Table of Contents for
SSH, The Secure Shell: The Definitive Guide, 2nd Edition

Version ebook / Retour

Cover image for bash Cookbook, 2nd Edition SSH, The Secure Shell: The Definitive Guide, 2nd Edition by Robert G. Byrnes Published by O'Reilly Media, Inc., 2005
  1. Cover
  2. SSH, the Secure Shell, 2nd Edition
  3. Preface
  4. Protect Your Network with SSH
  5. Intended Audience
  6. Reading This Book
  7. Our Approach
  8. Which Chapters Are for You?
  9. Supported Platforms
  10. Disclaimers
  11. Conventions Used in This Book
  12. Comments and Questions
  13. Safari Enabled
  14. Acknowledgments
  15. 1. Introduction to SSH
  16. What Is SSH?
  17. What SSH Is Not
  18. The SSH Protocol
  19. Overview of SSH Features
  20. History of SSH
  21. Related Technologies
  22. Summary
  23. 2. Basic Client Use
  24. A Running Example
  25. Remote Terminal Sessions with ssh
  26. Adding Complexity to the Example
  27. Authentication by Cryptographic Key
  28. The SSH Agent
  29. Connecting Without a Password or Passphrase
  30. Miscellaneous Clients
  31. Summary
  32. 3. Inside SSH
  33. Overview of Features
  34. A Cryptography Primer
  35. The Architecture of an SSH System
  36. Inside SSH-2
  37. Inside SSH-1
  38. Implementation Issues
  39. SSH and File Transfers (scp and sftp)
  40. Algorithms Used by SSH
  41. Threats SSH Can Counter
  42. Threats SSH Doesn’t Prevent
  43. Threats Caused by SSH
  44. Summary
  45. 4. Installation and Compile-Time Configuration
  46. Overview
  47. Installing OpenSSH
  48. Installing Tectia
  49. Software Inventory
  50. Replacing r-Commands with SSH
  51. Summary
  52. 5. Serverwide Configuration
  53. Running the Server
  54. Server Configuration: An Overview
  55. Getting Ready: Initial Setup
  56. Authentication: Verifying Identities
  57. Access Control: Letting People In
  58. User Logins and Accounts
  59. Forwarding
  60. Subsystems
  61. Logging and Debugging
  62. Compatibility Between SSH-1 and SSH-2 Servers
  63. Summary
  64. 6. Key Management and Agents
  65. What Is an Identity?
  66. Creating an Identity
  67. SSH Agents
  68. Multiple Identities
  69. PGP Authentication in Tectia
  70. Tectia External Keys
  71. Summary
  72. 7. Advanced Client Use
  73. How to Configure Clients
  74. Precedence
  75. Introduction to Verbose Mode
  76. Client Configuration in Depth
  77. Secure Copy with scp
  78. Secure, Interactive Copy with sftp
  79. Summary
  80. 8. Per-Account Server Configuration
  81. Limits of This Technique
  82. Public-Key-Based Configuration
  83. Hostbased Access Control
  84. The User rc File
  85. Summary
  86. 9. Port Forwarding and X Forwarding
  87. What Is Forwarding?
  88. Port Forwarding
  89. Dynamic Port Forwarding
  90. X Forwarding
  91. Forwarding Security: TCP-Wrappers and libwrap
  92. Summary
  93. 10. A Recommended Setup
  94. The Basics
  95. Compile-Time Configuration
  96. Serverwide Configuration
  97. Per-Account Configuration
  98. Key Management
  99. Client Configuration
  100. Remote Home Directories (NFS, AFS)
  101. Summary
  102. 11. Case Studies
  103. Unattended SSH: Batch or cron Jobs
  104. FTP and SSH
  105. Pine, IMAP, and SSH
  106. Connecting Through a Gateway Host
  107. Scalable Authentication for SSH
  108. Tectia Extensions to Server Configuration Files
  109. Tectia Plugins
  110. 12. Troubleshooting and FAQ
  111. Debug Messages: Your First Line of Defense
  112. Problems and Solutions
  113. Other SSH Resources
  114. 13. Overview of Other Implementations
  115. Common Features
  116. Covered Products
  117. Other SSH Products
  118. 14. OpenSSH for Windows
  119. Installation
  120. Using the SSH Clients
  121. Setting Up the SSH Server
  122. Public-Key Authentication
  123. Troubleshooting
  124. Summary
  125. 15. OpenSSH for Macintosh
  126. Using the SSH Clients
  127. Using the OpenSSH Server
  128. 16. Tectia for Windows
  129. Obtaining and Installing
  130. Basic Client Use
  131. Key Management
  132. Accession Lite
  133. Advanced Client Use
  134. Port Forwarding
  135. Connector
  136. File Transfers
  137. Command-Line Programs
  138. Troubleshooting
  139. Server
  140. 17. SecureCRT and SecureFX for Windows
  141. Obtaining and Installing
  142. Basic Client Use
  143. Key Management
  144. Advanced Client Use
  145. Forwarding
  146. Command-Line Client Programs
  147. File Transfer
  148. Troubleshooting
  149. VShell
  150. Summary
  151. 18. PuTTY for Windows
  152. Obtaining and Installing
  153. Basic Client Use
  154. File Transfer
  155. Key Management
  156. Advanced Client Use
  157. Forwarding
  158. Summary
  159. A. OpenSSH 4.0 New Features
  160. Server Features: sshd
  161. Client Features: ssh, scp, and sftp
  162. ssh-keygen
  163. B. Tectia Manpage for sshregex
  164. Regex Syntax: Egrep Patterns
  165. Regex Syntax: ZSH_FILEGLOB (or Traditional) Patterns
  166. Character Sets for Egrep and ZSH_FILEGLOB
  167. Regex Syntax: SSH Patterns
  168. Authors
  169. See Also
  170. C. Tectia Module Names for Debugging
  172. D. SSH-1 Features of OpenSSH and Tectia
  173. OpenSSH Features
  174. Tectia Features
  175. E. SSH Quick Reference
  176. Legend
  177. sshd Options
  178. sshd Keywords
  179. ssh Options
  180. scp Options
  181. ssh and scp Keywords
  182. ssh-keygen Options
  183. ssh-agent Options
  184. ssh-add Options
  185. Identity and Authorization Files, OpenSSH
  186. Identity and Authorization Files, Tectia
  187. Environment Variables
  188. Index
  189. Index
  190. Index
  191. Index
  192. Index
  193. Index
  194. Index
  195. Index
  196. Index
  197. Index
  198. Index
  199. Index
  200. Index
  201. Index
  202. Index
  203. Index
  204. Index
  205. Index
  206. Index
  207. Index
  208. Index
  209. Index
  210. Index
  211. Index
  212. Index
  213. Index
  214. About the Authors
  215. Colophon
  216. Copyright

