Didier Stevens

Friday 25 June 2010

Solving the Win7 Puzzle

Filed under: PDF,Puzzle — Didier Stevens @ 9:39

The Win7 puzzle is actually a “PDF bomb”, something I’ve hinted at long ago but I hadn’t published a sample.

The PDF contains a doubly compressed object stream, which is around 100 MB large when uncompressed. Some of you might have experienced problems opening this PDF file in your favorite PDF reader, this is because it couldn’t handle an uncompressed stream of 100 MB. Which isn’t actually that large, a PDF bomb of 1 GB or 10 GB isn’t that much larger in compressed form…

If you used my pdf-parser, you’ve also encountered a problem. The objects lack the endobj keyword. A simple solution: add the missing keyword and extract the stream with my parser. The stream is 100 MB of spaces, with a small text in the middle: “De Ultieme Hallucinatie”. One way to extract this text is to trim the spaces of the 100 MB string.

If you’re interested in different solutions, be sure to read the comments of the Win7 Puzzle.

De Ultieme Hallucinatie (The Ultimate Hallucination) was a nice Art Nouveau cafe/restaurant in Brussels. But the Windows 7 Ultimate license won by Vincent is no ultimate hallucination 😉

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