PDA

View Full Version : ROM checksum childish fun



hargle
March 10th, 2009, 09:46 AM
I won't go into all the details, but I was messing with my ROM emulator and various plug in cards, and one of them that I was using was a promise "FastTrak RAID controller".

For kicks, I edited the binary ROM file and changed the sign-on text from "FastTrak RAID" to "ButtCrak RAID" and restarted the machine. The PC didn't have any problems with the new ROM at all. I figured that the PC wasn't really checking the sum of the ROM contents, but after changing 1 additional byte in the binary file, the PC refused to load it.

So it turns out that changing "FastTrak" to "ButtCrak" still 8-bit checksums the same!

barythrin
March 10th, 2009, 03:04 PM
Yeah the adding a byte throws off all the jmp locations but for the most part any text can be replaced with the same amount of characters without a problem. ..er.. yeah ok I realize that's not what you did I was just mentioning that as a general statement.. We didn't mess with EPROMs much but did have some software to change the BIOS logo on a few motherboards with very specific details on the image size you can use for the logo (this was for rebranding systems with your company/OEM builder logo).

We used to do a lot of that as kids too though, hex editing our way around different applications like NAV and fileman.exe and having a few other choice words for your pulldown menus, etc. We modified a few playstation games also for a while which was kinda cool in a way. I just remember the one friend being pissed because he didn't show up for that "party" so we made him a girl in the game.

Some checksum algorithms just check every x byte (and it goes up in a factorial or something) which is an odd way to do things but somehow is accepted. We used a public checksum algorithm when we wrote an app to search your system for duplicate files. LOTS of false positives, I added my own fake checksum algorithm (adding up the first 4K of a file) since we wanted mainly to determine incomplete downloads at the time and that had a better ratio and much less false positives.

TandyMan100
March 18th, 2009, 02:32 PM
Yeah the adding a byte throws off all the jmp locations but for the most part any text can be replaced with the same amount of characters without a problem. ..er.. yeah ok I realize that's not what you did I was just mentioning that as a general statement.. We didn't mess with EPROMs much but did have some software to change the BIOS logo on a few motherboards with very specific details on the image size you can use for the logo (this was for rebranding systems with your company/OEM builder logo).



Can you remember any details on that?

Terry Yager
March 19th, 2009, 12:41 AM
Use a hex editor to replace the code then burn a new chip. What could be simpler?

--T

barythrin
March 19th, 2009, 01:42 PM
lol T. Yeah that'd be the simple txt editing unless you can use a resource editor and detect the bitmap in the binary dump. Then as long as you replace it with something the same color/dimensions (and bytes) you could replace the picture.

It was only on one chipset (Award I think) but it was something that from what I recall cost $2000 and was only for computer manufacturer companies to embed their own logo (ie Dell, etc) to make it look home brew.

We had a printed manual for the software and a floppy disk to boot off of. I don't recall how it worked or the file names, I just know it wasn't free. From the looks of it though there are a few motherboard companies (if you google around) that have free tools or options to upload a low res picture to your bios.

Although as Terry indicated get yourself a rom burner, dump it so you can restore it and you can hack away.

DreadStorm
March 29th, 2009, 05:00 AM
I remember doing similar back in the 90s with DOS 4.01, Toshiba's version I think it was. I hex edited all the displayed messages, so you'd get messages ranging from "I won't do that" to "What the hell does that mean?" and that sort of thing. I don't remember exactly what they were, but it was a blast playing with things like that.

The funniest thing wasn't general folks' reactions, it was the techs that worked there. THAT was hilarious. Serious computer nerds, no sense of humor, looked at me like I had a third arm or shot their dog or something.