2021DASCTF八月挑战赛Writeup

冥界王者

文章目次

MISC
签到
热王'sblog
stealer
CRYPTO 
easymath
let's play with rsa~
ezRSA
REVERSE
py

---

看年夜佬们皆没有念写那个wp那我写一个吧Orz
MISC

签到

看看通告

  flag{welcome_to_dasctf_aug}

热王'sblog

好家伙，没有明白gitee是甚么底子找没有到。间接正在url前面减上/flag.jpg会见堆栈：

1. https://hanwang2333.gitee.io/2020/03/12/outguess/flag.jpg

复造代码

拿到flag.jpg，然后按照热王专客里的outguess解稀拿到flag
stealer

翻开流量包，过滤DNS，发明有许多反复的数据，过滤ip

1. dns and ip.src==172.27.221.13

复造代码

将info掏出，察看发明是图片的base64编码，将字符串停止编纂便利转码。

1. 字符串的变革以下：
2. 本字符串：
3. Standard query 0x6a7a A iVBORw0KGgoAAAANSUhEUgAABMoAAAMxCAIAAACVY8g6AAAAAXNSR0IAr-.s4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsMAAA7DAcdvqGQAAP-.lSURBVHhe7P1HlBzZmd6NUxtqjrShdtzoHB6ttMROswlNp/U9OiGKwd-.f8KbRDtXw3hdQMGWBgjcF1432aDZN04MUySGHMxqvgUajGWg*6fsoffpL-.ctf.com.cn OPT
5. 操纵：
6. 1、来除过剩字符串”Standard query 0x6a7a A”、”ctf.com.cn OPT”、”-.”
7. 2、将“*”交换为“+”
9. 转化后字符串：iVBORw0KGgoAAAANSUhEUgAABMoAAAMxCAIAAACVY8g6AAAAAXNSR0IArs4c6QAAAARnQU1BAACxjwv8YQUAAAAJcEhZcwAADsMAAA7DAcdvqGQAAPlSURBVHhe7P1HlBzZmd6NUxtqjrShdtzoHB6ttMROswlNp/U9OiGKwdf8KbRDtXw3hdQMGWBgjcF1432aDZN04MUySGHMxqvgUajGWg+6fsoffpL

复造代码

拿到图片

 

   1d3f729ac02bbc15f00adccd79207ab0

CRYPTO 

easymath

标题问题：

1. assert(len(open(&#39;flag.txt&#39;, &#39;rb&#39;).read()) < 50)
2. assert(str(int.from_bytes(open(&#39;flag.txt&#39;, &#39;rb&#39;).read(), byteorder=&#39;big&#39;) << 10000).endswith(
3.     &#39;1862790884563160582365888530869690397667546628710795031544304378154769559410473276482265448754388655981091313419549689169381115573539422545933044902527020209259938095466283008&#39;))

复造代码

思绪：给您5个coin，相称于四次挑选疑息2、3的时机，当然是均匀分派啦。获得四组f、c，两组同q解n，两组差别q解p。

  计较n：
  

  计较q:
  

 

p、q、n、c皆明白了，常规RSA解稀。
REVERSE

py

标题问题简朴粗鲁，间接给py.exe，ida翻开shift+F12搜刮检察到pyinstaller字样（也可经由过程图标判定）认定为pyinstaller挨包，间接exe转pyc。

1. from sympy import isprime,nextprime
2. from Crypto.Util.number import getPrime as getprime ,long_to_bytes,bytes_to_long,inverse
3. flag=&#39;flag{***************}&#39;
5. def play():
6.     p=getprime(1024)
7.     q=getprime(1024)
9.     n=p*q
10.     e=65537
12.     print "Hello,let&#39;s play rsa~\n"
13.     print &#39;Now,I make some numbers,wait a second\n&#39;
14.     n1=getprime(200)
15.     n2=getprime(200)
16.     number=n1*n2
17.     print "Ok,i will send two numbers to you,one of them was encoded.\n"
18.     print "Encode n1:%d,\n"%(pow(n1,e,n))
19.     print "And n2:%d.\n"%n2
21.     print "Information that can now be made public:the public key (n,e):(%d,%d)\n"%(n,e)
22.     while True:
23.         try:
24.             c=int(raw_input("ok,now,tell me the value of the number (encode it for safe):"))
25.         except:
26.             print "Sorry,the input is illeagal, and the integer is accept~"
27.         else:
28.             break
29.     d=inverse(e,(p-1)*(q-1))
30.     m=pow(c,d,n)
31.     if m==number:
32.         print "It&#39;s easy and interesting,didn&#39;t it?\n"
33.         print "This is the gift for you :"+flag
34.     else:
35.         print "Emmmmm,there is something wrong, bye~\n"
37. if __name__ == &#39;__main__&#39;:
38.     play()

复造代码

拿到py.pyc，上uncompyle6反编译。

1. #n =
2. #n2 =
3. #e = 65537
4. a = pow(n1,e,n) #标题问题给出
5. c = (a * pow(n2,e,n)) % n
6. print(c)
7. #提交c及返回flag

复造代码

拿到py代码，简朴的同或操纵，写剧本停止顺运算输出flag。

1. from secret import flag
2. from Crypto.Util.number import *
3. from random import getrandbits
4. from hashlib import sha256
7. class EzRsa:
8.     def __init__(self):
9.         self.E = 0x10001
10.         self.P = getPrime(1024)
11.         self.Q = getPrime(1024)
12.         while GCD((self.P-1)*(self.Q-1), self.E) != 1:
13.             self.Q = getPrime(1024)
14.         self.N = self.P*self.Q
16.     def encrypt(self):
17.         f = getrandbits(32)
18.         c = pow(f, self.E, self.N)
19.         return (f, c)
21.     def encrypt_flag(self, flag):
22.         f = bytes_to_long(flag)
23.         c = pow(f, self.E, self.N)
24.         return c
27. def proof():
28.     seed = getrandbits(32)
29.     print(seed)
30.     sha = sha256(str(seed).encode()).hexdigest()
31.     print(f"sha256({seed>>18}...).hexdigest() = {sha}")
32.     sha_i = input("plz enter seed: ")
33.     if sha256(sha_i.encode()).hexdigest() != sha:
34.         exit(0)
37. if __name__ == "__main__":
38.     proof()
39.     print("welcome to EzRsa")
40.     print("""
41.     1. Get flag
42.     2. Encrypt
43.     3. Insert
44.     4. Exit
45.     """)
46.     A = EzRsa()
47.     coin = 5
48.     while coin > 0:
49.         choose = input("> ")
50.         if choose == "1":
51.             print(
52.                 f"pow(flag,e,n) = {A.encrypt_flag(flag)}\ne = 0x10001")
53.             exit(0)
54.         elif choose == "2":
55.             f, c = A.encrypt()
56.             print(f"plain = {f}\ncipher = {c}")
57.             coin -= 1
58.         elif choose == "3":
59.             q = getrandbits(1024)
60.             n = A.P*q
61.             f = getrandbits(32)
62.             c = pow(f, 0x10001, n)
63.             print(f"plain = {f}\ncipher = {c}")
64.             coin -= 1
65.         elif choose == "4":
66.             print("bye~")
67.         else:
68.             print("wrong input")
69.     print("Now you get the flag right?")

复造代码

免责声明：假如进犯了您的权益，请联络站少，我们会实时删除侵权内乱容，感谢协作！