Introduction to Network Security
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Preface xv
About the Authors xix
1 Network Security Overview 1
1.1 Mission and Definitions 1
1.2 Common Attacks and Defense Mechanisms 3
1.2.1 Eavesdropping 3
1.2.2 Cryptanalysis 4
1.2.3 Password Pilfering 5
1.2.4 Identity Spoofing 13
1.2.5 Buffer-Overflow Exploitations 16
1.2.6 Repudiation 18
1.2.7 Intrusion 19
1.2.8 Traffic Analysis 19
1.2.9 Denial of Service Attacks 20
1.2.10 Malicious Software 22
1.3 Attacker Profiles 25
1.3.1 Hackers 25
1.3.2 Script Kiddies 26
1.3.3 Cyber Spies 26
1.3.4 Vicious Employees 27
1.3.5 Cyber Terrorists 27
1.3.6 Hypothetical Attackers 27
1.4 Basic Security Model 27
1.5 Security Resources 29
1.5.1 CERT 29
1.5.2 SANS Institute 29
1.5.3 Microsoft Security 29
1.5.4 NTBugtraq 29
1.5.5 Common Vulnerabilities and Exposures 30
1.6 Closing Remarks 30
1.7 Exercises 30
1.7.1 Discussions 30
1.7.2 Homework 31
2 Data Encryption Algorithms 45
2.1 Data Encryption Algorithm Design Criteria 45
2.1.1 ASCII Code 46
2.1.2 XOR Encryption 46
2.1.3 Criteria of Data Encryptions 48
2.1.4 Implementation Criteria 50
2.2 Data Encryption Standard 50
2.2.1 Feistel's Cipher Scheme 50
2.2.2 DES Subkeys 52
2.2.3 DES Substitution Boxes 54
2.2.4 DES Encryption 55
2.2.5 DES Decryption and Correctness Proof 57
2.2.6 DES Security Strength 58
2.3 Multiple DES 59
2.3.1 Triple-DES with Two Keys 59
2.3.2 2DES and 3DES/3 59
2.3.3 Meet-in-the-Middle Attacks on 2DES 60
2.4 Advanced Encryption Standard 61
2.4.1 AES Basic Structures 61
2.4.2 AES S-Boxes 63
2.4.3 AES-128 Round Keys 65
2.4.4 Add Round Keys 66
2.4.5 Substitute-Bytes 67
2.4.6 Shift-Rows 67
2.4.7 Mix-Columns 67
2.4.8 AES-128 Encryption 68
2.4.9 AES-128 Decryption and Correctness Proof 69
2.4.10 Galois Fields 70
2.4.11 Construction of the AES S-Box and Its Inverse 73
2.4.12 AES Security Strength 74
2.5 Standard Block Cipher Modes of Operations 74
2.5.1 Electronic-Codebook Mode 75
2.5.2 Cipher-Block-Chaining Mode 75
2.5.3 Cipher-Feedback Mode 75
2.5.4 Output-Feedback Mode 76
2.5.5 Counter Mode 76
2.6 Offset Codebook Mode of Operations 77
2.6.1 Basic Operations 77
2.6.2 OCB Encryption and Tag Generation 78
2.6.3 OCB Decryption and Tag Verification 79
2.7 Stream Ciphers 80
2.7.1 RC4 Stream Cipher 80
2.7.2 RC4 Security Weaknesses 81
2.8 Key Generations 83
2.8.1 ANSI X9.17 PRNG 83
2.8.2 BBS Pseudorandom Bit Generator 83
2.9 Closing Remarks 84
2.10 Exercises 85
2.10.1 Discussions 85
2.10.2 Homework 85
3 Public-Key Cryptography and Key Management 93
3.1 Concepts of Public-Key Cryptography 93
3.2 Elementary Concepts and Theorems in Number Theory 95
3.2.1 Modular Arithmetic and Congruence Relations 96
3.2.2 Modular Inverse 96
3.2.3 Primitive Roots 98
3.2.4 Fast Modular Exponentiation 98
3.2.5 Finding Large Prime Numbers 100
3.2.6 The Chinese Remainder Theorem 101
3.2.7 Finite Continued Fractions 102
3.3 Diffie-Hellman Key Exchange 103
3.3.1 Key Exchange Protocol 103
3.3.2 Man-in-the-Middle Attacks 104
3.3.3 Elgamal PKC 106
3.4 RSA Cryptosystem 106
3.4.1 RSA Key Pairs, Encryptions, and Decryptions 106
3.4.2 RSA Parameter Attacks 109
3.4.3 RSA Challenge Numbers 112
3.5 Elliptic-Curve Cryptography 113
3.5.1 Commutative Groups on Elliptic Curves 113
3.5.2 Discrete Elliptic Curves 115
3.5.3 ECC Encodings 116
