Eleven SSH Tricks
If you connect from one server to another using public key authentication, you don't need to run an authentication agent on both. SSH automatically can pass any authentication requests coming from other servers, back to the agent running on your own computer. This way, it never passes your secret key to the remote computer; rather, it performs authentication on your computer and sends the results back to the remote computer.
To set up authentication agent forwarding, simply run ssh -A or add the following line to your config file:
You should use authentication agent forwarding only if you trust the administrators of the remote computer; you risk them using your keys as if they were you. Otherwise, it is quite secure.
Many people carry a floppy with PuTTY or another Windows SSH program, in case they need to use an unsecured computer while traveling. This method works if you have the ability to run programs from the floppy drive. You also can download PuTTY from the web site and run it.
Another alternative is putting an SSH Java applet on a web page that you can use from a browser. An excellent Java SSH client is Mindterm, which is free for noncommercial use. You can find it at www.appgate.com/mindterm.
An SSH configuration can go wrong in a few places if you are using these various tricks. You can catch many problems by using ssh -v and watching the output. Of course, none of these tricks is essential to using SSH. Eventually, though, you may encounter situations where you're glad you know them. So give a few of them a try.
Daniel R. Allen (email@example.com) discovered UNIX courtesy of a 1,200-baud modem, a free local dial-up and a guest account at MIT, back when those things existed. He has been an enthusiastic Linux user since 1995. He is president of Prescient Code Solutions, a software consulting company in Kitchener, Ontario and Ithaca, New York.
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