Calculating a SSH host key with paramiko

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I needed to compare a host key from something other than a known_hosts file with what paramiko reports as part of the SSH connection today. If you must know, the host keys for these machines are retrieved a XMLRPC API… It turned out to be a lot easier than I thought. Here’s how I produced the host key entry as it appears in that API (as well as in the known_hosts file):

    #!/usr/bin/python
    
    # A host key calculation example for Paramiko.
    # Args:
    #   1: hostname
    
    import base64
    import os
    import paramiko
    import socket
    import sys
    
    # Socket connection to remote host
    sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    sock.connect((sys.argv[1], 22))
    
    # Build a SSH transport
    t = paramiko.Transport(sock)
    t.start_client()
    key = t.get_remote_server_key()
    
    print '%s %s' %(key.get_name(),
                    base64.encodestring(key.__str__()).replace('\n', ''))
    
    t.close()
    sock.close()
    

Note that I could also have constructed a paramiko key object based on the output of the XMLRPC API and then compared those two objects, but I prefer the human readable strings.

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