# A Secure and Lightweight Group Mobility Authentication Scheme for 6 LoWPAN Networks
## 4 System Models
### The Proposed Scheme (SL_GAS)
#### 4.3.3 Group Handover Phase
Subsequently, the LMA forwards a de-registration proxy binding acknowledgment (De-PBA) to 6L\({}_{\rm MAG}\)\({}^{\rm old}\) (ON) and forwards a proxy binding  
Figure 5: Group handover phase. acknowledgment (PBA) message {\(ID_{LMA}\) | \(T_{LMA}\) | \(TID_{6G}\) | \(I\)\(HNP_{List}\) | \(ICT_{NG}\) | \(ICT_{GL}\) | \(T\)\({}_{Tag^{\prime}}\)\({}_{LMA}\)} to 6L\({}_{\text{MAG}}\),new, where \(M^{\prime}\)\({}_{LMA}\) = \(E_{\text{KNG}}\)\(\leftrightarrow\)\({}_{LMA}\) (\(ID_{LMA}\) | \(T\)\({}_{LMA}\) | \(T\)\({}_{TID_{6G}}\) | \(HNP_{List}\) | \(CT_{NG}\) | \(ICT_{GL}\)). Each node is assigned an HNPList for continuous communication. * Once the PBA message is received, the 6L\({}_{\text{MAG}}\)new forwards \(CT_{GL}\) in a RA message {\(ID_{NG}\) | \(T\)\({}_{NG}\) | \(T\)\({}_{TG}\) | \(I\)\({}_{HNP_{List}}\) | \(ICT_{GL}\) | \(M^{\prime}\)\({}_{NG}\)} by the 6L\({}_{\text{MAG}}\)new to the 6 MN\({}_{\text{GL}}\), where \(K_{GL}\)\(\leftrightarrow\)\({}_{NG}\) = \(H\) (\(AID_{GL}\) | \(N_{A}\) | \(ID_{NG}\) | \(T\)\({}_{TID_{6G}}\)) and \(M^{\prime}\)\({}_{NG}\) = \(E_{\text{KGL}}\)\(\leftrightarrow\)\({}_{NG}\) (\(ID_{NG* Privacy protection (unlinkability and anonymity): The SL_GAS scheme uses alias one-time identity (_AID_) to ensure the anonymity of 6 LMNi and AAA. The real identity of 6 LMNi is concealed using secret parameters (_SPs_) and _AID_ combined with _HF_. This identity is only known to the AAA and changes with each handover. Additionally, using random numbers in each message can make identifying two messages from the same group member difficult, thereby achieving anonymity and unlinkability. * PFS: Forward key secrecy is crucial for any key agreement mechanism. Due to this property, even if the long-term key is compromised, it will be computationally impossible for a third party to predict future session keys. The SL_GAS scheme uses a new random number, _AID_, and a secret parameter (_SP_) to compute hashed session keys. Since the _SP_ is known only to the AAA, an adversary cannot discover the _SP_ or the pairwise key from the communication. Both the 6 LMNi device and the AAA generate fresh keys in each session using a random number and _SP_ value, thus ensuring complete forward key security. * Protocol attack resistance: The 6 LMNGL uses random numbers, _RX_, for the generation of MAC to ensure that the verification codes are fresh. _Replay attack_: SL_GAS resists the replay attack using random numbers, and timestamps are employed in each message with the pairwise key. An adversary might resend a previous handover request message from a legitimate 6 LMNGL, but each SL_GAS message includes a timestamp. The receiver compares the received timestamp with the current time and ignores the message if the timestamp has expired. This mechanism ensures resistance to replay attacks. A variety of security mechanisms, including group public keys, shared keys, _HF_, session keys, and _SP_, are used to protect authentication messages, which are confidential and integral. These mechanisms are resistant to impersonation attacks and MITM attacks. _Impersonation attack:_ The SL_GAS scheme ensures all legitimate devices are registered with the AAA before deployment. If an adversary tries to impersonate a node, the AAA will send a warning message to the LMA and 6 LMNGL if the secret information differs from what is stored in the database. This prevents impersonation attacks. _MITM_: In the SL_GAS scheme, an adversary cannot masquerade as a legitimate _ID_\({}_{i}\) to deceive 6 LMNi because an alias one-time identity and secret parameters, part of the shared session key, have been established through secure channels by the AAA. The adversary cannot obtain or modify the temporary session keys and thus cannot establish communication with 6 LMNi. _Sybil attacks_: A Sybil attack involves forging multiple identities to disguise numerous non-existent devices. The goal is to deceive the 6 LMAG and LMA into believing these devices communicate within the domain, potentially consuming network resources and causing DoS attacks.