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

   1 /* -*-c-*-
   2  *
   3  * Generate Blum integers
   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 <stdio.h>
  31 #include <stdlib.h>
  32 #include <string.h>
  33
  34 #include "bbs.h"
  35 #include "mp.h"
  36 #include "mprand.h"
  37 #include "pgen.h"
  38 #include "strongprime.h"
  39
  40 /*----- Main code ---------------------------------------------------------*/
  41
  42 /* --- @bbs_gen@ --- *
  43  *
  44  * Arguments:   @bbs_priv *bp@ = pointer to parameter block
  45  *              @unsigned nbits@ = number of bits in the modulus
  46  *              @grand *r@ = pointer to random number source
  47  *              @unsigned n@ = number of attempts to make
  48  *              @pgen_proc *event@ = event handler function
  49  *              @void *ectx@ = argument for event handler
  50  *
  51  * Returns:     If it worked OK, @PGEN_DONE@, otherwise @PGEN_ABORT@.
  52  *
  53  * Use:         Finds two prime numbers %$p'$% and %$q'$% such that both are
  54  *              congruent to %$3 \bmod 4$%, and  $(p - 1)/2$% and
  55  *              %$(q - 1)/2$% have no common factors.  The product %$n = pq$%
  56  *              is eminently suitable for use as a modulus in a Blum-Blum-
  57  *              Shub pseudorandom bit generator.
  58  */
  59
  60 int bbs_gen(bbs_priv *bp, unsigned nbits, grand *r, unsigned n,
  61             pgen_proc *event, void *ectx)
  62 {
  63   rabin rb;
  64   pfilt jp;
  65   pgen_jumpctx j;
  66   pgen_gcdstepctx g;
  67   unsigned nb = nbits/2;
  68   mp *x = MP_NEW;
  69
  70   /* --- Generate @p@ --- */
  71
  72 again:
  73   if ((x = strongprime_setup("p", x, &jp, nb, r, n, event, ectx)) == 0)
  74     goto fail_x;
  75   j.j = &jp;
  76   bp->p = pgen("p", MP_NEW, x, event, ectx, n, pgen_jump, &j,
  77                rabin_iters(nb), pgen_test, &rb);
  78   pfilt_destroy(&jp);
  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 -------------------------------------------------*/