Apple II copy protection and IF

Many on this forum will already know something of the copy protection schemes applied to commercial floppy disks in the 80s and 90s. If you do or don’t, I link below to an interesting interview with the gent known as 4AM who’s busily been deprotecting old Apple II disks as of 2013 to preserve them.

What made this interview worth sharing here was his one-paragraph mention of the schemes on a lot of IF games. The protection schemes would try to trick hackers into thinking they had removed them if they didn’t test their efforts sufficiently. Quote:

“Scott Adams’ “Strange Odyssey” doesn’t run its protection check until you’ve started the game, climbed down the stairs, and taken the shovel. “The Count” doesn’t check until you’ve climbed into the dumbwaiter, which is about 15 moves into the game. And those are the easy ones, because they just reboot or crash immediately if they fail. “Transylvania” has a delayed protection check that deletes a vital location from the map and renders the game unwinnable. “Prince of Persia” neutralizes the effect of a potion you need to drink to finish level 7. “Conflict in Vietnam” has both on- and off-disk protection and 13 separate anti-tamper checks that can trigger a fatal error up to an hour later!”

Full interview: Confessions of a Disk Cracker: the secrets of 4am. - Paleotronic Magazine



… and, as we hardcore IFitsts (got the reference ? :wink: ) know, back then many crackers defaced Infocom’s “serial number” (actually the release date…) failing to note the real effective protection: the feelies ! (LOL !)

using the tools hackers in the day don’t have (actual sources & z-machine documentation) I can safely assert that the zcode itself can be classed as a very strong protection scheme (a complex and very efficient, in its days, pseudocode) “cracking” it means disassembling the 'terp, figuring out the z-machine architecture, then decode the z-code instruction set, write a debugger for it, then figuring how to hack in the story file the content what matters of the feelies…)

In the end, with this estimate, I can dare to advance the hypothesis that the unused piracy opcode was put in the instruction set for giving a substantial ease to prospective investors: it’s an intriguing hypothesis

Best regards from Italy,
dott. Piergiorgio.