title: Signing docker images with delegation key only
body: <p>I'm trying following scenario.</p>
  
  <p>On my laptop I have created a delegation key.
  On a server I have created the target and authorized my delegation key
  Now when signing my Docker image via docker trust I'm getting following error.</p>
  
  <pre><code>An error occurred during validation: rpc error: code = 5 desc = key 6505d5d177b8ad1868d721f0043d0f16f4fc7cdbf27a0940c6f1ef52a95b15b9 not found
  </code></pre>
  
  <p>This <code>6505…</code>. key is the private key for the target on the other machine, which I don’t have on my current machine.</p>
  
  <p>Is what I'm trying even possible? Do I somehow have to synchronize all the keys to be able to do this?</p>
  
  <p>Wanted to keep the targets on a server for backup reasons as well for limiting who has access to those keys.</p>
  
  <p>I have also filed a related github ticket.</p>
  
  <p><a href="https://github.com/theupdateframework/notary/issues/1558" rel="nofollow noreferrer">https://github.com/theupdateframework/notary/issues/1558</a></p>