36 lines
1.1 KiB
Markdown
36 lines
1.1 KiB
Markdown
# Phasors to Stun
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**Category:** Communication Systems
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**Points (final):** 62
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**Solves:** 71
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>Demodulate the data from an SDR capture and you will find a flag. It is a wav file, but that
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>doesn't mean its audio data.
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## Write-up
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by [haskal](https://awoo.systems)
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The provided WAV file contains a signal that looks like this:
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This looks suspiciously like Phase Shift Keying (PSK) and it's a very clean signal (this is also
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hinted at by the challenge name). We can use [Universal Radio Hacker](https://github.com/jopohl/urh)
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to demod this with very little effort.
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Select PSK modulation, then click "Autodetect parameters". Then move to Analysis:
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We discovered that the signal is NRZI (non-return-to-zero inverted) coded, and after selecting this
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in URH the flag is decoded in the data view.
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## Resources and other writeups
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* <https://github.com/jopohl/urh>
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* <https://en.wikipedia.org/wiki/Phase-shift_keying>
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* <https://en.wikipedia.org/wiki/Non-return-to-zero#NRZI>
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