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0bcb8184 MW |
1 | /* |
2 | * x25519.c: Bernstein's X25519 key-exchange function | |
3 | */ | |
4 | /* | |
5 | * This file is Free Software. It has been modified to as part of its | |
6 | * incorporation into secnet. | |
7 | * | |
8 | * Copyright 2017 Mark Wooding | |
9 | * | |
10 | * You may redistribute this file and/or modify it under the terms of | |
11 | * the permissive licence shown below. | |
12 | * | |
13 | * You may redistribute secnet as a whole and/or modify it under the | |
14 | * terms of the GNU General Public License as published by the Free | |
15 | * Software Foundation; either version 3, or (at your option) any | |
16 | * later version. | |
17 | * | |
18 | * This program is distributed in the hope that it will be useful, | |
19 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
20 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
21 | * GNU General Public License for more details. | |
22 | * | |
23 | * You should have received a copy of the GNU General Public License | |
24 | * along with this program; if not, see | |
25 | * https://www.gnu.org/licenses/gpl.html. | |
26 | */ | |
27 | /* | |
28 | * Imported from Catacomb, and modified for Secnet (2017-04-30): | |
29 | * | |
30 | * * Use `fake-mLib-bits.h' in place of the real <mLib/bits.h>. | |
31 | * | |
32 | * * Remove the test rig code: a replacement is in a separate source file. | |
33 | * | |
34 | * * Ignore the top bit of the input public key: in Secnet, conformance | |
35 | * with RFC7748 is more valuable than flexibility. | |
36 | * | |
37 | * * Strip out the key-management definitions. | |
38 | * | |
39 | * The file's original comment headers are preserved below. | |
40 | */ | |
b7a5ecfc MW |
41 | /* -*-c-*- |
42 | * | |
43 | * The X25519 key-agreement algorithm | |
44 | * | |
45 | * (c) 2017 Straylight/Edgeware | |
46 | */ | |
47 | ||
48 | /*----- Licensing notice --------------------------------------------------* | |
49 | * | |
50 | * This file is part of Catacomb. | |
51 | * | |
52 | * Catacomb is free software; you can redistribute it and/or modify | |
53 | * it under the terms of the GNU Library General Public License as | |
54 | * published by the Free Software Foundation; either version 2 of the | |
55 | * License, or (at your option) any later version. | |
56 | * | |
57 | * Catacomb is distributed in the hope that it will be useful, | |
58 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
59 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
60 | * GNU Library General Public License for more details. | |
61 | * | |
62 | * You should have received a copy of the GNU Library General Public | |
63 | * License along with Catacomb; if not, write to the Free | |
64 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, | |
65 | * MA 02111-1307, USA. | |
66 | */ | |
67 | ||
68 | /*----- Header files ------------------------------------------------------*/ | |
69 | ||
0bcb8184 | 70 | #include "fake-mLib-bits.h" |
b7a5ecfc MW |
71 | |
72 | #include "montladder.h" | |
73 | #include "f25519.h" | |
74 | #include "x25519.h" | |
75 | ||
76 | /*----- Important constants -----------------------------------------------*/ | |
77 | ||
78 | const octet x25519_base[32] = { 9, 0, /* ... */ }; | |
79 | ||
80 | #define A0 121665 | |
81 | ||
b7a5ecfc MW |
82 | /*----- Main code ---------------------------------------------------------*/ |
83 | ||
84 | /* --- @x25519@ --- * | |
85 | * | |
86 | * Arguments: @octet zz[X25519_OUTSZ]@ = where to put the result | |
87 | * @const octet k[X25519_KEYSZ]@ = pointer to private key | |
88 | * @const octet qx[X25519_PUBSZ]@ = pointer to public value | |
89 | * | |
90 | * Returns: --- | |
91 | * | |
92 | * Use: Calculates X25519 of @k@ and @qx@. | |
93 | * | |
94 | * Note that there is disagreement over whether the most | |
95 | * significant bit of @qx@ (i.e., the value @qx[31]&0x80@) | |
96 | * should be ignored or counted towards the represented value. | |
97 | * Historically implementations respected the bit; later | |
98 | * convention seems to be to ignore it. This implementation | |
99 | * honours the bit: a caller who wants to ignore the bit can | |
100 | * easily clear it, while caller who wants to respect it has a | |
101 | * difficult job if this function ignores it. | |
102 | */ | |
103 | ||
104 | void x25519(octet zz[X25519_OUTSZ], | |
