Sixth-generation (6G) wireless communication is anticipated to support massive sensor connectivity, real-time intelligence, and ultra-reliable services, thereby intensifying security requirements in Wireless Sensor Networks (WSNs). Conventional cryptographic solutions often impose excessive computational and energy overhead on sensor nodes, limiting their applicability in 6G environments. In this work, a lightweight security framework based on Elliptic Curve Cryptography (ECC) is presented for Software-Defined Networking (SDN)–controlled 6G Wireless Sensor Networks. The proposed framework exploits discrete elliptic curve structures over finite fields to provide secure key establishment and data confidentiality with minimal resource consumption. SDN is employed to decouple control and data planes, enabling centralized policy enforcement, adaptive key distribution, and programmable security management.