The Nintendo 3DS utilizes a similar title-based organization as seen in the Wii and DSi platforms. The update server is located here. When using SSL, the update/shop servers must be accessed via SSLv3.

The organization of Title IDs has not been documented fully yet. Region info isn't stored in title IDs however there does appear to be evidence that the regions are sequential, similar to how Wii System Menu Updates are ordered: JPN USA EUR KOR and CHN (introduced with the DSi). 3DS has one additional region: TWN.

Note: The terms 'Title ID', 'Partition ID' and 'Media ID' are interchangeable.

The 3DS retrieves system tickets with SOAP request GetSystemCommonETicket, instead of directly downloading the cetk with HTTPS. The cetk is still accessible via HTTP, however 3DS doesn't use direct HTTP for this.

TitleID Structure: 0xCCCCABCDLLLLLLRR

CCCC defines the console Platform (5=WiiU, 4=3DS, 3=DSi, 1=Wii)
ABCD defines the Content Category of the title, Demo, DLPChild, etc.
LLLLLL For CTR titles, this is the title's Unique ID. For TWL converted titles this is in two sections grouped as SSLLLL. SS is the old title identification used by the DSi and is made redundant by 'ABCD'. LLLL is the TWL title's 'Unique ID'. There are restrictions on the Unique ID, see below for more info.
RR This is the Title ID Variation, and has various uses.

Content Categories:

This u16 is a collection bit mask flag. Each Category is a group of one or more bit masks.

Specific Bitmask Flags:

Category	Bitmask
Normal	0x0
DlpChild	0x1
Demo	0x2
Contents	0x3
AddOnContents	0x4
Patch	0x6
CannotExecution	0x8
System	0x10
RequireBatchUpdate	0x20
NotRequireUserApproval	0x40
NotRequireRightForMount	0x80
CanSkipConvertJumpId	0x100
TWL	0x8000

TWL Category bit mask are carried over from original TWL category bitmasks (ignoring bit mask 0x8000), so TWL system titles have the bitmask of 0x8001.

System titles (TWL and CTR) are eligible to be updated during a System Update.

Bit Mask 0x4000 appears to be reserved, as it renders the TWL and System bit masks useless.

Unique ID Restrictions:

For the CTR titles, there appears to be is a correlation between Unique IDs (UID) and 3DS 'title types'. For developer titles this is known(shown below), and retail titles *appear* to follow suite. It is unknown if this correlation is enforced on retail units, or if it is just for organisation purposes.

TITLE TYPE	UNIQUE ID RANGE
System	0x0 - 0x2FF
Application	0x300 - 0xF7FFF
Evaluation	0xF8000 -0xFFFFF
Prototype*	0xFF000 - 0xFF3FF

*On the home menu, titles with UIDs within the 'Prototype' range, appear on the home menu after install without the gift fanfare.

ProgramID/titleID low bitmask 0xF0000000(uniqueID bitmask 0xF00000) seems to be related to which hardware the title is allowed to run on. 3DS code tends to clear this bitmask when handling programIDs. This bitmask is normally zero. When this is 0x2, this indicates that the title only runs on New_3DS(that is, programID-low 0x20000000 / uniqueID 0x200000).

TitleID Variation:

This u8 allows enumeration of titles from the same category and unique ID. Common uses are explained below:

CTR System Titles: The 3DS has two copies of most modules/applets/archives for usage with either the NATIVE_FIRM or SAFE_MODE_FIRM. This is allowed for, by changing the title ID variation of the title to match the core version set by the FIRM it is designed to be used with:

RR	MEANING
02	System Title (Core version 0x2)
03	SAFE_MODE System Title (Core version 0x3)

Normally on retail SAFE_MODE ARM11 CXI titles can't be launched, since the system core version doesn't match the CXI exheader core version.

Only most non-Normal Applications are known to utilise Title ID variation, this is explained in their respective sections on this page.

Dev Menu installs CTR Applications with a TitleID variation of 0x02 to the CTR NAND.

Title ID variation is ignored for TWL titles, this value is carried over from the original TWL title ID and is used for region lock:

Versions

v## = 0xHHHH = 0bBBBBBBBB...

The version major,minor and micro can be extracted from the version number by converting the 16 bit number to binary
6 bits : Major, this matches the NCCH remaster-version.
6 bits : Minor
4 bits : Micro ('Build' in some contexts)
i.e. v2069 (Taken from 000400DB00017302) = 0b000010 000001 0101 means that the title version is v2.1.5. For reasons unknown, the CVer build, stored in the RomFS of the title, has always been zero (at time of writing), regardless of the CVer build in the TMD. So when predicting the firmware version, this should be taken into account.

