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   1 /* -*-c-*-
   2  *
   3  * $Id: gdsa.c,v 1.1 2004/04/04 19:42:59 mdw Exp $
   4  *
   5  * Generalized version of DSA
   6  *
   7  * (c) 2004 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: gdsa.c,v $
  33  * Revision 1.1  2004/04/04 19:42:59  mdw
  34  * Add set -e.
  35  *
  36  */
  37
  38 /*----- Header files ------------------------------------------------------*/
  39
  40 #include "gdsa.h"
  41 #include "group.h"
  42 #include "ghash.h"
  43 #include "mpbarrett.h"
  44 #include "mprand.h"
  45
  46 /*----- Main code ---------------------------------------------------------*/
  47
  48 /* --- @gdsa_beginhash@ --- *
  49  *
  50  * Arguments:   @const gdsa *c@ = pointer to the context structure
  51  *
  52  * Returns:     A hashing context for you to hash the message.
  53  *
  54  * Use:         Initializes a hash function correctly for you to hash a
  55  *              message.  Requires @h@.
  56  */
  57
  58 ghash *gdsa_beginhash(const gdsa *c) { return (GH_INIT(c->h)); }
  59
  60 /* --- @gdsa_endhash@ --- *
  61  *
  62  * Arguments:   @const gdsa *c@ = pointer to the context structure
  63  *              @ghash *h@ = the hashing context
  64  *
  65  * Returns:     ---
  66  *
  67  * Use:         Does any final thing that DSA wants to do when hashing a
  68  *              message.  (Actually, there's nothing.)  The hashing context
  69  *              isn't finalized.
  70  */
  71
  72 void gdsa_endhash(gdsa *c, ghash *h) { ; }
  73
  74 /* --- @gdsa_sign@ --- *
  75  *
  76  * Arguments:   @const gdsa *c@ = my context structure
  77  *              @gdsa_sig *s@ = where to put the signature (initialized)
  78  *              @const void *m@ = pointer to message hash
  79  *              @mp *k@ = random exponent for this message or null
  80  *
  81  * Returns:     ---
  82  *
  83  * Use:         Signs a message.  Requires @g@, @u@, @h@, and @r@ if @k@ is
  84  *              null.  This is a better idea than inventing @k@ yourself.
  85  */
  86
  87 void gdsa_sign(const gdsa *c, gdsa_sig *s, const void *m, mp *k)
  88 {
  89   group *g = c->g;
  90   mp *mr = mp_loadb(MP_NEW, m, c->h->hashsz);
  91   ge *z = G_CREATE(g);
  92   mp *sr = s->r, *ss = s->s;
  93   mpbarrett b;
  94
  95   if (k) { MP_COPY(k); goto have_k; }
  96 new_k:
  97   k = mprand_range(k, g->r, c->r, 0);
  98 have_k:
  99   if (MP_ISZERO(k)) goto new_k;
 100   G_EXP(g, z, g->g, k);
 101   sr = G_TOINT(g, sr, z); assert(sr);
 102   if (MP_ISZERO(sr)) goto new_k;
 103
 104   mp_div(0, &sr, sr, g->r);
 105   mpbarrett_create(&b, g->r);
 106   ss = mp_mul(ss, sr, c->u); ss = mpbarrett_reduce(&b, ss, ss);
 107   ss = mp_add(ss, ss, mr); mp_div(0, &ss, ss, g->r);
 108   mp_gcd(0, 0, &k, g->r, k);
 109   ss = mp_mul(ss, ss, k); ss = mpbarrett_reduce(&b, ss, ss);
 110   s->r = sr; s->s = ss;
 111   mp_drop(k); mp_drop(mr); mpbarrett_destroy(&b); G_DESTROY(g, z);
 112 }
 113
 114 /* --- @gdsa_verify@ --- *
 115  *
 116  * Arguments:   @const gdsa *c@ = my context structure
 117  *              @const gdsa_sig *s@ = the signature to verify
 118  *              @const void *m@ = pointer to message hash
 119  *
 120  * Returns:     Zero if OK, negative on failure.
 121  *
 122  * Use:         Checks a signature on a message,  Requires @g@, @p@ and @h@.
