Compact Software Implementation of Public-Key Cryptography on MSP430X

Abstract

On the low-end embedded processors, the implementations of Elliptic Curve Cryptography (ECC) are considered to be a challenging task due to the limited computation power and storage of the low-end embedded processors. Particularly, the multi-precision multiplication and squaring operations are the most expensive operations for ECC implementations. In order to enhance the performance, many works presented efficient multiplication and squaring routines on the target devices. Recent works show that 128-bit security level ECC is available within a second and this is practically fast enough for IoT services. However, previous approaches missed the other important storage issues (i.e., program size, ROM). Considering that the embedded processors only have a few KB ROM, we need to pay attention to the compact ROM size with reasonable performance. In this article, we present very compact and generic implementations of multiplication and squaring operations on the 16-bit MSP430X processors for the ECC. The implementations utilize the new 32-bit multiplier and advanced multiplication and squaring routines. Since the proposed routines are generic, the arbitrary length of operand is available with high-speed and small code size. With proposed multiplication and squaring routines, we implemented Curve25519 on the MSP430X processors. The scalar multiplication is performed within 6,666,895 clock cycles and 4,054 bytes. Compared with previous works based on the speed-optimized version, our memory-efficient version reduces the code size by 59.8%, sacrificing the execution timing by 20.5%.