Embedded microprocessors are used in a wide variety of platforms, including Radio frequency identification (RFID) systems, sensor networks, and smartphones. Unfortunately, as practical use of microprocessors has increased, so have the security problems associated with them. Although public key cryptography (PKC) can mitigate these problems, standard implementations of PKC also impose a steep computational cost on resource-constrained devices. To reduce this cost, researchers have proposed alternative implementations that accelerate multiprecision multiplication, the most expensive operation involved in PKC. In this paper, we focus on a further optimization of this same operation, using several innovative methods: carry-once, optimized multiplication and accumulation (MAC), unbalanced comb, and optimized comb-window. These methods yield further performance improvements of 2%, 17%, 4.5%, and 9.5%, respectively, on representative modern microprocessors including ATmega128 and MSP430.

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Elliptic curve cryptography (ECC) is one of the most promising public-key techniques in terms of short key size and various crypto protocols. For this reason, many studies on the implementation of ECC on resource-constrained devices within a practical execution time have been conducted. To this end, we must focus on scalar multiplication, which is the most expensive operation in ECC. A number of studies have proposed pre-computation and advanced scalar multiplication using a non-adjacent form (NAF) representation, and more sophisticated approaches have employed a width-w NAF representation and a modified pre-computation table. In this paper, we propose a new pre-computation method in which zero occurrences are much more frequent than in previous methods. This method can be applied to ordinary group scalar multiplication, but it requires large pre-computation table, so we combined the previous method with ours for practical purposes. This novel structure establishes a new feature that adjusts speed performance and table size finely, so we can customize the pre-computation table for our own purposes. Finally, we can establish a customized look-up table for embedded microprocessors.

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