畫師
flag為有意義單詞
flag
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將透明度改為100%
以為是但是和flag{有點區別
垂直翻轉一下
flag{easy_diagram}
easy_signin1
絕對的misc 由此而生的簽到
教會ctfer們flag的是......
hint: image to 01 然後找一下2.png相對於1.png不同的地方
取黑白為二進位制，對比差異
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
提示說：image to 01 然後找一下2.png相對於1.png不同的地方，一開始以為是異或，結果就是傳統的找出2.png的二進位制和1.png不一樣的地方然後列印
from PIL import Image
import math
import sys
def is_black(pixel):
# 判斷畫素是否是黑色
# 如果紅、綠、藍通道的值都很低，則認為是黑色
return all(value < 10 for value in pixel[:3])
def is_white(pixel):
# 判斷畫素是否是白色
# 如果紅、綠、藍通道的值都很高，則認為是白色
return all(value > 245 for value in pixel[:3])
flag1=""
flag2=""
def scan_image(image_path):
global flag1
# 開啟影像檔案
image = Image.open(image_path)
# 獲取影像的畫素資料
pixels = image.load()
width, height = image.size
for y in range(height):
for x in range(width):
# 獲取畫素的RGB值
pixel = pixels[x, y]
# 判斷畫素是黑色還是白色
if is_black(pixel):
flag1=flag1+"1"
elif is_white(pixel):
flag1=flag1+"0"
else:
print("err")
def scan_image2(image_path):
global flag2
# 開啟影像檔案
image = Image.open(image_path)
# 獲取影像的畫素資料
pixels = image.load()
width, height = image.size
for y in range(height):
for x in range(width):
# 獲取畫素的RGB值
pixel = pixels[x, y]
# 判斷畫素是黑色還是白色
if is_black(pixel):
flag2=flag2+"1"
elif is_white(pixel):
flag2=flag2+"0"
else:
print("err")
# 呼叫函式掃描影像
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
00100011011010010110111001100011011011000111010101100100011001010011110001100010011010010111010001110011001011110111001101110100011001000110001100101011001010110010111001101000001111100000101001110101011100110110100101101110011001110010000001101110011000010110110101100101011100110111000001100001011000110110010100100000011100110111010001100100001110110000101001110011011101000111001001101001011011100110011100100000011010110110010101111001001000000011110100100000001000100010001000111011001000000000101000001010011010010110111001110100001000000110110101100001011010010110111000101000001010010111101100001010000010010111001101110100011100100110100101101110011001110010000001100011011100100111100101110000011101000110111101011111011101000111100001110100001110110000101000001001011000110110100101101110001111100011111001100011011100100111100101110000011101000110111101011111011101000111100001110100001110110010000000001010000010100000100101100110011011110111001000100000001010000110100101101110011101000010000001101001001000000011110100100000001100000011101100100000011010010010000000111100001000000110001101110010011110010111000001110100011011110101111101110100011110000111010000101110011011000110010101101110011001110111010001101000001010000010100100111011001000000010101100101011011010010010100101111011000010100010000000100000001000000010000000100000001000000010000000100000011000110110100001100001011100100010000001100101011011100110001101110010011110010111000001110100011001010110010001011111011101000111100001110100001000000011110100100000011000110110100001100001011100100010100001100011011100100111100101110000011101000110111101011111011101000111100001110100010110110110100101011101001000000101111000100000011010110110010101111001010110110110100100100000001001010010000001101011011001010111100100101110011011000110010101101110011001110111010001101000001010000010100101011101001000000101111000100000011000110111001001111001011100000111010001101111010111110111010001111000011101000101101100101000011010010010000000101011001000000011000100101001001000000010010100100000011000110111001001111001011100000111010001101111010111110111010001111000011101000010111001101100011001010110111001100111011101000110100000101000001010010101110100101001001110110000101000100000001000000010000000100000001000000010000000100000001000000110001101101111011101010111010000100000001111000011110000100000011010010110111001110100001010000110010101101110011000110111001001111001011100000111010001100101011001000101111101110100011110000111