Prototypes SealedP1 · Encrypted messages
The relay

What the relay sees

The relay shows every frame that passes between the two devices. It holds no key, so it can count, store and forward the messages, and it cannot read them.

Waiting for the first frame. Write a message on one of the devices.
TimeRouteWhatContent
How Sealed is built
  1. Each device makes an X25519 key pair when it opens, and sends only the public half. A browser without X25519 uses P-256.
  2. Each message gets a new random salt. HKDF turns the shared secret and the salt into an AES-GCM key, so no two messages use the same key.
  3. Both devices show a safety number made from both public keys. When the numbers match, nobody in the middle swapped a key.
  4. Send a changed copy flips one bit in the last message and sends it on. The receiving device refuses it, because the authentication tag no longer matches.