## CryptoDB

### Katsuyuki Okeya

#### Publications

Year
Venue
Title
2007
CHES
2007
EPRINT
This paper presents a new approach to precompute all odd points $[3]P, [5]P,\ldots, [2k-1]P$, $k \geq 2$ on an elliptic curve over $\mathbb{F}_p$. Those points are required for the efficient evaluation of a scalar multiplication, the most important operation in elliptic curve cryptography. The proposed method precomputes the points in affine coordinates and needs only one single field inversion for the computation. The new method is superior to all known methods that also use one field inversion. Compared to methods that require several field inversions for the precomputation, the proposed method is faster for a broad range of ratios of field inversions and field multiplications. The proposed method benefits especially from ratios as they occur on smart cards. %Scalar multiplications are the basic operations in elliptic curve cryptosystems. The evaluation of a scalar multiplication can be sped up by using signed representations of the scalar. In exchange for the speed up, the precomputation of a series of points is required. While a lot of research has been done in the direction of signed representations, little attention has been paid to efficient methods to precompute the required points. Such methods are important since costly field inversions are involved in the precomputation. This paper presents a new method for the precomputation that requires only one single field inversion, independent of the number of points to precompute. The points to precompute are all odd points $[3]P, [5]P,\ldots, [2k-1]P$, $k \geq 2$ on an elliptic curve over $\mathbb{F}_p$. The proposed method benefits especially from a large ratios between inversions and multiplications as they occur on smart cards.
2005
CHES
2004
CRYPTO
2004
EPRINT
The most common method for computing exponentiation of random elements in Abelian groups are sliding window schemes, which enhance the efficiency of the binary method at the expense of some precomputation. In groups where inversion is easy (e.g. elliptic curves), signed representations of the exponent are meaningful because they decrease the amount of required precomputation. The asymptotic best signed method is wNAF, because it minimizes the precomputation effort whilst the non-zero density is nearly optimal. Unfortunately, wNAF can be computed only from the least significant bit, i.e. right-to-left. However, in connection with memory constraint devices left-to-right recoding schemes are by far more valuable. In this paper we define the MOF (Mutual Opposite Form), a new canonical representation of signed binary strings, which can be computed in any order. Therefore we obtain the first left-to-right signed exponent-recoding scheme for general width w by applying the width w sliding window conversion on MOF left-to-right. Moreover, the analogue right-to-left conversion on MOF yields wNAF, which indicates that the new class is the natural left-to-right analogue to the useful wNAF. Indeed, the new class inherits the outstanding properties of wNAF, namely the required precomputation and the achieved non-zero density are exactly the same.
2003
CHES
2002
CHES
2001
CHES
2000
PKC

CHES 2008
CHES 2006
CHES 2003