## 2 Related Work and Design Challenges
### Related Work on Privacy Preserving Wireless Sensor Network including Secure Data Aggregation
The CBDA method did not use any authentication and authorization mechanisms in the proposed scheme. The privacy-preserving secure data aggregation approach involves two main techniques: the first technique applies cryptography to allow the aggregation process to decrypt the data aggregation or sum with different keys. The second technique uses the differential privacy approach to protect data from being compromised [30]. Consequently, the authors in [31] proposed an energy-preserving approach named secure data aggregation watermarking (SDAW) based in homogeneous WSNs. SDAW used lightweight, fragile watermarking without encryption to guarantee integrity and authentication. Malicious nodes in the network can attempt to inject false data to mislead the nodes and gather important information due to the limitation of authorization in the network. The proposed SDAW did not use any authentication and authorization security mechanism in the proposed scheme. Therefore, adversarial or malicious nodes in WSNs result in confidentiality concerns and compromise data. The compromised data cause additional energy consumption in the network and subsequently lead to communication overhead. As a solution to compromised data, a practical secure data aggregation (SDA) approach was proposed in [32] to ensure data privacy and prevent excess energy consumption. This SDA approach used additive homomorphic, identity-based signatures and batch verification schemes with a proposed algorithm to filter false data injected by malicious nodes without authorization, leading to communication overhead concerns. However, the proposed SDAAA security mechanism methodology needs an authentication and authorization mechanism. These design challenges in the privacy-preserving secure data aggregation protocols and well-known approaches such as SD, EEHA, HAS, IIF, and RHC (discussed in Section 1) must be outlined and investigated in WSNs. Design Challenges of SD, EEHA, HAS, IIF, and RHC, including Other Privacy-Preserving Secure Data Aggregation Protocols  
As noted in the preceding discussion, privacy-preserving wireless sensor networks' secure data aggregation protocols and the contending protocols, such as SD, EEHA, HAS IIF, and RHC, experience various network design challenges based on the following. 1. SD, EEHA, HAS, IIF, and RHC secure data aggregation protocols incur QoS concerns and communication overhead due to the absence of authentication, encryption, and authorization [33] security control mechanisms. The absence of these security control mechanisms leads to privacy preservation concerns such as data confidentiality and data integrity. SD, EEHA, HAS, IIF, and RHC secure data aggregation protocols and other privacy-preserving wireless sensor network secure data aggregation incur access control security mechanism concerns. The access control security limitation leads to data redundancy because of limited authorization security control mechanism that would authorize only legitimate SN to be part of the network. * SD, EEHA, HAS, IIF, and RHC secure data aggregation protocols, and other privacy-preserving wireless sensor network secure data aggregation protocols encounter network throughput issues. The throughput issue is due to vulnerable SNs and all other cyber-attacks. Hence, privacy protections were unavailable in their networks due to limited authentication and authorization security control mechanisms in the networks. * SD, EEHA, HAS, IIF, and RHC secure data aggregation protocols and many other privacy-preserving secure data aggregation protocols experience energy efficiency issues, leading to a shorter sensor node lifespan. Therefore, improving a network's residual energy efficiency algorithm using authentication and authorization security control mechanism is essential to ensure the network's availability. * SD, EEHA, HAS, IIF, and RHC secure data aggregation protocols and many other privacy-preserving wireless sensor network secure data aggregation protocols have experienced the ability to manage node failure.