CSAW’18 CTF Qualification: Short Circuit

Event	Challenge	Category	Points	Solves
CSAW’18 CTF Qualification	Short Circuit	Misc	75	162

Description

Start from the monkey’s paw and work your way down the high voltage line, for every wire that is branches off has an element that is either on or off. Ignore the first bit. Standard flag format.

-Elyk

TL;DR

This challenge consists in the analysis of a lovely electronic scheme. It is composed of diodes, wires, wires, wires and wires. The goal is to extract bits of data from the circuit.

The task was not really hard, but if your have a bad sight, you’ll have a bad time.

Methology

Few things to know, here are the keys :

• If a diode is attached to VCC on its flat side and 0 (aka GND) on its pointy side, it’ll be ON
• If it’s the opposite, it’ll be OFF (yup, direction matters !)
• If the input and output are attached to the same wire, it’s OFF

By using these rules, we extract the bits one by one, with our eyes glitching, and we obtain : 01100110 01101100 01100001 01100111 01111011 01101111 01110111 01101101 01111001 01101000 01100001 01101110 01100100 01111101

Once decoded : flag{owmyhand}

-Laluka