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1337UP LIVE CTF 2023

Keyless

My friend made a new encryption algorithm. Apparently it's so advanced, you don't even need a key!

Author: CryptoCat

keyless.zip

Tags: crypto

Solution

We get the following python code:

def encrypt(message):
    encrypted_message = ""
    for char in message:
        a = (ord(char) * 2) + 10
        b = (a ^ 42) + 5
        c = (b * 3) - 7
        encrypted_char = c ^ 23
        encrypted_message += chr(encrypted_char)
    return encrypted_message

flag = "INTIGRITI{REDACTED}"
encrypted_flag = encrypt(flag)

with open("flag.txt.enc", "w") as file:
    file.write(encrypted_flag)

All steps can be reversed quite easily, so we write a script to do so, and get the flag.

flag = open("flag.txt.enc", "r").read()

def decrypt(message):
    result = ""
    for char in message:
        char = ord(char) ^ 23
        char = (char + 7) // 3
        char = (char - 5) ^ 42
        char = (char - 10) // 2
        result += chr(char)
    return result

print(decrypt(flag))

Flag INTIGRITI{m4yb3_4_k3y_w0uld_b3_b3773r_4f73r_4ll}