Wii ISO Structure and Decryption Process

TODO

Probably need to split this page on smaller ones

Overview

A Wii disc is an ISO image of 4.7 GB (single-layer) or 8.5 GB (dual-layer) organized in successive layers. There are several levels: Disc Header, Partition Table, Partition Headers (containing the Ticket and TMD, then AES decryption of the data to finally access the File System Table (FST).

Disc Header (0x000 – 0x440)

The Disc Header sits at the very beginning of the ISO (offset 0x000). It is read unencrypted and holds the global disc metadata.

Offset	Size	Field	Description
0x000	0x06	Game ID	Unique game identifier (like RMGE01 for Super Mario Galaxy NTSC-U)
0x006	0x01	Disc Number	Disc number (0 for single-disc games)
0x007	0x01	Disc Version	Disc version
0x008	0x01	Audio Streaming	Audio streaming enable flag
0x009	0x01	Stream Buffer Size	Streaming buffer size
0x018	0x04	Wii Magic Word	Must be 0x5D1C9EA3 for a valid Wii disc
0x01C	0x04	GameCube Magic Word	0xC2339F3D for GameCube
0x020	0x40	Game Title	Game name in ASCII
0x060	0x01	Disable Hash Verification | If set, disables H3 hash verification
0x061	0x01	Disable Disc Encryption	If set, the disc is unencrypted
0x080	0x380	Padding	Just \x00

Internal Header (inside decrypted data)

Once the DATA partition is decrypted, a second Disc Header (internal, called boot.bin) is found at offset 0x000 of the decrypted data. It additionally contains the DOL and FST informations:

Offset	Size	Field	Description
0x420	0x04	DOL Offset	Executable file offset
0x424	0x04	FST Offset	File System Table offset
0x428	0x04	FST Size	FST size
0x42C	0x04	FST Max Size	Maximum allocated FST size

Important

DOL/FST offsets are stored right-shifted by 2 bits (>> 2). To get the actual offset, multiply by 4 (<< 2).

Partition Table (0x40000)

The partition table is always at the fixed offset 0x40000. It defines 4 partition group s, each consisting of:

Field	Size	Description
Count	0x04	Number of partitions in this group
Offset	0x04	Offset (shifted) to this group entries

Each partition entry consists of:

Field	Size	Description
Partition Offset	0x04	Partition offset (shifted)
Partition Type	0x04	0 = DATA, 1 = UPDATE, 2 = CHANNEL

• The DATA partition contains the game itself.

• The UPDATE partition holds system update.

• The CHANNEL partition holds when game have channels like wii fit, Mario Kart.

Note

Super Smash Bros Brawl has a lot of partitions. Each one for the virtual game

Partition Header

Each partition starts with a header containing:

Partition header structure

Here is the content of a Partition Header

Offset	Size	Field
0x000	0x2A4	Ticket
0x2A4	0x04	TMD Size
0x2A8	0x04	TMD Offset shifted
0x2AC	0x04	Cert Size
0x2B0	0x04	Cert Offset shifted
0x2B0	0x04	H3 table offset shifted
0x2B4	0x04	Data Size shifted
0x2B8	0x04	Data Offset shifted
0x2BC	0x04	FST Max Size

Note

All offsets in the partition header are relative to the partition start.

Ticket - Title key decryption

Tickets contains the encrypted AES title key and the title ID of the data. Ticket are signed from a certificate chain.

Title key decryption process

Sequence diagram for title key decryption

Important

For nintendo common key (16 bytes AES keys):

• Index 0: “Normal” common key, the most frequent

• Index 1: Korean common key

TMD (Title MetaData)

The Title MetaData is used to store information about a title and its contents and their SHA1 hashes.

Here is the structure

Offset	Size	Field
0x000	0x04	Signature type (always 0x10001 for RSA-2048 with SHA-1)
0x004	0x100	Signature
0x104	0x3C	Padding for 64 bytes aligment
0x140	0x3C	Certificate issuer
0x180	0x01	Version
0x181	0x01	ca_crl_version
0x182	0x01	signer_crl_version
0x183	0x01	Is vWii
0x184	0x08	System Version
0x18C	0x08	Title ID
0x194	0x04	Title type
0x198	0x02	Group ID
0x19A	0x02	—
0x19C	0x02	Region
0x19E	0x10	Ratings
0x1AE	0x0C	Reserved
0x1BA	0x0C	IPC Mask
0x1C6	0x12	Reserved
0x1D8	0x04	Access rights
0x1DC	0x02	Title version
0x1DE	0x02	Number of contents
0x1E0	0x02	boot index
0x1E2	0x02	Minor version, unused

CMD (Content MetaData)

Each CMD has this structre:

Offset	Size	Field
0x00	0x04	Content ID
0x04	0x02	Index
0x06	0x02	Type
0x08	0x08	Size
0x10	0x14	SHA1 hash

Certificate chain

Most chains contains 3 certificated, each padded to 0x40.

Each certificate contains this structure:

Offset	Length	Description
0x000	0x04	Signature type
0x004	X	Signature
0x040 + X	0x40	Issuer
0x080 + X	0x04	Key type
0x084 + X	0x40	Child Certificate Identity
0x0c4 + X	0x04	Key ID
0x0c8 + X	Y	Public Key

Since the signature depends on the signature type (see below), the offset depends on the signature type

Signatures types

Name	Signature Type	Signature Length
Elliptic Curve	0x00010002	0x03c
RSA-2048	0x00010001	0x100
RSA-4096	0x00010000	0x200

Key types

Name	Signature Type	Key length	Key Modulus	Key Public exponent	Key padding to 0x40
Elliptic Curve	0x00000002	0x238	0x200	0x04	0x34
RSA-2048	0x00000001	0x138	0x100	0x04	0x34
RSA-4096	0x00000000	0x78	0x3C	0x00	0x3C

Data decryption/encryption

Partition data is encrypted with AES-128-CBC using the title key. The layout is:

Tree of data encryption

Block structure

Each block has a Merkle Tree node, the IV and their encrypted data.

Offset	Length	Description
0x000	0x0400	Block header (H0, H1, etc.)
0x3D0	0x0010	Data IV
0x400	0x7C00	Encrypted Data

Block decryption process

• Read the 0x8000 bytes block from the ISO

• Extract the IV at offset 0x3D0 of the block header

• Decrypt data at offset 0x400 with AES-128-CBC using the title key and IV

• Result is 0x7C00 bytes of decrypted data

Encryption and hashing processes

This part is quite difficult. Data within block, group are hashed then encrypted. So, if we need to change files, we also need to hash then encrypt all datas. Before, in the header we said that it contains H0, H1, etc. It’s from a Merkle Tree, a tree with every node that is not a leaf is a hash of its child. For Wii ISO, it’s like this:

Merkle Tree for Wii ISO

Since the algorithm is pretty hard to understand, here a good sequence diagram:

Sequence diagram for encryption

References

• WiiBrew - Wii Disc Header

• WiiBrew - Decrypted Header

• WiiBrew - Wii Disc

• WiiBrew - Ticket

• WiiBrew - Title Metadata

• WiiBrew - Certificate Chain

• WiiBrew - DOL

• WiiBrew - Partitions Information

• WiiBrew - Partition

• WiiBrew - Wii Disc - Encrytped