Gamecard Format

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Known internally as "XCI" (NX Card Image), this is the format used for storing the contents of a Nintendo Switch Gamecard.

Gamecard Header

This header is 0x200 bytes and is located at offset 0 in the Gamecard.

Offset Size Description
0x0 0x100 RSA-2048 PKCS #1 signature over the header (data from 0x100 to 0x200)
0x100 0x4 Magicnum "HEAD"
0x104 0x4 Secure Area Start Address (in Media Units which are 0x200 bytes)
0x108 0x4 Backup Area Start Address (always 0xFFFFFFFF)
0x10C 0x1 Title KEK Index (high nibble) and KEK Index (low nibble)
0x10D 0x1 Gamecard Size (0xFA = 1GB, 0xF8 = 2GB, 0xF0 = 4GB, 0xE0 = 8GB, 0xE1 = 16GB, 0xE2 = 32GB)
0x10E 0x1 Gamecard Header Version
0x10F 0x1 Gamecard Flags (bit0 = AutoBoot, bit1 = HistoryErase)
0x110 0x8 Package Id (used for challenge–response authentication)
0x118 0x8 Valid Data End Address (in Media Units which are 0x200 bytes)
0x120 0x10 Gamecard Info IV (reversed)
0x130 0x8 HFS0 partition offset
0x138 0x8 HFS0 header size
0x140 0x20 SHA-256 hash of the HFS0 Header
0x160 0x20 SHA-256 hash of the Initial Data
0x180 0x4 Secure Mode Flag (always 1, which means Secure Mode is available)
0x184 0x4 Title Key Flag (always 2)
0x188 0x4 Key Flag (always 0)
0x18C 0x4 Normal Area End Address (in Media Units which are 0x200 bytes)
0x190 0x70 Gamecard Info (AES-128-CBC encrypted)

Gamecard Info

When decrypted, this 0x70 byte region is as follows:

Offset Size Description
0x0 0x8 Firmware Version (0x01 for old Gamecards, 0x02 for new Gamecards with the "logo" partition)
0x8 0x4 Access Control Flags (0x00A10011 for 25MHz access or 0x00A10010 for 50MHz access)
0xC 0x4 Read Wait Time (always 0x1388)
0x10 0x4 Read Wait Time2 (always 0)
0x14 0x4 Write Wait Time (always 0)
0x18 0x4 Write Wait Time2 (always 0)
0x1C 0x4 Firmware Mode
0x20 0x4 CUP Version
0x24 0x4 Empty
0x28 0x8 Update Partition Hash
0x30 0x8 CUP Id (always 0x0100000000000816, which is the title-listing data archive's title ID)
0x38 0x38 Empty

Gamecard Certificate

This is the Gamecard's unique certificate and is located at offset 0x7000.

FS IDeviceOperator cmd 206 "GetGameCardDeviceCertificate" retrieves this data.

Offset Size Description
0x0 0x100 RSA-2048 PKCS #1 signature over the data from 0x100 to 0x200
0x100 0x4 Magicnum "CERT"
0x104 0x4
0x108 0x1 KEK Index
0x109 0x7
0x110 0x10 Device ID
0x120 0xA
0x12A 0xD6 Encrypted data. Some kind of key?

The data between the Gamecard Certificate and the start of the HFS0 region is all 0xFF.

Initial Data

This data is used for challenge–response authentication when changing to the Gamecard's secure mode.

FS calculates a SHA-256 hash over the whole 0x200 bytes and compares it with the hash stored at offset 0x160 in the Gamecard Header.

Offset Size Description
0x0 0x8 Package Id from Gamecard Header at offset 0x110
0x8 0x8 Empty
0x10 0x10 Challenge–response authentication data
0x20 0x10 Challenge–response authentication MAC
0x30 0xC Challenge–response authentication Nonce
0x3C 0x1C4 Reserved (must be empty)

HFS0

This is the Gamecard file system which starts with magicnum "HFS0".

Header

The "SHA-256 File System" or "HFS0" starts at offset 0xF000 in the Gamecard. The first 0x200 bytes act as a global header and represent the root partition which points to the other partitions ("normal", "logo", "update" and "secure).

A hash for this header is stored at offset 0x140 in the Gamecard Header.

File System

The actual file system is as follows (also valid for the root partition):

Offset Size Description
0x0 0x4 Magicnum "HFS0"
0x4 0x4 Number of files
0x8 0x4 Size of the string table
0xC 0x4 Zero/Reserved
0x10 X File Entry Table
0x10 + X Y String Table
0x10 + X + Y Z Raw File Data

Where File Entry Table consists of Number of Files FileEntries:

Offset Size Description
0x0 0x8 Offset of file in Data
0x8 0x8 Size of file in Data
0x10 0x4 Offset of filename in String Table
0x14 0x4 Size of Hashed region of file (for HFS0s, this is the size of the pre-filedata portion, for NCAs this is usually 0x200)
0x18 8 Zero/Reserved
0x20 0x20 SHA-256 hash of the first (size of hashed region) bytes of filedata

The string table is 00-padded to align the start of raw filedata with a sector/media unit boundary (usually?).

Cartridge Layout

Observed gamecards contain three partitions: "update", "normal", and "secure".

The update partition (Gamecard partition 0 for fsp-srv cmd 31) contains .cnmt.nca + .nca files for the entire system update required to play the game. Launch day carts contain a full copy of 1.0 ncas, newer carts contain newer sysupdate NCAs etc.

The normal partition contains the .cnmt.nca and the game icondata nca. This is presumably for future compatibility so that if a future update changes the cryptographic protocol for the secure partition, Game icon data can still be shown in the home menu on old firmwares.

The secure partition contains an identical copy of the .cnmt.nca and game icondata nca, as well as all other ncas required for the game.

The entire rest of the Gamecard after the secure partition ends is all FF padding.

[4.0.0+] The "normal" partition is now empty and a new partition "logo" was added.