'Verifies the signature of a XML document.
:param signedtext: The XML document as a string
:param cert_file: The public key that was used to sign the document
:param cert_type: The file type of the certificate
:param node_name: The name of the class that is signed
:param node_id: The identifier of the node
:param id_attr: Should normally be one of "id", "Id" or "ID"
:return: Boolean True if the signature was correct otherwise False.'

def verify_signature(self, signedtext, cert_file=None, cert_type='pem', node_name=NODE_NAME, node_id=None, id_attr=''):

    if (not cert_file):
        cert_file = self.cert_file
        cert_type = self.cert_type
    if (not id_attr):
        id_attr = ID_ATTR
    return self.crypto.validate_signature(signedtext, cert_file=cert_file, cert_type=cert_type, node_name=node_name, node_id=node_id, id_attr=id_attr)
