End-to-end key setup
Difficulty 3 of 5
Alice wants to send Bob an end-to-end encrypted first message while his phone is offline. The server only relays data and must never see a private key. Put the key setup in order, from Bob's first install to Bob reading the message.
Put these steps in order
- Alice's phone makes a fresh key and combines it with Bob's keys into a shared secret
- Alice's phone downloads Bob's key bundle, with one one-time prekey
- Bob's phone builds the same secret, reads the message and deletes the used prekey
- Bob's phone makes an identity key, a signed prekey and one-time prekeys
- Alice sends the first message with her public keys and the ID of the prekey she used
- Alice's phone checks the prekey signature with Bob's identity key
- Bob's phone uploads the public keys and the prekey signature to the server
Goals and limits
- p99 latency
- under 400 ms
- Monthly cost
- under 10 USD/mo
- Traffic
- 100 req/s
Concepts
How players did
Player results load from the server.