Use a secure encryption scheme

[AndyVale]

Currently, the repository uses an XOR-based scheme with a fixed key derived from a secret. This approach is not secure and can be vulnerable to attacks (e.g., known-plaintext attacks).

I noticed that the code already mentions replacing this with a more robust encryption scheme (e.g., AES-GCM) at a later stage. However, I thought it might be useful to track this as an issue.

I’d be happy to work on this if you think it’s worth addressing at this stage.