  Nowadays, machine learning based Automatic Speech Recognition (ASR) technique
has widely spread in smartphones, home devices, and public facilities. As
convenient as this technology can be, a considerable security issue also raises
-- the users' speech content might be exposed to malicious ASR monitoring and
cause severe privacy leakage. In this work, we propose HASP -- a
high-performance security enhancement approach to solve this security issue on
mobile devices. Leveraging ASR systems' vulnerability to the adversarial
examples, HASP is designed to cast human imperceptible adversarial noises to
real-time speech and effectively perturb malicious ASR monitoring by increasing
the Word Error Rate (WER). To enhance the practical performance on mobile
devices, HASP is also optimized for effective adaptation to the human speech
characteristics, environmental noises, and mobile computation scenarios. The
experiments show that HASP can achieve optimal real-time security enhancement:
it can lead an average WER of 84.55% for perturbing the malicious ASR
monitoring, and the data processing speed is 15x to 40x faster compared to the
state-of-the-art methods. Moreover, HASP can effectively perturb various ASR
systems, demonstrating a strong transferability.