3.5.4 ECC Encryption and Decryption 117
3.5.5 ECC Key Exchange 118
3.5.6 ECC Strength 118
3.6 Key Distributions and Management 118
3.6.1 Master Keys and Session Keys 119
3.6.2 Public-Key Certificates 119
3.6.3 CA Networks 120
3.6.4 Key Rings 121
3.7 Closing Remarks 123
3.8 Exercises 123
3.8.1 Discussions 123
3.8.2 Homework 124
4 Data Authentication 129
4.1 Cryptographic Hash Functions 129
4.1.1 Design Criteria of Cryptographic Hash Functions 130
4.1.2 Quest for Cryptographic Hash Functions 131
4.1.3 Basic Structure of Standard Hash Functions 132
4.1.4 SHA-512 132
4.1.5 WHIRLPOOL 135
4.1.6 SHA-3 Standard 139
4.2 Cryptographic Checksums 143
4.2.1 Exclusive-OR Cryptographic Checksums 143
4.2.2 Design Criteria of MAC Algorithms 144
4.2.3 Data Authentication Algorithm 144
4.3 HMAC 144
4.3.1 Design Criteria of HMAC 144
4.3.2 HMAC Algorithm 145
4.4 Birthday Attacks 145
4.4.1 Complexity of Breaking Strong Collision Resistance 146
4.4.2 Set Intersection Attack 147
4.5 Digital Signature Standard 149
4.5.1 Signing 149
4.5.2 Signature Verifying 150
4.5.3 Correctness Proof of Signature Verification 150
4.5.4 Security Strength of DSS 151
4.6 Dual Signatures and Electronic Transactions 151
4.6.1 Dual Signature Applications 152
4.6.2 Dual Signatures and Electronic Transactions 152
4.7 Blind Signatures and Electronic Cash 153
4.7.1 RSA Blind Signatures 153
4.7.2 Electronic Cash 154
4.7.3 Bitcoin 156
4.8 Closing Remarks 158
4.9 Exercises 158
4.9.1 Discussions 158
4.9.2 Homework 158
5 Network Security Protocols in Practice 165
5.1 Crypto Placements in Networks 165
5.1.1 Crypto Placement at the Application Layer 168
5.1.2 Crypto Placement at the Transport Layer 168
5.1.3 Crypto Placement at the Network Layer 168
5.1.4 Crypto Placement at the Data-Link Layer 169
5.1.5 Implementations of Crypto Algorithms 169
5.2 Public-Key Infrastructure 170
5.2.1 X.509 Public-Key Infrastructure 170
5.2.2 X.509 Certificate Formats 171
5.3 IPsec: A Security Protocol at the Network Layer 173
5.3.1 Security Association 173
5.3.2 Application Modes and Security Associations 174
5.3.3 AH Format 176
5.3.4 ESP Format 178
5.3.5 Secret Key Determination and Distribution 179
5.4 SSL/TLS: Security Protocols at the Transport Layer 183
5.4.1 SSL Handshake Protocol 184
5.4.2 SSL Record Protocol 187
5.5 PGP and S/MIME: Email Security Protocols 188
5.5.1 Basic Email Security Mechanisms 189
5.5.2 PGP 190
5.5.3 S/MIME 191
5.6 Kerberos: An Authentication Protocol 192
5.6.1 Basic Ideas 192
5.6.2 Single-Realm Kerberos 193
5.6.3 Multiple-Realm Kerberos 195
5.7 SSH: Security Protocols for Remote Logins 197
5.8 Electronic Voting Protocols 198
5.8.1 Interactive Proofs 198
5.8.2 Re-encryption Schemes 199
5.8.3 Threshold Cryptography 200
5.8.4 The Helios Voting Protocol 202
5.9 Closing Remarks 204
5.10 Exercises 204
5.10.1 Discussions 204
5.10.2 Homework 204
6 Wireless Network Security 211
6.1 Wireless Communications and 802.11 WLAN Standards 211
6.1.1 WLAN Architecture 212
6.1.2 802.11 Essentials 213
6.1.3 Wireless Security Vulnerabilities 214
6.2 Wired Equivalent Privacy 215
6.2.1 Device Authentication and Access Control 215
6.2.2 Data Integrity Check 215
6.2.3 LLC Frame Encryption 216
6.2.4 Security Flaws of WEP 218
6.3 Wi-Fi Protected Access 221
6.3.1 Device Authentication and Access Controls 221
