(Delphi DLL) Verify XML Signature having KeyInfo / X509Data / X509SKI

This example demonstrates how to verify an XML Digital Signature where the KeyInfo element contains an X509Data element,
which in turn contains an X509SKI element which contains only the signing certificate's Subject Key Identifier (SKI).

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, XmlDSig, XmlCertVault;

...

procedure TForm1.Button1Click(Sender: TObject);
var
signedSoapXmlUrl: PWideChar;
http: HCkHttp;
sbXml: HCkStringBuilder;
success: Boolean;
sbCertPem: HCkStringBuilder;
certVault: HCkXmlCertVault;
verifier: HCkXmlDSig;
bVerified: Boolean;

begin
// This example requires the Chilkat API to have been previously unlocked.
// See Global Unlock Sample for sample code.

// The SOAP XML with digital signature verified in this example is available at 
// https://www.chilkatsoft.com/exampleData/sigWithX509SKI.xml

signedSoapXmlUrl := 'https://www.chilkatsoft.com/exampleData/sigWithX509SKI.xml';

// First, let's get the signed SOAP XML..
http := CkHttp_Create();
sbXml := CkStringBuilder_Create();
success := CkHttp_QuickGetSb(http,signedSoapXmlUrl,sbXml);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkHttp__lastErrorText(http));
    Exit;
  end;

// The signed XML downloaded from the above URL contains the following.

// <?xml version="1.0" encoding="UTF-8" standalone="no" ?>
// <SOAP-ENV:Envelope xmlns:SOAP-ENV="http://schemas.xmlsoap.org/soap/envelope/">
//     <SOAP-ENV:Header>
//         <wsse:Security xmlns:wsse="http://docs.oasis-open.org/wss/2004/01/oasis-200401-wss-wssecurity-secext-1.0.xsd" SOAP-ENV:mustUnderstand="1"><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#"><InclusiveNamespaces xmlns="http://www.w3.org/2001/10/xml-exc-c14n#" PrefixList="wsse SOAP-ENV"/></ds:CanonicalizationMethod><ds:SignatureMethod Algorithm="http://www.w3.org/2001/04/xmldsig-more#rsa-sha256"/><ds:Reference URI="#Body"><ds:Transforms><ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/></ds:Transforms><ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/><ds:DigestValue>PIiVPpuMc1jGpWaL8ftzTOcc4gc=</ds:DigestValue></ds:Reference></ds:SignedInfo><ds:SignatureValue>Rlta8LplnFH0q8L+UeVmh4Smdn6oVETi4RoUmpT/KQX3RNAIOdCVE3b7gjmx5+3vp3DhjphOsZvW6dXzkI46xt9pD5otp3b/ZppGqKzltggo9gyQtPvJ8ltJZqVKYOGo5uElRFF/xm/zcx5Y3E14t+LYVSlv2lbem/zZ5zQ7ai8DmGD33id7nGu+MXVwb3kGkJFYoB/GOXtwsep+bcilMglTp8/7SBfBaVFKxWVBp4N2NW7bGlyDct8FaCk9hXQDNm/kqne9GU87tgh8/rbsFCYgyqIRMIvMPvhRWr2EKdEKyLtlZ8w0KYJYpgsf4T7SDghemzXkJoJPrfUQmHudIw==</ds:SignatureValue><ds:KeyInfo><ds:X509Data><ds:X509SKI>bDMtm8bAimMlGLU2M/82W8+y3tM=</ds:X509SKI></ds:X509Data></ds:KeyInfo></ds:Signature></wsse:Security>
//     </SOAP-ENV:Header>
//     <SOAP-ENV:Body xmlns:SOAP-SEC="http://schemas.xmlsoap.org/soap/security/2000-12" SOAP-SEC:id="Body">
//         <z:FooBar xmlns:z="http://example.com" />
//     </SOAP-ENV:Body>
// </SOAP-ENV:Envelope>

// Note: We don't have everything we need to verify the signature.
// The KeyInfo part of the Signature contains only the signing cert's Subject Key Identifier.  
// We must obtain the certificate locally using this information.  
// 
// On a Windows system, if the matching certificate is already installed in the registry-based
// certificate stores, then your application does not need to do anything.  Chilkat will automatically
// locate and use the matching certificate installed on the Windows system.
// 
// This example will assume we're not on a Windows system, or that the matching certificate
// is not already installed on the system.
// 

// One strategy for providing certificates to the application doing the XML signature verification 
// is to load all possible certificates into an in-memory XmlCertVault beforehand, and then call
// UseCertVault to allow for Chilkat to automatically find the matching cert from the pre-loaded certificates.
// We'll do that here with the one certificate that we already know is the matching certificate.

sbCertPem := CkStringBuilder_Create();
success := CkHttp_QuickGetSb(http,'https://chilkatdownload.com/example_data/testcertificate.pem',sbCertPem);
if (success <> True) then
  begin
    Memo1.Lines.Add(CkHttp__lastErrorText(http));
    Exit;
  end;

// Create a cert vault and add the certificates.
// In this example, we're only adding a single certificate.  An application
// could load many certificates into the cert vault..
certVault := CkXmlCertVault_Create();
success := CkXmlCertVault_AddCertString(certVault,CkStringBuilder__getAsString(sbCertPem));
if (success <> True) then
  begin
    Memo1.Lines.Add(CkXmlCertVault__lastErrorText(certVault));
    Exit;
  end;

verifier := CkXmlDSig_Create();

// Tell the verifier to use the certVault as a source for locating
// matching certificates.
CkXmlDSig_UseCertVault(verifier,certVault);

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

bVerified := CkXmlDSig_VerifySignature(verifier,True);
if (bVerified <> True) then
  begin
    Memo1.Lines.Add(CkXmlDSig__lastErrorText(verifier));
    Exit;
  end;

Memo1.Lines.Add('Signature verified!');

CkHttp_Dispose(http);
CkStringBuilder_Dispose(sbXml);
CkStringBuilder_Dispose(sbCertPem);
CkXmlCertVault_Dispose(certVault);
CkXmlDSig_Dispose(verifier);

end;