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Hearing Check Failed: Using Laser Vibrometry to Analyze the Potential for Hard Disk Drives to Eavesdrop Speech Vibrations

Sound waves from speech can potentially induce vibrations, proportional to the speech signal, on nearby objects. Each of these objects introduces the risk for a malicious attacker to exploit the induced vibrations to eavesdrop on the speech. Such an eavesdropping attack is critical when we consider the potential for induced vibrations in standard magnetic hard disk drives (HDDs). As an instance of this threat, prior research has demonstrated that speech in certain scenarios can induce vibrations on the read/write head of an HDD in order to eavesdrop on the speech (Kwong et al.; Oakland'19). In this paper, we revisit this line of research and aim to provide a closer investigation into whether HDDs can in fact be used as a source for eavesdropping on speech vibrations. As a foundation for our study, we utilize an effective, and robust methodology using laser vibrometry to measure the subtle speech vibrations induced on the read/write head. The prior study tested only a single HDD and only machine-rendered speech in a single setting with very loud speech. Our work broadens the scope of this research in many significant ways. First, we test multiple popular HDDs of different models and sizes to evaluate the generalizability of the overall threat. Second, we evaluate the threat from live human speech spoken near an HDD, expanding the scope of the attack to include most real-world speech settings involving normal human conversations. Third, we define machine-rendered speech scenarios to explore different propagation media and degrees of speech loudness. Our findings are two-fold. First, we observed that live human speech traveling through the air is not generally strong enough to impact HDDs such that intelligible speech information is leaked. Second, most tested HDDs did not seem capable of eavesdropping on machine-rendered speech unless the speech is loud enough, or the HDD shares a surface or is in direct contact with the speaker device. This implies HDDs cannot eavesdrop live human speech.