| 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 | */ |
| 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 | |
| 70 | #include "fake-mLib-bits.h" |
| 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 | |
| 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]; |
| 109 | uint8_t b[X25519_PUBSZ]; |
| 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 | |
| 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 | |
| 126 | /* And run the ladder. */ |
| 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 -------------------------------------------------*/ |