# A Secure and Lightweight Group Mobility Authentication Scheme for 6 LoWPAN Networks
## 3 System Background
### Threat Model  
SL_GAS was designed based on the DY, CK, and eCK adversary models, which are summarized in Figure 2 based on the key security attributes considered. Despite insecure communication channels, all models differ in terms of adversary query capability.  
The DY threat model considers communication parties to be honest and allows them to operate multiple sessions simultaneously [4]. There is a high level of security throughout the communication channel, and an adversary can capture, redirect, delete, rearrange, replay, and program the communication schedules. The adversary can act as the attack director for MITM attacks, resulting in various MITM techniques. The security attributes are PFS, key confirmation, key independence, and session state compromise. The CK and eCK models are widely accepted for AKE schemes. This adversary model allows attackers to access a session's secret randomness by compromising a pseudo-random number generator. The CK model considers PFS, key confirmation, key independence, and compromise of the session state. The eCK model considers ESL, key compromise impersonation, and session state compromise. An adversary may also be able to compromise the session and access it. An attacker can access long-term keys. The eCK model is inherently more vulnerable to ESL attacks than the CK model due to its major disadvantage: the adversary can access ephemeral secrets [22]. As a result of the leak of ephemeral keys, it appears that the attacker is capable of determining the randomness generated by the generator with high probability. Specifically, SL_GAS is designed to secure the 6 LoWPAN against the following attacks:  
* Replay attack: A malicious actor intercepts legitimate packets and retransmits them at a new time or place, typically intending to cause resource depletion. A replay protection mechanism between LMA, 6L\({}_{\text{MAG}}\), and 6L\({}_{\text{MNi}}\) (e.g., timestamps and nonces) detects and blocks malicious behavior on the channel when integrity checks (e.g., HMAC) are violated or compromised.
* Impersonation attacks involve adversaries attempting to assume the identities of access and mobility functions, 6L\({}_{\text{MNi}}\), 6L\({}_{\text{MAG}}\), and AAA, to deliver packets using their credentials.  
Figure 2: Key security attributes considered in DY, CK, and eCK adversary models.  
* Unauthorized access refers to the attempt made by external attackers, who are not authorized node 6L\({}_{\text{MNi}}\), to gain access to the network. Intra-group messages are encrypted at the group level to prevent unauthorized access.
* Session key leak and PFS: Ephemeral keys ensure each session's security and independence. However, if these keys are leaked, an attacker can decrypt communications, impersonate nodes within the session, and compromise forward secrecy. Ephemeral keys provide forward secrecy as one of their primary purposes, meaning that capturing these keys allows attackers to decrypt past communications, thus undermining both session-specific security and the overall integrity of the communication system. AAA and destination 6L\({}_{\text{MNi}}\) establish a shared key during handover protocols. With this key, a malicious 6L\({}_{\text{MAG}}\) entity may attempt to retrieve the past keys employed by the AAA and those utilized in forthcoming communications.
* MITM attack: A malicious node attempts to create a shared key with the AAA, LAM, 6L\({}_{\text{MAG}}\), and 6L\({}_{\text{MNi}}\). This allows the attacker to manipulate and decrypt the messages being sent.
* DoS attack involves an assailant engaging in malicious actions to obstruct a legitimate user's access to network resources.
* A privacy-preserving authentication system safeguards the confidentiality of all device information during the authentication process by employing privacy protection measures.