Creates and returns a Handshake packet that authenticates
    on the channel with the given stream key.

def _create_handshake(channel, key):
    """
    Creates and returns a Handshake packet that authenticates
    on the channel with the given stream key.
    """
    hsk = Handshake()
    hsk.channel = channel
    hsk.streamKey = key
    return hsk