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

   1 /* -*-c-*-
   2  *
   3  * $Id$
   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 "dsa.h"
  33 #include "gdsa.h"
  34 #include "group.h"
  35 #include "ghash.h"
  36 #include "mpbarrett.h"
  37 #include "mprand.h"
  38
  39 /*----- Main code ---------------------------------------------------------*/
  40
  41 /* --- @gdsa_beginhash@ --- *
  42  *
  43  * Arguments:   @const gdsa *c@ = pointer to the context structure
  44  *
  45  * Returns:     A hashing context for you to hash the message.
  46  *
  47  * Use:         Initializes a hash function correctly for you to hash a
  48  *              message.  Requires @h@.
  49  */
  50
  51 ghash *gdsa_beginhash(const gdsa *c) { return (GH_INIT(c->h)); }
  52
  53 /* --- @gdsa_endhash@ --- *
  54  *
  55  * Arguments:   @const gdsa *c@ = pointer to the context structure
  56  *              @ghash *h@ = the hashing context
  57  *
  58  * Returns:     ---
  59  *
  60  * Use:         Does any final thing that DSA wants to do when hashing a
  61  *              message.  (Actually, there's nothing.)  The hashing context
  62  *              isn't finalized.
  63  */
  64
  65 void gdsa_endhash(const gdsa *c, ghash *h) { ; }
  66
  67 /* --- @gdsa_sign@ --- *
  68  *
  69  * Arguments:   @const gdsa *c@ = my context structure
  70  *              @gdsa_sig *s@ = where to put the signature (initialized)
  71  *              @const void *m@ = pointer to message hash
  72  *              @mp *k@ = random exponent for this message or null
  73  *
  74  * Returns:     ---
  75  *
  76  * Use:         Signs a message.  Requires @g@, @u@, @h@, and @r@ if @k@ is
  77  *              null.  This is a better idea than inventing @k@ yourself.
  78  */
  79
  80 void gdsa_sign(const gdsa *c, gdsa_sig *s, const void *m, mp *k)
  81 {
  82   group *g = c->g;
  83   mp *mr = dsa_h2n(MP_NEW, g->r, m, c->h->hashsz);
  84   ge *z = G_CREATE(g);
  85   mp *sr = s->r, *ss = s->s;
  86   mpbarrett b;
  87
  88   if (k) { MP_COPY(k); goto have_k; }
  89 new_k:
  90   k = mprand_range(k, g->r, c->r, 0);
  91 have_k:
  92   if (MP_ZEROP(k)) goto new_k;
  93   G_EXP(g, z, g->g, k);
  94   sr = G_TOINT(g, sr, z); assert(sr);
  95   if (MP_ZEROP(sr)) goto new_k;
  96
  97   mp_div(0, &sr, sr, g->r);
  98   mpbarrett_create(&b, g->r);
  99   ss = mp_mul(ss, sr, c->u); ss = mpbarrett_reduce(&b, ss, ss);
 100   ss = mp_add(ss, ss, mr); mp_div(0, &ss, ss, g->r);
 101   k = mp_modinv(k, k, g->r);
 102   ss = mp_mul(ss, ss, k); ss = mpbarrett_reduce(&b, ss, ss);
 103   s->r = sr; s->s = ss;
 104   mp_drop(k); mp_drop(mr); mpbarrett_destroy(&b); G_DESTROY(g, z);
 105 }
 106
 107 /* --- @gdsa_verify@ --- *
 108  *
 109  * Arguments:   @const gdsa *c@ = my context structure
 110  *              @const gdsa_sig *s@ = the signature to verify
 111  *              @const void *m@ = pointer to message hash
 112  *
 113  * Returns:     Zero if OK, negative on failure.
 114  *
 115  * Use:         Checks a signature on a message,  Requires @g@, @p@ and @h@.
