Dreamcast Guides : Header Data Swapping

Editing header data
by comradesnarky

Header protections are simple, but tricky. It's similar to protections
like the ones in Capcom vs. SNK where there's about 2kb of data in a massive
file of junk, but the game only wants the 2kb of data. In Capcom vs. SNK,
you can get rid of that data with no repercussions. In a game like JoJo's
Bizarre Adventure for Matching Service, the game is checking to make sure
that the entire file is intact. This is easy to beat though. If you modify
the file size data by using data from an image that has the original file
intact, the game will think that nothing has been modified and boot
normally.

The best way to do this is by using FamilyGuy's data/data selfboot pack. If
you use this, then you can create an image with the unaltered files on your
desktop so that you have the unedited file's size easily available. If
you're going to stick with audio/data, then you'll probably have to kill a
disc and burn the files that you need the proper sizes to (if they even fit
on a disc). Likewise,once you do have your game burned with the edited
version of the file, you'll have to rip it and hex edit it. If you do it
this way, you'll never even have to touch a CD-R until you're done and it's
time to do a hardware test on the game.

1. Rip the files out of your GDI using whatever method you prefer. Set
up FamilyGuy's data pack, put the files from your game into the data folder
and double click selfboot to make an image. The pack will create an image
no matter how much data you put into it. The resulting image is an .nrg, but
this is fine for our purposes. For the untouched files in Vampire Chronicle
I actually couldn't get DiscJuggler to rip it to a CDI. Set aside the
untouched game image for now.


NOTE: You need to put more than one file in the ISO. I tried only putting
the file that I needed the modified size for into an ISO; it doesn't
result in a file list that indicates the size of the files.

Also note: Vampire Chronicle actually didn't need the file size to be
edited for the files that were dummied.

2. Go about doing whatever you need to do to reduce the size of the files
that you'll be spoofing the data for. For JoJo's Bizarre Adventure for
Matching Service, the file was just 0s, so nothing special needed to be
done. This may not be the case for all games though, and it isn't for
Vampire Chronicle.

3. Once you're done fucking with the game, make an image of the game with
the modified files.

4. Open up your ISO that has the original files in a hex editor. Search
for the name of the file. If you're looking for something like JUNK.BIN
then do a text search for that. I'm using WinHex, I don't know what it
would be called in other editors, but I can't imagine they vary too
wildly. You'll find JUNK.BIN; and after the ; there will be a whole
bunch of shit after it. Eventually the shit will end, and the next
file will be there. Copy all of the junk after the ; and up to the
start of the next file name. So if it goes JUNK.BIN; ASKTJANa12iuoy1ST_READ.BIN
then take  ASKTJANa12iuoy

5. Open up the ISO that you modified the files in. Search for JUNK.BIN
and then replace everything after the ; with the shit from the unmodified
file.

6. You're good to go!