Generate Authorized Key File With Ssh-keygen Ubuntu

SSH, the secure shell, is often used to access remote Linux systems. But its authentication mechanism, where a private local key is paired with a public remote key, is used to secure all kinds of online services, from GitHub and Launchpad to Linux running on Microsoft’s Azure cloud.

Oct 20, 2014 By default, this will create a 2048 bit RSA key pair, which is fine for most uses. On your local computer, generate a SSH key pair by typing: ssh-keygen Generating public/private rsa key pair. Enter file in which to save the key (/home/ username /.ssh/idrsa): The utility will prompt you to select a location for the keys that will be generated. Jul 30, 2015 No matter how your public key was generated, you can add it to your Ubuntu system by opening the file.ssh/authorizedkeys in your favourite text editor and adding the key to the bottom of the file. You can also limit the SSH features that the key can use, such as disallowing port-forwarding or only allowing a specific command to be run. Jul 17, 2017 Create a file /.ssh/authorizedkeys if already exist ignore this step $ vim /.ssh/authorizedkeys Changes are made in file /.ssh/authorizedkeys such as copy the pub in file /.ssh/authorizedkeys on the machine to which you want to connect, appending it to its end if the file already exists. The file /.ssh/authorizedkeys (on the server) is supposed to have a mode of 600. The permissions of the (private) key on the client-side should be 600. If the private key was not protected with a password, and you put it on the server, I recommend you to generate a new one: ssh-keygen -t rsa. New key pairs can be generated using the ssh-keygen program and the ssh-copy-id tool can be used for copying keys in an authorizedkeys file on a server. It is almost too easy, and that is one of the reasons why the number of SSH keys has become so uncontrolled.

As you can see, it’s very easy to generate SSH keys on Windows these days. Basically, the ssh-keygen command does all the work. If you find it difficult to understand how to add the public key to the server, look up your provider’s documentation. They always have a page that describes, in detail, how to do this.

Generating these keys from Linux is easy, and thanks to Ubuntu on Windows, you can follow the same process from Windows 10. But even without Ubuntu, SSH keys can also be generated with the free and open source Windows application, PuTTy

Over the following few steps, we’ll guide you through the process of generating SSH keys using both Ubuntu on Windows and PuTTY.

Requirements

All you need is a PC running Windows 10 and either of the following installed:

  • The puttygen.exe executable from PuTTY

If you don’t already have Ubuntu on Windows, take a look at our Install Ubuntu on Windows 10 tutorial.

Overview

Public key authentication is a way of logging into an SSH/SFTP account using a cryptographic key rather than a password.

If you use very strong SSH/SFTP passwords, your accounts are already safe from brute force attacks. However, using public key authentication provides many benefits when working with multiple developers. For example, with SSH keys you can

  • allow multiple developers to log in as the same system user without having to share a single password between them;
  • revoke a single developer's access without revoking access by other developers; and
  • make it easier for a single developer to log in to many accounts without needing to manage many different passwords.

How Public Key Authentication Works

Keys come in pairs of a public key and a private key. Each key pair is unique, and the two keys work together.

These two keys have a very special and beautiful mathematical property: if you have the private key, you can prove you have it without showing what it is. It's like proving you know a password without having to show someone the password.

Public key authentication works like this:

  1. Generate a key pair.
  2. Give someone (or a server) the public key.
  3. Later, anytime you want to authenticate, the person (or the server) asks you to prove you have the private key that corresponds to the public key.
  4. You prove you have the private key.

You don't have to do the math or implement the key exchange yourself. The SSH server and client programs take care of this for you.

Generate an SSH Key Pair

You should generate your key pair on your laptop, not on your server. All Mac and Linux systems include a command called ssh-keygen that will generate a new key pair.

If you're using Windows, you can generate the keys on your server. Just remember to copy your keys to your laptop and delete your private key from the server after you've generated it.

To generate an SSH key pair, run the command ssh-keygen.

How To Generate Ssh Key

/generate-public-key-from-private-key-ubuntu.html. It will look like this when you run it:

How To Open Key File Icon

You'll be prompted to choose the location to store the keys. The default location is good unless you already have a key. Press Enterhow to write thesis pdf to choose the default location.

Next, you'll be asked to choose a password. Using a password means a password will be required to use the private key. It's a good idea to use a password on your private key.

After you choose a password, your public and private keys will be generated. There will be two different files. The one named id_rsa is your private key. The one named id_rsa.pub is your public key.

You'll also be shown a fingerprint and 'visual fingerprint' of your key. You do not need to save these.

Configure an SSH/SFTP User for Your Key

Method 1: Using ssh-copy-id

Now that you have an SSH key pair, you're ready to configure your app's system user so you can SSH or SFTP in using your private key.

To copy your public key to your server, run the following command. Be sure to replace 'x.x.x.x' with your server's IP address and SYSUSER with the name of the the system user your app belongs to.

Method 2: Manual Configuration

If you don't have the ssh-copy-id command (for example, if you are using Windows), you can instead SSH in to your server and manually create the .ssh/authorized_keys file so it contains your public key.

First, run the following commands to make create the file with the correct permissions.

Next, edit the file .ssh/authorized_keys using your preferred editor. Copy and paste your id_rsa.pub file into the file.

Log In Using Your Private Key

You can now SSH or SFTP into your server using your private key. From the command line, you can use:

If you didn't create your key in the default location, you'll need to specify the location:

If you're using a Windows SSH client, such as PuTTy, look in the configuration settings to specify the path to your private key.

Granting Access to Multiple Keys

The .ssh/authorized_keys file you created above uses a very simple format: it can contain many keys as long as you put one key on each line in the file.

If you have multiple keys (for example, one on each of your laptops) or multiple developers you need to grant access to, just follow the same instructions above using ssh-copy-id or manually editing the file to paste in additional keys, one on each line.

When you're done, the .ssh/authorized_keys file will look something like this (don't copy this, use your own public keys):

Additional Information

Retrieve Your Public Key from Your Private Key

The following command will retrieve the public key from a private key:

This can be useful, for example, if your server provider generated your SSH key for you and you were only able to download the private key portion of the key pair.

Note that you cannot retrieve the private key if you only have the public key.

Correcting Permissions on the .ssh Directory

The instructions in this article will create your server's .ssh directory and .ssh/authorized_keys file with the correct permissions. However, if you've created them yourself and need to fix permissions, you can run the following commands on your server while SSH'd in as your app's system user.

Disabling Password Authentication

Generate Authorized Key File With Ssh-keygen Ubuntu Windows 7

NOTE: When changing anything about the way SSH is accessed(ports, authentication methods, et cetera), it is very strongly recommended to leave an active root SSH session open until everything is working as intended. This ensures you have a way to revert changes in the event something goes wrongand logins are not working properly.

Generate Authorized Key File With Ssh-keygen Ubuntu Free

As an extra security precaution, once you have set up SSH keys, you may wish to disable password authentication entirely. This will mean no users will be able to log into SSH or SFTP without SSH keys. Anyone entering a password will receive a message like:

Or:

Disabling password authentication is an excellent way to improve server security. Please see our guide here for the steps to accomplish this goal.

.key File Converter

Then, test whether you're able to log in with a password by opening a new SSH or SFTP session to the server. Passwords should not be able to be used and, if everything has been done correctly, an error will be issued when someone tries to use a password. Unless this setting is changed back to allow password authentication, no users will be able to log in without an SSH key set up.