Thread: Unbelievable
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Old 30 June 2001, 23:49   #47
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Join Date: May 2001
Location: Auckland / New Zealand
Posts: 3,099
Identifying disks

OK guys, I will put my 2c worth in here from a programmers point of view:

Identifying disks does seem strange to me as I have them all named correctly anyway. However, if there are a lot of dud cracked versions out there it is nice to be able to identify each disk as the dud without having to check it yourself.

Anyway, an old virus library recognition system called BBBF used a simple but quite elegant way of identifying bootblock viruses, it searched for 4 key longwords in the bootblock that would uniquely identify each virus, by storing only $10 bytes (16 in decimal) it could identify each virus.

If someone was prepared to manually check each disk and include the data, I think it could work pretty well...

Let's say we have a dos game, Line of Fire. No matter what else is on the disk, the database should know the main game file is called "line" and filesize is 123456 bytes, crc is 12345678. The cracked version has same filesize but crc 87654321.

In case there are other games with the file "line" on the disk, it is unlikely to have that exact same filesize. You could always include some other check like game must have both line+credits.iff or something and CRC both files...

If someone is so stupid as to rename the main file, well tough - that person is an idiot. The game won't be identified...

Now for NDOS games, CRC the entire disk image as most people are not capable of changing NDOS games, possibly you could also see where the high scores are saved and skip that track - generally the very final track or the very first one contains the high scores, so maybe CRC the whole disk, + the disk from tracks 2-159 and tracks 0-157?

The other idea would be the specific longwords technique again, check the values at theh start of each track on the disk or something like this, but some corrupt versions might again slip through the cracks...
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