..................................................................................................................................... 3 Collaboration Statement ............................................................................................................. 3 Introduction ................................................................................................................................ 4 Initial Theory Summary and Pre-testing ..................................................................................... 5 How this paper is organized ................................................................................................... 6 Overview, Research, and Discussion ......................................................................................... 7 Overview of Ultrasound and Potential Applications .................................................................... 7 Advertising ............................................................................................................................. 7 Meshnets ................................................................................................................................ 8 Discrete Paging ...................................................................................................................... 8 Behind the Scenes: the Science of Ultrasonic Audio .................................................................. 9 Sound Waves ......................................................................................................................... 9 Modulation .............................................................................................................................10 Human Hearing .....................................................................................................................10 Background Noise (Environments) ........................................................................................11 Behind the Scenes: Computers and Communication ................................................................12 Equipment .............................................................................................................................12 Modulation Types ..................................................................................................................12 Networking (Communication) ................................................................................................14 File Embedding, audio compression, and sampling ...............................................................15 Security Concepts .....................................................................................................................16 Security in General ................................................................................................................16 “Air gaps” ...............................................................................................................................17 Encryption & Steganography .................................................................................................18 Malware .................................................................................................................................19 Data Exfiltration .....................................................................................................................20 Reported/Suspected Instances of Use...................................................................................20 Experimentation, Results, and Inferences .................................................................................23 Hypothesis ............................................................................................................................23 Constraints ............................................................................................................................23 Original expectations .........................................................................................................23 Ultrasonic Data Transmission and Steganography Hunter Young 2 Methods and Materials ..........................................................................................................24 Hardware ...........................................................................................................................24 Software ............................................................................................................................25 Testing Narrative ...................................................................................................................25 Results ..................................................................................................................................29 Conclusions ...........................................................................................................................41 Physical Limits ...................................................................................................................41 Technological Limits ..........................................................................................................42 Security Considerations and Recommendations ...................................................................42 Removal of microphone and speaker .................................................................................42 Heuristics ...........................................................................................................................43 Extrapolations ........................................................................................................................43 Laser Microphones and Ultrasound....................................................................................43 Power line Signal Modulators and Ultrasound ....................................................................44 Wall Transducers and Infrasound ......................................................................................44 References ...............................................................................................................................45 Ultrasonic Data Transmission and Steganography Hunter Young