# Math Trap

## Background

In this challenge, you have to make a few simple calculations for me, but pretty quickely. Maybe the pwntools python library will help you ?

PS: control your inputs.

Host : **nc static-01.heroctf.fr 8000**
Format : **Hero{flag}**
Author : **Log_s**

## Find the flag

**In this challenge, we can `nc` into the instance machine:**
```shell
┌[siunam♥earth]-(~/ctf/HeroCTF-v5/Prog/Math-Trap)-[2023.05.13|16:49:53(HKT)]
└> nc static-01.heroctf.fr 8000
Can you calculate these for me ?

70 // 98
=0
Too slow
```

In here, we need to calculate some math equations.

**To automate that, we can write a Python script:**
```py
#!/usr/bin/env python3
from pwn import *

def solveTheFirstEquation(r):
# Can you calculate these for me ?\n\n
r.recvuntil(b'?\n\n')
solveEquation(r)
r.recvuntil(b'\n')

def solveEquation(r):
# 78 * 72
equation = r.recvline().decode()
answer = str(eval(equation)).encode('utf-8')
r.sendlineafter(b'=', answer)

if __name__ == '__main__':
context.log_level = 'debug'
HOST = 'static-01.heroctf.fr'
PORT = 8000
r = remote(HOST, PORT)

for i in range(500):
if i == 0:
solveTheFirstEquation(r)
else:
solveEquation(r)
print(r.recvline())
```

```shell
┌[siunam♥earth]-(~/ctf/HeroCTF-v5/Prog/Math-Trap)-[2023.05.13|17:21:56(HKT)]
└> python3 solve.py
[+] Opening connection to static-01.heroctf.fr on port 8000: Done
[DEBUG] Received 0x2b bytes:
b'Can you calculate these for me ?\n'
b'\n'
b'51 - 53\n'
b'='
[DEBUG] Sent 0x3 bytes:
b'-2\n'
[DEBUG] Received 0xb bytes:
b'\n'
b'44 - 100\n'
b'='
[DEBUG] Sent 0x4 bytes:
b'-56\n'
[DEBUG] Received 0x9 bytes:
b'\n'
b'8 * 58\n'
b'='
b'\n'
[DEBUG] Sent 0x4 bytes:
b'464\n'
[DEBUG] Received 0xa bytes:
b'\n'
b'36 - 29\n'
b'='
b'\n'
[DEBUG] Sent 0x2 bytes:
b'7\n'
[...]
```

However, when I saw the flag, it shuts down my VM :(

**Then, I fired up OBS to record and catch the flag:**


Nice troll in the `shutdown` command lmao :D (This is because the evil equation was parsed to `eval()`)

- **Flag: `Hero{E4sy_ch4ll3ng3_bu7_tr4pp3d}`**

## Conclusion

What we've learned:

1. Using Python To Solve Math Problems

Original writeup (https://siunam321.github.io/ctf/HeroCTF-v5/Prog/Math-Trap/).