NCryptStreamOpenToProtect function

The NCryptStreamOpenToProtect function opens a stream object that can be used to encrypt large amounts of data to a given protection descriptor. Call NCryptStreamUpdate to encrypt the content. To encrypt smaller messages such as keys and passwords, call NCryptProtectSecret.

Syntax

SECURITY_STATUS NCryptStreamOpenToProtect(
  NCRYPT_DESCRIPTOR_HANDLE   hDescriptor,
  DWORD                      dwFlags,
  HWND                       hWnd,
  NCRYPT_PROTECT_STREAM_INFO *pStreamInfo,
  NCRYPT_STREAM_HANDLE       *phStream
);

Parameters

hDescriptor

Handle of the protection descriptor. Create the handle by calling NCryptCreateProtectionDescriptor.

dwFlags

The flag can be zero or the following value.

Value Meaning
NCRYPT_SILENT_FLAG
Requests that the key service provider not display a user interface.

hWnd

Handle to the parent window of the user interface, if any, to be displayed.

pStreamInfo

Pointer to an NCRYPT_PROTECT_STREAM_INFO structure that contains the address of a user defined callback function to receive the encrypted data and a pointer to user-defined context data.

phStream

Pointer to the stream object handle.

Return Value

Returns a status code that indicates the success or failure of the function. Possible return codes include, but are not limited to, the following.

Return code Description
ERROR_SUCCESS
The function was successful.
NTE_BAD_FLAGS
The dwFlags parameter must contain zero (0), NCRYPT_MACHINE_KEY_FLAG, or NCRYPT_SILENT_FLAG.
NTE_INVALID_HANDLE
The handle specified by the hDescriptor parameter is not valid.
NTE_INVALID_PARAMETER
The phStream and pStreamInfo parameters cannot be NULL.

The callback function pointed to by the pfnStreamOutput member of the NCRYPT_PROTECT_STREAM_INFO structure pointed to by the pStreamInfo parameter cannot be NULL.

NTE_NO_MEMORY
There was insufficient memory to allocate a data stream.

Remarks

The NCryptStreamOpenToProtect function creates an internal stream object that can be used to encrypt large messages. You cannot use the object directly. Instead, you must use the object handle returned by this function.

Call this function before calling the NCryptStreamUpdate function. If you are encrypting a large file, use NCryptStreamUpdate in a loop that advances through the file block by block, encrypting each block as it advances and notifying your callback when each block is finished. For more information, see NCryptStreamUpdate.

The NCryptStreamOpenToProtect function writes the unencrypted protection descriptor rule string to the stream object header so that NCryptStreamOpenToUnprotect will be able to start the decrypting the stream by using the same protector used during encryption.

Requirements

   
Minimum supported client Windows 8 [desktop apps only]
Minimum supported server Windows Server 2012 [desktop apps only]
Target Platform Windows
Header ncryptprotect.h
Library NCrypt.lib
DLL NCrypt.dll

See Also

CNG DPAPI Functions

NCRYPT_PROTECT_STREAM_INFO

NCryptCreateProtectionDescriptor

NCryptStreamClose

NCryptStreamOpenToUnprotect

NCryptStreamUpdate