Leaping Brain's "Virtually Uncrackable" DRM is just an XOR with "RANDOM_STRING"

Re:Leaping Brain's "Virtually Uncrackable" DRM is just an XO... by tptacek on Monday November 26, 2012 @07:30PM (#4834836)

It's so easy to solve repeating-key XOR for the key that the solution is a practical way to detect the scheme; you wouldn't even necessarily bother trying to detect it, you'd just run the "solver" (even calling it a solver sort of dignifies it a bit too much).

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Re:Leaping Brain's "Virtually Uncrackable" DRM is just an XO... by ahh on Thursday November 29, 2012 @02:51AM (#4846701)

So that's generally true--Babbage's solution to the Vigenere was one of my favorite things to learn in basic crypto--but amusingly I'm not sure it would be easy in this case!

In particular, while I don't know the .mov file format backwards, the last step (after lossy encoding) is probably a lossless encoder, either LZ-type or some sort of entropy coder. This means that the plaintext is going to be a very good approximation of IID coinflips; in other words, a one-time pad _key_.

"Decoding" the repeated-key XOR also decodes the one-time-pad encryption of the repeated-key interpreted as plaintext. This is, well, hard.

(mov may have enough frame structure/boilerplate that this doesn't apply; I don't know.)

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Re:Leaping Brain's "Virtually Uncrackable" DRM is just an XO... by tekromancr on Tuesday November 27, 2012 @02:21AM (#4836054)

Is the solver just (cyphertext XOR plaintext)?

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Re:Leaping Brain's "Virtually Uncrackable" DRM is just an XO... by tptacek on Tuesday November 27, 2012 @08:52AM (#4837076)

No (although that's how this guy solved this system).

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