Which key is established using the four-way handshake during the WPA authentication process?
A.
Pairwise Master Key
B.
Pairwise Multiple Key
C.
Pairwise Session Key
D.
Pairwise Transient Key
E.
Pairwise Transverse Key
Which key is established using the four-way handshake during the WPA authentication process?
Which key is established using the four-way handshake during the WPA authentication process?
The authentication process leaves two considerations: the access point (AP) still needs to authenticate itself to the client station (STA), and keys to encrypt the traffic need to be derived.
The earlier EAP exchange or WPA2-PSK configuration has provided the shared secret key PMK (Pairwise Master Key). To derive the PMK from the WPA-PSK, the PSK is put through PI3KDF2- SHA1 as the cryptographic hash function.
This key is, however, designed to last the entire session and should be exposed as little as possible. Therefore the four-way handshake is used to establish another key called the PTK (Pairwise Transient Key).
transient
The four-way handshake is designed so that the access point (or authenticator) and wireless client (or supplicant) can independently prove to each other that they know the PSK/PMK, without ever disclosing the key. Instead of disclosing the key, the access point & client each encrypt messages to each other—that can only be decrypted by using the PMK that they already share—and if decryption of the messages was successful, this proves knowledge of the PMK. The four-way handshake is critical for protection of the PMK from malicious access points—for example, an attacker’s SSID impersonating a real access point—so that the client never has to tell the access point its PMK.
The PMK is designed to last the entire session and should be exposed as little as possible; therefore, keys to encrypt the traffic need to be derived. A four-way handshake is used to establish another key called the Pairwise Transient Key (PTK). The PTK is generated by concatenating the following attributes: PMK, AP nonce (ANonce), STA nonce (SNonce), AP MAC address, and STA MAC address. The product is then put through a pseudo random function. The handshake also yields the GTK (Group Temporal Key), used to decrypt multicast and broadcast traffic.
The STA sends a confirmation to the AP.
The Pairwise Transient Key (64 bytes) is divided into five separate keys:
16 bytes of EAPOL-Key Confirmation Key (KCK)– Used to compute MIC on WPA EAPOL Key message
16 bytes of EAPOL-Key Encryption Key (KEK) – AP uses this key to encrypt additional data sent (in the ‘Key Data’ field) to the client (for example, the RSN IE or the GTK)
16 bytes of Temporal Key (TK) – Used to encrypt/decrypt Unicast data packets
8 bytes of Michael MIC Authenticator Tx Key – Used to compute MIC on unicast data packets transmitted by the AP
8 bytes of Michael MIC Authenticator Rx Key – Used to compute MIC on unicast data packets transmitted by the station