title: Paramiko SSH client is unable to unpack ED25519 key
body: <p>I'm trying to use a keypair for the SSH connection to an SFTP server.</p>
  
  <p>I am able to do so if I generate an RSA key via <code>ssh-keygen -t rsa</code>.</p>
  
  <p>When I connect to the server via Paramiko, things work fine:</p>
  
  <pre class="lang-py prettyprint-override"><code>    private_key = paramiko.RSAKey.from_private_key_file("/path/to/my/private/key")
      client = paramiko.SSHClient()
      client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
      print("Connecting.")
      client.connect(hostname="host.sftp.com", username="user", pkey=private_key)
      print("Connected.")
  </code></pre>
  
  <p>However, if I try to do this with a ED25519 key, I get the below error:</p>
  
  <pre><code>ssh-keygen -t ed25519
  </code></pre>
  
  <pre><code>  File "/usr/local/lib/python3.7/site-packages/paramiko/pkey.py", line 235, in from_private_key_file
      key = cls(filename=filename, password=password)
    File "/usr/local/lib/python3.7/site-packages/paramiko/rsakey.py", line 55, in __init__
      self._from_private_key_file(filename, password)
    File "/usr/local/lib/python3.7/site-packages/paramiko/rsakey.py", line 176, in _from_private_key_file
      self._decode_key(data)
    File "/usr/local/lib/python3.7/site-packages/paramiko/rsakey.py", line 192, in _decode_key
      n, e, d, iqmp, q, p = self._uint32_cstruct_unpack(data, "iiiiii")
    File "/usr/local/lib/python3.7/site-packages/paramiko/pkey.py", line 529, in _uint32_cstruct_unpack
      raise SSHException(str(e))
  paramiko.ssh_exception.SSHException: unpack requires a buffer of 4 bytes
  </code></pre>
  
  <p>I'm a bit at a loss here since googling around doesn't seem to yield any relevant solutions. Is this a bug within <code>paramiko</code>? It is an issue with how I am initializing my <code>SSHClient</code>? Or is it actually a theoretical issue (ie. the way ED25519 creates the key, it is not possible to read in via the low-level <code>unpack()</code> call)?</p>