  In-network data aggregation is an essential technique in mission critical
wireless sensor networks (WSNs) for achieving effective transmission and hence
better power conservation. Common security protocols for aggregated WSNs are
either hop-by-hop or end-to-end, each of which has its own encryption schemes
considering different security primitives. End-to-end encrypted data
aggregation protocols introduce maximum data secrecy with in-efficient data
aggregation and more vulnerability to active attacks, while hop-by-hop data
aggregation protocols introduce maximum data integrity with efficient data
aggregation and more vulnerability to passive attacks.
  In this paper, we propose a secure aggregation protocol for aggregated WSNs
deployed in hostile environments in which dual attack modes are present. Our
proposed protocol is a blend of flexible data aggregation as in hop-by-hop
protocols and optimal data confidentiality as in end-to-end protocols. Our
protocol introduces an efficient O(1) heuristic for checking data integrity
along with cost-effective heuristic-based divide and conquer attestation
process which is $O(\ln{n})$ in average -O(n) in the worst scenario- for
further verification of aggregated results.