010000101001001000000011110000111100001000000010001000100000001000100011101100001010001000000010000000100000001000000111110100100000001000000010000000001010001000000010000000100000001000000111001001100101011101000111010101110010011011100010000000110000001110110000101001111101000010100000101000101111001011110010000001100101011011100110001101110010011110010111000001110100011001010110010001011111011101000111100001110100001100010010000000111101001000000011000100110010001100100010110000110001001100100011011100101100001100010011000100110001001011000011000100110001001100010010110000111001001101100010110000110001001100010011010000101100001100010011000100110101001011000011000100110010001101110010110000110111001101110010110000111001001100000010110000110001001100010011100100101100001110010011001000101100001110000011100100101100001100010011000100110111001011000011000100110010001101100010110000111000001101010010110000111000001101110010110000110001001100010011011100101100001100010011000100110001001011000011000100110001001100010010110000111000001101100010110000111000001101000010110000110001001100100011001000101100001100010011001000110111001011000011000100110001001100010010110000110111001101010010110000111000001100010010110000111001001101110010110000110001001100100011000000101100001110010011010000101100001110010011001100101100001100010011000100110000001011000011100100111000001011000011011000110101001011000011100000110100001011000011000100110010001101110010110000110001001100000011010100101100001101100011100100101100001110000011011100101100001100010011001000110101001011000011100100111000001011000011000100110000001101110010110000111000001101110010110000110111001100000010110000110001001100000011100000101100001100010011001000110111001011000011100000110011001011000011100000111000001011000011000100110000001101010010110000110001001100000011010100101100001110010011100000101100001110010011010100101100001110000011100000101100001100010011000000110010001011000011100100110110001011000011000100110001001110000010110000110001001100000011010000101100001100010011000100110100000010100010111100101111001000000110010001101110011000110111001001111001011100000111010001100101011001000101111101110100011110000111010000100000001111010010000001100110011011000110000101100111011110110111010001101000011010010111001101011111011010010111001101011111011101000110100001100101010111110110011001100001011010110110010101011111011001100110110001100001011001110101111101100001011011100110010001011111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解密會得到一個cpp原始碼
#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
給了一個fakeflag的明文和密文，很明顯是要算金鑰
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
拿到金鑰解密即可，推測最後一個字元是}，依次還原
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簽到題來放鬆吧！
相信你一定可以愉快的簽到
flag以NSSCTF{}格式提交
hint: 二進位制異或 pngchunk
hint2: 抽象畫
附件看到兩張圖，先去看一下here_is_your_flag.png，用010打卡發現根本不是png圖片資料，題目給了提示是要異或pngchunk，但是不知道異或什麼，因為我們知道png的是89開始的，所以用現在的第一個位元組去異或89，就可以得到應該要異或的位元組了
>>> print(hex(0xcd^0x89))
0x44
可以看到我們要異或的應該是0x44，所以我們把這個檔案的每一位元組提取出來然後去異或0x44並寫入檔案
得到
透過提示可以看到檢視pngchunk
從這裡開始往下複製，然後新增檔案頭89 50 4e 47 0d 0a 1a 0a即可得到
hint2提示抽象畫，可以想到用npiet
去這裡下載：http://www.bertnase.de/npiet/
然後看另一個png，10xbig_to_more_clear.png
用指令碼放大十倍
from PIL import Image
def process_image(input_image_path, output_image_path):
# 開啟影像
image = Image.open(input_image_path).convert('L')
# 獲取影像的畫素資料
pixels = image.load()
width, height = image.size
# 遍歷影像的每個畫素
for y in range(height):
for x in range(width):
# 獲取當前畫素的灰度值
pixel_value = pixels[x, y]
# 如果畫素值在10到200之間，將其設定為255
if 0 < pixel_value < 250:
pixels[x, y] = 0
# 儲存修改後的影像
image.save(output_image_path)
# 輸入和輸出影像的檔案路徑
input_image_path = "10xbig_to_more_clear.png"
output_image_path = "out.png"
# 處理影像
process_image(input_image_path, output_image_path)
得到字串di`f{cfd7d1fd1ba254dcfa7f4155cfdadadc}
\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}