 key, the TK, and the TSCO and TSC1 vectors. The TTAK constitutes an intermediary key produced during phase one. Phase 1 Key Mixing Initialisation vector Phase 2 RC4 key Key Mixing process (transmission) Ciphered DA/SA Priority Fragmentation MICHAEL Figure 2.19. TKIP processing of the transmission chain The processing of the reception chain is shown in Figure 2.20. Phase 1 Key Mixing Phase 2 Key Mixing RC4 key Ciphered MICHAEL Fragment process assembly (reception) Clear Clear Figure 2.20. TKIP processing of the reception chain Wi-Fi Integration to the 4G Mobile Network The receiver extracts the TSC fields from the TKIP header and verifies the sequencing in order to protect itself from replays. The combination of the TSC fields with the TK and the MAC transmit address (TA) enables the initialization vector and the RC4 key to be reconstituted for the WEP decryption. If the WEP processing indicates a positive check from the ICV field, the fragments are reassembled. The result of the MIC seal calculation using the MIC key and unscrambled MSDU data is compared to the value of the MIC field received. If the two values match, the integrity control is positive and the MSDU data are accepted. 2.3.3.3. CCMP The CCMP adds 16 bytes to the MAC header (Figure 2.21): - eight bytes for the CCMP header; - eight bytes for the MIC seal. The CCMP header resembles the TKIP header. It is constructed from the packet number (PN), the ExtIV field, coded on one bit and indicating the presence (bit set at ONE) of the PN2 to PN5 fields, and the KeyID field, coded on two bits, used to select a key from among four possible keys. 4 bytes 4 bytes 8 bytes 4 bytes header header Ciphered part 1 byte 1 byte 1 byte 1 byte 1 byte Reserved 1 byte b0 to b4 Reserved 1 byte Ext IV b6, b7 KeyID Figure 2.21. Format of CCMP encapsulation MAC Layer The processing of the transmission chain is shown in Figure 2.22. header construction Address 2 Nonce Priority construction Ciphered Algorithm increment TK key Clear Figure 2.22. CCMP processing of the transmissio