Scalar multiplication on Weierstraß elliptic curves from Co-Z arithmetic
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In 2007, Meloni introduced a new type of arithmetic on elliptic curves when adding projective points sharing the same Z-coordinate. This paper presents further co-Z addition formulæ (and register allocations) for various point additions on Weierstraß elliptic curves. It explains how the use of conjugate point addition and other implementation tricks allow one to develop efficient scalar multiplication algorithms making use of co-Z arithmetic. Specifically, this paper describes efficient co-Z based versions of Montgomery ladder, Joye’s double-add algorithm, and certain signed-digit algorithms, as well as faster (X, Y)-only variants for left-to-right versions. Further, the proposed implementations are regular, thereby offering a natural protection against a variety of implementation attacks.