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From: Al Kossow <aek@bitsavers.org>
Newsgroups: comp.arch
Subject: Re: older copy protection...
Date: Wed, 14 May 2025 16:37:40 -0700
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On 5/14/25 4:04 PM, Chris M. Thomasson wrote:
> On 5/13/2025 3:55 PM, Chris M. Thomasson wrote:
>> Does anybody know the hardware used to create the copy protection in the old Dungeon Master game?

>   Does anybody know the hardware? Here is a relevant snip from the links:
> _________________
> As the developer of both Dungeon Master and the software portion of its copy protection, I knew that eventually the copy protection would be 
> broken, but that the longer it held out the less damage we would suffer when it was broken. We had the advantage of owning the patent on a 
> floppy-disk copy protection scheme that required a $40,000 specialized hardware device to write the disks. It was impossible to create a 
> disk image without this hardware, and the hardware itself was out of production. That meant that as long as there were enough layers on the 
> copy protection, and these layers took long enough to crack, the only way to own the game was to buy it. The copy protection scheme took a 
> couple of weeks to create, and while this added cost to the production without adding value for the customer, it was time well spent. The 
> copy protection was based on many redundant, overlapping and isolated checks and cross checks. The copy protection was developed with the 
> assumption that the cracker would be armed with a hardware emulator and developed with an awareness of the capabilities and limitations of 
> the commonly available emulators of the time.
> _________________


this has been discussed on the Applesauce discord

"sector has that criss-cross pattern between the 1st and 2nd signal bands? That is use to put flux transition right at the edge of bitcell 
windows. Slight motor speed fluctuations mean that the nibbles in the area will shift between different values every time you read the sector. "

so very precise timing changes on only one sector of the disk to make non-deterministic recovered bits.

the "bands" referred to is looking at a histogram of the flux transition times of the track

"It was impossible to create a disk image without this hardware"

The disk has been cloned on the Applesauce.