Python Wrangling

Python Wrangling Author: syreal Description Python scripts are invoked kind of like programs in the Terminal… Can you run this Python script using this password to get the flag?

Este requiere que te descargues un script en Python una password y supongo que ejecutando el script con la password obtienes la flag. Analizemos el contenido del script:

import sys
import base64
from cryptography.fernet import Fernet

usage_msg = "Usage: "+ sys.argv[0] +" (-e/-d) [file]"
help_msg = usage_msg + "\n" +\
        "Examples:\n" +\
        "  To decrypt a file named 'pole.txt', do: " +\
        "'$ python "+ sys.argv[0] +" -d pole.txt'\n"

if len(sys.argv) < 2 or len(sys.argv) > 4:
    print(usage_msg)
    sys.exit(1)

if sys.argv[1] == "-e":
    if len(sys.argv) < 4:
        sim_sala_bim = input("Please enter the password:")
    else:
        sim_sala_bim = sys.argv[3]

    ssb_b64 = base64.b64encode(sim_sala_bim.encode())
    c = Fernet(ssb_b64)

    with open(sys.argv[2], "rb") as f:
        data = f.read()
        data_c = c.encrypt(data)
        sys.stdout.write(data_c.decode())

elif sys.argv[1] == "-d":
    if len(sys.argv) < 4:
        sim_sala_bim = input("Please enter the password:")
    else:
        sim_sala_bim = sys.argv[3]

    ssb_b64 = base64.b64encode(sim_sala_bim.encode())
    c = Fernet(ssb_b64)

    with open(sys.argv[2], "r") as f:
        data = f.read()
        data_c = c.decrypt(data.encode())
        sys.stdout.buffer.write(data_c)

elif sys.argv[1] == "-h" or sys.argv[1] == "--help":
    print(help_msg)
    sys.exit(1)

else:
    print("Unrecognized first argument: "+ sys.argv[1])
    print("Please use '-e', '-d', or '-h'.")

No supuso un reto entender este script y ejecutarlo de las dos maneras posibles que parece ofrecer

pablo☠office Python_Wrangling$ python ende.py -d flag.txt.en pablo☠office Python_Wrangling$ python ende.py -d flag.txt.en 
Please enter the password:aa821c16aa821c16aa821c16aa821c16
picoCTF{4p0110_1n_7h3_h0us3_aa821c16}

pablo☠office Python_Wrangling$ python ende.py -d flag.txt.en aa821c16aa821c16aa821c16aa821c16
picoCTF{4p0110_1n_7h3_h0us3_aa821c16}

He codificado una versión reducida del script:

import base64
from cryptography.fernet import Fernet

sim_sala_bim = "aa821c16aa821c16aa821c16aa821c16"
ssb_b64 = base64.b64encode(sim_sala_bim.encode())
c = Fernet(ssb_b64)

with open("flag.txt.en", "r") as f:
        data = f.read()
        data_c = c.decrypt(data.encode())
        print(f"{data_c}")

pablo☠office Python_Wrangling$ python test.py     
b'picoCTF{4p0110_1n_7h3_h0us3_aa821c16}\n'

flag: picoCTF{4p0110_1n_7h3_h0us3_aa821c16}