The three-year, $360K NSF Secure and Trustworthy Cyberspace grant will fund Wu's investigation of the scientific and technological foundations of the time, location and integrity of sensor recordings by exploiting novel intrinsic fingerprints in the environment. For example, such fingerprints include the small, random-like fluctuations of the electricity frequency, known as the Electric Network Frequency (ENF). These environmental fingerprints reflect the attributes and conditions of the power grid and become naturally "embedded" into video, audio or other types of sensor signals at the time of recording. They carry time and location information and may facilitate integrity verification of the primary sensing data. Answering questions about the time, location, and integrity of sensor recordings will have important applications in crime solving, counter-terrorism, journalism, infrastructure monitoring, smart grid management, and other commercial operations.