Which cryptography does Tor use to set up a connection versus to carry the actual data?

Tor uses asymmetric RSA + Diffie-Hellman to negotiate keys during setup, then encrypts all in-network user data with fast symmetric AES.

When the client connects to the first node:

1. An asymmetric RSA key is used to negotiate a symmetric key.
2. A Diffie-Hellman key exchange generates further symmetric keys for the deeper layers.
3. Once the circuit is established, all user data inside the Tor network is encrypted with AES (symmetric).

This mirrors the general crypto pattern: public-key crypto is expensive, so it's used only briefly to bootstrap trust and exchange keys, after which fast symmetric crypto (AES) handles the bulk traffic.

Tip: Asymmetric to agree on a secret, symmetric to use it — the same hybrid design as TLS.