(Java) Verify XML Signature with External URL References

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

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import com.chilkatsoft.*;

public class ChilkatExample {

  static {
    try {
        System.loadLibrary("chilkat");
    } catch (UnsatisfiedLinkError e) {
      System.err.println("Native code library failed to load.\n" + e);
      System.exit(1);
    }
  }

  public static void main(String argv[])
  {
    // 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>

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

    // First load the signed XML
    CkStringBuilder sbSignedXml = new CkStringBuilder();
    boolean success = sbSignedXml.LoadFile("qa_data/xml_dsig_verify/signedWithExternalUrlRefs.xml","utf-8");
    if (success == false) {
        System.out.println("Failed to load signed XML.");
        return;
        }

    success = verifier.LoadSignatureSb(sbSignedXml);
    if (success == false) {
        System.out.println(verifier.lastErrorText());
        return;
        }

    // Iterate over each reference.  If it is an external URL reference, download the data and provide it to the verifier.
    CkStringBuilder sbRefUri = new CkStringBuilder();
    CkBinData bd = new CkBinData();
    int numRefs = verifier.get_NumReferences();
    int i = 0;
    while (i < numRefs) {
        if (verifier.IsReferenceExternal(i) == true) {
            sbRefUri.Clear();
            sbRefUri.Append(verifier.referenceUri(i));
            if (sbRefUri.StartsWith("https://",false) == true) {
                System.out.println("External URL Reference: " + sbRefUri.getAsString());

                // Download the data at the URL and provide to the verifier.
                success = http.DownloadBd(sbRefUri.getAsString(),bd);
                if (success == false) {
                    System.out.println(http.lastErrorText());
                    return;
                    }

                success = verifier.SetRefDataBd(i,bd);
                if (success == false) {
                    System.out.println(verifier.lastErrorText());
                    return;
                    }

                }

            }

        i = i+1;
        }

    // Now that we have the external data, verify the signature..
    boolean bVerified = verifier.VerifySignature(true);
    if (bVerified == false) {
        System.out.println(verifier.lastErrorText());
        }

    System.out.println("Signature verified = " + bVerified);
  }
}