AscCAPTCHA: An Invisible Sensor CAPTCHA for PCs Based on Acoustic Side Channel

Our growing reliance on the digital world has caused a similar growth in the sophistication of bots trying to impersonate humans. The most classic tool to tell human and computers apart is the CAPTCHA, however CAPTCHAs based on cognitive challenges are becoming either insecure or very difficult to be solved by humans too. A possible solution is leveraging the rich sensor set of modern mobile devices to capture the physical nature of humans while they are interacting with the system, however, traditional PCs do not have the same opportunity. In this paper we describe ascCAPTCHA, a CAPTCHA based on an acoustic side-channel that leveraging a simple microphone is compatible with PCs lacking the rich sensor set of smart devices.