| 1 | /* -*-c-*- |
| 2 | * |
| 3 | * $Id: dsa-verify.c,v 1.6 2001/06/16 12:56:38 mdw Exp $ |
| 4 | * |
| 5 | * DSA signature verification |
| 6 | * |
| 7 | * (c) 1999 Straylight/Edgeware |
| 8 | */ |
| 9 | |
| 10 | /*----- Licensing notice --------------------------------------------------* |
| 11 | * |
| 12 | * This file is part of Catacomb. |
| 13 | * |
| 14 | * Catacomb is free software; you can redistribute it and/or modify |
| 15 | * it under the terms of the GNU Library General Public License as |
| 16 | * published by the Free Software Foundation; either version 2 of the |
| 17 | * License, or (at your option) any later version. |
| 18 | * |
| 19 | * Catacomb is distributed in the hope that it will be useful, |
| 20 | * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| 21 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the |
| 22 | * GNU Library General Public License for more details. |
| 23 | * |
| 24 | * You should have received a copy of the GNU Library General Public |
| 25 | * License along with Catacomb; if not, write to the Free |
| 26 | * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, |
| 27 | * MA 02111-1307, USA. |
| 28 | */ |
| 29 | |
| 30 | /*----- Revision history --------------------------------------------------* |
| 31 | * |
| 32 | * $Log: dsa-verify.c,v $ |
| 33 | * Revision 1.6 2001/06/16 12:56:38 mdw |
| 34 | * Fixes for interface change to @mpmont_expr@ and @mpmont_mexpr@. |
| 35 | * |
| 36 | * Revision 1.5 2000/10/08 12:13:17 mdw |
| 37 | * Use @MP_EQ@ instead of @MP_CMP@. |
| 38 | * |
| 39 | * Revision 1.4 2000/06/17 10:53:35 mdw |
| 40 | * Typesetting fixes. |
| 41 | * |
| 42 | * Revision 1.3 1999/12/10 23:18:38 mdw |
| 43 | * Change interface for suggested destinations. |
| 44 | * |
| 45 | * Revision 1.2 1999/11/23 00:20:04 mdw |
| 46 | * Remove stray debugging code. |
| 47 | * |
| 48 | * Revision 1.1 1999/11/19 19:28:00 mdw |
| 49 | * Implementation of the Digital Signature Algorithm. |
| 50 | * |
| 51 | */ |
| 52 | |
| 53 | /*----- Header files ------------------------------------------------------*/ |
| 54 | |
| 55 | #include "dsa.h" |
| 56 | #include "mp.h" |
| 57 | #include "mpmont.h" |
| 58 | |
| 59 | /*----- Main code ---------------------------------------------------------*/ |
| 60 | |
| 61 | /* --- @dsa_vrfy@ --- * |
| 62 | * |
| 63 | * Arguments: @const dsa_param *dp@ = pointer to DSA parameters |
| 64 | * @mp *y@ = public verification key |
| 65 | * @mp *m@ = message which was signed |
| 66 | * @mp *r, *s@ = the signature |
| 67 | * |
| 68 | * Returns: Zero if the signature is a forgery, nonzero if it's valid. |
| 69 | * |
| 70 | * Use: Verifies a DSA digital signature. |
| 71 | */ |
| 72 | |
| 73 | int dsa_vrfy(const dsa_param *dp, mp *y, mp *m, mp *r, mp *s) |
| 74 | { |
| 75 | mpmont pm, qm; |
| 76 | mp *w; |
| 77 | mp_expfactor f[2]; |
| 78 | int ok; |
| 79 | |
| 80 | /* --- Ensure that all of the signature bits are in range --- */ |
| 81 | |
| 82 | if ((r->f | s->f) & MP_NEG) |
| 83 | return (0); |
| 84 | if (MP_CMP(r, >=, dp->q) || MP_CMP(s, >=, dp->q)) |
| 85 | return (0); |
| 86 | |
| 87 | /* --- Set up Montgomery contexts --- */ |
| 88 | |
| 89 | mpmont_create(&pm, dp->p); |
| 90 | mpmont_create(&qm, dp->q); |
| 91 | |
| 92 | /* --- Compute %$w = s^{-1} \bmod q$% --- */ |
| 93 | |
| 94 | { |
| 95 | mp *z = MP_NEW; |
| 96 | mp_gcd(0, 0, &z, dp->q, s); |
| 97 | w = mpmont_mul(&qm, MP_NEW, z, qm.r2); |
| 98 | mp_drop(z); |
| 99 | } |
| 100 | |
| 101 | /* --- Compute %$wr$% and %$wm$% --- */ |
| 102 | |
| 103 | f[0].exp = mpmont_mul(&qm, MP_NEW, w, m); |
| 104 | f[1].exp = mpmont_mul(&qm, MP_NEW, w, r); |
| 105 | mp_drop(w); |
| 106 | mpmont_destroy(&qm); |
| 107 | |
| 108 | /* --- Do the exponentiation and take residue mod @q@ --- */ |
| 109 | |
| 110 | f[0].base = dp->g; |
| 111 | f[1].base = y; |
| 112 | w = mpmont_mexp(&pm, MP_NEW, f, 2); |
