Internet cryptography

Topics include:

• Essentials of cryptography
• Networking and Internet fundamentals
• Encryption building blocks
• Virtual private networks
• Legal considerations
• Setting realistic security objectives
• Secured electronic mail
• World Wide Web transaction security
• Internet Firewalls

Table of contents :
Preface ..... xv
Who this Book is For ..... xv
How this Book is Organized ..... xvi
Crypto Today and Tomorrow ..... xviii
Comments and Questions ..... xviii
Acknowledgments ..... xix
Chapter 1 Introduction ..... 1
1.1 The Basic Problem ..... 1
1.2 Essentials of Crypto ..... 4
1.2.1 Crypto is Hard to Use ..... 6
1.2.2 Balancing Crypto Use with Your Objectives ..... 7
1.3 Essentials of Networking and the Internet ..... 8
1.3.1 Protocol Layers and Network Products ..... 9
1.3.2 Internet Technology ..... 12
1.3.3 Internet Protocols in Your Host ..... 14
1.3.4 The Internet Security Problem ..... 16
1.3.5 An Internet Rogue's Gallery ..... 19
1.4 Setting Realistic Security Objectives ..... 20
1.5 Appropriate Communications Security ..... 22
1.5.1 Communications Security Goals ..... 23
1.5.2 Internet Crypto Techniques ..... 25
1.6 Legal Restrictions ..... 27
1.7 For Further Information ..... 30
Chapter 2 Encryption Basics ..... 33
2.1 Encryption Building Blocks ..... 33
2.1.1 Stream Ciphers ..... 34
2.1.2 Block Ciphers ..... 36
2.2 How Crypto Systems Fail ..... 42
2.2.1 Cryptanalysis and Modern Codes ..... 44
2.2.2 Brute Force Cracking of Secret Keys ..... 46
2.2.3 Attacks on Improper Crypto Use ..... 50
2.3 Choosing Between Strong and Weak Crypto ..... 51
2.3.1 Properties of Good Crypto Algorithms ..... 52
2.3.2 Crypto Algorithms to Consider ..... 55
2.3.3 Selecting a Block Cipher Mode ..... 57
2.3.4 Identifying a Safe Key Length ..... 58
2.3.5 Levels of Risk for Different Applications ..... 60
2.4 For Further Information ..... 62
Chapter 3 Link Encryption ..... 63
3.1 Security Objectives ..... 63
3.2 Product Example: In-line Encryptor ..... 65
3.2.1 Red/Black Separation ..... 66
3.2.2 Crypto Algorithm and ..... 67
3.2.3 Encryptor Vulnerabilities ..... 68
3.2.4 Product Security Requirements ..... 71
3.3 Deployment Example: Point-to-Point Encryption ..... 72
3.3.1 Point-to-Point Practical Limitations ..... 73
3.3.2 Physical Protection and Control ..... 74
3.3.3 Deployment Security Requirements ..... 75
3.4 Deployment Example: IP-routed Configuration ..... 76
3.4.1 Site Protection ..... 77
3.4.2 Networkwide Security ..... 78
3.4.3 Deployment Security Requirements ..... 81
3.5 Key Recovery and Escrowed Encryption ..... 82
3.6 For Further Information ..... 85
Chapter 4 Managing Secret Keys ..... 87
4.1 Security Objectives ..... 87
4.2 Basic Issues in Secret Key Management ..... 88
4.3 Technology: Random Key Generation ..... 89
4.3.1 Random Seeding ..... 90
4.3.2 Pseudorandom Number Generators ..... 92
4.3.3 Technical Security Requirements ..... 95
4.4 Deployment Example: Manual Key Distribution ..... 95
4.4.1 Preparing Secret Keys for Delivery ..... 96
4.4.2 Batch Generation of Keys ..... 98
4.4.3 Printing Keys on Paper ..... 102
4.4.4 Key Packaging and Delivery ..... 103
4.4.5 Key Splitting for Safer Delivery ..... 104
