nullcon HackIM 2019: Captcha Forest Harder=============================
## Description
A harder captcha for you if you felt the first one was too easy
`nc miscc.ctf.nullcon.net 6002`
The server sent us a `png` image in hexadecimal. We have to solve the captcha and output 4 corresponding characters.
This challenge need to be solved 120 times out of 200 tries to output the flag.
The image is a concatenation of 4 characters from the Bill Cipher (a code in Gravity Fall).![The code mapping](gravityfallsdecode.png)
This is the harder problem of [Captcha Forest](../Captcha-forest)
The difference is that the image has rotation and scaling over the characters.
#### Example of Captcha with rotation and scaling
![captcha](Captcha.png)
## Solution
This is a similiar solution as the previous one. We had the luck to find good enough character to match the code. [source](https://www.dcode.fr/gravity-falls-bill-cipher)
Instead of just testing our mapping symbol with the captcha, we combine it with multiple rotations and scalings.
With a family of 30 different rotations {-45, -42, ..., 0 , 3, ... 45} and 5 different scalings, we reach around 95% of accuracy in the captcha. It is enough to recover the flag.
## Code
The code is written [here](script2.py)
The image mapping is stored [here](mapping)
## Flag
`hackim19{I_guess_I_will_stop_making_captchas_now}`