Overview

bin200 is a web service that dumps the key if provided with a pair of values that form a collision for the Tangle hash function.

Writeup

We quickly reversed this binary and found that it read in two numbers and dumped the key if they were a collision for some hash function. Googling the constants used revealed that it is the proposed SHA-3 Tangle hash function.

As there are several papers on attacking this particular hash function, we quickly wrote up a solution:

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#!/usr/bin/python
import struct
import socket
import time

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(('140.197.217.155', 18703))

# Provide the magic constants expected by the service.
payload =  struct.pack('>I', 0x94A4C265)
payload += struct.pack('>I', 0xFE732D6F)
payload += struct.pack('>I', 0xEEF814CB)
payload += struct.pack('>I', 0x6EC8A126)

# The length.
payload += struct.pack('I', 40)
# Send the colliding values.
payload += '\xc8\x19\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'
payload += '\xc8\x19\x00\x80\x00\x00\x00\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x80\x00\x00\x00\x80'

s.send(payload)

time.sleep(1)

print s.recv(1024)