Homework pragyan ctf writeup

Challenge name: Homework

• This is the only misc challenge in pragyan CTF ! I managed to solve this with the help of my teammates from TamilCTF! cheers to everyone.

• The challenge gave us an link and the description says something about a traitor submitted home work and we have to find him maybe?lets try!

• Visting the link we are presented with the webpage ! hmm nothing interesting.

• The webpage has the response as "Sorry the portal is not accepting new assignments at this time"

• Source code does not have anything interesting too! so going on with directory brutefoce we found an interesting directory named "response".

• Upon visiting the endpoint,we get the below response.

• Voilà ! it seems we found the culprit who submitted the assignment! Its dipensu and we have an option to download his assignment.

• Downloading the assignment gave us an zip file named pieces and inside the zip we can see lot of image files.

• Seems a image was separated into multiple parts and i thought of merging them together btw is it sorted in a order? and there was 90 separate images.

• After a initial analysis on the image we were to find there are coordinates on each image metadata !

• The total 90 images contains X coordinate ranges from 1 to 9 and y coordinates ranges from 1 to 10 but the images were not sorted!

• We can merge the images but first we need to sort them according to the coordinates and better i decided to change the images name according to the coordinates

• I wrote a script to name the images with coordinates and i attached the script below.[Added comments for explanation]

import os
#Directory which has images
a = os.listdir()

# Command = exifool -G -Artist filename
# The above command is used for extracting only particular information from exiftool data and we only interested in coordinates.
command = "exiftool -G -Artist "
for i in a:
    x=os.popen('exiftool -G -Artist '+i).read()
    # we getting the cordinates in the variable x
    x =x.replace(' ', '')
    # removing whitespaces
    x =x[20:]
    os.system("cp "+i+" "+x)
    #renaming the images with coordinate names
    os.system("rm "+i)
    #removing the orginal file

• With the above script,we get the beautiful output as follows.

• We got the result and to our plus,our images comes sorted and we can easily merge them with x and y coordinates.

• Below paperwork explains how to arrange the images!

• I used opencv to merge the images and below is the script!

import cv2
import numpy as np
import os

a = os.listdir()

a = sorted(a)

im1 = cv2.imread(a[0])
im2 = cv2.imread(a[1])
im3 = cv2.imread(a[2])
im4 = cv2.imread(a[3])
im5 = cv2.imread(a[4])
im6 = cv2.imread(a[5])
im7 = cv2.imread(a[6])
im8 = cv2.imread(a[7])
im9 = cv2.imread(a[8])
im10 = cv2.imread(a[9])

#horizontal image set 1
im_h1 = cv2.hconcat([im1, im2,im3,im4,im5,im6,im7,im8,im9,im10])

im1 = cv2.imread(a[10])
im2 = cv2.imread(a[11])
im3 = cv2.imread(a[12])
im4 = cv2.imread(a[13])
im5 = cv2.imread(a[14])
im6 = cv2.imread(a[15])
im7 = cv2.imread(a[16])
im8 = cv2.imread(a[17])
im9 = cv2.imread(a[18])
im10 = cv2.imread(a[19])

#horizontal image set 2
im_h2 = cv2.hconcat([im1, im2,im3,im4,im5,im6,im7,im8,im9,im10])

im1 = cv2.imread(a[20])
im2 = cv2.imread(a[21])
im3 = cv2.imread(a[22])
im4 = cv2.imread(a[23])
im5 = cv2.imread(a[24])
im6 = cv2.imread(a[25])
im7 = cv2.imread(a[26])
im8 = cv2.imread(a[27])
im9 = cv2.imread(a[28])
im10 = cv2.imread(a[29])

#horizontal image set 3
im_h3 = cv2.hconcat([im1, im2,im3,im4,im5,im6,im7,im8,im9,im10])

im1 = cv2.imread(a[30])
im2 = cv2.imread(a[31])
im3 = cv2.imread(a[32])
im4 = cv2.imread(a[33])
im5 = cv2.imread(a[34])
im6 = cv2.imread(a[35])
im7 = cv2.imread(a[36])
im8 = cv2.imread(a[37])
im9 = cv2.imread(a[38])
im10 = cv2.imread(a[39])

#horizontal image set 4
im_h4 = cv2.hconcat([im1, im2,im3,im4,im5,im6,im7,im8,im9,im10])

im1 = cv2.imread(a[40])
im2 = cv2.imread(a[41])
im3 = cv2.imread(a[42])
im4 = cv2.imread(a[43])
im5 = cv2.imread(a[44])
im6 = cv2.imread(a[45])
im7 = cv2.imread(a[46])
im8 = cv2.imread(a[47])
im9 = cv2.imread(a[48])
im10 = cv2.imread(a[49])

#horizontal image set 5
im_h5 = cv2.hconcat([im1, im2,im3,im4,im5,im6,im7,im8,im9,im10])

im1 = cv2.imread(a[50])
im2 = cv2.imread(a[51])
im3 = cv2.imread(a[52])
im4 = cv2.imread(a[53])
im5 = cv2.imread(a[54])
im6 = cv2.imread(a[55])
im7 = cv2.imread(a[56])
im8 = cv2.imread(a[57])
im9 = cv2.imread(a[58])
im10 = cv2.imread(a[59])

#horizontal image set 6
im_h6 = cv2.hconcat([im1, im2,im3,im4,im5,im6,im7,im8,im9,im10])

im1 = cv2.imread(a[60])
im2 = cv2.imread(a[61])
im3 = cv2.imread(a[62])
im4 = cv2.imread(a[63])
im5 = cv2.imread(a[64])
im6 = cv2.imread(a[65])
im7 = cv2.imread(a[66])
im8 = cv2.imread(a[67])
im9 = cv2.imread(a[68])
im10 = cv2.imread(a[69])

#horizontal image set 7
im_h7 = cv2.hconcat([im1, im2,im3,im4,im5,im6,im7,im8,im9,im10])

im1 = cv2.imread(a[70])
im2 = cv2.imread(a[71])
im3 = cv2.imread(a[72])
im4 = cv2.imread(a[73])
im5 = cv2.imread(a[74])
im6 = cv2.imread(a[75])
im7 = cv2.imread(a[76])
im8 = cv2.imread(a[77])
im9 = cv2.imread(a[78])
im10 = cv2.imread(a[79])

#horizontal image set 8
im_h8 = cv2.hconcat([im1, im2,im3,im4,im5,im6,im7,im8,im9,im10])

im1 = cv2.imread(a[80])
im2 = cv2.imread(a[81])
im3 = cv2.imread(a[82])
im4 = cv2.imread(a[83])
im5 = cv2.imread(a[84])
im6 = cv2.imread(a[85])
im7 = cv2.imread(a[86])
im8 = cv2.imread(a[87])
im9 = cv2.imread(a[88])
im10 = cv2.imread(a[89])

#horizontal image set 9
im_h9 = cv2.hconcat([im1, im2,im3,im4,im5,im6,im7,im8,im9,im10])

#Connecting everything veritically
im_v1 = cv2.vconcat([im_h1,im_h2,im_h3,im_h4,im_h5,im_h6,im_h7,im_h8,im_h9])

cv2.imwrite('output.jpg', im_v1)

• Merging them together! we got our flag : D