## 2 Related Work
### Secure Authentication of Cluster Head  
Secure authentication of cluster head utilizes authentication and secure data aggregation optimized methods to authenticate each USN or cluster node (CN) in the UVWSN. Therefore, cluster heads (CHs) [23] are a gateway between UNS and BS. CH deployment is vital in securing data aggregation and authentication in the UVWSN.  
In addition, through the secure authentication of CH, route establishment among clusters and all the CHs are authenticated to a GW. Here, every CH in the network initially generates a secret key and sends a registration request with a GW. CH further creates a hash value and signs it. Thus, CH uses a secret key and sends a request to another GW. The request is decrypted at GW using the public key of CH. CH also retrieves the time stamp. GW generates registration confirmation using the hash value received, including the time stamp. Both hash values are compared. Whenever any variation is observed, it is ignored, and this further authenticates CH. GW sends a registration response to CH after signing the hash value. Thus, CH uses the secret key of GW. Subsequently, CH determines that it has been authenticated. It does that by decrypting the registration response received using the public key of a GW. The process of CH authentication is also described in Algorithm 1.  
Figure 2: System model for secure data aggregation and authentication in cluster-based network design.  
```
1. Every \(CH\) initially generates \(SK_{CH}\).
2. \(CH\) creates \(CH_{RR}\) which consists of \([CH_{id}\), \(GW_{id}\), \(T_{s1}]\)
3. \(CH\) signs \(T_{s1}\) with \(SK_{CH}\) to create \(SK_{CH}\) (\(T_{s1}\))
4. \(CH\) generates a hash value of \(CH_{RR}\) as \(H_{1}=H\) (\(CH_{id}\), \(GW_{id}\), \(T_{s1}\))
5. \(CH\) generates \(M_{RREQ}\) by signing \(H_{1}\) using \(SK_{CH}\) as \(M_{RREQ}=SK_{CH}\) [\(H\) (\(CH_{id}\), \(GW_{id}\), \(T_{s1}\))]
6. \(CH\) sends \(SK_{CH}\)(\(T_{s1}\)) and \(M_{RREQ}\) to \(GW\)
7. \(GW\) decrypts \(SK_{CH}\)(\(T_{s1}\)) using \(PK_{CH}\) and retrieves \(T_{s1}\)
8. \(GW\) decrypts \(M_{RREQ}\) using \(PK_{CH}\) and retrieves \(CH_{RR}\)
9. \(GW\) creates hash value of \(CH_{RR}\) as \(H_{2}=H\) (\(CH_{id}\), \(GW_{id}\), \(T_{s1}\))
10. GW compares \(H_{1}\) and \(H_{2}\)

If \(H_{1}\) does not match with \(H_{2}\),

Then, \(GW\) discards \(M_{RREQ}\)

Else \(GW\) confirms that \(CH\) is a valid node.

\(GW\) creates as \(CH_{C}\) [\(CH_{id}\), \(GW_{id}\), \(T_{s2}\)]

\(GW\) creates hash value of \(CH_{C}\) as \(H_{3}=[H\)(\(CH_{C}\))]

\(GW\) signs [\(H\) (\(CH_{C}\), \(T_{s2}\))] using \(CK_{CW}\) to create \(M_{RRES}\) as \(M_{RRES}\)\(=SK_{CH}\) [\(H\)(\(CH_{C}\))]

\(M_{RRES}\) is sent to \(CH\) by \(GW\)

End If

11. \(CH\) decrypts it using \(PK_{GW}\) and retrieves \(H\) (\(CH_{C}\), \(T_{s2}\))
12. \(CH\) determines that \(GW\) has authenticated it
```  
**Algorithm 1**Cluster head authentication process  
Following, a GW individually and securely authenticates every CH. This ensures that any vulnerable or malicious node attacker (MNA) encountered in the UVWSN does not control the cluster operation, protecting the cluster from being compromised. Table 1 shows the used notation of the proposed secure authentication algorithm.