Breaking ‘80s Dungeon Master Disk Copy Protection with a Vintage BBC Micro
Chris Evans, AKA scarybeasts, used a BBC Micro to successfully circumvent Dungeon Master's floppy disk copy protection.
There are many arguments for and against DRM (Digital Rights Management), but there is no denying that some DRM techniques can be very interesting. For cartridge-based systems, there was little worry that users would be copying them. But games stored on cassette tapes, floppy disks, hard disks, and optical discs were a different story. Without additional copy protection schemes, those were all easily copied. Dungeon Master was a game released in 1987 for the Atari ST, and had some of the most advanced copy protection every implemented at the time. Chris Evans, AKA scarybeasts, used a vintage BBC Micro to successfully circumvent that protection.
In the era Dungeon Master was released, most other games used simple checks at startup to ensure you had purchased a legit copy. Often, those checks were as simple as looking up a generated code sequence in the booklet that came with the game. Dungeon Master, on the other hand, had multiple checks embedded throughout the game. Those checks relied on “fuzzy” bits stored on the floppy disk. Those are bits that hover between a zero and a one. Sometimes reading the bit will show a zero, and sometimes it will show a one. Those fuzzy bits could only be written with expensive, specialized hardware, which made it extremely difficult to successfully duplicate a Dungeon Master floppy disk.
A typical floppy disk drive’s controller won’t let you write fuzzy bits, because they are undesirable in every other scenario. To get around that, Evans connected his floppy drive directly to the BBC Micro’s user port to bypass the controller. But there was still an issue of timing. The BBC Micro’s user port is driven by a 1MHz 6522 Versatile Interface Adapter, and that can’t generate signals fast enough for writing a floppy disk on its own. The ingenious solution was to use the BBC Micro’s RGB output port, which can produce signals far more quickly. That is hardly an intuitive workaround, but it did work and allowed Evans to write fuzzy bits — making it possible to copy Dungeon Master floppy disks using hardware that was actually available at the time the game was released.