Dr. Mordechai Guri

In this paper, we evaluate an optical covert channel in which sensitive information (textual or binary) is exfiltrated from air-gapped computers through the LCD screen. Our experiments show that low contrast and fast blinking images which are invisible to human subjects, can be recovered from photos taken by a local camera. Consequentially, we show that malware on a compromised computer can obtain sensitive data (e.g., files, images, encryption keys, passwords), and project it onto a computer LCD screen, invisible and unbeknownst to users. An attacker can reconstruct the hidden data using a photo taken by a local camera. In order to demonstrate the feasibility of this type of attack and evaluate the channel's stealth, we conducted a battery of tests with 40 users. We also examined the channel's boundaries under various parameters, with different types of encoded objects, at several distances, and using several kinds of cameras.