpose had an extremely strong smell. Having performed his task in the most conscientious manner, he perceived with some surprise that the dog did not appear much the better for it, and was further surprised by finding his own nails ulcerating away in the course of the next few days. “How was I to know that carbolic acid has to be diluted?” he mutters indignantly, from time to time, with a troubled gaze at his mutilated finger-tips.

Since we came to Newala we have been making excursions in all directions through the surrounding country, in accordance with old habit, and also because the akida Sefu did not get together the tribal elders from whom I wanted information so speedily as he had promised. There is, however, no harm done, as, even if seen only from the outside, the country and people are interesting enough.

The Makonde plateau is like a large rectangular table rounded off at the corners. Measured from the Indian Ocean to Newala, it is about seventy-five miles long, and between the Rovuma and the Lukuledi it averages fifty miles in breadth, so that its superficial area is about two-thirds of that of the kingdom of Saxony. The surface, however, is not level, but uniformly inclined from its south-western edge to the ocean. From the upper edge, on which Newala lies, the eye ranges for many miles east and north-east, without encountering any obstacle, over the Makonde bush. It is a green sea, from which here and there thick clouds of smoke rise, to show that it, too, is inhabited by men who carry on their tillage like so many other primitive peoples, by cutting down and burning the bush, and manuring with the ashes. Even in the radiant light of a tropical day such a fire is a grand sight.

Much less effective is the impression produced just now by the great western plain as seen from the edge of the plateau. As often as time permits, I stroll along this edge, sometimes in one direction, sometimes in another, in the hope of finding the air clear enough to let me enjoy the view; but I have always been disappointed.

Wherever one looks, clouds of smoke rise from the burning bush, and the air is full of smoke and vapour. It is a pity, for under more favourable circumstances the panorama of the whole country up to the distant Majeje hills must be truly magnificent. It is of little use taking photographs now, and an outline sketch gives a very poor idea of the scenery. In one of these excursions I went out of my way to make a personal attempt on the Makonde bush. The present edge of the plateau is the result of a far-reaching process of destruction through erosion and denudation. The Makonde strata are everywhere cut into by ravines, which, though short, are hundreds of yards in depth. In consequence of the loose stratification of these beds, not only are the walls of these ravines nearly vertical, but their upper end is closed by an equally steep escarpment, so that the

western edge of the Makonde plateau is hemmed in by a series of deep, basin-like valleys. In order to get from one side of such a ravine to the other, I cut my way through the bush with a dozen of my men.

It was a very open part, with more grass than scrub, but even so the short stretch of less than two hundred yards was very hard work; at the end of it the men’s calicoes were in rags and they themselves bleeding from hundreds of scratches, while even our strong khaki suits had not escaped scatheless.

NATIVE PATH THROUGH THE MAKONDE BUSH, NEAR MAHUTA

I see increasing reason to believe that the view formed some time back as to the origin of the Makonde bush is the correct one. I have no doubt that it is not a natural product, but the result of human occupation. Those parts of the high country where man—as a very slight amount of practice enables the eye to perceive at once—has not yet penetrated with axe and hoe, are still occupied by a splendid timber forest quite able to sustain a comparison with our mixed forests in Germany. But wherever man has once built his hut or tilled his field, this horrible bush springs up. Every phase of this process

may be seen in the course of a couple of hours’ walk along the main road. From the bush to right or left, one hears the sound of the axe— not from one spot only, but from several directions at once. A few steps further on, we can see what is taking place. The brush has been cut down and piled up in heaps to the height of a yard or more, between which the trunks of the large trees stand up like the last pillars of a magnificent ruined building. These, too, present a melancholy spectacle: the destructive Makonde have ringed them— cut a broad strip of bark all round to ensure their dying off—and also piled up pyramids of brush round them. Father and son, mother and son-in-law, are chopping away perseveringly in the background—too busy, almost, to look round at the white stranger, who usually excites so much interest. If you pass by the same place a week later, the piles of brushwood have disappeared and a thick layer of ashes has taken the place of the green forest. The large trees stretch their smouldering trunks and branches in dumb accusation to heaven—if they have not already fallen and been more or less reduced to ashes, perhaps only showing as a white stripe on the dark ground.

This work of destruction is carried out by the Makonde alike on the virgin forest and on the bush which has sprung up on sites already cultivated and deserted. In the second case they are saved the trouble of burning the large trees, these being entirely absent in the secondary bush.

After burning this piece of forest ground and loosening it with the hoe, the native sows his corn and plants his vegetables. All over the country, he goes in for bed-culture, which requires, and, in fact, receives, the most careful attention. Weeds are nowhere tolerated in the south of German East Africa. The crops may fail on the plains, where droughts are frequent, but never on the plateau with its abundant rains and heavy dews. Its fortunate inhabitants even have the satisfaction of seeing the proud Wayao and Wamakua working for them as labourers, driven by hunger to serve where they were accustomed to rule.

