Lightweight code-based cryptography: QC-MDPC McEliece encryption on reconfigurable devices

With the break of RSA and ECC cryptosystems in an era of quantum computing, asymmetric code-based cryptography is an established alternative that can be a potential replacement. A major drawback are large keys in the range between 50kByte to several MByte that prevented real-world applications of code-based cryptosystems so far. A recent proposal by Misoczki et al. showed that quasi-cyclic moderate density parity-check (QC-MDPC) codes can be used in McEliece encryption — reducing the public key to just 0.6 kByte to achieve a 80-bit security level. Despite of reasonably small key sizes that could also enable small designs, previous work only report highperformance implementations with high resource consumptions of more than 13,000 slices on a large Xilinx Virtex-6 FPGA for a combined en-/decryption unit. In this work we focus on lightweight implementations of code-based cryptography and demonstrate that McEliece encryption using QC-MDPC codes can be implemented with a significantly smaller resource footprint — still achieving reasonable performance sufficient for many applications, e.g., challenge-response protocols or hybrid firmware encryption. More precisely, our design requires just 68 slices for the encryption and around 150 slices for the decryption unit and is able to en-/decrypt an input block in 2.2ms and 13.4 ms, respectively.