  The vision of battery-free communication has made backscatter a compelling
technology for on-body wearable and implantable devices. Recent advances have
facilitated the communication between backscatter tags and on-body smart
devices. These studies have focused on the communication dimension, while the
security dimension remains vulnerable. It has been demonstrated that wireless
connectivity can be exploited to send unauthorized commands or fake messages
that result in device malfunctioning. The key challenge in defending these
attacks stems from the minimalist design in backscatter. Thus, in this paper,
we explore the feasibility of authenticating an on-body backscatter tag without
modifying its signal or protocol. We present SecureScatter, a physical-layer
solution that delegates the security of backscatter to an on-body smart device.
To this end, we profile the on-body propagation paths of backscatter links, and
construct highly sensitive propagation signatures to identify on-body
backscatter links. We implement our design in a software radio and evaluate it
with different backscatter tags that work at 2.4 GHz and 900 MHz. Results show
that our system can identify on-body devices at 93.23% average true positive
rate and 3.18% average false positive rate.
