Content.bin

Overview

Wii Channels and savegames can (almost everytime, some exeptions) be stored on SD cards inserted into the Wii through the front SD slot. They are stored in the directory /private/wii/title/ on the card and consist of a single .bin-file. Channels are stored in files called content.bin while savegames are stored in data.bin files. Each Wii channel and game have a unique four letter ID. data.bin and content.bin are stored in subdirectories named after the game's or program's ID. Renaming the directory will make the Wii not recognize the file anymore. Some games like Virtual Console titles can have both a content.bin and a data.bin.

Technical details

Looking at the bin-files reveals that they are structured in 64 byte segments. There is for example plaintext information about the certificate used to encrypt and decrypt the file stored in the content bin which is artificially padded by leading and trailing blocks of 64 zero bytes (0x00) and the ASCII strings are also padded with zeros to reach the 64 byte block size.

See the content.bin file format page for detailed discussion of this format.

Header

Each bin file starts with a header which can be decrypted successfully by every Wii console, since the icon, banner, title and description of the game are all readable in the Wii SD card menu, even if the file was not originally created on this Wii or is even from the same region. The header is broken into 64 byte segments and its last block is followed by a block with the first four bytes 0x00000070 being followed by the four bytes 0x426B0001. The next four bytes are the Wii ID of the specific console this file was created on stored in binary. Further information in the header includes the size of the following data and later the ID of the program in plaintext ASCII. The more colorful the icon of the file the bigger the header will be, strongly indicating an image compression of some sort.

Data

The data is encrypted and little can be said about its plaintext. At the end of the data two certificates are described, each one referring to the unique Wii ID thus making it plausible that the data is encrypted with a secret key only known to ones own Wii. A checksum of some sort might be the last piece of information stored in the penultimate block which is then followed by a last 64 byte block of zeros.

WiiLi contain additional discussion about the data format.

Copying a bin file to the Wii

A content.bin or data.bin file with a well-formed header will appear in the Wii's data manager on the SD card displaying it's icon and name and description if clicked upon. If a savegame or channel is not already present in the Wii's internal memory the bin-file can be encrypted and copied successfully.

Copying files from one Wii to the other

When copying a file that was created on another Wii the copying will fail with a corresponding message.

"Data was not copied."

Changing anything in the data (not the header, see below) will cause the copying to end with this message. Deleting or adding bytes at the end of the file will also yield this message. A checksum seems to check the integrity of the whole file or at least the data segment, since even changing something in the obviously useless and uninterpreted 64 byte zero segments or in the dead space beyond the plaintext strings in the certificate information will cause the copy process to fail with this message.

The White "?" Box

Every manipulation of the bin-file's header will cause the channel or savegame to appear as a white box with a black question mark inside it in the Wii's SD card manager. The file can still be examined but the name and description are filled with question marks also. Interestingly the file will still appear fine even if all blocks beyond the header are deleted. Only one byte needs to follow the isolated header, possibly to prevent the last byte of the header to be the end of file also. The value of the one byte is of no importance.

File does not appear at all

The file will not appear when its directory is renamed. Combined with the last statement this might mean that the Wii checks only the headers first and either the directoy's name is stored in the header in encrypted form or it is part of the key that is used by the Wii to decrypt the header.

File structure

These are the details of the Content.bin file structure.

VC games and Wii channels, when saved to a SD card, will be stored in a file named "private/wii/title/XXXX/content.bin", where XXXX is the four-character name of the game/channel.

A program to help parse and analyze the structure of content.bin files: parse-channel.c. Put it in the same directory as a compiled version of Segher's Wii.git tools, since it depends on them.

General layout

The general layout of this file is as follows. Most of the data here is sketchy, at best.

Length	Description
0x0640	Part A: Encrypted header
variable, padded to 64-byte boundary	Part B: Encrypted icon
0x70, padded to 64-byte boundary	Part C: Cleartext "Bk" header
0x1E4 + num_contents*0x24, padded to 64-byte boundary	Part D: Cleartext TMD block, including content_records for the following files
num_contents*variable, padded to 64-byte boundary	Part E: Encrypted data contents
0x340	Part F: Cleartext certificates

Part A: Encrypted header

The header is encrypted by the SD key and SD IV. When decrypted, it contains the following structure: (* means the field is discussed below)

Start	End	Length	Description
0x000	0x007	8	Title ID (which is 00 01 00 01 followed by the four-character code)
0x008	0x00B	4	Size of part B
0x00C	0x01B	16	MD5 Hash of header
0x01C	0x02B	16	MD5 Hash of decrypted icon
0x02C	0x02F	4	* unknown_2
0x030	0x037	8	* Title-ID-reference_1
0x038	0x03F	8	* Title-ID-reference_2
			The part below is identical to the start of opening.bnr
0x040	0x07F	64	* Zeroes_1
0x080	0x09B	28	* IMET data
0x09C	0x0EF	42*2	Channel name in Unicode, padded with 00 (Japanse version -- can be empty).
0x0F0	0x143	42*2	Channel name in Unicode, padded with 00 (English version).
0x144	0x197	42*2	Channel name in Unicode, padded with 00 (German version).
0x198	0x1EB	42*2	Channel name in Unicode, padded with 00 (French version).
0x1EC	0x23F	42*2	Channel name in Unicode, padded with 00 (Spanish version).
0x240	0x293	42*2	Channel name in Unicode, padded with 00 (Italian version).
0x294	0x2E7	42*2	Channel name in Unicode, padded with 00 (Dutch version).
0x2E8	0x63F	0x358	* Padding (normally zero)

• unknown_2

This value looks almost like the four-letter code of a channel/game. I have found HADP on most files, but HAGP on Super Mario/NES and '\0UPD' (that is, the first byte is 00, then UPD) on two N64-games.

