norlin@uokmax.ecn.uoknor.edu (Norman Lin) (02/26/91)
dave@interlan.Interlan.COM (Dave Goldblatt) writes: [more fascinating stuff about Atari copy protection] >One of the more interesting programs I saw had a one-sector boot >loader, which then loaded another loader sector by sector, XORing all >of the data in each sector with an incrementing count and the sector >number. Normally, just XORing the data with an incrementing count was >standard, and this particular one was a tough one to figure out (it >was self-modifying as well). But since every program HAD to have just >one normal, executable sector (the boot sector), everything else could >be derived. :-) This reminds me; I never could figure out how the heck the data was encrypted on Infocom adventure disks. Scott Adams adventures were a piece of cake, since all the text was stored as straight ATASCII on the disk, but Infocom employed some means of encryption. Was this, also, XORing the data with an incrementing count? For fun, I used to swap data disks in the middle of playing an Infocom game just to see what would happen. Surprisingly, instead of getting garbage, I often got bits and pieces of sentences and words. For instance, one time substituting the Zork II data disk for the Zork III one, I got something like "xipuuwoier tpesoufpoer gnomes." In case you don't know, Zork II had some rather amusing "gnomes" appear if you somehow trapped yourself in an inescapable situation, but Zork III didn't, so apparently the data is not only encrypted but also somehow "blocked" into logical bits and pieces -- perhaps words, perhaps phrases. I also tried modifying large chunks of data at random on the disk to see what kind of garbage the program would spit out, and, again, it seemed not to be totally random but rather random _groupings_ of apparently preset determination. Any information on this? >-dg- >-- > "Hey, Copperfield! * Dave Goldblatt [dave@interlan.com] > Suck on this!" * > - Penn Jillette, of * (No longer working for, or > Penn & Teller * representing Racal InterLan, Inc.) ---|\-#-/_|-------/|-------,*.----||---Norman Lin, University of Oklahoma---- ---|/-----|------/-|---,"--|---,"-||------norlin@uokmax.ecn.uoknor.edu------- --/|------------/-*'---|/------|--||-----(IP addr: 129.15.[20|22|24].2)------ -|/|\---/_|-----|-----------------||-"I gazed in your eyes, and saw the moon- --\|/-----|----*'-----------------||------------and the skies"---------------