# [EN] Trending Cats
###### tags: `Writeup` `Web` `English`
> [name=FlyDragon]

## Step.1
When opening the image in a new tab, you can see that each cat has a four-digit number.


## Step.2
It is known that there is no cat with the number 1. Taking advantage of this fact, we can write a program to search for the cats.

import requests

NotFound = requests.get(f"http://lotuxctf.com:20003/1.jpg").text

found = []

for i in range(6000, 7000):
    print(i)
    response = requests.get(f"http://lotuxctf.com:20003/{i}.jpg").text
    if(response != NotFound):
        print(f"found at {i}")
        found.append(i)

print(found)

We can find the cat with the number 6166, called "spin cat."


## Step.3
Based on the naming pattern on other pages, we can infer that there might be a "spin.php" file.


## Step.4
Clicking the button reveals that it sends the parameter `cat=aGFwcHk%3D`.
Base64 decoding `aGFwcHk%3D` results in "happy".
Base64 encoding "spin" results in `c3Bpbg==`.

Therefore, the URL becomes `spin.php?cat=c3Bpbg==`.

We obtain the flag:


{%hackmd M1bgOPoiQbmM0JRHWaYA1g %}