Updated by LinodeWritten by Linode
Sep 26, 2019 Generating an SSH key. To generate an SSH key with PuTTYgen, follow these steps: Open the PuTTYgen program. For Type of key to generate, select SSH-2 RSA. Click the Generate button. Move your mouse in the area below the progress bar. When the progress bar is full, PuTTYgen generates your key pair. Type a passphrase in the Key passphrase field. Create an SSH key pair. 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.
If you don’t have these files (or you don’t even have a.ssh directory), you can create them by running a program called ssh-keygen, which is provided with the SSH package on Linux/macOS systems and comes with Git for Windows: $ ssh-keygen -o Generating public/private rsa key pair. Create an SSH key pair. 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.
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Password authentication is the default method most SSH (Secure Shell) clients use to authenticate with remote servers, but it suffers from potential security vulnerabilities, like brute-force login attempts. An alternative to password authentication is public key authentication, in which you generate and store on your computer a pair of cryptographic keys and then configure your server to recognize and accept your keys. Using key-based authentication offers a range of benefits:
- Key-based login is not a major target for brute-force hacking attacks.
- If a server that uses SSH keys is compromised by a hacker, no authorization credentials are at risk of being exposed.
- Because a password isn’t required at login, you are able to able to log in to servers from within scripts or automation tools that you need to run unattended. For example, you can set up periodic updates for your servers with a configuration management tool like Ansible, and you can run those updates without having to be physically present.
This guide will explain how the SSH key login scheme works, how to generate an SSH key, and how to use those keys with your Linode.
NoteIf you’re unfamiliar with SSH connections, review the Getting Started with Linode guide.
How SSH Keys Work
SSH keys are generated in pairs and stored in plain-text files. The key pair (or keypair) consists of two parts:
- A private key, usually named
id_rsa
. The private key is stored on your local computer and should be kept secure, with permissions set so that no other users on your computer can read the file.Caution
- A public key, usually named
id_rsa.pub
. The public key is placed on the server you intend to log in to. You can freely share your public key with others. If someone else adds your public key to their server, you will be able to log in to that server.
When a site or service asks for your SSH key, they are referring to your SSH public key (
id_rsa.pub
). For instance, services like GitHub and Gitlab allow you to place your SSH public key on their servers to streamline the process of pushing code changes to remote repositories.The authorized_keys File
In order for your Linode to recognize and accept your key pair, you will need to upload your public key to your server. More specifically, you will need to upload your public key to the home directory of the user you would like to log in as. If you would like to log in to more than one user on the server using your key pair, you will need to add your public key to each of those users.
To set up SSH key authentication for one of your server’s users, add your public key to a new line inside the user’s
authorized_keys
file. This file is stored inside a directory named .ssh/
under the user’s home folder. A user’s authorized_keys
file can store more than one public key, and each public key is listed on its own line. If your file contains more than one public key, then the owner of each key listed will be able to log in as that user.Granting Someone Else Access to your Server
To give someone else access to your server’s user, simply add their public key on a new line in your
authorized_keys
file, just as you would add your own. To revoke access for that person, remove that same line and save the changes.Challenge-Response
When logging in to a server using SSH, if there is a public key on file on that server, the server will create a challenge. This challenge will be crafted in such a way that only the holder of the private SSH key will be able to decipher it.
This challenge-response action happens without any user interaction. If the person attempting to log in has the corresponding private key, then they will be safely logged in. If not, the login will either fail or fall back to a password-based authentication scheme.
SSH Key Passphrases
You can optionally provide an additional level of security for your SSH keys by encrypting them with a passphrase at the time of creation. When you attempt to log in using an encrypted SSH key, you will be prompted to enter its passphrase. This is not to be confused with a password, as this passphrase only decrypts the key file locally and is not transferred over the Internet as a password might be.
If you’d like to set up your logins so that they require no user input, then creating a passphrase might not be desirable, but it is strongly recommended nevertheless.
Linux and macOS
Generate a Key Pair
Perform the steps in this section on your local machine.
- Create a new key pair.
