  One-time login process in conventional authentication systems does not
guarantee that the identified user is the actual user throughout the session.
However, it is necessary to re-verify the user identity periodically throughout
a login session without reducing the user convenience. Continuous
authentication can address this issue. However, existing methods are either not
reliable or not usable. In this paper, we introduce a usable and reliable
method called Wearable Assisted Continuous Authentication (WACA). WACA relies
on the sensor based keystroke dynamics, where the authentication data is
acquired through the built in sensors of a wearable (e.g., smartwatch) while
the user is typing. We implemented the WACA framework and evaluated its
performance on real devices with real users. The empirical evaluation of WACA
reveals that WACA is feasible and its error rate is as low as 1 percent with 30
seconds of processing time and 2 3% for 20 seconds. The computational overhead
is minimal. Furthermore, we tested WACA against different attack scenarios.
WACA is capable of identifying insider threats with very high accuracy (99.2%)
and also robust against powerful adversaries such as imitation and statistical
attackers.
