Wireless Body Area Network (WBAN) is one of the best modern inventions that supports medical science significantly. Reliability, Latency, Security and Power consumption are the vital parameters to determine the quality of a WBAN architecture. Security Key Generation and Authentication are the important tasks which impact the vital parameters. A Body Gauss-Markov Mobility model (BGMM) based lightweight key generation and authentication method is introduced in this work to improve the quality of WBAN. Enhanced BGMM, Legacy Key Generator and Idle State Key Manager are the three functional blocks used to construct the proposed system. These new function blocks are introduced in this work to achieve higher throughput, packet delivery ratio and security. The proposed work is also indented to reduce the communication delays and power consumption. Adopting new body sensor nodes and discarding unused or damaged nodes from existing network without affecting other operating nodes is the requirements of modern WBAN as well. The proposed method named as “Enhanced BGMM based Lightweight Key Generation and Authentication method for WBAN” (EBLKGAW) is deigned to manage the network stability during adaptation of new nodes and elimination of existing nodes.