NSSCTF Round#23 Misc个人专项赛WP

画师

flag为有意义单词
flag{[a-zA-Z_]}

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image-20240428134947291

将透明度改为100%

image-20240502105906861

以为是但是和flag{有点区别

垂直翻转一下

image-20240502110051668

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不同的地方

取黑白为二进制，对比差异

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from PIL import Image

img1 = Image.open("1.png")
img2 = Image.open("2.png")

img1s = ''
img2s = ''

for i in img1.getdata():
    if i == (255,255,255,255):
        img1s += '0'
    else:
        img1s += '1'
for i in img2.getdata():
    if i == (255,255,255,255):
        img2s += '0'
    else:
        img2s += '1'
code = ''
for i in range(len(img1s)):
    if img1s[i] != img2s[i]:
        code += img2s[i]
with open('enc.c','w') as fw:
    for i in range(0,len(code),8):
        fw.write(chr(int(code[i:i+8],2)))

或者

提示说：image to 01 然后找一下2.png相对于1.png不同的地方，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

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from PIL import Image
import math
import sys

def is_black(pixel):
    # 判断像素是否是黑色
    # 如果红、绿、蓝通道的值都很低，则认为是黑色
    return all(value < 10 for value in pixel[:3])


def is_white(pixel):
    # 判断像素是否是白色
    # 如果红、绿、蓝通道的值都很高，则认为是白色
    return all(value > 245 for value in pixel[:3])

flag1=""
flag2=""
def scan_image(image_path):
    global flag1
    # 打开图像文件
    image = Image.open(image_path)
    # 获取图像的像素数据
    pixels = image.load()
    width, height = image.size

    for y in range(height):
        for x in range(width):
            # 获取像素的RGB值
            pixel = pixels[x, y]
            # 判断像素是黑色还是白色
            if is_black(pixel):
                flag1=flag1+"1"
            elif is_white(pixel):
                flag1=flag1+"0"
            else:
                print("err")
def scan_image2(image_path):
    global flag2
    # 打开图像文件
    image = Image.open(image_path)
    # 获取图像的像素数据
    pixels = image.load()
    width, height = image.size

    for y in range(height):
        for x in range(width):
            # 获取像素的RGB值
            pixel = pixels[x, y]
            # 判断像素是黑色还是白色
            if is_black(pixel):
                flag2=flag2+"1"
            elif is_white(pixel):
                flag2=flag2+"0"
            else:
                print("err")
# 调用函数扫描图像
scan_image("1.png")

scan_image2("2.png")
for i in range(len(flag1)):
    if flag1[i] != flag2[i]:
        print(flag2[i],end="")

得到

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00100011011010010110111001100011011011000111010101100100011001010011110001100010011010010111010001110011001011110111001101110100011001000110001100101011001010110010111001101000001111100000101001110101011100110110100101101110011001110010000001101110011000010110110101100101011100110111000001100001011000110110010100100000011100110111010001100100001110110000101001110011011101000111001001101001011011100110011100100000011010110110010101111001001000000011110100100000001000100010001000111011001000000000101000001010011010010110111001110100001000000110110101100001011010010110111000101000001010010111101100001010000010010111001101110100011100100110100101101110011001110010000001100011011100100111100101110000011101000110111101011111011101000111100001110100001110110000101000001001011000110110100101101110001111100011111001100011011100100111100101110000011101000110111101011111011101000111100001110100001110110010000000001010000010100000100101100110011011110111001000100000001010000110100101101110011101000010000001101001001000000011110100100000001100000011101100100000011010010010000000111100001000000110001101110010011110010111000001110100011011110101111101110100011110000111010000101110011011000110010101101110011001110111010001101000001010000010100100111011001000000010101100101011011010010010100101111011000010100010000000100000001000000010000000100000001000000010000000100000011000110110100001100001011100100010000001100101011011100110001101110010011110010111000001110100011001010110010001011111011101000111100001110100001000000011110100100000011000110110100001100001011100100010100001100011011100100111100101110000011101000110111101011111011101000111100001110100010110110110100101011101001000000101111000100000011010110110010101111001010110110110100100100000001001010010000001101011011001010111100100101110011011000110010101101110011001110111010001101000001010000010100101011101001000000101111000100000011000110111001001111001011100000111010001101111010111110111010001111000011101000101101100101000011010010010000000101011001000000011000100101001001000000010010100100000011000110111001001111001011100000111010001101111010111110111010001111000011101000010111001101100011001010110111001100111011101000110100000101000001010010101110100101001001110110000101000100000001000000010000000100000001000000010000000100000001000000110001101101111011101010111010000100000001111000011110000100000011010010110111001110100001010000110010101101110011000110111001001111001011100000111010001100101011001000101111101110100011110000111010000101001001000000011110000111100001000000010001000100000001000100011101100001010001000000010000000100000001000000111110100100000001000000010000000001010001000000010000000100000001000000111001001100101011101000111010101110010011011100010000000110000001110110000101001111101000010100000101000101111001011110010000001100101011011100110001101110010011110010111000001110100011001010110010001011111011101000111100001110100001100010010000000111101001000000011000100110010001100100010110000110001001100100011011100101100001100010011000100110001001011000011000100110001001100010010110000111001001101100010110000110001001100010011010000101100001100010011000100110101001011000011000100110010001101110010110000110111001101110010110000111001001100000010110000110001001100010011100100101100001110010011001000101100001110000011100100101100001100010011000100110111001011000011000100110010001101100010110000111000001101010010110000111000001101110010110000110001001100010011011100101100001100010011000100110001001011000011000100110001001100010010110000111000001101100010110000111000001101000010110000110001001100100011001000101100001100010011001000110111001011000011000100110001001100010010110000110111001101010010110000111000001100010010110000111001001101110010110000110001001100100011000000101100001110010011010000101100001110010011001100101100001100010011000100110000001011000011100100111000001011000011011000110101001011000011100000110100001011000011000100110010001101110010110000110001001100000011010100101100001101100011100100101100001110000011011100101100001100010011001000110101001011000011100100111000001011000011000100110000001101110010110000111000001101110010110000110111001100000010110000110001001100000011100000101100001100010011001000110111001011000011100000110011001011000011100000111000001011000011000100110000001101010010110000110001001100000011010100101100001110010011100000101100001110010011010100101100001110000011100000101100001100010011000000110010001011000011100100110110001011000011000100110001001110000010110000110001001100000011010000101100001100010011000100110100000010100010111100101111001000000110010001101110011000110111001001111001011100000111010001100101011001000101111101110100011110000111010000100000001111010010000001100110011011000110000101100111011110110111010001101000011010010111001101011111011010010111001101011111011101000110100001100101010111110110011001100001011010110110010101011111011001100110110001100001011001110101111101100001011011100110010001011111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解密会得到一个cpp源码

