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.

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.

Now click on Bitbucket settings option: Now click on SSH keys option: Now press the Add key button. If you previously configured a SSH key then it will be listed (like mine): For last, enter whatever name you'd like and paste the content you saw on step 2: And that's all. Very easy isn't? Step 4: Clone your repository using SSH protocol. You can use SSH keys to establish a secure connection between your computer and Bitbucket Server for when you are performing read-only (pull, clone) Git operations from your local machine. Personal keys are attached to your Bitbucket Server account – they are bound by that account's permissions and use the account's identity for any operations. You can use SSH keys to establish a secure connection between your computer and Bitbucket Server for when you are performing read-only (pull, clone) Git operations from your local machine. Personal keys are attached to your Bitbucket Server account – they are bound by that account's permissions and use the account's identity for any operations.

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.

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.

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?
This page explains a public key and shows you how to set up SSH keys on a Linux or Unix-like server. I am assuming that you are using Linux or Unix-like server and client with the following software:
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  • OpenSSH SSHD server
  • OpenSSH ssh client and friends on Linux (Ubuntu, Debian, {Free,Open,Net}BSD, RHEL, CentOS, MacOS/OSX, AIX, HP-UX and co).

What is a public key authentication?

OpenSSH server supports various authentication schema. The two most popular are as follows:

  1. Passwords based authentication
  2. Public key based authentication. It is an alternative security method to using passwords. This method is recommended on a VPS, cloud, dedicated or even home based server.

How to set up SSH keys

Steps to setup secure ssh keys:

  1. Create the ssh key pair using ssh-keygen command.
  2. Copy and install the public ssh key using ssh-copy-id command on a Linux or Unix server.
  3. Add yourself to sudo or wheel group admin account.
  4. Disable the password login for root account.
  5. Test your password less ssh keys login using ssh user@server-name command.

Let us see all steps in details.

By convention, the private key is usually called idrsa and the public key idrsa.pub, but this isn’t a requirement. Generate ssh key ubuntu 18.04 github.

How do I set up public key authentication?

You must generate both a public and a private key pair. For example:
Where,

  • server1.cyberciti.biz – You store your public key on the remote hosts and you have an accounts on this Linux/Unix based server.
  • client1.cyberciti.biz – Your private key stays on the desktop/laptop/ computer (or local server) you use to connect to server1.cyberciti.biz 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 server1.cyberciti.biz and client1.cyberciti.biz names with your actual setup. Enough talk, let’s set up public key authentication. Open the Terminal and type following commands if .ssh directory does not exists:

1: Create the key pair

On the computer (such as client1.cyberciti.biz), generate a key pair for the protocol.

Sample outputs:

You need to set the Key Pair location and name. I recommend you use the default location if you do not yet have another key there, for example: $HOME/.ssh/id_rsa. You will be prompted to supply a passphrase (password) for your private key. I suggest that you setup a passphrase when prompted. You should see two new files in $HOME/.ssh/ directory:

  1. $HOME/.ssh/id_rsa– contains your private key.
  2. $HOME/.ssh/id_rsa.pub – contain your public key.

Optional syntax for advance users

The following syntax specifies the 4096 of bits in the RSA key to creation (default 2048):
$ ssh-keygen -t rsa -b 4096 -f ~/.ssh/vps-cloud.web-server.key -C 'My web-server key'
Where,

  • -t rsa : Specifies the type of key to create. The possible values are “rsa1” for protocol version 1 and “dsa”, “ecdsa”, “ed25519”, or “rsa” for protocol version 2.
  • -b 4096 : Specifies the number of bits in the key to create
  • -f ~/.ssh/vps-cloud.web-server.key : Specifies the filename of the key file.
  • -C 'My web-server key' : Set a new comment.

2: Install the public key in remote server

Use scp or ssh-copy-id command to copy your public key file (e.g., $HOME/.ssh/id_rsa.pub) to your account on the remote server/host (e.g., nixcraft@server1.cyberciti.biz). To do so, enter the following command on your client1.cyberciti.biz:

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OR just copy the public key in remote server as authorized_keys in ~/.ssh/ directory:

A note about appending the public key in remote server

On some system ssh-copy-id command may not be installed, so use the following commands (when prompted provide the password for remote user account called vivek) to install and append the public key:

3: Test it (type command on client1.cyberciti.biz)

The syntax is as follows for the ssh command:

Or copy a text file called foo.txt:

You will be prompted for a passphrase. To get rid of passphrase whenever you log in the remote host, try ssh-agent and ssh-add commands.

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

To get rid of a passphrase for the current session, add a passphrase to ssh-agent 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:

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:

Enter your private key passphrase. Now try again to log into user@server1.cyberciti.biz and you will not be prompted for a password:

One can list public key parameters of all identities with the -L option:
ssh-add -L
Deleting all private keys from the ssh-agent can be done with the -D option as follows:
ssh-add -D
When you log out kill the ssh agent, run:
kill $SSH_AGENT_PID
You can also add something like the below to your shell startup to kill ssh-agent at logout:
trap 'kill $SSH_AGENT_PID' 0

4: Disable the password based login on a server

Login to your server, type:

Edit /etc/ssh/sshd_config on server1.cyberciti.biz using a text editor such as nano or vim:

Warning: Make sure you add yourself to sudoers files. Otherwise you will not able to login as root later on. See “How To Add, Delete, and Grant Sudo Privileges to Users on a FreeBSD Server” for more info.

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$ sudo vim /etc/ssh/sshd_config
OR directly jump to PermitRootLogin line using a vim text editor:
$ sudo vim +/PermitRootLogin /etc/ssh/sshd_config
Find PermitRootLogin and set it as follows:

Save and close the file. I am going to add a user named vivek to sudoers on Ubuntu Linux:
# adduser vivek
Finally, reload/restart the sshd server, type command as per your Linux/Unix version:

5: How to add or replace a passphrase for an existing private key?

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

6: How do I backup an existing private/public key?

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

How do I protect my ssh keys?

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

How do I create and setup an OpenSSH config file to create shortcuts for servers I frequently access?

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

Conclusion

This page explained how to set up ssh keys for authentication purposes. For more info see the following resources:

  • Man pages – ssh-keygen(1)
  • OpenSSH project homepage here.

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And, there you have it, ssh set up with public key based authentication for Linux or Unix-like systems.

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