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From: "Chris M. Thomasson" <chris.m.thomasson.1@gmail.com>
Newsgroups: comp.arch
Subject: Re: older copy protection...
Date: Sun, 18 May 2025 01:21:46 -0700
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On 5/14/2025 4:37 PM, Al Kossow wrote:
> 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.

Thanks! I need to ponder on this. Thanks again.