[WUSTCTF2020]level3

附件

步骤：

1. 例行检查，64位程序，无壳
   

2. 64位ida载入，找到关键函数
   
   看样子是个base64加密，但又感觉没那么简单，再翻翻左边的函数，找到了base64加密变表的函数
   
   将加密表变换一下写个解密exp

   import base64
   table = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='
   model = list("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=")
   s = "d2G0ZjLwHjS7DmOzZAY0X2lzX3CoZV9zdNOydO9vZl9yZXZlcnGlfD=="

   for i in range(10):
   model[i], model[19-i] = model[19-i], model[i]

   model = ''.join(model)
   print (model)

   table = str.maketrans(model, table)
   print (base64.b64decode(s.translate(table)))

用到了python3里的几个函数来制作翻译表
https://www.runoob.com/python3/python3-string-translate.html