DEF CON CTF 2021 Qual back-to-qoo

qoo.rb

#!/usr/bin/env ruby

# qoo_run.rb の結果を ruby qoo.rb log として食べさせると secret を出すやつ

c1s = []
c2s = []
p1s = []
wins = []
msgs = []
no_changes = []

File.readlines(ARGV[0] || 'qoo2.log').each do |line|
  if line =~ /Your competitor bets on (\d+)/
    c1s << $1.to_i
  end

  if line =~ /zardus's competitor bets on (\d+), you bet on (\d+)/
    c2s << $1.to_i
    p1s << $2.to_i
  end

  if line =~ /\[-\] OK/
    no_changes << 1
  end
  if line =~ /\[-\] ZZZ/
    no_changes << 0
  end

  if line =~ /Win|Lose/
    wins << (($& == "Win") ? 1 : 0)
  end

  if line =~ /zardus receives from adamd: \d+:(\d)/
    msgs << $1.to_i
  end
end

p [c1s.size, c2s.size, wins.size, msgs.size, p1s.size, no_changes.size]

# p c1s
# p c2s
# p p1s
# p wins
# p msgs

key_str = ''

t = 0
c1s.zip(c2s, p1s, wins, msgs, no_changes).each do |c1, c2, p1, win, msg, nc|
  if c2 == 1
    measure = "H|Q>"
  else
    measure = "|Q>"
  end

  #p2 = (c1*c2) ^ p1
  if win == 1
    p2 = (c1*c2) ^ p1
  else
    p2 = (c1*c2) ^ p1 ^ 1
  end

  sec = c2 == msg ? 1 : 0

  puts "turn=#{t} m=#{measure} c1=#{c1} c2=#{c2} c1*c2=#{c1*c2} p1=#{p1} p2=#{p2} sec=#{sec} nc=#{nc} win=#{win} chk=#{(p1^p2)==(c1*c2)}"

  if sec == 1
    # if c2 == 1
    #   key_str += '?'
    # else
    #   key_str += p2.to_s
    # end

    # rotate してない & base が 0 だったら信用できて、残り 32bit くらい総当たり、という問題だと思ってた
    #if nc == 1 && msg == 0
    #if nc == 1 && c2 == 0
    # ……が、なんか rotate した後の measure も信用できて、フラグは取れたけどよくわからん
    if nc == 1 || true
      key_str += p2.to_s
    else
      key_str += '?'
    end

  end

  t += 1
end

puts "#{key_str.count("?")} / #{key_str.size}"
puts key_str

p key_str.each_char.map{|c|
  c == '?' ? 2 : c.to_i
}.to_a

#num = 0
#refs.zip(msgs).each do |r, m|
#  if r == m
#    #puts "hm"
#    num += 1
#  end
#end
#p num

qoo_run.rb

# まあおおむね勝てるやつ

require_relative 'ctfutils'

serv = ARGV[0] || "back-to-qoo.challenges.ooo"

pipe = popen("nc #{serv} 5000")

bets = []
num_wins = 0
128.times do |t|
  m = pipe.wait_until(/competitor bets on /)
  bet = pipe.get.to_i
  STDERR.puts "[-] bet=#{bet}"
  bets << bet

  # このへん調節して勝率落として rotate の頻度を落とそうとしていました
  #if num_wins + (128 - t) * 0.75 > 108 && bet == 0
  #if bet == 0
  if false
    STDERR.puts "[-] OK 0"
    #pipe.puts "0"
    pipe.puts "2"
    pipe.puts "0"
  else
    STDERR.puts "[-] ZZZ #{num_wins}/#{t+1}"
    pipe.puts "2"
    pipe.puts bet + 1
    #pipe.puts 2 - bet
  end

  m = pipe.wait_until(/(Win|Lose)/)
  if m[0] =~ /Win/
    num_wins += 1
  end
end

STDERR.puts "[-] #{num_wins}"

pipe.puts ""
pipe.puts ""
pipe.puts ""
pipe.interactive