[CSAW 2013] [reverse 300]: cracking aid script.

crack.rb

# use rubinius!



M = 0x100000000
RESULT = 0xEF2E3558


def poly(a)
  ret = a.inject(1337) do |sum, c|
    sum + (32 * sum) + c
  end
  ret
end


def calc(a)
  poly(a) % M
end


def check(a)
  res = calc(a)
  #puts "a: #{a}, poly(a): #{poly(a)} calc(a): #{calc(a).to_s 16}"
  if (res == RESULT)
    puts "SUCCESS! a: #{a}, poly(a): #{poly(a)} calc(a): #{calc(a).to_s 16}"
    puts a.map{ |n| n.chr }.join
elsif ((res - RESULT).abs < 0xFF)
    #puts "close .. a: #{a}, poly(a): #{poly(a)} calc(a): #{calc(a).to_s 16}"
  end
end


def str_enumerator(len)
  #(91..128).to_a.repeated_permutation(len)
  
  # this is harcoded with length 6
  (96..96).each do |i1|
    (115..115).each do |i2|
      (97..97).each do |i3|
        (86..86).each do |i4|
          (31..128).each do |i5|
            (31..128).each do |i6|
              a = [i1,i2,i3,i4,i5,i6]
              #puts a.inspect
              yield a
            end
          end
        end
      end
    end
  end
end



# Script.

N_THREADS = ARGV[0].to_i
N_CHARS = ARGV[1].to_i


queue = Queue.new

threads = N_THREADS.times.collect do |thr_idx|
  Thread.new do
    $stderr.print '.'
    # Worker Thread Task
    begin
      a = queue.pop
      check(a)
    end while true
  end
end

#master = Thread.new do
#  # Master Thread Task
  $stderr.puts 'Start'
  last = [0] * 2
  str_enumerator(N_CHARS) do |s|
    if last[0..2] != s[0..2]
      last = s
      $stderr.puts "#{last[0..2]}  ..."
    end
    a = s.map(&:ord).to_a
    queue << a
  end
  $stderr.puts 'End'
  threads.each { |t| Thread.kill(t) }
# end

Signal.trap('SIGINT') do
  threads.each { |t| t.kill }
end