In this paper we propose a decentralized, efficient and selective aggregation (DESA) scheme for secure and privacy-preserving communication in AMI. Unlike existing aggregation schemes, DESA uses a multi-recipient system model that is more applicable to liberalized electricity markets. It uses the homomorphic Paillier cryptosystem to encrypt users' consumption data, which are selectively aggregated by local gateways. In this way, the aggregated data of different subsets of users are only delivered to their intended authorized entities. DESA adopts the BLS signature and batch verification methods to reduce computation and communication overheads. Through security analysis and performance evaluation, we show that DESA resists various attacks and preserve users' privacy in an efficient manner.