Example C Program: Getting and Setting Certificate Properties

The following example gets and sets certificate properties, and illustrates the following tasks and CryptoAPI functions.

• Opening a system store by using CertOpenSystemStore.
• Using CertEnumCertificatesInStore to list all of the certificates in the open store.
• Retrieving and printing the subject name from the certificate by using CertGetNameString.
• Setting the enhanced key usage property on certificates by using the CertAddEnhancedKeyUsageIdentifier function.
• Setting the display name property on the certificate by using CertSetCertificateContextProperty.
• Retrieving a certificate's properties by using CertGetCertificateContextProperty.
• Closing a certificate store by using CertCloseStore with the CERT_CLOSE_STORE_CHECK_FLAG flag.

#include <stdio.h>
#include <windows.h>
#include <wincrypt.h>
#pragma comment(lib, "crypt32.lib")

//--------------------------------------------------------------------
// Copyright (C) Microsoft. All rights reserved.
// Declare functions MyHandleError and My_Wait.
// These functions are defined at the end of the file.

void MyHandleError(char *s );

void My_Wait();

//--------------------------------------------------------------------
// Begin main.

void main (void)
{

//--------------------------------------------------------------------
// This program shows all of the certificates in a 
// certificate store and lists all of the property ID numbers of all 
// of the certificate contexts.

// It also adds an enhanced key usage identifier to every other
// certificate.

//--------------------------------------------------------------------
// Declare and initialize local variables.

HANDLE hCertStore; 
PCCERT_CONTEXT pCertContext=NULL; 
CRYPT_KEY_PROV_INFO *pCryptKeyProvInfo;
char pszNameString[256];
char pszStoreName[256];
char fResponse;
char fExtra;
BYTE *pName = (BYTE *)"Temp Name.";
CRYPT_DATA_BLOB Friendly_Name_Blob={32,pName};
void* pvData;
DWORD cbData;
DWORD dwFlags = CERT_STORE_NO_CRYPT_RELEASE_FLAG;
DWORD dwPropId = 0; // 0 must be used on the first
 // call to the function. After that,
 // the last returned property ID is 
 // passed.
LPCSTR pszUsageIdentifier = szOID_RSA_RC4;
int count = 0;

fprintf(stderr,"Please enter the store name :");
scanf_s("%s",pszStoreName);
fprintf(stderr,"The store name is %s .\n",pszStoreName);
My_Wait();

//--------------------------------------------------------------------
// Open the named system certificate store. 

if (!( hCertStore = CertOpenSystemStore(
 NULL,
 pszStoreName)))
{
 MyHandleError("Store not opened.");
}

//--------------------------------------------------------------------
// The file is open. Continue.
// In a loop, use CertEnumCertificatesInStore to get the each
// certificate in the store. 

while(pCertContext= CertEnumCertificatesInStore(
 hCertStore,
 pCertContext))
{
//--------------------------------------------------------------------
// First, retrieve and print the subject name from the certificate.

 if(CertGetNameString(
 pCertContext,
 CERT_NAME_SIMPLE_DISPLAY_TYPE,
 0,
 NULL,
 pszNameString,
 128))
 {
 printf("\nNew Cert for %s \n",pszNameString);
 }
 else
 {
 printf("The get name failed.\n");
 }
//--------------------------------------------------------------------
// Set the enhanced key usage property on every other certificate.

 if(count == 0)
 {
 count++;
 if(CertAddEnhancedKeyUsageIdentifier(
 pCertContext,
 pszUsageIdentifier))
 {
 printf("Enhanced key usage set.\n");
 }
 else
 {
 printf("Enhanced key usage was not set.\n");
 }
 }
 else
//--------------------------------------------------------------------
// Do not set the usage, but reset the counter so that the property
// will be set on the next certificate.
// Ask if the user would like to set a display name.
 {
 printf("Would you like to set the display name ?");
 scanf_s("%c%c",&fResponse,&fExtra);
 if(fResponse == 'y')
 {
 if(CertSetCertificateContextProperty(
 pCertContext, 
 CERT_FRIENDLY_NAME_PROP_ID, 
 0,
 &Friendly_Name_Blob))
 {
 printf("A name has been set.\n");
 }
 else
 {
 printf("The display name was not set.\n");
 }
 }
 count = 0;
 }

//--------------------------------------------------------------------
// In a loop, find all of the property IDs for the given certificate.
// The loop continues until the CertEnumCertificateContextProperties 
// returns 0.

 while(dwPropId = CertEnumCertificateContextProperties(
 pCertContext, // the context whose properties are to be listed.
 dwPropId)) // number of the last property found. Must be
 // 0 to find the first property ID.
 {
//--------------------------------------------------------------------
// Each time through the loop, a property ID has been found.
// Print the property number and information about the property.

