An SSH key is an access credential for the SSH (secure shell) network protocol. This authenticated and encrypted secure network protocol is used for remote communication between machines on an unsecured open network. SSH is used for remote file transfer, network management, and remote operating system access. The SSH acronym is also used to describe a set of tools used to interact with the SSH protocol.

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SSH uses a pair of keys to initiate a secure handshake between remote parties. The key pair contains a public and private key. The private vs public nomenclature can be confusing as they are both called keys. It is more helpful to think of the public key as a 'lock' and the private key as the 'key'. You give the public 'lock' to remote parties to encrypt or 'lock' data. This data is then opened with the 'private' key which you hold in a secure place.

Aug 07, 2019 I recently read that SSH keys provide a secure way of logging into a Linux and Unix-based server. How do I set up SSH keys on a Linux or Unix based systems? In SSH for Linux/Unix, how do I set up public key authentication? Jun 22, 2012  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. No root password will be emailed to you and you can log in to your new server from your chosen client.

How to Create an SSH Key

SSH keys are generated through a public key cryptographic algorithm, the most common being RSA or DSA. At a very high level SSH keys are generated through a mathematical formula that takes 2 prime numbers and a random seed variable to output the public and private key. This is a one-way formula that ensures the public key can be derived from the private key but the private key cannot be derived from the public key.

SSH keys are created using a key generation tool. The SSH command line tool suite includes a keygen tool. Most git hosting providers offer guides on how to create an SSH Key.

How To Generate Ssh Keys

Generate an SSH Key on Mac and Linux

Both OsX and Linux operating systems have comprehensive modern terminal applications that ship with the SSH suite installed. The process for creating an SSH key is the same between them.

1. execute the following to begin the key creation

This command will create a new SSH key using the email as a label

2. You will then be prompted to 'Enter a file in which to save the key.'
You can specify a file location or press “Enter” to accept the default file location.

3. The next prompt will ask for a secure passphrase.
A passphrase will add an additional layer of security to the SSH and will be required anytime the SSH key is used. If someone gains access to the computer that private keys are stored on, they could also gain access to any system that uses that key. Adding a passphrase to keys will prevent this scenario.

At this point, a new SSH key will have been generated at the previously specified file path.

4. Add the new SSH key to the ssh-agent

The ssh-agent is another program that is part of the SSH toolsuite. The ssh-agent is responsible for holding private keys. Think of it like a keychain. In addition to holding private keys it also brokers requests to sign SSH requests with the private keys so that private keys are never passed around unsecurly.

Before adding the new SSH key to the ssh-agent first ensure the ssh-agent is running by executing:

Once the ssh-agent is running the following command will add the new SSH key to the local SSH agent.

The new SSH key is now registered and ready to use!

Generate an SSH Key on Windows

Windows environments do not have a standard default unix shell. External shell programs will need to be installed for to have a complete keygen experience. The most straight forward option is to utilize Git Bash. Once Git Bash is installed the same steps for Linux and Mac can be followed within the Git Bash shell.

Windows Linux Subsystem

Modern windows environments offer a windows linux subsystem. The windows linux subsystem offers a full linux shell within a traditional windows environment. If a linux subsystem is available the same steps previously discussed for Linux and Mac can be followed with in the windows linux subsystem.

Summary

SSH keys are used to authenticate secure connections. Following this guide, you will be able to create and start using an SSH key. Git is capable of using SSH keys instead of traditional password authentication when pushing or pulling to remote repositories. Modern hosted git solutions like Bitbucket support SSH key authentication.

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.

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.

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

Linux Use Ssh 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. /diablo-3-cd-key-generator-v3-01-skidrow-password.html.

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

Generate Ssh Key For Linux Users Manual

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.

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.

Generate Ssh Key For Linux Users List

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.