"Market" for old macs?
trixter at oldskool.org
Fri Dec 2 17:42:47 CST 2005
Chuck Guzis wrote:
> games were infamous for it. Oddly, many copy protection schemes could be
> defeated by simply patching the code to dummy up the subroutine that
> reported that the copy protection was intact.
Replace "many" with "some" and I'd agree. There were some schemes that were
simply evil in their cleverness and ingenuity. King's Quest 2 encrypted the
main code with a cypher kept somewhere abnormal (like a 10th sector or 41st
track, can't remember the exact one) that was transparently missed by DISKCOPY:
you could make a copy without errors, but it wouldn't work... and the
decryption routine was itself obfuscated with some clever self-modifying code,
so you couldn't just dump the raw code and (U)nassemble it -- in fact, you
couldn't do THAT EITHER because the game was a bootable program with it's own
disk routines. Took three weeks to unravel that monster, starting with the
only code you *could* look at: the 512-byte boot sector.
By far the worst was another bootable game (Dunzhin: Warriors of Ras) that
didn't use INT 13h BIOS services to read diskette sectors, but rather raw NEC
FDC commands. Int 13h is easy to work with; raw NEC commands are not, and I'm
no Guzis or Dunfield :-)
But I agree with you that some DOS-based games were so trivial that they could
be cracked with a hex editor and not a debugger. For example, replace INT 13h
disk call opcodes (CD13) with NOP opcodes (9090) and the program would just
"fall through" the protection routine... or finding a list of null-terminated
manual code words and changing them to ALL nuls and then you could merely hit
Enter at the password request.
I'm giving away too much information about myself, aren't I? :-)
The future of software protection is coming, and it's not pretty. Public-key
assymetric encryption schemes are already in use; your software phones the
mothership to authenticate. Joy.
Jim Leonard (trixter at oldskool.org) http://www.oldskool.org/
Want to help an ambitious games project? http://www.mobygames.com/
Or check out some trippy MindCandy at http://www.mindcandydvd.com/
More information about the cctalk