Abstract: Data aggregation protocols are required in Wireless Sensor Networks (WSNs) to extend the network lifetime by reducing the energy consumption. The existing DAO-LEACH (Data Aggregation-Optimal LEACH) protocol for WSN is insecure and prone to false data injection. This is enhanced in terms of security and fault-tolerance based on Gracefully Degraded Data Aggregation (GDDA) to ensure the integrity of the aggregated data and Hybrid Layer User Authentication (HLUA) to ensure the confidentiality of the aggregated data. This data aggregation scheme rejects the false data from compromised and malfunctioning Sensor Nodes (SNs). HLUA consists of a combination of Secret Key Cryptography (SKC) Method such as MAC (Message Authentication Code) algorithm and Public Key Cryptography (PKC) Method such as Elliptic Curve Cryptography (ECC). MAC algorithm is used between the Cluster Heads (CHs) and SNs to fulfill lower power demand while ECC is applied for User Authentication (UA) between CHs and users. The enhanced DAO-LEACH protocol is resistant to security attacks such as replay attacks, node compromising attacks and impersonation attacks. It performs better in terms of energy consumption, number of alive nodes, End to End Delay (EED) and false data detection, compared to SCAR (Simple Cluster-based data Aggregation and Routing), ESPA (Energy-efficient Secure Path Algorithm), DKS-LEACH (Deterministic Key management based LEACH), SEDAN (Secure and Efficient Data Aggregation protocol for WSNs) and DAA (Data Aggregation and Authentication).