How to SSH Using Private Key Linux

Secure SHEEL, commonly known as SSH, is a popular open-source network protocol used to secure connections from a client to an SSH server. SSH allows remote control of the target host, port forwarding, executing commands, and files transfer.

SSH uses two types of methods to authenticate users; passwords and public-key authentication.

This guide will walk you through creating and initiating SSH connections using pubic/private keys. Using public-key authentication removes the need to enter a password every time you need to connect to a remote SSH host.

Step 1: Install OpenSSH

To create public and private SSH keys, we need to install the OpenSSH package. Use the default package manager.

For Debian/Ubuntu:

$ sudo apt-get install OpenSSH-client -y

For Arch/Manjaro:

On an Arch-based distribution, use the command:

$ sudo pacman -S openssh

REHL/CentOS:

On CentOS:

$ sudo yum install openssh-client

Step 2: Generate SSH keys

With OpenSSH packages installed, we can create public/private key pairs to authenticate SSH connections.

To generate a new key pair on your Linux machine, use the ssh-keygen command. This command will overwrite your old key pair and provision a new one.

Generate an RSA ssh key pair with 4096 bits using the command:

$ ssh-keygen -t rsa -b 4096

The command will prompt you for a file name. By default, the ssh key pairs are stored as id_rsa and id_rsa.pub for private key and public key, respectively.

$ Enter file in which to save the key (/home/ubuntu/.ssh/id_rsa):

To use the default filename, press ENTER and proceed.

In the next part, enter a passphrase to secure your key pairs. You can skip this by pressing ENTER.

$  Enter passphrase (empty for no passphrase):

$  Enter same passphrase again:

Executing this will complete your SSH key pair creation, and you can use it to log in to SSH.

Step 3: Copy Publick Key to Remote Host

To use the SSH key pair you created, we need to copy the public key to the remote server we wish to manage. Luckily, OpenSSH provides us with the ssh-copy-id command to do this.

Use the command:

$ ssh-copy-id remote_user@remote_ip

The command will prompt you to enter the SSH password. Once authenticated, the command appends the public key to the ~/.ssh/authorized_keys file.

Step 4: SSH using Private Key

Once you complete the above process, you should log in to the remote server using an SSH private key, i.e., not prompted for a password.

Use the command as:

$ ssh remote_user@remote_ip

And with that, you have successfully used SSH key-based authentication. You can add an extra layer of security by disabling password logins.

Conclusion

This guide has walked you through the basics of creating SSH key pairs and copying the keys to remote hosts. The above operations allow you to authenticate SSH sessions without a password. In addition, using a single key pair, you can manage multiple servers at once.

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