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Once SSH key pairs are created, perform the following steps to enable this feature for your VCL account.
1. Go to your VCL "User Preferences".
2. Select "General Preferences".
3. Click the Enable radio button under Use public key authentication
  for  for SSH logins
4. Paste the contents of your public key file in the "Public keys" box.
5. Click the "Submit General Preferences" button.

On your next VCL reservation, your public key will be inserted onto the assigned machine.

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To test this change, make a new reservation as normal.
Specify When connecting to your reservation, specify the private key that matches the public key you used in the
 previous steps when you attempt to make an SSH connection with the
  VCL image.

If you are using a Linux or Mac machine to connect with the VCL image
  you can use the following SSH syntax in a terminal window.

  ssh -i <path_to_private_ssh_key> <username>@<ipaddress>

Replace <path_to_private_ssh_key> with the actual directory path to
  your private ssh key (e.g. .ssh/id_rsa). Replace <username> with
  your actual username. Replace <ipaddress> with the IP address of
  the VCL image listed in the Current reservation page.

If you are using a local Windows machine, you'll probably be using Putty for
you   your SSH connection. Make sure you specify the "private key file for
  authentication" in the "Options controlling SSH authentication"
  section of Putty. You can find this section by navigating through the
  options on the left side of Putty...

  Connection >> SSH >> Auth

WARNING: The ssh identity key will not work for images where your home directory
  resides on a network file system that cannot be accessed until you
  authenticate to the remote computer. Such , such as OpenAFS.