Inside SSH-1

With a solid understanding of the current SSH protocol behind us, we now quickly summarize SSH-1 in terms of its differences, weaknesses, and shortcomings in comparison with SSH-2:

Non-modular

SSH-1 is defined as a single monolithic protocol, rather than the modular approach taken with the SSH-2 suite.

Less negotiation

SSH-1 has more fixed parameters; in fact, only the bulk cipher is negotiated. The integrity algorithm, host key type, key-exchange methods, etc., are all fixed.

Ad hoc naming

SSH-1 lacks the well-defined naming syntax for SSH-2 entities which allows for smooth, implementation-specific extensions.

Single authentication

SSH-1’s user authentication process allows only one method to succeed; the server can’t require multiple methods.

RhostsRSA authentication

SSH-1’s RhostsRSA authentication, analogous to hostbased, is in principle limited to using a network address as the client host identifier. This limits its usefulness in the face of network issues such as NAT, proxying, mobile clients, etc.

Less flexible remote forwarding

SSH-1 remote forwarding specifies only a port, not a full socket, so can’t be bound to different addresses on multihomed servers, and the gatewayhosts option must be set globally for all remote forwardings rather than per port.

Weaker integrity checking

SSH-1 uses a weak integrity check, the CRC-32 algorithm. CRC-32 is not cryptographically strong, and its weakness is the basis of the Futoransky/Kargieman “insertion attack”; see http://seclists.org/lists/firewall-wizards/1998/Jun/0095.html.

Server keys

The fixed key exchange of SSH-1 employs an extra asymmetric key called the server key, not to be confused with a host key. [3.6.1] The server key is an ephemeral public/private key pair, regenerated once per hour and used to provide forward secrecy for the session key. Forward secrecy means that even if long-term secrets such as user or host private keys are compromised later, these can’t be used to decrypt SSH sessions recorded earlier; the use of an extra key which is never written to disk assures this. The Diffie-Hellman algorithm which is the basis of all the SSH-2 key exchanges provides forward secrecy by itself, and so an extra “server key” is not needed.

Weak key exchange

The SSH-1 key exchange is weak in that the client alone determines the session key, and simply sends it to the server. A Trojaned client can easily use weak keys to compromise all its sessions undetectably.