Generate Ssh Public Keys Linux
Overview
A SSH private key as generated by ssh-keygen contains a public key part. How do I retrieve this public key from the private key? How do I retrieve this public key from the private key? I've lost my public key and need to put the contents of this public key in the servers authorizedkeys file and do not want to create a new key pair. Dec 18, 2019 In this tutorial, we will walk through how to generate SSH keys on Ubuntu 18.04 machines. We will also show you how to set up an SSH key-based authentication and connect to your remote Linux servers without entering a password.
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
- Jun 22, 2012 The DigitalOcean control panel allows you to add public keys to your new Droplets when they’re created. You can generate the SSH Key in a convenient location, such as the computer, and then upload the public key to the SSH key section. Then, when you create a new Droplet, you can choose to include that public key on the server.
- Use the ssh-keygen command to generate SSH public and private key files. By default, these files are created in the /.ssh directory. You can specify a different location, and an optional password (passphrase) to access the private key file. If an SSH key pair with the same name exists in the given location, those files are overwritten.
- Dec 18, 2019 We will also show you how to set up an SSH key-based authentication and connect to your remote Linux servers without entering a password. Creating SSH keys on Ubuntu # Before generating a new SSH key pair first, check for existing SSH keys on your Ubuntu client machine. You can do that by running the following ls command: ls -l /.ssh/id.pub.
- 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:
- Generate a key pair.
- Give someone (or a server) the public key.
- 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.
- 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.
It will look like this when you run it:
You'll be prompted to choose the location to store the keys. The default location is good unless you already have a key. Press Enter to choose the default location.
Generate Ssh Key Linux
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):
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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.
Linux Ssh Public Key Location
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
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.
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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.
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.
Several tools exist to generate SSH public/private key pairs. The following sections show how to generate an SSH key pair on UNIX, UNIX-like and Windows platforms.
Generating an SSH Key Pair on UNIX and UNIX-Like Platforms Using the ssh-keygen Utility
UNIX and UNIX-like platforms (including Solaris and Linux) include the ssh-keygen utility to generate SSH key pairs.
- Navigate to your home directory:
- Run the ssh-keygen utility, providing as
filename
your choice of file name for the private key:The ssh-keygen utility prompts you for a passphrase for the private key.
- Enter a passphrase for the private key, or press Enter to create a private key without a passphrase:
Note:
While a passphrase is not required, you should specify one as a security measure to protect the private key from unauthorized use. When you specify a passphrase, a user must enter the passphrase every time the private key is used.
The ssh-keygen utility prompts you to enter the passphrase again.
- Enter the passphrase again, or press Enter again to continue creating a private key without a passphrase:
- The ssh-keygen utility displays a message indicating that the private key has been saved as
filename
and the public key has been saved asfilename
.pub
. It also displays information about the key fingerprint and randomart image.
Generating an SSH Key Pair on Windows Using the PuTTYgen Program
The PuTTYgen program is part of PuTTY, an open source networking client for the Windows platform.
- Download and install PuTTY or PuTTYgen.
To download PuTTY or PuTTYgen, go to http://www.putty.org/ and click the You can download PuTTY here link.
- Run the PuTTYgen program.
- Set the Type of key to generate option to SSH-2 RSA.
- In the Number of bits in a generated key box, enter 2048.
- Click Generate to generate a public/private key pair.
As the key is being generated, move the mouse around the blank area as directed.
- (Optional) Enter a passphrase for the private key in the Key passphrase box and reenter it in the Confirm passphrase box.
Note:
While a passphrase is not required, you should specify one as a security measure to protect the private key from unauthorized use. When you specify a passphrase, a user must enter the passphrase every time the private key is used.
- Click Save private key to save the private key to a file. To adhere to file-naming conventions, you should give the private key file an extension of
.ppk
(PuTTY private key).Note:
The.ppk
file extension indicates that the private key is in PuTTY's proprietary format. You must use a key of this format when using PuTTY as your SSH client. It cannot be used with other SSH client tools. Refer to the PuTTY documentation to convert a private key in this format to a different format. - Select all of the characters in the Public key for pasting into OpenSSH authorized_keys file box.
Make sure you select all the characters, not just the ones you can see in the narrow window. If a scroll bar is next to the characters, you aren't seeing all the characters.
- Right-click somewhere in the selected text and select Copy from the menu.
- Open a text editor and paste the characters, just as you copied them. Start at the first character in the text editor, and do not insert any line breaks.
- Save the text file in the same folder where you saved the private key, using the
.pub
extension to indicate that the file contains a public key. - If you or others are going to use an SSH client that requires the OpenSSH format for private keys (such as the
ssh
utility on Linux), export the private key:- On the Conversions menu, choose Export OpenSSH key.
- Save the private key in OpenSSH format in the same folder where you saved the private key in
.ppk
format, using an extension such as.openssh
to indicate the file's content.