DNA & Design

DNA

The challenge provided this image:

Extracted the string by reading the characters from left to right starting from the top going down. The resulting extracted string from the image: TCATAGGCTAGCTACACTCGTTGTACACTAGACAGCTACACTCTCTGAAGCTAGCTATGAAGCGTCCTACTCCTATGA

The challenge also has the following instructions There are some pretty unusual encoding methods. Find the flag PS: Replace spaces with “_”

From research this seems to be some kind of DNA type of encryption. I also learnt that I need to break the string into 3s, so that made it look like this:

TCA TAG GCT AGC TAC ACT CGT TGT ACA CTA GAC AGC TAC ACT CTC TGA AGC TAG CTA TGA AGC GTC CTA CTC CTA TGA

One of my team leads gave me this link that has mappings that could decode the above string. Managed to decode from here

The resulting string: CTF DAHOMEY DANS TES GENES

I then replaced the spaces (“ “) with underscores as per the instructions, then embedded the flag prefix to the string. NGCCTF{CTF_DAHOMEY_DANS_TES_GENES}

DESIGN

This was yet another interesting misc challenge. We were presented with this CSV file. The instructions simply asked: Can you sculpt me ? Opening the file using Microsoft Excel, we find a long list of values mapped in two columns labelled X and Y. Given the name of the challenge, file and instructions I immediately assumed that these might be image pixel coordinates. I therefore went ahead and asked chatGPT to come up with a python script that could reconstruct the image and it came up with this awesome script that did just that:

import pandas as pd
import numpy as np
import matplotlib.pyplot as plt

file_path = 'Art.csv'

# Step 1: Load and inspect the data
try:
    data = pd.read_csv(file_path)
    print("Column names:", data.columns)
except Exception as e:
    print(f"Error reading the file: {e}")
    exit()

# Step 2: Adjust column names as needed
if 'x' in data.columns and 'y' in data.columns:
    x_coords = data['x']
    y_coords = data['y']
elif 'X' in data.columns and 'Y' in data.columns:  # Example alternative
    x_coords = data['X']
    y_coords = data['Y']
else:
    print("Error: Could not find 'x' and 'y' columns in the file.")
    exit()

# Continue as before
max_x = x_coords.max()
max_y = y_coords.max()
image = np.zeros((max_y + 1, max_x + 1), dtype=np.uint8)
for x, y in zip(x_coords, y_coords):
    image[y, x] = 255
plt.imshow(image, cmap='gray')
plt.axis('off')
plt.show()

I then ran the script using the command:

pyhon3 image_reconstructor.py

Then managed to retrieve this image:

I therefore just added the flag prefix and submitted the final flag as: NGCCTF{CTF_Navigating_the_Digital_Maze_4f8ae63f9}