CTF论坛练习平台密码学writeup

#coding:utf-8
#python 2.7
import urllib
import re#1. 第一层base64
with open(&＃39;base64.txt&＃39;) as f:cipher1 &＃61; f.read()
plain1 &＃61; cipher1.decode(&＃39;base64&＃39;)
# print plain1, type(plain1)#2. 第二层&＃xff0c;根据plain1的形式&＃xff08;0-7的整数&＃xff09;&＃xff0c;推测为8进制加密
cipher2 &＃61; plain1
cipher2 &＃61; re.findall(r&＃39;\d&＃43;&＃39;, cipher2)
# print cipher2
plain2 &＃61; &＃39;&＃39;
for i in cipher2:plain2 &＃43;&＃61; chr(int(i, 8))
# print plain2#3. 第三层&＃xff0c;根据plain2的形式&＃xff08;\xdd&＃xff09;&＃xff0c;推测为16进制加密
cipher3 &＃61; plain2
cipher3 &＃61; re.findall(r&＃39;\d&＃43;&＃39;, cipher3)
# print cipher3
plain3 &＃61; &＃39;&＃39;
for i in cipher3:plain3 &＃43;&＃61; chr(int(i, 16))
# print plain3#4. 第四层&＃xff0c;根据plain3的形式&＃xff08;udd*&＃xff09;&＃xff0c;推测为unicode
cipher4 &＃61; plain3
cipher4 &＃61; re.findall(r&＃39;u[\d\w]&＃43;&＃39;, cipher4)
# print cipher4
cipher4 &＃61; &＃39;&＃39;.join(cipher4).replace(&＃39;u&＃39;, &＃39;\u&＃39;)
# print cipher4
plain4 &＃61; cipher4.decode(&＃39;unicode-escape&＃39;).encode(&＃39;utf-8&＃39;)#将unicode转中文&＃xff0c;来自知乎
# print plain4 #5. 第5层&＃xff0c;根据plain4形式&＃xff0c;将所有数字转ASCII即可
cipher5 &＃61; plain4
cipher5 &＃61; re.findall(&＃39;\d&＃43;&＃39;, cipher5)
# print cipher5
plain5 &＃61; &＃39;&＃39;
for i in cipher5:plain5 &＃43;&＃61; chr(int(i))
# print plain5#6. 第6层&＃xff0c;百度plain5的编码格式(&＃x)得到解码方法
cipher6 &＃61; plain5
# print cipher6
cipher6 &＃61; re.findall(r&＃39;\d&＃43;\w?&＃39;, cipher6)
# print cipher6
plain6 &＃61; &＃39;&＃39;
for i in cipher6:plain6 &＃43;&＃61; chr(int(i, 16))
# print plain6#7. 第7层&＃xff0c;百度plain6的编码格式&＃xff08;&＃&＃xff09;得到解码方法
cipher7 &＃61; plain6
cipher7 &＃61; re.findall(&＃39;\d&＃43;&＃39;, cipher7)
# print cipher7
flag &＃61; &＃39;&＃39;
for i in cipher7:flag &＃43;&＃61; unichr(int(i))
# print flag
flag &＃61; urllib.unquote(flag)
print flag