mdw@git.distorted.org.uk Git - catacomb/blob - pub/dh-kcdsa.c

   1 /* -*-c-*-
   2  *
   3  * Generate KCDSA prime groups
   4  *
   5  * (c) 2006 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 "mprand.h"
  34 #include "pgen.h"
  35 #include "prim.h"
  36
  37 /*----- Main code ---------------------------------------------------------*/
  38
  39 /* --- @dh_kcdsagen@ --- *
  40  *
  41  * Arguments:   @dh_param *dp@ = pointer to output parameter block
  42  *              @unsigned ql@ = size of small factor of %$(p - 1)/2$%
  43  *              @unsigned pl@ = size of %$p$% in bits
  44  *              @unsigned flags@ = other generation flags
  45  *              @unsigned steps@ = number of steps to go
  46  *              @grand *r@ = random number source
  47  *              @pgen_proc *ev@ = event handler function
  48  *              @void *ec@ = context for the event handler
  49  *
  50  * Returns:     @PGEN_DONE@ if it worked, @PGEN_ABORT@ if it failed.
  51  *
  52  * Use:         Generates a KCDSA prime group.  That is, it chooses a prime
  53  *              %$p$%, such that $%p = 2 q v + 1$%, for primes %$q$% and
  54  *              %$v$%.  The actual group of interest is the subgroup of order
  55  *              %$q$%.
  56  */
  57
  58 int dh_kcdsagen(dh_param *dp, unsigned ql, unsigned pl,
  59                 unsigned flags, unsigned steps, grand *r,
  60                 pgen_proc *ev, void *ec)
  61 {
  62   pgen_filterctx pf;
  63   pgen_simulprime sp[2];
  64   pgen_simulctx ss;
  65   prim_ctx pc;
  66   rabin rb;
  67   int rc = PGEN_ABORT;
  68   int i;
  69   mp *x = MP_NEW, *t = MP_NEW;
  70
  71   /* --- First trick: find %$v$% --- */
  72
  73 retry:
  74   pf.step = 2;
  75   x = mprand(x, pl - ql - 1, r, 1);
  76   x = pgen("v", x, x, ev, ec,
  77            steps, pgen_filter, &pf,
  78            rabin_iters(pl - ql), pgen_test, &rb);
  79   if (!x)
  80     goto fail_0;
  81
  82   /* --- Second trick: find %$p$% and %$q$% --- */
  83
  84   x = mp_lsl(x, x, 1);
  85   sp[0].add = MP_ZERO; sp[0].mul = MP_ONE; sp[0].f = 0;
  86   sp[1].add = MP_ONE; sp[1].mul = x; sp[1].f = PGENF_KEEP; x = MP_NEW;
  87   ss.step = MP_TWO; ss.v = sp; ss.n = N(sp);
  88   do {
  89     x = mprand(x, ql, r, 1);
  90     t = mp_mul(t, x, sp[1].mul);
  91   } while (mp_bits(t) != pl);
  92   dp->q = pgen("p", MP_NEW, x, ev, ec,
  93                steps, pgen_simulstep, &ss,
  94                rabin_iters(ql), pgen_simultest, &ss);
  95   mp_drop(sp[1].mul);
  96   dp->p = sp[1].u.x;
  97   if (!dp->q)
  98     goto fail_1;
  99   if (mp_bits(dp->q) != ql || mp_bits(dp->p) != pl) {
 100     if (steps) goto fail_1;
 101     MP_DROP(dp->p);
 102     MP_DROP(dp->q);
 103     goto retry;
 104   }
 105
 106   /* --- Third trick: find a generator --- */
 107
 108   mpmont_create(&pc.mm, dp->p);
 109   mp_div(&x, 0, dp->p, dp->q);
 110   i = 0;
 111   pc.exp = x;
 112   pc.n = 0;
 113   dp->g = pgen("g", MP_NEW, MP_NEW, ev, ec,
 114                0, prim_step, &i, 1, prim_test, &pc);
 115   mpmont_destroy(&pc.mm);
 116   if (!dp->g)
 117     goto fail_1;
 118
 119   rc = PGEN_DONE;
 120   goto done;
 121
 122   /* --- Tidying up and going home --- */
 123
 124 fail_1:
 125   mp_drop(dp->p);
 126   mp_drop(dp->q);
 127 fail_0:
 128 done:
 129   mp_drop(x);
 130   mp_drop(t);
 131   return (rc);
 132 }
 133
 134 /*----- That's all, folks -------------------------------------------------*/