1 /* eddsa-sign.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 <assert.h>
37
38 #include "eddsa.h"
39 #include "eddsa-internal.h"
40
41 #include "ecc.h"
42 #include "ecc-internal.h"
43 #include "nettle-meta.h"
44
45 mp_size_t
_eddsa_sign_itch(const struct ecc_curve * ecc)46 _eddsa_sign_itch (const struct ecc_curve *ecc)
47 {
48 assert (ecc->mul_g_itch <= _eddsa_compress_itch (ecc));
49 return 5*ecc->p.size + _eddsa_compress_itch (ecc);
50 }
51
52 void
_eddsa_sign(const struct ecc_curve * ecc,const struct ecc_eddsa * eddsa,void * ctx,const uint8_t * pub,const uint8_t * k1,const mp_limb_t * k2,size_t length,const uint8_t * msg,uint8_t * signature,mp_limb_t * scratch)53 _eddsa_sign (const struct ecc_curve *ecc,
54 const struct ecc_eddsa *eddsa,
55 void *ctx,
56 const uint8_t *pub,
57 const uint8_t *k1,
58 const mp_limb_t *k2,
59 size_t length,
60 const uint8_t *msg,
61 uint8_t *signature,
62 mp_limb_t *scratch)
63 {
64 mp_size_t size;
65 size_t nbytes;
66 mp_limb_t q, cy;
67
68 #define rp scratch
69 #define hp (scratch + size)
70 #define P (scratch + 2*size)
71 #define sp (scratch + 2*size)
72 #define hash ((uint8_t *) (scratch + 3*size))
73 #define scratch_out (scratch + 5*size)
74
75 size = ecc->p.size;
76 nbytes = 1 + ecc->p.bit_size / 8;
77
78 eddsa->dom (ctx);
79 eddsa->update (ctx, nbytes, k1);
80 eddsa->update (ctx, length, msg);
81 eddsa->digest (ctx, 2*nbytes, hash);
82 _eddsa_hash (&ecc->q, rp, 2*nbytes, hash);
83
84 ecc->mul_g (ecc, P, rp, scratch_out);
85 _eddsa_compress (ecc, signature, P, scratch_out);
86
87 eddsa->dom (ctx);
88 eddsa->update (ctx, nbytes, signature);
89 eddsa->update (ctx, nbytes, pub);
90 eddsa->update (ctx, length, msg);
91 eddsa->digest (ctx, 2*nbytes, hash);
92 _eddsa_hash (&ecc->q, hp, 2*nbytes, hash);
93
94 ecc_mod_mul (&ecc->q, sp, hp, k2, sp);
95 ecc_mod_add (&ecc->q, sp, sp, rp); /* FIXME: Can be plain add */
96 if (ecc->p.bit_size == 255)
97 {
98 /* FIXME: Special code duplicated in ecc_curve25519_modq
99 Define a suitable method for canonical reduction? */
100
101 /* q is slightly larger than 2^252, underflow from below
102 mpn_submul_1 is unlikely. */
103 unsigned shift = 252 - GMP_NUMB_BITS * (ecc->p.size - 1);
104 q = sp[ecc->p.size-1] >> shift;
105 }
106 else
107 {
108 unsigned shift;
109
110 assert (ecc->p.bit_size == 448);
111 /* q is slightly smaller than 2^446 */
112 shift = 446 - GMP_NUMB_BITS * (ecc->p.size - 1);
113 /* Add one, then it's possible but unlikely that below
114 mpn_submul_1 does *not* underflow. */
115 q = (sp[ecc->p.size-1] >> shift) + 1;
116 }
117
118 cy = mpn_submul_1 (sp, ecc->q.m, ecc->p.size, q);
119 assert (cy < 2);
120 cy -= mpn_cnd_add_n (cy, sp, sp, ecc->q.m, ecc->p.size);
121 assert (cy == 0);
122
123 mpn_get_base256_le (signature + nbytes, nbytes, sp, ecc->q.size);
124 #undef rp
125 #undef hp
126 #undef P
127 #undef sp
128 #undef hash
129 }
130