Dart Requires Chilkat v11.0.0+

RSASSA-PSS Sign String to Create Base64 PCKS7 Signature

See more Digital Signatures Examples

Signs a string to create a PKCS7 signature in the base64 encoding. The signature algorithm is RSASSA-PSS with SHA256. Dart

import 'package:chilkat/chilkat.dart';

void main() {
  var success = false;

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

  final crypt = CkCrypt2();

  // Get a digital certificate with private key from a .pfx
  // (Chilkat has many different ways to provide a cert + private key for siging.
  // Using a PFX is just one possible option.)
  final pfx = CkPfx();
  try {
    pfx.loadPfxFile('qa_data/rsassa-pss/privatekey.pfx', 'PFX_PASSWORD');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Get the certificate to be used for signing.
  // (The typical case for a PFX is that it contains a cert with an associated private key,
  // as well as other certificates in the chain of authentication.  The cert with the private
  // key should be in the first position at index 0.)

  final cert = CkCert();
  try {
    pfx.certAt(0, cert);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  crypt.setSigningCert(cert);

  // Indicate that RSASSA-PSS with SHA256 should be used.
  crypt.signingAlg = 'pss';
  crypt.hashAlgorithm = 'sha256';

  crypt.encodingMode = 'base64';

  // Sign a string and return the base64 PKCS7 detached signature
  final originalText = 'This is a test';
  final pkcs7sig = crypt.signStringENC(originalText);
  print('Detached Signature:');
  print(pkcs7sig);

  // This signature looks like this:
  // MIIG5wYJKoZIhvcNAQcCoIIG2DCCBtQCAQExDzANBgl .. YToLqEwTdU87ox5g7rvw==

  // The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
  // then copy-and-paste the Base64 signature into the form and decode..

  // The signature can be verified against the original data like this:
  success = true;
  try {
    crypt.verifyStringENC(originalText, pkcs7sig);
  } on ChilkatException {
    success = false;
  }
  print('Signature verified: $success');
  success = true;
  try {
    crypt.verifyStringENC('Not the original text', pkcs7sig);
  } on ChilkatException {
    success = false;
  }
  print('Signature verified: $success');

  // Now we'll create an opaque signature (the opposite of a detached signature). 
  // An opaque signature is a PKCS7 message that contains both the original data and
  // the signature.  The verification process extracts the original data.
  final opaqueSig = crypt.opaqueSignStringENC(originalText);
  print('Opaque Signature:');
  print(opaqueSig);

  // The ASN.1 of the signature can be examined by browsing to https://lapo.it/asn1js/ ,
  // then copy-and-paste the Base64 signature into the form and decode..

  // We can verify and extract the original data:
  final String origTxt;
  try {
    origTxt = crypt.opaqueVerifyStringENC(opaqueSig);
  } on ChilkatException catch (e) {
    print('Signature verification failed.');
    print(e.lastErrorText);
    return;
  }

  print('Signature verified.');
  print('Extracted text:$origTxt');
}