Linux Server Security, Second Edition

This is the Title of the Book, eMatter Edition

Copyright © 2007 O’Reilly & Associates, Inc. All rights reserved.

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Chapter 4: Secure Remote Administration

I keep saying ssh is more secure than Telnet, but how? Nothing after the ssh login

seems different from Telnet. You may be asked whether to accept the remote server’s

public key, it may in general take a little longer for the session to get started, and

depending on network conditions, server load, etc., the session may seem slightly

slower than Telnet; but for the most part, you won’t notice much difference.

But remember that before ssh even prompts you for a password or passphrase, it has

already transparently negotiated an encrypted session with the remote server. When

I do type my username and password, it will be sent over the network through this

encrypted session, not in cleartext as with Telnet. Furthermore, all subsequent shell-

session data will be encrypted as well. I can do whatever I need to do, including

su -,

without worrying about eavesdroppers. And all it costs me is a little bit of latency!

Using sftp and scp for Encrypted File Transfers

With Version 2.0 of SSH, Tatu Ylönen introduced a new feature: sftp. Server-side

support for sftp is built into sshd. In other words, it’s hardcoded to invoke the sftp-

server process when needed; it isn’t necessary for you to configure anything or add

any startup scripts. You don’t even