XCI

Header

The header is 0x200-bytes, at Gamecard+0.

Offset	Size	Description
0x0	0x100	RSA-2048 signature, presumably.
0x100	0x4	Magicnum "HEAD"
0x104	0x4	Offset of Secure partition (Size of non-secure data?), in Media Units
0x108	0x4	0xFFFFFFFF
0x10C	0x4	?
0x110	0x8	?
0x118	0x8	Size of the Gamecart, in Media Units
0x120	0x10	?
0x130	0x8	Offset of HFS0 FS partition
0x138	8	HFS0 Header size
0x140	0x20	SHA256 hash of the HFS0 Header
0x160	0x20	SHA256 hash of ?
0x180	0x4	1?
0x184	0x4	2?
0x188	0x4	0?
0x18C	0x4	Offset of Secure partition (Size of non-secure data?), in Media Units, again.
0x190	0x70	Encrypted data/hashes of some kind

Cert

This is for the CERT, located at Gamecard + 0x7000 (always?). This matches exactly the output from fsp-srv IDeviceOperator cmd 206 "GetGameCardDeviceCertificate".

Offset	Size	Description
0x0	0x100	RSA-2048 signature, presumably.
0x100	0x4	Magicnum "CERT"
0x110	0x10	?
0x12A	0xD6	Encrypted data. Some kind of key?

The data between the CERT and the start of the HFS0 is all 0xFF.

HFS0

This is the FS which has magicnum "HFS0" at header+0.

Offset	Size	Description
0x0	0x4	HFS0 Magic
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	SHA256 hash of the first (size of hashed region) bytes of filedata.