After creating the private and public key and copying the latter on your Ubuntu 18.04 server, go ahead and disable SSH password authentication. This will make sure that no-one can log on to the server using a username and a password combination. How to Generate and Manage GPG Keys on Ubuntu 18.04 16.04. When you’re ready to get GPG working on Ubuntu, follow the steps below: Step 1: Install GnuPG. GnuPG is a free software implementation of the OpenPGP standard that allows you to encrypt and sign your data and communications using GPG encryptions.

1. How To Ssh Into Ubuntu 18.04
2. Ubuntu 18.04 Allow Ssh

I am a new Ubuntu 18.04 LTS user and I would like to setup ssh public key authentication. How do I set up ssh keys based authentication on Ubuntu Linux 18.04 LTS server? How do I set up SSH keys on an Ubuntu Linux 18.04 LTS server? In Ubuntu 18.04 LTS, how do I set up public key authentication?
Introduction: OpenSSH is a free and open source client/server technology for secure remote login. It is an implementation of the SSH protocol. OpenSSH divided into sshd (server) and various client tools such as sftp, scp, ssh and more. One can do remote login with OpenSSH either using password or combination of private and public keys named as public key based authentication. It is an alternative security method for user passwords. This method is recommended on a VPS, cloud, dedicated or even home-based server or laptop. This page shows how to set up SSH keys on Ubuntu 18.04 LTS server.

Ubuntu 18.04 Setup SSH Public Key Authentication

The procedure to set up secure ssh keys on Ubuntu 18.04:

1. Create the key pair using ssh-keygen command.
2. Copy and install the public key using ssh-copy-id command.
3. Add yourself to sudo admin account on Ubuntu 18.04 server.
4. Disable the password login for root account on Ubuntu 18.04.

Sample set up for SSH Keys on Ubuntu 18.04

Where,

• 202.54.1.55 – You store your public key on the remote hosts and you have an accounts on this Ubuntu Linux 18.04 LTS server.
• Linux/macbook laptop – Your private key stays on the desktop/laptop/computer (or local server) you use to connect to 202.54.1.55 server. Do not share or give your private file to anyone.

In public key based method you can log into remote hosts and server, and transfer files to them, without using your account passwords. Feel free to replace 202.54.1.55 and client names with your actual setup. Enough talk, let’s set up public key authentication on Ubuntu Linux 18.04 LTS.

How to create the RSA/ed25519 key pair on your local desktop/laptop

Open the Terminal and type following commands if .ssh directory does not exists:
$ mkdir -p $HOME/.ssh
$ chmod 0700 $HOME/.ssh
Next generate a key pair for the protocol, run:
$ ssh-keygen
OR
$ ssh-keygen -t rsa 4096 -C 'My key for Linode server'
These days ED25519 keys are favored over RSA keys when backward compatibility is not needed:
$ ssh-keygen -t ed25519 -C 'My key for Linux server # 42'

How to install the public key in Ubuntu 18.04 remote server

The syntax is as follows:
ssh-copy-id your-user-name@your-ubuntu-server-name
ssh-copy-id -i ~/.ssh/file.pub your-user-name@your-ubuntu-server-name
For example:
## for RSA KEY ##
ssh-copy-id -i $HOME/.ssh/id_rsa.pub user@202.54.1.55
## for ED25519 KEY ##
ssh-copy-id -i $HOME/.ssh/id_ed25519.pub user@202.54.1.55
## install SSH KEY for root user ##
ssh-copy-id -i $HOME/.ssh/id_ed25519.pub root@202.54.1.55

I am going to install ssh key for a user named vivek (type command on your laptop/desktop where you generated RSA/ed25519 keys):
$ ssh-copy-id -i ~/.ssh/id_ed25519.pub vivek@202.54.1.55

Test it

Now try logging into the Ubuntu 18.04 LTS server, with ssh command from your client computer/laptop using ssh keys:
$ ssh your-user@your-server-name-here
$ ssh vivek@202.54.1.55

What are ssh-agent and ssh-add, and how do I use them on Ubuntu 18.04?

How To Ssh Into Ubuntu 18.04

To get rid of a passphrase for the current session, add a passphrase to ssh-agent (see ssh-agent command for more info) and you will not be prompted for it when using ssh or scp/sftp/rsync to connect to hosts with your public key. The syntax is as follows:
$ eval $(ssh-agent)
Type the ssh-add command to prompt the user for a private key passphrase and adds it to the list maintained by ssh-agent command:
$ ssh-add
Enter your private key passphrase. Now try again to log into vivek@202.54.1.55 and you will NOT be prompted for a password:
$ ssh vivek@202.54.1.55

