1 /* curve25519-mul-g.c
2
3 Copyright (C) 2014 Niels Möller
4
5 This file is part of GNU Nettle.
6
7 GNU Nettle is free software: you can redistribute it and/or
8 modify it under the terms of either:
9
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.
13
14 or
15
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.
19
20 or both in parallel, as here.
21
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.
26
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/.
30 */
31
32 #if HAVE_CONFIG_H
33 # include "config.h"
34 #endif
35
36 #include <string.h>
37
38 #include "curve25519.h"
39
40 #include "ecc.h"
41 #include "ecc-internal.h"
42
43 /* Intended to be compatible with NaCl's crypto_scalarmult_base. */
44 void
curve25519_mul_g(uint8_t * r,const uint8_t * n)45 curve25519_mul_g (uint8_t *r, const uint8_t *n)
46 {
47 const struct ecc_curve *ecc = &_nettle_curve25519;
48 uint8_t t[CURVE25519_SIZE];
49 mp_limb_t *scratch;
50 mp_size_t itch;
51
52 #define ng scratch
53 #define x (scratch + 3*ecc->p.size)
54 #define scratch_out (scratch + 4*ecc->p.size)
55
56 memcpy (t, n, sizeof(t));
57 t[0] &= ~7;
58 t[CURVE25519_SIZE-1] = (t[CURVE25519_SIZE-1] & 0x3f) | 0x40;
59
60 itch = 4*ecc->p.size + ecc->mul_g_itch;
61 scratch = gmp_alloc_limbs (itch);
62
63 mpn_set_base256_le (x, ecc->p.size, t, CURVE25519_SIZE);
64
65 ecc_mul_g_eh (ecc, ng, x, scratch_out);
66 curve25519_eh_to_x (x, ng, scratch_out);
67
68 mpn_get_base256_le (r, CURVE25519_SIZE, x, ecc->p.size);
69 gmp_free_limbs (scratch, itch);
70 #undef p
71 #undef x
72 #undef scratch_out
73 }
74