6.3.2 TKIP Key Generations 222
6.3.3 TKIP Message Integrity Code 224
6.3.4 TKIP Key Mixing 226
6.3.5 WPA Encryption and Decryption 229
6.3.6 WPA Security Strength and Weaknesses 229
6.4 IEEE 802.11i/WPA2 230
6.4.1 Key Generations 231
6.4.2 CCMP Encryptions and MIC 231
6.4.3 802.11i Security Strength and Weaknesses 232
6.5 Bluetooth Security 233
6.5.1 Piconets 233
6.5.2 Secure Pairings 235
6.5.3 SAFER+ Block Ciphers 235
6.5.4 Bluetooth Algorithms E1, E21, and E22 238
6.5.5 Bluetooth Authentication 240
6.5.6 A PIN Cracking Attack 241
6.5.7 Bluetooth Secure Simple Pairing 242
6.6 ZigBee Security 243
6.6.1 Joining a Network 243
6.6.2 Authentication 244
6.6.3 Key Establishment 244
6.6.4 Communication Security 245
6.7 Wireless Mesh Network Security 245
6.7.1 Blackhole Attacks 247
6.7.2 Wormhole Attacks 247
6.7.3 Rushing Attacks 247
6.7.4 Route-Error-Injection Attacks 247
6.8 Closing Remarks 248
6.9 Exercises 248
6.9.1 Discussions 248
6.9.2 Homework 248
7 Cloud Security 253
7.1 The Cloud Service Models 253
7.1.1 The REST Architecture 254
7.1.2 Software-as-a-Service 254
7.1.3 Platform-as-a-Service 254
7.1.4 Infrastructure-as-a-Service 254
7.1.5 Storage-as-a-Service 255
7.2 Cloud Security Models 255
7.2.1 Trusted-Third-Party 255
7.2.2 Honest-but-Curious 255
7.2.3 Semi-Honest-but-Curious 255
7.3 Multiple Tenancy 256
7.3.1 Virtualization 256
7.3.2 Attacks 258
7.4 Access Control 258
7.4.1 Access Control in Trusted Clouds 259
7.4.2 Access Control in Untrusted Clouds 260
7.5 Coping with Untrusted Clouds 263
7.5.1 Proofs of Storage 264
7.5.2 Secure Multiparty Computation 265
7.5.3 Oblivious Random Access Machines 268
7.6 Searchable Encryption 271
7.6.1 Keyword Search 271
7.6.2 Phrase Search 274
7.6.3 Searchable Encryption Attacks 275
7.6.4 Searchable Symmetric Encryptions for the SHBC Clouds 276
7.7 Closing Remarks 280
7.8 Exercises 280
7.8.1 Discussions 280
7.8.2 Homework 280
8 Network Perimeter Security 283
8.1 General Firewall Framework 284
8.2 Packet Filters 285
8.2.1 Stateless Filtering 285
8.2.2 Stateful Filtering 287
8.3 Circuit Gateways 288
8.3.1 Basic Structures 288
8.3.2 SOCKS 290
8.4 Application Gateways 290
8.4.1 Cache Gateways 291
8.4.2 Stateful Packet Inspections 291
8.5 Trusted Systems and Bastion Hosts 291
8.5.1 Trusted Operating Systems 292
8.5.2 Bastion hosts and Gateways 293
8.6 Firewall Configurations 294
8.6.1 Single-Homed Bastion Host System 294
8.6.2 Dual-Homed Bastion Host System 294
8.6.3 Screened Subnets 296
8.6.4 Demilitarized Zones 297
8.6.5 Network Security Topology 297
8.7 Network Address Translations 298
8.7.1 Dynamic NAT 298
8.7.2 Virtual Local Area Networks 298
8.7.3 Small Office and Home Office Firewalls 299
8.8 Setting Up Firewalls 299
8.8.1 Security Policy 300
8.8.2 Building a Linux Stateless Packet Filter 300
8.9 Closing Remarks 301
8.10 Exercises 301
8.10.1 Discussions 301
8.10.2 Homework 302
9 Intrusion Detections 309
9.1 Basic Ideas of Intrusion Detection 309
9.1.1 Basic Methodology 310
9.1.2 Auditing 311
9.1.3 IDS Components 312
9.1.4 IDS Architecture 313
9.1.5 Intrusion Detection Policies 315
9.1.6 Unacceptable Behaviors 316
9.2 Network-Based Detections and Host-Based Detections 316
9.2.1 Network-Based Detections 317
9.2.2 Host-Based Detections 318
9.3 Signature Detections 319
9.3.1 Network Signatures 320
