This page describes the format and encryption of extdata, "extra data" stored on SD card and NAND. At /Nintendo 3DS/<SomeID>/<SomeID>/extdata/<ExtdataID-High> on SD is directories for each title.(ExtdataID-High is always 00000000) 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.
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 AES engine keyslot(s) used for extdata crypto and the AES-CCM MAC has the console-unique portion of the keyslot(s) initialized from movable.sed.(The nonce used for the AES-CCM MAC is unknown) Both SD extdata and NAND extdata use the same AES engine keyslot(s). 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
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 what Quota.dat is used for.
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, likely contains an ExBanner |
| 0000020d | 0000021d | 0000022d | Face Raiders, likely contains an ExBanner |
| 00000200 | 00000210 | 00000220 | System Settings extdata added with 2.0.0-2. |
| 00000209 | 00000219 | 00000229 | eShop |
| 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) |