Programma C di esempio: uso di CryptAcquireContext

Nell'esempio seguente vengono illustrati diversi modi per usare le funzioni CryptAcquireContext e cryptoAPI correlate per usare un provider di servizi di crittografia e un contenitore di chiavi.

In questo esempio vengono illustrate le attività seguenti e le funzioni CryptoAPI:

• Usare la funzione CryptAcquireContext per acquisire un handle per il CSP predefinito e il contenitore di chiavi predefinito. Se non esiste alcun contenitore di chiavi predefinito, usare la funzione CryptAcquireContext per creare il contenitore di chiavi predefinito.
• Usare la funzione CryptGetProvParam per recuperare informazioni su un CSP e un contenitore di chiavi.
• Aumentare il conteggio dei riferimenti nel provider usando la funzione CryptContextAddRef .
• Rilasciare un CSP usando la funzione CryptReleaseContext .
• Creare un contenitore di chiavi denominato usando la funzione CryptAcquireContext .
• Acquisire un handle per un CSP usando il contenitore di chiavi appena creato.
• Eliminare un contenitore di chiavi usando la funzione CryptAcquireContext .

In questo esempio viene usata la funzione MyHandleError. Il codice per questa funzione è incluso nell'esempio. Il codice per questa e altre funzioni ausiliarie sono elencate anche in funzioni per utilizzo generico.

//-------------------------------------------------------------------
//  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.