Blink Logic CTF Challenge Writeup

Challenge Information

• Name: Blink Logic
• Points: 100
• Category: IoT
• Objective: Analyze a firmware file and determine the correct keypad input to unlock an IoT system running on Wokwi simulation.

Solution

To solve the “Blink Logic” challenge, follow these steps:

1. Challenge Setup:

   • The challenge provides a compiled firmware file in .hex format and instructs the user to simulate an IoT project using Wokwi, a popular online Arduino/IoT simulation platform.

   • The goal is to determine the correct key combination on a virtual keypad to “unlock” the system and retrieve the flag.

     

2. Converting the Firmware:

   • Started by converting the .hex file into a binary format using the objcopy tool:

     1	objcopy -I ihex BlinkLogic.ino.hex firmware.bin

   • This step makes it easier to inspect the raw data inside the firmware.

     

3. Static Analysis:

   • Ran the strings command on the .bin file to extract human-readable content.

     1	strings firmware.bin

   • Among the output, several familiar keypad characters were visible (123A456B789C*0#D), which appeared to represent a standard 4x4 keypad layout.

     

4. Identifying the Flag:

   • Noticed an unusual string near the end of the readable content: 630B.
   • This did not match the keypad layout directly but stood out from the rest of the data — suggesting it was the intended key sequence.

5. Testing the Key on Wokwi:

   • Loaded the given project on Wokwi and manually entered 630B on the virtual keypad.

   • The system responded with an “unlocked” message, confirming the key was correct.

     

Flag

netsa{630B}