Counter-Screen – A No-Hardware Method to Prevent Eavesdropping of Video Using TMDS

TEMPEST, a form of electronic eavesdropping, poses significant risks to sensitive information transmitted through High-Definition Multimedia Interface (HDMI) and Digital Visual Interface - Digital (DVI-D) connections. This paper investigates a novel technique to mitigate TEMPEST attacks by manipulating Transition Minimized Differential Signaling (TMDS) values. By introducing a secondary screen that displays TMDS values with opposite transition characteristics, the emitted electromagnetic interference (EMI) can be countered, thereby concealing information from potential eavesdroppers. This paper details the implementation of this method, provides experimental validation, and discusses the potential benefits and implications of this approach.