 in the EPC/UE from key material that was generated by a NAS (EPC/UE) level 8.8 3GPP LTE security aspects DL Synchronization AAI_RNG-REQ (MS ID* is transmitted over the air) AAI_RNG-RSP (TSTID is assigned by the BS) Basic Capability Negotiation MS Authentication and Authorization Key Exchange AAI_RNG-REQ (MS ID is transmitted over the air) AAI_RNG-RSP (STID is assigned by the BS) Data and Control Plane Establishment FIGURE 8-6 User identity protection during network entry [2] AKA procedure' iv (KASME) and is identified with a key identifier (KSIASME) The eNB key (KeNB) is sent from the EPC to the eNB when the UE is entering ECM-CONNECTED state, i.e., during RRC connection or S1 context set-up. Separate AS and NAS level security mode procedures are used. The AS level security mode procedure configures AS security (i.e., RRC and user-plane) and the NAS iv The Authentication and Key Agreement (AKA) mechanism is based on challenge-response mechanisms and symmetrical cryptography. The AKA scheme typically operates in a UMTS Subscriber Identity Module (USIM) or a cdma2000 Removable User Identity Module (RUIM). The third generation AKA provides substantially longer key lengths and mutual authentication compared to the second generation mechanisms, such as GSM AKA. The introduction of AKA inside EAP further enables several new applications, including the use of the AKA as a secure PPP authentication method in devices that already contain an identity module, the use of the third generation mobile network authentication infrastructure in the context of wireless LANs, as well as relying on AKA and the existing infrastructure in a seamless way with any other technology that can use EAP. In AKA, the identity module and the home environment have agreed on a secret key in advance. The "home environment" refers to the home operator's authentication network infrastructure. Furthermore, the actual authentication process starts by having the home environment produce an authentication vector, based on the secret key and a sequence n