HackVent 2023 - [HV23.H2] Grinch's Secret
Difficulty: Medium
Category: Fun
Santa usually only gifts one present per kid, but one of his elves accidentally put two presents in the bag for a single kid! Somewhere in the medium challenges, you can find the second gift.
The flag is hidden in the [HV23.11] challenge. The alternations of “Never gonna give you up.” and “Never gonna let you down.” represent a 0 or 1 respectively.
We can update the solve script to include the hidden flag:
#!/usr/bin/python3
from PIL import Image
input = Image.open('pi.png')
output = ""
for row in range(input.size[0]):
for col in range(input.size[1]):
pixel = input.getpixel((row, col))
output += chr(pixel[2] ^ pixel[0])
#print(output)
bit_0 = "Never gonna give you up"
bit_1 = "Never gonna let you down"
bin_msg = ""
words = output.split(".")
for w in words:
if bit_0 in w:
bin_msg += "0"
elif bit_1 in w:
bin_msg += "1"
chunks = [bin_msg[i:i+8] for i in range(0, len(bin_msg), 8)]
ascii_string = ''.join([chr(int(chunk, 2)) for chunk in chunks if len(chunk) == 8])
print(ascii_string)
The flag is: HV23{h1dden_r1ckr011}