SEP.H

The public symbol file NTKRPAMP.PDB for the original release of Windows 10 tells that the kernel is built with the SEP.H header at

d:\th\minkernel\ntos\se

and draws from it the following type definitions:

Line Number Type
560 struct _SEP_LOWBOX_NUMBER_ENTRY
568 struct _SEP_LOWBOX_HANDLES_ENTRY
576 struct _SEP_LOWBOX_NUMBER_MAPPING
583 struct _SEP_LOWBOX_HANDLES_TABLE
593 struct _SEP_SID_VALUES_BLOCK
617 struct _SEP_LOGON_SESSION_REFERENCES
657 struct _SESSION_LOWBOX_MAP
1768 struct _LEARNING_MODE_DATA

The header SEP.H is not known in any Device Driver Kit (DDK) or Windows Driver Kit (WDK).