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

   1 /* -*-c-*-
   2  *
   3  * Generate Diffie-Hellman parameters
   4  *
   5  * (c) 1999 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 <mLib/macros.h>
  31
  32 #include "dh.h"
  33 #include "grand.h"
  34 #include "mp.h"
  35 #include "mpmont.h"
  36 #include "mprand.h"
  37 #include "pfilt.h"
  38 #include "pgen.h"
  39 #include "prim.h"
  40 #include "rabin.h"
  41
  42 /*----- Main code ---------------------------------------------------------*/
  43
  44 /* --- @dh_gen@ --- *
  45  *
  46  * Arguments:   @dh_param *dp@ = pointer to output parameter block
  47  *              @unsigned ql@ = length of %$q$% in bits, or zero
  48  *              @unsigned pl@ = length of %$p$% in bits
  49  *              @unsigned steps@ = number of steps to go
  50  *              @grand *r@ = random number source
  51  *              @pgen_proc *event@ = event handler function
  52  *              @void *ectx@ = argument for the event handler
  53  *
  54  * Returns:     @PGEN_DONE@ if it worked, @PGEN_ABORT@ if it didn't.
  55  *
  56  * Use:         Generates Diffie-Hellman parameters.
  57  *
  58  *              The parameters are a prime %$q$%, relatively small, and a
  59  *              large prime %$p = kq + 1$% for some %$k$%, together with a
  60  *              generator %$g$% of the cyclic subgroup of order %$q$%.  These
  61  *              are actually the same as the DSA parameter set, but the
  62  *              generation algorithm is different.  Also, if @ql@ is zero,
  63  *              this algorithm forces %$k = 2$%, and chooses %$g = 4$%.  Make
  64  *              sure you have something interesting to do if you choose this
  65  *              option.
  66  */
  67
  68 int dh_gen(dh_param *dp, unsigned ql, unsigned pl, unsigned steps, grand *r,
  69            pgen_proc *event, void *ectx)
  70 {
  71   /* --- If @ql@ is zero, do the time consuming safe-prime thing --- */
  72
  73   if (!ql) {
  74     pgen_simulprime sp[2];
  75     pgen_simulctx ss;
  76
  77     mp *m = mprand(MP_NEW, pl - 1, r, 1);
  78     ss.step = MP_TWO;
  79     sp[0].mul = MP_ONE; sp[0].add = MP_ZERO; sp[0].f = 0;
  80     sp[1].mul = MP_TWO; sp[1].add = MP_ONE; sp[1].f = PGENF_KEEP;
  81     ss.v = sp; ss.n = N(sp);
  82     dp->q = pgen("p", MP_NEW, m, event, ectx, steps, pgen_simulstep, &ss,
  83                  rabin_iters(pl), pgen_simultest, &ss);
  84     mp_drop(m);
  85     if (!dp->q) {
  86       mp_drop(sp[1].u.x);
  87       return (PGEN_ABORT);
  88     }
  89     dp->p = sp[1].u.x;
  90     dp->g = MP_FOUR;
  91     return (PGEN_DONE);
  92   }
  93
  94   /* --- Otherwise the job is much simpler --- *
  95    *
  96    * But doesn't look it...
  97    */
  98
  99   else {
 100     pgen_filterctx c;
 101     pgen_jumpctx j;
 102     rabin rb;
 103     prim_ctx p;
 104     int i;
 105     mp *m = MP_NEW;
 106     mp *x, *y;
 107
 108     /* --- Generate @q@ first --- */
 109
 110     c.step = 2;
 111     m = mprand(MP_NEW, ql, r, 1);
 112     dp->q = pgen("q", MP_NEW, m, event, ectx, steps, pgen_filter, &c,
 113                  rabin_iters(ql), pgen_test, &rb);
 114     if (!dp->q)
 115       goto fail_q;
 116
 117     /* --- Now pick a suitable @p@ --- */
 118
 119     m = mp_lsl(m, dp->q, 1);
 120     x = mprand(MP_NEW, pl, r, 0);
 121     y = MP_NEW; mp_div(0, &y, x, m);
 122     x = mp_sub(x, x, y);
 123     x = mp_add(x, x, MP_ONE);
 124     mp_drop(y);
 125     pfilt_create(&c.f, m);
 126     j.j = &c.f;
 127     dp->p = pgen("p", MP_NEW, x, event, ectx, steps, pgen_jump, &j,
 128                  rabin_iters(pl), pgen_test, &rb);
 129     pfilt_destroy(&c.f);
 130     mp_drop(x);
 131     if (!dp->p)
 132       goto fail_p;
 133
 134     /* --- And finally a suitable @g@ --- */
 135
 136     mpmont_create(&p.mm, dp->p);
 137     mp_div(&m, 0, dp->p, dp->q);
 138     i = 0;
 139     p.exp = m;
 140     p.n = 0;
 141     dp->g = pgen("g", MP_NEW, MP_NEW, event, ectx, 0, prim_step, &i,
 142                  1, prim_test, &p);
 143     mpmont_destroy(&p.mm);
 144     if (!dp->g)
 145       goto fail_g;
 146     mp_drop(m);
 147     return (PGEN_DONE);
 148
 149     /* --- Tidy up --- */
 150
 151   fail_g:
 152     mp_drop(dp->q);
 153   fail_q:
 154     mp_drop(dp->p);
 155   fail_p:
 156     mp_drop(m);
 157     return (PGEN_ABORT);
 158   }
 159 }
 160
 161 /*----- That's all, folks -------------------------------------------------*/