title: Python pysft/paramiko 'EOF during negotiation' error
body: <p>I'm using pysftp to download and upload some files. This exact same code I just run an hour before and was fine, but now I got this 'EOF during negotiation' error. What am I missing here?</p>
  
  <pre><code>&gt;&gt;&gt; sftp = pysftp.Connection(host, username=user, password=pasw)
  &gt;&gt;&gt; sftp
  &lt;pysftp.Connection object at 0x7f88b25bb410&gt;
  &gt;&gt;&gt; sftp.cd('data')
  &lt;contextlib.GeneratorContextManager object at 0x7f88b1a86910&gt;
  &gt;&gt;&gt; sftp.exists(filename)
  Traceback (most recent call last):
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
    File "/usr/local/lib/python2.7/dist-packages/pysftp/__init__.py", line 827, in exists
      self._sftp_connect()
    File "/usr/local/lib/python2.7/dist-packages/pysftp/__init__.py", line 205, in _sftp_connect
      self._sftp = paramiko.SFTPClient.from_transport(self._transport)
    File "/usr/local/lib/python2.7/dist-packages/paramiko/sftp_client.py", line 132, in from_transport
      return cls(chan)
    File "/usr/local/lib/python2.7/dist-packages/paramiko/sftp_client.py", line 101, in __init__
      raise SSHException('EOF during negotiation')
  paramiko.ssh_exception.SSHException: EOF during negotiation
  </code></pre>
  
  <p><strong>EDIT:</strong>
  Enabled loggin for paramiko.transport and got the following:</p>
  
  <pre><code>&gt;&gt;&gt; import logging; logging.basicConfig(); logging.getLogger('paramiko.transport').setLevel(logging.DEBUG)
  &gt;&gt;&gt; sftp = pysftp.Connection(host, username=user, password=pasw)
  DEBUG:paramiko.transport:starting thread (client mode): 0x27313b0L
  DEBUG:paramiko.transport:Local version/idstring: SSH-2.0-paramiko_1.16.0
  DEBUG:paramiko.transport:Remote version/idstring: SSH-2.0-OpenSSH_4.3p2
  INFO:paramiko.transport:Connected (version 2.0, client OpenSSH_4.3p2)
  DEBUG:paramiko.transport:kex algos:[...] client lang:[u''] server lang:[u''] kex follows?False
  DEBUG:paramiko.transport:Kex agreed: diffie-hellman-group1-sha1
  DEBUG:paramiko.transport:Cipher agreed: aes128-ctr
  DEBUG:paramiko.transport:MAC agreed: hmac-sha2-256
  DEBUG:paramiko.transport:Compression agreed: none
  DEBUG:paramiko.transport:kex engine KexGroup1 specified hash_algo &lt;built-in function openssl_sha1&gt;
  DEBUG:paramiko.transport:Switch to new keys ...
  DEBUG:paramiko.transport:Attempting password auth...
  DEBUG:paramiko.transport:userauth is OK
  INFO:paramiko.transport:Authentication (password) successful!
  &gt;&gt;&gt; sftp.cd('data')
  &lt;contextlib.GeneratorContextManager object at 0x027371D0&gt;
  &gt;&gt;&gt; sftp.exists(filename)
  DEBUG:paramiko.transport:[chan 0] Max packet in: 32768 bytes
  DEBUG:paramiko.transport:[chan 0] Max packet out: 32768 bytes
  DEBUG:paramiko.transport:Secsh channel 0 opened.
  DEBUG:paramiko.transport:[chan 0] Sesch channel 0 request ok
  Traceback (most recent call last):
  DEBUG:paramiko.transport:[chan 0] EOF received (0)
    File "&lt;stdin&gt;", line 1, in &lt;module&gt;
    File "C:\Python27\lib\site-packages\pysftp.py", line 802, in exists
  DEBUG:paramiko.transport:[chan 0] EOF sent (0)
      self._sftp_connect()
    File "C:\Python27\lib\site-packages\pysftp.py", line 192, in _sftp_connect
      self._sftp = paramiko.SFTPClient.from_transport(self._transport)
    File "C:\Python27\lib\site-packages\paramiko\sftp_client.py", line 132, in from_transport
      return cls(chan)
    File "C:\Python27\lib\site-packages\paramiko\sftp_client.py", line 101, in __init__
      raise SSHException('EOF during negotiation')
  paramiko.ssh_exception.SSHException: EOF during negotiation
  &gt;&gt;&gt;
  </code></pre>
  
  <p>Still no clue of what is wrong...</p>