Lightweight Coprocessor for Koblitz Curves: 283-bit ECC Including Scalar Conversion with

Abstract. We propose a lightweight coprocessor for 16-bit microcon-trollers that implements high security elliptic curve cryptography. It uses a 283-bit Koblitz curve and offers 140-bit security. Koblitz curves offer fast point multiplications if the scalars are given as specific τ-adic ex-pansions, which results in a need for conversions between integers and τ-adic expansions. We propose the first lightweight variant of the con-version algorithm and, by using it, introduce the first lightweight imple-mentation of Koblitz curves that includes the scalar conversion. We also include countermeasures against side-channel attacks making the copro-cessor the first lightweight coprocessor for Koblitz curves that includes a set of countermeasures against timing attacks, SPA, DPA and safe-error fault attacks. When the coprocessor is synthesized for 130 nm CMOS, it has an area of only 4,323 GE. When clocked at 16 MHz, it computes one 283-bit point multiplication in 98 ms with a power consumption of 97.70µW, thus, consuming 9.56µJ of energy