Which of the following is an infrastructure system that allows the secure exchange of data over an
unsecured network?
A.
PMK
B.
PTK
C.
PKI
D.
GTK
Explanation:
A PKI (public key infrastructure) enables users of a basically unsecured public network
such as the Internet to securely and privately exchange
data and money through the use of a public and a private cryptographic key pair that is obtained and
shared through a trusted authority. The
public key infrastructure assumes the use of public key cryptography, which is the most common
method on the Internet for authenticating a
message sender or encrypting a message.
Answer option D is incorrect. Group Temporal Key (GTK) is a random value that is assigned by the
broadcast/multicast source. It is used to
protect broadcast/multicast medium access control (MAC) protocol data units. It is derived from a
group master key (GMK).
Answer option B is incorrect. Pairwise Transient Key (PTK) is a 64-byte key that comprises the
following:
16 bytes of EAPOL-Key Confirmation Key (KCK): This key is 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.
16 bytes of Temporal Key (TK): This key is used to encrypt/decrypt unicast data packets.
8 bytes of Michael MIC Authenticator Tx Key: This key is used to compute MIC on unicast data
packets transmitted by the AP.
8 bytes of Michael MIC Authenticator Rx Key: This key is used to compute MIC on unicast data
packets transmitted by the station.
Pairwise Transient Key is derived from the pairwise master key (PMK), Authenticator address (AA),
Supplicant address (SPA), Authenticator
nonce (A Nonce), and Supplicant nonce (S Nonce) using pseudo-random function (PRF).
Answer option A is incorrect. Pairwise Master Key (PMK) is the highest order key used within the
802.11i amendment. It is derived directly from
a preshared key and can also be derived from the Extensible Authentication Protocol (EAP). It is a
cryptography key that is used to derive
lower level keys.