Architecture

MikroText is a static browser app paired with an in-memory Node relay.

Runtime Boundaries

• The browser creates room keys, invite tokens, and participant signing keys.
• The browser derives per-message keys, encrypts, and signs messages before upload.
• The relay authenticates participant sessions and stores encrypted envelopes.
• Other browsers fetch room state, verify signatures, and decrypt locally.
• Room state disappears on expiry, burn, or API restart.

Browser App

The app is written in vanilla JavaScript, HTML, and CSS, then bundled with esbuild.

The browser stores active room data in sessionStorage:

• room ID
• room key
• participant ID and pseudonym
• session token
• signing public/private key pair
• sender chain key and message index
• participant list

Closing the browser session removes practical access unless an invite URL is still usable.

Relay API

The API is written in TypeScript with MikroServe. It handles:

• room creation
• one-time invite creation and consumption
• participant session authorization
• ciphertext relay
• room state polling
• room burn
• expiry cleanup

The relay does not decrypt, inspect, index, search, preview, or summarize message content.

Protocol Shape

Messages use a small envelope:

• server-assigned message ID
• room ID
• server-authenticated sender ID
• AES-GCM nonce
• message key version
• sender chain ID and message index
• encrypted sender chain-key checkpoint
• ciphertext
• ECDSA signature
• creation and expiry timestamps

Version 3 envelopes sign the room ID, sender ID, key version, sender chain metadata, chain-key checkpoint, nonce, and ciphertext.

The sender chain advances after each message. This improves on static room-key encryption, but it is not a full Double Ratchet because the room key still bootstraps checkpoints for reload and polling recovery.

Source Layout

The server code uses a shallow domain/application/infrastructure split:

• src/interfaces defines request, response, and protocol contracts.
• src/domain contains room policy, validation, errors, and envelope rules.
• src/application contains the in-memory relay service.
• src/infrastructure adapts the application service to HTTP.
• src/shared holds small generic helpers.

MikroText keeps this split small while the relay remains in-memory.

Build Outputs

• dist/ - static browser app
• dist/config.json - public browser runtime config, including apiBaseUrl
• lib/mikrotext.mjs - Node relay bundle