In autonomous assistance systems, accurate camera vision is indispensable for driving safety. Featuring this safety-critical scenario, physical adversarial examples are arguably the most threatening. However, existing physical adversarial attacks are either conspicuous or ineffective, leaving a dilemma for balancing between attack effectiveness and stealthiness. In this paper, we put forth a new type of adversarial patch attack, leveraging the behavior characteristic of high-speed shutters in autonomous driving cameras. Instead of deploying static images onto real-world objects, we embed adversarial examples into videos and cast them with projectors. By delicately deciding the frame contents and display frequencies, the adversarial frame contents are almost invisible to humans, but high-speed shutters can capture them (see our demos ¹ ). We demonstrate the attack feasibility by fooling traffic sign detectors, altering speed limit signs to be mis-detected or undetected, and hence manipulating the driving speed of victims. We conduct extensive experiments under various conditions, confirming that our new attack is effective and robust: It can deceive state-of-the-art detector models with success rates of 99% and over 90% in untargeted and targeted manners, respectively. Our further investigations unravel the transferability of our attack to other detectors in a black-box setting.

Face authentication usually utilizes deep learning models to verify users with high accuracy. However, it is vulnerable to various attacks that cheat the models by manipulating the digital counterparts of human faces. So far, lots of liveness detection schemes have been developed to prevent such attacks. Unfortunately, the attacker can still bypass them by constructing sophisticated attacks. We study the security of existing face authentication services and typical liveness detection approaches. Particularly, we develop a new type of attack, i.e., the low-cost 3D projection attack that projects manipulated face videos on a 3D face model, which can easily evade these face authentication services and liveness detection approaches. To this end, we propose FaceLip, a novel face liveness detection scheme on mobile devices, which utilizes lip motion patterns built upon well-designed acoustic signals to enable a strong security guarantee. The unique lip motions for each user are unforgeable because FaceLip verifies the patterns by analyzing acoustic signals that are dynamically generated according to random challenges, which ensures that our signals for liveness detection cannot be manipulated. We prototype FaceLip on off-the-shelf smartphones and conduct extensive experiments under different settings. Our evaluation with 44 participants validates the effectiveness and robustness of FaceLip.

Voice authentication is increasingly used for sensitive operations in mobile devices. However, voice biometrics focuses on distinguishing individuals by their spectral features, which cannot deal with spoofing attacks. In this paper, we design and implement a novel software-only anti-spoofing system on smartphones. Our system leverages the pop noise, which is generated by the users oral airflow when speaking the passphrase opposite the microphone. The pop noise is delicate and subject to user diversity, making it hard to be recorded by replay attacks beyond a certain distance and to be imitated precisely by impersonators. Especially, we design a new pop noise detection scheme to pinpoint pop noises at the phonemic level, based on which we establish a theoretical model to calculate the sound pressure level from the speech signal in order to get the estimated pressure signal, and then analyze the consistency with the actual pressure signal extracted from the pop noise. Our evaluation on a dataset of 30 participants and three smartphones shows that our system achieves over 94.79% accuracy. Our system requires no additional hardware and is robust to various factors including authentication angle, authentication distance, the length of passphrase, ambient noise, etc.

Mobile two-factor authentication (TFA), which uses mobile devices as a second security layer to online accounts, has been widely applied with the proliferation of mobile phones. Currently, many studies propose to use acoustic fingerprints as the second factor. However, these solutions ignore the variations of the extracted static acoustic fingerprints incurred by the acoustic propagation process. In this paper, we propose SoundID, a secure and novel authentication system that introduces a dual challenge-response design via the acoustic signals of the enrolled phone and the login device. In SoundID, the enrolled phone evaluates its proximity to the login device by the similarity of their audio recordings, and then the server compares the calculated dynamic acoustic fingerprint with the one received from the enrolled phone. To the best of our knowledge, SoundID is the first scheme that extracts dynamic acoustic fingerprints and can effectively defend against the enhanced MITM attack. We build a prototype of SoundID with off-the-shelf smartphones to validate its robustness and effectiveness. Our results show that SoundID is user-friendly and achieves over 96.62% accuracy at around 4.27% equal error rate.

PIN authentication is widely used on mobile devices due to its usability and simplicity. However, it is known to be susceptible to shoulder surfing attacks, where an adversary spies the users PIN by direct human observation or camera-based recording. This paper proposes PressPIN, a novel enhanced PIN authenticator on mobile devices by sensing pressures from the users finger. Since pressure-sensitive touch screens are unavailable on most phones, we leverage the structure-borne propagation of sounds to estimate the pressure on the screen. The pressure code is difficult to be inferred by snooping or videotaping, and increases the entropy of passwords. In this way, PressPIN provides a low-cost, user-friendly, and more secure solution resistant to shoulder surfing attacks. Our extensive experiments with 30 participants and three types of smartphones demonstrate that PressPIN can authenticate legitimate users with high accuracy (e.g., as high as 96.7% within two trials), and is robust to various types of attacks (e.g., only 2.5% attack success rate even when the adversary can observe the legitimate users PIN sequence and finger pressing clearly). Additionally, PressPIN requires no additional hardware (e.g., the pressure sensor) and can be readily integrated into existing authentication systems of mobile devices.

Pattern lock is widely used for user authentication in mobile devices due to its simplicity and ease of remembering. However, it is vulnerable to various attacks, e.g., shoulder surfing attacks. In this paper, we propose FingerPattern, a novel enhanced pattern lock authentication system by using friction sound as a second authentication factor. When the user inputs the pattern by swiping his/her fingertip on the screen, the friction sound is generated based on the user's fingerprint and is unique. Thus, FingerPattern can identify and rule out the illegality by utilizing fingerprint-dependent friction sound even if the adversary has inferred the pattern. By this method, FingerPattern secures pattern lock without the need for a change in user unlocking habits. Extensive experiments demonstrate that FingerPattern can identify legitimate users with 97.5% TAR in one attempt and defend against various attacks (e.g., only 16.8% FAR in five attempts even if the adversary can clearly spy on the user's unlocking process). FingerPattern can be incorporated into the existing pattern lock of mobile devices, which is cost-free. Furthermore, a user experience study shows that FingerPattern is well-received by users.