C/C++ Source: getVerifyingCert.cpp

#include <stdio.h>
#import <msxml5.dll>
using namespace MSXML2;

#import <capicom.dll>
using namespace CAPICOM;

#define DSIGNS "xmlns:ds='http://www.w3.org/2000/09/xmldsig#'"
#define INFILE "signature_signed.rsa.cert.xml"

IXMLDOMDocument3Ptr xmldoc = NULL;
IXMLDigitalSignaturePtr xmldsig = NULL;

VARIANT_BOOL objectsAreInitialized = VARIANT_FALSE;

VARIANT_BOOL LoadXML(_bstr_t sigFile)
{
   if (!objectsAreInitialized) {
      printf("Must initialize objects before loading signature.\n");
      return VARIANT_FALSE;
   }

   if (xmldoc->load(sigFile) == VARIANT_FALSE) {
      printf("Can't load %s\n", (LPCSTR)sigFile);
      return VARIANT_FALSE;
   }

   _bstr_t ns= DSIGNS;
   xmldoc->setProperty("SelectionNamespaces", ns);

   // Set the signature property to a <ds:Signature> DOM node.
   xmldsig->signature = xmldoc->selectSingleNode(".//ds:Signature");

   if (xmldsig->signature == NULL) {
      printf("Failed to set the signature property.\n");
      return VARIANT_FALSE;
   }

   return VARIANT_TRUE;

}

VARIANT_BOOL IsCertificateValid(IXMLDSigKeyPtr pKey)
{
   if (pKey == NULL) {
      printf("invalid key object.\n");
      return VARIANT_FALSE;
   }

   // Retrieve the ceritificate from the verifying key.
   ICertificatePtr pCert=NULL;
   pCert = pKey->getVerifyingCertificate();
   if (pCert == NULL) {
      printf ("Can't get verifying certificate\n");
      return VARIANT_FALSE;
   }

   // Build and walk through the certificate's trust chain.
   IChain2Ptr pChain = NULL;
   HRESULT hr = pChain.CreateInstance(__uuidof(Chain));
   if (FAILED(hr)) {
      printf("Can't instantiate a trust chain.\n");
      return VARIANT_FALSE;
   }

   if (VARIANT_FALSE == pChain->Build(pCert)) {
      printf("broken trust chain.\n");
      return VARIANT_FALSE;
   }

   printf("Examining certificate chain:\n");
   long count = pChain->Certificates->Count;
   for (long i=1; i<=count; i++) {
      printf("  Certificate No. %d:\n", i);
      if (pCert) {
         pCert.Release(); 
         pCert=NULL; 
      }
      pCert = pChain->Certificates->Item[i];
      if (pCert == NULL) {
         printf("Can't get the %d-th certificate.\n",i);
         return VARIANT_FALSE;
      }
      printf("     subject: %s\n",(LPSTR)pCert->SubjectName); 
      printf("     issuer:  %s\n\n",(LPSTR)pCert->IssuerName);
   }

   // Examine the root certificate in the chain.
   if (pCert) {
      pCert.Release();
      pCert=NULL;
   }

   pCert = pChain->Certificates->Item[count];
   if (pCert == NULL) {
      printf("Can't get root certificate.\n");
      return VARIANT_FALSE;
   }
   printf("Display the Root certificate:\n");
   printf("   subject:  %s\n",(LPSTR)pCert->SubjectName);
   printf("   issuer:   %s\n\n",(LPSTR)pCert->IssuerName);

   if (pCert) pCert.Release();
   if (pChain) pChain.Release();

   return VARIANT_TRUE;
}

VARIANT_BOOL VerifyXML(XMLDSIG_WRITEKEYINFO fWriteKeyInfo)
{
   IXMLDOMNodePtr pKeyInfo, pNode;
   IXMLDSigKeyPtr pKey, pKeyOut;

   if (xmldsig->signature == NULL) {
      printf("Invalid signature.\n");
      return VARIANT_FALSE;
   }

