Light Switch Crypto

This is my solution to the McAfee ATR Hax 2021 cryptography challenge Light Switch Crypto. You are provided with a couple of logic statements, an encrypted message, a key, and a partially complete Python script. The challenge is to introduce the logic statements to the python code. This will allow you to run the code and retrieve the flag.

I began this challenge by noting that the output of Circuit 1 is boolean A OR B. I called this result C.

The output of Circuit 2 is boolean A NAND B. I called this result D.

The output of Circuit 3 is then C AND D. I called this output E.

Working this into the provided Python program, you can code this as:

def magic_func(A, B):
    C = A | B
    D = not(A & B)
    E = int(C & D)
    o = E
    return o

Running this program will return the flag, which suggests there might be a cleaner solution….

ATR[3way_light_switches_are_xor]

Let’s create a logic table, showing what E is for given values of A and B:

Comparing output E with the original inputs A and B, we see that it is an XOR function, as the flag suggested. We can therefore clean up the code as follows, obtaining the same result:

def magic_func(A, B):
    o = int(A ^ B)
    return o