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IDirect3DCryptoSession9::EncryptionBlt method (d3d9.h)

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Reads encrypted data from a protected surface.

Syntax

HRESULT EncryptionBlt(
  IDirect3DSurface9 *pSrcSurface,
  IDirect3DSurface9 *pDstSurface,
  UINT              DstSurfaceSize,
  VOID              *pIV
);

Parameters

pSrcSurface

Pointer to the protected surface.

pDstSurface

Pointer to a surface that receives the encrypted data.

DstSurfaceSize

The size of the surface memory that pDstSurface points to, in bytes. The size must be aligned to the value of BlockAlignmentSize in the driver capabilities structure; see Remarks.

pIV

Pointer to a buffer that receives the initialization vector (IV). The caller allocates this buffer, but the driver generates the IV.

If the encryption type is D3DCRYPTOTYPE_AES128_CTR (128-bit AES-CTR), pIV points to a D3DAES_CTR_IV structure. When the driver generates the first IV, it initializes the structure to a random number. For each subsequent IV, the driver simply increments the IV member of the structure, ensuring that the value always increases. This procedure enables the application to validate that the same IV is never used more than once with the same key pair.

For other encryption types, a different structure might be used, or the encryption might not use an IV.

Return value

If this method succeeds, it returns S_OK. Otherwise, it returns an HRESULT error code.

Remarks

If the driver supports this method, it sets the D3DCPCAPS_ENCRYPTEDREADBACK flag in the capabilities structure returned by the IDirect3DDevice9Video::GetContentProtectionCaps method.

If the driver sets the D3DCPCAPS_ENCRYPTEDREADBACKKEY capabilities flag, it means the driver uses a separate key to encrypt the data. To get this key, call the IDirect3DCryptoSession9::GetEncryptionBltKey method. Otherwise, the driver uses the session key to encrypt the data.

Allocate the destination surface (pDstSurface) as follows:

  1. Call IDirect3DCryptoSession9::GetSurfacePitch to get the stride of the protected surface.
  2. Call the GetContentProtectionCaps method to get the value of the BufferAlignmentStart and BlockAlignmentSize members in the D3DCONTENTPROTECTIONCAPS structure.
  3. Calculate the minimum size of the surface memory as SysMemSize = protected surface stride × protected surface height.
  4. Add padding to accommodate the values of BufferAlignmentStart and BlockAlignmentSize.
  5. Allocate a buffer in system memory, with size equal to SysMemSize (including padding).
  6. If the address of the system memory buffer is not aligned to the value of BufferAlignmentStart, calculate a memory-aligned pointer that is an offset from the start of the buffer.
  7. Call IDirect3DDevice9Ex::CreateOffscreenPlainSurfaceEx to create the destination surface. Pass the memory-aligned pointer as the shared-resource handle (pSharedHandle).
This method has the following limitations:
  • The method cannot read back subrectangles or partially encrypted surfaces.
  • The protected surface must be either an offscreen plain surface or a render target.
  • The destination surface must be a system-memory surface, created with the proper alignment, as described earlier.
  • The protected surface cannot be multisampled.
  • The method does not support stretching or colorspace conversion.
If you lock the destination surface, the stride reported in the D3DLOCKED_RECT structure might not match the stride of the protected surface. When you interpret the data, however, always use the stride of the protected surface.

Requirements

Requirement Value
Minimum supported client Windows 7 [desktop apps only]
Minimum supported server Windows Server 2008 R2 [desktop apps only]
Target Platform Windows
Header d3d9.h

See also

GPU-Based Content Protection

IDirect3DCryptoSession9