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traffic secret / traffic keys
The per-direction keys TLS derives to encrypt the actual data flowing each way.
After the handshake, TLS derives a traffic secret for each direction, and from it the traffic keys that encrypt and authenticate records. They are bound to a transcript hash of the handshake, so the keys are cryptographically tied to exactly what was negotiated. Separate keys per direction and per session limit the damage if any one is compromised.
See also
- transcript hashA running fingerprint of every handshake message, used to lock the keys to what was actually said.
- TLS 1.3 record layerThe part of TLS 1.3 that chops the data stream into chunks and encrypts each one.
- TLS 1.3The current, streamlined version of the TLS encryption protocol.