Creating public/private key authentication for SSH

If you use ssh to connect to the remote host, one way to ensure the security of the connection is the use of public/private SSH key, because password is not passed across the network and the system is resistant to attacks by “brute force”.

Create a public/private SSH key in Linux or Mac OS is very simple.

On the local machine

If needed create a .ssh directory in our home directory:

mkdir ~/.ssh

Create the SSH keys. Enter the command below and press enter, when asked for a pass phrase leave blank, since our purpose is to automate things:

ssh-keygen -t rsa

Or we can choose DSA (Digital Signing Algorithm) instead of RSA:

ssh-keygen -t dsa

There will be created two files in the .ssh directory: id_dsa and id_dsa.pub. The pub file has the public key and will be placed on the remote server.

Copy the id_dsa.pub file to the remote server via SCP:

scp ~/.ssh/id_dsa.pub username@example.com:/home/username/

On the remote server

Connect to the remote server with SSH:

ssh username@example.com

If needed create a .ssh directory in our home directory:

mkdir ~/.ssh

Copy the public key to the file authorized_keys:

cat id_dsa.pub >> ~/.ssh/authorized_keys

Remove file id_dsa.pub:

rm id_dsa.pub

Setting the correct permissions on the key:

chown -R username:username /home/username/.ssh
chmod 700 /home/username/.ssh
chmod 600 /home/username/.ssh/authorized_keys

Open the configuration file of SSH:

sudo nano /etc/ssh/sshd_config

And check this lines:

RSAAuthentication yes
PubkeyAuthentication yes
AuthorizedKeysFile %h/.ssh/authorized_keys
PasswordAuthentication no

Restart the server SSH:

sudo /etc/init.d/ssh reload

Done.

And now you can connect to the remote server with SSH:

ssh -i /path-to-private-key username@remote-host-ip-address

Or just this:

ssh username@remote-host-ip-address

If this article has helped you then please leave a comment

Thanks for reading!