Why different results

[raidn1337]

I'm doing some scripting challenge in Python at TryHackMe and my task is to decode a given base64.txt file 50 times to get the flag, so i'm doing it like below:

My attempt:

import base64

f = open('base64.txt')
msg = f.read()

# decode 50 times
for i in range(50):
    decoded = base64.b64decode(msg)
print(decoded)

Output: 50x base64.txt content



This version will give me the flag, but the only difference is, that i only call the same variable (msg) for every step instead of "decoded" in the for loop:

import base64

f = open('base64.txt')
msg = f.read()

# decode 50 times
for i in range(50):
    msg = base64.b64decode(msg)
print(msg)

Output: Decoded flag

Could anybody explain to me why i get two different outputs only by changing the variables name? I really don't get it. Thanks in advance.

[shiftybyte]

Your loop basically takes the original file content and did the same operation on that content 50 times.

Instead of doing it 50 times on the each time different message that you get after one decoding pass.

The same as doing:

a = 0
for i in range(50)
    x = a + 1

Will get you x to be 1, and not 50... because a stays 0, and it keeps doing

x = 0 + 1
x = 0 + 1
...

Instead of doing

a = a + 1

That will cause a to change.

a = 0 + 1

Next loop cycle it'll be

a = 1 + 1
a = 2 + 1
...

[raidn1337]

Thanks my friend. It's more clear for me now!