2018 HITCON Crypto lost key

lost key

赛后学习了一下这道密码题的攻击姿势。

题目脚本如下：

#!/usr/bin/env python
from Crypto.Util.number import *
from gmpy2 import *
from random import *
import sys,os


sys.stdin  = os.fdopen(sys.stdin.fileno(), 'r', 0)
sys.stdout = os.fdopen(sys.stdout.fileno(), 'w', 0)
rnd = SystemRandom()

def calcA(g,n,data):
  num = bytes_to_long(data)
  res = pow(g,num,n*n)
  r = rnd.randint(0,n-1)
  magic = pow(r,n,n*n)
  res = (res*magic)%(n*n)
  return long_to_bytes(res).encode('hex')

def calcB(phi,n,u,data):
  num = bytes_to_long(data)
  res = pow(num,phi,n*n)
  res = (res - 1)/n
  res = (res*u)%n
  return long_to_bytes(res).encode