In wireless sensor networks, performing data aggregation while preserving data confidentiality and integrity is challenging. Recently, privacy homomorphism-based secure data aggregation schemes have been proposed to seamlessly integrate confidentiality and data aggregation. However, these schemes do not provide data integrity or allow hierarchical data aggregation if more than one encryption key is used in the network. This paper presents a novel integrity protecting hierarchical concealed data aggregation protocol that allows the aggregation of data packets that are encrypted with different encryption keys. In addition, during the decryption of aggregated data, the base station is able to classify the encrypted and aggregated data based on the encryption keys. The proposed data aggregation scheme employs an elliptic curve cryptography-based homomorphic encryption algorithm to offer data integrity and confidentiality along with hierarchical data aggregation. (C) 2011 Elsevier B.V. All rights reserved.