NSSCTF Round#23 Misc个人专项赛

画师

flag为有意义单词
flag

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将透明度改为100%

以为是但是和flag{有点区别
垂直翻转一下

flag{easy_diagram}
easy_signin1

绝对的misc 由此而生的签到
教会ctfer们flag的是......

hint: image to 01 然后找一下2.png相对于1.png差别的地方

取黑白为二进制，对比差异

1. from PIL import Image
3. img1 = Image.open("1.png")
4. img2 = Image.open("2.png")
6. img1s = ''
7. img2s = ''
9. for i in img1.getdata():
10.     if i == (255,255,255,255):
11.         img1s += '0'
12.     else:
13.         img1s += '1'
14. for i in img2.getdata():
15.     if i == (255,255,255,255):
16.         img2s += '0'
17.     else:
18.         img2s += '1'
19. code = ''
20. for i in range(len(img1s)):
21.     if img1s[i] != img2s[i]:
22.         code += img2s[i]
23. with open('enc.c','w') as fw:
24.     for i in range(0,len(code),8):
25.         fw.write(chr(int(code[i:i+8],2)))

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或者
提示说：image to 01 然后找一下2.png相对于1.png差别的地方，一开始以为是异或，结果就是传统的找出2.png的二进制和1.png不一样的地方然后打印

1. from PIL import Image
2. import math
3. import sys
5. def is_black(pixel):
6.     # 判断像素是否是黑色
7.     # 如果红、绿、蓝通道的值都很低，则认为是黑色
8.     return all(value < 10 for value in pixel[:3])
11. def is_white(pixel):
12.     # 判断像素是否是白色
13.     # 如果红、绿、蓝通道的值都很高，则认为是白色
14.     return all(value > 245 for value in pixel[:3])
16. flag1=""
17. flag2=""
18. def scan_image(image_path):
19.     global flag1
20.     # 打开图像文件
21.     image = Image.open(image_path)
22.     # 获取图像的像素数据
23.     pixels = image.load()
24.     width, height = image.size
26.     for y in range(height):
27.         for x in range(width):
28.             # 获取像素的RGB值
29.             pixel = pixels[x, y]
30.             # 判断像素是黑色还是白色
31.             if is_black(pixel):
32.                 flag1=flag1+"1"
33.             elif is_white(pixel):
34.                 flag1=flag1+"0"
35.             else:
36.                 print("err")
37. def scan_image2(image_path):
38.     global flag2
39.     # 打开图像文件
40.     image = Image.open(image_path)
41.     # 获取图像的像素数据
42.     pixels = image.load()
43.     width, height = image.size
45.     for y in range(height):
46.         for x in range(width):
47.             # 获取像素的RGB值
48.             pixel = pixels[x, y]
49.             # 判断像素是黑色还是白色
50.             if is_black(pixel):
51.                 flag2=flag2+"1"
52.             elif is_white(pixel):
53.                 flag2=flag2+"0"
54.             else:
55.                 print("err")
56. # 调用函数扫描图像
57. scan_image("1.png")
59. scan_image2("2.png")
60. for i in range(len(flag1)):
61.     if flag1[i] != flag2[i]:
62.         print(flag2[i],end="")

