—Create the RSA Key Pair
The first step is to create the key pair on the client machine (there is a good chance that this will just be your computer):
# ssh-keygen -t rsa
—Store the Keys and Passphrase
Once you have entered the Gen Key command, you will get a few more questions:
Enter file in which to save the key (/home/demo/.ssh/id_rsa):
You can press enter here, saving the file to the user home (in this case, my example user is called demo).
Enter passphrase (empty for no passphrase):
Use it or leave it empty.
The entire key generation process looks like this:
ssh-keygen -t rsa
Generating public/private rsa key pair.
Enter file in which to save the key (/home/demo/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/demo/.ssh/id_rsa.
Your public key has been saved in /home/demo/.ssh/id_rsa.pub.
The key fingerprint is:
4a:dd:0a:c6:35:4e:3f:ed:27:38:8c:74:44:4d:93:67 demo@a
The key's randomart image is:
+--[ RSA 2048]----+
| .oo. |
| . o.E |
| + . o |
| . = = . |
| = S = . |
| o + = + |
| . o + o . |
| . o |
| |
+-----------------+
The public key is now located in /home/demo/.ssh/id_rsa.pub The private key (identification) is now located in /home/demo/.ssh/id_rsa
—Copy the Public Key
Once the key pair is generated, it's time to place the public key on the virtual server that we want to use.
You can copy the public key into the new machine's authorized_keys file with the ssh-copy-id command. Make sure to replace the example username and IP address below.
# ssh-copy-id user@123.45.56.78
Alternatively, you can paste in the keys using SSH:
# cat ~/.ssh/id_rsa.pub | ssh user@123.45.56.78 "mkdir -p ~/.ssh && cat >> ~/.ssh/authorized_keys"
No matter which command you chose, you should see something like:
The authenticity of host '12.34.56.78 (12.34.56.78)' can't be established.
RSA key fingerprint is b1:2d:33:67:ce:35:4d:5f:f3:a8:cd:c0:c4:48:86:12.
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '12.34.56.78' (RSA) to the list of known hosts.
user@12.34.56.78's password:
Now try logging into the machine, with "ssh 'user@12.34.56.78'", and check in:
~/.ssh/authorized_keys
to make sure we haven't added extra keys that you weren't expecting.
Now you can go ahead and log into user@12.34.56.78 and you will not be prompted for a password. However, if you set a passphrase, you will be asked to enter the passphrase at that time (and whenever else you log in in the future).
—Disable the Password for Root Login
Once you have copied your SSH keys unto your server and ensured that you can log in with the SSH keys alone, you can go ahead and restrict the root login to only be permitted via SSH keys.
In order to do this, open up the SSH config file:
sudo nano /etc/ssh/sshd_config
Within that file, find the line that includes PermitRootLogin and modify it to ensure that users can only connect with their SSH key:
PermitRootLogin without-password
Put the changes into effect:
reload ssh