Place-and-route impact on the security of DPL designs in FPGAs

Straightforward implementations of cryptographic algorithms are known to be vulnerable to attacks aimed not at the mathematical structure of the cipher but rather at the weak points of the electronic devices which implement it. These attacks, known as side-channel attacks, have proved to be very powerful in retrieving secret keys from any kind of unprotected electronic device. Amongst the various protection strategies, side-channel hiding is very popular and well studied. The principle of information hiding is to make any leak constant, thus uncorrected to the device internal secrets. The so-called "dual-rail with precharge logic" (DPL) style is indicated to achieve that goal. For DPL protection to be effective, it further requires a carefully balanced layout so as to obtain equal propagation delays and power consumption on both rails. In this article, we study to which extent the differential place-and-route constraints must be strict in FPGA technology. We describe placement techniques suitable for Xilinx and Altera FPGAs, and quantify the gain of balance they confer. On the one hand, we observed that Xilinx fitting tool achieves naturally good balancing results. On the other hand, the symmetry can be greatly improved with Altera devices, using a manual placement, leading to unprecedented dual netlists balancing. side-channel attacks, differential power analysis, secure logic style,.