You can try the first discovery and the 3D controls now. Stella unlocks every stage.
Public-key Cryptography: Sharing a Secret Without Sending the Key
Move between Alice, Bob, and Eve to explore the key-distribution problem, one-way functions, Diffie–Hellman, public-key padlocks, certificates, and the TLS handoff to a symmetric session key.
How do you hand over a secret key?
Symmetric encryption, where the same key locks and unlocks, is fast and good at protecting the message body. But first that key has to reach the other side while staying secret. Send the key itself down a public channel and Eve, sitting in the middle, can copy it too. This is the key-distribution problem, still standing since the Enigma era.
Send the shared key and watch Eve see the same key partway down the channel.
You can try the first discovery and the 3D controls now. Stella unlocks every stage.