I. INTRODUCTION  
II. BACKGROUND  
III. AUDIO CHANNELS FOR TWO-FACTOR AUTHENTICATION  
IV. AUDIO CHANNELS FOR SECURE DEVICE PAIRING  
V. DEVICE AUTHORIZATION AND USER VERIFICATION VIA SHORT-RANGE AUDIO  
VI. ATTACKS VIA AUDIO  
VII. DEFENSE MECHANISMS USING SHORT-RANGE AUDIO  
VIII. RESEARCH CHALLENGES AND FUTURE RESEARCH DIRECTIONS  
IX. CONCLUSIONS