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

   1 /* -*-c-*-
   2  *
   3  * $Id: bbs-gen.c,v 1.4 2000/06/17 10:43:57 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 /*----- Revision history --------------------------------------------------*
  31  *
  32  * $Log: bbs-gen.c,v $
  33  * Revision 1.4  2000/06/17 10:43:57  mdw
  34  * Move GCD filter to separate file.  Handle failures from pgen_jump.
  35  *
  36  * Revision 1.3  2000/02/12 18:21:02  mdw
  37  * Overhaul of key management (again).
  38  *
  39  * Revision 1.2  1999/12/22 15:52:28  mdw
  40  * Reworking for new prime-search system.
  41  *
  42  * Revision 1.1  1999/12/10 23:14:59  mdw
  43  * Blum-Blum-Shub generator, and Blum-Goldwasser encryption.
  44  *
  45  */
  46
  47 /*----- Header files ------------------------------------------------------*/
  48
  49 #include <stdio.h>
  50 #include <stdlib.h>
  51 #include <string.h>
  52
  53 #include "bbs.h"
  54 #include "mp.h"
  55 #include "mprand.h"
  56 #include "pgen.h"
  57 #include "strongprime.h"
  58
  59 /*----- Main code ---------------------------------------------------------*/
  60
  61 /* --- @bbs_gen@ --- *
  62  *
  63  * Arguments:   @bbs_param *bp@ = pointer to parameter block
  64  *              @unsigned nbits@ = number of bits in the modulus
  65  *              @grand *r@ = pointer to random number source
  66  *              @unsigned n@ = number of attempts to make
  67  *              @pgen_proc *event@ = event handler function
  68  *              @void *ectx@ = argument for event handler
  69  *
  70  * Returns:     If it worked OK, @PGEN_DONE@, otherwise @PGEN_ABORT@.
  71  *
  72  * Use:         Finds two prime numbers %$p'$% and %$q'$% such that both are
  73  *              congruent to %$3 \bmod 4$%, and  $(p - 1)/2$% and
  74  *              %$(q - 1)/2$% have no common factors.  The product %$n = pq$%
  75  *              is eminently suitable for use as a modulus in a Blum-Blum-
  76  *              Shub pseudorandom bit generator.
  77  */
  78
  79 int bbs_gen(bbs_param *bp, unsigned nbits, grand *r, unsigned n,
  80             pgen_proc *event, void *ectx)
  81 {
  82   rabin rb;
  83   pgen_safejumpctx j;
  84   pgen_gcdstepctx g;
  85   unsigned nb = nbits/2;
  86   mp *x = MP_NEW;
  87
  88   /* --- Generate @p@ --- */
  89
  90 again:
  91   if ((x = strongprime_setup("p", x, &j.jq, nb, r, n, event, ectx)) == 0)
  92     goto fail_x;
  93   bp->p = pgen("p", MP_NEW, x, event, ectx, n, pgen_safejump, &j,
  94                rabin_iters(nb), pgen_test, &rb);
  95   pfilt_destroy(&j.jq);
  96   if (!bp->p) {
  97     if (n)
  98       goto fail_p;
  99     goto again;
 100   }
 101
 102   /* --- Generate @q@ --- */
 103
 104   nb = nbits - nb;
 105   if ((x = strongprime_setup("q", x, &g.jp, nb, r, n, event, ectx)) == 0)
 106     goto fail_q;
 107   if ((x->v[0] & 3) != 3)
 108     x = mp_add(x, x, g.jp.m);
 109   pfilt_muladd(&g.jp, &g.jp, 2, 0);
 110   g.r = mp_lsr(MP_NEW, bp->p, 1);
 111   g.g = MP_NEW;
 112   g.max = MP_ONE;
 113   bp->q = pgen("q", MP_NEW, x, event, ectx, n, pgen_gcdstep, &g,
 114                rabin_iters(nb), pgen_test, &rb);
 115   pfilt_destroy(&g.jp);
 116   mp_drop(g.r);
 117   mp_drop(g.g);
 118   if (!bp->q) {
 119     if (n)
 120       goto fail_q;
 121     mp_drop(bp->p);
 122     goto again;
 123   }
 124
 125   /* --- Compute @n@ --- */
 126
 127   bp->n = mp_mul(MP_NEW, bp->p, bp->q);
 128   mp_drop(x);
 129   return (PGEN_DONE);
 130
 131   /* --- Tidy up if things went wrong --- */
 132
 133 fail_q:
 134   mp_drop(bp->p);
 135 fail_p:
 136   mp_drop(x);
 137 fail_x:
 138   return (PGEN_ABORT);
 139 }
 140
 141 /*----- That's all, folks -------------------------------------------------*/