Improving Security of SDDL Designs through Interleaved Placement on Xilinx FPGAs

Implementations of mathematically secure cryptographic algorithms leak information through side channels during run time. Differential Power Analysis (DPA) attacks exploit power leakage to obtain the secret information. Dynamic and Differential Logic (DDL), one of the popular countermeasures against DPA attacks, tries to achieve constant power consumption thereby decor relating the leakage with the data being processed. Separated Dynamic and Differential Logic (SDDL), a variant of DDL, achieves this goal by duplicating the original design into Direct and Complementary parts which exhibit constant switching activity per clock cycle and have balanced net delays. Traditionally, on Field Programmable Gate Arrays (FPGAs) both parts are placed side-by-side to ensure symmetrical routing. However, due to process variations both parts will have slightly different delays. This limits the effectiveness of SDDL. In this paper we introduce a design flow to achieve interleaved placement of SDDL designs on Xilinx Spartan-3E FPGAs while preserving symmetric routing. We explore several placement configurations with respect to routing and security. The results of our experiments show that a well-balanced placement of SDDL can double the effectiveness of the SDDL countermeasures on FPGAs.