From Cryptography to Hardware: Analyzing Embedded Xilinx BRAM for Cryptographic Applications

Design of cryptographic applications need special care. For instance, physical attacks like Side-Channel Analysis (SCA) are able to recover the secret key, just by observing the activity of the computation, even for mathematically robust algorithms like AES. SCA considers the "leakage" of a well chosen intermediate variable correlated with the secret. Field programmable gate-arrays (FPGA) are often used for hardware implementations for low to medium volume productions or when flexibility is needed. They offer many possibilities for the computation, like small Look-Up Tables (LUT) and embedded block memories (BRAM). Certain countermeasures can be deployed, like dual-rail logic or masking, to resist SCA on FPGA. However to design an effective countermeasure, it is of prime importance for a designer to know the main leakage sources of the device. In this article, we analyze the leakage source of a Xilinx Virtex V FPGA by studying 3 different AES architectures. The analysis is based on real measurements by using specific leakage models of the sensitive variable, adapted to each architecture. Our results demonstrate that, BRAM which were considered to leak less traditionally, are found to be equally vulnerable if we change the attack target from address register to output latch. Hence by providing important clues about the leakage, this study allows the designers to enhance the robustness of their implementation in FPGA.