Example C Program: Using CryptAcquireContext

The following example demonstrates several different ways to use the CryptAcquireContext and related CryptoAPI functions to work with a cryptographic service provider (CSP) and a key container.

This example demonstrates the following tasks and CryptoAPI functions:

• Use the CryptAcquireContext function to acquire a handle for the default CSP and the default key container. If no default key container exists, use the CryptAcquireContext function to create the default key container.
• Use the CryptGetProvParam function to retrieve information about a CSP and a key container.
• Increase the reference count on the provider by using the CryptContextAddRef function.
• Release a CSP by using the CryptReleaseContext function.
• Create a named key container by using the CryptAcquireContext function.
• Acquire a handle for a CSP by using the newly created key container.
• Delete a key container by using the CryptAcquireContext function.

This example uses the function MyHandleError. The code for this function is included with the sample. Code for this and other auxiliary functions is also listed under General Purpose Functions.

//-------------------------------------------------------------------
//  Copyright (C) Microsoft.  All rights reserved.
//  Example code using CryptAcquireContext.
#pragma comment(lib, "crypt32.lib")

#include <stdio.h>
#include <tchar.h>
#include <windows.h>
#include <Wincrypt.h>

//-------------------------------------------------------------------
// This example uses the function MyHandleError, a simple error
// handling function to print an error message and exit 
// the program. 
// For most applications, replace this function with one 
// that does more extensive error reporting.

void MyHandleError(LPTSTR psz)
{
    _ftprintf(stderr, TEXT("An error occurred in the program. \n"));
    _ftprintf(stderr, TEXT("%s\n"), psz);
    _ftprintf(stderr, TEXT("Error number %x.\n"), GetLastError());
    _ftprintf(stderr, TEXT("Program terminating. \n"));
    exit(1);
} // End of MyHandleError.

void main(void)
{
    //---------------------------------------------------------------
    // Declare and initialize variables.
    HCRYPTPROV hCryptProv;

    //---------------------------------------------------------------
    // Get a handle to the default PROV_RSA_FULL provider.
    if(CryptAcquireContext(
        &hCryptProv, 
        NULL, 
        NULL, 
        PROV_RSA_FULL, 
        0)) 
    {
        _tprintf(TEXT("CryptAcquireContext succeeded.\n"));
    }
    else
    {
        if (GetLastError() == NTE_BAD_KEYSET)
        {
            // No default container was found. Attempt to create it.
            if(CryptAcquireContext(
                &hCryptProv, 
                NULL, 
                NULL, 
                PROV_RSA_FULL, 
                CRYPT_NEWKEYSET)) 
            {
                _tprintf(TEXT("CryptAcquireContext succeeded.\n"));
            }
            else
            {
                MyHandleError(TEXT("Could not create the default ")
                    TEXT("key container.\n"));
            }
        }
        else
        {
            MyHandleError(TEXT("A general error running ")
                TEXT("CryptAcquireContext."));
        }
    }

    CHAR pszName[1000];
    DWORD cbName;

    //---------------------------------------------------------------
    // Read the name of the CSP.
    cbName = 1000;
    if(CryptGetProvParam(
        hCryptProv, 
        PP_NAME, 
        (BYTE*)pszName, 
        &cbName, 
        0))
    {
        _tprintf(TEXT("CryptGetProvParam succeeded.\n"));
        printf("Provider name: %s\n", pszName);
    }
    else
    {
        MyHandleError(TEXT("Error reading CSP name.\n"));
    }

    //---------------------------------------------------------------
    // Read the name of the key container.
    cbName = 1000;
    if(CryptGetProvParam(
        hCryptProv, 
        PP_CONTAINER, 
        (BYTE*)pszName, 
        &cbName, 
        0))
    {
        _tprintf(TEXT("CryptGetProvParam succeeded.\n"));
        printf("Key Container name: %s\n", pszName);
    }
    else
    {
        MyHandleError(TEXT("Error reading key container name.\n"));
    }
    //---------------------------------------------------------------
    // Perform cryptographic operations.
    //...

