3 Copyright (C) 2013 Niels Möller
5 This file is part of GNU Nettle.
7 GNU Nettle is free software: you can redistribute it and/or
8 modify it under the terms of either:
10 * the GNU Lesser General Public License as published by the Free
11 Software Foundation; either version 3 of the License, or (at your
12 option) any later version.
16 * the GNU General Public License as published by the Free
17 Software Foundation; either version 2 of the License, or (at your
18 option) any later version.
20 or both in parallel, as here.
22 GNU Nettle is distributed in the hope that it will be useful,
23 but WITHOUT ANY WARRANTY; without even the implied warranty of
24 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
25 General Public License for more details.
27 You should have received copies of the GNU General Public License and
28 the GNU Lesser General Public License along with this program. If
29 not, see http://www.gnu.org/licenses/.
32 /* Development of Nettle's ECC support was funded by the .SE Internet Fund. */
39 #include "ecc-internal.h"
42 ecc_add_jjj (const struct ecc_curve *ecc,
43 mp_limb_t *r, const mp_limb_t *p, const mp_limb_t *q,
46 /* Formulas, from djb,
47 http://www.hyperelliptic.org/EFD/g1p/auto-shortw-jacobian-3.html#addition-add-2007-bl:
49 Computation Operation Live variables
52 Z2Z2 = Z2^2 sqr Z1Z1, Z2Z2
53 U1 = X1*Z2Z2 mul Z1Z1, Z2Z2, U1
54 U2 = X2*Z1Z1 mul Z1Z1, Z2Z2, U1, U2
55 H = U2-U1 Z1Z1, Z2Z2, U1, H
56 Z3 = ((Z1+Z2)^2-Z1Z1-Z2Z2)*H sqr, mul Z1Z1, Z2Z2, U1, H
57 S1 = Y1*Z2*Z2Z2 mul, mul Z1Z1, U1, H, S1
58 S2 = Y2*Z1*Z1Z1 mul, mul U1, H, S1, S2
59 W = 2*(S2-S1) (djb: r) U1, H, S1, W
60 I = (2*H)^2 sqr U1, H, S1, W, I
61 J = H*I mul U1, S1, W, J, V
62 V = U1*I mul S1, W, J, V
63 X3 = W^2-J-2*V sqr S1, W, J, V
64 Y3 = W*(V-X3)-2*S1*J mul, mul
66 mp_limb_t *z1z1 = scratch;
67 mp_limb_t *z2z2 = scratch + ecc->p.size;
68 mp_limb_t *u1 = scratch + 2*ecc->p.size;
69 mp_limb_t *u2 = scratch + 3*ecc->p.size;
70 mp_limb_t *s1 = scratch; /* overlap z1z1 */
71 mp_limb_t *s2 = scratch + ecc->p.size; /* overlap z2z2 */
72 mp_limb_t *i = scratch + 4*ecc->p.size;
73 mp_limb_t *j = scratch + 5*ecc->p.size;
74 mp_limb_t *v = scratch + 6*ecc->p.size;
76 /* z1^2, z2^2, u1 = x1 x2^2, u2 = x2 z1^2 - u1 */
77 ecc_modp_sqr (ecc, z1z1, p + 2*ecc->p.size);
78 ecc_modp_sqr (ecc, z2z2, q + 2*ecc->p.size);
79 ecc_modp_mul (ecc, u1, p, z2z2);
80 ecc_modp_mul (ecc, u2, q, z1z1);
81 ecc_modp_sub (ecc, u2, u2, u1); /* Store h in u2 */
83 /* z3, use i, j, v as scratch, result at i. */
84 ecc_modp_add (ecc, i, p + 2*ecc->p.size, q + 2*ecc->p.size);
85 ecc_modp_sqr (ecc, v, i);
86 ecc_modp_sub (ecc, v, v, z1z1);
87 ecc_modp_sub (ecc, v, v, z2z2);
88 ecc_modp_mul (ecc, i, v, u2);
89 /* Delayed write, to support in-place operation. */
91 /* s1 = y1 z2^3, s2 = y2 z1^3, scratch at j and v */
92 ecc_modp_mul (ecc, j, z1z1, p + 2*ecc->p.size); /* z1^3 */
93 ecc_modp_mul (ecc, v, z2z2, q + 2*ecc->p.size); /* z2^3 */
94 ecc_modp_mul (ecc, s1, p + ecc->p.size, v);
95 ecc_modp_mul (ecc, v, j, q + ecc->p.size);
96 ecc_modp_sub (ecc, s2, v, s1);
97 ecc_modp_mul_1 (ecc, s2, s2, 2);
100 mpn_copyi (r + 2*ecc->p.size, i, ecc->p.size);
103 ecc_modp_sqr (ecc, i, u2);
104 ecc_modp_mul_1 (ecc, i, i, 4);
105 ecc_modp_mul (ecc, j, u2, i);
106 ecc_modp_mul (ecc, v, u1, i);
108 /* now, u1, u2 and i are free for reuse .*/
109 /* x3, use u1, u2 as scratch */
110 ecc_modp_sqr (ecc, u1, s2);
111 ecc_modp_sub (ecc, r, u1, j);
112 ecc_modp_submul_1 (ecc, r, v, 2);
115 ecc_modp_mul (ecc, u1, s1, j); /* Frees j */
116 ecc_modp_sub (ecc, u2, v, r); /* Frees v */
117 ecc_modp_mul (ecc, i, s2, u2);
118 ecc_modp_submul_1 (ecc, i, u1, 2);
119 mpn_copyi (r + ecc->p.size, i, ecc->p.size);