CSAW 2014 crypto 200

psi.py

#coding=utf-8
import os
import socket
import select
from time import sleep
import binascii
from subprocess import Popen,STDOUT,PIPE
import os
from math import *
import string
from fractions import gcd

def next_line(stdout):
  line = ""
  while True:
    r = stdout.read(1)
    if r == '\n':
      break
    line += r
  print "<read> : " + line
  return line


def write(stdin,val):
  stdin.write(val)
  print "<write> : " + val

def solve1(s):
  diff = (ord('t') - ord(s[0])) % 26
  x = string.ascii_lowercase
  x = x[diff:] + x[:diff]
  ans = string.translate(s,string.maketrans(string.ascii_lowercase,x))
  return ans.split()[-1]

def solve2(s):
  for w in xrange(2,len(s)):
    decode = ['0'] * len(s)
    decode_id = 0
    gap = 0
    for i in xrange(len(s)):
      decode[decode_id] = s[i]
      decode_id += w
      if decode_id >= len(s):
        gap += 1
        decode_id = gap
    decode = "".join(decode)
    if "I hope you don't have a problem with this challenge." not in decode: continue
    return decode.split('"')[1]

def solve3(s):
  s = s.replace(" ","")
  keys = []
  for i,cry in enumerate(s):
    key_part = ((ord(cry) - ord('A')) - (ord("thistimewewillgiveyou"[i])  - ord('a')) ) % 26
    key = chr(key_part % 26 + ord('a'))
    keys.append(key)
    if len(keys) >= 6 and "".join(keys[:5]) == "".join(keys[-5:]):
      keys = keys[:-5]
      break
  keys = "".join(keys)
  print "key is '%s' " % keys

  ans = []
  for i,cry in enumerate(s):
    val = (ord(cry) - ord('A') - (ord(keys[i % len(keys)]) - ord('a'))) % 26 + ord('A')
    ans.append(chr(val))

  return "".join(ans)[296:-526]

def main():
  cmdline = "nc 54.209.5.48 12345"
  p = Popen(cmdline, shell=True, cwd="./", stdin=PIPE,
    stdout=PIPE, stderr=STDOUT,close_fds=True)

  print "-" * 80  # 区切り表示(開始)

  def nl(): return next_line(p.stdout)
  def wr(val): write(p.stdin,val)

  def ntext():
    line = ""
    while "psifer text:" not in line:
      line = nl()
    return line[len("psifer text:") + 1:]

  while True:
    text = ntext()
    ans = solve1(text)
    wr(ans + '\n')
    text = ntext()
    ans = solve2(text)
    wr(ans + '\n')
    text = ntext()
    ans = solve3(text)
    wr(ans + '\n')

  print "-" * 80
  ret = p.wait()
  print "Return code: %d" % ret

# A = "THISTIMEWEWILLGIVEYOUMOREPLAINTEXTTOWORKWITHYOUWILLPROBABLYFINDTHATHAVINGEXTRACONTENTTHATISASCIIMAKESTHISONEMORESOLVABLEITWOULDBESOLVABLEWITHOUTTHATBUTWEWILLMAKESURETOGIVELOTSOFTEXTJUSTTOMAKESURETHATWECANHANDLEITIWONDERHOWMUCHWILLBEREQUIREDLETSPUTTHEMAGICPHRASEFORTHENEXTLEVELINTHEMIDDLERIGHTHERENOTHINGTRICKYOKNOWMORETEXTTOMAKESURETHATITISSOLVABLEISHOULDPROBABLYJUSTPUTINSOMENURSERYRHYMEORSOMETHINGMARYHADALITTLELAMBLITTLELAMBLITTLELAMBMARYHADALITTLELAMBWHOSEFLEEZEWASWHITEASSNOWIDONTWANTTOMAKETHISHARDERTHANITNEEDSTOBEIFYOUVESOLVEDALOTOFSIMPLECRYPTOCHALLENGESYOUPROBABLYALREADYHAVETHECODEANDWILLBREEZERIGHTTHROUGHITIFITHELPSMOSTOFTHEPLAINTEXTISSTATICATEACHOFTHELEVELSIMNOTAMASOCHISTTHEFUNNYTHINGISTHATDEPENDINGONWHICHRANDOMKEYYOUGETTHATPOEMMIGHTBEEXACTLYTHERIGHTOFFSETTOSUCCESSFULLYMOUNTANATTACKWELLSEELITTLEBITMORELITTLEBITMORETHERE"
# B = "THISTIMEWEWILLGIVEYOUMOREPLAINTEXTTOWORKWITHYOUWILLPROBABLYFINDTHATHAVINGEXTRACONTENTTHATISASCIIMAKESTHISONEMORESOLVABLEITWOULDBESOLVABLEWITHOUTTHATBUTWEWILLMAKESURETOGIVELOTSOFTEXTJUSTTOMAKESURETHATWECANHANDLEITIWONDERHOWMUCHWILLBEREQUIREDLETSPUTTHEMAGICPHRASEFORTHENEXTLEVELINTHEMIDDLERIGHTHEREBLAHLAHOKNOWMORETEXTTOMAKESURETHATITISSOLVABLEISHOULDPROBABLYJUSTPUTINSOMENURSERYRHYMEORSOMETHINGMARYHADALITTLELAMBLITTLELAMBLITTLELAMBMARYHADALITTLELAMBWHOSEFLEEZEWASWHITEASSNOWIDONTWANTTOMAKETHISHARDERTHANITNEEDSTOBEIFYOUVESOLVEDALOTOFSIMPLECRYPTOCHALLENGESYOUPROBABLYALREADYHAVETHECODEANDWILLBREEZERIGHTTHROUGHITIFITHELPSMOSTOFTHEPLAINTEXTISSTATICATEACHOFTHELEVELSIMNOTAMASOCHISTTHEFUNNYTHINGISTHATDEPENDINGONWHICHRANDOMKEYYOUGETTHATPOEMMIGHTBEEXACTLYTHERIGHTOFFSETTOSUCCESSFULLYMOUNTANATTACKWELLSEELITTLEBITMORELITTLEBITMORETHERE"

# def f(A,B):
#   for i in xrange(min(len(A),len(B))):
#     if A[i] != B[i]: return i

# print A[296:-526]

# x = f(A,B)
# print x
# A = A[x:][::-1]
# B = B[x:][::-1]
# x = f(A,B)
# print x
# A = A[x:][::-1]
# B = B[x:][::-1]

# print A,B

main()