But the light, sandy soil is soon exhausted, and would yield no harvest the second year if cultivated twice running. This fact has been familiar to the native for ages; consequently he provides in time, and, while his crop is growing, prepares the next plot with axe and firebrand. Next year he plants this with his various crops and

lets the first piece lie fallow. For a short time it remains waste and desolate; then nature steps in to repair the destruction wrought by man; a thousand new growths spring out of the exhausted soil, and even the old stumps put forth fresh shoots. Next year the new growth is up to one’s knees, and in a few years more it is that terrible, impenetrable bush, which maintains its position till the black occupier of the land has made the round of all the available sites and come back to his starting point.

The Makonde are, body and soul, so to speak, one with this bush.

According to my Yao informants, indeed, their name means nothing else but “bush people.” Their own tradition says that they have been settled up here for a very long time, but to my surprise they laid great stress on an original immigration. Their old homes were in the south-east, near Mikindani and the mouth of the Rovuma, whence their peaceful forefathers were driven by the continual raids of the Sakalavas from Madagascar and the warlike Shirazis[47] of the coast, to take refuge on the almost inaccessible plateau. I have studied African ethnology for twenty years, but the fact that changes of population in this apparently quiet and peaceable corner of the earth could have been occasioned by outside enterprises taking place on the high seas, was completely new to me. It is, no doubt, however, correct.

The charming tribal legend of the Makonde—besides informing us of other interesting matters—explains why they have to live in the thickest of the bush and a long way from the edge of the plateau, instead of making their permanent homes beside the purling brooks and springs of the low country.

“The place where the tribe originated is Mahuta, on the southern side of the plateau towards the Rovuma, where of old time there was nothing but thick bush. Out of this bush came a man who never washed himself or shaved his head, and who ate and drank but little.

He went out and made a human figure from the wood of a tree growing in the open country, which he took home to his abode in the bush and there set it upright. In the night this image came to life and was a woman. The man and woman went down together to the Rovuma to wash themselves. Here the woman gave birth to a stillborn child. They left that place and passed over the high land into the valley of the Mbemkuru, where the woman had another child, which

was also born dead. Then they returned to the high bush country of Mahuta, where the third child was born, which lived and grew up. In course of time, the couple had many more children, and called themselves Wamatanda. These were the ancestral stock of the Makonde, also called Wamakonde,[48] i.e., aborigines. Their forefather, the man from the bush, gave his children the command to bury their dead upright, in memory of the mother of their race who was cut out of wood and awoke to life when standing upright. He also warned them against settling in the valleys and near large streams, for sickness and death dwelt there. They were to make it a rule to have their huts at least an hour’s walk from the nearest wateringplace; then their children would thrive and escape illness.”

The explanation of the name Makonde given by my informants is somewhat different from that contained in the above legend, which I extract from a little book (small, but packed with information), by Pater Adams, entitled Lindi und sein Hinterland. Otherwise, my results agree exactly with the statements of the legend. Washing?

Hapana—there is no such thing. Why should they do so? As it is, the supply of water scarcely suffices for cooking and drinking; other people do not wash, so why should the Makonde distinguish himself by such needless eccentricity? As for shaving the head, the short, woolly crop scarcely needs it,[49] so the second ancestral precept is likewise easy enough to follow. Beyond this, however, there is nothing ridiculous in the ancestor’s advice. I have obtained from various local artists a fairly large number of figures carved in wood, ranging from fifteen to twenty-three inches in height, and representing women belonging to the great group of the Mavia, Makonde, and Matambwe tribes. The carving is remarkably well done and renders the female type with great accuracy, especially the keloid ornamentation, to be described later on. As to the object and meaning of their works the sculptors either could or (more probably) would tell me nothing, and I was forced to content myself with the scanty information vouchsafed by one man, who said that the figures were merely intended to represent the nembo—the artificial deformations of pelele, ear-discs, and keloids. The legend recorded

by Pater Adams places these figures in a new light. They must surely be more than mere dolls; and we may even venture to assume that they are—though the majority of present-day Makonde are probably unaware of the fact—representations of the tribal ancestress.

The references in the legend to the descent from Mahuta to the Rovuma, and to a journey across the highlands into the Mbekuru valley, undoubtedly indicate the previous history of the tribe, the travels of the ancestral pair typifying the migrations of their descendants. The descent to the neighbouring Rovuma valley, with its extraordinary fertility and great abundance of game, is intelligible at a glance—but the crossing of the Lukuledi depression, the ascent to the Rondo Plateau and the descent to the Mbemkuru, also lie within the bounds of probability, for all these districts have exactly the same character as the extreme south. Now, however, comes a point of especial interest for our bacteriological age. The primitive Makonde did not enjoy their lives in the marshy river-valleys.

