Ssh Generate Rsa Public Key

Ssh Generate Rsa Public Keys
Ssh Generate New Public Key From Rsa

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. May 27, 2010 H ow do I generate ssh RSA keys under Linux operating systems? You need to use the ssh-keygen command as follows to generate RSA keys (open terminal and type the following command): ssh-keygen -t rsa OR ssh-keygen.

Before you begin

Using SSH public-key authentication to connect to a remote system is a robust, more secure alternative to logging in with an account password or passphrase. SSH public-key authentication relies on asymmetric cryptographic algorithms that generate a pair of separate keys (a key pair), one 'private' and the other 'public'. You keep the private key a secret and store it on the computer you use to connect to the remote system. Conceivably, you can share the public key with anyone without compromising the private key; you store it on the remote system in a .ssh/authorized_keys directory.

To use SSH public-key authentication:

The remote system must have a version of SSH installed. The information in this document assumes the remote system uses OpenSSH. If the remote system is using a different version of SSH (for example, Tectia SSH), the process outlined below may not be correct.
The computer you use to connect to the remote server must have a version of SSH installed. This document includes instructions for generating a key pair with command-line SSH on a Linux or macOS computer, and with PuTTY on a Windows computer.
You need to be able to transfer your public key to the remote system. Therefore, you must either be able to log into the remote system with an established account username and password/passphrase, or have an administrator on the remote system add the public key to the ~/.ssh/authorized_keys file in your account.
Two-factor authentication using Two-Step Login (Duo) is required for access to the login nodes on IU research supercomputers, and for SCP and SFTP file transfers to those systems. SSH public-key authentication remains an option for researchers who submit the 'SSH public-key authentication to HPS systems' user agreement (log into HPC everywhere using your IU username and passphrase), in which you agree to set a passphrase on your private key when you generate your key pair. If you have questions about how two-factor authentication may impact your workflows, contact the UITS Research Applications and Deep Learning team. For help, see Get started with Two-Step Login (Duo) at IU and Help for Two-Step Login (Duo).

Set up public-key authentication using SSH on a Linux or macOS computer

To set up public-key authentication using SSH on a Linux or macOS computer:

Log into the computer you'll use to access the remote host, and then use command-line SSH to generate a key pair using the RSA algorithm.
To generate RSA keys, on the command line, enter:
You will be prompted to supply a filename (for saving the key pair) and a password (for protecting your private key):
- Filename: To accept the default filename (and location) for your key pair, press Enter or Return without entering a filename.
  Alternatively, you can enter a filename (for example, my_ssh_key) at the prompt, and then press Enter or Return. However, many remote hosts are configured to accept private keys with the default filename and path (~/.ssh/id_rsa for RSA keys) by default. Consequently, to authenticate with a private key that has a different filename, or one that is not stored in the default location, you must explicitly invoke it either on the SSH command line or in an SSH client configuration file (~/.ssh/config); see below for instructions.
- Password: Enter a password that contains at least five characters, and then press Enter or Return. If you press Enter or Return without entering a password, your private key will be generated without password-protection.
  If you don't password-protect your private key, anyone with access to your computer conceivably can SSH (without being prompted for a password) to your account on any remote system that has the corresponding public key.
Your private key will be generated using the default filename (for example, id_rsa) or the filename you specified (for example, my_ssh_key), and stored on your computer in a .ssh directory off your home directory (for example, ~/.ssh/id_rsa or ~/.ssh/my_ssh_key).

