As the Internet of Things (IoT) gains attraction, wireless devices will face the dual challenge of obtaining power while keeping wireless communications private.
“Most of these devices will be small and thus have limited energy storage; harvesting power wirelessly will be key to avoiding the need to frequently replace batteries,” explained Roohollah Rezaei, a Graduate Student at A*STAR’s Institute for Infocomm Research (I2R). “In addition, since these devices will transmit information wirelessly, their over-the-air communications are inherently insecure and can be picked up by eavesdroppers.”
Although conventional cryptographic methods can be used to encrypt messages that are transmitted wirelessly, Rezaei was keen to create physical layer security that would rely on the communication protocol itself to prevent eavesdropping. “Unlike the usual cryptographic algorithms, physical layer security would not require additional structures for distributing and managing secret keys,” he said.
Together with collaborators in China and Iran, Rezaei's team devised a communication protocol that creates a large difference between the communication rate of legitimate IoT nodes and eavesdroppers. In effect, their protocol raises the rate at which information can be transmitted securely from IoT nodes to a base station where information processing occurs. The network therefore achieves a higher secrecy rate.
To validate the security of their protocol, the researchers constructed a model network in which several IoT nodes, including possible eavesdropper nodes, transmit information wirelessly to a base station. Each node harvests power from the base station before its transmission time, then uses that power to transmit its information during an allocated time slot.
“Using our model, we showed that the base station running our protocol assumes that none of the IoT nodes can be trusted—at each time slot, one of the nodes transmits information to the base station while the remaining nodes are considered as potential eavesdroppers,” Rezaei said. During this stage, artificial noise is generated to blind non-transmitting nodes, so even if one of them has been compromised by a hacker (i.e., it becomes an eavesdropper), the information being transmitted remains secure.
“Having worked out the right signal structure, the second stage consists of allocating time slots so that the total communication throughput between the base station and the nodes is maximized,” he added.
The researchers demonstrated that their two-stage process outperformed common algorithms in securing wireless communications. Moving forward, Rezaei’s team plans to explore whether their technique allows the detection of other types of eavesdroppers—especially passive eavesdroppers which are typically more difficult for base stations to identify.
“We are also considering more sophisticated bandwidth schemes that allow more nodes to transmit their information at the same time, to see if we can overcome signal interference and maintain the same level of secrecy,” he concluded.
The A*STAR-affiliated researchers contributing to this research are from the Institute for Infocomm Research (I2R).