2.3. Server as an encrypted mailbox

The backend in Obscura is intentionally boring.

It does not inspect messages. It does not transform them. It does not index their contents. Its role is closer to a mailbox than to a chat engine. Messages arrive already encrypted, get stored, and are later delivered to the intended recipient.

In the current MVP, the backend stores encrypted message blobs along with basic routing information such as sender wallet, recipient wallet, and timestamps. This is enough to support a familiar messaging experience: inboxes, threads, and message history. What it does not store is plaintext or decryption keys.

This design changes the trust model. Instead of trusting the service operator to protect your data, the system assumes the backend is untrusted by default. Even if the database is copied, leaked, or inspected, it contains no readable conversations. The only place where messages exist in human-readable form is on user devices.