transmitted or used directly. It is only used to derive the entire
key hierarchy.
-E. Access-Stratum and Non-Access-Stratum Security
(AS/NAS)
-In contrast with UMTS, LTE incorporates a secondary
security layer with an extra encryption and hashing level.
These two layers are AS and NAS security. AS security
protects the signalling and data traffic between the UE and
the e-NodeB, where all signalling messages are confidentially
protected by KRRCenc and integrity protected by KRRCint.
User plane traffic is only encrypted using the key KUPenc,
leaving integrity protection as free choice of the operator.
-On the other hand, NAS security duplicates the robustness
of the system against attacks, incorporating another integrity
and confidentiality protection for both data flows (signalling
and user plane) between UE and MME. The keys used to
encrypt and calculate hash codes are KNASenc and KNASint
respectively.