Titles installed to the 3DS are installed to either the NAND(System and Application) or SD Card(Application only), and their respective directory locations are:
NAND:
- nand/title - Title Data
- nand/data/<ID0>/sysdata - Save Data
- sdmc/Nintendo 3DS/<ID0>/<ID1>/title - Title Data/Save Data
ID0 is the first 0x10-bytes from a SHA256 hash.
Note: While all title data found on the SD Card is encrypted, it is not known whether title data on the NAND has additional encryption.
And the title data is contained in this directory structure:
NAND Directory Structure:
Title Data:
<Title ID High>
└── <Title ID Low>
├── 00000000.ctx
└── content
├── XXXXXXXX.app
├── XXXXXXXX.tmd
└── cmd
└── XXXXXXXX.cmd
Save Data:
<SaveID0>
└── <SaveID1>
└── 00000001.sav
SD Card Directory Structure:
Title Data/Save Data:
<Title ID High>
└── <Title ID Low>
├── 00000000.ctx
├── content
│ ├── XXXXXXXX.app
│ ├── XXXXXXXX.tmd
│ └── cmd
│ └── XXXXXXXX.cmd
└── data
└── 00000001.sav
For a list of 3DS titles see the Title list.
"XXXXXXXX.tmd" - (file name starts with 00000000.tmd and increases with an increment of "1" for each title version the 3DS is introduced to) This is the Title Metadata associated with the title, it is encrypted with a console-unique keyslot. The decrypted TMD is available on Nintendo's CDN server at "http://nus.cdn.c.shop.nintendowifi.net/ccs/download/TitleIDhere/tmd". Though CDN version of the title TMD has a certificate chain attached at the end of the TMD, so removing it will give you the 1:1 decrypted TMD. After installation the "00000000.tmd" is redundant, because important title data is extracted and imported into the title.db and ".cmd" files.
"XXXXXXXX.app" - (There is no pattern to the file name, however for a given title, ".app" file names are not reused) These files are NCCH files, where the entire file is encrypted with a console-unique keyslot(this is on top of the encryption of the NCCH contents). There can be more than one NCCH in this directory, as seen with .CCI files, the game executable (CXI) can be accompanied with additional non-executable NCCH files (CFA) such as the electronic manual and DLP Child containers. Determining the function of the encrypted NCCH, is done by finding the Content Index of the "XXXXXXXX.app" file in the title's TMD(see above for retrieving decrypted TMD), interpreting the Content Index is as follows:
| Index | Content Type |
|---|---|
| 0000 | Main Executable (.CXI)(In the case of System Data Archives, this is a CFA file) |
| 0001 | Home Menu Manual (.CFA) |
| 0002 | DLP Child Container (.CFA) |
Unlike the TMD, a decrypted version of the NCCH files cannot be retrieved from Nintendo's CDN, the NCCH files do exist on Nintendo's CDN but are encrypted. Of course editing/deleting ".app" files will have an effect. Deleting/renaming the manual ".app' will cause the manual not to load when clicked on. And deleting/renaming the executable ".app" will cause the application to not load, and the 3D Banner does not show(The banner is loaded each time from the game's executable NCCH when the home menu loads, it is not cached like the icon and name).
"XXXXXXXX.cmd" - (file name starts with 00000001.cmd and increases with an increment of "1" for each title version the 3DS is introduced to) This file contains data taken from the title's TMD during install. The data includes the title ID, file names and hashes (possibly sizes as well) of the .app files to prevent tampering. This file appears to be signed(or contains a hash of itself), and keeps a record of its true file name(alternatively it could store the title version, which can be used to determine its true file name). In addition it is also encrypted with a console-unique keyslot. This acts as part of the DRM for installed titles, along with the import.db and title.db
"00000001.sav" - This is the title's encrypted savegame. Although these saves look similar to FLASH savegames, these savegames use proper unique CTR for each AES block in the file, and the CTR properly changes for each savegame write. Renaming these savegames causes home-menu to hang while launching titles, modifying saves throws the usual MAC/hash corruption like gamecard flash saves.
"00000000.ctx" - This file encrypted with a console-unique keyslot is temporarily stored on SD card while a title is being downloaded from the eShop, it is deleted after the download is completed. This is presumably moved to NAND once installation is finished. This contains an AP0000000000000000 cert used to sign the data following the cert, this cert is signed by the console-unique CTCert.(This CTCert is the 3DS equivalent of the DSi TWCert, but unlike DSi the CTCert isn't stored on NAND)
The unknown signed data is likely an ECDSA public key.