GetSignerCert

La fonction GetSignerCert passe en revue (énumère) les certificats dans un magasin de certificats jusqu’à ce qu’un certificat avec une clé de signature soit trouvé. Si un certificat est trouvé, un pointeur vers le certificat est retourné. Ce code illustre :

• Recherche d’un certificat avec une propriété de certificat.
• Vérification de cette propriété.
• Retour d’un pointeur vers le CERT_CONTEXT où l’attribut a été trouvé.

Ce code utilise un gestionnaire d’erreurs appelé MyHandleError. Pour afficher l’implémentation de ce gestionnaire d’erreurs, consultez la rubrique MyHandleError .

#include <windows.h>

PCCERT_CONTEXT GetSignerCert(
        HCERTSTORE hCertStore)
//--------------------------------------------------------------------
//   Parameter passed in:
//      hCertStore, the handle of the store to be searched.
{
//--------------------------------------------------------------------
//   Declare and initialize local variables.

PCCERT_CONTEXT       pCertContext = NULL;
BOOL                 fMore = TRUE;
DWORD                dwSize = NULL;
CRYPT_KEY_PROV_INFO* pKeyInfo = NULL;
DWORD                PropId = CERT_KEY_PROV_INFO_PROP_ID;

//--------------------------------------------------------------------
//  Find certificates in the store until the end of the store
//  is reached or a certificate with an AT_SIGNATURE key is found.

while(fMore && 
  (pCertContext= CertFindCertificateInStore(
     hCertStore,           // Handle of the store to be searched.
     0,                    // Encoding type. Not used for this search.
     0,                    // dwFindFlags. Special find criteria.
                           // Not used in this search.
     CERT_FIND_PROPERTY,   // Find type that determines the kind of 
                           // search to do. In this case, search for 
                           // certificates that have a specific 
                           // extended property.
     &PropId,              // pvFindPara. Gives the specific 
                           // value searched for, here the identifier 
                           // of an extended property.
     pCertContext)))       // pCertContext is NULL for the 
                           // first call to the function. 
                           // If the function is called
                           // in a loop, after the first call
                           // pCertContext is the certificate
                           // returned by the previous call.
{
//-------------------------------------------------------------
// For simplicity, this code only searches 
// for the first occurrence of an AT_SIGNATURE key. 
// In many situations, a search would also look for a 
// specific subject name as well as the key type.

//-------------------------------------------------------------
// Call CertGetCertificateContextProperty once to get the
// returned structure size.

   if(!(CertGetCertificateContextProperty(
                 pCertContext,
                 CERT_KEY_PROV_INFO_PROP_ID,
                 NULL,
                 &dwSize)))
   {
      MyHandleError("Error Getting Key Property");
   }

//--------------------------------------------------------------
// Allocate memory for the returned structure.
    
   if(pKeyInfo)
        free(pKeyInfo);
   if(!(pKeyInfo = (CRYPT_KEY_PROV_INFO*)malloc(dwSize)))
   {
       MyHandleError("Error Allocating Memory for pKeyInfo");
   }
 
   //--------------------------------------------------------------
   // Get the key information structure.

   if(!(CertGetCertificateContextProperty(
       pCertContext,
       CERT_KEY_PROV_INFO_PROP_ID,
       pKeyInfo,
       &dwSize)))
   {
       MyHandleError("The second call to the function failed.");
   }
   
   //-------------------------------------------     
   // Check the dwKeySpec member for a signature key.
   if(pKeyInfo->dwKeySpec == AT_SIGNATURE)
   {
        fMore  = FALSE;
    }
}  // End of while loop

if(pKeyInfo)
   free(pKeyInfo);
return (pCertContext);
}  // End of GetSignerCert