MAC Aggregation with Message Multiplicity

Abstract

Wireless sensor networks (WSN) collect and report measurements, such as temperature, to a central node. Because sensors are usually low-powered devices, data is transmitted hop-by-hop, through neighboring nodes, before it reaches the destination.

Each nodes’ messages are authenticated with a MAC (Message Authentication Code), keyed with a key known to the generating sensor and the control node. Because transmission channel capacity is often small, MACs represent a significant overhead. Indeed, a typical 128-bit MAC is as much as an order of magnitude larger than the data it authenticates – a temperature or consumption reading, even with a timestamp, can be stored in 10-15 bits. To mitigate these overheads, methods to compute aggregate MACs, of length much shorter than the concatenation of constituent MACs, were proposed.

Unfortunately, known MAC aggregation techniques require that any message may not appear twice in the aggregate MAC. This is entrenched both in the definitions and constructions/proofs. This is a significant impediment in many typical practical deployments of WSNs. Indeed, one typical message relay strategy, flooding, relies on each node retransmitting received packets to all neighbors, almost certainly causing message repetition and inability to aggregate MACs. Further, we are not aware of any WSN protocols that guarantee non-duplication of messages.

We propose a simple and very practical new way of MAC aggregation which allows message duplicates, and hence is usable in many more deployment scenarios. We derive a new security definition of this type of aggregate MAC, and discuss several variants of our construction and additional benefits such as Denial-of-Service resilience.