Key Information Key Info

The bits that say which message of the handshake this is and what the receiver should do with it.

Reading a capture

Read these four in order and the whole exchange falls out: Key Ack set with no MIC is message 1, MIC with no Ack is message 2, both set with Install is message 3, and Secure with a MIC and nothing to install is message 4. There is no message-number field — this is the message number.

Subfields

• Key Descriptor Version — Which algorithms compute the MIC and wrap the key data.
• Key Type — Set for a pairwise key, clear for a group key.
• Install — Tells the receiver to install the derived pairwise key for use.
• Key Ack — A response is expected to this message.
• Key MIC — The MIC field further down is populated.
• Secure — Both sides now hold the keys; protection is established.
• Encrypted Key Data — The Key Data field is wrapped rather than plaintext.

Where it sits

EAPOL-Key > Key Information

• Open in the explorer — Four-way handshake message 1
• Open in the explorer — Four-way handshake message 2
• Open in the explorer — Four-way handshake message 3
• Open in the explorer — Four-way handshake message 4

Accuracy

Clause

802.11-2024 §12.7.2

Byte order

big-endian — network byte order

Verified

Not verified against the standard. Treat this as a claim, not a fact.