Python Wrangling

Challenge 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?

For this challenge, we are given ende.py, flag.txt.en, and pw.txt

Let’s look at each file we’re given.

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'.")

gAAAAABgUAIV8D5MJdzgLLTkkMlbU84ARVwfX4brMt2rJQCjkpLItytfWVZe1L2dp4K8VrKgRU3axStKJEAqcM0iDaxiYE54Boh8UfAAo1RNifKnlDrFz0gLaznVSFVj2xAUa4V35180

68f88f9368f88f9368f88f9368f88f93

Hm, looks like a python script, an encoded flag, and the password to decrypt said flag. Let’s run the python script and see what the usage looks like.

❯ python ende.py
Usage: ende.py (-e/-d) [file]

Okay, so since we want to decrypt, lets use the -d flag, along with the flag.txt.en file.

❯ python ende.py -d flag.txt.en
Please enter the password:

Alrighty, and let’s throw the password in that we got from the pw.txt file.

❯ python ende.py -d flag.txt.en
Please enter the password:68f88f9368f88f9368f88f9368f88f93
picoCTF{4p0110_1n_7h3_h0us3_68f88f93}

FLAG: picoCTF{4p0110_1n_7h3_h0us3_68f88f93}