 116  */
 117
 118 int gdsa_verify(const gdsa *c, const gdsa_sig *s, const void *m)
 119 {
 120   group *g = c->g;
 121   group_expfactor e[2];
 122   mpbarrett b;
 123   mp *h, *t;
 124   ge *w;
 125   int rc = -1;
 126
 127   if (MP_CMP(s->r, <, MP_ONE) || MP_CMP(s->r, >=, g->r) ||
 128       MP_CMP(s->s, <, MP_ONE) || MP_CMP(s->s, >=, g->r))
 129     return (-1);
 130   mpbarrett_create(&b, g->r); h = mp_modinv(MP_NEW, s->s, g->r);
 131   e[0].base = g->g; e[1].base = c->p;
 132   t = dsa_h2n(MP_NEW, g->r, m, c->h->hashsz); mp_div(0, &t, t, g->r);
 133   t = mp_mul(t, t, h); e[0].exp = t = mpbarrett_reduce(&b, t, t);
 134   h = mp_mul(h, s->r, h); e[1].exp = h = mpbarrett_reduce(&b, h, h);
 135   w = G_CREATE(g); G_MEXP(g, w, e, 2);
 136   t = G_TOINT(g, t, w); if (!t) goto done;
 137   mp_div(0, &t, t, g->r); if (MP_EQ(t, s->r)) rc = 0;
 138 done:
 139   G_DESTROY(g, w); mp_drop(t); mp_drop(h); mpbarrett_destroy(&b);
 140   return (rc);
 141 }
 142
 143 /*----- Test rig ----------------------------------------------------------*/
 144
 145 #ifdef TEST_RIG
 146
 147 static group *getgroup(const char *p) {
 148   group *g; qd_parse qd;
 149   qd.p = p; qd.e = 0; g = group_parse(&qd);
 150   if (g && !qd_eofp(&qd)) { G_DESTROYGROUP(g); g = 0; qd.e = "junk at eof"; }
 151   if (!g) { fprintf(stderr, "bad group string `%.*s|%s': %s\n", qd.p - p,
 152                     p, qd.p, qd.e); exit(1); }
 153   return (g);
 154 }
 155
 156 static ge *getge(group *g, const char *p) {
 157   ge *x = G_CREATE(g);
 158   if (group_readstring(g, x, p, 0)) {
 159     fprintf(stderr, "bad group element `%s'\n", p);
 160     exit(1);
 161   }
 162   return (x);
 163 }
 164
 165 static void showge(group *g, const char *p, ge *x) {
 166   fprintf(stderr, "*** %s = ", p); group_writefile(g, x, stderr);
 167   putc('\n', stderr);
 168 }
 169
 170 static void showmp(const char *p, mp *x, int r) {
 171   fprintf(stderr, "*** %s = ", p); mp_writefile(x, stderr, r);
 172   putc('\n', stderr);
 173 }
 174
 175 static int tsign(dstr *v)
 176 {
 177   gdsa c;
 178   gdsa_sig s, ss = GDSA_SIG_INIT;
 179   ghash *h;
 180   mp *k;
 181   int ok = 1;
 182
 183   c.g = getgroup(v[0].buf); c.h = ghash_byname(v[1].buf);
 184   c.u = *(mp **)v[2].buf; k = *(mp **)v[4].buf;
 185   s.r = *(mp **)v[5].buf; s.s = *(mp **)v[6].buf;
 186
 187   h = gdsa_beginhash(&c);
 188   GH_HASH(h, v[3].buf, v[3].len);
 189   gdsa_endhash(&c, h);
 190   gdsa_sign(&c, &ss, GH_DONE(h, 0), k);
 191   if (!MP_EQ(s.r, ss.r) || !MP_EQ(s.s, ss.s)) {
 192     ok = 0;
 193     fprintf(stderr, "*** sign failed!\n");
 194     fprintf(stderr, "*** group: %s\n", v[0].buf);
 195     fprintf(stderr, "*** hash: %s\n", c.h->name);
 196     showmp("private key", c.u, 16);
 197     fprintf(stderr, "*** message: `%s'\n", v[3].buf);
 198     showmp("computed r", ss.r, 16); showmp("computed s", ss.s, 16);
 199     showmp("expected r", s.r, 16); showmp("expected s", s.s, 16);
 200   }
 201   mp_drop(s.r); mp_drop(s.s); mp_drop(ss.r); mp_drop(ss.s);
 202   mp_drop(k); mp_drop(c.u); G_DESTROYGROUP(c.g); GH_DESTROY(h);
 203   assert(mparena_count(MPARENA_GLOBAL) == 0);
 204   return (ok);
 205 }
 206
 207 static int tverify(dstr *v)
 208 {
 209   gdsa c;
 210   gdsa_sig s;
 211   ghash *h;
 212   int rc, erc;
 213   int ok = 1;
 214
 215   c.g = getgroup(v[0].buf); c.h = ghash_byname(v[1].buf);
 216   c.p = getge(c.g, v[2].buf);
 217   s.r = *(mp **)v[4].buf; s.s = *(mp **)v[5].buf;
 218   erc = *(int *)v[6].buf;
 219
 220   h = gdsa_beginhash(&c);
 221   GH_HASH(h, v[3].buf, v[3].len);
 222   gdsa_endhash(&c, h);
 223   rc = gdsa_verify(&c, &s, GH_DONE(h, 0));
 224   if (!rc != !erc) {
 225     ok = 0;
 226     fprintf(stderr, "*** verify failed!\n");
 227     fprintf(stderr, "*** group: %s\n", v[0].buf);
 228     fprintf(stderr, "*** hash: %s\n", c.h->name);
 229     showge(c.g, "public key", c.p);
 230     fprintf(stderr, "*** message: `%s'\n", v[3].buf);
 231     showmp("sig r", s.r, 16); showmp("sig s", s.s, 16);
 232     fprintf(stderr, "*** expected %s\n", !erc ? "pass" : "fail");
 233   }
 234   mp_drop(s.r); mp_drop(s.s); G_DESTROY(c.g, c.p); G_DESTROYGROUP(c.g);
 235   GH_DESTROY(h);
 236   assert(mparena_count(MPARENA_GLOBAL) == 0);
 237   return (ok);
 238 }
 239
 240 static const test_chunk tests[] = {
 241   { "sign", tsign, { &type_string, &type_string, &type_mp, &type_string,
 242                      &type_mp, &type_mp, &type_mp } },
 243   { "verify", tverify, { &type_string, &type_string, &type_string,
 244                          &type_string, &type_mp, &type_mp, &type_int } },
 245   { 0 }
 246 };
 247
 248 int main(int argc, char *argv[])
 249 {
 250   sub_init();
 251   test_run(argc, argv, tests, SRCDIR "/tests/gdsa");
 252   return (0);
 253 }
 254
 255 #endif
 256
 257 /*----- That's all, folks -------------------------------------------------*/