NCSD

This page documents the format of NCSD.

Overview

There are two known specialisations of the NCSD container format. The CTR Cart Image (CCI) format and the 3DS' raw NAND format. CCI is the format of game ROM images.

CTR System Update (CSU) is a variant of CCI, where the only difference is in the file extension. This is used with developer System Updates and associated Tools.

NCSD images start with a NCSD header, followed by up to a maximum of 8 NCCH partitions.

For CCI images, the partitions are reserved as follows:

NCCH Index	Reserved Use
0	Executable Content (CXI)
1	E-Manual (CFA)
2	Download Play Child container (CFA)
6	New3DS Update Data (CFA)
7	Update Data (CFA)

The format of partitions can be determined from the partition FS flags (normally these are zero for CCI/CSU NCSD Images).

NCSD header

Offset	Size	Description
0x000	0x100	RSA-2048 SHA-256 signature of the NCSD header
0x100	4	Magic Number 'NCSD'
0x104	4	Size of the NCSD image, in media units (1 media unit = 0x200 bytes)
0x108	8	Media ID
0x110	8	Partitions FS type (0=None, 1=Normal, 3=FIRM, 4=AGB_FIRM save)
0x118	8	Partitions crypt type (each byte corresponds to a partition in the partition table)
0x120	0x40=(4+4)*8	Offset & Length partition table, in media units
0x160	0xA0	...

For carts,

Offset	Size	Description
0x160	0x20	Exheader SHA-256 hash
0x180	0x4	Additional header size
0x184	0x4	Sector zero offset
0x188	8	Partition Flags (See Below)
0x190	0x40=8*8	Partition ID table
0x1D0	0x20	Reserved
0x1F0	0xE	Reserved?
0x1FE	0x1	Support for this was implemented with 9.6.0-X FIRM. Bit0=1 enables using bits 1-2, it's unknown what these two bits are actually used for(the value of these two bits get compared with some other value during NCSD verification/loading). This appears to enable a new, likely hardware-based, antipiracy check on cartridges.
0x1FF	0x1	Support for this was implemented with 9.6.0-X FIRM, see below regarding save crypto.

For NAND,

Offset	Size	Description
0x160	0x5E	Unknown
0x1BE	0x42	Encrypted MBR partition-table, for the TWL partitions(key-data used for this keyslot is console-unique).

NCSD Signature

The RSA public key used for gamecard NCSD is stored in ITCM. The separate public key used for NAND NCSD is stored in Process9 .(ro)data instead of ITCM, and in boot ROM.

For the boot ROM check, sighax may be used to fake-sign NAND headers. Process9's check will fail, however, unless patched.

Partition Flags

Byte Index	Description
0	Backup Write Wait Time (The time to wait to write save to backup after the card is recognized (0-255 seconds)).NATIVE_FIRM loads this flag from the gamecard NCSD header starting with 6.0.0-11.
3	Media Card Device (1 = NOR Flash, 2 = None, 3 = BT) (SDK 3.X+)
4	Media Platform Index (1 = CTR)
5	Media Type Index (0 = Inner Device, 1 = Card1, 2 = Card2, 3 = Extended Device)
6	Media Unit Size i.e. u32 MediaUnitSize = 0x200*2^flags[6];
7	Media Card Device (1 = NOR Flash, 2 = None, 3 = BT) (Only SDK 2.X)

Partition Flags (In Terms of Save Crypto Determination)

Byte Index	Description
1	Starting with 6.0.0-11 NATIVE_FIRM will use this flag to determine the gamecard savegame keyY method, when flag[3] is set. 0 = 2.0.0-2 hashed keyY, 1 = new keyY method implemented with 6.0.0-11. 0x0A = implemented with 9.3.0-X. On Old3DS this is identical to the 2.2.0-4 crypto. On New3DS this is identical to the 2.2.0-4 crypto, except with New3DS-only gamecard savedata keyslots. Starting with 9.6.0-X FIRM, Process9 now sets <savecrypto_stateval> to partitionflag[1] + <the u8 value from NCSD+0x1FF>, instead of just setting it to partitionflag[1].
3	Support for this flag was implemented in NATIVE_FIRM with 2.0.0-2. When this flag is set the hashed gamecard savegame keyY method is used, this likely still uses the repeating-CTR however. With 6.0.0-11 the system will determine the gamecard savegame keyY method via flag[1], instead of just using the hashed keyY via this flag.
7	This flag enables using the hashed gamecard savegame keyY method, support for this flag was implemented in NATIVE_FIRM with 2.2.0-4. All games with the NCSD image finalized since 2.2.0-4(and contains 2.2.0-4+ in the system update partition) have this flag set, this flag also enables using new CTR method as well.

Starting with 9.6.0-X FIRM, Process9 will just write val0 to a state field then return 0, instead of returning an error when the save crypto type isn't recognized. This was the *only* actual functionality change in the Old3DS Process9 function for gamecard savedata crypto init.

Card Info Header

OFFSET	SIZE	DESCRIPTION
0x200	4	CARD2: Writable Address In Media Units (For 'On-Chip' Savedata). CARD1: Always 0xFFFFFFFF.
0x204	4	Card Info Bitmask
0x208	0x108	Reserved1
0x310	2	Title version
0x312	2	Card revision
0x208	0xCEE	Reserved2
0x1000	0x10	Card seed keyY (first u64 is Media ID (same as first NCCH partitionId))
0x1010	0x10	Encrypted card seed (AES-CCM, keyslot 0x3B for retail cards, see CTRCARD_SECSEED)
0x1020	0x10	Card seed AES-MAC
0x1030	0xC	Card seed nonce
0x103C	0xC4	Reserved3
0x1100	0x100	Copy of first NCCH header (excluding RSA signature)

Development Card Info Header Extension

OFFSET	SIZE	DESCRIPTION
0x1200	0x200	CardDeviceReserved1
0x1400	0x10	TitleKey
0x1410	0xF0	CardDeviceReserved2

Note that a particular flashcard vendor puts what many refer to as "private headers" here in place of actual development card information. This header is constituted by a cartridge-unique Id obtained from pxi:ps9::GetRomId and the title-unique cart ID (identical for all carts of the same title; can be retrieved using the NTR gamecard protocol command 0x90 or through the CTR protocol commands 0x90 or 0xA2).

Tools

ctrtool - (CMD)(Windows/Linux) Parsing NCSD files

3DSExplorer - (GUI)(Windows Only) Parsing NCSD files