COPPKeyExchange function

Article
02/16/2018

The sample COPPKeyExchange function retrieves the digital certificate used by the graphics hardware.

Syntax

HRESULT COPPKeyExchange(
  _In_  COPP_DeviceData pThis,
  _Out_ GUID            *pRandom,
  _Out_ BYTE            *pGHCertificate
);

Parameters

pThis [in]

Pointer to the COPP DirectX VA device object.

pRandom [out]

Pointer to a variable that receives a 128-bit random number.

pGHCertificate [out]

Pointer to a list of bytes that receives the graphics hardware certificate.

Return value

Returns zero (S_OK or DD_OK) if successful; otherwise, returns an error code.

Remarks

A COPP DirectX VA device should provide the size of the graphics hardware certificate to the VMR before receiving a call to its COPPKeyExchange function. That is, the COPPGetCertificateLength function should be called before COPPKeyExchange. If COPPKeyExchange is called before COPPGetCertificateLength, COPPKeyExchange should return E_UNEXPECTED.

Mapping RenderMoComp to COPPKeyExchange

The sample COPPKeyExchange function maps directly to a call to the RenderMoComp member of the DD_MOTIONCOMPCALLBACKS structure. The RenderMoComp member points to the display driver-supplied DdMoCompRender callback function that references the DD_RENDERMOCOMPDATA structure.

The RenderMoComp callback function is called without the display driver-supplied BeginMoCompFrame or EndMoCompFrame function being called first.

The DD_RENDERMOCOMPDATA structure is filled as follows.

Member	Value
dwNumBuffers	Number of buffers at lpBufferInfo. The value is 1.
lpBufferInfo	Pointer to a single RGB32 system memory surface that contains the space required to hold the hardware certificate. The required length of the surface was returned in the call to COPPGetCertificateLength. Note that a system memory surface is used to return the certificate because the size of the certificate can exceed the size of the maximum buffer passed via the lpOutputData parameter.
dwFunction	DXVA_COPPKeyExchangeFnCode constant (defined in dxva.h).
lpInputData	NULL.
lpOutputData	Pointer to a 128-bit random number generated by the driver.

Example Code

The following code provides an example of how you can implement your COPPKeyExchange function:

DWORD
COPP_Generate128BitRandomNumber()
{
    GUID RandNum;
    DWORD* pdw = (DWORD*)&RandNum;
    pdw[0] = rand();
    pdw[1] = rand();
    pdw[2] = rand();
    pdw[3] = rand();
    return RandNum;
}

HRESULT
COPPKeyExchange(
    COPP_DeviceData* pThis,
    GUID* pRandNumber,
    BYTE* pGHCertificate
    )
{
    if (pThis->m_COPPDevState != COPP_CERT_LENGTH_RETURNED) {
        return E_UNEXPECTED;
    }
    memcpy(pGHCertificate, (LPVOID)&TestCert, sizeof(TestCert));
    pThis->m_rGraphicsDriver = *pRandNumber = COPP_Generate128BitRandomNumber();
    pThis->m_COPPDevState = COPP_KEY_EXCHANGED;
    return NO_ERROR;
}

Requirements

Target platform	Version
Desktop	This function applies only to Windows Server 2003 with SP1 and later, and Windows XP with SP2 and later.

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