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Last updated on Oct-18-2019 Download

Question to Martin F. (Nestopia) about some FDS protections

Question to Martin F. (Nestopia) about some FDS protections
by on (#22608)
If the disk of Deep Dungeon II - Yuushi no Monshou (Japan) is dumped with "normal mode" it does not work on Nestopia and displays an anti-piracy message (it asks to buy the game for 3400 yens)

In "protection mode", the dump work on Nestopia

I checked the difference in hexeditor between "normal mode" dump & "protection mode" dump

result:
http://img232.imageshack.us/img232/5151/couper5dy7.jpg
http://img339.imageshack.us/img339/8273/couper6ps7.jpg

My question to Martin is: does that data added/changed in "protecion mode" exist on the real disk (with word "DUMMY") or not ??

Thank you.

by on (#22609)
Well, I'm not Marty, but I can answer your question - yes, that "DUMMY" is on the real disk. It is a form of copy protection.

At the beginning of each disk/side, there is a file counter that indicates how many files are on the disk (that is the first byte your hex editor found to be different). This game (among others) had this byte set to the wrong value, making it seem like there are fewer files on disk than there really are. If a copier/dumper relies on this byte to determine how many files to read, it will fail to copy all the data on the disk.

When you start the game, it changes (temporarily) the file counter to indicate the correct number of files. It then scans the disk in an attempt to find the hidden file (in this case, the file is named "DUMMY"). If the file cannot be found, then the game concludes that it must have been copied illegally and will refuse to proceed as a result.

by on (#22610)
dvdmth wrote:
Well, I'm not Marty, but I can answer your question - yes, that "DUMMY" is on the real disk. It is a form of copy protection.

At the beginning of each disk/side, there is a file counter that indicates how many files are on the disk (that is the first byte your hex editor found to be different). This game (among others) had this byte set to the wrong value, making it seem like there are fewer files on disk than there really are. If a copier/dumper relies on this byte to determine how many files to read, it will fail to copy all the data on the disk.

When you start the game, it changes (temporarily) the file counter to indicate the correct number of files. It then scans the disk in an attempt to find the hidden file (in this case, the file is named "DUMMY"). If the file cannot be found, then the game concludes that it must have been copied illegally and will refuse to proceed as a result.


Thank You!
So if I understand everything the correct value at the begining is 0x0D and not 0x0E (as in the "protection mode" dump)
it changes to 0x0E only in memory while the game is running?

by on (#22633)
Anyone to confirm please?

by on (#22640)
What is "normal mode"/"protection mode"? Some feature in Nestopia?

0x0D is the proper file count and should have been changed back manually from 0x0E after the game was copied.

The game will know how many files are really on the disk and not need the header value.

by on (#22647)
"normal mode"/"protection mode" are backup modes of the FDS copier

by on (#22650)
Which FDS copier? Just about every has one mode of operation, the one which fails to copy undeclared files. One could get around this by modifying the original disk to the proper file count using Tonkachi editor, copy the disk, and return the original count to both the original disk and copied disk again with Tonkachi.

by on (#22651)
Doesn't "protection mode" just copy 65,536 bytes without respect to files? Or am I misunderstanding something fundamental about QuickDisk?

by on (#22652)
kyuusaku wrote:
Which FDS copier? Just about every has one mode of operation, the one which fails to copy undeclared files. One could get around this by modifying the original disk to the proper file count using Tonkachi editor, copy the disk, and return the original count to both the original disk and copied disk again with Tonkachi.
I have no idea what you're talking about, Sir. :$
Please confirm if the real value in the disk is indeed 0x0d and not 0x0e (which I believe you did confirm indirectly but a direct confirmation is still better).

by on (#22655)
kyuusaku wrote:
0x0D is the proper file count and should have been changed back manually from 0x0E after the game was copied.


If the game's original file count was 0x0D (13 decimal), but there are really 0x0E (14 decimal) files, early copy software which looked at the FDS header for a file count would only copy the first 13 files; it would not copy the last file (14) because the software would stop after 13. It would assume the rest of the disk is garbage left over from the last game that was on the disk. As a form of protection, the game program itself may scan to the 14th file's location to check whether it's present. If it isn't, the game would know that the disk was illegally copied. If somebody changed the file count to represent the true number in order to copy that 14th file, the game could also detect that the file count was changed from the original 0x0D and presume it was illegally copied.