NCryptStreamOpenToUnprotect function (ncryptprotect.h)
The NCryptStreamOpenToUnprotect function opens a stream object that can be used to decrypt large amounts of data to the same protection descriptor used for encryption. Call NCryptStreamUpdate to perform the decryption. To decrypt smaller messages such as keys and passwords, call NCryptUnprotectSecret.
Syntax
SECURITY_STATUS NCryptStreamOpenToUnprotect(
[in] NCRYPT_PROTECT_STREAM_INFO *pStreamInfo,
DWORD dwFlags,
[in, optional] HWND hWnd,
[out] NCRYPT_STREAM_HANDLE *phStream
);
Parameters
[in] pStreamInfo
Pointer to an NCRYPT_PROTECT_STREAM_INFO structure that contains the address of a user defined callback function to receive the decrypted data and a pointer to user-defined context data.
dwFlags
A flag that specifies additional information for the key service provider. This can be zero or the following value.
| Value | Meaning |
|---|---|
|
Requests that the key service provider not display a user interface. |
[in, optional] hWnd
Handle to the parent window of the user interface, if any, to be displayed.
[out] phStream
Pointer to the handle of the decrypted stream of data.
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 |
|---|---|
|
The function was successful. |
|
The dwFlags parameter must contain zero (0) or NCRYPT_SILENT_FLAG. |
|
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. |
|
There was insufficient memory to allocate a data stream. |
Remarks
The NCryptStreamOpenToUnprotect 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 NCryptStreamOpenToUnprotect function retrieves the unencrypted protection descriptor rule string from the stream header. The rule string is placed in the header by the NCryptStreamOpenToUnprotect function.
Requirements
| Requirement | Value |
|---|---|
| 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 |