Dart

Sign PDF with Long-Term Validation (LTV Enabled)

See more PDF Signatures Examples

This example demonstrates how to a sign a PDF with long-term validation (LTV) enabled.

Note: This example requires Chilkat v9.5.0.85 or greater.

Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // This example requires the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  final pdf = CkPdf();

  // Load a PDF to be signed.
  // The "hello.pdf" is available at https://chilkatsoft.com/hello.pdf
  try {
    pdf.loadFile('qa_data/pdf/hello.pdf');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Options for signing are specified in JSON.
  final json = CkJsonObject();

  // In most cases, the signingCertificateV2 and signingTime attributes are required.
  json.updateInt('signingCertificateV2', 1);
  json.updateInt('signingTime', 1);

  // Add the "ltvOcsp" instruction to the JSON passed to SignPdf.
  // This is what causes Chilkat to create an LTV-enabled signature.
  // 
  // If we are signing a PDF that already has signatures, then the existing signatures
  // are automatically verified, and Chilkat will do OCSP certificate status checking (if possible) 
  // for those certs in existing signatures (including certs in the certificate chains) 
  // that do not yet have a valid OCSP response in the DSS (Document Security Store).
  // Chilkat will add the OCSP responses to the /OCSPs in the Document Security Store (/DSS).
  // Also, and certificates from existing signatures not yet in the DSS are added to the /Certs 
  // in the DSS.
  // 
  // Also, the "ltvOcsp" causes Chilkat to add the pdfRevocationInfoArchival authenticated attribute
  // to the CMS signature.  The pdfRevocationInfoArchival attribute (1.2.840.113583.1.1.8)
  // contains OCSP responses and the CRL for the issuer of the signing certificate.
  // Therefore, Chilkat will send an OCSP request to the signing certificate's OCSP URl (if one exists)
  // and will download the CRL from the issuer certificate's CRL Distribution Point (if one exists).
  json.updateBool('ltvOcsp', true);

  // -----------------------------------------------------------------------------------
  // Note: If Chilkat produces a signed PDF, but the signature is not LTV-enabled,
  // the cause might be related to a failure to download CRL's or OCSP requests.
  // See Possible Solution for Failure to Produce LTV-enabled PDF Signature
  // -----------------------------------------------------------------------------------
  // You can add the following to UncommonOptions to get detailed information about the CRL and OCSP requests
  // You shouldn't set the following logging options unless there is a need, because it adds a large amount of information to the LastErrorText.
  pdf.uncommonOptions = 'LOG_OCSP_HTTP,LOG_CRL_HTTP';

  // Define the appearance of the signature.
  json.updateInt('page', 1);
  json.updateString('appearance.y', 'top');
  json.updateString('appearance.x', 'left');
  json.updateString('appearance.fontScale', '10.0');
  json.updateString('appearance.text[0]', 'Digitally signed by: cert_cn');
  json.updateString('appearance.text[1]', 'current_dt');
  json.updateString('appearance.text[2]', 'This is an LTV-enabled signature.');

  // Load the signing certificate. (Use your own certificate.)
  final cert = CkCert();
  try {
    cert.loadPfxFile('qa_data/pfx/myPdfSigningCert.pfx', 'pfxPassword');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Tell the pdf object to use the certificate for signing.
  try {
    pdf.setSigningCert(cert);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  try {
    pdf.signPdf(json, 'qa_output/hello_ltv_signed.pdf');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('The PDF has been successfully cryptographically signed with long-term validation.');

  // If you open the Signature Panel in Adobe Acrobat, it will indicate that the signature is LTV enabled
  // as shown here:
  // (image:https://example-code.com/images/ltv_signature.jpg/endImage)
}