1. A method of data gathering by a data collection device in a sensor network, the method comprising: receiving aggregate data from at least one sensor node of a group of N sensor nodes each of which including at least one respective sensor, the aggregate data including M weighted sums of sensor readings, each weighted sum including a respective sum of N products each of which being a product of a respective coefficient and a sensor reading from a respective one of the N sensor nodes, M and N being positive integers and M<N; and performing computation on the aggregate data to recover sensor readings from the N sensor nodes.