PicoCTF - PW Crack 5

First, download all the files provided. They are the following. All of them are needed to live in the same directory in order for this to work.

level5.py
level5.flag.txt.enc
level5.hash.bin
dictionary.txt

Now let’s open up the main file which is the level5.py

import hashlib

### THIS FUNCTION WILL NOT HELP YOU FIND THE FLAG --LT ########################
def str_xor(secret, key):
    #extend key to secret length
    new_key = key
    i = 0
    while len(new_key) < len(secret):
        new_key = new_key + key[i]
        i = (i + 1) % len(key)        
    return "".join([chr(ord(secret_c) ^ ord(new_key_c)) for (secret_c,new_key_c) in zip(secret,new_key)])
###############################################################################

flag_enc = open('level5.flag.txt.enc', 'rb').read()
correct_pw_hash = open('level5.hash.bin', 'rb').read()


def hash_pw(pw_str):
    pw_bytes = bytearray()
    pw_bytes.extend(pw_str.encode())
    m = hashlib.md5()
    m.update(pw_bytes)
    return m.digest()


def level_5_pw_check():
    user_pw = input("Please enter correct password for flag: ")
    user_pw_hash = hash_pw(user_pw)
    
    if( user_pw_hash == correct_pw_hash ):
        print("Welcome back... your flag, user:")
        decryption = str_xor(flag_enc.decode(), user_pw)
        print(decryption)
        return
    print("That password is incorrect")



level_5_pw_check()

This time, we have an external .txt file, which is a dictionary containing possible values that unlock the flag.

f = open("dictionary.txt")
dictionary = f.readlines()
n_list = []

for i in dictionary:
    n_list.append(i.strip())

for item in range(0, len(n_list)):
    print(n_list[item])

f.close()

First, we open the file and then read all its contents. After that, we append each value to an empty list and print each value. Finally, through a loop, we pass each value as an input to the program.

 for item in range(0, len(n_list)):
        user_pw = n_list[item]
        user_pw_hash = hash_pw(user_pw)

python3 level5.py

Nice, you’ve got the flag!