   switch (fWriteKeyInfo & CERTIFICATES) 
   {
      case CERTIFICATES:
         pKeyInfo = xmldoc->selectSingleNode(
                  ".//ds:KeyInfo/ds:X509Data");
         break;
      case KEYVALUE:
         pKeyInfo = xmldoc->selectSingleNode(
                  ".//ds:KeyInfo/ds:KeyValue");
         break;
   }

   if (pKeyInfo == NULL) {
      printf("Invalid <ds:KeyInfo>\n");
      return VARIANT_FALSE;
   }

   pKey = xmldsig->createKeyFromNode(pKeyInfo);
   if (pKey== NULL) {
      printf("Invalid key from <ds:KeyInfo>\n");
      return VARIANT_FALSE;
   }

   pKeyOut = xmldsig->verify(pKey);
   if (pKeyOut== NULL) {
      printf("Invalid signature.\n");
      return VARIANT_FALSE;
   }

   printf("Signature verified on the data.\n\n");

   if ( (fWriteKeyInfo & CERTIFICATES) == CERTIFICATES) {
      if (IsCertificateValid(pKeyOut)) {
         printf("Certificate used is valid.\n");
      }
   }

   return VARIANT_TRUE;
}

VARIANT_BOOL initObjects()
{
   if (FAILED(xmldsig.CreateInstance(__uuidof(MXDigitalSignature50)) )) {
      printf("Installation of msxml5 is required to run this app.\n");
      return VARIANT_FALSE;
   }

   if (FAILED(xmldoc.CreateInstance(__uuidof(DOMDocument50)) )) {
      printf("Installation of msxml5 is required to run this app.\n");
      return VARIANT_FALSE;
   }
   xmldoc->async = VARIANT_FALSE;
   xmldoc->validateOnParse = VARIANT_FALSE;
   xmldoc->preserveWhiteSpace = VARIANT_TRUE;
   xmldoc->resolveExternals = VARIANT_FALSE;
   objectsAreInitialized = VARIANT_TRUE;

   return VARIANT_TRUE;
}

void cleanObjects()
{
   if (xmldoc) xmldoc.Release();
   if (xmldsig) xmldsig.Release();
}

void main() 
{

   if ( CoInitialize(NULL) == E_FAIL) {
      printf("can't initialize COM Lib\n");
      exit(-1);
   }

   if (!initObjects()) {
      cleanObjects();
      exit(-1);
   }

   printf("Verifying %s\n\n", INFILE);
   if (VARIANT_TRUE == LoadXML(INFILE)) {
      VerifyXML(CERTIFICATES);
   }

   cleanObjects();
   CoUninitialize();
}

Try It!

1. Ensure that you have completed all the procedures in Getting Started with XML Digital Signatures.
2. Start Visual C++.
3. From the File menu, select New. On the Projects tab of the New dialog box that appears, select Win32 Console Application in the left pane. Then type "getVerifyingCertProj" in the Project name field. For the project Location field, either accept the default setting or choose another location. Click OK.
4. The Win32 Console Application property page will appear. For the type of Console Application, select An empty project and click Finish. When the New Project Information box displays, click OK.
5. Select FileView on the project browser, and highlight getVerifyingCertProj files. From the File menu, select New.
6. On the Files tab of the New dialog box, highlight C++ Source File. Then type "signature_signed.rsa.cert.xml" in the File name text box.
7. Click OK.
8. Copy the XML signature template file from Resource Files (signature_signed.rsa.cert.xml), and paste it into the text file you just created.

   Note   You can also copy the file into the project's main directory using Windows Explorer (or a command prompt).

9. Repeat steps 5-8 for the C++ file above (getVerifyingCert.cpp).
10. From the Project menu, click Settings..., then click the Link tab.
11. In Object/library modules, type "crypt32.lib". Insert this text either before or after the existing string that lists all objects and modules for the current project. Then click OK.
12. Build the sample by selecting Build getVerifyingCertProj.exe from the Build menu.
13. Execute the sample application by selecting !Execute getVerifyingCertProj.exe from the Build menu.
14. Verify that your output is similar to that listed in the Output topic.