Difference between revisions of "NCA Format"

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(Header)
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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.
 
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]].
+
'''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.
  
With [[3.0.2]], all updated titles use the crypto from [[3.0.1]] for non-ncatype0, except for firm {data-content}.
+
'''Key Generation''' is always '''Master Key Version''' + 1, except for generations 0 and 1 which are both version 0.
 
 
Note: in some cases various game content uses the above newer crypto as well.
 
  
 
The keyindex passed to <key-generation-related code> is determined as follows:
 
The keyindex passed to <key-generation-related code> is determined as follows:

Revision as of 20:09, 13 September 2019

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.

See also the PFS0 superblock above.

Offset Size Description
0x0 0x4 Magicnum "PFS0"
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 Normally zero?