private String assinaCancelametoInutilizacao(String xml,
            String certificado, String senha, String tagCancInut)
            throws Exception {
        Document document = documentFactory(xml);

        XMLSignatureFactory signatureFactory = XMLSignatureFactory
                .getInstance("DOM");
        ArrayList<Transform> transformList = signatureFactory(signatureFactory);
        loadCertificates(certificado, senha, signatureFactory);

        NodeList elements = document.getElementsByTagName(tagCancInut);
        org.w3c.dom.Element el = (org.w3c.dom.Element) elements.item(0);
        String id = el.getAttribute("Id");

        Reference ref = signatureFactory.newReference("#" + id,
                signatureFactory.newDigestMethod(DigestMethod.SHA1, null),
                transformList, null, null);

        SignedInfo si = signatureFactory.newSignedInfo(signatureFactory
                .newCanonicalizationMethod(CanonicalizationMethod.INCLUSIVE,
                        (C14NMethodParameterSpec) null), signatureFactory
                .newSignatureMethod(SignatureMethod.RSA_SHA1, null),
                Collections.singletonList(ref));

        XMLSignature signature = signatureFactory.newXMLSignature(si, keyInfo);

        DOMSignContext dsc = new DOMSignContext(privateKey, document.getFirstChild());
        signature.sign(dsc);

        return outputXML(document);
    }