'Get signed arguments from the response message.  Return a
dict of all arguments in the specified namespace.  If any of
the arguments are not signed, return None.'

def getSignedNS(self, ns_uri):

    msg_args = self.message.getArgs(ns_uri)
    for key in msg_args.iterkeys():
        if (not self.isSigned(ns_uri, key)):
            oidutil.log(('SuccessResponse.getSignedNS:    (%s,    %s)    not    signed.' % (ns_uri, key)))
            return None
    return msg_args
