# TokyoWesterns CTF 2019 - Meow

* **Category:** reverse
* **Points:** (dependant on solve time)

## Challenge

### Description
A 7zip archive was provided, along with an ASCII art picture of a cat.

### Files
meow.7z

## Solution

The 7zip archive contained two files:
* meow.n
* flag_enc.png

The `meow.n` file was a [NekoVM](https://nekovm.org/) executable. Running it produced...

```
andrew@WOPR /tmp/meow % neko meow.n
Usage: meow INPUT OUTPUT
```

When run with `flag_enc.png`, it produced a similarly broken image.

We couldn't immediatly find any tools for RE'ing NekoVM executables, so [@BaileyBelisario](https://github.com/BaileyBelisario) wrote a script to keep feeding the output image back in as input, saving each file along the way.

```bash
#!/bin/bash

#neko meow.n flag_enc.png flag_dec0.png

for ((i = 1 ; i < 10000 ; i++)); do
let k=$i-1
neko meow.n flag_dec$k.png flag_dec$i.png
done
```

Eventually, some of them started to look like a Nyan Cat image (although still severely broken). However even after several thousand iterations they never became clean enough to read.

### Iteration #2098

### Iteration #2108

On a whim I opened one in GIMP, and carefully deleted all of the incorrect pixels around the flag. To my suprise, it was just enough to make it readable!


### Flag

```
TWCTF{Ny4nNyanNy4n_M30wMe0wMeow}
```

Original writeup (https://github.com/kernelpoppers/ctf_writeups/tree/master/TokyoWesterns2019/meow).