Caution
This command will overwrite an existing RSA key pair, potentially locking you out of other systems.If you’ve already created a key pair, skip this step. To check for existing keys, runls ~/.ssh/id_rsa*
.If you accidentally lock yourself out of the SSH service on your Linode, you can still use the Lish console to login to your server. After you’ve logged in via Lish, update yourauthorized_keys
file to use your new public key. This should re-establish normal SSH access.The-b
flag instructsssh-keygen
to increase the number of bits used to generate the key pair, and is suggested for additional security. - Press Enter to use the default names
id_rsa
andid_rsa.pub
in the/home/your_username/.ssh
directory before entering your passphrase. - While creating the key pair, you will be given the option to encrypt the private key with a passphrase. This means that the key pair cannot be used without entering the passphrase (unless you save that passphrase to your local machine’s keychain manager). We suggest that you use the key pair with a passphrase, but you can leave this field blank if you don’t want to use one.
Upload your Public Key
There are a few different ways to upload your public key to your Linode from Linux and macOS client systems:
Using ssh-copy-id
ssh-copy-id
is a utility available on some operating systems that can copy a SSH public key to a remote server over SSH.- To use
ssh-copy-id
, pass your username and the IP address of the server you would like to access: - You’ll see output like the following, and a prompt to enter your user’s password:
- Verify that you can log in to the server with your key.
Using Secure Copy (scp)
Secure Copy (
Cautionscp
) is a tool that copies files from a local computer to a remote server over SSH:These instructions will overwrite any existing contents of the
authorized_keys
file on your server. If you have already set up other public keys on your server, use the ssh-copy-id
command or enter your key manually.- Connect to your server via SSH with the user you would like to add your key to:
- Create the
~/.ssh
directory andauthorized_keys
file if they don’t already exist: - Give the
~/.ssh
directory andauthorized_keys
files appropriate file permissions: - In another terminal on your local machine, use
scp
to copy the contents of your SSH public key (id_rsa.pub
) into theauthorized_keys
file on your server. Substitute in your own username and your server’s IP address: - Verify that you can log in to the server with your key.
Manually Copy an SSH Key
You can also manually add an SSH key to a server:
- Begin by copying the contents of your public SSH key on your local computer. You can use the following command to output the contents of the file:You should see output similar to the following:Note that the public key begins with
ssh-rsa
and ends with[email protected]
. - Once you have copied that text, connect to your server via SSH with the user you would like to add your key to:
- Create the
~/.ssh
directory andauthorized_keys
file if they don’t already exist: - Give the
~/.ssh
directory andauthorized_keys
files appropriate file permissions: - Open the
authorized_keys
file with the text editor of your choice (nano
, for example). Then, paste the contents of your public key that you copied in step one on a new line at the end of the file. - Save and close the file.
Note
If you initially logged into the server asroot
but edited theauthorized_keys
file of another user, then the.ssh/
folder andauthorized_keys
file of that user may be owned byroot
. Set that other user as the files’ owner: - Verify that you can log in to the server with your key.
Connect to the Remote Server
- SSH into the server from your local machine:
- If you chose to use a passphrase when creating your SSH key, you will be prompted to enter it when you attempt to log in. Depending on your desktop environment, a window may appear:
Caution
Do not allow the local machine to remember the passphrase in its keychain unless you are on a private computer which you trust.You may also see the passphrase prompt at your command line: - Enter your password. You should see the connection establish in the local terminal.
Windows
The following instructions use the PuTTY software to connect over SSH, but other options are available on Windows too.
Generate a Key Pair with PuTTY
- Download PuTTYgen (
puttygen.exe
) and PuTTY (putty.exe
) from the official site. - Launch
puttygen.exe
. TheRSA
key type at the bottom of the window is selected by default for an RSA key pair butED25519
(EdDSA using Curve25519) is a comparable option if your remote machine’s SSH server supports DSA signatures. Do not use theSSH-1(RSA)
key type unless you know what you’re doing. - Increase the RSA key size from
2048
bits4096
and click Generate: - PuTTY uses the random input from your mouse to generate a unique key. Once key generation begins, keep moving your mouse until the progress bar is filled:
- When finished, PuTTY will display the new public key. Right-click on it and select Select All, then copy the public key into a Notepad file.
