IACR News item: 13 April 2012
Jean-Charles Faugère, Pierrick Gaudry, Louise Huot, Guénaël Renault
ePrint Reportcurves defined over a non prime finite field $\\F_{q^n}$. One of the
main steps of this algorithm requires decomposing points of the curve
$E(\\F_{q^n})$ with respect to a factor base, this problem is denoted PDP. In this paper, we will apply this algorithm to the case of Edwards curves, the well known family of elliptic curves that allow faster arithmetic as shown by Bernstein and Lange. More precisely, we show how to take advantage of some symmetries of twisted Edwards and
twisted Jacobi intersections curves to gain an exponential factor
$2^{3 (n-1)}$ to solve the corresponding PDP. Practical experiments
supporting the theoretical result are also given. For instance, the
complexity of solving the ECDLP for twisted Edwards curves defined
over $\\F_{q^5}$, with $q\\approx2^{64}$, is supposed to be $2^{160}$
operations in $E(\\F_{q^5})$ using generic algorithms compared to
$2^{127}$ operations (multiplication of two $32$ bits words) with
our method. For these parameters the PDP is untractable with the
original algorithm.
The main tool to achieve these results relies on the use of the
symmetries during the polynomial system solving step. Also, we use a
recent work on a new strategy for the change of ordering of Gröbner
basis which provides a better heuristic complexity of the total
solving process.
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