Efficient and secure threshold-based event validation for vanets

Determining whether the number of vehicles reporting anevent is above a threshold is an important mechanism for
VANETs, because many applications rely on a threshold
number of notifications to reach agreement among vehicles,
to determine the validity of an event, or to prevent the abuse
of emergency alarms. We present the first efficient and se-
cure threshold-based event validation protocol for VANETs.
Quite counter-intuitively, we found that the z-smallest ap-
proach offers the best tradeoff between security and effi-
ciency since other approaches perform better for probabilis-
tic counting. Analysis and simulation shows that our pro-
tocol provides > 99% accuracy despite the presence of at-
tackers, collection and distribution of alerts in less than 1
second, and negligible impact on network performance.