Generate New Public Key File Ubuntu

Save the public and private keys by clicking the Save public key and Save private key buttons. From the Public key for pasting into OpenSSH authorizedkeys file field at the top of the window, copy all the text (starting with ssh-rsa ) to your clipboard by pressing Ctrl-C. If you use the Azure CLI to create your VM, you can optionally generate SSH public and private key files by running the az vm create command with the -generate-ssh-keys option. The keys are stored in the /.ssh directory. Note that this command option does not overwrite keys if.

Introduction

Establishing an SSH (Secure Shell) connection is essential to log in and effectively manage a remote server. Encrypted keys are a set of access credentials used to establish a secure connection.

This guide will walk you how to generate SSH keys on Ubuntu 18.04. We will also cover setting up SSH key-based authentication to connect to a remote server without requiring a password.

  • A server running Ubuntu 18.04
  • A user account with sudo privileges
  • Access to a terminal window / command line (Ctrl-Alt-T)

If you are already running an Ubuntu 18.04 server, you can skip this step. If you are configuring your server for the first time, you may not have SSH installed.

1. Start by installing the tasksel package:

Public

The system will first ask for confirmation before proceeding:

2. Next, use tasksel to install the ssh-server:

3. Load the SSH server service, and set it to launch at boot:

On your client system – the one you’re using to connect to the server – you need to create a pair of key codes.

To generate a pair of SSH key codes, enter the commands:

This will create a hidden directory to store your SSH keys, and modify the permissions for that directory. The ssh-keygen command creates a 2048-bit RSA key pair.

For extra security, use RSA4096:

If you’ve already generated a key pair, this will prompt to overwrite them, and those old keys will not work anymore.

The system will ask you to create a passphrase as an added layer of security. Input a memorable passphrase, and press Enter.

This process creates two keys. One is a public key, which you can hand out to anyone – in this case, you’ll save it to the server. The other one is a private key, which you will need to keep secure. The secure private key ensures that you are the only person who can encrypt the data that is decrypted by the public key.

Step 2- Copy Public Key to the Ubuntu Server

First, get the IP address of the Ubuntu server you want to connect to.

In a terminal window, enter:

The system’s IP address is listed in the second entry:

On the client system, use the ssh-copy-id command to copy the identity information to the Ubuntu server:

Replace server_IP with the actual IP address of your server.

If this is the first time you’re connecting to the server, you may see a message that the authenticity of the host cannot be established:

Type yes and press Enter.

The system will check your client system for the id_rsa.pub key that was previously generated. Then it will prompt you to enter the password for the server user account. Type it in (the system won’t display the password), and press Enter.

The system will copy the contents of the ~/.ssh/id_rsa.pub from the client system into the ~/.ssh/authorized_keys directory of the server system.

The system should display:

If your system does not have the ssh-copy-id command, you can copy the key manually over the SSH.

Use the following command:

To log in to a remote server, input the command:

The system should not ask for a password as it is negotiating a secure connection using the SSH keys. If you used a security passphrase, you would be prompted to enter it. After you do so, you are logged in.

If this is the first time you’ve logged into the server, you may see a message similar to the one in part two. It will ask if you are sure you want to connect – type yes and press Enter.

Step 4- Disable Password Authentication

This step creates an added layer of security. If you’re the only person logging into the server, you can disable the password. The server will only accept a login with your private key to match the stored public key.

Edit the sshd_config file:

Search the file and find the PasswordAuthentication option.

Edit the file and change the value to no:

Save the file and exit, then restart the SSH service:

Verify that SSH is still working, before ending the session:

If everything works, you can close out and resume work normally.

By following the instructions in this tutorial, you have setup SSH-key-based authentication on an Ubuntu 18.04 server.

The connection is now highly secure as it uses a set of unique, encrypted SSH keys.

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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.
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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

Search Ubuntu For File

The syntax is as follows:
ssh-copy-id [email protected]
ssh-copy-id -i ~/.ssh/file.pub [email protected]

For example:
## for RSA KEY ##
ssh-copy-id -i $HOME/.ssh/id_rsa.pub [email protected]
## for ED25519 KEY ##
ssh-copy-id -i $HOME/.ssh/id_ed25519.pub [email protected]
## install SSH KEY for root user ##
ssh-copy-id -i $HOME/.ssh/id_ed25519.pub [email protected]

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 [email protected]

Test it

Now try logging into the Ubuntu 18.04 LTS server, with ssh command from your client computer/laptop using ssh keys:
$ ssh [email protected]
$ ssh [email protected]

What are ssh-agent and ssh-add, and how do I use them on 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 [email protected] and you will NOT be prompted for a password:
$ ssh [email protected]

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 [email protected]

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 [email protected]
## 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

How do I backup my existing private/public SSH keys

Generate New Public Key File Ubuntu Windows 7

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

Generate New Public Key File Ubuntu Version

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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