This page describes the format of savegames contained in NAND. NAND savegames do not use an container with the entire file encrypted. Various areas of the saveimage is uninitialized data, resulting in encrypted data in those areas (like 3DS did).
=== AES CMAC header ===
=== Files ===
==== File Offset Table ====
* Indexes 0 and 1 are reserved to point towards the folder and file tables.
===== File Offset Table Entry =====
==== File/Folder Table Entry ====
* The root file/folder index is generally 2