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   1 /* -*-c-*-
   2  *
   3  * $Id: gdsa.c,v 1.2 2004/04/08 01:36:15 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 /*----- Header files ------------------------------------------------------*/
  31
  32 #include "gdsa.h"
  33 #include "group.h"
  34 #include "ghash.h"
  35 #include "mpbarrett.h"
  36 #include "mprand.h"
  37
  38 /*----- Main code ---------------------------------------------------------*/
  39
  40 /* --- @gdsa_beginhash@ --- *
  41  *
  42  * Arguments:   @const gdsa *c@ = pointer to the context structure
  43  *
  44  * Returns:     A hashing context for you to hash the message.
  45  *
  46  * Use:         Initializes a hash function correctly for you to hash a
  47  *              message.  Requires @h@.
  48  */
  49
  50 ghash *gdsa_beginhash(const gdsa *c) { return (GH_INIT(c->h)); }
  51
  52 /* --- @gdsa_endhash@ --- *
  53  *
  54  * Arguments:   @const gdsa *c@ = pointer to the context structure
  55  *              @ghash *h@ = the hashing context
  56  *
  57  * Returns:     ---
  58  *
  59  * Use:         Does any final thing that DSA wants to do when hashing a
  60  *              message.  (Actually, there's nothing.)  The hashing context
  61  *              isn't finalized.
  62  */
  63
  64 void gdsa_endhash(gdsa *c, ghash *h) { ; }
  65
  66 /* --- @gdsa_sign@ --- *
  67  *
  68  * Arguments:   @const gdsa *c@ = my context structure
  69  *              @gdsa_sig *s@ = where to put the signature (initialized)
  70  *              @const void *m@ = pointer to message hash
  71  *              @mp *k@ = random exponent for this message or null
  72  *
  73  * Returns:     ---
  74  *
  75  * Use:         Signs a message.  Requires @g@, @u@, @h@, and @r@ if @k@ is
  76  *              null.  This is a better idea than inventing @k@ yourself.
  77  */
  78
  79 void gdsa_sign(const gdsa *c, gdsa_sig *s, const void *m, mp *k)
  80 {
  81   group *g = c->g;
  82   mp *mr = mp_loadb(MP_NEW, m, c->h->hashsz);
  83   ge *z = G_CREATE(g);
  84   mp *sr = s->r, *ss = s->s;
  85   mpbarrett b;
  86
  87   if (k) { MP_COPY(k); goto have_k; }
  88 new_k:
  89   k = mprand_range(k, g->r, c->r, 0);
  90 have_k:
  91   if (MP_ISZERO(k)) goto new_k;
  92   G_EXP(g, z, g->g, k);
  93   sr = G_TOINT(g, sr, z); assert(sr);
  94   if (MP_ISZERO(sr)) goto new_k;
  95
  96   mp_div(0, &sr, sr, g->r);
  97   mpbarrett_create(&b, g->r);
  98   ss = mp_mul(ss, sr, c->u); ss = mpbarrett_reduce(&b, ss, ss);
  99   ss = mp_add(ss, ss, mr); mp_div(0, &ss, ss, g->r);
 100   k = mp_modinv(k, k, g->r);
 101   ss = mp_mul(ss, ss, k); ss = mpbarrett_reduce(&b, ss, ss);
 102   s->r = sr; s->s = ss;
 103   mp_drop(k); mp_drop(mr); mpbarrett_destroy(&b); G_DESTROY(g, z);
 104 }
 105
 106 /* --- @gdsa_verify@ --- *
 107  *
 108  * Arguments:   @const gdsa *c@ = my context structure
 109  *              @const gdsa_sig *s@ = the signature to verify
 110  *              @const void *m@ = pointer to message hash
 111  *
 112  * Returns:     Zero if OK, negative on failure.
 113  *
 114  * Use:         Checks a signature on a message,  Requires @g@, @p@ and @h@.