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得到

1. 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复制代码

解密会得到一个cpp源码

1. #include<bits/stdc++.h>
2. using namespace std;
3. string key = "";
5. int main(){
6.     string crypto_txt;
7.     cin>>crypto_txt;
9.     for (int i = 0; i < crypto_txt.length(); ++i){
10.         char encrypted_txt = char(crypto_txt[i] ^ key[i % key.length()] ^ crypto_txt[(i + 1) % crypto_txt.length()]);
11.         cout << int(encrypted_txt) << " ";
12.     }   
13.     return 0;
14. }
16. // encrypted_txt1 = 122,127,111,111,96,114,115,127,77,90,119,92,89,117,126,85,87,117,111,111,86,84,122,127,111,75,81,97,120,94,93,110,98,65,84,127,105,69,87,125,98,107,87,70,108,127,83,88,105,105,98,95,88,102,96,118,104,114
17. // dncrypted_txt = flag{this_is_the_fake_flag_and_can_you_find_the_true_flag}
18. // encrypted_txt2 = 76,127,33,63,108,127,110,102,120,109,124,56,47,118,107,125,121,104,98,123,106,123,57,42,117,126,39,49,101,115,103,117,117,109,117,96,57,46,109,115,110,104,105,106,123,100,105,44,55,114,127,45,60,121,122,113,110,104,48,53,113,117,39,56,125,105,114,121,100,101,49,58,100,127,57,53,118,50,51,106,106,124,38,54,127,60,108,109,112,114,105,19,114,110,98,114,115,81,115,85,65,99,85,67,44,36,108,102,107,92,31,44,88,88,115,55,48,73,86,68,93,112,123,79,127,15,51,120,96,121,74,114,94,120,82,91,41,44,105,82,71,37,110,28,69,96,100,42,2,75,118,122,35,49,89

复制代码

可以看到我们要异或的应该是0x44，所以我们把这个文件的每一字节提取出来然后去异或0x44并写入文件

得到

通过提示可以看到检察pngchunk

从这里开始往下复制，然后添加文件头89 50 4e 47 0d 0a 1a 0a即可得到

hint2提示抽象画，可以想到用npiet
去这里下载：http://www.bertnase.de/npiet/
然后看另一个png，10xbig_to_more_clear.png
用脚本放大十倍

1. c = [122,127,111,111,96,114,115,127,77,90,119,92,89,117,126,85,87,117,111,111,86,84,122,127,111,75,81,97,120,94,93,110,98,65,84,127,105,69,87,125,98,107,87,70,108,127,83,88,105,105,98,95,88,102,96,118,104,114]
2. m = 'flag{this_is_the_fake_flag_and_can_you_find_the_true_flag}'
3. for i in range(len(m)):
4.     print(chr(ord(m[i])^ord(m[(i+1)%len(m)])^c[i]),end='')
5. # prisonrealmprisonrealmprisonrealmprisonrealmprisonrealmpri
6. # key = prisonrealm

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得到字符串di`f{cfd7d1fd1ba254dcfa7f4155cfdadadc}

1. key = 'prisonrealm'
2. enc = [76,127,33,63,108,127,110,102,120,109,124,56,47,118,107,125,121,104,98,123,106,123,57,42,117,126,39,49,101,115,103,117,117,109,117,96,57,46,109,115,110,104,105,106,123,100,105,44,55,114,127,45,60,121,122,113,110,104,48,53,113,117,39,56,125,105,114,121,100,101,49,58,100,127,57,53,118,50,51,106,106,124,38,54,127,60,108,109,112,114,105,19,114,110,98,114,115,81,115,85,65,99,85,67,44,36,108,102,107,92,31,44,88,88,115,55,48,73,86,68,93,112,123,79,127,15,51,120,96,121,74,114,94,120,82,91,41,44,105,82,71,37,110,28,69,96,100,42,2,75,118,122,35,49,89]
3. # flag[-1] = '}' 即flag[-1] = 125
4. flag = []
5. for i in range(len(enc)):
6.     flag.append(enc[i]^ord(key[i%len(key)]))
7. t = [0]*len(flag)
8. t[0] = 125 ^ flag[-1]
9. t[1:len(flag)] = flag[:-1]
10. print()
11. for i in range(len(flag)-1):
12.     print(chr(t[i]),end='')
13.     t[i+1] = flag[i]^t[i]
14. print('}')
15. # The-absolute-powerhouse,the-resulting-loneliness,the-person-who-teaches-you-to-love-is......NSSCTF{e@sy_s1gnin_0n_th1s_h@ppy_S3nday_@nd_w1sh_y03_hav3_fun!}

复制代码

flag{dge8f3hf3da45cd414f7affc5db5dadd}
NSSCTF{dge8f3hf3da45cd414f7affc5db5dadd}

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