The corresponding public key will be generated using the same filename (but with a .pub extension added) and stored in the same location (for example, ~/.ssh/id_rsa.pub or ~/.ssh/my_ssh_key.pub).
Use SFTP or SCP to copy the public key file (for example, ~/.ssh/id_rsa.pub) to your account on the remote system (for example, darvader@deathstar.empire.gov); for example, using command-line SCP:
You'll be prompted for your account password. Your public key will be copied to your home directory (and saved with the same filename) on the remote system.
Log into the remote system using your account username and password.
If the remote system is not configured to support password-based authentication, you will need to ask system administrators to add your public key to the ~/.ssh/authorized_keys file in your account (if your account doesn't have ~/.ssh/authorized_keys file, system administrators can create one for you). Once your public key is added to your ~/.ssh/authorized_keys file on the remote system, the setup process is complete, and you should now be able to SSH to your account from the computer that has your private key.
If your account on the remote system doesn't already contain a ~/.ssh/authorized_keys file, create one; on the command line, enter the following commands:
If your account on the remote system already has a ~/.ssh/authorized_keys file, executing these commands will not damage the existing directory or file.
On the remote system, add the contents of your public key file (for example, ~/id_rsa.pub) to a new line in your ~/.ssh/authorized_keys file; on the command line, enter:
You may want to check the contents of ~/.ssh/authorized_keys to make sure your public key was added properly; on the command line, enter:
You may now safely delete the public key file (for example, ~/id_rsa.pub) from your account on the remote system; on the command line, enter:
Alternatively, if you prefer to keep a copy of your public key on the remote system, move it to your .ssh directory; on the command line, enter:
Optionally, repeat steps 3-7 to add your public key to other remote systems that you want to access from the computer that has your private key using SSH public-key authentication.
You now should be able to SSH to your account on the remote system (for example, username@host2.somewhere.edu) from the computer (for example, host1) that has your private key (for example, ~/.ssh/id_rsa):
- If your private key is password-protected, the remote system will prompt you for the password or passphrase (your private key password/passphrase is not transmitted to the remote system):
- If your private key is not password-protected, the remote system will place you on the command line in your home directory without prompting you for a password or passphrase:
If the private key you're using does not have the default name, or is not stored in the default path (not ~/.ssh/id_rsa), you must explicitly invoke it in one of two ways:
- On the SSH command line: Add the -i flag and the path to your private key.
  For example, to invoke the private key host2_key, stored in the ~/.ssh/old_keys directory, when connecting to your account on a remote host (for example, username@host2.somewhere.edu), enter:
- In an SSH client configuration file: SSH gets configuration data from the following sources (in this order):
  1. From command-line options
  2. From the user's client configuration file (~/.ssh/config), if it exists
  3. From the system-wide client configuration file (/etc/ssh/ssh_config)
  The SSH client configuration file is a text file containing keywords and arguments. To specify which private key should be used for connections to a particular remote host, use a text editor to create a ~/.ssh/config that includes the Host and IdentityFile keywords.
  
  For example, for connections to host2.somewhere.edu, to make SSH automatically invoke the private key host2_key, stored in the ~/.ssh/old_keys directory, create a ~/.ssh/config file with these lines included:
  
  Once you save the file, SSH will use the specified private key for future connections to that host.
  
  You can add multiple Host and IdentityFile directives to specify a different private key for each host listed; for example:
  
  Alternatively, you can use a single asterisk ( * ) to provide global defaults for all hosts (specify one private key for several hosts); for example:
  
  For more about the SSH client configuration file, see the OpenSSH SSH client configuration file on the web or from the command line (man ssh_config).

Set up public-key authentication using PuTTY on a Windows 10 or Windows 8.x computer

The PuTTY command-line SSH client, the PuTTYgen key generation utility, the Pageant SSH authentication agent, and the PuTTY SCP and SFTP utilities are packaged together in a Windows installer available under The MIT License for free download from the PuTTY development team.

After installing PuTTY:

