# Hash Browns

### Challenge Description

My friend and me has been playing a game. I am trying to reconstruct an image sent by him. Can you help me?

### Write Up

- In this challenge we are actually sending the png image byte by byte.
- One byte will be `matched` the other will be `ERROR` byte and thus we need to extract the ascii value of the character using the hash of original byte by brute force.
- Using `Scapy` you can extract the data.

from scapy.all import *
import hashlib

r=rdpcap("p11.pcap")
happy=open("flag.png","wb")

l=[]

for i in range(256):
    l.append(str(hashlib.md5(str(i).encode()).hexdigest()))
    
for i in range(len(r)):
    
    b=len(r[i][TCP].payload)
    c=str(r[i][TCP].payload)
    
    z=c[c.rfind("=")+1:]
    
    if(b==14 or b==15 or b==16):
        happy.write(chr(int(z)))
    
    if(b==109):
        happy.write(chr(l.index(z)))

- In the above script we are using scapy to read the data in pcap and if we analyse pcap properly we can find that the length of the `byte matched` packets will be 14 or 15 or 16.
- When it comes to the `ERROR` it will be 109.
- Using payload we are extracting the data send in packet and convering it into `string` and stored it in the variable c.
- In the variable `z` we are storing the value after`=` such that we get ascii value of matched byte or md5 hash of the ascii value of the character.
- Finally open the file and write the ascii value in it.
- Opening the png gives you the flag. :)

### Flag

`inctf{g00d_joB_m4te!!}`