Dart

Verify XML Signature with External Data Reference

See more XML Digital Signatures Examples

Demonstrates how to verify an XML digital signature where the data is external. In this case, the data is a JPG file.

This example requires Chilkat v9.5.0.69 or greater.

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 XML containing the Signature to be verified contains the following:
  // <?xml version="1.0" encoding="UTF-8" standalone="no"?>
  // <abc>
  //   <xyz>
  //     <jpg>
  //         <name>starfish.jpg</name>
  //         <url>https://www.chilkatsoft.com/images/starfish.jpg</url>
  //     <ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#"><ds:SignedInfo><ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/><ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/><ds:Reference 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:SignedInfo><ds:SignatureValue>MbHOti6nOh9DJP/u7u1+a1u0wRYIGEdaAVk5ehxqeBhcR4qvGvCQ7wLxcfDuwFG2grSg43ANxDYngLqZTeFb5nCfywcuNBQI8FrNRVY5hkyv6kDW1BVN8ot9qPYX9oHxJp1e+nMszIiSxqHX3XDI7YnvFt/0CyeO5JaQQEzXzIwqqb8iUNcH/bJzR6CrTf1hGuQ5MPorG0bRwbYPPHHzipUqHBinK8VbHobnxL7GQHAhR8k9gDD35kZcMxf/74U7pGO19ZzTbdJW5S7q4bVVxvsuU3itTbhHI60pOE14ibrjZtIrPZLVUD3TQqIIF04TChW2NXdYOo3+ij4ZnP8x+g==</ds:SignatureValue><ds:KeyInfo><ds:KeyValue><ds:RSAKeyValue><ds:Modulus>sXeRhM55P13FbpNcXAMR3olbw2Wa6keZIHu5YTZYUBTlYWId+pNiwUz3zFIEo+0IfYR0H27ybIycQO+1IIzJofUFNMAL3tZps2OKPlsjuCPls6kXpXhv/gvhux8LrCtp4PcKWqJ6QVOZKChc7WAx40qFWzHi57ueqRTv3x0kESqGg/VjsqyTEvb55psJO2RsfhLT7+YVh3hImRM3RDaJdkTkPuOxeFyT6N7VXD09329sLuS3QkUbE9zEKDnz9X3d8dEQdJhSI9ba5fxl8R7fu8pB67ElfzFml96X1jLFtzy1pzOT5Fc4ROcaqlYckVzdBq9sxezm6MYmDBjNAcibRw==</ds:Modulus><ds:Exponent>AQAB</ds:Exponent></ds:RSAKeyValue></ds:KeyValue></ds:KeyInfo></ds:Signature></jpg>
  //   </xyz>
  // </abc>

  // The above XML is available at https://www.chilkatsoft.com/exampleData/xmlsig_external_jpg_reference.xml
  // First fetch the XML..

  final url = 'https://www.chilkatsoft.com/exampleData/xmlsig_external_jpg_reference.xml';
  final http = CkHttp();
  final sbXml = CkStringBuilder();
  try {
    http.quickGetSb(url, sbXml);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  final verifier = CkXmlDSig();

  // Load the XML containing the signatures to be verified.
  // Note that this particular Signature already contains the RSA public key that will be used
  // for verification.
  try {
    verifier.loadSignatureSb(sbXml);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Get the Reference URI, which in this case is the URL to the binary data that was hashed.
  // This fetchs the URI attribute value from:  <ds:Reference URI="https://www.chilkatsoft.com/images/starfish.jpg">
  final String refUri;
  try {
    refUri = verifier.referenceUri(0);
  } on ChilkatException {
    print('No reference URI found.');
    return;
  }

  // Download the JPG data to be verified.
  final jpgData = CkBinData();
  try {
    http.quickGetBd(refUri, jpgData);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  // Provide the JPG data to the verifier
  verifier.setRefDataBd(0, jpgData);

  // Verify the signature
  var bVerified = true;
  try {
    verifier.verifySignature(true);
  } on ChilkatException {
    bVerified = false;
  }
  print('Signature verified = $bVerified');
}