PicoCTF - fixme2.py

Download the fixme2.py file, open it in an editor and change it to the following.

import random

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 = chr(0x15) + chr(0x07) + chr(0x08) + chr(0x06) + chr(0x27) + chr(0x21) + chr(0x23) + chr(0x15) + chr(0x58) + chr(0x18) + chr(0x11) + chr(0x41) + chr(0x09) + chr(0x5f) + chr(0x1f) + chr(0x10) + chr(0x3b) + chr(0x1b) + chr(0x55) + chr(0x1a) + chr(0x34) + chr(0x5d) + chr(0x51) + chr(0x40) + chr(0x54) + chr(0x09) + chr(0x05) + chr(0x04) + chr(0x57) + chr(0x1b) + chr(0x11) + chr(0x31) + chr(0x0e) + chr(0x51) + chr(0x5c) + chr(0x44) + chr(0x51) + chr(0x0a) + chr(0x5b) + chr(0x5a) + chr(0x19)

flag = str_xor(flag_enc, 'enkidu')

# Check that flag is not empty
if flag == "":
  print('String XOR encountered a problem, quitting.')
else:
  print('That is correct! Here\'s your flag: ' + flag)

The problem was at the if statement

if flag = "":

When we need to compare two values, we use ==. Assignment happens with just =, like when we want to assign a value to a variable, for example…

i = 0

Finally, run the program with the following command.

python3 fixme2.py

Nice, you’ve got the flag!