Dart

A3/A4 Certificate to Create and Verify an Opaque PKCS7/CMS Signature

See more Digital Signatures Examples

Demonstrates how to use an A3 or A4 certificate w/ private key on a smartcard or token to create a PKCS7 opaque signature, and also how to verify an opaque signature.

An opaque signature is different than a detached PKCS7 signature in that it contains the original data. Verifying an opaque signature retrieves the original content.

Dart

import 'package:chilkat/chilkat.dart';

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

  final crypt = CkCrypt2();

  // A certificate and private key is needed to create a signature.
  // Chilkat provides many different ways to load a certificate and private key, such
  // as from a smartcards and hardware tokens, PFX/.p12, Java keystore, JWK, Windows registry-based certificate stores, and other sources.
  // This example will load the default certificate from the smartcard that is currently in
  // the smartcard reader.

  final cert = CkCert();

  // If the smartcard or token requires a PIN, we can set it here to avoid the dialog...
  cert.smartCardPin = '000000';

  try {
    cert.loadFromSmartcard('');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Tell it to use the cert and private key we've loaded.
  try {
    crypt.setSigningCert(cert);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Indicate we want the opaque signature in base64 format:
  crypt.encodingMode = 'base64';

  // Sign the string using the "utf-8" byte representation:
  crypt.charset = 'utf-8';

  // Create the opaque signature:
  final originalData = 'This is the string to be signed.';
  final String opaqueSig;
  try {
    opaqueSig = crypt.opaqueSignStringENC(originalData);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print(opaqueSig);

  // The output looks like this:
  // MIIPgQYJKoZIhvcNAQcCoIIPcjCCD24CAQExCzAJBgUrDgMCGgUAMC8GCSqGSIb3DQEHAaAiBCBUaGlzIGlzIHRoZSBzdHJpbmcgdG8gYmUgc...

  // ----------------------------------------------------------------------------------------------
  // Now let's verify the signature and retrieve the original data.
  // We'll use a new Crypt2 object to keep things completely separate...

  final vCrypt = CkCrypt2();

  // We only need the certificate to verify a signature (and extract the data from
  // an opaque signature).  The public key is always embedded within a certificate.
  try {
    vCrypt.setVerifyCert(cert);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  vCrypt.encodingMode = 'base64';
  vCrypt.charset = 'utf-8';

  final String extractedData;
  try {
    extractedData = vCrypt.opaqueVerifyStringENC(opaqueSig);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print('The extracted data: $extractedData');

  // The output is:
  // The extracted data: This is the string to be signed.
}