From 389c787e790fe81036f2ff5303c7afe21ceb2afd Mon Sep 17 00:00:00 2001 From: Daiki Ueno Date: Sat, 30 Nov 2019 10:29:23 +0100 Subject: Implement Curve448 primitives This patch adds the necessary primitives for "curve448", defined in RFC 7748. Those primitives are namely: addition, doubling, scalar multiplication of the generator or an arbitrary point, inversion, and square root. --- curve448-eh-to-x.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 73 insertions(+) create mode 100644 curve448-eh-to-x.c (limited to 'curve448-eh-to-x.c') diff --git a/curve448-eh-to-x.c b/curve448-eh-to-x.c new file mode 100644 index 00000000..4bc78303 --- /dev/null +++ b/curve448-eh-to-x.c @@ -0,0 +1,73 @@ +/* curve448-eh-to-x.c + + Copyright (C) 2017 Daiki Ueno + Copyright (C) 2017 Red Hat, Inc. + + This file is part of GNU Nettle. + + GNU Nettle is free software: you can redistribute it and/or + modify it under the terms of either: + + * the GNU Lesser General Public License as published by the Free + Software Foundation; either version 3 of the License, or (at your + option) any later version. + + or + + * the GNU General Public License as published by the Free + Software Foundation; either version 2 of the License, or (at your + option) any later version. + + or both in parallel, as here. + + GNU Nettle is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + General Public License for more details. + + You should have received copies of the GNU General Public License and + the GNU Lesser General Public License along with this program. If + not, see http://www.gnu.org/licenses/. +*/ + +#if HAVE_CONFIG_H +# include "config.h" +#endif + +#include + +#include "curve448.h" + +#include "ecc.h" +#include "ecc-internal.h" + +/* Transform a point on the edwards448 Edwards curve to the curve448 + Montgomery curve, and return the x coordinate. */ +void +curve448_eh_to_x (mp_limb_t *xp, const mp_limb_t *p, mp_limb_t *scratch) +{ +#define vp (p + ecc->p.size) +#define t0 scratch +#define t1 (scratch + ecc->p.size) +#define t2 (scratch + 2*ecc->p.size) + + const struct ecc_curve *ecc = &_nettle_curve448; + mp_limb_t cy; + + /* If u = U/W and v = V/W are the coordinates of the point on + edwards448 we get the curve448 x coordinate as + + x = v^2 / u^2 = (V/W)^2 / (U/W)^2 = (V/U)^2 + */ + /* Needs a total of 9*size storage. */ + ecc->p.invert (&ecc->p, t0, p, t1 + ecc->p.size); + ecc_modp_mul (ecc, t1, t0, vp); + ecc_modp_mul (ecc, t2, t1, t1); + + cy = mpn_sub_n (xp, t2, ecc->p.m, ecc->p.size); + cnd_copy (cy, xp, t2, ecc->p.size); +#undef vp +#undef t0 +#undef t1 +#undef t2 +} -- cgit v1.2.1