git.distorted.org.uk Git - u/mdw/catacomb/blob - pub/gdsa.c

   1 /* -*-c-*-
   2  *
   3  * Generalized version of DSA
   4  *
   5  * (c) 2004 Straylight/Edgeware
   6  */
   7
   8 /*----- Licensing notice --------------------------------------------------*
   9  *
  10  * This file is part of Catacomb.
  11  *
  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.
  16  *
  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.
  21  *
  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,
  25  * MA 02111-1307, USA.
  26  */
  27
  28 /*----- Header files ------------------------------------------------------*/
  29
  30 #include "dsa.h"
  31 #include "gdsa.h"
  32 #include "group.h"
  33 #include "ghash.h"
  34 #include "mpbarrett.h"
  35 #include "mprand.h"
  36
  37 /*----- Main code ---------------------------------------------------------*/
  38
  39 /* --- @gdsa_beginhash@ --- *
  40  *
  41  * Arguments:   @const gdsa *c@ = pointer to the context structure
  42  *
  43  * Returns:     A hashing context for you to hash the message.
  44  *
  45  * Use:         Initializes a hash function correctly for you to hash a
  46  *              message.  Requires @h@.
  47  */
  48
  49 ghash *gdsa_beginhash(const gdsa *c) { return (GH_INIT(c->h)); }
  50
  51 /* --- @gdsa_endhash@ --- *
  52  *
  53  * Arguments:   @const gdsa *c@ = pointer to the context structure
  54  *              @ghash *h@ = the hashing context
  55  *
  56  * Returns:     ---
  57  *
  58  * Use:         Does any final thing that DSA wants to do when hashing a
  59  *              message.  (Actually, there's nothing.)  The hashing context
  60  *              isn't finalized.
  61  */
  62
  63 void gdsa_endhash(const gdsa *c, ghash *h) { ; }
  64
  65 /* --- @gdsa_sign@ --- *
  66  *
  67  * Arguments:   @const gdsa *c@ = my context structure
  68  *              @gdsa_sig *s@ = where to put the signature (initialized)
  69  *              @const void *m@ = pointer to message hash
  70  *              @mp *k@ = random exponent for this message or null
  71  *
  72  * Returns:     ---
  73  *
  74  * Use:         Signs a message.  Requires @g@, @u@, @h@, and @r@ if @k@ is
  75  *              null.  This is a better idea than inventing @k@ yourself.
  76  */
  77
  78 void gdsa_sign(const gdsa *c, gdsa_sig *s, const void *m, mp *k)
  79 {
  80   group *g = c->g;
  81   mp *mr = dsa_h2n(MP_NEW, g->r, m, c->h->hashsz);
  82   ge *z = G_CREATE(g);
  83   mp *sr = s->r, *ss = s->s;
  84   mpbarrett b;
  85
  86   if (k) { MP_COPY(k); goto have_k; }
  87 new_k:
  88   k = mprand_range(k, g->r, c->r, 0);
  89 have_k:
  90   if (MP_ZEROP(k)) goto new_k;
  91   G_EXP(g, z, g->g, k);
  92   sr = G_TOINT(g, sr, z); assert(sr);
  93   if (MP_ZEROP(sr)) goto new_k;
  94
  95   mp_div(0, &sr, sr, g->r);
  96   mpbarrett_create(&b, g->r);
  97   ss = mp_mul(ss, sr, c->u); ss = mpbarrett_reduce(&b, ss, ss);
  98   ss = mp_add(ss, ss, mr); mp_div(0, &ss, ss, g->r);
  99   k = mp_modinv(k, k, g->r);
 100   ss = mp_mul(ss, ss, k); ss = mpbarrett_reduce(&b, ss, ss);
 101   s->r = sr; s->s = ss;
 102   mp_drop(k); mp_drop(mr); mpbarrett_destroy(&b); G_DESTROY(g, z);
 103 }
 104
 105 /* --- @gdsa_verify@ --- *
 106  *
 107  * Arguments:   @const gdsa *c@ = my context structure
 108  *              @const gdsa_sig *s@ = the signature to verify
 109  *              @const void *m@ = pointer to message hash
 110  *
 111  * Returns:     Zero if OK, negative on failure.
 112  *
 113  * Use:         Checks a signature on a message,  Requires @g@, @p@ and @h@.
