The entire raw NCAs are encrypted.

The only known area which is not encrypted in the raw NCA is the logo section, when the NCA includes that section. Everything else documented on this page is for the plaintext version of that data.

Encryption

The first 0xC00 bytes are encrypted with AES-XTS with sector size 0x200 with a non-standard "tweak" (endianness is reversed, see here), this encrypted data is an 0x400 NCA header + an 0x200 header for each section in the section table.

For pre-1.0.0 "NCA2" NCAs, the first 0x400 byte are encrypted the same way as in NCA3. However, each section header is individually encrypted as though it were sector 0, instead of the appropriate sector as in NCA3.

Header

Offset	Size	Description
0x0	0x100	RSA-2048 signature over the header (data from 0x200 to 0x400) using a fixed key
0x100	0x100	RSA-2048 signature over the header (data from 0x200 to 0x400) using a key from NPDM (or zeroes if not a program)
0x200	0x4	Magicnum "NCA3" ("NCA2", "NCA1" or "NCA0" for pre-1.0.0 NCAs)
0x204	0x1	Distribution Type (0x00 = System NCA, 0x01 = Gamecard NCA)
0x205	0x1	Content Type (0x00 = Program, 0x01 = Meta, 0x02 = Control, 0x03 = Manual, 0x04 = Data, 0x05 = PublicData)
0x206	0x1	Old Key Generation (0x00 = Pre-1.0.0, 0x01 = 1.0.0, 0x02 = 3.0.0)
0x207	0x1	Key Area Encryption Key Index (0x00 = Application, 0x01 = Ocean, 0x02 = System)
0x208	0x8	Size of the entire NCA
0x210	0x8	Title ID
0x218	0x4	Content Index
0x21C	0x4	SDK AddOn Version (used in "FS_ACCESS: { sdk_version: {byte3}.{byte2}.{byte1}, ..." with byte0 set to 0 and compared with a required minimum value: 0x000B0000)
0x220	0x1	Key Generation (0x03 = 3.0.1, 0x04 = 4.0.0, 0x05 = 5.0.0, 0x06 = 6.0.0, 0x07 = 6.2.0, 0x08 = 7.0.0, 0x09 = 8.1.0, 0x0A = 9.0.0, 0xFF = Invalid)
0x230	0x10	Rights ID (Ticket)
0x240	0x10*0x4(0x40)	Table for each section (see below)
0x280	0x20*0x4(0x80)	Table of SHA256 hashes (over each 0x200-byte Section Header Block)
0x300	0x10*0x4(0x40)	Key area

The header is 0x400-bytes, at NCA+0.

When the above Old Key Generation field is 0x2 on >= v3.0, different {crypto/keydata} is used for the sections' data. With system content, this is used with every ncatype except ncatype0. The only other exception is {data-content} for the firm titles: this is required in order for older-system-versions to install it.

Key Generation 0x3 (with Old Key Generation set to 0x2) is used for all 3.0.1 sysmodules and the System_Version_Title. With 3.0.2, all updated titles use the crypto from 3.0.1 for non-ncatype0, except for firm {data-content}. In some cases various game content uses the above newer crypto as well.

Key Generation is always Master Key Version + 1, except for generations 0 and 1 which are both version 0.

The keyindex passed to <key-generation-related code> is determined as follows:

Pre-3.0.0: The Key Area Encryption Key Index field (0x207) is passed directly.
3.0.0+: It's determined using the Key Area Encryption Key Index field (0x207) and the Old Key Generation field (0x206). The latter field must be 0, 1 or 2. In each ncahdr_keyindex block, it executes "if(ncahdr_x206>=3)<panic>", but that won't trigger due to the earlier check. The end result is basically the same as pre-3.0.0, except when ncahdr_x206 == 0x2, final_index is new_base_index+ncahdr_keyindex. Actual implementation loads index from u32_array[ncahdr_crypto_type], where the address of u32_array is different for each ncahdr_keyindex.
3.0.1+: The dedicated range check for the Old Key Generation field (0x206) was removed, since the updated code no longer needs it. The output from a function masked with 0xFF is now used instead of ncahdr_x206. The range check for that field was changed from {ncahdr_x206 check with panic described above}, to "if(index>=4)final_index=10;"(skips accessing the array and uses 10 directly). The arrays were updated with an additional entry: final_index=v301_base_index+ncahdr_keyindex.
- The keydata for the above index10 is not(?) known to be initialized.
- The new function called by the code described above does:
- if(ncahdr_x206 < ncahdr_x220){ret = ncahdr_x220; } else { ret = ncahdr_x206; } return ret;

Section Table Entry

Offset	Size	Description
0x0	0x4	Media Start Offset
0x4	0x4	Media End Offset
0x8	0x4	Unknown
0xC	0x4	Unknown

Entry size is 0x10-bytes.

Media offset is absoluteoffset/{mediasize}, where mediasize is 0x200 bytes.

Section Header Block

Offset	Size	Description
0x0	0x2	Version (always 2)
0x2	0x1	Filesystem Type (0 = RomFS, 1 = PFS0)
0x3	0x1	Hash Type (2 = PFS0, 3 = RomFS)
0x4	0x1	Encryption Type (1 = None, 2 = AesCtrOld, 3 = AesCtr, 4 = AesCtrEx)
0x5	0x1	Padding
0x8	0xF8	FS-specific superblock
0x100	?	Optional BKTR header (can be used with any section, but only known to be used with game-updates RomFS)

The Section Header Block for each section is at absoluteoffset+0x400+(sectionid*0x200), where sectionid corresponds to the index used with the entry/hash tables.

The total size is 0x200-bytes.

