Solution to HITCON CTF 16 -- [PPC] Beelzemon

beelzemon.py

#!/usr/bin/python
'''
xinan@nusgreyhats.org
'''

from copy import deepcopy
from pwn import *

a1 = [0, 3]
b1 = [1, 2]

base = {}

# Pre-compute solution for all the n=k cases. Takes about 4 seconds.
for i in range(1, 21):
	A1 = map(lambda x: x - 2**i, a1)
	B1 = map(lambda x: x - 2**i, b1)
	base[i] = (A1, B1)
	a1_temp = deepcopy(a1)
	for b in b1:
		a1.append(b + 2**(i + 1))
	for a in a1_temp:
		b1.append(a + 2**(i + 1))

r = remote('52.198.217.117', 6666)

while True:
	try:
		line = r.readline_regex('\d+ \d+').split(' ')
	except:
		print r.recvall()
		break
	x = int(line[0])
	y = int(line[1])
	n = max(x, y)
	k = min(x, y)
	print 'n: ' + str(n) + ' k: ' + str(k)
	# Get the solution for n = k, and generate the solution for n > k.
	current_base = base[k]
	a1 = deepcopy(current_base[0])
	b1 = deepcopy(current_base[1])
	while k < n:
		k += 1
		a1_temp = deepcopy(a1)
		for b in b1:
			next = b + 2**k if b < 0 else b - 2**k
			a1.append(next)
		for a in a1_temp:
			next = a + 2**k if a < 0 else a - 2**k
			b1.append(next)
	answer = ' '.join([str(i) for i in a1])
	r.sendline(answer)