Tags: misc 

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# Sir Scope

> This circuit used to write out the flag using an array of 8 LEDs, but the LEDs are all burnt out now.

As file we have several osciloscope images with signals for LED. We can see 3 traces (yellow, pink and cyan). Cyan one on the bottom seems to have exact group of 8 peaks representing 8 LED. Which can be assumed as 8 bits of ASCII.

![](https://github.com/pteacher/CTF_WRITEUPS/raw/main/irisCTF_2024/Sir_Scope/capture_0.png)

Lets check this hypothesis. I used dumb, but yet simple method. Drawing lines in paint from synchronization track on bottom to signal on top.

![](https://github.com/pteacher/CTF_WRITEUPS/raw/main/irisCTF_2024/Sir_Scope/method.png)

Assuming endiannes bits may be BE or LE. Checking both we find that we see LE order.

Next applying this technique I entered all group of bits to CyberChef and got first string which gives us expected result.

![chef](https://github.com/pteacher/CTF_WRITEUPS/raw/main/irisCTF_2024/Sir_Scope/chef.jpg)

P.S. For sure you might think that this chal could be solved using automated methods, like openCV or PIL. I would like to see if someone will implement that method as well.

Original writeup (https://github.com/pteacher/CTF_WRITEUPS/tree/main/irisCTF_2024/Sir_Scope).