LTE, LTE-Advanced and WiMAX: Towards IMT-Advanced Networks

EPS Key Hierarchy

Two requirements bound the EPS key hierarchy and derivation. The first is that the EPC and E-UTRAN shall allow for use of encryption and integrity protection algorithms for AS and NAS protection having keys of length 128 and for future use the network interfaces shall be prepared to support 256 bit keys. The second is that keys for the user plane, NAS and AS protection shall be dependent on the algorithm with which they are used.

Figure 14.3 EPS Key Hierarchy and Derivation. Reproduced by permission of © 2010 3GPP. Further use is strictly prohibited.

The hierarchy, shown in Figure 14.3, includes the following keys: K_eNB, K_NASint, K_NASenc, K_UPenc, K_RRCint and K_RRCenc. A brief description of the different keys and how they are derived is provided below.

• K_eNB is a key derived by UE and MME from K_ASME. K_eNB may also be derived by the target eNB from NH at handover. K_eNB shall be used for the derivation of K_RRCint, K_RRCenc and K_UPenc, and for the derivation of K_eNB* upon handover.

Keys for NAS traffic:

• K_NASint is a key, which shall only be used for the protection of NAS traffic with a particular integrity algorithm. This key is derived by UE and MME from K_ASME, as well as an identifier for the integrity algorithm.
• K_NASenc is a key, which shall only be used for the protection of NAS traffic with a particular encryption algorithm. This key is derived by UE and MME ...