MOGG File Format
MOGG files are often used in Harmonix games for all platforms except for PS2 and DS. They are an extension of the OGG Vorbis container with an extra header prepending it, and almost all official MOGGs starting with Rock Band shipped on-disk and as DLC are encrypted.
The version value in the MOGG header is used to indicate which encryption key and format should be used for decryption.
Structure
MOGG Header
| Name | Type | Size | Function |
|---|---|---|---|
| Version | Integer (LE) | 4 bytes | Version of the MOGG file. Related to encryption (10 / 0xA = unencrypted) |
| Header Size | Integer (LE) | 4 bytes | Length of the MOGG header / offset in the file where the OGG begins. |
| Map Version | Integer (LE) | 4 bytes | Version of the MOGG map. (usually 16 / 0x10) |
| Seek Interval | Integer (LE) | 4 bytes | The interval between samples in the sample table. (Usually 20000 / 0x4E20) |
| Entry Count | Integer (LE) | 4 bytes | The number of entries in the MOGG header. |
| OggMap | #MOGG Sample Entry Array | sizeof(MOGG Entry) * Entry Count | A lookup table to help the game stream the OGG file from disk. |
| AES Key | Byte Array | 16 bytes | An AES key used to encrypt the file. Only present if MOGG version is >= 11 / 0xB. |
MOGG Sample Entry
To help the game seek in an OGG file (rewinding after pausing, practice mode, etc), a lookup table is used to locate the byte offset in the file to look for a sample.
When the game wants to seek to sample N, it looks up entry (N / Seek Interval) in the table, that gives a byte offset and sample offset. It then seeks the file over to the byte offset and skips (N - Sample Offset) samples.
| Name | Type | Size | Function |
|---|---|---|---|
| Byte Offset | Integer (LE) | 4 bytes | Offset into the file that the entry starts. |
| Sample | Integer (LE) | 4 bytes | The sample in the OGG stream that corresponds to the byte offset. |
OGG File
Past this point is a regular (optionally encrypted) OGG Vorbis format file containing multiple tracks. The tracks corresponding to instruments are defined in the songs.dta file.
Encryption
At its core, files are encrypted with a 128-bit AES EBC cipher. Each "generation" of MOGG files changes the encryption keys and scheme used. There is also an additional bit-shuffling obfuscation step prior to encryption or after decryption. For legal reasons this wiki can not document any keys themselves, or any explicit details about 0x11 encryption.
| Generation | Info | Games |
|---|---|---|
| 10 / 0xA | Unencrypted. Lacks key in MOGG header. | Used in Guitar Hero 2 (Xbox 360). Also used throughout the games for unimportant MOGGs. Notably, does not work on PS3. |
| 11 / 0xB | Encryption is done with a static key. Uses nonce stored in MOGG header as IV. | Used in Rock Band on-disc and DLC songs. |
| 12 / 0xC | The true decryption key is derived through a custom algorithm. Changes the format of the header. Treated as exactly the same by all games that support at least this version of encryption. | Used in Rock Band 2 on-disc songs. Delivered to RB1 via title update. |
| 13 / 0xD | Used in encrypted C3 songs. | |
| 14 / 0xE | Increases the complexity of the key derivation step. | Used in Rock Band 2 DLC songs. |
| 15 / 0xF | Used in Rock Band Network. Delivered to RB2 via title update. | |
| 16 / 0x10 | Used in Rock Band 3, Rock Band 4 and Rock Band VR on-disc and DLC until November 2018. | |
| 17 / 0x11 | A new value is added in the header and a new set of keys are used for a more complex key derivation step. | Used in Rock Band 4 DLC after November 2018, as well as DropMix, Dance Central VR, Audica, and Fuser. The non-RB games each have their own keyset, and only support their own variant of 0x11, as well as unencrypted 0xA. |
Keys in Rock Band 2 (Xbox 360) and later are additionally protected behind the console's native XeKeys functions (XeKeysAesCbc). This was likely to prevent those with development kits from reverse engineering the new algorithm, as XeKeys uses different keys depending on the console's key vault. Rock Band 4 on PlayStation 4 also seems to follow the Xbox 360 key path.
TODO: Validate if the games and descriptions are correct.
The Beatles: Rock Band used version 16/0x10 behind a Cloakware's white-box crypto algorithm in order to protect the original keyset.
Tools
Several tools are available for working with MOGG files (creation/extraction, encryption, etc)
- Onyx Music Game Toolkit
- Magma
- ArkTool
- C3 CON Tools
- Audacity (supports reading smaller unencrypted MOGG files if the header is small)