Temporal Thermal Covert Channels in Cloud FPGAs

With increasing interest in Cloud FPGAs, such as Amazon's EC2 F1 instances or Microsoft's Azure with Catapult servers, FPGAs in cloud computing infrastructures can become targets for information leakages via convert channel communication. Cloud FPGAs leverage temporal sharing of the FPGA resources between users. This paper shows that heat generated by one user can be observed by another user who later uses the same FPGA. The covert data transfer can be achieved through simple on-off keying (OOK) and use of multiple FPGA boards in parallel significantly improves data throughput. The new temporal thermal covert channel is demonstrated on Microsoft's Catapult servers with FPGAs running remotely in the Texas Advanced Computing Center (TACC). A number of defenses against the new temporal thermal covert channel are presented at the end of the paper.