Generalizations of the Karatsuba Algorithm for Efficient Implementations

André Weimerskirch, Chris­tof Paar

Cryptology ePrint Archive: Report 2006/224.


Abstract

In this work we generalize the classical Karatsuba Algorithm (KA) for polynomial multiplica- tion to (i) polynomials of arbitrary degree and (ii) recursive use. We determine exact complexity expressions for the KA and focus on how to use it with the least number of operations. We develop a rule for the optimum order of steps if the KA is used recursively. We show how the usage of dummy coe±cients may improve performance. Finally we provide detailed information on how to use the KA with least cost, and also provide tables that describe the best possible usage of the KA for polynomials up to a degree of 127. Our results are especially useful for e±cient implementations of cryptographic and coding schemes over fixed-size fields like GF(p^m).

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