- Save the public key as a
.txt
file or some other plaintext format. This is important–a rich text format such as.rtf
or.doc
can add extra formatting characters and then your private key won’t work: - Enter a passphrase for the private key in the Key passphrase and Confirm passphrase text fields. Important: Make a note of your passphrase, you’ll need it later:
- Click Save private key. Choose a file name and location in Explorer while keeping the
ppk
file extension. If you plan to create multiple key pairs for different servers, be sure to give them different names so that you don’t overwrite old keys with new:
Manually Copy the SSH Key with PuTTY
- Launch
putty.exe
. Find the Connection tree in the Category window, expand SSH and select Auth. Click Browse and navigate to the private key you created above: - Scroll back to the top of the Category window and click Session. Enter the hostname or IP address of your Linode. PuTTY’s default TCP port is
22
, the IANA assigned port for for SSH traffic. Change it if your server is listening on a different port. Name the session in the Saved Sessions text bar and click Save: - Click the Open button to establish a connection. You will be prompted to enter a login name and password for the remote server.
- Once you’re logged in to the remote server, configure it to authenticate with your SSH key pair instead of a user’s password. Create an
.ssh
directory in your home directory on your Linode, create a blankauthorized_keys
file inside, and set their access permissions: - Open the
authorized_keys
file with the text editor of your choice (nano
, for example). Then, paste the contents of your public key that you copied in step one on a new line at the end of the file. - Save, close the file, and exit PuTTY.
- Verify that you can log in to the server with your key.
Using WinSCP
![Generate Generate](/uploads/1/2/5/8/125872289/693341869.png)
Uploading a public key from Windows can also be done using WinSCP:
CautionThese instructions will overwrite any existing contents of the
authorized_keys
file on your server. If you have already set up other public keys on your server, use the PuTTY instructions instead.- In the login window, enter your Linode’s public IP address as the hostname, the user you would like to add your key to, and your user’s password. Click Login to connect.
- Once connected, WinSCP will show two file tree sections. The left shows files on your local computer and the right shows files on your Linode. Using the file explorer on the left, navigate to the file where you saved your public key in Windows. Select the public key file and click Upload in the toolbar above.
- You’ll be prompted to enter a path on your Linode where you want to upload the file. Upload the file to
/home/your_username/.ssh/authorized_keys
. - Verify that you can log in to the server with your key.
Connect to the Remote Server with PuTTY
Start PuTTY and Load your saved session. You’ll be prompted to enter your server user’s login name as before. However, this time you will be prompted for your private SSH key’s passphrase rather than the password for your server’s user. Enter the passphrase and press Enter.
Troubleshooting
If your SSH connections are not working as expected, or if you have locked yourself out of your system, review the Troubleshooting SSH guide for troubleshooting help.
Upload your SSH Key to the Cloud Manager
It is possible to provision each new Linode you create with an SSH public key automatically through the Cloud Manager.
- Log in to the Cloud Manager.
- Click on your username at the top right hand side of the page. Then click on My Profile in the dropdown menu that appears:
Note
If you are viewing the Cloud Manager in a smaller browser window or on a smaller device, then the My Profile link will appear in the sidebar links. To view the sidebar links, click on the disclosure button to the left of the blue Create button at the top of the page. - From the My Profile page, select the SSH Keys tab, and then click Add a SSH Key:
- Create a label for your key, then paste in the contents of your public SSH key (
id_rsa.pub
): - Click Add Key.
- When you next create a Linode you’ll be given the opportunity to include your SSH key in the Linode’s creation. This key will be added to the root user of the new Linode.In the Create Linode form, select the SSH key you’d like to include. This field will appear below the Root Password field:
Next Steps
After you set up your SSH keys and confirm they are working as expected, review the How to Secure Your Server guide for instructions on disabling password authentication for your server.
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This guide is published under a CC BY-ND 4.0 license.
If you want to create automatic logins to your ExaVault SFTP service, you can do so via an SSH key pair. You can create such a key pair automatically or manually.
