Measurements gathered by Smart Meters and collected through the Automatic Metering Infrastructure of Smart Grids can be accessed by numerous external subjects for different purposes, ranging from billing to grid monitoring and management. Therefore, metering data must be securely handled, in order to protect the users' privacy and to prevent the disclosure of personal information through the analysis of energy consumption patterns. This paper proposes the implementation of a protocol for privacy-preserving aggregation of metering data in a distributed scenario, which relies on communication Gateways located in the customers' households. Measurements are encrypted by using a secret sharing scheme. The routing of the information flows is performed exploiting a variant of the Chord protocol. We evaluate the performance of the protocol and discuss how they are affected by two well known attacks to the Chord routing, namely the Sybil and Eclipse attacks.