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

   1 /* -*-c-*-
   2  *
   3  * $Id: bbs-gen.c,v 1.6 2004/04/08 01:36:15 mdw Exp $
   4  *
   5  * Generate Blum integers
   6  *
   7  * (c) 1999 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 <stdio.h>
  33 #include <stdlib.h>
  34 #include <string.h>
  35
  36 #include "bbs.h"
  37 #include "mp.h"
  38 #include "mprand.h"
  39 #include "pgen.h"
  40 #include "strongprime.h"
  41
  42 /*----- Main code ---------------------------------------------------------*/
  43
  44 /* --- @bbs_gen@ --- *
  45  *
  46  * Arguments:   @bbs_priv *bp@ = pointer to parameter block
  47  *              @unsigned nbits@ = number of bits in the modulus
  48  *              @grand *r@ = pointer to random number source
  49  *              @unsigned n@ = number of attempts to make
  50  *              @pgen_proc *event@ = event handler function
  51  *              @void *ectx@ = argument for event handler
  52  *
  53  * Returns:     If it worked OK, @PGEN_DONE@, otherwise @PGEN_ABORT@.
  54  *
  55  * Use:         Finds two prime numbers %$p'$% and %$q'$% such that both are
  56  *              congruent to %$3 \bmod 4$%, and  $(p - 1)/2$% and
  57  *              %$(q - 1)/2$% have no common factors.  The product %$n = pq$%
  58  *              is eminently suitable for use as a modulus in a Blum-Blum-
  59  *              Shub pseudorandom bit generator.
  60  */
  61
  62 int bbs_gen(bbs_priv *bp, unsigned nbits, grand *r, unsigned n,
  63             pgen_proc *event, void *ectx)
  64 {
  65   rabin rb;
  66   pgen_safejumpctx j;
  67   pgen_gcdstepctx g;
  68   unsigned nb = nbits/2;
  69   mp *x = MP_NEW;
  70
  71   /* --- Generate @p@ --- */
  72
  73 again:
  74   if ((x = strongprime_setup("p", x, &j.jq, nb, r, n, event, ectx)) == 0)
  75     goto fail_x;
  76   bp->p = pgen("p", MP_NEW, x, event, ectx, n, pgen_safejump, &j,
  77                rabin_iters(nb), pgen_test, &rb);
  78   pfilt_destroy(&j.jq);
  79   if (!bp->p) {
  80     if (n)
  81       goto fail_p;
  82     goto again;
  83   }
  84
  85   /* --- Generate @q@ --- */
  86
  87   nb = nbits - nb;
  88   if ((x = strongprime_setup("q", x, &g.jp, nb, r, n, event, ectx)) == 0)
  89     goto fail_q;
  90   if ((x->v[0] & 3) != 3)
  91     x = mp_add(x, x, g.jp.m);
  92   pfilt_muladd(&g.jp, &g.jp, 2, 0);
  93   g.r = mp_lsr(MP_NEW, bp->p, 1);
  94   g.g = MP_NEW;
  95   g.max = MP_ONE;
  96   bp->q = pgen("q", MP_NEW, x, event, ectx, n, pgen_gcdstep, &g,
  97                rabin_iters(nb), pgen_test, &rb);
  98   pfilt_destroy(&g.jp);
  99   mp_drop(g.r);
 100   mp_drop(g.g);
 101   if (!bp->q) {
 102     if (n)
 103       goto fail_q;
 104     mp_drop(bp->p);
 105     goto again;
 106   }
 107
 108   /* --- Compute @n@ --- */
 109
 110   bp->n = mp_mul(MP_NEW, bp->p, bp->q);
 111   mp_drop(x);
 112   return (PGEN_DONE);
 113
 114   /* --- Tidy up if things went wrong --- */
 115
 116 fail_q:
 117   mp_drop(bp->p);
 118 fail_p:
 119   mp_drop(x);
 120 fail_x:
 121   return (PGEN_ABORT);
 122 }
 123
 124 /*----- That's all, folks -------------------------------------------------*/