4.4.6 Deployment Security Requirements ..... 106
4.5 Technology: Automatic Rekeying ..... 107
4.5.1 ANSI X9.17 Point-to-Point Rekeying ..... 108
4.5.2 Variations of X9.17 ..... 110
4.5.3 Technical Security Requirements ..... 112
4.6 Key Distribution Centers (KDCs) ..... 113
4.7 Maintaining Keys and System Security ..... 116
4.8 For Further Information ..... 117
Chapter 5 Security at the IP Layer ..... 119
5.1 Security Objectives ..... 119
5.2 Basic Issues with Using IPSEC ..... 120
5.3 Technology: Cryptographic Checksums ..... 121
5.3.1 One-way Hash Functions ..... 123
5.3.2 Technical Security Requirements ..... 126
5.4 IPSEC: IP Security Protocol ..... 127
5.4.1 IPSEC Authentication ..... 130
5.4.2 IPSEC Encryption ..... 131
5.5 IPSEC Key Management ..... 134
5.6 Other TCP/IP Network Security Protocols ..... 137
5.7 For Further Information ..... 139
Chapter 6 Virtual Private Networks ..... 141
6.1 Security Objectives ..... 142
6.2 Basic Issues with VPNs ..... 142
6.3 Technology: IPSEC Proxy Cryptography ..... 143
6.3.1 ESP Tunnel Mode ..... 145
6.3.2 ESP Transport Mode ..... 147
6.4 Product Example: IPSEC Encrypting Router ..... 148
6.4.1 Blocking Classic Internet Attacks ..... 149
6.4.2 Product Security Requirements ..... 151
6.5 Deployment Example: Site-to-Site Encryption ..... 153
6.5.1 Header Usage and Security ..... 156
6.5.2 Deployment Security Requirements ..... 159
6.6 For Further Information ..... 159
Chapter 7 Remote Access with IPSEC ..... 161
7.1 Security Objectives ..... 161
7.2 Basic Issues with IPSEC Clients ..... 162
7.3 Product Example: IPSEC Client ..... 163
7.3.1 Client Security Associations ..... 165
7.3.2 Client Self-Defense on the Internet ..... 166
7.3.3 Client Theft and Key Protection ..... 167
7.3.4 Product Security Requirements ..... 169
7.4 Deployment Example: Client-to-Server Site Access ..... 171
7.4.1 Remote Access Security Issues ..... 172
7.4.2 Deployment Security Requirements ..... 175
7.5 For Further Information ..... 176
Chapter 8 IPSEC and Firewalls ..... 177
8.1 Security Objectives ..... 177
8.2 Basic Issues with IPSEC and Firewalls ..... 178
8.3 Internet Firewalls ..... 179
8.3.1 What Firewalls Control ..... 180
8.3.2 How Firewalls Control Access ..... 181
8.3.3 Firewall Control Mechanisms ..... 183
8.4 Product Example: IPSEC Firewall ..... 187
8.4.1 Administering Multiple Sites ..... 189
8.4.2 Product Security Requirements ..... 190
8.5 Deployment Example: A VPN with a Firewall ..... 191
8.5.1 Establishing a Site Security Policy ..... 192
8.5.2 Chosen Plaintext Attack on a Firewall ..... 193
8.5.3 Deployment Security Requirements ..... 195
8.6 For Further Information ..... 195
Chapter 9 Public Key Crypto and SSL ..... 197
9.1 Public Key Cryptography ..... 197
9.1.1 Evolution of Public Key Crypto ..... 199
9.1.2 Diffie-Hellman Public Key Technique 200
9.2.1 Brute Force Attacks on RSA ..... 205
9.2.2 Other RSA Vulnerabilities ..... 208
9.2.3 Technical Security Requirements ..... 211
9.3 Technology: Secret Key Exchange with RSA Crypto ..... 212
9.3.1 Attacking Public Key Distribution ..... 213
9.3.2 Public Key versus Secret Key Exchange ..... 215
9.3.3 Technical Security Requirements ..... 218
9.4 Secure Sockets Layer ..... 218
