│ Category: Reverse Engineering
│ Author: Imattas aka Zemi
│ Flag: byuctf{l3ft_bl1nk3r_5c9125be}
│ Source Path: rev/mixed_signals
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--[ Challenge Description ]--
-- text --
### Description
Legend has it, this checks a flag
Files:
- [mixed_signals](https://github.com/BYU-CSA/BYUCTF-2026/blob/main/rev/mixed_signals/mixed_signals)
- [program](https://github.com/BYU-CSA/BYUCTF-2026/blob/main/rev/mixed_signals/program)
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--[ Provided Materials ]--
- Repository folder
https://github.com/BYU-CSA/BYUCTF-2026/tree/main/rev/mixed_signals
- rev/mixed_signals/README.md
https://github.com/BYU-CSA/BYUCTF-2026/blob/main/rev/mixed_signals/README.md
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--[ Recon / Initial Analysis ]--
This page imports the BYUCTF 2026 source material for the Reverse Engineering
challenge Mixed Signals. The prompt is kept separate from the solve notes, and
upstream artifacts are linked so the challenge can be replayed from the original
repository.
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--[ Vulnerability / Observation ]--
The useful observation comes from the imported solve notes below. I kept the
original technical path intact while normalizing the page metadata, challenge
grouping, and author attribution for the Volume 2 writeup archive.
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--[ Exploitation / Solution ]--
Source: rev/mixed_signals/README.md
https://github.com/BYU-CSA/BYUCTF-2026/blob/main/rev/mixed_signals/README.md
mixed_signals is a VM that is based on signals sent to the program. program has
a number of signals that it throws at mixed_signals that triggers actions in the
VM that checks the inputted flag in constant time (that's important lol).
Basically we put the flag in a data section in mixed_signals, then the opcodes
sent by program actually go through and do stuff to it. If you reverse it, you
can verify that you have the right flag by running ./mixed_signals <flag> then
running ./program in a separate tab (they interact).
There is no solve script for this one
Flag: byuctf{l3ft_bl1nk3r_5c9125be}
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--[ Full Exploit Script ]--
No standalone exploit script was present in the selected source material.
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--[ Key Takeaways ]--
- The BYUCTF 2026 challenge material is preserved with local archive formatting.
- The page author is normalized to Imattas aka Zemi.
- The source repository remains linked for handouts, services, and solve
artifacts.