Abstract
Desynchronized clocks among network nodes in critical infrastructures can degrade system performance and even lead to safety incidents. Clock synchronization protocols based on network message exchanges, though widely used in current network systems, are susceptible to delay attacks against the packet transmission. This vulnerability cannot be solved by conventional security measures, such as encryption, and remains an open problem. This article proposes to use the sine voltage waveform of a utility power grid to synchronize network nodes connected to the same grid. Our experiments demonstrate that minute fluctuations of the voltage's cycle length encode fine-grained global time information in Singapore's utility grid. Based on this key result, we develop a clock synchronization approach that achieves good accuracy and is provably secure against packet-delay attacks. Implementation results show that our approach achieves an average synchronization error of 0.1 ms between two network nodes that are deployed in office and residential buildings 10 km apart. When the proposed system is deployed within the same floor of an office building, the error reduces to 10 mu s. When there are heavy industrial loads close to one of the two nodes 10 km apart, the system can still maintain subsecond accuracy. Moreover, when the two nodes are deployed within the same building floor with industrial loads nearby, the average synchronization error is 34 mu s.