Joy is a big fan of the Matrix. She has this DVD which contains hidden easter eggs from the actors of the Matrix, especially the 8x16 version. Can you find out the easter egg?
Note: Format flag adalah FindITCTF{string} dengan kapitalisasi sesuai seperti petunjuk (lowercase)
Solution
Initially when we take a look at the ‘chall’ file, the first thought was that it was some sort of hexdump of a binary file and we need to convert it to an executable before reversing it. And then there was a hunch telling that it was just a basic hex encoding applied to it. We then headed over to CyberChef to decode it and our hunch quickly revealed that it's a source code.
By thoroughly inspecting the source code, it became evident that the code was an Arduino Sketch. Our analysis revealed that its purpose was to display content on an 8x16 LED matrix. To simplify the process, we considered an alternative approach using Python's Turtle module. Consequently, we swiftly developed a Python program utilising Turtle, which would dynamically move based on the input obtained from the cmd.txt file. u for moving upwards, d for down, r for right and l for left
From this point onward, most of the solution is handled by Aeryx since he has the most experience in terms of dealing with Arduino. Below is the python implementation code.
go_turtle_go.py
import turtle
def draw_text_formation(string_array):
turtle.setup(width=1400, height=100) # Set the window width to 1400 pixels
turtle.hideturtle() # hide turtle
turtle.speed(0)
window_width = turtle.window_width() # Get the window width
window_height = turtle.window_height() # Get the window height
turtle.penup() # Pull the pen up
# Set the initial position of the turtle
turtle.goto(-window_width / 2 + 30, -window_height / 2 + 30)
turtle.pendown() # Pull the pen down
for string in string_array:
start_position = turtle.position() # Store the starting position of the string
for char in string:
if char == 'u':
turtle.setheading(90) # Face upwards
turtle.forward(3) # Move up by 3 units
elif char == 'r':
turtle.setheading(0) # Face right
turtle.forward(3) # Move right by 3 units
elif char == 'd':
turtle.setheading(270) # Face downwards
turtle.forward(3) # Move down by 3 units
elif char == 'l':
turtle.setheading(180) # Face left
turtle.forward(3) # Move left by 3 units
# Teleport to the right while maintaining the y-axis position
turtle.penup()
turtle.goto(start_position[0] + 30, start_position[1])
turtle.pendown()
turtle.done()
# read string from cmd file where splitted by new line
strings = []
with open('cmd.txt', 'r') as f:
for line in f:
strings.append(line.strip())
draw_text_formation(strings)
