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Create Session Key Example

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[The feature associated with this page, Windows Media Format 11 SDK, is a legacy feature. It has been superseded by Source Reader and Sink Writer. Source Reader and Sink Writer have been optimized for Windows 10 and Windows 11. Microsoft strongly recommends that new code use Source Reader and Sink Writer instead of Windows Media Format 11 SDK, when possible. Microsoft suggests that existing code that uses the legacy APIs be rewritten to use the new APIs if possible.]

The session key is used to protect the content key. The following code demonstrates how to create a session key, but leaves out the details of random key generation.

HRESULT CreateSessionKey( WMDRM_IMPORT_SESSION_KEY **ppSessionKey, DWORD *pcbSessionKey )
{
    // TODO: Set this value to the desired number of bytes for the session key data. 
    const DWORD SESSION_KEY_DATA_SIZE = 20; 

    HRESULT hr = S_OK;
    WMDRM_IMPORT_SESSION_KEY *pSessionKey = NULL;

    if( NULL == ppSessionKey )
    {
        hr = E_POINTER;
        goto EXIT;
    }
    
    // Compute the size of the session key structure plus the session key.
    DWORD cbSessionKey = sizeof( WMDRM_IMPORT_SESSION_KEY ) + SESSION_KEY_DATA_SIZE;

    // Allocate memory for the session key.
    pSessionKey = (WMDRM_IMPORT_SESSION_KEY *)new BYTE[ cbSessionKey ];
    if( NULL == pSessionKey )
    {
        hr = E_OUTOFMEMORY;
        goto EXIT;
    }
    ZeroMemory( pSessionKey, cbSessionKey );

    // Set the key type and the key size.
    pSessionKey->dwKeyType = WMDRM_KEYTYPE_RC4;
    pSessionKey->cbKey = SESSION_KEY_DATA_SIZE;
    
    // Set the key to a random value. Note that the random number
    //  generator is not very good. It is only intended to be demonstrative
    //  and it is not recommended for use in shipping code.
    srand((unsigned int)time(NULL));
    BYTE* pKeyData = pSessionKey->rgbKey;
    for (size_t i = 0; i < SESSION_KEY_DATA_SIZE; ++i)
    {
        *pKeyData++ = (BYTE)(rand() & 0xFF); 
    }
    
    // If all has been successful set the parameters.
    *ppSessionKey = pSessionKey;
    pSessionKey = NULL;
    *pcbSessionKey = cbSessionKey;

EXIT:
    
    SAFE_ARRAY_DELETE( pSessionKey );
    return hr;
}

DRM Import Examples