The key descriptor carried by every message of a four-way handshake.
Reading a capture
Defined by 802.11 rather than by 802.1X, even though it travels in an 802.1X frame. That split is why the citation changes at this boundary and not at the one above it.
Subfields
Descriptor Type — Which key descriptor this is. 2 for the RSN descriptor.
Key Information — The bits that say which message of the handshake this is and what the receiver should do with it.
Key Length — Length of the pairwise key to be installed, in octets. 16 for CCMP-128.
Key Replay Counter — Increments per exchange, and a reply must carry the counter of the message it answers.
Key Nonce — A number used once. The AP's in message 1, the station's in message 2.
EAPOL Key IV — An initialisation vector for the older RC4 key wrap.
Key RSC — The starting packet number for the group key being installed.
Key MIC — Proof that the sender derived the same pairwise key, computed over this whole EAPOL frame with this field zeroed.
Key Data Length — Octets of key data following. Zero in message 4.
Key Data — The RSN element in messages 2 and 3, plus the wrapped group key in message 3. Empty in messages 1 and 4.