SSH Secure Shell is a network protocol, its primary purpose is to allow you to securely connect to a remote system over a network. Using SSH you can connect to the remote system using username and password based authentication or using a key-based authentication. In this tutorial, you will learn to setup key-based authentication on a Linux based system.

Why use key-based authentication, what are the advantages?

Public key authentication is more secure than password-based authentication Make it difficult for hackers to break into your system due to a weak password Another layer of security is available by adding a passphrase, as it can be left out blank Forcing key authentication allows you to disable password authentication which in effect prevents brute force attacks

Steps to setup key-based authentication on a Linux computer

1. Generate SSH Key Pair on the client machine

On the client machine run the following commands to generate SSH keys:
cd ~/.ssh
ssh-keygen -t rsa

When asked for passphrase, leave it blank or enter your desired passphrase. Having a passphrase makes automation difficult for some of the processes. Output of the above command will look something like the following:

2. On server machine create an SSH folder

mkdir -p ~/.ssh/

3. Copy public key file from client to the server machine

Run the following command on the client machine to secure copy id_rsa.pub file to the remote machine:
scp -P "ssh-port" ~/.ssh/id_dsa.pub username@serverip-address:~/.ssh

4. On server machine append public key to authorized keys file

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

5. On server machine change authorized keys file permissions

chmod 700 .sshchmod 600 .ssh/authorized_keysrm .ssh/id_rsa.pub

6. Successfully done, test your result

On the client machine run the following command to verify correctly logging onto server machine using private SSH key:
ssh -P "ssh-port" username@serverip-address

References

https://devops.profitbricks.com/tutorials/secure-the-ssh-server-on-ubuntu/

https://www.ssh.com/manuals/server-zos-product/55/ch06s02s02.html

https://debian-administration.org/article/530/SSH_with_authentication_key_instead_of_password