Dart

Sign PDF: Choosing RSASSA-PSS or PKCS1-v1_5 and Hash Algorithm

See more PDF Signatures Examples

This example demonstrates how to choose between RSASSA-PSS vs. PKCS1-v1_5 and the hash algorithm when signing a PDF. 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 attribute is needed.
  json.updateInt('signingCertificateV2', 1);

  // ---------------------------------------------------------------------------------------------------------------------------
  // This example is the same as the example at Sign a PDF (Simplest Example Possible)
  // but with the following lines added to specify the signature scheme and hash algorithm.

  // The signature schemes PKCS-v1_5 and RSASSA-PSS have differences. 
  // PKCSV1_5 is deterministic. The same message and key will produce an identical signature value each time. 
  // PSS is randomized and will produce a different signature value each time.

  // To choose the hash algorithm:
  // (The typical choices are sha1, sha256, sha384, and sha512.)
  json.updateString('hashAlgorithm', 'sha256');

  // To choose PKCSV1_5:
  json.updateString('signingAlgorithm', 'pkcs');
  // Alternatively, to choose RSASSA-PSS:
  json.updateString('signingAlgorithm', 'pss');

  // If not specified, the default is SHA256 with PKCS-v1_5.

  // The remainder of this example is the same as the example at Sign a PDF (Simplest Example Possible)
  // ---------------------------------------------------------------------------------------------------------------------------

  // Put the signature on page 1, top left
  json.updateInt('page', 1);
  json.updateString('appearance.y', 'top');
  json.updateString('appearance.x', 'left');

  // Use a font scale of 10.0
  json.updateString('appearance.fontScale', '10.0');

  // In this example, the appearance of the digital signature will contain three lines:
  // 1) The signing certificate's common name
  // 2) The current date/time
  // 3) Some arbitrary text.
  // The keyword "cert_cn" is replaced with the Certificate's Subject Common Name.
  // The keyword "current_dt" is replaced with the current date/time.
  // Any number of appearance text lines can be added.
  json.updateString('appearance.text[0]', 'Digitally signed by: cert_cn');
  json.updateString('appearance.text[1]', 'current_dt');
  json.updateString('appearance.text[2]', 'The crazy brown fox jumps over the lazy dog.');

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

  print('The PDF has been successfully cryptographically signed.');

  // The appearance of the signature appears in Adobe Acrobat as shown here:

  // (image:https://example-code.com/images/signature1.jpg/endImage)
}