Dart

Create and Verify an Opaque PKCS7/CMS Signature

See more Digital Signatures Examples

Demonstrates how 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 PFX/.p12, Java keystore, JWK, Windows registry-based certificate stores, and other sources.
  // This example will load the certificate from a .crt and the private key from a .key file

  final cert = CkCert();
  // The LoadFromFile method will automatically detect the format and load it.
  try {
    cert.loadFromFile('qa_data/certs/test_12345678a.cer');
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Our private key is in an encrypted PKCS8 format.
  // If you don't know the format of your key, but you do know it's encrypted,
  // and requires a password, then just call any of the Chilkat methods that load
  // a private key w/ a password argument.  Chilkat will auto-detect the format
  // and load it correctly even if it's not the format indicated by the method name..
  final privKey = CkPrivateKey();
  final password = '12345678a';
  try {
    privKey.loadPkcs8EncryptedFile('qa_data/certs/test_12345678a.key', password);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Set properties required for signing.

  // Tell it to use the cert and private key we've loaded.
  try {
    crypt.setSigningCert2(cert, privKey);
  } 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();

  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.
}