CSAW CTF 2016 | Coinslot (misc50)

coinslot.py

import socket

remoteip   = "misc.chal.csaw.io"
remoteport = 8000

def sock(remoteip, remoteport):
    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    s.connect((remoteip, remoteport))
    return s, s.makefile('rw', bufsize=0)

def read_until(f, delim='\n'):
    data = ''
    while not data.endswith(delim):
        data += f.read(1)
    return data

s, f = sock(remoteip, remoteport)

def solve(target):
	target = int(round(target * 100, 0))
	bills = [10000, 5000, 1000, 500, 100, 50, 20, 10, 5, 1,
		0.5, 0.25, 0.1, 0.05, 0.01]
	ans = ""
	for bi in bills:
		bi = int(bi * 100)
		num = target // bi
		ans += (str(num) + "\n")
		target = target % bi
	s.send(ans)
	read_until(f, "(1c): ")
	print read_until(f, "!\n")

count = 0
while True:
	print "[+] Iter:", count
	line = read_until(f, "\n")
	print line,
	target = float(line.replace("$", "").strip())
	print "[+] target:", target
	solve(target)
	count += 1

s.close()

# flag: flag{started-from-the-bottom-now-my-whole-team-fucking-here}

指定された金額どおりに紙幣の枚数を選択する問題×300問。小数（セント）を整数に変換するときの浮動小数点数誤差に気をつければあとはやるだけ。