9.3.2 Host-Based Signatures 321
9.3.3 Outsider Behaviors and Insider Misuses 322
9.3.4 Signature Detection Systems 323
9.4 Statistical Analysis 324
9.4.1 Event Counter 324
9.4.2 Event Gauge 324
9.4.3 Event Timer 325
9.4.4 Resource Utilization 325
9.4.5 Statistical Techniques 325
9.5 Behavioral Data Forensics 325
9.5.1 Data Mining Techniques 326
9.5.2 A Behavioral Data Forensic Example 326
9.6 Honeypots 327
9.6.1 Types of Honeypots 327
9.6.2 Honeyd 328
9.6.3 MWCollect Projects 331
9.6.4 Honeynet Projects 331
9.7 Closing Remarks 331
9.8 Exercises 332
9.8.1 Discussions 332
9.8.2 Homework 332
10 The Art of Anti-Malicious Software 337
10.1 Viruses 337
10.1.1 Virus Types 338
10.1.2 Virus Infection Schemes 340
10.1.3 Virus Structures 341
10.1.4 Compressor Viruses 342
10.1.5 Virus Disseminations 343
10.1.6 Win32 Virus Infection Dissection 344
10.1.7 Virus Creation Toolkits 345
10.2 Worms 346
10.2.1 Common Worm Types 346
10.2.2 The Morris Worm 346
10.2.3 The Melissa Worm 347
10.2.4 The Code Red Worm 348
10.2.5 The Conficker Worm 348
10.2.6 Other Worms Targeted at Microsoft Products 349
10.2.7 Email Attachments 350
10.3 Trojans 351
10.3.1 Ransomware 353
10.4 Malware Defense 353
10.4.1 Standard Scanning Methods 354
10.4.2 Anti-Malicious-Software Products 354
10.4.3 Malware Emulator 355
10.5 Hoaxes 356
10.6 Peer-to-Peer Security 357
10.6.1 P2P Security Vulnerabilities 357
10.6.2 P2P Security Measures 359
10.6.3 Instant Messaging 359
10.6.4 Anonymous Networks 359
10.7 Web Security 360
10.7.1 Basic Types of Web Documents 361
10.7.2 Security of Web Documents 362
10.7.3 ActiveX 363
10.7.4 Cookies 364
10.7.5 Spyware 365
10.7.6 AJAX Security 365
10.7.7 Safe Web Surfing 367
10.8 Distributed Denial-of-Service Attacks 367
10.8.1 Master-Slave DDoS Attacks 367
10.8.2 Master-Slave-Reflector DDoS Attacks 367
10.8.3 DDoS Attacks Countermeasures 368
10.9 Closing Remarks 370
10.10 Exercises 370
10.10.1 Discussions 370
10.10.2 Homework 370
Appendix A 7-bit ASCII code 377
Appendix B SHA-512 Constants (in Hexadecimal) 379
Appendix C Data Compression Using ZIP 381
Exercise 382
Appendix D Base64 Encoding 383
Exercise 384
Appendix E Cracking WEP Keys Using WEPCrack 385
E.1 System Setup 385
AP 385
Trim Size: 170mm x 244mm Wang ftoc.tex V1 - 04/21/2015 10:14 P.M. Page xiv
xiv Contents
User's Network Card 385
Attacker's Network Card 386
E.2 Experiment Details 386
Step 1: Initial Setup 386
Step 2: Attacker Setup 387
Step 3: Collecting Weak Initialization Vectors 387
Step 4: Cracking 387
E.3 Sample Code 388
Appendix F Acronyms 393
Further Reading 399
Index 406
Preface
People today are increasingly relying on public computer networks to conduct business and take care of household needs. However, public networks may be insecure because data stored in networked computers or transmitted through networks can be stolen, modified, or fabricated by malicious users. Thus, it is important to know what security measures are available and how to use them. Network security practices are designed to prevent these potential problems. Originating from meeting the needs of providing data confidentiality over public networks, network security has grown into a major academic discipline in both computer science and computer engineering, and also an important sector in the information industry.
