# A Secure and Lightweight Group Mobility Authentication Scheme for 6 LoWPAN Networks
## 3 System Background
### Network Model  
As shown in Figure 1, the components of the network model are explained as follows:  
* The 6 LoWPAN mobile nodes (6L\({}_{\text{MNi}}\)): There are two categories of 6L\({}_{\text{MNi}}\), which are portable devices utilized for gathering sensory data. Full Function Devices (FFDs) are devices with full functions, while Reduced Functions Devices (RFDs) have limited functions. There is sufficient power and memory in FFDs to enable them to be used as routers, while RFDs cannot serve as routers. Whenever a cluster of 6L\({}_{\text{MNi}}\) is in operation, the supervisory node or group leader (6L\({}_{\text{MNGL}}\)) must be an FFD responsible for managing. Mobility-related messages are sent between the mobile access gateways and the supervisory node. All 6 LMNi nodes in a 6 LoWPAN network can move as a group across multiple domains.
* The 6 LoWPAN mobile access gateways (6 LMAGs): It is 6 LMAGs' responsibility to track the movement of the 6 LMNi to transmit mobility-related signals to the local mobility anchor (LMA). Data packets are transmitted between 6 LMAGs and an LMA using a bidirectional tunnel. The hierarchical architecture of 6 LMAGs ensures that a compromised 6 LMAGs affects only its connected nodes. The integrity of the data is protected by integrity checks and mutual authentication.
* LMA: Among its responsibilities is maintaining the binding states of all 6 LMNi currently attached to the router; in addition, every registered node is assigned a unique network prefix. This enables a 6 LMNi to configure its IP address by its needs. LMA is used to route messages intended for these addresses. Deploying redundant LMA instances with secure failover mechanisms is essential to ensure network resilience. This strategy allows backup LMAs to maintain network operations seamlessly in the event of a compromise. Regularly updating cryptographic keys and employing secure storage techniques minimize potential attacks' impact by limiting the window of opportunity for exploitation. Additionally, protecting communication channels between the LMA and other network entities with secure protocols, such as IPsec or TLS, ensures transmitted messages' confidentiality, integrity, and authenticity.
* The accounting, authorization, and authentication server (AAA): AAA's important function is to identify and authenticate 6 LMNi users and authorize their access to the network. Policy files of the 6 LMNi are stored in AAA as configuration information. A wired link is established between the 6 LMAGs, LMA, and AAA using high-speed copper cables with a low bit error rate. Signaling messages are protected by Internet Protocol Security (IPsec), which offers authentication, confidentiality, and integrity of data, as well as other network security services [21]. Establishing secure associ  
Figure 1: A group handover transitioning from one gateway to another in a 6 LoWPAN-based PMIPv6.  
ations using the Internet Key Exchange Protocol version 2 (IKEv2) to pre-share the symmetric keys between different parties is also possible. Despite IKEv2 and IPsec being mandatory with IPv6, they may not be appropriate for 6L\({}_{\text{MNi}}\) due to their insufficient capabilities.