9.4.1 Other SSL Properties ..... 222
9.4.2 Basic Attacks Against SSL ..... 223
9.4.3 SSL Security Evolution ..... 226
9.5 For Further Information ..... 228
Chapter 10 World Wide Web Transaction Security ..... 229
10.1 Security Objectives ..... 229
10.2 Basic Issues in Internet Transaction Security ..... 230
10.3 Transactions on the World Wide Web ..... 232
10.3.1 Transactions with Web Forms ..... 233
10.3.2 Web Form Security Services ..... 235
10.4 Security Alternatives for Web Forms ..... 236
10.4.1 Password Protection ..... 237
10.4.2 Network-level Security (IPSEC) ..... 237
10.4.3 Transport-level Security (SSL) ..... 238
10.4.4 Application-level Security (SHTTP) ..... 239
10.4.5 Client Authentication Alternatives ..... 240
10.5 Product Example: Web Browser with SSL ..... 242
10.5.1 Browser Cryptographic Services ..... 244
10.5.2 Authentication Capabilities ..... 245
10.5.3 Client Security and Executable Contents ..... 247
10.5.4 Product Security Requirements ..... 250
10.6 Product Example: Web Server with SSL ..... 252
10.6.1 Web Server Vulnerabilities ..... 253
10.6.2 Mandatory Protection ..... 257
10.6.3 Product Security Requirements ..... 258
10.7 Deployment Example: Vending with Exportable Encryption ..... 259
10.7.1 Export Restrictions and Transaction Security ..... 261
10.7.2 Site Configuration ..... 262
10.7.3 Deployment Security Requirements ..... 264
10.8 For Further Information ..... 266
Chapter 11 Secured Electronic Mail ..... 267
11.1 Security Objectives ..... 267
11.2 Basic Issues with E-Mail Security ..... 268
11.3 Basics of Internet Electronic Mail ..... 269
11.3.1 Internet E-Mail Software Architecture ..... 271
11.3.2 E-Mail Security Problems ..... 272
11.4 Technology: Off-line Message Keying ..... 275
11.4.1 Encryption Tokens ..... 276
11.4.2 Technical Security Requirements ..... 277
11.5 Technology: Digital Signatures ..... 278
11.5.1 Attacks on Digital Signatures ..... 280
11.5.2 The Digital Signature Standard ..... 284
11.5.3 Technical Security Requirements ..... 286
11.6 Product Example: Secure E-Mail Client ..... 287
11.6.1 Basic Secure Client Features ..... 288
11.6.2 E-Mail Client Security Issues ..... 290
11.6.3 Product Security Requirements ..... 292
11.7 E-Mail Deployment ..... 293
11.8 For Further Information ..... 294
Chapter 12 Public Key Certificates ..... 295
12.1 Security Objectives ..... 295
12.2 Distributing Public Keys ..... 296
12.3 Technology: Public Key Certificates ..... 299
12.3.1 Generating Public Key Pairs ..... 301
12.3.2 Certificate Revocation ..... 302
12.3.3 Certification Authority Workstation ..... 303
12.3.4 Technical Security Requirements ..... 305
12.4 Certificate Distribution ..... 306
12.4.1 Transparent Distribution ..... 307
12.4.2 Interactive Distribution ..... 308
12.5 Centralized Certification Authority ..... 310
12.5.1 Netscape Server Authentication ..... 311
12.5.2 Handling Multiple Certification Authorities ..... 312
12.6 Hierarchical Certification Authority ..... 313
12.6.1 PEM Internet Certification Hierarchy ..... 314
12.6.2 Private Trees ..... 316
12.7 PGP "Web of Trust" ..... 316
12.8 For Further Information ..... 319
Appendix A: Glossary ..... 321
Appendix B: Bibliography ..... 341
Index