(Delphi DLL) Verify XML Signature with External Data Reference

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.

Chilkat for Delphi Downloads Chilkat non-ActiveX DLL for Delphi Chilkat ActiveX DLL for Delphi * The examples here use the non-ActiveX DLL.

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Http, StringBuilder, BinData, XmlDSig;

...

procedure TForm1.Button1Click(Sender: TObject);
var
url: PWideChar;
http: HCkHttp;
sbXml: HCkStringBuilder;
success: Boolean;
verifier: HCkXmlDSig;
refUri: PWideChar;
jpgData: HCkBinData;
bVerified: Boolean;

begin
// 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..

url := 'https://www.chilkatsoft.com/exampleData/xmlsig_external_jpg_reference.xml';
http := CkHttp_Create();
sbXml := CkStringBuilder_Create();
success := CkHttp_QuickGetSb(http,url,sbXml);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkHttp__lastErrorText(http));
    Exit;
  end;

verifier := CkXmlDSig_Create();

// 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.
success := CkXmlDSig_LoadSignatureSb(verifier,sbXml);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkXmlDSig__lastErrorText(verifier));
    Exit;
  end;

// 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">
refUri := CkXmlDSig__referenceUri(verifier,0);
if (CkXmlDSig_getLastMethodSuccess(verifier) <> True) then
  begin
    Memo1.Lines.Add('No reference URI found.');
    Exit;
  end;

// Download the JPG data to be verified.
jpgData := CkBinData_Create();
success := CkHttp_QuickGetBd(http,refUri,jpgData);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkHttp__lastErrorText(http));
    Exit;
  end;

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

// Verify the signature
bVerified := CkXmlDSig_VerifySignature(verifier,True);
Memo1.Lines.Add('Signature verified = ' + IntToStr(Ord(bVerified)));

CkHttp_Dispose(http);
CkStringBuilder_Dispose(sbXml);
CkXmlDSig_Dispose(verifier);
CkBinData_Dispose(jpgData);

end;