caesar_tuctf_crypto.py

import string
import sys
import nclib
import time
"""
	Script to resolv challengue CTF:
	The Never Ending Crypto

	Welcome to the never ending crypto!
	How quickly can you make it through?

	nc neverending.tuctf.com 12345

	First step. need calculate ROT
	Second step. decipher the challengue with first step ROT
  Finally we need 50 steps to get the flag

"""
plaintext = "abc09.#dz"
host = 'neverending.tuctf.com'
port = 12345

alphabet = [chr(i) for i in xrange(32,95+32)]
alphabet = "".join(alphabet)
print("USE this alphabet: {}".format(alphabet))

def caesar(plaintext, shift, alphabet):
    shifted_alphabet = alphabet[shift:] + alphabet[:shift]
    table = string.maketrans(alphabet, shifted_alphabet)
    return plaintext.translate(table)

def connect_netcat(host, port):
	nc = nclib.Netcat((host, port), udp=False, verbose=False)
	nc.echo_hex = True
	print("Netcat conect")

def send_netcat(nc, text): 
	time.sleep(1)
	nc.send(u'{}\n'.format(text))
	time.sleep(1)

def recv_netcat(nc):
	return nc.recv()

nc = connect_netcat(host, port)
while 1:
	try:

		send_netcat(nc, plaintext)
		retr = recv_netcat(nc)

		for row in str(retr).split("\n"):
			if "encrypted is " in row:
				solution = row.split(" encrypted is ")[-1]
			if "decrypted?" in row:
				next_r = row.replace("What is ","").replace(" decrypted?", "")

		print("Looking ROT: plaintext->{} | cipher->{} | next_one->{}".format(plaintext, solution, next_r))
		for i in xrange(1,len(alphabet)):
			if caesar(plaintext, i, alphabet) == solution:
				print("Find ROT{}".format(i))
				
				final_solution  = caesar(next_r, len(alphabet)-i, alphabet)
				
				print("Sending: {}".format(final_solution))

				send_netcat(nc, final_solution)
				print(recv_netcat(nc))
	except:		
		nc = connect_netcat(host, port)