Generate RSA keys with SSH by using PuTTYgen

  • Last updated on: 2016-06-23
  • Authored by: Rackspace Support

One effective way of securing SSH access to your cloud server is to use a public-private key pair. This means that a public key is placed on the server and a private key is placed on your local workstation. Using a key pair makes it impossible for someone to log in by using just a password, as long as you set up SSH to deny password-based authentication.

This article provides steps for generating RSA keys by using PuTTYgen on Windows for secure SSH authentication with OpenSSH.

Generate keys

In Windows, use PuTTYgen to generate your public and private keys.

  1. If needed, download PuTTYgen from the PuTTY download page. (PuTTYgen might have been installed previously with PuTTY or WinSCP.)
  2. Launch the program, and then click the Generate button. The program generates the keys for you.
  3. Enter a unique key passphrase in the Key passphrase and Confirm passphrase fields. For additional information about using passphrases, see Log in with a SSH Private Key on Windows.
  4. Save the public and private keys by clicking the Save public key and Save private key buttons.
  5. From the Public key for pasting into OpenSSH authorized_keys file field at the top of the window, copy all the text (starting with ssh-rsa) to your clipboard by pressing Ctrl-C. You need this key available on your clipboard to paste either into the public key tool in the Control Panel or directly into the authorized keys on your cloud server.

Use the key pair

You can use the RSA key pair in the following ways.

Specify your SSH key when creating a new cloud server

When you create a cloud server, you can assign a public key from the list of keys. If your key is not already in the list, you may add it, and then assign it.

Add a new public key to the list

  1. Under Advanced Options on the Create Server page, click Manage SSH Keys.
  2. Select public key for the cloud server from the SSH Keys list and click Add Public Key.
  3. Enter the key name, select the region, and paste the entire public key into the Public Key field. Then click Add Public Key.
  4. Go back to the Create Server page, and confirm that your key is listed in the SSH Key list.

Assign a public key

  1. Under Advanced Options on the Create Server page, select the public key you want to use from the SSH key drop-down menu.
  2. When you are done specifying the all the other details for the server, click Create Server.

Assign your SSH Key to an existing cloud server

To make use of your newly generated RSA key pair, you must tell PuTTY to use it when connecting to your cloud server.

  1. To edit the file (or create it), run the following command on the cloud server:

    nano ~/.ssh/authorized_keys
  2. Paste the text onto its own line in the file.

    You must have the key available in your clipboard to paste it. The key and its associated text (the ssh-rsa identified at the start and the comment at the end) must be on one line in the file. If the text is word-wrapped onto multiple lines an error might occur when connecting.

  3. If you created the authorized_keys file, change its permissions after you’re done editing it by running the following command:

    chmod 600 ~/.ssh/authorized_keys
  4. Open PuTTY, and go to the SSH > Auth section.

  5. Browse to the location of the key file, and load the private key.

  6. Go to the Session page, and save the session. This saves the configuration so that PuTTY uses the key every time that you connect to your cloud server.

After you save your session, your key is loaded automatically when you connect to your server.

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