Problem checking whether a document has been signed

I'm using iText to check whether some input PDF document has been signed. I don't need do actually check or certify the signature validity. I only need to know whether the document is signed, even though it is signed with a self-signed test certificate.

So I have the following method to check this "signature existance" in the informed PDFReader. The red line is the one throwing the exception, in the stack trace below.

public static boolean isAssinado(PdfReader documentoPDF) throws IOException, SignatureException {
  Object[] falhas = null;
  boolean assinado = false;
  // Obter o keystore
  KeyStore kall = PdfPKCS7.loadCacertsKeyStore();

// Recuperar AcroFields do documento
AcroFields af = documentoPDF.getAcroFields();

  // Recuperar nomes de assinaturas
  ArrayList names = af.getSignatureNames();
  LOG.debug("Nomes de Assinatura: "+names);
  assinado = names != null && names.size () > 0;

  // Itera os nomes de assinaturas obtidos
  if (assinado) {
   for (int k = 0; k < names.size(); ++k) {
    String name = (String) names.get(k);
    LOG.debug("Nome da Assinatura: " + name);
    LOG.debug("Assinatura todo o documento? " + af.signatureCoversWholeDocument(name));
    LOG.debug("Revisão do Documento: " + af.getRevision(name) + " de " + af.getTotalRevisions());
    PdfPKCS7 pk = af.verifySignature(name);
    Calendar cal = pk.getSignDate();
    LOG.debug("Data de Assinatura: "+formatter.format(cal.getTime()));
    LOG.debug("Assunto: " + PdfPKCS7.getSubjectFields(pk.getSigningCertificate()));
    boolean verificado = pk.verify();
    assinado &= verificado;
    LOG.debug("Documento foi modificado? " + !verificado);
   }
  }
  LOG.info("Documento Assinado? "+assinado);
  return assinado;
}

When I execute this code with real Tokens (A3), I get the following exception:

ExceptionConverter:
java.security.cert.CertificateException: sun.security.pkcs.ParsingException: toDerInputStream rejects tag type -96
        at sun.security.provider.X509Factory.engineGenerateCertificates (Unknown Source)
        at java.security.cert.CertificateFactory.generateCertificates(Unknown Source)
        at com.lowagie.text.pdf.PdfPKCS7.<init>(PdfPKCS7.java:250)
        at com.lowagie.text.pdf.AcroFields.verifySignature (AcroFields.java:1627)
        at com.lowagie.text.pdf.AcroFields.verifySignature(AcroFields.java:1583)
        at br.com.ect.sadel.common.PDFUtils.isAssinado (PDFUtils.java:50)
        at br.com.ect.sadel.control.PreparacaoDocumentoControle.executarPreparacao(PreparacaoDocumentoControle.java:267)
        at br.com.ect.sadel.control.PreparacaoDocumentoControle.executarPreparacao (PreparacaoDocumentoControle.java:129)
        at br.com.ect.sadel.control.PreparacaoDocumentoControle.run(PreparacaoDocumentoControle.java:475)
        at java.lang.Thread.run(Unknown Source)
Caused by: sun.security.pkcs.ParsingException : toDerInputStream rejects tag type -96
        at sun.security.pkcs.PKCS7.parse(Unknown Source)
        at sun.security.pkcs.PKCS7.<init>(Unknown Source)
        at sun.security.provider.X509Factory.parseX509orPKCS7Cert (Unknown Source)
        ... 10 more
Caused by: java.io.IOException: toDerInputStream rejects tag type -96
        at sun.security.util.DerValue.toDerInputStream(Unknown Source)
        at sun.security.pkcs.PKCS7.parseSignedData (Unknown Source)
        at sun.security.pkcs.PKCS7.parse(Unknown Source)
        ... 13 more

Do you have any idea about why this exception is being thrown?

Is my code correct? I mean, is this the right way to check whether the document has been signed? Like I said, I don't want to certify or validate the signature, I only need to know whether the document has been somehow signed, no matter what type the signature is and what origin or validity it has.

Thank you all in advance,

Filipe Fedalto

Cansado dos disparates e despautérios da República?
Quer um basta nas desventuras de nossos governantes?
Acesse http://www.monarquia.org.br e http://www.brasilimperial.org.br
e saiba mais a respeito.

By Date:	<-- -->
By Thread:	<-- -->