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
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	0x30	Reserved

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).

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.
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.

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	0xDF8	Reserved1
0x1000	8	Media ID (same as first NCCH partitionId)
0x1008	8	Reserved2
0x1010	0x30	Initial Data
0x1040	0xC0	Reserved
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

Tools

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

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