Dart

Verify XML Signature with External URL References

See more XML Digital Signatures Examples

Demonstrates how to verify an XML digital signature that includes references to URLs where the data to be digested is on a web server. 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.

  // The signed XML we wish to verify contains external references such as this:

  //     <ds:Reference Id="xmldsig-e7ae7ce2-9133-4d56-bd97-0a6aef738cc2-ref0" URI="https://www.chilkatsoft.com/images/starfish.jpg">
  //       <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
  //       <ds:DigestValue>AOU810yJV5Np/DnO29qpObqiTSTTCDvxGsX5ayiTYXI=</ds:DigestValue>
  //     </ds:Reference>
  //     <ds:Reference Id="xmldsig-e7ae7ce2-9133-4d56-bd97-0a6aef738cc2-ref1" URI="https://www.chilkatsoft.com/hamlet.xml">
  //       <ds:DigestMethod Algorithm="http://www.w3.org/2001/04/xmlenc#sha256"/>
  //       <ds:DigestValue>4sRRyWOzC7EOic4fQ9+Op1pa10DbgoBGjBvkq09LZmE=</ds:DigestValue>
  //     </ds:Reference>

  final verifier = CkXmlDSig();
  final http = CkHttp();

  // First load the signed XML
  final sbSignedXml = CkStringBuilder();
  try {
    sbSignedXml.loadFile('qa_data/xml_dsig_verify/signedWithExternalUrlRefs.xml', 'utf-8');
  } on ChilkatException {
    print('Failed to load signed XML.');
    return;
  }

  try {
    verifier.loadSignatureSb(sbSignedXml);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Iterate over each reference.  If it is an external URL reference, download the data and provide it to the verifier.
  final sbRefUri = CkStringBuilder();
  final bd = CkBinData();
  final numRefs = verifier.numReferences;
  var i = 0;
  while (i < numRefs) {
    if (verifier.isReferenceExternal(i)) {
      sbRefUri.clear();
      sbRefUri.append(verifier.referenceUri(i));
      if (sbRefUri.startsWith('https://', false)) {
        print('External URL Reference: ${sbRefUri.getAsString()}');

        // Download the data at the URL and provide to the verifier.
        try {
          http.downloadBd(sbRefUri.getAsString(), bd);
        } on ChilkatException catch (e) {
          print(e.lastErrorText);
          return;
        }

        try {
          verifier.setRefDataBd(i, bd);
        } on ChilkatException catch (e) {
          print(e.lastErrorText);
          return;
        }
      }
    }

    i++;
  }

  // Now that we have the external data, verify the signature..
  var bVerified = true;
  try {
    verifier.verifySignature(true);
  } on ChilkatException {
    bVerified = false;
  }
  if (!bVerified) {
    print(verifier.lastErrorText);
  }

  print('Signature verified = $bVerified');
}