Disease raged among them, and many died. It was only after they had returned to their original home near Mahuta, that the health conditions of these people improved. We are very apt to think of the African as a stupid person whose ignorance of nature is only equalled by his fear of it, and who looks on all mishaps as caused by evil spirits and malignant natural powers. It is much more correct to assume in this case that the people very early learnt to distinguish districts infested with malaria from those where it is absent.

This knowledge is crystallized in the ancestral warning against settling in the valleys and near the great waters, the dwelling-places of disease and death. At the same time, for security against the hostile Mavia south of the Rovuma, it was enacted that every settlement must be not less than a certain distance from the southern edge of the plateau. Such in fact is their mode of life at the present day. It is not such a bad one, and certainly they are both safer and more comfortable than the Makua, the recent intruders from the south, who have made USUAL METHOD OF good their footing on the western edge of the CLOSING HUT-DOOR plateau, extending over a fairly wide belt of country. Neither Makua nor Makonde show in their dwellings anything of the size and comeliness of the Yao houses in the plain, especially at Masasi, Chingulungulu and Zuza’s. Jumbe Chauro, a Makonde hamlet not far from Newala, on the road to Mahuta, is the

most important settlement of the tribe I have yet seen, and has fairly spacious huts. But how slovenly is their construction compared with the palatial residences of the elephant-hunters living in the plain.

The roofs are still more untidy than in the general run of huts during the dry season, the walls show here and there the scanty beginnings or the lamentable remains of the mud plastering, and the interior is a veritable dog-kennel; dirt, dust and disorder everywhere. A few huts only show any attempt at division into rooms, and this consists merely of very roughly-made bamboo partitions. In one point alone have I noticed any indication of progress—in the method of fastening the door. Houses all over the south are secured in a simple but ingenious manner. The door consists of a set of stout pieces of wood or bamboo, tied with bark-string to two cross-pieces, and moving in two grooves round one of the door-posts, so as to open inwards. If the owner wishes to leave home, he takes two logs as thick as a man’s upper arm and about a yard long. One of these is placed obliquely against the middle of the door from the inside, so as to form an angle of from 60° to 75° with the ground. He then places the second piece horizontally across the first, pressing it downward with all his might.

It is kept in place by two strong posts planted in the ground a few inches inside the door. This fastening is absolutely safe, but of course cannot be applied to both doors at once, otherwise how could the owner leave or enter his house? I have not yet succeeded in finding out how the back door is fastened.

MAKONDE LOCK AND KEY AT JUMBE CHAURO

This is the general way of closing a house. The Makonde at Jumbe Chauro, however, have a much more complicated, solid and original one. Here, too, the door is as already described, except that there is only one post on the inside, standing by itself about six inches from one side of the doorway. Opposite this post is a hole in the wall just large enough to admit a man’s arm. The door is closed inside by a large wooden bolt passing through a hole in this post and pressing with its free end against the door. The other end has three holes into which fit three pegs running in vertical grooves inside the post. The door is opened with a wooden key about a foot long, somewhat curved and sloped off at the butt; the other end has three pegs corresponding to the holes, in the bolt, so that, when it is thrust through the hole in the wall and inserted into the rectangular opening in the post, the pegs can be lifted and the bolt drawn out.[50]

MODE OF INSERTING THE KEY

With no small pride first one householder and then a second showed me on the spot the action of this greatest invention of the Makonde Highlands. To both with an admiring exclamation of “Vizuri sana!” (“Very fine!”). I expressed the wish to take back these marvels with me to Ulaya, to show the Wazungu what clever fellows the Makonde are. Scarcely five minutes after my return to camp at Newala, the two men came up sweating under the weight of two heavy logs which they laid down at my feet, handing over at the same time the keys of the fallen fortress. Arguing, logically enough, that if the key was wanted, the lock would be wanted with it, they had taken their axes and chopped down the posts—as it never occurred to them to dig them out of the ground and so bring them intact. Thus I have

two badly damaged specimens, and the owners, instead of praise, come in for a blowing-up.

The Makua huts in the environs of Newala are especially miserable; their more than slovenly construction reminds one of the temporary erections of the Makua at Hatia’s, though the people here have not been concerned in a war. It must therefore be due to congenital idleness, or else to the absence of a powerful chief. Even the baraza at Mlipa’s, a short hour’s walk south-east of Newala, shares in this general neglect. While public buildings in this country are usually looked after more or less carefully, this is in evident danger of being blown over by the first strong easterly gale. The only attractive object in this whole district is the grave of the late chief Mlipa. I visited it in the morning, while the sun was still trying with partial success to break through the rolling mists, and the circular grove of tall euphorbias, which, with a broken pot, is all that marks the old king’s resting-place, impressed one with a touch of pathos.

Even my very materially-minded carriers seemed to feel something of the sort, for instead of their usual ribald songs, they chanted solemnly, as we marched on through the dense green of the Makonde bush:—