Ssh Private Key
Your private key. For more information about generating a key on Linux or macOS, see Connect to a server by using SSH on Linux or Mac OS X. Log in with a private key. Using a text editor, create a file in which to store your private key. This example uses the file deploymentkey.txt. To edit the file in vim, type the following command. On execution, we are prompted to specify a file in which to save the private key, the default being /home/user/.ssh/idrsa; here idrsa is the name of our Private Key file. You can always specify a different path and name for the Private Key file. For our demonstration, we shall use the default configuration.
- Ssh Private Key
- Ssh Private Key Permissions
- Ssh Private Key File
- Ssh Private Key Chmod
- Ssh Private Key Login
This tutorial explains the Passwordless SSH using Public Key and Private Key in Linux.
SSH stands for Secure SHELL, is a protocol used to connect remote hosts to login or performing some tasks using scripts.
When we want to automate some tasks on remote hosts using scripts from a centralized server like Jenkins/Ansible or any Linux Server, we may require a password less connection between the remote hosts and the centralized Server.
In this tutorial, we will learn to create Passwordless SSH login using public key and private key. Follow the step by step guide to make your ssh connection passwordless.
This tutorial will work for Linux Destro such as Centos, Ubuntu, Redhat, Amazon Linux(AWS EC2) and Other as well.
Recommended Read:How to Install Jenkins on Ubuntu
Also Read : Git Tutorial for beginners (Part I)
Scenario
We have one Local Machine and one Remote Server.We will setup a passwordless connection to login Remote Server from the local Machine.
Perform following steps on the remote Server
Step 1– Create an User and login or login as an existing user.
$ useradd devops
$ su – devops
Step 2 – Generate a key pair ( Public key and Private Key) using ssh-keygen command.
Before running this command make sure you are on home directory of the user.If not you can go to the home directory by cd ~ command.
$ cd ~
$ ssh-keygen -t rsa
It will ask for some details. Do not put anything here and press ENTER only.
By ls -al command you can see a hidden directory .ssh and two files namely id_rsa and id_rsa.pub inside .ssh directory are created.Here id_rsa is the Private key and id_rsa.pub is the Public Key.
Private key(id_rsa) is kept at source computer(local machine) from where you have to ssh. Public Key(id_rsa) is kept at Destination Server(Remote Server) , the Server you want to access.
Step 3- Create a file name authorized_keys in side .ssh directory and copy the content of id_rsa.pub file to authorized_keys file.
Go to .ssh directory
$ cd ~/.ssh/
Create an empty file name authorized_keys
$ touch authorized_keys
Copy the content of id_rsa.pub to authorized_keys
$ cat id_rsa.pub > authorized_keys
Check the authorized_keys file if contents are copied.
$cat authorized_keys
Step 4 – Change the permission of authorized_keys
$ chmod 600 authorized_keys
Step 5– Copy the content of id_rsa file
Use cat command to display the content of id_rsa and copy its content.
$ cat id_rsa
On the local Machine
Step 1– Create a file and paste the content of id_rsa copied from remote server inside this file. You can use nano command to perform this action.
Create a file name devops.key using nano command , paste the content and pres Ctrl+X to save and close the file.
$ nano devopys.key
Step 2 – SSH remote Server from local machine without using password.
$ sudo ssh -i path-to-private-key [email protected]
$ sudo ssh -i devops.key [email protected]
I hope you enjoyed this tutorial and learned Passwordless SSH login using public key and private key. If you think this is really helpful, please do share this to other as well. Please also share your valuable feedback, comment or any query in the comment box.I will really happy to resolve your all queries.
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If you interact regularly with SSH commands and remote hosts, you may find that using a key pair instead of passwords can be convenient. Instead of the remote system prompting for a password with each connection, authentication can be automatically negotiated using a public and private key pair.
The private key remains secure on your own workstation, and the public key gets placed in a specific location on each remote system that you access. Your private key may be secured locally with a passphrase. A local caching program such as ssh-agent or gnome-keyring allows you to enter that passphrase periodically, instead of each time you use the key to access a remote system.
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Generating a key pair and propagating the public key
Generating your key pair and propagating your public key is simpler than it sounds. Let’s walk through it.
Generating the key
The minimum effort to generate a key pair involves running the ssh-keygen command, and choosing the defaults at all the prompts:
The default location to store the keys is in the ~/.ssh directory, which will be created if it does not exist:
Allowing this command to create the directory also ensures that the owner and permissions are set correctly. Some applications will not use keys if the permissions to the private key are too open.
The file ending in .pub is the public key that needs to be transferred to the remote systems. It is a file containing a single line: The protocol, the key, and an email used as an identifier. Options for the ssh-keygen command allow you to specify a different identifier:
After generating the key pair, the ssh-keygen command also displays the fingerprint and randomart image that are unique to this key. This information can be shared with other people who may need to verify your public key.