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#include<bits/stdc++.h>
using namespace std;
string key = ""; 

int main(){
    string crypto_txt;
    cin>>crypto_txt; 

    for (int i = 0; i < crypto_txt.length(); ++i){
        char encrypted_txt = char(crypto_txt[i] ^ key[i % key.length()] ^ crypto_txt[(i + 1) % crypto_txt.length()]);
        cout << int(encrypted_txt) << " ";
    }   
    return 0;
}

// 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
// dncrypted_txt = flag{this_is_the_fake_flag_and_can_you_find_the_true_flag}
// 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

给了一个fakeflag的明文和密文，很明显是要算密钥

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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]
m = 'flag{this_is_the_fake_flag_and_can_you_find_the_true_flag}'
for i in range(len(m)):
    print(chr(ord(m[i])^ord(m[(i+1)%len(m)])^c[i]),end='')
# prisonrealmprisonrealmprisonrealmprisonrealmprisonrealmpri
# key = prisonrealm

拿到密钥解密即可，推测最后一个字符是}，依次还原

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key = 'prisonrealm'
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]
# flag[-1] = '}' 即flag[-1] = 125
flag = []
for i in range(len(enc)):
    flag.append(enc[i]^ord(key[i%len(key)]))
t = [0]*len(flag)
t[0] = 125 ^ flag[-1]
t[1:len(flag)] = flag[:-1]
print()
for i in range(len(flag)-1):
    print(chr(t[i]),end='')
    t[i+1] = flag[i]^t[i]
print('}')
# 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!}

easy_signin2

做做misc签到题来放松吧！
相信你一定可以愉快的签到
flag以NSSCTF{}格式提交

hint: 二进制异或 pngchunk
hint2: 抽象画

附件看到两张图，先去看一下here_is_your_flag.png，用010打卡发现根本不是png图片数据，题目给了提示是要异或pngchunk，但是不知道异或什么，因为我们知道png的是89开始的，所以用现在的第一个字节去异或89，就可以得到应该要异或的字节了

image-20240516093546408

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>>> print(hex(0xcd^0x89))
0x44

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

image-20240516095435045

image-20240516095509457

image-20240516104523600

得到

here_is_your_flag

通过提示可以看到查看pngchunk

image-20240516110245852

image-20240516110306386

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

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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

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from PIL import Image

def process_image(input_image_path, output_image_path):
    # 打开图像
    image = Image.open(input_image_path).convert('L')
    # 获取图像的像素数据
    pixels = image.load()
    width, height = image.size

    # 遍历图像的每个像素
    for y in range(height):
        for x in range(width):
            # 获取当前像素的灰度值
            pixel_value = pixels[x, y]

            # 如果像素值在10到200之间，将其设置为255
            if 0 < pixel_value < 250:
                pixels[x, y] = 0

    # 保存修改后的图像
    image.save(output_image_path)

# 输入和输出图像的文件路径
input_image_path = "10xbig_to_more_clear.png"
output_image_path = "out.png"

# 处理图像
process_image(input_image_path, output_image_path)

out

得到字符串di`f{cfd7d1fd1ba254dcfa7f4155cfdadadc}

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\npiet-1.3a-win32>npiet.exe -v 1.png
info: verbose set to 1
info: using file 1.png
info: got 495 x 495 pixel with 256 cols
info: codelsize guessed is 15 pixel
? di`f{cfd7d1fd1ba254dcfa7f4155cfdadadc}
f? l? a? g? {? d? g? e? 8? f? 3? h? f? 3? d? a? 4? 5? ? ? cd4? ? ? ? ? ? 14f7af? ? ? ? fc5? d? b5? ? ? dad? d? }? ?

flag{dge8f3hf3da45cd414f7affc5db5dadd}

NSSCTF{dge8f3hf3da45cd414f7affc5db5dadd}