sm0ke

Challenge author
Ian Klatzko (SIGPwny)
Write-up author
Vanilla (Batman's Kitchen)
Points
200
Category
forensics

Help!!! Some hackers got into my stempania song dir and did something weird to one of my simfiles.

ikywt.sm

We're given a StepMania stepfile. I looked up the file format, but it turns out to be basically irrelevant. Look for patterns, and you see that in each measure, everything off the diagonal is zeroes. Throw that away. Now we end up with four-bit pairs. How many bits in a byte? Eight (or 7.5 if you're Justin, hi Justin). So let's throw consecutive four-bit pairs together. It doesn't immediately work, but if you reverse the bits in each nibble, it works, and oh look, flag.