How to Setup SSH with Public Key Authentication on Ubuntu 14.04

This blog will let you know how to set up an SSH server with public-key authorization  SSH is a great tool to control Linux-based computers remotely.

Installing SSH On The Server

First Step:

First of all we need to install the SSH on our server. To achieve this write the following command: (Note: Login with root)

apt-get install ssh

Preparations On Our Client (Desktop) System

Second Step:

Desktop machine need to be prepare to connect the server. So, the SSH-server has been installed on a different machine.  We will install ssh client to your desktop machine. Then install the client:

apt-get install openssh-client

Switch back to your normal user (not root, respectively). Then type these commands in order:

mkdir ~/.ssh
chmod 700 ~/.ssh
cd ~/.ssh

Private-key and public-key pairs need to be generated first. Public-key will be uploaded to the server and private-key will be used to log in to the server. When it will ask to enter passphrase then enter it for security purpose so don't forget your passphrase.

ssh-keygen -t rsa -C "A comment..."

Then we copy the public key (which we've generated just before) to our (remote) server. The remoteuser should not be root! Choose the default non-root user as remoteuser. (Note the colon at the end of the line! It's important.)

scp -p id_rsa.pub remoteuser@remotehost:

Then we log in with SSH, and we copy the public key to its right place:

ssh remoteuser@remotehost
mkdir ~/.ssh
chmod 700 ~/.ssh
cat id_rsa.pub >> ~/.ssh/authorized_keys
chmod 600 ~/.ssh/authorized_keys
mv id_rsa.pub ~/.ssh
logout

SSH client will not allow to login to the server so we need to delete the public key on the desktop. Type this command to do so:

rm id_rsa.pub

And then we log back:

ssh remoteuser@remotehost

Disabling Password Authentication

cd /etc/ssh
cp sshd_config sshd_config.orig
nano sshd_config

Now change these lines from the nano text-editor on the screen, open it with the main SSH configuration file.

PermitRootLogin		yes
PasswordAuthentication	yes
UsePAM			yes

To these:

PermitRootLogin		no
PasswordAuthentication	no
UsePAM			no

Then save the file with Ctrl + O , and restart the SSH server:

/etc/init.d/ssh restart

Note: You will not be able to login if you disable the password authentication!

Thanks for reading the blog.