evan_tech

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10:10 am, 21 Jan 07

legality of decryption

Yesterday xaosenkosmos, danerat, and brad came by for some .PUZ format hacking. We figured out some new bits and also hacked my JS viewer into a multiplayer state (with a lot of Gobby's help), but now we've got an interesting side project:

PUZ files typically (always?) have the solution contained within them. Newer .PUZ files have the solution, but it's been "scrambled" (encrypted?) and have associated keys to decrypt them. It seems like figuring out this algorithm would be fun -- using the above multiplayer game we painstakingly "gathered" some plaintext versions of puzzles (their encryption scheme has a side channel attack in that the cyphertext is accompanied by clues as to what the plaintext is :P) and we also have the keys (which are in a fairly limited space: almost always in (1000,10000)). We poked around a bit and found it's not a simple substitution cypher (character distribution of cyphertext is nearly random) but it can't be that bad. Surely someone on LJ would love to take a crack at it!

So here are some problems:
  1. The puzzles are surely copyrighted. Is posting plaintext+cyphertext+key a problem? It's not like you can play them without the clues...
  2. Is it violating the DMCA to do this? We're not circumventing copy protection, and it's all just for hobbyist fun anyway...