Encryption and your users in Express

What your app sends through WordPlus Cloud is sealed on the way: the realtime servers carry it, and keep the history of a room, without being able to read or change it. You write no encryption code. Your server holds the keys and gives each user the ones they may have. The page opens everything before your listener sees it.

What is sealed

What	Sealed with	Who can open it
Events to a room, from your server or a page, and its kept history	the room key	whoever the room rule lets in
The info of a presence member	the room key	the same
Events your server sends a user (toUser)	the key of the user	the pages of that user
What the people in a call see of each other	the day key	everyone your app knows
Your users in the directory	the day key	everyone your app knows
The media of a call	a key for that call	its people

A room declared public: true is not sealed, and neither is one with seal: false. The realtime servers see room names, event names, user ids, which key a value needs, and sealed values. They never hold a key.

Your local key

WORDPLUS_LOCAL_KEY is the master every key is derived from. Keep it the same on every server of the app (Node, PHP and Python derive the same keys from it), as long as the app, and out of every page. A new one means pages holding old keys cannot open what comes, until they reload, and the history kept before cannot be opened at all.

When someone loses access

Move a key on, and what comes next is sealed from them. That needs a store every server of the app shares, for the key generations:

import { createClient } from 'redis';

const redis = await createClient( { url: process.env.REDIS_URL } ).connect();

const realtime = createRealtime( {
    // …
    generations: {
        get: async ( name ) => Number( await redis.get( 'wordplus:gen:' + name ) ) || null,
        set: ( name, n ) => redis.set( 'wordplus:gen:' + name, String( n ) ),
    },
} );

await realtime.in( 'chat:34:42' ).kick( 43 );   // out of the room now, and its key moves on
await realtime.rotateRoom( 'order:1042' );      // an order moved to another customer
await realtime.rotateUser( userId );            // their own key moves on

Those still let in get the new key from your server with the next event, and keep the old ones for the history before it.

Your users

A directory of your users, each profile sealed with the day key, that every page of your app reads. Your server says what a user profile is:

createRealtime( {
    // …
    profile: async ( user ) => {
        const person = await db.users.find( user );
        return person ? { name: person.name, avatar: person.avatarUrl, url: `/people/${ person.id }` } : null;
    },
} );

const users = await rt.users( [ 34, 42 ] );   // { 34: { user_id: 34, name: 'Ann', avatar: '…' }, 42: { … } }

• A user is in the directory once they have connected: a page sends its user identity, signed by your server with their profile, and may then read those of others. Ask again when someone comes online for a user not there yet.
• The same profile is what the ready-made parts and calls show of them, and the info of a presence member when the rule gives none.

Your own sealed values

realtime.kind( 'note', async ( rest, user ) => user !== null && ( await mayRead( user, rest ) ) );
const sealed = await realtime.keys.seal( JSON.stringify( note ), 'note:' + note.id );   // send it any way you like

import { keyring, labelOf } from '@wordplus/realtime';

await keyring().ensure( [ labelOf( sealed ) ] );   // asks your keys route for `note:…` if the page lacks it
const note = keyring().openJson( sealed );         // undefined when this user may not have it

The key derivation, and every label: encryption in depth.