| 113 | mp_div(0, &w, w, dp->q); |
| 114 | ok = MP_EQ(w, r); |
| 115 | |
| 116 | /* --- Tidy up --- */ |
| 117 | |
| 118 | mp_drop(w); |
| 119 | mp_drop(f[0].exp); |
| 120 | mp_drop(f[1].exp); |
| 121 | mpmont_destroy(&pm); |
| 122 | return (ok); |
| 123 | } |
| 124 | |
| 125 | /* --- @dsa_verify@ --- * |
| 126 | * |
| 127 | * Arguments: @const dsa_param *dp@ = pointer to DSA parameters |
| 128 | * @mp *y@ = public verification key |
| 129 | * @const void *m@ = pointer to message block |
| 130 | * @size_t msz@ = size of message block |
| 131 | * @const void *r@ = pointer to @r@ signature half |
| 132 | * @size_t rsz@ = size of @r@ |
| 133 | * @const void *s@ = pointer to @s@ signature half |
| 134 | * @size_t ssz@ = size of @s@ |
| 135 | * |
| 136 | * Returns: Zero if the signature is a forgery, nonzero if it's valid. |
| 137 | * |
| 138 | * Use: Verifies a DSA digital signature. |
| 139 | */ |
| 140 | |
| 141 | int dsa_verify(const dsa_param *dp, mp *y, |
| 142 | const void *m, size_t msz, |
| 143 | const void *r, size_t rsz, |
| 144 | const void *s, size_t ssz) |
| 145 | { |
| 146 | mp *mm = mp_loadb(MP_NEW, m, msz); |
| 147 | mp *rm = mp_loadb(MP_NEW, r, rsz); |
| 148 | mp *sm = mp_loadb(MP_NEW, s, ssz); |
| 149 | int ok = dsa_vrfy(dp, y, mm, rm, sm); |
| 150 | mp_drop(mm); |
| 151 | mp_drop(rm); |
| 152 | mp_drop(sm); |
| 153 | return (ok); |
| 154 | } |
| 155 | |
| 156 | /*----- Test rig ----------------------------------------------------------*/ |
| 157 | |
| 158 | #ifdef TEST_RIG |
| 159 | |
| 160 | #include <mLib/testrig.h> |
| 161 | |
| 162 | #include "sha.h" |
| 163 | |
| 164 | static int verify(int good, dstr *v) |
| 165 | { |
| 166 | dsa_param dp; |
| 167 | mp *y; |
| 168 | sha_ctx c; |
| 169 | octet hash[SHA_HASHSZ]; |
| 170 | int ok = 1; |
| 171 | int rc; |
| 172 | |
| 173 | dp.q = *(mp **)v[0].buf; |
| 174 | dp.p = *(mp **)v[1].buf; |
| 175 | dp.g = *(mp **)v[2].buf; |
| 176 | y = *(mp **)v[3].buf; |
| 177 | |
| 178 | sha_init(&c); |
| 179 | sha_hash(&c, v[4].buf, v[4].len); |
| 180 | sha_done(&c, hash); |
| 181 | |
| 182 | rc = dsa_verify(&dp, y, hash, sizeof(hash), |
| 183 | v[5].buf, v[5].len, v[6].buf, v[6].len); |
| 184 | |
| 185 | if (!rc != !good) { |
| 186 | if (good) |
| 187 | fputs("\n*** verification failed", stderr); |
| 188 | else |
| 189 | fputs("\n*** verification succeeded", stderr); |
| 190 | fputs("\nq = ", stderr); mp_writefile(dp.q, stderr, 16); |
| 191 | fputs("\np = ", stderr); mp_writefile(dp.p, stderr, 16); |
| 192 | fputs("\ng = ", stderr); mp_writefile(dp.g, stderr, 16); |
| 193 | fputs("\ny = ", stderr); mp_writefile(y, stderr, 16); |
| 194 | fprintf(stderr, "\nmessage = `%s'", v[4].buf); |
| 195 | fputs("\nr = ", stderr); type_hex.dump(&v[5], stderr); |
| 196 | fputs("\ns = ", stderr); type_hex.dump(&v[6], stderr); |
| 197 | fputc('\n', stderr); |
| 198 | ok = 0; |
| 199 | } |
| 200 | |
| 201 | mp_drop(dp.p); |
| 202 | mp_drop(dp.q); |
| 203 | mp_drop(dp.g); |
| 204 | mp_drop(y); |
| 205 | assert(mparena_count(MPARENA_GLOBAL) == 0); |
| 206 | return (ok); |
| 207 | } |
| 208 | |
| 209 | static int vgood(dstr *v) { return verify(1, v); } |
| 210 | static int vbad(dstr *v) { return verify(0, v); } |
| 211 | |
| 212 | static test_chunk tests[] = { |
| 213 | { "verify-good", vgood, |
| 214 | { &type_mp, &type_mp, &type_mp, &type_mp, |
| 215 | &type_string, &type_hex, &type_hex, 0 } }, |
| 216 | { "verify-bad", vbad, |
| 217 | { &type_mp, &type_mp, &type_mp, &type_mp, |
| 218 | &type_string, &type_hex, &type_hex, 0 } }, |
| 219 | { 0, 0, { 0 } } |
| 220 | }; |
| 221 | |
| 222 | int main(int argc, char *argv[]) |
| 223 | { |
| 224 | sub_init(); |
| 225 | test_run(argc, argv, tests, SRCDIR "/tests/dsa"); |
| 226 | return (0); |
| 227 | } |
| 228 | |
| 229 | #endif |
| 230 | |
| 231 | /*----- That's all, folks -------------------------------------------------*/ |