Data Structure

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

SD Card:

sdmc/Nintendo 3DS/<ID0>/<ID1>/title - Title Data/Save Data

ID0 is the first 0x10-bytes from a SHA256 hash.

Title data stored on the SD Card is encrypted with the console-unique keyslots, however the NAND title data is stored as cleartext.

The base CTR for files stored under /title is likely based on the /title path, similar to extdata. This base CTR is unique per titleID and filename. The base CTR never changes after creation of each file.

When a newer version of a title is installed, the new .app content, .tmd, and .cmd(and .ctx for NAND titles) are written to the /title directory, however the old files here are not yet deleted. Once installation of the title is finalized, the info from import.db is moved to title.db so that the system uses the newer files instead, then the old /title files are deleted.

And the title data is contained in this directory structure:

NAND Directory Structure:

Title Data:

<Title ID High>
└── <Title ID Low>
    ├── 00000000.ctx
    └── content
        ├── <ContentID>.app
        ├── <ContentID>.tmd
        └── cmd
            └── <ContentID>.cmd

Save Data:

<SaveID0>
└── <SaveID1>
    └── 00000001.sav

SD Card Directory Structure:

Title Data/Save Data:

<Title ID High>
└── <Title ID Low>
    ├── 00000000.ctx
    ├── content
    │   ├── <ContentID>.app
    │   ├── <ContentID>.tmd
    │   └── cmd
    │       └── <ContentID>.cmd
    └── data
        └── 00000001.sav

The structure differs for DLC Titles:

0004008C
└── <Title ID Low>
    ├── 00000000.ctx
    └── content
        ├── <ContentID>.tmd
        ├── 00000000
        │   └── <ContentID>.app
        └── cmd
            └── <ContentID>.cmd

For a list of 3DS titles see the Title list.

"<ContentID>.tmd" - (The Content ID is a u32, initially: 00000000 when the title is first installed. Changing by an increment of +0x1 for each title update the 3DS installs) 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 "<ContentID>.tmd" is redundant, because important title data is extracted and imported into the title.db and ".cmd" files, but is however kept as a reference.

"<ContentID>.app" - (The Content ID is a u32, taken from the title's TMD) 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)

The above table does not apply to DLC content.

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. Decrypting CDN versions of content, requires the title's ticket, and the common key specified by an index in the ticket. 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).

"<ContentID>.cmd" - (The Content ID is a u32, initially: 00000001 when the title is first installed. Changing by an increment of +0x1 for each time the 3DS adds/removes '.app' files) This file contains data taken from the title's TMD. See the below table for the format of the cleartext .cmd file. The Title.db contains the Content ID for the '.cmd' file, but does not contain a hash of the '.cmd' file. In addition it is also encrypted with a console-unique keyslot. This acts as part of the DRM for installed titles, along with the title.db.

The below AES-MACs(including the last 0x10-bytes of the header) are only used for SD titles, and for NAND download-play titles. For other titles, these MACs are set to all-zero.

Offset	Size	Description
0x0	0x4	.cmd ContentID, for the .cmd filename. This is the beginning of the header.
0x4	0x1C	For NAND titles' .cmd these 2 words are usually value 1, the rest of the header is all-zero. The last 0x10-bytes of this header is an AES MAC?
0x20	0x8*(No. of entries)	Entries for each content begin here with size 0x8.
0x20+0x8*(No. of entries)	0x10*(No. of entries)	These are MACs, one for each content.

Entries format:

Start	Size	Description
0x0	0x4	ContentID
0x4	0x8	Unknown

"00000001.sav" - This is the title's encrypted savegame. Renaming these savegames causes home-menu to hang while launching titles, modifying these saves results in the same corruption errors as other savegames.

"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 contains an AP0000000000000000 cert used to sign the data following the cert, this cert is signed by the CTCert. The unknown signed data is likely an ECDSA public key. There's .ctx files stored under the /title directory for NAND CTR/TWL titles, however those use the CTXT format which is completely different from this SD .ctx format. These .ctx files for NAND/SD titles only exist for titles where installation was not yet finalized(like when a system update install was not yet finalized).

DLC Titles

DLC titles have a different directory structure to most installed titles. This is because all DLC content for a given title is installed under the same Title ID, but DLC add-ons are usually separate purchases, hense the structure altered so any combination of DLC content can be installed. DLC titles can receive 'updates', this is usually in the form of more DLC content and/or DLC bug fixes. Individual DLC content can only be managed from with-in the application using the DLC.

"00000000" - This extra directory only found in DLC titles, contains the DLC NCCH content.

"<ContentID>.tmd" - This is not modified by the 3DS, and contains the details for all DLC content(installed or not).

"<ContentID>.cmd" - This contains entries for all installed DLC NCCH content, and is updated(<ContentID> will change) every time DLC content is installed/removed.