Temperature-based covert channel in FPGA systems

This paper reports the temperature-based covert communication channel implemented in FPGA system. The channel enables bidirectional transmission and exchange of an arbitrary bit stream between two, electrically separated parts of the FPGA circuit during its normal operation. Transmission to and from the FPGA device is also reported. Transmitter and receiver modules are based on ring-oscillator which utilize 60 and 51 look-up tables respectively. The proof of concept was implemented in the Xilinx Spartan-IIE device and allows for transmission speed of 1/8 bit/s between FPGA and external transceiver. Internal communication is faster and allows to transmit up to 1 bit per second.