3 * The X25519 key-agreement algorithm
5 * (c) 2017 Straylight/Edgeware
8 /*----- Licensing notice --------------------------------------------------*
10 * This file is part of Catacomb.
12 * Catacomb is free software; you can redistribute it and/or modify
13 * it under the terms of the GNU Library General Public License as
14 * published by the Free Software Foundation; either version 2 of the
15 * License, or (at your option) any later version.
17 * Catacomb is distributed in the hope that it will be useful,
18 * but WITHOUT ANY WARRANTY; without even the implied warranty of
19 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
20 * GNU Library General Public License for more details.
22 * You should have received a copy of the GNU Library General Public
23 * License along with Catacomb; if not, write to the Free
24 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
28 /*----- Header files ------------------------------------------------------*/
30 #include <mLib/bits.h>
32 #include "montladder.h"
36 /*----- Important constants -----------------------------------------------*/
38 const octet x25519_base[32] = { 9, 0, /* ... */ };
42 /*----- Key fetching ------------------------------------------------------*/
44 const key_fetchdef x25519_pubfetch[] = {
45 { "pub", offsetof(x25519_pub, pub), KENC_BINARY, 0 },
49 static const key_fetchdef priv[] = {
50 { "priv", offsetof(x25519_priv, priv), KENC_BINARY, 0 },
54 const key_fetchdef x25519_privfetch[] = {
55 { "pub", offsetof(x25519_priv, pub), KENC_BINARY, 0 },
56 { "private", 0, KENC_STRUCT, priv },
60 /*----- Main code ---------------------------------------------------------*/
64 * Arguments: @octet zz[X25519_OUTSZ]@ = where to put the result
65 * @const octet k[X25519_KEYSZ]@ = pointer to private key
66 * @const octet qx[X25519_PUBSZ]@ = pointer to public value
70 * Use: Calculates X25519 of @k@ and @qx@.
72 * Note that there is disagreement over whether the most
73 * significant bit of @qx@ (i.e., the value @qx[31]&0x80@)
74 * should be ignored or counted towards the represented value.
75 * Historically implementations respected the bit; later
76 * convention seems to be to ignore it. This implementation
77 * honours the bit: a caller who wants to ignore the bit can
78 * easily clear it, while caller who wants to respect it has a
79 * difficult job if this function ignores it.
82 void x25519(octet zz[X25519_OUTSZ],
83 const octet k[X25519_KEYSZ],
84 const octet qx[X25519_PUBSZ])
89 /* Load and clamp the key. The low bits are cleared to kill the small
90 * subgroups on the curve and its twist, and a high bit is set to guard
91 * against careless implementations, though this isn't one of those.
93 kw[0] = LOAD32_L(k + 0); kw[1] = LOAD32_L(k + 4);
94 kw[2] = LOAD32_L(k + 8); kw[3] = LOAD32_L(k + 12);
95 kw[4] = LOAD32_L(k + 16); kw[5] = LOAD32_L(k + 20);
96 kw[6] = LOAD32_L(k + 24); kw[7] = LOAD32_L(k + 28);
97 kw[0] &= 0xfffffff8; kw[7] = (kw[7]&0x3fffffff) | 0x40000000;
99 /* And run the ladder. */
100 f25519_load(&x1, qx);
101 #define MULA0(z, x) do { f25519_mulconst((z), (x), A0); } while (0)
102 MONT_LADDER(f25519, MULA0, kw, 8, 32, &x1, &x1);
104 f25519_store(zz, &x1);
107 /*----- Test rig ----------------------------------------------------------*/
114 #include <mLib/report.h>
115 #include <mLib/testrig.h>
117 static int vrf_x25519(dstr dv[])
122 if (dv[0].len != 32) die(1, "bad key length");
123 if (dv[1].len != 32) die(1, "bad public length");
124 if (dv[2].len != 32) die(1, "bad result length");
126 dstr_ensure(&dz, 32); dz.len = 32;
127 x25519((octet *)dz.buf,
128 (const octet *)dv[0].buf,
129 (const octet *)dv[1].buf);
130 if (memcmp(dz.buf, dv[2].buf, 32) != 0) {
132 fprintf(stderr, "failed!");
133 fprintf(stderr, "\n\t k = "); type_hex.dump(&dv[0], stderr);
134 fprintf(stderr, "\n\t p = "); type_hex.dump(&dv[1], stderr);
135 fprintf(stderr, "\n\twant = "); type_hex.dump(&dv[2], stderr);
136 fprintf(stderr, "\n\tcalc = "); type_hex.dump(&dz, stderr);
137 fprintf(stderr, "\n");
144 static int vrf_mct(dstr dv[])
146 octet b0[32], b1[32], *k = b0, *x = b1, *t;
147 unsigned long i, niter;
151 if (dv[0].len != sizeof(b0)) { fprintf(stderr, "k len\n"); exit(2); }
152 if (dv[1].len != sizeof(b1)) { fprintf(stderr, "x len\n"); exit(2); }
153 if (dv[3].len != sizeof(b0)) { fprintf(stderr, "result len\n"); exit(2); }
154 memcpy(b0, dv[0].buf, sizeof(b0));
155 memcpy(b1, dv[1].buf, sizeof(b1));
156 niter = *(unsigned long *)dv[2].buf;
157 dstr_ensure(&d, 32); d.len = 32; t = (octet *)d.buf;
159 for (i = 0; i < niter; i++) {
164 memcpy(d.buf, k, d.len);
166 if (memcmp(d.buf, dv[3].buf, d.len) != 0) {
168 fprintf(stderr, "failed...");
169 fprintf(stderr, "\n\tinitial k = "); type_hex.dump(&dv[0], stderr);
170 fprintf(stderr, "\n\tinitial x = "); type_hex.dump(&dv[1], stderr);
171 fprintf(stderr, "\n\titerations = %lu", niter);
172 fprintf(stderr, "\n\texpected = "); type_hex.dump(&dv[3], stderr);
173 fprintf(stderr, "\n\tcalculated = "); type_hex.dump(&d, stderr);
181 static test_chunk tests[] = {
182 { "x25519", vrf_x25519, { &type_hex, &type_hex, &type_hex } },
183 { "x25519-mct", vrf_mct,
184 { &type_hex, &type_hex, &type_ulong, &type_hex } },
188 int main(int argc, char *argv[])
190 test_run(argc, argv, tests, SRCDIR "/t/x25519");
196 /*----- That's all, folks -------------------------------------------------*/