baby_morse.md

Baby Morse

Categories: intro, hardware

Challenge

For this challenge, we have to send FLAG to the CTF server on a specific port.

nc challenges.france-cybersecurity-challenge.fr 2250

Write-up

By reading the challenge name, we can guess that we have to send the word FLAG in morse code to the server. To translate into morse code and to communicate with the server, I used a Python script. (available here).

from pwn import *
import numpy as np

# Connection parameters
HOST = "challenges.france-cybersecurity-challenge.fr"
PORT = 2250

alphabet = {'A': '.-', 'B': '-...',
            'C': '-.-.', 'D': '-..', 'E': '.',
            'F': '..-.', 'G': '--.', 'H': '....',
            'I': '..', 'J': '.---', 'K': '-.-',
            'L': '.-..', 'M': '--', 'N': '-.',
            'O': '---', 'P': '.--.', 'Q': '--.-',
            'R': '.-.', 'S': '...', 'T': '-',
            'U': '..-', 'V': '...-', 'W': '.--',
            'X': '-..-', 'Y': '-.--', 'Z': '--..',
            '1': '.----', '2': '..---', '3': '...--',
            '4': '....-', '5': '.....', '6': '-....',
            '7': '--...', '8': '---..', '9': '----.',
            '0': '-----', ', ': '--..--', '.': '.-.-.-',
            '?': '..--..', '/': '-..-.', '-': '-....-',
            '(': '-.--.', ')': '-.--.-'}

rev_alphabet = {v: k for k, v in alphabet.items()}


def morse_encode(msg: str):
    """
    Encodes a message into morse code.
    """
    cipher = []

    for word in msg.split(' '):
        for char in word:
            cipher.append(alphabet.get(char))
            cipher.append(' ')
        cipher[-1] = ' '
    return "".join(cipher).strip()


def main():
    # Connect to the server
    c = remote(HOST, PORT)

    # Wait for the server to be ready
    c.recvuntil(b'> ')

    msg = "FLAG"
    morse_msg = morse_encode(msg)
    print(f"Message: {msg}, Morse encoded: {morse_msg}")
    c.sendline(bytes(morse_msg, 'utf8'))

    # Wait for server response
    flag = str(c.recv(), 'utf8')
    print(flag)


if __name__ == '__main__':
    main()