 printf("Property # %d found->", dwPropId);
 switch(dwPropId)
 {
 case CERT_FRIENDLY_NAME_PROP_ID:
 {
//--------------------------------------------------------------------
// Retrieve the actual display name certificate property.
// First, get the length of the property setting the
// pvData parameter to NULL to get a value for cbData
// to be used to allocate memory for the pvData buffer.
 printf("FRIENDLY_NAME_PROP_ID ");
 if(!(CertGetCertificateContextProperty(
 pCertContext, 
 dwPropId, 
 NULL, 
 &cbData)))
 {
 MyHandleError("Call #1 to property length failed.");
 }
//--------------------------------------------------------------------
// The call succeeded. Use the size to allocate memory for the 
// property.
 if(!(pvData = (void*)malloc(cbData)))
 {
 MyHandleError("Memory allocation failed.");
 }
//--------------------------------------------------------------------
// Allocation succeeded. Retrieve the property data.
 if(!(CertGetCertificateContextProperty(
 pCertContext,
 dwPropId,
 pvData, 
 &cbData)))
 {
 MyHandleError("Call #2 getting the data failed.");
 }
 else
 {
 printf("\n The display name is -> %s.", pvData);
 free(pvData);
 }
 break;
 }
 case CERT_SIGNATURE_HASH_PROP_ID:
 {
 printf("Signature hash ID. ");
 break;
 }
 case CERT_KEY_PROV_HANDLE_PROP_ID:
 {
 printf("KEY PROVE HANDLE.");
 break;
 }
 case CERT_KEY_PROV_INFO_PROP_ID:
 {
 printf("KEY PROV INFO PROP ID.");
 if(!(CertGetCertificateContextProperty(
 pCertContext, // A pointer to the certificate
 // where the property will be set.
 dwPropId, // An identifier of the property to get. 
 // In this case,
 // CERT_KEY_PROV_INFO_PROP_ID
 NULL, // NULL on the first call to get the
 // length.
 &cbData))) // The number of bytes that must be
 // allocated for the structure.
 {
 MyHandleError("The property length was not retrieved.");
 }
 if(!(pCryptKeyProvInfo = 
 (CRYPT_KEY_PROV_INFO *)malloc(cbData)))
 {
 MyHandleError("Error in allocation of memory.");
 }
 if(CertGetCertificateContextProperty(
 pCertContext,
 dwPropId,
 pCryptKeyProvInfo,
 &cbData))
 {
 printf("\n The current key container is %S.",
 pCryptKeyProvInfo->pwszContainerName);
 free(pCryptKeyProvInfo);
 }
 else
 {
 free(pCryptKeyProvInfo);
 MyHandleError("The property was not retrieved.");
 }
 break;
 }
 case CERT_SHA1_HASH_PROP_ID:
 {
 printf("SHA1 HASH id.");
 break;
 }
 case CERT_MD5_HASH_PROP_ID:
 {
 printf("md5 hash id. ");
 break;
 }
 case CERT_KEY_CONTEXT_PROP_ID:
 {
 printf("KEY CONTEXT PROP id.");
 break;
 }
 case CERT_KEY_SPEC_PROP_ID:
 {
 printf("KEY SPEC PROP id.");
 break;
 }
 case CERT_ENHKEY_USAGE_PROP_ID:
 {
 printf("ENHKEY USAGE PROP id.");
 break;
 }
 case CERT_NEXT_UPDATE_LOCATION_PROP_ID:
 {
 printf("NEXT UPDATE LOCATION PROP id.");
 break;
 }
 case CERT_PVK_FILE_PROP_ID:
 {
 printf("PVK FILE PROP id. ");
 break;
 }
 case CERT_DESCRIPTION_PROP_ID:
 {
 printf("DESCRIPTION PROP id. ");
 break;
 }
 case CERT_ACCESS_STATE_PROP_ID:
 {
 printf("ACCESS STATE PROP id. ");
 break;
 }
 case CERT_SMART_CARD_DATA_PROP_ID:
 {
 printf("SMAART_CARD DATA PROP id. ");
 break;
 }
 case CERT_EFS_PROP_ID:
 {
 printf("EFS PROP id. ");
 break;
 }
 case CERT_FORTEZZA_DATA_PROP_ID:
 {
 printf("FORTEZZA DATA PROP id.");
 break;
 }
 case CERT_ARCHIVED_PROP_ID:
 {
 printf("ARCHIVED PROP id.");
 break;
 }
 case CERT_KEY_IDENTIFIER_PROP_ID:
 {
 printf("KEY IDENTIFIER PROP id. ");
 break;
 }
 case CERT_AUTO_ENROLL_PROP_ID:
 {
 printf("AUTO ENROLL id. ");
 break;
 }
 } // end switch
 printf("\n");
 } // end the inner while loop. This is the end of the display of
 // a single property of a single certificate.

 My_Wait();
} // end the outer while loop. Move on to the next certificate.

//--------------------------------------------------------------------
// Free Memory and close the open store.
if(pCertContext)
{
 CertFreeCertificateContext(pCertContext);
}
CertCloseStore(hCertStore,0);
printf("The function completed successfully.\n");
}

//--------------------------------------------------------------------
// Define functions MyHandleError and My_Wait.

void MyHandleError( char *s)
{
 printf("%s\n",s);
 exit(1);
}

void My_Wait()
{

 printf("Hit enter to continue.");
 getchar();
}