Challenge 22: PW Crack 2

Description

Can you crack the password to get the flag? Download the password checker here and you’ll need the encrypted flag in the same directory too.

Tags

Beginner picoMini 2022 General Skills password_cracking

Points

100

Solution

In this challenge we are given a script and an encrypted flag. The script is a simple password checker, if we entered the correct password it will print the flag. we can take a look at the script. It might has something useful to us.

### 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('level2.flag.txt.enc', 'rb').read()



def level_2_pw_check():
    user_pw = input("Please enter correct password for flag: ")
    if( user_pw == chr(0x34) + chr(0x65) + chr(0x63) + chr(0x39) ):
        print("Welcome back... your flag, user:")
        decryption = str_xor(flag_enc.decode(), user_pw)
        print(decryption)
        return
    print("That password is incorrect")

level_2_pw_check()

As we can see, the password is 0x34 0x65 0x63 0x39 and it will be used to decrypt the flag. We can convert it first to ASCII using chr() function. like this:

>>> chr(0x34) + chr(0x65) + chr(0x63) + chr(0x39)
'4ec9'

let’s run the script and enter the password.

$ python3 level2.py
Please enter correct password for flag: 4ec9

Welcome back... your flag, user:
picoCTF{tr45h_51ng1ng_9701e681}

Flag

picoCTF{tr45h_51ng1ng_9701e681}