How to use SSH with RSA keys: (Hisham Mardam Bey || CodeWarrior || hisham@hisham.cc)
=============================

So you ssh to several machines everyday, and you always get those
annoying password promtps. You hate them, dont you? Well, I do too.
And frankly I'd rather live without them. Thanks to RSA heys and
ssh-agent we can live without having to memorize and enter a million
passwords everytime a simple ssh session is required. So, the main
idea here is that you have a private and a public key. Those keys will
identify you and your machine on the remote machines. You private key
is very important, an must be kept at the highest security level
possible. The public key is "given" to the remote machine so you can
simply handshake with it and login without suuplying a password. This
public key can be used on all the machines which you need to log into
at one point or another.

This whole process starts by firstly generating a pair of public and
private keys. This is accomplished by the following:


[hisham@guardian hisham]$ ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/hisham/.ssh/id_rsa): Enter
passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/hisham/.ssh/id_rsa.
Your public key has been saved in /home/hisham/.ssh/id_rsa.pub.
The key fingerprint is:
40:75:20:91:40:48:e2:91:2d:7d:ab:6d:ea:94:95:b0 hisham@guardian
[hisham@guardian hisham]$


Having done that, we just generated a pair of public and private keys.
I cant stress this enough, gaurd them well. They represent you and
your machine. Right, now its time to get those keys into gear. The
first thing we need to do is copy the public key over to the correct
location on the remote server. That allows us to automatically get identified to the
opposite machine we want to ssh or scp to. We'll copy it over using
scp like this:


[hisham@guardian hisham]$ scp ~/.ssh/id_rsa.pub hisham@hisham.cc:~/
id_rsa.pub         100% |************************|   225       00:00
[hisham@guardian hisham]$


Now that we have out public RSA key on the server, we should add it to 
the list of authorized keys, so we can use it. First ssh to the remote 
server, then:


[hisham@guardian hisham]$ cat id_rsa.pub >> ~/.ssh/authorized_keys


This will append the key to that file, allowing us to use it 
properly.At this point, we are basically done. All we need to do know 
is run ssh-agent and ssh-add to login remotely without being asked for 
a password. Basically, ssh-agent acts as a gaurd that will 
"automatically give" the password to the key once needed. So, anything 
that is to use the key without needing the password must be run 
"under" or "within" ssh-agent. The best bet to do this is:


[hisham@guardian hisham]$ ssh-agent bash
[hisham@guardian hisham]$


This basically puts us in a shell, which is entirely managed by
ssh-agent. Hence, anything run in there will automatically be able to
make use of the RSA key. The final step now is to add the password for
that key, since we specified one when we created the key.


[hisham@guardian hisham]$ ssh-add
Enter passphrase for /home/hisham/.ssh/identity:
[hisham@guardian hisham]$


Now you should be able to ssh or scp to the remote server directly without
typing a password.