CXI

The following text tries to document the structure of the CTR Executable Image (CXI) format.

Overview

A CXI file contains the 'application' program code, which runs on a single ARM11 core. It can communicate through SVC calls with the other ARM11 core running the 'system' program code. For reasons of clarity, the ARM11 cores will sometimes be called the 'appcore' and 'syscore' respectively.

The CXI file format contains application ARM11 code, the menu icon, the menu 3D model, and an embedded read-only (ROM) filesystem for external filestorage. In fact, the application ARM11 code, menu icon, and menu 3D model are embedded into its own filesystem too, called the ExeFS.

More specifically, the CXI file format is structured in the following order:

• first an NCCH header,
• followed by an extended header,
• followed by a plain binary region,
• followed by an embedded executable filesystem (ExeFS),
• and finally followed by a read-only filesystem (RomFS).

The extended header contains additional information regarding access control. The plain binary region is an area specifically stored in plaintext, mostly containing SDK library strings for identification.

The extended header, the ExeFS and the RomFS are encrypted using 128-bit AES CTR.

NCCH Header

OFFSET	SIZE	DESCRIPTION
0x000	0x100	RSA-2048 signature of the NCCH header, using SHA-256.
0x100	4	Magic ID, always 'NCCH'
0x104	4	Content size, in media units (1 media unit = 0x200 bytes)
0x108	8	Partition ID
0x110	2	Maker code
0x112	2	Version
0x114	4	Reserved
0x118	8	Program ID
0x120	1	Temp flag
0x121	0x2F	Reserved
0x150	0x10	Product code
0x160	0x20	Extended header hash
0x180	4	Extended header size
0x184	4	Reserved
0x188	8	Flags
0x190	4	Plain region offset, in media units
0x194	4	Plain region size, in media units
0x198	8	Reserved
0x1A0	4	ExeFS offset, in media units
0x1A4	4	ExeFS size, in media units
0x1A8	4	ExeFS hash region size, in media units
0x1AC	4	Reserved
0x1B0	4	RomFS offset, in media units
0x1B4	4	RomFS size, in media units
0x1B8	4	RomFS hash region size, in media units
0x1BC	4	Reserved
0x1C0	0x20	ExeFS superblock hash
0x1E0	0x20	RomFS superblock hash

NCCH header example for Lego Starwars III

Signature:              720FF8F83F2A1E998322A026D1434165
                        ED19642ABC1CB2722135AA202BEAD60A
                        80BCD21C768C597B8268FEF2C64EA710
                        4C9BA5E12CFFBD1D0C619F4EF7B42CA7
                        DD8482CB4EB26720AD66CDA57ABCBCFB
                        D63268A6E2896A59B3B744E39E45B88A
                        ABB4C0980ACC6210818DCE6DAC838A10
                        95D0F66B352474D4B3DA4B333F49912D
                        29AF7EA58BC8C890B18C70B7D540A9FB
                        EBE24A5312055617D3353B28C3EB1D17
                        61021BEFF6AD22C384835B40BD44DFAD
                        981F6350F9458B17BCB5F768C92ABC93
                        2BCE9888855A8998F4CDE40C9543514A
                        C57B84EB75A680E7C742632614620D1D
                        A253284DF3DC01091EB3800C36FD62EE
                        BA15340F1FD498FAB67C0302E9CDA397
Magic:                  NCCH
Content size:           0x1cfef400
Partition id:           0004000000038c00
Maker code:             3436 ("46")
Version:                0002
Program id:             0004000000038c00
Temp flag:              00
Product code:           CTR-P-ALGP
Extended header hash:   0C27E3C1DE7B2AE2D3114F32A4EEBF46
                        9AFD0CF352C11D4984C2A9F1D2144C63
Extended header size:   00000400
Flags:                  0000030100000000
Plain region offset:    0x00004a00
Plain region size:      0x00000200
ExeFS offset:           0x00004c00
ExeFS size:             0x00143800
ExeFS hash region size: 0x00000200
RomFS offset:           0x00148400
RomFS size:             0x1ceab000
RomFS hash region size: 0x00000200
ExeFS Superblock Hash:  130C042615F647C4C63225EA9E67F8A2
                        7B15246B88FBC7A927257B84977B787B
RomFS Superblock Hash:  A65BEE1060BB6A6821BBCEC600035B7E
                        64FB6EACA7F0960CFB1F5A37087728F7
Note: Offsets and sizes in media units have been converted to byte sizes.

Plain region example for Lego Starwars III

0004a00: 5b 53 44 4b 2b 4e 49 4e 54 45 4e 44 4f 3a 43 54  [SDK+NINTENDO:CT    [SDK+NINTENDO:CTR_SDK-0_14_23_200_none]
0004a10: 52 5f 53 44 4b 2d 30 5f 31 34 5f 32 33 5f 32 30  R_SDK-0_14_23_20
0004a20: 30 5f 6e 6f 6e 65 5d 00 5b 53 44 4b 2b 4e 49 4e  0_none].[SDK+NIN    [SDK+NINTENDO:Firmware-02_27]
0004a30: 54 45 4e 44 4f 3a 46 69 72 6d 77 61 72 65 2d 30  TENDO:Firmware-0
0004a40: 32 5f 32 37 5d 00 5b 53 44 4b 2b 4d 6f 62 69 63  2_27].[SDK+Mobic    [SDK+Mobiclip:Deblocker_1_0_2]
0004a50: 6c 69 70 3a 44 65 62 6c 6f 63 6b 65 72 5f 31 5f  lip:Deblocker_1_
0004a60: 30 5f 32 5d 00 5b 53 44 4b 2b 4d 6f 62 69 63 6c  0_2].[SDK+Mobicl    [SDK+Mobiclip:ImaAdpcmDec_1_0_0]
0004a70: 69 70 3a 49 6d 61 41 64 70 63 6d 44 65 63 5f 31  ip:ImaAdpcmDec_1
0004a80: 5f 30 5f 30 5d 00 5b 53 44 4b 2b 4d 6f 62 69 63  _0_0].[SDK+Mobic    [SDK+Mobiclip:MobiclipDec_1_0_1]
0004a90: 6c 69 70 3a 4d 6f 62 69 63 6c 69 70 44 65 63 5f  lip:MobiclipDec_
0004aa0: 31 5f 30 5f 31 5d 00 5b 53 44 4b 2b 4d 6f 62 69  1_0_1].[SDK+Mobi    [SDK+Mobiclip:MoflexDemuxer_1_0_2]
0004ab0: 63 6c 69 70 3a 4d 6f 66 6c 65 78 44 65 6d 75 78  clip:MoflexDemux
0004ac0: 65 72 5f 31 5f 30 5f 32 5d 00 00 00 00 00 00 00  er_1_0_2].......
0004ad0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
0004ae0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................

A tool for parsing this format is available here