    //---------------------------------------------------------------
    //  Add to the reference count on the provider. When the 
    //  reference count on a provider is greater than one,  
    //  CryptReleaseContext reduces the reference count but does not 
    //  free the provider.

    if(CryptContextAddRef(
        hCryptProv, 
        NULL, 
        0)) 
    {
        _tprintf(TEXT("CryptcontextAddRef succeeded.\n"));
    }
    else
    {
        MyHandleError(TEXT("Error during CryptContextAddRef!\n"));
    }

    //---------------------------------------------------------------
    //  The reference count on hCryptProv is now greater than one. 
    //  The first call to CryptReleaseContext will not release the 
    //  provider handle. 

    //---------------------------------------------------------------
    //  Release the context once.
    if (CryptReleaseContext(hCryptProv, 0))
    {
        _tprintf(TEXT("The first call to CryptReleaseContext ")
            TEXT("succeeded.\n"));
    }
    else
    {
        MyHandleError(TEXT("Error during ")
            TEXT("CryptReleaseContext #1!\n"));
    }

    //---------------------------------------------------------------
    // Release the provider handle again.
    if (CryptReleaseContext(hCryptProv, 0)) 
    {
        _tprintf(TEXT("The second call to CryptReleaseContext ")
            TEXT("succeeded.\n"));
    }
    else
    {
        MyHandleError(TEXT("Error during ")
            TEXT("CryptReleaseContext #2!\n"));
    }

    //---------------------------------------------------------------
    // Get a handle to a PROV_RSA_FULL provider and
    // create a key container named "My Sample Key Container".
    LPCTSTR pszContainerName = TEXT("My Sample Key Container");

    hCryptProv = NULL;
    if(CryptAcquireContext(
        &hCryptProv, 
        pszContainerName,
        NULL, 
        PROV_RSA_FULL, 
        CRYPT_NEWKEYSET)) 
    {
        _tprintf(TEXT("CryptAcquireContext succeeded. \n"));
        _tprintf(TEXT("New key set created. \n")); 

        //-----------------------------------------------------------
        // Release the provider handle and the key container.
        if(hCryptProv)
        {
            if(CryptReleaseContext(hCryptProv, 0)) 
            {
                hCryptProv = NULL;
                _tprintf(TEXT("CryptReleaseContext succeeded. \n"));
            }
            else
            {
                MyHandleError(TEXT("Error during ")
                    TEXT("CryptReleaseContext!\n"));
            }
        }
    }
    else
    {
        if(GetLastError() == NTE_EXISTS)
        {
            _tprintf(TEXT("The named key container could not be ")
                TEXT("created because it already exists.\n"));
            
            // Just continue the program. The named container 
            // will be reopened below.
        }
        else
        {
            MyHandleError(TEXT("Error during CryptAcquireContext ")
                TEXT("for a new key container."));
        }
    }

    //---------------------------------------------------------------
    // Get a handle to the provider by using the new key container. 
    // Note: This key container will be empty until keys
    // are explicitly created by using the CryptGenKey function.
    if(CryptAcquireContext(
        &hCryptProv, 
        pszContainerName, 
        NULL, 
        PROV_RSA_FULL,
        0)) 
    {
        _tprintf(TEXT("Acquired the key set just created. \n"));
    }
    else
    {
        MyHandleError(TEXT("Error during CryptAcquireContext!\n"));
    }

    //---------------------------------------------------------------
    // Perform cryptographic operations.

    //---------------------------------------------------------------
    // Release the provider handle.
    if(CryptReleaseContext(
        hCryptProv, 
        0)) 
    {
        _tprintf(TEXT("CryptReleaseContext succeeded. \n"));
    }
    else
    {
        MyHandleError(TEXT("Error during CryptReleaseContext!\n"));
    }

    //---------------------------------------------------------------
    // Delete the new key container.
    if(CryptAcquireContext(
        &hCryptProv, 
        pszContainerName, 
        NULL, 
        PROV_RSA_FULL,
        CRYPT_DELETEKEYSET)) 
    {
        _tprintf(TEXT("Deleted the key container just created. \n"));
    }
    else
    {
        MyHandleError(TEXT("Error during CryptAcquireContext!\n"));
    }
} // End of main.