Captcha Hacking(1) - Defining the Problem

Captcha Hacking Series

Project Repo

Captcha Hacking(1) - Defining the Problem

Captcha Hacking(2) - Collecting Data and Analyzing

Captcha Hacking(3) - Data Cleaning

Captcha Hacking(4) - Training with KNN Algorithm

Captcha Hacking(5) - Automating to solve the Captcha problem

Topic

• Before we start
• Setting up
• Defining Problem
• How to Approach this problem
• Thinking point of this problem

Before we start

This problem was one of Samsung’s Capture the Flag question from 2017.

You can check out the problem here

Setting up

1. First clone the repository using git
   • git clone https://github.com/ndb796/SCTF2017-Writeups.git
2. Inside the folder create src/images folder
   • Inside the folder that we cloned, go to ASM/src
   • in here create a folder ‘static’
   • create another folder called ‘images’ in ‘static’ folder
3. Using your command prompt, inside ASM/src folder run ‘python3 run.py’
   • if you don’t have flask library, make sure to install all the modules ‘pip install x’
4. Once you see that program is running, you can go to localhost:10000
   • 
5. Once you press ‘START!’
   • you will be able to see image popping up on the screen
   • 
   • you can answer the math problem below inside ‘answer’ section
6. Your goal here is to automate this so that your program automates solving this math problem

Defining Problem

• Once you press START, 80 second timer starts
• The math problem shows up in Captcha form, and you have to solve this by submitting the answer in ‘Answer’
• Within 80 seconds, you’re supposed to get 100 questions correctly consecutively

How to approach this problem

• Using OpenCV, we’re going to separate each character
• We’re going to label what each character is to make it a mathematical quesiton
• We’re finally going to solve this problem using the information

Thinking point of this problem

• The more you solve, the math question becomes harder (Example: 52379819 * 9849271)
• Each characters in the image are distinguished by color, how can we use this information?