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/* ecc-dup-jj.c
Copyright (C) 2013 Niels Möller
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/.
*/
/* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
#if HAVE_CONFIG_H
# include "config.h"
#endif
#include "ecc.h"
#include "ecc-internal.h"
/* NOTE: Behaviour for corner cases:
+ p = 0 ==> r = 0, correct!
*/
void
ecc_dup_jj (const struct ecc_curve *ecc,
mp_limb_t *r, const mp_limb_t *p,
mp_limb_t *scratch)
{
/* Formulas (from djb,
http://www.hyperelliptic.org/EFD/g1p/auto-shortw-jacobian-3.html#doubling-dbl-2001-b):
Computation Operation Live variables
delta = z^2 sqr delta
gamma = y^2 sqr delta, gamma
z' = (y+z)^2-gamma-delta sqr delta, gamma
alpha = 3*(x-delta)*(x+delta) mul gamma, beta, alpha
beta = x*gamma mul gamma, beta, alpha
x' = alpha^2-8*beta sqr gamma, beta, alpha
y' = alpha*(4*beta-x')-8*gamma^2 mul, sqr
*/
#define delta scratch
#define gamma (scratch + ecc->p.size)
#define beta (scratch + 2*ecc->p.size)
#define g2 (scratch + 3*ecc->p.size)
#define sum (scratch + 4*ecc->p.size)
#define alpha scratch /* Overlap delta */
#define xp p
#define yp (p + ecc->p.size)
#define zp (p + 2*ecc->p.size)
/* delta */
ecc_modp_sqr (ecc, delta, zp);
/* gamma */
ecc_modp_sqr (ecc, gamma, yp);
/* z'. Can use beta area as scratch. */
ecc_modp_add (ecc, r + 2*ecc->p.size, yp, zp);
ecc_modp_sqr (ecc, beta, r + 2*ecc->p.size);
ecc_modp_sub (ecc, beta, beta, gamma);
ecc_modp_sub (ecc, r + 2*ecc->p.size, beta, delta);
/* alpha. Can use beta area as scratch, and overwrite delta. */
ecc_modp_add (ecc, sum, xp, delta);
ecc_modp_sub (ecc, delta, xp, delta);
ecc_modp_mul (ecc, beta, sum, delta);
ecc_modp_mul_1 (ecc, alpha, beta, 3);
/* beta */
ecc_modp_mul (ecc, beta, xp, gamma);
/* Do gamma^2 and 4*beta early, to get them out of the way. We can
then use the old area at gamma as scratch. */
ecc_modp_sqr (ecc, g2, gamma);
ecc_modp_mul_1 (ecc, sum, beta, 4);
/* x' */
ecc_modp_sqr (ecc, gamma, alpha); /* Overwrites gamma and beta */
ecc_modp_submul_1 (ecc, gamma, sum, 2);
mpn_copyi (r, gamma, ecc->p.size);
/* y' */
ecc_modp_sub (ecc, sum, sum, r);
ecc_modp_mul (ecc, gamma, sum, alpha);
ecc_modp_submul_1 (ecc, gamma, g2, 8);
mpn_copyi (r + ecc->p.size, gamma, ecc->p.size);
}
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