Later you can view these with:
The -l option lists the fingerprint, and the -v option adds the ASCII art.
Propagating the public key to a remote system
If password authentication is currently enabled, then the easiest way to transfer the public key to the remote host is with the ssh-copy-id command. If you used the default name for the key all you need to specify is the remote user and host:
Following the instructions from the output, verify that you can connect using the key pair. If you implemented a passphrase, you will be prompted for the passphrase to use the private key:
Examine the resulting authorized key file. This is where the public key was appended. If the directory or file did not exist, then it was (or they were) created with the correct ownership and permissions. Each line is a single authorized public key:
To revoke access for this key pair, remove the line for the public key.
There are many other options that can be added to this line in the authorized key file to control access. These options are usually used by administrators placing the public keys on a system with restrictions. These restrictions may include where the connection may originate, what command(s) may be run, and even a date indicating when to stop accepting this key. These and more options are listed in the sshd man page.
Changing the passphrase
If you need to change a passphrase on your private key or if you initially set an empty passphrase and want that protection at a later time, use the ssh-keygen command with the -p option:
Ssh Private Key
You can add additional options to specify the key (-f), and the old (-P) or new (-N) passphrases on the command line. Remember that any passwords specified on the command line will be saved in your shell history.
See the ssh-keygen man page for additional options.
Rotating keys
While the public key by itself is meant to be shared, keep in mind that if someone obtains your private key, they can then use that to access all systems that have the public key. These key pairs also do not have a period of validity like GNU Privacy Guard (GPG) keys or public key infrastructure (PKI) certificates.
If you have any reason to suspect that a private key has been stolen or otherwise compromised, you should replace that key pair. The old public key has to be removed from all systems, a new key has to be generated with ssh-keygen, and the new public key has to be transferred to the desired remote systems.
If you are rotating keys as a precaution and without any concern of compromise, you can use the old key pair to authenticate the transfer of the new public key before removing the old key.
Is using empty passphrases ever a good idea?
There are several things to think about when considering an empty passphrase for your SSH private key.
How secure is the private key file?
If you tend to work from multiple client systems and want to either have multiple copies of your key or keep a copy on removable media, then it really is a good idea to have a passphrase on the private key. This practice is in addition to protecting access to the key file with encrypted media.
Ssh Private Key Permissions
However, if you have only one copy of the private key and it is kept on a system that is well secured and not shared, then having a passphrase is simply one more level of protection just in case.
Remember that changing the passphrase on one copy does not change the passphrase on other copies. The passphrase is simply locking access to a specific key file.
Ssh Private Key File
Why do think you need an empty passphrase?
There are cases for keys with empty passphrases. Some utilities that need to automatically transfer files between systems need a passwordless method to authenticate. The kdump utility, when configured to dump the kernel to a remote system using SSH, is one example.
Another common use is to generate a key pair for a script that is designed to run unattended, such as from a cron job.
How about a middle ground alternative?
By itself, a passphrase-protected private key requires the passphrase to be entered each time the key is used. This setup does not feel like passwordless SSH. However, there are caching mechanisms that allow you to enter the key passphrase once and then use the key over and over without reentering that passphrase.
More Linux resources
OpenSSH comes with an ssh-agent daemon and an ssh-add utility to cache the unlocked private key. The GNOME desktop also has a keyring daemon that stores passwords and secrets but also implements an SSH agent.
The lifetime of the cached key can be configured with each of the agents or when the key is added. In many cases, it defaults to an unlimited lifetime, but the cache is cleared when the user logs out of the system. You will be prompted for the passphrase only once per login session.
If there is a scheduled application that needs to run outside of a user login session, it may be possible to use a secret or other password manager to automate the unlocking of the key. For example, Ansible Tower stores credentials in a secure database. This database includes an SSH private key used to connect to the remote systems (managed nodes), and any passphrases necessary for those private keys. Once those credentials are stored, a job can be scheduled to run a playbook on a regular schedule.
Automating propagation
A centralized identity manager such as FreeIPA can assist with key propagation. Upload the public key to the server as an attribute of a user account, and then propagate it to the hosts in the domain as needed. FreeIPA can also provide additional host-based access control for where a key may be used.
Keys can also be distributed using Ansible modules. The openssh_keypair module uses ssh-keygen to generate keys and the authorized_key module adds and removes SSH authorized keys for particular user accounts.
Ssh Private Key Chmod
Wrapping up
SSH key pairs are only one way to automate authentication without passwords. Using the Generic Security Services Application Program Interface (GSSAPI) authentication is also common when trying to reduce the use of passwords on a network with centralized user management. SSH key pairs are the easier option to implement when single sign-on (SSO) is not already available.
Ssh Private Key Login
Many source code repositories grant access using SSH keys. You can upload a public key to an account in the hosting organization such as the Fedora Account System, GitLab, or GitHub sites and use that key pair to authenticate when pulling and pushing content to repositories.
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