Optimised squaring of long integers using precomputed partial products

This paper considers the combination of two familiar, but hitherto incompatible, arithmetic techniques: optimised squaring and precomputing partial products. Optimised squaring reduces the total accumulation effort required for squaring when compared with multiplication, by removing repeated digit products from the accumulation tree. Iterative implementations of integer multiplication, in which each partial product is evaluated and accumulated in turn, can often be accelerated by precomputing the set of partial products and accumulating these as required. Iterative implementations of optimised squaring cannot benefit from the same straightforward technique. A new algorithm for optimised squaring is developed which reconciles the these two techniques and which is an improvement over squaring by multiplication for some platforms. The result is of significance for the implementation of public key cryptography on smart cards or other small footprint devices