48 lines
2.3 KiB
Markdown
48 lines
2.3 KiB
Markdown
# Lo-Fi
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writeup by [haskal](https://awoo.systems) for [BLÅHAJ](https://blahaj.awoo.systems)
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**Forensics/OSINT**
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**499 points**
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**7 solves**
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**(BLÅHAJ got 1st solve 🦈📈)**
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>I made a "inspirational" lo-fi track! ft. Alec's very smooth aussie accent
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>
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>You know, "Just do it", "Don't let your dreams be ones and zeroes", I'm pretty sure he says
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>something along those lines... all inspirational sayings mean the same thing anyway
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provided file: <lofi.wav>
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## writeup
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listening to the provided file, it's just a short lo-fi hip hop beat to study/chill/pwn to but at
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the very end you can notice the sound of encoding something in the spectrogram (it's a very
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distinctive sound). visualize the spectrogram to see this, here i used audacity.
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this is all we get here, no full url yet. it's not going to be that easy :P. however from the flavor
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text we can deduce that the rest of the url might be encoded in this song as ones and zeroes. here i
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listened to the song again and noticed that in the second part, the synth notes are really off-beat,
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which is strange even for lo-fi. they don't seem to follow any sort of pattern. this must be where
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the encoded data is.
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here i go really jank low tech and take a gigantic w i d e screenshot of audacity and load it into
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glimpse to try to extract these notes. i overlaid a grid and tweaked it until it matched the pattern
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of synth notes in the waveform. it's important here to realize the synth notes are the ones that
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rise going from quiet to loud. the loud to quiet parts are the bass drum and the snare that make up
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the beat. therefore, look for triangles that point left, and ignore the ones that point right. if
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you listen to the song while doing this it's also more obvious where the notes are exactly. we find
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that the synth notes are triplets, with 6 intervals (6 bits) per measure.
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write down the bits, 1 if there's a note and 0 if there's no note, and then decode as 8-bit ascii.
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append this to `https://tinyurl.com/<data goes here>` and the resulting url contains the flag.
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## addendum
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i'm really surprised by how few solves this got. i guess it's kinda hard to notice what's going on
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unless you listen carefully and read the flavor text.
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