The one asymmetric step in sharing is sealing the capability to a per-friend folder to the friend's public key, with a hybrid of X25519 and ML-KEM-1024 so that recording it today is useless to a future quantum computer; later shares go into that folder; unshared files need none of this.

Sharing is where long-term secrecy is at risk.

Sharing starts with one sealed message: the capability to a folder you made for that friend. A card works for whoever holds it. The seal to their public key is what keeps it private. Everything you share later goes into that folder.

Here is the catch. Someone can record that sealed card today, and wait for a quantum computer.

So the seal uses two locks. X twenty five five nineteen, and ML KEM ten twenty four, a post quantum scheme.

An attacker must break both. What you share today stays sealed if one of them falls.

Files you never share need none of this. Hashing and symmetric encryption are not much weakened by a quantum computer.

Check yourself. Which files are already safe from a quantum computer, and why?