This guide describes how to generate and use a private/public key pair to log in to a remote system with SSH using PuTTY. PuTTY is an SSH client that is available for Windows and Linux (although it is more common on Windows systems). Using key-based SSH logins, you can disable the normal username/password login procedure which means that only people with a valid private/public key pair can log in. That way, there is no way for brute-force attacks to be successful, so your system is more secure.
I do not issue any guarantee that this will work for you!
1 Preliminary Note
In this tutorial I use a Windows desktop to connect to a Linux SSH server (Debian Sarge, IP address: 192.168.0.100).
2 Install PuTTY, PuTTYgen, And Pageant On The Windows System
First we need to install PuTTY, PuTTYgen, and Pageant on our Windows system. All we need to do is download the executable files (.exe) and save them somewhere, e.g. on the desktop. We don’t need to install them as they are standalone applications. To start them, we only need to double-click them.
Download the following files from the PuTTY download page and save them on your Windows system, e.g. on the desktop:
http://the.earth.li/~sgtatham/putty/latest/x86/putty-0.63-installer.exe
http://the.earth.li/~sgtatham/putty/latest/x86/puttygen.exe
http://the.earth.li/~sgtatham/putty/latest/x86/pageant.exe
3 Create A Profile With Settings For Our 192.168.0.100 Server
In PuTTY, you can create profiles for connections to your various SSH servers, so you don’t have to type in the settings again when you want to connect to a certain server again.
Let’s create a profile for our 192.168.0.100 server. Start PuTTY by double-clicking its executable file. You are now in the category Session (see the tree on the left side of the screenshot). Enter 192.168.0.100 under Host Name (or IP address), enter 22 under Port and select SSH under Protocol:
Then go to Connection -> Data and specify the username with that you want to log in to your SSH server under Auto-login username. In this article I use root:
Then go to Session again. Under Saved Sessions enter a name for the profile, e.g. 192.168.0.100 or any other string that lets you remember for which server the profile is. Then click on Save:
The next time you use PuTTY, you can simply select the appropriate profile from the Saved Sessions text area, click on Load and then Open.
Now we can connect to our SSH server simply by clicking on Open.
If you connect to the server for the first time, a security warning pops up. This is because PuTTY doesn’t know the server’s host key yet, so it is safe to click on Yes. (If this happens again later on, this can mean that another server is now running under the same IP address, or that someone has broken in and changed the key.)
We have saved the username with which we connect in our profile settings, so we don’t have to type it here again. We only have to specify that user’s password
Now this was the “normal” way of logging in, i.e., with a username and a password. If anyone else knows the username and password, he can log in, too. So if you have weak passwords and/or are the victim of a brute-fore attack, this can become a problem. Let’s change that now.
