Setting up ssh keys

gistfile1.html

<h3>Generating the keys</h3>

<p>Generating the key isn't difficult.</p>

<code>
[root@server1 ~]# <b>ssh-keygen</b>
Generating public/private rsa key pair.
Enter file in which to save the key (/root/.ssh/id_rsa): <b>test_key</b>
Enter passphrase (empty for no passphrase): <b>my passphrase</b>
Enter same passphrase again:<b>my passphrase</b>
Your identification has been saved in test_key.
Your public key has been saved in test_key.pub.
The key fingerprint is:
54:ae:59:31:8c:fc:64:a2:70:4a:03:21:6d:39:66:82 root@xen1
[root@server1 ~]#
</code>

<p> I recommend using a passphrase to secure the key unless you are pretty sure you know what you are doing. 
Since without a passphrase the owner of the private half of the key is able to login to any server you 
install the public key to without any passwords.</p>

<h3>Installing the keys on a server</h3>

<p>Installing the keys to the server is fairly easy.</p>

<p><b>EDIT: or just use ssh-copy-id -i test_key [email protected]</b></p>


<code>
[root@xen1 ~]# <b>scp test_key.pub [email protected]:/root/</b>
[email protected]'s password: <b>password</b>
test_key.pub                                  100%  391     0.4KB/s   00:00
[root@xen1 ~]# <b>ssh [email protected]</b>
[email protected]'s password: <b>password</b>

Linux debian 2.6.26-2-686 #1 SMP Mon May 11 19:00:59 UTC 2009 i686

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.

debian:~# <b>cat test_key.pub >> ~/.ssh/authorized_keys</b>
-bash: /root/.ssh/authorized_keys: No such file or directory
debian:~# <b>ls -l</b>
total 4
-rw-r--r-- 1 root root 391 2009-05-20 17:47 test_key.pub
debian:~# <b>mkdir .ssh</b>
debian:~# <b>chmod 700 .ssh</b>
debian:~# <b>cat test_key.pub >> ~/.ssh/authorized_keys</b>
</code>

<p>This was a virgin debian system and the .ssh directory didn't exist, because of this we failed to copy our key into the required file initially.</p>
<p> The key is only installed for a single user, if you want to be able to login with multiple users with a key you need to install it for each user.</p>

<h3>Testing and using the keys</h3>

<p>Testing and using the key is very simple</p>
<code>
[root@xen1 ~]# <b>ssh -i test_key [email protected]</b>
Linux debian 2.6.26-2-686 #1 SMP Mon May 11 19:00:59 UTC 2009 i686

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.
Last login: Wed May 20 17:48:15 2009 from xen1.local
debian:~#
</code>

<p>If there was a passphrase on this key, you would have been prompted for it as a second step before logging you in.</p>

<p>Without a passphrase you can do interesting things such as</p>

<code>
[root@xen1 ~]# <b>ssh -i test_key [email protected] df -h</b>
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/VolGroup00-lennyroot
                       19G  3.1G   16G  17% /
tmpfs                 245M     0  245M   0% /lib/init/rw
udev                   10M  148K  9.9M   2% /dev
tmpfs                 245M     0  245M   0% /dev/shm
/dev/md0               99M   23M   72M  24% /boot
192.168.20.250:/mnt/download
                      939G  932G  6.6G 100% /mnt/download
/dev/sdc1             2.0G  232M  1.7G  12% /media/EXTERNAL
[root@xen1 ~]#
</code>