 115  */
 116
 117 int gdsa_verify(const gdsa *c, const gdsa_sig *s, const void *m)
 118 {
 119   group *g = c->g;
 120   group_expfactor e[2];
 121   mpbarrett b;
 122   mp *h, *t;
 123   ge *w;
 124   int rc = -1;
 125
 126   if (MP_CMP(s->r, <, MP_ONE) || MP_CMP(s->r, >=, g->r) ||
 127       MP_CMP(s->s, <, MP_ONE) || MP_CMP(s->s, >=, g->r))
 128     return (-1);
 129   mpbarrett_create(&b, g->r); h = mp_modinv(MP_NEW, s->s, g->r);
 130   e[0].base = g->g; e[1].base = c->p;
 131   t = mp_loadb(MP_NEW, m, c->h->hashsz); mp_div(0, &t, t, g->r);
 132   t = mp_mul(t, t, h); e[0].exp = t = mpbarrett_reduce(&b, t, t);
 133   h = mp_mul(h, s->r, h); e[1].exp = h = mpbarrett_reduce(&b, h, h);
 134   w = G_CREATE(g); G_MEXP(g, w, e, 2);
 135   t = G_TOINT(g, t, w); if (!t) goto done;
 136   mp_div(0, &t, t, g->r); if (MP_EQ(t, s->r)) rc = 0;
 137 done:
 138   G_DESTROY(g, w); mp_drop(t); mp_drop(h); mpbarrett_destroy(&b);
 139   return (rc);
 140 }
 141
 142 /*----- Test rig ----------------------------------------------------------*/
 143
 144 #ifdef TEST_RIG
 145
 146 static group *getgroup(const char *p) {
 147   group *g; qd_parse qd;
 148   qd.p = p; qd.e = 0; g = group_parse(&qd);
 149   if (g && !qd_eofp(&qd)) { G_DESTROYGROUP(g); g = 0; qd.e = "junk at eof"; }
 150   if (!g) { fprintf(stderr, "bad group string `%.*s|%s': %s\n", qd.p - p,
 151                     p, qd.p, qd.e); exit(1); }
 152   return (g);
 153 }
 154
 155 static ge *getge(group *g, const char *p) {
 156   ge *x = G_CREATE(g);
 157   if (group_readstring(g, x, p, 0)) {
 158     fprintf(stderr, "bad group element `%s'\n", p);
 159     exit(1);
 160   }
 161   return (x);
 162 }
 163
 164 static void showge(group *g, const char *p, ge *x) {
 165   fprintf(stderr, "*** %s = ", p); group_writefile(g, x, stderr);
 166   putc('\n', stderr);
 167 }
 168
 169 static void showmp(const char *p, mp *x, int r) {
 170   fprintf(stderr, "*** %s = ", p); mp_writefile(x, stderr, r);
 171   putc('\n', stderr);
 172 }
 173
 174 static int tsign(dstr *v)
 175 {
 176   gdsa c;
 177   gdsa_sig s, ss = GDSA_SIG_INIT;
 178   ghash *h;
 179   mp *k;
 180   int ok = 1;
 181
 182   c.g = getgroup(v[0].buf); c.h = ghash_byname(v[1].buf);
 183   c.u = *(mp **)v[2].buf; k = *(mp **)v[4].buf;
 184   s.r = *(mp **)v[5].buf; s.s = *(mp **)v[6].buf;
 185
 186   h = gdsa_beginhash(&c);
 187   GH_HASH(h, v[3].buf, v[3].len);
 188   gdsa_endhash(&c, h);
 189   gdsa_sign(&c, &ss, GH_DONE(h, 0), k);
 190   if (!MP_EQ(s.r, ss.r) || !MP_EQ(s.s, ss.s)) {
 191     ok = 0;
 192     fprintf(stderr, "*** sign failed!\n");
 193     fprintf(stderr, "*** group: %s\n", v[0].buf);
 194     fprintf(stderr, "*** hash: %s\n", c.h->name);
 195     showmp("private key", c.u, 16);
 196     fprintf(stderr, "*** message: `%s'\n", v[3].buf);
 197     showmp("computed r", ss.r, 16); showmp("computed s", ss.s, 16);
 198     showmp("expected r", s.r, 16); showmp("expected s", s.s, 16);
 199   }
 200   mp_drop(s.r); mp_drop(s.s); mp_drop(ss.r); mp_drop(ss.s);
 201   mp_drop(k); mp_drop(c.u); G_DESTROYGROUP(c.g); GH_DESTROY(h);
 202   assert(mparena_count(MPARENA_GLOBAL) == 0);
 203   return (ok);
 204 }
 205
 206 static int tverify(dstr *v)
 207 {
 208   gdsa c;
 209   gdsa_sig s;
 210   ghash *h;
 211   int rc, erc;
 212   int ok = 1;
 213
 214   c.g = getgroup(v[0].buf); c.h = ghash_byname(v[1].buf);
 215   c.p = getge(c.g, v[2].buf);
 216   s.r = *(mp **)v[4].buf; s.s = *(mp **)v[5].buf;
 217   erc = *(int *)v[6].buf;
 218
 219   h = gdsa_beginhash(&c);
 220   GH_HASH(h, v[3].buf, v[3].len);
 221   gdsa_endhash(&c, h);
 222   rc = gdsa_verify(&c, &s, GH_DONE(h, 0));
 223   if (!rc != !erc) {
 224     ok = 0;
 225     fprintf(stderr, "*** verify failed!\n");
 226     fprintf(stderr, "*** group: %s\n", v[0].buf);
 227     fprintf(stderr, "*** hash: %s\n", c.h->name);
 228     showge(c.g, "public key", c.p);
 229     fprintf(stderr, "*** message: `%s'\n", v[3].buf);
 230     showmp("sig r", s.r, 16); showmp("sig s", s.s, 16);
 231     fprintf(stderr, "*** expected %s\n", !erc ? "pass" : "fail");
 232   }
 233   mp_drop(s.r); mp_drop(s.s); G_DESTROY(c.g, c.p); G_DESTROYGROUP(c.g);
 234   GH_DESTROY(h);
 235   assert(mparena_count(MPARENA_GLOBAL) == 0);
 236   return (ok);
 237 }
 238
 239 static const test_chunk tests[] = {
 240   { "sign", tsign, { &type_string, &type_string, &type_mp, &type_string,
 241                      &type_mp, &type_mp, &type_mp } },
 242   { "verify", tverify, { &type_string, &type_string, &type_string,
 243                          &type_string, &type_mp, &type_mp, &type_int } },
 244   { 0 }
 245 };
 246
 247 int main(int argc, char *argv[])
 248 {
 249   sub_init();
 250   test_run(argc, argv, tests, SRCDIR "/tests/gdsa");
 251   return (0);
 252 }
 253
 254 #endif
 255
 256 /*----- That's all, folks -------------------------------------------------*/