  Website Fingerprinting attacks enable a passive eavesdropper to recover the
user's otherwise anonymized web browsing activity by matching the observed
traffic with prerecorded web traffic templates. The defenses that have been
proposed to counter these attacks are impractical for deployment in real-world
systems due to their high cost in terms of added delay and bandwidth overhead.
Further, these defenses have been designed to counter attacks that, despite
their high success rates, have been criticized for assuming unrealistic attack
conditions in the evaluation setting. In this paper, we propose a novel,
lightweight defense based on Adaptive Padding that provides a sufficient level
of security against website fingerprinting, particularly in realistic
evaluation conditions. In a closed-world setting, this defense reduces the
accuracy of the state-of-the-art attack from 91% to 20%, while introducing zero
latency overhead and less than 60% bandwidth overhead. In an open-world, the
attack precision is just 1% and drops further as the number of sites grows.
