Emerging applications in 6G networks, such as autonomous driving management, mixed reality games, and industrial robotics, demand robust security solutions for seamless integration of sensing, communication, computing, and networking at the edge. Addressing the critical need for secure multi-user interactions, we introduce Suitcase, a novel group key agreement framework designed for edge intelligence in 6G environments. Based on the principle of positional similarity and leveraging threshold encryption and secure information share schemes, Suitcase ensures consistent key generation across devices without requiring information conciliation. and facilitates key pieces pre-distribution, overcoming traditional limitations in multi-user group encryption. Implemented using off-the-shelf devices, Suitcase demonstrates superior safety and effectiveness through extensive experimental validation, making it a promising solution for secure edge intelligence in 6G networks.