TLS 1.3 : Base Key Meaning

Question

What is significance of following Base Key in TLS1.3 draft (28).

1. server_handshake_traffic_secret
2. client_handshake_traffic_secret
3. client_application_traffic_secret_N

So far I understand

1. server_handshake_traffic_secret should be private key using which certificate has been acquired.

2. client_handshake_traffic_secret ??

3. client_application_traffic_secret_N should be symmetric keys established after the handshake where N denotes number of up-gradation in keys after handshake.

Please suggest correction and explanation for client_handshake_traffic_secret . Thanks.

Answer 1

See sections 7.2 and 7.3 of the draft.

Each secret is used by a specific endpoint (client or server) at a specific moment of the exchange: so first the handshake secrets are used then the application ones, and keys are derived from the secrets.

So the server_handshake_traffic_secret is what the server side uses to exchange data during the handshake and client_handshake_traffic_secret is the exact equivalent from the client part.