Standard Lattice-Based Key Encapsulation on Embedded Devices

Lattice-based cryptography is one of the most promising candidates being considered to replace current public-key systems in the era of quantum computing. In 2016, Bos et al. proposed the key exchange scheme FrodoCCS, that is also a submission to the NIST post-quantum standardization process, modified as a key encapsulation mechanism (FrodoKEM). The security of the scheme is based on standard lattices and the learning with errors problem. Due to the large parameters, standard latticebased schemes have long been considered impractical on embedded devices. The FrodoKEM proposal actually comes with parameters that bring standard lattice-based cryptography within reach of being feasible on constrained devices. In this work, we take the final step of efficiently implementing the scheme on a low-cost FPGA and microcontroller devices and thus making conservative post-quantum cryptography practical on small devices. Our FPGA implementation of the decapsulation (the computationally most expensive operation) needs 7,220 look-up tables (LUTs), 3,549 flip-flops (FFs), a single DSP, and only 16 block RAM modules. The maximum clock frequency is 162 MHz and it takes 20.7 ms for the execution of the decapsulation. Our microcontroller implementation has a 66% reduced peak stack usage in comparison to the reference implementation and needs 266 ms for key pair generation, 284 ms for encapsulation, and 286 ms for decapsulation. Our results contribute to the practical evaluation of a post-quantum standardization candidate

Efficient Implementation of ECDH Key Exchange for MSP430-Based Wireless Sensor Networks

Public-Key Cryptography (PKC) is an indispensable building block of modern security protocols, and, thus, essential for secure communication over insecure networks. Despite a significant body of research devoted to making PKC more "lightweight," it is still commonly perceived that software implementations of PKC are computationally too expensive for practical use in ultra-low power devices such as wireless sensor nodes. In the present paper we aim to challenge this perception and present a highly-optimized implementation of Elliptic Curve Cryptography (ECC) for the TI MSP430 series of 16-bit microcontrollers. Our software is inspired by MoTE-ECC and supports scalar multiplication on two families of elliptic curves, namely Montgomery and twisted Edwards curves. However, in contrast to MoTE-ECC, we use pseudo-Mersenne prime fields as underlying algebraic structure to facilitate inter-operability with existing ECC implementations. We introduce a novel "zig-zag" technique for multiple-precision squaring on the MSP430 and assess its execution time. Similar to MoTE-ECC, we employ the Montgomery model for variable-base scalar multiplications and the twisted Edwards model if the base point is fixed (e.g. to generate an ephemeral key pair). Our experiments show that the two scalar multiplications needed to perform an ephemeral ECDH key exchange can be accomplished in 4.88 million clock cycles altogether (using a 159-bit prime field), which sets a new speed record for ephemeral ECDH on a 16-bit processor. We also describe the curve generation process and analyze the execution time of various field and point arithmetic operations on curves over a 159-bit and a 191-bit pseudo-Mersenne prime field