PFS0 superblock

Offset	Size	Description
0x0	0x20	SHA256 hash over the hash-table at section-start+0 with the below hash-table size
0x20	0x4	Block size in bytes
0x24	0x4	Must be 0x2
0x28	0x8	Offset of hash-table (normally zero)
0x30	0x8	Size of hash-table
0x38	0x8	Offset relative to section-start where the PFS0 header is located
0x40	0x8	Actual byte-size of the PFS0 filesystem relative to the PFS0 header
0x48	0xB0	Empty

RomFS superblock

Offset	Size	Description
0x8	0xE0	IVFC header (basically the same as Savegames IVFC except with 2 more levels and +0x0C is non-zero, see below)

This documents the structure of Section Header Block +0 for RomFS.

IVFC

Start	Length	Description
0x00	4	Magicnum "IVFC"
0x04	4	Magic Number (0x20000)
0x08	4	Master hash size?
0x0C	4	Usually 7? Unknown, could be related to total number of levels maybe?
0x10	8	Level 1 offset
0x18	8	Level 1 size
0x20	4	Level 1 block size (in log2)
0x24	4	Reserved
0x28	8	Level 2 offset
0x30	8	Level 2 size
0x38	4	Level 2 block size (in log2)
0x3C	4	Reserved
0x40	8	Level 3 offset
0x48	8	Level 3 size
0x50	4	Level 3 block size (in log2)
0x54	4	Reserved
0x58	8	Level 4 offset
0x60	8	Level 4 size
0x68	4	Level 4 block size (in log2)
0x6C	4	Reserved
0x70	8	Level 5 offset
0x78	8	Level 5 size
0x80	4	Level 5 block size (in log2)
0x84	4	Reserved
0x88	8	Level 6 offset
0x90	8	Level 6 size
0x98	4	Level 6 block size (in log2)
0x9C	4	Reserved
0xA0	32	Unknown, reserved?
0xC0	32	Hash

BKTR

Start	Length	Description
0x0	0x8	Offset
0x8	0x8	Size
0x10	0x4	Magicnum "BKTR"
0x14	0x4	u32, must be <=1.
0x18	0x4	s32, must be >=1.
0x1C	0x4	?
0x20	0x20	Same as the above 0x20-bytes except with different data.
0x40	0x4?	?
0x44	0x4?	?

Using this header is enabled when offset 0x8 in this header is non-zero.

The above byte-offsets are relative to the start of the section-data.

The two sections specified by the two BKTR entries are usually(?) at the very end of the section data(section_endoffset-{size of BKTR sections}).

RomFS Patching

The BKTR section enables combining data from an update NCA with the RomFS from a base NCA to create a single patched RomFS image.

The first BKTR entry describes how to map regions of the two RomFS images to create the patched RomFS. It has the following format:

Start	Length	Description
0x0	0x4	Padding/Unused?
0x4	0x4	Number of Buckets
0x8	0x8	Total Size of the Virtual RomFS Image
0x10	0x3FF0	Base Virtual Offset for each Bucket (u64s, padded with 0s until end)
0x4000	0x4000*X	Relocation Buckets

Where relocation buckets are as follows:

Start	Length	Description
0x0	0x4	Padding/Unused?
0x4	0x4	Number of Entries
0x8	0x8	End offset for this Bucket
0x10	0x3FF0	Relocation Entries

Where relocation entries are as follows:

Start	Length	Description
0x0	0x8	Address in Patched RomFS
0x8	0x8	Address in Source RomFS
0x10	0x4	1=Is from Patch RomFS, 0=Is from Base RomFS

The second BKTR entry describes the subsections within the Patch RomFS. It has the following format:

Start	Length	Description
0x0	0x4	Padding/Unused?
0x4	0x4	Number of Buckets
0x8	0x8	Total Size of the Physical Patch Image
0x10	0x3FF0	Base Physical Offset for each Bucket (u64s, padded with 0s until end)
0x4000	0x4000*X	Subsection Buckets

Where subsection buckets are as follows:

Start	Length	Description
0x0	0x4	Padding/Unused?
0x4	0x4	Number of Entries
0x8	0x8	End offset for this Bucket
0x10	0x3FF0	Subsection Entries

Where subsection entries are as follows:

Start	Length	Description
0x0	0x8	Address in Patch RomFS
0x8	0x4	Padding/Unused?
0xC	0x4	Value for subsection AES-CTR

Official code assumes the relocation entries are sorted, and performs a binary search when determining where to read from. Each subsection in the Patch RomFS has its CTR calculated separately from the others based on the value in its entry (the BKTR entries use normal crypto). Thus decrypting a Patch RomFS requires decrypting and parsing the BKTR entries before anything else.

Logo section

This is a PFS0.

See here for the mounted-FS logo contents.

ExeFS section

This is a PFS0.

See here for mounted-FS ExeFS contents.

Game-updates

The section-data for ncatype1 RomFS section(section1) uses section-crypto-type 0x4.

Game-updates also contain multiple ncatype6 content, which contain "section0_pfs0/fragment". Some of these are just NCAs, unknown for the rest(presumably NCAs with additional crypto?). The first ncatype6 content fragment file has a NDV0 header, with the NCA starting at offset 0x44.

PFS0

Offset	Size	Description
{Hash-table offset from superblock}	{Hash-table size from superblock}	Table of SHA256 hashes.
{Hash-table <offset+size> from superblock}		Zeros for alignment to {alignment size}.
{PFS0 offset from superblock}	{PFS0 size from superblock}	The actual PFS0.

This is the FS which has magicnum "PFS0" at header+0. This is very similar to HFS0. A tool for extracting this FS is available here.

The hash table is hashes for every {Block size from superblock} starting at the PFS0 header. The size used for the last hash is {PFS0 filesystem size from superblock} - offset_relativeto_header.

NCA

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