How to disable the password based login on a Ubuntu 18.04 server

Login to your server, type:
## client commands ##
$ eval $(ssh-agent)
$ ssh-add
$ ssh vivek@202.54.1.55
Now login as root user:
$ sudo -i
OR
$ su -i
Edit sshd_config file:
# vim /etc/ssh/sshd_config
OR
# nano /etc/ssh/sshd_config
Find PermitRootLogin and set it as follows:
PermitRootLogin no
Save and close the file. I am going to add a user named vivek to sudoers group on Ubuntu 18.04 server so that we can run sysadmin tasks:
# adduser vivek sudo
Restart/reload the sshd service:
# systemctl reload ssh
You can exit from all session and test it as follows:
$ ssh vivek@202.54.1.55
## become root on server for sysadmin task ##
$ sudo -i

How do I add or replace a passphrase for an existing private key?

To to change your SSH passphrase type the following command:
$ ssh-keygen -p

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How do I backup my existing private/public SSH keys

Just copy files to your backup server or external USB pen/hard drive:

How do I protect my ssh keys?

1. Always use a strong passphrase.
2. Do not share your private keys anywhere online or store in insecure cloud storage or gitlab/github servers.
3. Restrict privileges of the account.

Tip: Create and setup an OpenSSH config file to create shortcuts for servers

See how to create and use an OpenSSH ssh_config file for more info.

How do I secure my OpenSSH server?

See “OpenSSH Server Best Security Practices” for more info.

Conclusion

You learned how to create and install ssh keys for SSH key-based authentication for Ubuntu Linux 18.04 LTS server. See OpenSSH server documents here and here for more info.

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SSH stands for “Secure Shell” and is an encrypted protocol used to log in and manage a remote server. SSH also supports various authentication mechanisms. SSH uses password-based authentication and public key-based authentication for a secure connection between a client and a server. SSH key-based authentication is more secure than password-based authentication because keys are very hard to guess or crack using currently available computing power.

In this tutorial, we will show you how to set up SSH key-based authentication on an Ubuntu 18.04 server.

Prerequisites

Ubuntu 18.04 Allow Ssh

• Two fresh Ubuntu 18.04 VPS on the Atlantic.Net Cloud Platform.
• Root passwords configured on both servers.

Step 1 – Create an Atlantic.Net Cloud Server

First, log in to your Atlantic.Net Cloud Server. Create a new server, choosing Ubuntu 18.04 as the operating system with at least 2GB RAM. Connect to your Cloud Server via SSH and log in using the credentials highlighted at the top of the page.

Once you are logged into your Ubuntu 18.04 server, run the following command to update your base system with the latest available packages.

Step 2 – Generate the SSH Key on the Client Machine

First, log in to your client machine and generate a new SSH key pair by running the following command:

You will need to press Enter to accept the default file location and provide a passphrase to add an extra layer of security, as shown below:

The above command will generate a 2048-bit RSA key pair with a secure passphrase to prevent unauthorized users from logging in.

You can see the generated public and private keys with the following command:

Enter the verification code that was sent to one of your trusted devices or by text message in order to proceed. Apple id recovery key generate. Click on Replace Lost Key. Click on Password and Security in the left hand navigation. Click Next.

You should see the following output:

At this point, you have public and private keys that you can use to authenticate with your Ubuntu server.

Step 3 – Copy the Public Key to the Ubuntu Server

Next, you will need to copy the public key from the client machine to your Ubuntu 18.04 server. You can copy the public key with ssh-copy-id utility as shown below:

You should see the following output:

Type “yes” and press ENTER to continue. You should see the following output:

Next, you will be prompted to enter the remote username and password. After the successful authentication, the content of the public key ~/.ssh/id_rsa.pub will be appended to the remote user ~/.ssh/authorized_keys file as shown below:

Step 4 – Disable SSH Password Authentication

Next, log in to your Ubuntu 18.04 server machine and disable SSH password-based authentication to add an extra layer of security to your server.

You can disable password-based authentication by editing the file /etc/ssh/sshd_config:

Find the following lines and change the value to “no”:

Save and close the file, then restart SSH service to apply the configuration:

Step 5 – Log in to the Server using SSH Keys

At this point, SSH key-based authentication is configured. Now it’s time to log in to the Ubuntu 18.04 server machine with the public key.

You can login to your Ubuntu 18.04 server by simply running the following command:

If you are logging in for the first time, you will be prompted as shown below:

Type Yes and hit Enter key to continue. Next, you will be prompted to enter the passphrase for your private key as shown below:

Provide your private key passphrase and hit Enter to log in to your server.

Conclusion

In the above tutorial, we learned how to set up an SSH key-based authentication with a passphrase on Ubuntu 18.04. The connection between your client machine and Ubuntu 18.04 server machine is now highly secure. You can also use the same key for another remote server. If you’re ready to get started with SSH key-based authentication, try VPS hosting with Atlantic.Net today.