Comment by leijurv

`for char in message: encrypted_char = ord(char) ^ (shared_secret[0] % 256)`

This is not real encryption, it picks only one byte of shared secret and XORs it into the plaintext. Therefore, there are only 256 possible decryption keys to check, which is trivial.

Instead, you'd want to use the shared secret as a key to something strong and symmetric like AES.