A comprehensive study of what is now a key part of many network systems, SSH, The Secure Shell is a valuable resource for system administrators and users. Its explanations are clear and thorough: I'm not sure about the "definitive" claim, but Barrett and Silverman do go into considerable detail, often to the limits of "if you want to play with this you really ought to look at the source code". Perhaps most importantly, The Secure Shell is organised so one can easily skip unwanted detail and find just those portions that are relevant. As a result, it can be used in different ways — read through to learn about ssh and what it can be used for, or just consulted as necessary to answer particular questions or solve particular problems.

Chapter one puts ssh in context, looking at its history and related technologies, and chapter two introduces basic client operation. Anyone who uses ssh and scp as simple telnet and ftp replacements and isn't curious about how they work can stop reading here — and doesn't really need their own copy of The Secure Shell. Chapter three is an "under the covers" look at ssh. After a three page introduction to cryptography (not really suitable for the reader with absolutely no background), it explains the ssh1 protocol and then how ssh2 differs from that and the extra features it offers. There is also a brief overview of the cryptographic algorithms commonly used in ssh implementations, and an explanation what ssh secures and what it doesn't.

The rest of the book is more implementation-specific: the primary implementations covered are SSH, SSH2, and OpenSSH. Being a lazy user of packages, I skipped chapter four, on installation and compile-time configuration. Chapter five is a guide to server configuration, working systematically through the sshd configuration file options.

The next four chapters are aimed at power users, covering client use in much greater depth. Chapter six explains key management: what identities are, how to create them, how to manage them with ssh agents, and how they can be used (to automate logons, most obviously, but fancy things can be done with multiple identities). Chapter seven goes through client configuration in detail, working through the configuration file options, chapter eight covers account configuration on the server-side (including forced commands), and chapter nine looks at port and X11 forwarding.

For those overwhelmed by all of this, chapter ten describes a sample "recommended setup" for everything from compilation to client configuration. Chapter eleven covers some special topics — unattended SSH, FTP forwarding, mail over SSH, Kerberos, using SSH through a gateway host — and chapter twelve is a troubleshooting FAQ.

Chapter thirteen is an overview of other implementations, with a table of products, and four short chapters then cover specific Windows and Mac clients. Of the three Windows clients covered here, two are proprietary and the third is only distributed as a bzipped tar file: it would have been good to have a chapter on one of the free and more user-friendly Windows clients, perhaps PuTTY or TTSSH, both of which get a "recommended" tag in the table of products.

Note: a 2nd edition of SSH, The Secure Shell is now available.

May 2002

External links:

- buy from Amazon.com or Amazon.co.uk
- details at O'Reilly & Associates

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- Daniel J. Barrett - MediaWiki: Wikipedia and Beyond
- Daniel J. Barrett - Bandits on the Information Superhighway
- books about computing
- books published by O'Reilly & Associates