Don't ask how to hack password. (BIOS Passwords)
#44252 by ciper
Wed Mar 21, 2007 9:21 pm
After many hours of research I have found a way to add a new mini pci wireless card to my systems bios, however I have ran into an issue calculating the checksum of the file. This is on a Dell Latitude D800.

So far I have figured out how to extract the current bios of the system, extract the image from the dell upgrade utility and write an external file to the bios. I tested this method by flashing the Precision M60 bios to my machine.

I have hex edited the new PCI ID of my wireless card but I need to recalculate the checksum. The only tool I have found that can write the bios files is the dell update executable but it doesnt have a command line switch to ignore the checksum error.

I have a good guess where the checksum was stored in the HDR file (by comparing it to the rom that I extracted from the machine). The major difference lies in the header and footer of the files. This page documents the checksum and a girlfriend of mine helped me read it. She isnt technical so the translation may not be correct but according to her the checksum is stored in the last 8 bytes of the file and only 4 bytes are used?

Anyways I need your help. From what others have told me the checksum is calculated by adding up the entire file in hex. If you download any of the d800 or m60 bios and use the writehdrfile option you can will see the CRC stored within the last 8 bites of the file.