Method for operating a smart grid including a plurality of smart meters configured to monitor at least one physical measured quantity and to provide measurement results of the at least one physical measured quantity to a central entity, includes the following steps: partitioning the smart grid into groups of smart meters, such that each of the smart meters belongs to exactly one group, all smart meters of one of the groups encrypt their measured value by applying a bihomomorphic encryption scheme and send it to the central entity, one smart meter per group is designated as key aggregator to which all smart meters of that group send their key employed for the encryption, the key aggregator computes the aggregation of all received keys and sends the aggregated key to the central entity, the central entity aggregates all received encrypted measured values and decrypts the aggregation by employing the aggregated key.