Patent ID: 8832429

Claim:
Method for operating a smart grid including a plurality of smart meters, said smart meters being configured to monitor at least one physical measured quantity and to provide measurement results of said at least one physical measured quantity to a central entity, comprising the steps of: said smart grid being partitioned into groups G of smart meters sm i , such that each of said smart meters belongs to exactly one group, all smart meters sm i of one of said groups G encrypting their measured value e i by applying a bihomomorphic encryption scheme E ki and send it to said central entity, one smart meter per group being designated as key aggregator to which all smart meters sm i of that group send their key k i employed for said encryption, said key aggregator computing the aggregation of all received keys k i and sends the aggregated key K to said central entity, said central entity aggregating all received encrypted measured values e i and decrypts said aggregation by employing said aggregated key K, wherein reporting periods j are defined and wherein each smart meter sm i uses a different key k i,j per reporting period for encrypting said at least one specific physical measured quantity, wherein smart meters sm i of the same group G are composed as a ring, wherein each smart meter sends to the subsequent smart meter in said ring a random value δ i,j , and wherein each smart meter sm i , for establishing a new key k i,j for a subsequent reporting period j, subtracts from its key k i,j−1 employed in the preceding reporting period j−1 the random value δ i,j sent to the next smart meter in said ring and adds the random value δ i−1,j received from the preceding smart meter in said ring.