## 2 Related Work and Design Challenges  
### Related Work on Privacy Preserving Wireless Sensor Network including Secure Data Aggregation  
The authors in [22] proposed preserving data and key privacy (PDKP) data aggregation for wireless sensors that attained data and privacy protection of keys in data aggregation in WSN. Using simple techniques, PDKP uses encrypted data without exposing data content and its key to other SNs. The protocol preserves the key and the data content from an adversary while using less computational overhead. PDKP has no authentication and authorization mechanism in the proposed method. In [1], the authors proposed an energy-efficient and privacy-preserving data aggregation algorithm (EPDA) for less energy consumption, decreased energy consumption, and prolonged network lifetime. Sensor nodes (SNs) were organized in a tree and connected to the tree's leaf nodes to form chains. The EPDA used only sensed data through the tail SN nodes of the chains, which were sliced to ensure privacy in the network. However, no authentication and authorization mechanisms are in the proposed method. The authors in [23] proposed secure data aggregation to preserve data and key privacy (SAPDKP) in wireless sensor networks with multiple sinks to protect keys and data in the data aggregation to preserve data and critical privacy in WSNs with multiple sinks. Multiple sinks consume less energy in computation and communication overhead. However, security concerns include data confidentiality [24], data integrity freshness [25], and data authentication. SAPDKP uses a straightforward technique to perform aggregation and encryption, and uses no authorization security measures. In [12], the authors proposed multi-dimensional privacy-preserving average consensus (MPPAC) in wireless sensor networks as a solution to the privacy-preserving average consensus (PPAC) [26] problem only; this solution focused solely on a one-dimensional state, not a realistic simulation of an actual scenario. MPPAC divides nodes into two types: sink nodes and ordinary nodes. MPPAC was used to introduce a super-increasing sequence and an RSA algorithm into the network. This super-increasing sequence played a key role and dealt with any multi-dimensional measurement in the sensors, while the RSA achieved privacy, preserving average consensus only among sink nodes--however, the proposed method needed authentication and authorization mechanisms. In [27], to create an efficient privacy- and integrity-preserving data aggregation in WSNs, the authors proposed an aggregation scheme for multiple applications (PIMA) in WSNs, using homomorphic encryption which aggregates hybrid sensor data into real WSN applications. The proposed protocol had to satisfy multi-application environment requirements and make use of sensors deployed in heterogeneous environments. PIMA employed Paillier encryption and homomorphic MAC to protect data privacy and check the integrity of the aggregated data. However, there were no authentication and authorization security mechanisms in place. The authors in [28] proposed a design for a privacy and energy-efficient data aggregator (EPSDA) for WSNs. The EPSDA was proposed to overcome energy-intensive aggregator node decryption that reveals a large amount of privacy-protected information to adversaries of the network, which result in the generation of inaccurate results. The proposed EPSDA protocol overcame these limitations and performed direct aggregation on the data, encrypted using homomorphic encryption. The EPSDA restricted old data transferred in the network. However, authentication and authorization mechanisms were not proposed in the scheme. The authors in [29] proposed a novel energy-efficient and privacy-preserving data aggregation algorithm for WSN known as CBDA (chain-based data aggregation). CBDA organized sensor nodes (SNs) into tree topology, where leaf nodes sequentially reconnect with each other and form chain topologies. Tail nodes in the topology ensure data privacy by gathering and slicing sensing data into fragments.