The goal of network security is to give people the liberty of enjoying computer networks without the fear of compromising their rights and interests. Network security accomplishes this goal by providing confidentiality, integrity, nonrepudiation, and availability of useful data that are transmitted in open networks or stored in networked computers.
Network security will remain an active research area for several reasons. Firstly, security measures that are effective today may no longer be effective tomorrow because of advancements and breakthroughs in computing theory, algorithms, and computer technologies. Secondly, after the known security problems are solved, other security loopholes that were previously unknown may at some point be discovered and exploited by attackers. Thirdly, when new applications are developed or new technologies are invented, new security problems may also be created with them. Thus, network security is meant to be a long-lasting scuffle between the offenders and the defenders.
Research and development in network security has mainly followed two lines. One line studies computer cryptography and uses it to devise security protocols. The other line examines loopholes and side effects of the existing network protocols, software, and system configurations. It develops firewalls, intrusion detection systems, anti-malicious-software software, and other countermeasures. Interweaving these two lines together provides the basic building blocks for constructing deep layered defense systems against network security attacks.
This book is intended to provide a balanced treatment of network security along these two lines, with adequate materials and sufficient depth for teaching a one-semester introductory course on network security for graduate and upper-level undergraduate students. It is intended to inspire students to think about network security and prepare them for taking advanced network security courses. This book may also be used as a reference for IT professionals.
This book is a revision and extension of an early textbook written by the first author under the title of "Computer Network Security: Theory and Practice," which was co-published in 2008 by the Higher Education Press and Springer. The book is structured into 10 chapters.
Chapter 1 presents an overview of network security. It discusses network security goals, describes common network attacks, characterizes attackers, and defines a basic network security model.
Chapter 2 presents standard symmetric-key encryption algorithms, including DES, AES, and RC4. It discusses their strength and weaknesses. It also describes common block-cipher modes of operations and a recent block-cipher offset-codebook mode of operations. Finally, it presents key generation algorithms.
Chapter 3 presents standard public-key encryption algorithms and key-exchange algorithms, including Diffie-Hellman key exchange, RSA public-key cryptosystem, and elliptic-curve cryptography. It also discusses how to transmit and manage keys.
Chapter 4 presents secure hash functions and message authentication code algorithms for the purpose of authenticating data, including SHA-512, Whirlpool, SHA-3, cryptographic checksums, and the standard hash message authentication codes. It then discusses birthday attacks on secure hash functions and describes the digital signature standard. It presents a dual signature scheme used for electronic transactions and a blind signature scheme used for producing electronic cash. It concludes with a description of the Bitcoin protocol.
Chapter 5 presents several network security protocols commonly used in practice. It first describes a standard public-key infrastructure for managing public-key certificates. It then presents IPsec, a network-layer security protocol; SSL/TLS, a transport-layer security protocol; and several application-layer security protocols, including PGP and S/MIME for sending secure email messages, Kerberos for authenticating users in local area networks, and SSH for protecting remote logins.
