Mobile Network This procedure enables the two end points to derive the PTK from the PMK and the distribution of the GTK by the authenticator. The authenticator sends the first message to the supplicant if 802.1x authentication has been successful. This message contains the ANonce random number. Upon reception of the first message, the supplicant generates a random number (SNonce), derives the PTK and constructs the second message containing the message integrity code (MIC) calculated from the KCK. Upon reception of the second message, the authenticator derives the PTK, extracts the KCK from it and checks the MIC seal. The third message is sent by the authenticator to the supplicant. It contains the GTK encrypted with the KEK and an MIC seal calculated using the KCK. Upon reception of the third message, the supplicant checks that the MIC seal value is correct. The fourth message is sent by the supplicant to complete the four-way handshake procedure. Upon reception of the fourth message, the authenticator checks the MIC seal. 6.2.3. Group Key Handshake procedure The group key handshake procedure (Figure 6.7) defines two EAPOL-Key messages exchanged between the authenticator and the supplicant. It takes place when the authenticator transmits a new GTK to the supplicant. The supplicant can start the procedure by sending an EAPOL-Key message. The first message is initialized by the authenticator. It sends the new GTK encrypted with the KEK and the MIC seal calculated using the KCK. Mutual Authentication Upon reception of the first message, the supplicant checks the MIC seal. It responds to the authenticator with the second message to acknowledge the first message. Upon reception of the second message, the authenticator checks the MIC seal. Supplicant Authenticator The authenticator generates the GTK key EAPOL-Key (MIC, GTK) The authenticator encrypts the GTK key with the KEK key EAPOL-Key (MIC) Figure 6.7. Group key handshake procedure 6.3. Application to the 4G mobile network 6.3.1. EAP-AKA method The authentication 