The goal is to move mobile cellular wireless technology into its fourth generation by using 3GP Long Term Evolution/System Architecture Evolution (LTE/SAE) .To close a security gap through which a single compromised or malicious device can endanger an entire mobile network because of the open nature of these networks is one of the unique challenges of fourth-generation technology. To revoke any compromised key(s) and as a consequence isolate corrupted network devices Hand over key management in

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... the 3GPPLTE/SAE has been designed.This.paper, identifies .and .details .the .vulnerability .of. this hand over key management to what are called resynchronization attacks; such attacks jeopardize secure communication between users and mobile networks. Although period updates of the root key are an integral part of hand over key management, our work here emphasizes how essential these updates are to minimizing the effect of resynchronization attacks that ,as of now ,cannot be effectively prevented. Our main contribution, however, is to explore how network operators can determine for themselves an most favorable interval for updates that minimizes the signaling load they impose while protecting the security of user traffic. Our analytical and simulation studies demonstrate the impact of the key update interval on such performance criteria as network topology and user mobility.