Extdata数据

页面介绍了extdata的文件格式和加密方式。"extra data"记录在SD card和NAND中的：

• nand/data/<ID>/extdata/<ExtdataID-High>
• sdmc/Nintendo 3DS/<ID0>/<ID1>/extdata/<ExtdataID-High>

(ExtdataID-High is always 00000000 for SD, and always 00048000 for NAND) Some titles can have Quota.dat stored in these directories. The directory-name for these directories is the ExtdataID-Low. Then there's a sub-directory 00000000, which contains the actual extdata. Size and number of files in this dir varies per title. NAND stores the shared extdata and is structured exactly the same way, see Flash Filesystem.

Extdata image 00000001 contains a VSXE partition for the FST, the actual file data is stored in the subsequent extdata images.

Regular apps can only mount SD 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, the keyslot is initialized by movable.sed. The same keyslot is used for the NAND/SD extdata MAC. The NAND extdata images are stored in cleartext. The WCHAR LowPath "/extdata/<ExtdataIDHigh>/<ExtdataIDLow>/<PathToImage>" text path is hashed with SHA-256, including the WCHAR null-terminator. A separate hash is used for Quota.dat. The base CTR seems to be then generated by XORing the calculated hash: CTRword[i] = Hashword[i] ^ Hashword[4+i].

The base CTR is fixed therefore 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

Title extdata contains a series of extdata images which comprise an independent file system. The first image (00000001) contains the VSXE (FST) partition, and subsequent images each containing a single file. Non-title extdata, usually contain single files, or a database. Quota.dat is an extdata image, however it's unknown what this is used for.

QUOT

• This is contained in the Quota.dat extdata image.

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 can only be downloaded to this /boss directory.

• /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)

SD Extdata

Usually the ExtdataID low is in the format '00<Unique ID>'

JPN ExtdataID	USA ExtdataID	EUR ExtdataID	Description	Extdata images
00000082	0000008f	00000098	Homemenu extdata, this contains home-menu savedata and cached icons for applications.
00000200	00000210	00000220	System Settings extdata added with 2.0.0-2.
00000207	00000217	00000227	Mii Maker, contains an ExBanner	cleartext
00000208	00000217	00000228	Streetpass Mii Plaza	11 mb big!
00000209	00000219	00000229	eShop
0000020d	0000021d	0000022d	Face Raiders, likely contains an ExBanner
0000020b	0000021b	0000022b	Nintendo Zone
?	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.
?	00000308	00000307	Mario Kart 7
0000030b	0000030d	0000030c	Nintendogs + Cats
?	00000326	00000326	Pokédex 3D
00000305	0000032d	0000033c	Super Street Fighter IV 3D
00000328	00000358	0000033b	Ridge Racer 3D
?	0000034d	00000402	Samurai Warriors Chronicles
?	0000034f	0000038a	Dead or Alive Dimensions
00000481	N/A	N/A	Monster Hunter Tri G (Download-Quests)
?	?	00000a86	Professor Layton and the Miracle Mask
?	?	00000c24	Denpa men
?	00000c73	00000c73	Save Data Transfer Tool
?	?	00000d9a	Donkey Kong Country Returns 3d Trailer

NAND Shared Extdata

ExtdataID	Description
0xf0000001	NAND JPEG/MPO files and phtcache.bin from the camera application are stored here. This also contains UploadData.dat.
0xf0000002	NAND M4A files from the sound application are stored here
0xf0000009	?
0xf000000b	Contains idb.dat, idbt.dat, gamecoin.dat, ubll.lst, CFL_DB.dat, and CFL_OldDB.dat. These files contain cleartext Miis and some data relating (including cached ICN data) to Play/Usage Records.
0xf000000c	Contains bashotorya.dat and bashotorya2.dat.
0xf000000d	?

Tools

• extdata_tool - Extract standalone extdata images, aswell as title extdata FS.