Create Key Pair Automatically through ExaVault file manager (Recommended)
You can create keys directly from your account:
- Log in into your account as the master user or as an admin user.
- Pick the user you want to create keys for and choose the Generate SSH Keys button from the drop-down menu. This will create the
.sftp
folder in the home folder of the user, and the public key will be added to theauthorized_keys
file and placed inside the.sftp
folder ( e.g./.sftp/authorized_keys
). You will be prompted to download the private key file. - Import the private key into your SFTP software on your local computer.
You should now be able to connect without a password.
Generate Ssh Key Osx
Linux / Mac OS X - Manual Key Creation (Experts Only)
- Open a terminal and use OpenSSH to generate a public/private key pair. You should not enter a password when prompted (e.g. just press return):
- Convert the public key to RFC-4716 format, which is the only format our SFTP server accepts for public keys:
Prior to OpenSSH v5.4, there was a bug which allows for comments longer than 72 characters, which is in violation of the RFC-4716 spec. Our FTP server will reject such keys as invalid. If you're using a version of OpenSSH prior to v5.4, you should open the key file and delete any comment longer than 72 characters. - Change the name of the public key to read
authorized_keys
. - Using an SFTP client with a username and password, upload the RFC-4716 format key to your ExaVault SFTP server. It must be placed inside of a folder named
.sftp
in the home folder of the user (e.g./.sftp/authorized_keys
). - Import the private key into your SFTP software on your local machine. There are many ways to do this, depending on the software. For example, if you use sftp you would enter:
You should now be able to connect without a password.
Windows - Manual Key Creation (Experts Only)
Due to the multiple applications necessary to create an SSH key in Windows, we strongly recommend using an ExaVault-generated SSH key for Windows machines. However, ExaVault does support the use of SSH keys manually created in Windows as long as they are converted properly.
- Download and install the PuTTy application from http://www.putty.org/. Version 0.70 is the latest version. Install the 32-bit version of the application. When installing, use the default settings for installation.
- Start the PuTTyGen application. This application is installed as part of the PuTTy installation. Under the Key menu, verify that the key is set to SSH-2 RSA key. Under the Parameters section, confirm that the type of key is set to RSA. Confirm that the number of bits is set to 2048.
- Click the Generate button. When prompted move the mouse over the blank area in the application.
- Click the Save Public Key button. When prompted, name the file authorized_keys and make note of where you save this file.
- Click the Save Private Key button. Take note of the name and location of this file. When prompted, click the Yes button if you do not want to include a passphrase on the key.
- Convert the public key (the one you named authorized_keys) to a UNIX file format. The key will not be recognized by the server if it contains Windows line endings. Open the file in a text editor that can convert line endings from Windows to UNIX. Notepad++ is a free software that can convert Windows line endings to UNIX line endings. Save the file after converting the line endings.
- Using an SFTP client with a username and password, upload the authorized_keys file to your ExaVault SFTP server. It must be placed inside of a folder named
.sftp
in the home folder of the user (e.g./.sftp/authorized_keys
). - Import the private key into your SFTP software on your local machine. There are many ways to do this, depending on the software.
You should now be able to connect without a password.
Example SSH Keys
If you are having trouble generating your SSH keys, you can find an example pair here to verify that your keys are formatted correctly. These keys are for verification purposes only. Because both the public and private keys are provided in this example to anyone, please do not upload the public key to your SFTP server!
SSH Keys FAQ
Can I use multiple SSH keys with SFTP?
Yes! Simply append each additional public key into the authorized_keys file on the FTP server asdescribed above.
Can I use a key that was provided to me?
You may have a customer or client who already has an SSH key pair that you need to import.
You can upload a public key that was provided to you as long as it conforms to the RFC-4716 format. Often you will need to convert your key to the RFC-4716 format. To convert the key, see Steps 2 and 3 of the Linux/Mac OS X key creation instructions.
If the key was created on a Windows machine, you may need to edit the public key so that it does not contain Windows line endings using a text editor that can convert Windows line endings to UNIX line endings.
If you run into problems using your key, email us at [email protected].