105 | const octet k[X25519_KEYSZ], | |
106 | const octet qx[X25519_PUBSZ]) | |
107 | { | |
108 | uint32 kw[8]; | |
0bcb8184 | 109 | uint8_t b[X25519_PUBSZ]; |
b7a5ecfc MW |
110 | f25519 x1; |
111 | ||
112 | /* Load and clamp the key. The low bits are cleared to kill the small | |
113 | * subgroups on the curve and its twist, and a high bit is set to guard | |
114 | * against careless implementations, though this isn't one of those. | |
115 | */ | |
116 | kw[0] = LOAD32_L(k + 0); kw[1] = LOAD32_L(k + 4); | |
117 | kw[2] = LOAD32_L(k + 8); kw[3] = LOAD32_L(k + 12); | |
118 | kw[4] = LOAD32_L(k + 16); kw[5] = LOAD32_L(k + 20); | |
119 | kw[6] = LOAD32_L(k + 24); kw[7] = LOAD32_L(k + 28); | |
120 | kw[0] &= 0xfffffff8; kw[7] = (kw[7]&0x3fffffff) | 0x40000000; | |
121 | ||
0bcb8184 MW |
122 | /* Copy the input point and clamp the top bit. */ |
123 | memcpy(b, qx, sizeof(b)); b[31] &= 0x7f; | |
124 | f25519_load(&x1, b); | |
125 | ||
b7a5ecfc | 126 | /* And run the ladder. */ |
b7a5ecfc MW |
127 | #define MULA0(z, x) do { f25519_mulconst((z), (x), A0); } while (0) |
128 | MONT_LADDER(f25519, MULA0, kw, 8, 32, &x1, &x1); | |
129 | #undef MULA0 | |
130 | f25519_store(zz, &x1); | |
131 | } | |
132 | ||
133 | /*----- Test rig ----------------------------------------------------------*/ | |
134 | ||
135 | #ifdef TEST_RIG | |
136 | ||
137 | #include <stdio.h> | |
138 | #include <string.h> | |
139 | ||
140 | #include <mLib/report.h> | |
141 | #include <mLib/testrig.h> | |
142 | ||
143 | static int vrf_x25519(dstr dv[]) | |
144 | { | |
145 | dstr dz = DSTR_INIT; | |
146 | int ok = 1; | |
147 | ||
148 | if (dv[0].len != 32) die(1, "bad key length"); | |
149 | if (dv[1].len != 32) die(1, "bad public length"); | |
150 | if (dv[2].len != 32) die(1, "bad result length"); | |
151 | ||
152 | dstr_ensure(&dz, 32); dz.len = 32; | |
153 | x25519((octet *)dz.buf, | |
154 | (const octet *)dv[0].buf, | |
155 | (const octet *)dv[1].buf); | |
156 | if (memcmp(dz.buf, dv[2].buf, 32) != 0) { | |
157 | ok = 0; | |
158 | fprintf(stderr, "failed!"); | |
159 | fprintf(stderr, "\n\t k = "); type_hex.dump(&dv[0], stderr); | |
160 | fprintf(stderr, "\n\t p = "); type_hex.dump(&dv[1], stderr); | |
161 | fprintf(stderr, "\n\twant = "); type_hex.dump(&dv[2], stderr); | |
162 | fprintf(stderr, "\n\tcalc = "); type_hex.dump(&dz, stderr); | |
163 | fprintf(stderr, "\n"); | |
164 | } | |
165 | ||
166 | dstr_destroy(&dz); | |
167 | return (ok); | |
168 | } | |
169 | ||
170 | static int vrf_mct(dstr dv[]) | |
171 | { | |
172 | octet b0[32], b1[32], *k = b0, *x = b1, *t; | |
173 | unsigned long i, niter; | |
174 | dstr d = DSTR_INIT; | |
175 | int ok = 1; | |
176 | ||
177 | if (dv[0].len != sizeof(b0)) { fprintf(stderr, "k len\n"); exit(2); } | |
178 | if (dv[1].len != sizeof(b1)) { fprintf(stderr, "x len\n"); exit(2); } | |
179 | if (dv[3].len != sizeof(b0)) { fprintf(stderr, "result len\n"); exit(2); } | |
180 | memcpy(b0, dv[0].buf, sizeof(b0)); | |
181 | memcpy(b1, dv[1].buf, sizeof(b1)); | |
182 | niter = *(unsigned long *)dv[2].buf; | |
183 | dstr_ensure(&d, 32); d.len = 32; t = (octet *)d.buf; | |
184 | ||
185 | for (i = 0; i < niter; i++) { | |
186 | x[31] &= 0x7f; | |
187 | x25519(x, k, x); | |
188 | t = x; x = k; k = t; | |
189 | } | |
190 | memcpy(d.buf, k, d.len); | |
191 | ||
192 | if (memcmp(d.buf, dv[3].buf, d.len) != 0) { | |
193 | ok = 0; | |
194 | fprintf(stderr, "failed..."); | |
195 | fprintf(stderr, "\n\tinitial k = "); type_hex.dump(&dv[0], stderr); | |
196 | fprintf(stderr, "\n\tinitial x = "); type_hex.dump(&dv[1], stderr); | |
197 | fprintf(stderr, "\n\titerations = %lu", niter); | |
198 | fprintf(stderr, "\n\texpected = "); type_hex.dump(&dv[3], stderr); | |
199 | fprintf(stderr, "\n\tcalculated = "); type_hex.dump(&d, stderr); | |
200 | fputc('\n', stderr); | |
201 | } | |
202 | ||
203 | dstr_destroy(&d); | |
204 | return (ok); | |
205 | } | |
206 | ||
207 | static test_chunk tests[] = { | |
208 | { "x25519", vrf_x25519, { &type_hex, &type_hex, &type_hex } }, | |
209 | { "x25519-mct", vrf_mct, | |
210 | { &type_hex, &type_hex, &type_ulong, &type_hex } }, | |
211 | { 0, 0, { 0 } } | |
212 | }; | |
213 | ||
214 | int main(int argc, char *argv[]) | |
215 | { | |
216 | test_run(argc, argv, tests, SRCDIR "/t/x25519"); | |
217 | return (0); | |
218 | } | |
219 | ||
220 | #endif | |
221 | ||
222 | /*----- That's all, folks -------------------------------------------------*/ |