 123  */
 124
 125 int gdsa_verify(const gdsa *c, const gdsa_sig *s, const void *m)
 126 {
 127   group *g = c->g;
 128   group_expfactor e[2];
 129   mpbarrett b;
 130   mp *h = MP_NEW, *t;
 131   ge *w;
 132   int rc = -1;
 133
 134   if (MP_CMP(s->r, <, MP_ONE) || MP_CMP(s->r, >=, g->r) ||
 135       MP_CMP(s->s, <, MP_ONE) || MP_CMP(s->s, >=, g->r))
 136     return (-1);
 137   mpbarrett_create(&b, g->r); mp_gcd(0, 0, &h, g->r, s->s);
 138   e[0].base = g->g; e[1].base = c->p;
 139   t = mp_loadb(MP_NEW, m, c->h->hashsz); mp_div(0, &t, t, g->r);
 140   t = mp_mul(t, t, h); e[0].exp = t = mpbarrett_reduce(&b, t, t);
 141   h = mp_mul(h, s->r, h); e[1].exp = h = mpbarrett_reduce(&b, h, h);
 142   w = G_CREATE(g); G_MEXP(g, w, e, 2);
 143   t = G_TOINT(g, t, w); if (!t) goto done;
 144   mp_div(0, &t, t, g->r); if (MP_EQ(t, s->r)) rc = 0;
 145 done:
 146   G_DESTROY(g, w); mp_drop(t); mp_drop(h); mpbarrett_destroy(&b);
 147   return (rc);
 148 }
 149
 150 /*----- Test rig ----------------------------------------------------------*/
 151
 152 #ifdef TEST_RIG
 153
 154 static group *getgroup(const char *p) {
 155   group *g; qd_parse qd;
 156   qd.p = p; qd.e = 0; g = group_parse(&qd);
 157   if (g && !qd_eofp(&qd)) { G_DESTROYGROUP(g); g = 0; qd.e = "junk at eof"; }
 158   if (!g) { fprintf(stderr, "bad group string `%.*s|%s': %s\n", qd.p - p,
 159                     p, qd.p, qd.e); exit(1); }
 160   return (g);
 161 }
 162
 163 static ge *getge(group *g, const char *p) {
 164   ge *x = G_CREATE(g);
 165   if (group_readstring(g, x, p, 0)) {
 166     fprintf(stderr, "bad group element `%s'\n", p);
 167     exit(1);
 168   }
 169   return (x);
 170 }
 171
 172 static void showge(group *g, const char *p, ge *x) {
 173   fprintf(stderr, "*** %s = ", p); group_writefile(g, x, stderr);
 174   putc('\n', stderr);
 175 }
 176
 177 static void showmp(const char *p, mp *x, int r) {
 178   fprintf(stderr, "*** %s = ", p); mp_writefile(x, stderr, r);
 179   putc('\n', stderr);
 180 }
 181
 182 static int tsign(dstr *v)
 183 {
 184   gdsa c;
 185   gdsa_sig s, ss = GDSA_SIG_INIT;
 186   ghash *h;
 187   mp *k;
 188   int ok = 1;
 189
 190   c.g = getgroup(v[0].buf); c.h = ghash_byname(v[1].buf);
 191   c.u = *(mp **)v[2].buf; k = *(mp **)v[4].buf;
 192   s.r = *(mp **)v[5].buf; s.s = *(mp **)v[6].buf;
 193
 194   h = gdsa_beginhash(&c);
 195   GH_HASH(h, v[3].buf, v[3].len);
 196   gdsa_endhash(&c, h);
 197   gdsa_sign(&c, &ss, GH_DONE(h, 0), k);
 198   if (!MP_EQ(s.r, ss.r) || !MP_EQ(s.s, ss.s)) {
 199     ok = 0;
 200     fprintf(stderr, "*** sign failed!\n");
 201     fprintf(stderr, "*** group: %s\n", v[0].buf);
 202     fprintf(stderr, "*** hash: %s\n", c.h->name);
 203     showmp("private key", c.u, 16);
 204     fprintf(stderr, "*** message: `%s'\n", v[3].buf);
 205     showmp("computed r", ss.r, 16); showmp("computed s", ss.s, 16);
 206     showmp("expected r", s.r, 16); showmp("expected s", s.s, 16);
 207   }
 208   mp_drop(s.r); mp_drop(s.s); mp_drop(ss.r); mp_drop(ss.s);
 209   mp_drop(k); mp_drop(c.u); G_DESTROYGROUP(c.g); GH_DESTROY(h);
 210   assert(mparena_count(MPARENA_GLOBAL) == 0);
 211   return (ok);
 212 }
 213
 214 static int tverify(dstr *v)
 215 {
 216   gdsa c;
 217   gdsa_sig s;
 218   ghash *h;
 219   int rc, erc;
 220   int ok = 1;
 221
 222   c.g = getgroup(v[0].buf); c.h = ghash_byname(v[1].buf);
 223   c.p = getge(c.g, v[2].buf);
 224   s.r = *(mp **)v[4].buf; s.s = *(mp **)v[5].buf;
 225   erc = *(int *)v[6].buf;
 226
 227   h = gdsa_beginhash(&c);
 228   GH_HASH(h, v[3].buf, v[3].len);
 229   gdsa_endhash(&c, h);
 230   rc = gdsa_verify(&c, &s, GH_DONE(h, 0));
 231   if (!rc != !erc) {
 232     ok = 0;
 233     fprintf(stderr, "*** verify failed!\n");
 234     fprintf(stderr, "*** group: %s\n", v[0].buf);
 235     fprintf(stderr, "*** hash: %s\n", c.h->name);
 236     showge(c.g, "public key", c.p);
 237     fprintf(stderr, "*** message: `%s'\n", v[3].buf);
 238     showmp("sig r", s.r, 16); showmp("sig s", s.s, 16);
 239     fprintf(stderr, "*** expected %s\n", !erc ? "pass" : "fail");
 240   }
 241   mp_drop(s.r); mp_drop(s.s); G_DESTROY(c.g, c.p); G_DESTROYGROUP(c.g);
 242   GH_DESTROY(h);
 243   assert(mparena_count(MPARENA_GLOBAL) == 0);
 244   return (ok);
 245 }
 246
 247 static const test_chunk tests[] = {
 248   { "sign", tsign, { &type_string, &type_string, &type_mp, &type_string,
 249                      &type_mp, &type_mp, &type_mp } },
 250   { "verify", tverify, { &type_string, &type_string, &type_string,
 251                          &type_string, &type_mp, &type_mp, &type_int } },
 252   { 0 }
 253 };
 254
 255 int main(int argc, char *argv[])
 256 {
 257   sub_init();
 258   test_run(argc, argv, tests, SRCDIR "/tests/gdsa");
 259   return (0);
 260 }
 261
 262 #endif
 263
 264 /*----- That's all, folks -------------------------------------------------*/