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CSecureChannelClient::MACFinal

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The MACFinal method releases the message authentication code (MAC) channel and retrieves a final MAC value.

Syntax

HRESULT MACFinal(HMAChMAC,
  BYTEabData[WMDM_MAC_LEN]
);

Parameters

hMAC

[in] Handle for the MAC for the current parameter data. This handle is created by calling the MACInit method. This datatype is declared in the SDK file ...\inc\Sac.h. After this method is called, the handle passed in is no longer valid.

abData

[out] Array of bytes to receive the final MAC value for the current parameter data.

Return Values

The method returns an HRESULT. All the interface methods in Windows Media Device Manager can return any of the following classes of error codes:

  • Standard COM error codes
  • Windows error codes converted to HRESULT values
  • Windows Media Device Manager error codes

For an extenstive list of possible error codes, see Error Codes.

Possible values include, but are not limited to, those in the following table.

Return code Description
S_OK The method succeeded.
E_INVALIDARG A parameter is invalid.
E_FAIL An unspecified error occurred.

Remarks

This method completes  creating a MAC key. For information about MAC creation, see

Example Code

The following example code checks the MAC received by a call to IWMDMStorage::GetRights to verify that the data has not been tampered with.

HRESULT hr;
CSecureChannelClient *pSPClient = NULL;
hr = m_pStorage->GetRights(ppRights, pnRightsCount, abTempMAC);
if (SUCCEEDED(hr))
{
    // Verify MAC returned by GetRights on the service provider.
    pSPClient->MACInit(&hMAC);
    pSPClient->MACUpdate(hMAC, (BYTE*)(*ppRights),
                       sizeof(WMDMRIGHTS) * (*pnRightsCount));
    pSPClient->MACUpdate(hMAC, (BYTE*)(pnRightsCount),
                        sizeof(*pnRightsCount));
    pSPClient->MACFinal(hMAC, abMACVerify);
    if (memcmp(abMACVerify, abTempMAC, WMDM_MAC_LENGTH) != 0)
    {
        hr = WMDM_E_MAC_CHECK_FAILED;
        goto exit;
    }
}

Requirements

Header: Include scclient.h.

Library: mssachlp.lib

See Also