Extdata

This page describes the format and encryption of extdata, "extra data" stored on SD card and NAND. At /Nintendo 3DS/<SomeID>/<SomeID>/extdata/<ExtdataIDHigh> on SD is directories for each title.(ExtdataIDHigh is always 00000000) Some titles have Quota.dat stored in these directories, not all titles use it. The dirname for these directories is the ExtdataIDLow. Then there's a sub-directory 00000000, which contains the actual extdata. Size and number of files in this dir varies per title.

Regular apps can only mount SD/NAND extdata using the same extdataID which is stored in the CXI exheader. Therefore, regular apps which have the exheader extdataID set to zero can't use extdata. This restriction doesn't apply for shared extdata with extdataID high bitmask 0x48000 stored on NAND. System apps with a certain access right can mount arbitrary extdata. All NAND extdata is shared extdata, while all SD extdata is normal extdata. Thus, normal extdata doesn't exist on NAND, and shared extdata doesn't exist on SD. The extdataID high excluding that bitmask is always zero for shared extdata.

Encryption

These files are encrypted with AES-CTR, with a per-console key. The CTR includes the ExtdataID and filename. The base CTR is fixed: the CTR never changes after each write. Thus it is possible to obtain some cleartext by XORing one file(like newly created extdata) with a newer file, where the newer file overwrote zeros in the original file with non-zero data.

Filesystem

Most extdata uses the same FS as savegames, except extdata uses DIFF instead of DISA. However some extdata files are raw, without any FS. Quota.dat uses the same encryption as extdata, and seems to use the same FS as the actual extdata. It's unknown whether Quota.dat is used anymore on the latest system version at all.

QUOT

• This seems to be stored in Quota.dat FS somewhere?

Start	Length	Description
0x0	4	Magic ("QUOT")
0x4	4	Magic Number (0x30000)
0x8	8	Unknown
0x10	0x38	Unknown

Filesystem structure

When extdata is created, these are *always* created regardless of whether the title actually uses them. User extdata and SpotPass extdata use separate mount points at /user and /boss. Therefore one mount can't access the other directory, and also can't access /icon.(The title's SpotPass extdata can be mounted by the title itself, if it uses SpotPass)

• /icon This file contains the extdata icon displayed in data management. This icon can only be written to by titles when creating extdata, titles would have to recreate extdata to change the icon. This file can't be read directly, instead it is read via FS:ReadExtSaveDataIcon.
• /user/ Contains the title's actual extdata files.
• /boss/ Can contain SpotPass content. SpotPass content is *always* stored in SD extdata.

• /user/ExBanner This directory can optionally store extended banners. When this is available, this banner is displayed instead of the CXI ExeFS banner. COMMON.bin stores the common exbanner, while <regionlang_code>.bin stores an optional separate region/language specific banner.(regionlang_code can be "JPN_JP", "USA_EN", etc)

Titles extdata

Usually the ExtdataID low is the titleID low shifted to the right by 8.

JPN ExtdataID	USA ExtdataID	EUR ExtdataID	Description
00000082	0000008f	00000098	Homemenu extdata
?	000004aa	000004ab	Nintendo Video Extra Data This is where the video files are stored, and includes the thumbnail, the description, and possibly some checksum info in each video file stored in the extdata images. There are always 9 files within the subdirectory "00000000" of this folder, even without any videos downloaded. The files are "00000001" - "00000009", and "00000003" - "00000008" have the same filesize of 50.7 MB. It is possible to restore the older videos by overwriting all the files within this directory. Provided of course you have made a backup of the files before hand, by copying all the files within this directory to your computer. As far I'm aware its not possible to mix and match the files in order to get certain videos in one grouping, ie. having all 3 Zelda orchestral recordings in one group of 4 Nintendo videos.
00000207	00000217	00000227	Mii Maker
0000020d	0000021d	0000022d	Face Raiders
00000200	00000210	00000220	System Settings extdata added with 2.0.0-2.
00000209	00000219	00000229	eShop
?	?	0000030c	Nintendogs + Cats
?	?	00000326	Pokédex 3D
?	0000032d	0000033c	Super Street Fighter IV 3D
?	00000358	0000033b	Ridge Racer 3D
?	0000034d	?	Samurai Warriors Chronicles
?	?	0000038a	Dead or Alive Dimensions
00000481	?	?	Monster Hunter Tri G (Download-Quests)