• Title-ID-reference_1 and Title-ID-reference_2

These two looks like two Title-ID:s. On most files I have analyzed they are: 00 01 00 08 HALP and 00 01 00 08 HAKP (this is from a PAL Wii). However, on Super Mario/NES I found 00 01 00 02 HAFP and 00 01 00 02 HAGA. A guess is that they might stipulate some kind of dependencies on system files. (HALx and HAKx correspond to the EULA and Region Select Channels where x is the region code.)

• Zeroes_1

If the guess about depencencies is correct, then this might be a padding field which is zero only if not more than two dependencies are needed.

• IMET data

The IMET data follows a quite strict format, with a few changes between files. I don't have any good idea what those changes represent. The only major difference is found i Metroid Prime 3 Preview, which have everyting zero except the "IMET" header. The values indicated below is for all other files I've studied, which was non-zero.

Start	End	Length	Description
0x000	0x003	4	IMET header "IMET"
0x004	0x00B	8	Fixed value, always 00 00 06 00 00 00 00 03.
0x00C	0x017	12	Three 32-bit numbers (sizes?), typically in the range of 0x84BC to 0x56318.
0x018	0x01B	4	Flags? This is normally just zero, but Everybody Votes has 0050 0000 and Mii Contest has 0060 4100.

• Padding (normally zero)

For Metroid Prime 3 Preview, this field was not completely zero. The three bytes with positions 0x313, 0x367 and 0x3BB was 0x20 instead of 0. My guess is that this doesn't matter, but then again, it could have something to do with the weird IMET data of MP3preview.

Part B: Encrypted icon

This part is also encrypted by the SD key and SD IV. It contains a small header followed by LZ77 compressed data. The compressed data is the icon.bin portion of opening.bnr for the title.

Part C: Cleartext "Bk" header

This part is not encrypted. It is similar to the Bk header found in savegames, but the contents only partially match. The header could also be exactly 0x80 long; the size of 0x70 is a guess based on the first field being a size parameter.

Start	End	Length	Description
0x000	0x003	4	Size of this part (presumably; always 0x70)
0x004	0x007	4	Magic word, always 0x42 0x6B 0x00 0x01 (Bk..)
0x008	0x00B	4	NG-id
0x00C	0x015	10	Always zero.
0x016	0x021	12	Not yet analyzed, first byte is 0x03 or 0x02. On VCs, this always starts with 0x02 0xE0 and ends with 0x63 0x00.
0x022	0x06F	0x4E	Always zero.

Part D: Cleartext TMD block

This part is not encrypted. It is well described on the TMD file format page. Some things to note:

• Only the tmd struct is included here, not the certificates.
• As described on the TMD file format page, after the main struct (with a size of 0x1E4), there follows an array of content_record structs.
• There is as many structs as the num_contents field in the tmd struct indicates. For VC, this seems to be always 7.
• The type and size file of the content_record is of special interest, since they describe part E.
• If type is 0x00 0x01, then the content is included in part E, and the size of the content is given by the size field.
• Otherwise, type will be 0x80 0x01, and the content is (presumably) shared between VCs and stored elsewere on the Wii.

Part E: Encrypted data contents

This part is encrypted. The encryption key is the PRNG seed, extracted with [xyzzy], with an IV of the 2 byte content index, followed by 14 0x00's. This key is unique to the Wii that created content.bin It consists of several separate "files", one for each of the contents with the 0x0001 type flag in the TMD content_record, padded to 64-byte boundary.

Part F: Cleartext certificates

This part is not encrypted. The exact details of this field is not yet analyzed, but it is likely related to the chain of certificates as described on the TMD file format page.

Part G: Making back-ups / copies of a channel / VC game

Disclaimer: This is only legal to do when you have the right to use the VC game / channel, in other words: when you have bought the VC game or channel, or when it is/was free. Also, you're only allowed to install the software at one Wii at a time, and only on a Wii you own. Of course you may create homebrew channels too, and copy them as many times as you like.

As said above, the Wii channels and VC games are encrypted by two AES/RSA keys. The first part (the header) is encrypted by a public key, which is the same on every Wii system. This explains why you can see what Wii channels/VC games are on a SD card on every Wii. The key used to encrypt the header is called the SD Key. The second part includes the software itself. It is encrypted with a key unique to each console. This explains why you can only copy software back to the Wii on which it was copied to the SD Card. The third part includes several checksums and certificates, for which I refer to the explanations above.

The only way to copy Wii channels / VC games for use on another Wii is decompiling them on the Wii itself or on the computer. If this has been done, you obtain a WAD file, which is in fact slightly reverse engineered version of the original file.

With the homebrew application WAD Packer it is then possible to convert the WAD file on the SD Card to a compiled version in your Wii NAND Memory. The installation can only be done on the Wii itself. When this is done, the WAD Installer gets your Wii unique key, and encrypts the WAD Package with this one. Once the installation is done, the new channel / VC game appears in the Wii menu, and you are able to use it as it was genuine. Further, it is then possible to copy the channels/games to an SD card, but again, when using this way, it can only be copied back to the Wii it was copied from.