Adaptive Session Key Lifetime Control for Mobility-Aware Security in SDN-Controlled LiFi 6G Networks

Light Fidelity (LiFi) has emerged as a promising wireless communication technology for enabling indoor networks in future sixth-generation (6G) systems. It can offer very high data rates, low electromagnetic interference, elevated spatial reuse and inherent physical layer security advantages. In LiFi-based indoor deployments, however, the characteristically small coverage footprint of each AP can produce frequent handovers when users move across the indoor environment. Conventional key management approaches adopt static key lifetime policies that expire session keys after a fixed duration regardless of user movement conditions. This creates a fundamental inefficiency where static policies can generate key refresh operations that are not required. Further, an additional signaling overhead can happen when users are stationary or leave session keys active for comparatively long periods under high mobility conditions. This paper proposes a lightweight mobility-aware adaptive session key lifetime control mechanism that dynamically adjusts session key validity duration. The mechanism introduces a three-component mobility metric that aggregates user speed, handover frequency and AP residence time which is used to compute a normalized mobility risk score. The mobility score drives an adaptive lifetime formula that contracts or extends key validity according to mobility-associated exposure conditions. The proposed mechanism operates entirely within the post-authentication session phase and does not introduce new cryptographic primitives, authentication protocols or key generation algorithms. Compared with fixed session key lifetime policies of 120 s, 300 s and 600 s, the Adaptive Key Lifetime Control Engine (AKLCE) dynamically adapts the session key lifetime according to user mobility, reducing refresh operations and signaling overhead under low mobility while progressively shortening the scheduled key lifetime under higher mobility to limit key exposure. This adaptive behavior enables AKLCE to provide mobility-dependent adaptation of session key lifetime that enables a flexible trade-off between key exposure duration and signaling overhead.