 114  */
 115
 116 int gdsa_verify(const gdsa *c, const gdsa_sig *s, const void *m)
 117 {
 118   group *g = c->g;
 119   group_expfactor e[2];
 120   mpbarrett b;
 121   mp *h, *t;
 122   ge *w;
 123   int rc = -1;
 124
 125   if (MP_CMP(s->r, <, MP_ONE) || MP_CMP(s->r, >=, g->r) ||
 126       MP_CMP(s->s, <, MP_ONE) || MP_CMP(s->s, >=, g->r))
 127     return (-1);
 128   mpbarrett_create(&b, g->r); h = mp_modinv(MP_NEW, s->s, g->r);
 129   e[0].base = g->g; e[1].base = c->p;
 130   t = dsa_h2n(MP_NEW, g->r, m, c->h->hashsz); mp_div(0, &t, t, g->r);
 131   t = mp_mul(t, t, h); e[0].exp = t = mpbarrett_reduce(&b, t, t);
 132   h = mp_mul(h, s->r, h); e[1].exp = h = mpbarrett_reduce(&b, h, h);
 133   w = G_CREATE(g); G_MEXP(g, w, e, 2);
 134   t = G_TOINT(g, t, w); if (!t) goto done;
 135   mp_div(0, &t, t, g->r); if (MP_EQ(t, s->r)) rc = 0;
 136 done:
 137   G_DESTROY(g, w); mp_drop(t); mp_drop(h); mpbarrett_destroy(&b);
 138   return (rc);
 139 }
 140
 141 /*----- Test rig ----------------------------------------------------------*/
 142
 143 #ifdef TEST_RIG
 144
 145 static group *getgroup(const char *p) {
 146   group *g; qd_parse qd;
 147   qd.p = p; qd.e = 0; g = group_parse(&qd);
 148   if (g && !qd_eofp(&qd)) { G_DESTROYGROUP(g); g = 0; qd.e = "junk at eof"; }
 149   if (!g) { fprintf(stderr, "bad group string `%.*s|%s': %s\n", qd.p - p,
 150                     p, qd.p, qd.e); exit(1); }
 151   return (g);
 152 }
 153
 154 static ge *getge(group *g, const char *p) {
 155   ge *x = G_CREATE(g);
 156   if (group_readstring(g, x, p, 0)) {
 157     fprintf(stderr, "bad group element `%s'\n", p);
 158     exit(1);
 159   }
 160   return (x);
 161 }
 162
 163 static void showge(group *g, const char *p, ge *x) {
 164   fprintf(stderr, "*** %s = ", p); group_writefile(g, x, stderr);
 165   putc('\n', stderr);
 166 }
 167
 168 static void showmp(const char *p, mp *x, int r) {
 169   fprintf(stderr, "*** %s = ", p); mp_writefile(x, stderr, r);
 170   putc('\n', stderr);
 171 }
 172
 173 static int tsign(dstr *v)
 174 {
 175   gdsa c;
 176   gdsa_sig s, ss = GDSA_SIG_INIT;
 177   ghash *h;
 178   mp *k;
 179   int ok = 1;
 180
 181   c.g = getgroup(v[0].buf); c.h = ghash_byname(v[1].buf);
 182   c.u = *(mp **)v[2].buf; k = *(mp **)v[4].buf;
 183   s.r = *(mp **)v[5].buf; s.s = *(mp **)v[6].buf;
 184
 185   h = gdsa_beginhash(&c);
 186   GH_HASH(h, v[3].buf, v[3].len);
 187   gdsa_endhash(&c, h);
 188   gdsa_sign(&c, &ss, GH_DONE(h, 0), k);
 189   if (!MP_EQ(s.r, ss.r) || !MP_EQ(s.s, ss.s)) {
 190     ok = 0;
 191     fprintf(stderr, "*** sign failed!\n");
 192     fprintf(stderr, "*** group: %s\n", v[0].buf);
 193     fprintf(stderr, "*** hash: %s\n", c.h->name);
 194     showmp("private key", c.u, 16);
 195     fprintf(stderr, "*** message: `%s'\n", v[3].buf);
 196     showmp("computed r", ss.r, 16); showmp("computed s", ss.s, 16);
 197     showmp("expected r", s.r, 16); showmp("expected s", s.s, 16);
 198   }
 199   mp_drop(s.r); mp_drop(s.s); mp_drop(ss.r); mp_drop(ss.s);
 200   mp_drop(k); mp_drop(c.u); G_DESTROYGROUP(c.g); GH_DESTROY(h);
 201   assert(mparena_count(MPARENA_GLOBAL) == 0);
 202   return (ok);
 203 }
 204
 205 static int tverify(dstr *v)
 206 {
 207   gdsa c;
 208   gdsa_sig s;
 209   ghash *h;
 210   int rc, erc;
 211   int ok = 1;
 212
 213   c.g = getgroup(v[0].buf); c.h = ghash_byname(v[1].buf);
 214   c.p = getge(c.g, v[2].buf);
 215   s.r = *(mp **)v[4].buf; s.s = *(mp **)v[5].buf;
 216   erc = *(int *)v[6].buf;
 217
 218   h = gdsa_beginhash(&c);
 219   GH_HASH(h, v[3].buf, v[3].len);
 220   gdsa_endhash(&c, h);
 221   rc = gdsa_verify(&c, &s, GH_DONE(h, 0));
 222   if (!rc != !erc) {
 223     ok = 0;
 224     fprintf(stderr, "*** verify failed!\n");
 225     fprintf(stderr, "*** group: %s\n", v[0].buf);
 226     fprintf(stderr, "*** hash: %s\n", c.h->name);
 227     showge(c.g, "public key", c.p);
 228     fprintf(stderr, "*** message: `%s'\n", v[3].buf);
 229     showmp("sig r", s.r, 16); showmp("sig s", s.s, 16);
 230     fprintf(stderr, "*** expected %s\n", !erc ? "pass" : "fail");
 231   }
 232   mp_drop(s.r); mp_drop(s.s); G_DESTROY(c.g, c.p); G_DESTROYGROUP(c.g);
 233   GH_DESTROY(h);
 234   assert(mparena_count(MPARENA_GLOBAL) == 0);
 235   return (ok);
 236 }
 237
 238 static const test_chunk tests[] = {
 239   { "sign", tsign, { &type_string, &type_string, &type_mp, &type_string,
 240                      &type_mp, &type_mp, &type_mp } },
 241   { "verify", tverify, { &type_string, &type_string, &type_string,
 242                          &type_string, &type_mp, &type_mp, &type_int } },
 243   { 0 }
 244 };
 245
 246 int main(int argc, char *argv[])
 247 {
 248   sub_init();
 249   test_run(argc, argv, tests, SRCDIR "/t/gdsa");
 250   return (0);
 251 }
 252
 253 #endif
 254
 255 /*----- That's all, folks -------------------------------------------------*/