Hardware/software co-design of computationally intensive cryptosystems is the preferred solution to achieve the required speed for resource-limited embedded applications. This paper presents a microcode instruction set coprocessor which is designed to work with 8-bit microcontrollers to implement a hyperelliptic curve cryptosystem. The microcode coprocessor is capable of performing a range of Galois Field operations using a dual-multiplier/dual-adder datapath and storing the intermediate results in the external RAM unit of the coprocessor. This coprocessor is programmed using the software routines of the 8-bit microcontroller which implement the HECC divisor's doubling and addition operations. The Jacobian scalar multiplication was computed in a 656 ms (7.87 M cycles) on 8051 microcontroller running at 12 MHz clock frequency which is 228 times faster than the pure software implementation. This number is 78 ms (1 M cycles) on the Atmel AVR microcontoller runing at 12 MHz clock which is 106 times faster than the pure software implementation. Both HW/SW co-design implementations are comparable to existing HECC implementations on the 32-bit ARM7 at 80 MHz. (C) 2006 Published by Elsevier B.V.
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