Launch PuTTYgen.
In the 'PuTTY Key Generator' window, under 'Parameters':
- For 'Type of key to generate', select RSA. (In older versions of PuTTYgen, select SSH2-RSA.)
- For 'Number of bits in a generated key', leave the default value (2048).
Under 'Actions', click Generate.
When prompted, use your mouse (or trackpad) to move your cursor around the blank area under 'Key'; this generates randomness that PuTTYgen uses to generate your key pair.
When your key pair is generated, PuTTYgen displays the public key in the area under 'Key'. In the 'Key passphrase' and 'Confirm passphrase' text boxes, enter a passphrase to passphrase-protect your private key.
If you don't passphrase-protect your private key, anyone with access to your computer will be able to SSH (without being prompted for a passphrase) to your account on any remote system that has the corresponding public key.
Save your public key:
1. Under 'Actions', next to 'Save the generated key', click Save public key.
2. Give the file a name (for example, putty_key), select a location on your computer to store it, and then click Save.
Save your private key:
1. Under 'Actions', next to 'Save the generated key', click Save private key.
  If you didn't passphrase-protect your private key, the utility will ask whether you're sure you want to save it without a passphrase. Click Yes to proceed or No to go back and create a passphrase for your private key.
2. Keep 'Save as type' set to PuTTY Private Key Files (*.ppk), give the file a name (for example, putty_private_key), select a location on your computer to store it, and then click Save.
3. If you wish to connect to a remote desktop system such as Research Desktop (RED), click Conversions > Export OpenSSH key, give the file a name (for example, putty_rsa), select a location on your computer to store it, and then click Save.
Log into the remote system using your account username and password.
If the remote system does not support password-based authentication, you will need to ask system administrators to add your public key to the ~/.ssh/authorized_keys file in your account (if your account doesn't have ~/.ssh/authorized_keys file, system administrators can create one for you). Once your public key is added to your account's ~/.ssh/authorized_keys file on the remote system...
If your account on the remote system doesn't already contain a ~/.ssh/authorized_keys file, create one; on the command line, enter the following commands:
If your account on the remote system already has ~/.ssh/authorized_keys, executing these commands will not damage the existing directory or file.
On your computer, in the PuTTYgen utility, copy the contents of the public key (displayed in the area under 'Key') onto your Clipboard. Then, on the remote system, use your favorite text editor to paste it onto a new line in your ~/.ssh/authorized_keys file, and then save and close the file.
On your computer, open the Pageant SSH authentication agent. This utility runs in the background, so when it opens, you should see its icon displayed in the Windows notification area.
In the Windows notification area, right-click on the Pageant icon, select Add Key, navigate to the location where you saved your private key (for example, putty_private_key.ppk), select the file, and then click Open.
If your private key is passphrase-protected, Pageant will prompt you to enter the passphrase; enter the passphrase for your private key, and then click OK.
If your private key is not passphrase-protected, Pageant will add your private key without prompting you for a passphrase.

Either way, Pageant stores the unencrypted private key in memory for use by PuTTY when you initiate an SSH session to the remote system that has your public key.
On your computer, open the PuTTY SSH client:
1. On the Session screen:
  - Under 'Host Name (or IP address)', enter your username coupled with the hostname of the remote server that has your public key; for example:
  - Under 'Connection type', make sure SSH is selected.
2. In the 'Category' list on the left, navigate to the Auth screen (Connection > SSH > Auth). On the Auth screen, under 'Authentication methods', select Attempt authentication using Pageant.
3. Return to the Session screen, and under 'Saved Sessions', enter a name (for example, Deathstar), and then click Save.
4. Click Open to connect to your account on the remote system. With Pageant running in the background, PuTTY will retrieve the unencrypted private key automatically from Pageant and use it to authenticate. Because Pageant has your private key's passphrase saved (if applicable), the remote system will place you on the command line in your account without prompting you for the passphrase.
Technically, at this point, the setup is complete. In the future, whenever you log into your Windows desktop, you can run Pageant, add the private key, and then use PuTTY to SSH to any remote resource that has your public key. Alternatively, you can create a shortcut in your Windows Startup folder to launch Pageant and load your private key automatically whenever you log into your desktop. For instructions, finish the rest of the following steps.
Open your Startup folder. Press Win-r, and in the 'Open' field, type shell:startup, and then press Enter.
Right-click inside the Startup folder, and then select New and Shortcut.
In the 'Type the location of the item' text box, enter the path to the Pageant executable (pageant.exe) followed by the path to your private key file (for example, putty_private_key.ppk); enclose both paths in double quotes; for example:
Click Next, and then, in the 'Type a name for this shortcut' text box, enter a name for the shortcut (for example, PAGEANT).
Click Finish.

The next time you log into your Windows desktop, Pageant will start automatically, load your private key, and (if applicable) prompt you for the passphrase.

Did you know you can passwordless SSH? Here's how, and how to decide whether you should.

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.

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.

Ssh Generate Rsa 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:

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.

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.

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.

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.

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.