Chapter 6 presents common security protocols for wireless local area networks at the data-link layer, including WEP for providing wired-equivalent privacy, WPA and IEEE 802.11i/WPA2 for providing wireless protected access, and IEEE 802.1X for authenticating wireless users. It then presents the Bluetooth security protocol and the ZigBee security protocol for wireless personal-area networks. Finally, it discusses security issues in wireless mesh networks.
Chapter 7 presents the key security issues involved in the burgeoning area of cloud computing, including a discussion of the multitenancy problem and issues of access control. It then presents advanced topics of searchable encryption for cryptographic cloud storage.
Chapter 8 presents firewall technologies and basic structures, including network-layer packet filtering, transport-layer stateful inspections, transport-layer gateways, application-layer proxies, trusted systems and bastion hosts, screened subnets, and network address translations.
Chapter 9 presents intrusion detection technologies, including intrusion detection system architecture and common intrusion detection methods. It also discusses event signatures, statistical analysis, and data mining methods. Finally, it introduces honeypot technologies.
Chapter 10 describes malicious software, such as viruses, worms, and Trojan horses, and introduces countermeasures. It also covers Web security and discusses mechanisms against denial of service attacks.
Since the publication of the first edition, a number of readers have kindly shared with us their personal experiences in dealing with network security attacks. Some of their stories, after minor editing, are included in the text and the exercise problems.
To get the most out of this book, readers are assumed to have taken undergraduate courses on discrete mathematics, algorithms, data communications, and network programming, or have equivalent preparations. For convenience, Chapter 3 includes a section reviewing basic concepts and results of number theory used in public-key cryptography. While it does not introduce socket programming, the book contains socket API client-server programming exercises. These exercises are designed for computer science and computer engineering students. Readers who do not wish to do them or simply do not have time to write code may skip them. Doing so would not affect much the learning of materials presented in the book.
Exercise problems for each chapter are divided into discussion problems and homework problems. There are six discussion problems in each chapter, designed to hep stimulate readers to think about the materials presented in that chapter at the conceptual level. These problems are intended to be discussed in class, with the instructor being the moderator. The homework problems are designed to have three levels of difficulty: regular, difficult (designated with *), and challenging (designated with **). This book contains a number of hands-on drills, presented as exercise problems. Readers are encouraged to try them all.
This book is intended to provide a concise and balanced treatment of network security with sufficient depth suitable for teaching a one-semester introductory course on network security. It was written on the basis of what the first author learned and experienced during the last 18 years from teaching these courses and on student feedback accumulated over the years. Powerpoint slides of these lectures can be found at http://www.cs.uml.edu/~wang/NetSec. Due to space limitations, some interesting topics and materials are not presented in this book. After all, one book can only accomplish one book's mission. We only hope that this book can achieve its objective. Of course, only you, the reader, can be the judge of it. We will be grateful if you will please offer your comments, suggestions, and corrections to us at wang@cs.uml.edu or kisselz@merrimack.edu.
We have benefited a great deal from numerous discussions over the last 20 years with our academic advisors, colleagues, teaching assistants, as well as current and former students. We are grateful to Sarah Agha, Stephen Bachelder, Yiqi Bai, William Baker, Samip Banker, David Bestor, Robert Betts, Ann Brady, Stephen Brinton, Jeff Brown, William Brown, Matthew Byrne, Robert Carbone, Jason Chan, Guanling Chen, Mark Conway, Michael Court, Andrew Cross, Daniel DaSilva, Paul Downing, Matthew Drozdz, Chunyan Du, Paul Duvall, Adam Elbirt, Zheng Fang, Daniel Finch, Jami Foran, Xinwen Fu, Anthony Gendreau, Weibo Gong, Edgar Goroza, Swati Gupta, Peter Hakewessell, Liwu Hao, Steve Homer, Qiang Hou, Marlon House, Bei Huang, Jared Karro, Christopher Kraft, Fanyu Kong, Lingfa Kong, Zaki Jaber, Ming Jia, Kimberly Johnson, Ken Kleiner, Minghui (Mark) Li, You (Stephanie) Li, Joseph Litman, Benyuan Liu, Yan...
