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Creare un esempio di chiave di contenuto

  • Articolo

La chiave di contenuto viene usata per crittografare esempi multimediali per l'importazione DRM di Windows Media. Nell'esempio di codice seguente viene illustrato come creare e inizializzare una struttura della chiave di contenuto.

HRESULT CreateContentKey( WMDRM_IMPORT_CONTENT_KEY **ppContentKey, DWORD *pcbContentKey)
{
    // TODO: Set this value to the desired number of bytes for the content key data. 
    const DWORD IV_DATA_SIZE = 16;
    HRESULT hr = S_OK;
    WMDRM_IMPORT_CONTENT_KEY *pContentKey = NULL;

    // The content key.
    const BYTE rgbContentKey[] = {
        0x67, 0x39, 0x83, 0xb9,
        0x52, 0xa8, 0xe3
    };        
    const DWORD CONTENT_KEY_DATA_SIZE = sizeof(rgbContentKey);

    // Compute the total size of the content key structure
    DWORD cbContentKey = sizeof( WMDRM_IMPORT_CONTENT_KEY ) +
      IV_DATA_SIZE + CONTENT_KEY_DATA_SIZE;

    // Make sure we have a valid 
    if( NULL == ppContentKey )
    {
        hr = E_POINTER;
        goto EXIT;
    }

    // Allocate the content key, locally first
    pContentKey = (WMDRM_IMPORT_CONTENT_KEY *)new BYTE[ cbContentKey ];
    
    // Check the allocation was successful 
    if( NULL == pContentKey )
    {
        hr = E_OUTOFMEMORY;
        goto EXIT;
    }

    // Ininitalize the key
    ZeroMemory( pContentKey, cbContentKey );
    pContentKey->dwVersion = 0;
    pContentKey->cbStructSize = cbContentKey;

    // Set the initialization vector key type 
    pContentKey->dwIVKeyType = WMDRM_KEYTYPE_RC4;
    pContentKey->cbIVKey = IV_DATA_SIZE;
    
    // Generate a random initialization vector. Note that this random number
    //  generator is not very good. It is only intended to be demonstrative
    //  and it is not recommended for use in commercial strength code.
    srand((unsigned int)time(NULL));
    BYTE* pKeyData = pContentKey->rgbKeyData;
    for (size_t i = 0; i < IV_DATA_SIZE; ++i)
    {
        *pKeyData++ = (BYTE)(rand() & 0xFF); 
    }   
    
    // Set the content key type.
    pContentKey->dwContentKeyType = WMDRM_KEYTYPE_COCKTAIL;
    pContentKey->cbContentKey = CONTENT_KEY_DATA_SIZE;

    // Fill out the content key. 
    for (size_t i = 0; i < CONTENT_KEY_DATA_SIZE; ++i)
    {
        *pKeyData++ = rgbContentKey[i]; 
    }   
    

    // If all has been successful, set the parameters
    *ppContentKey = pContentKey;
    pContentKey = NULL;
    *pcbContentKey = cbContentKey;

EXIT:
    SAFE_ARRAY_DELETE( pContentKey );
    return hr;
}

Esempi di importazione DRM