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

   1 /* -*-c-*-
   2  *
   3  * $Id: bbs-gen.c,v 1.2 1999/12/22 15:52:28 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 1.2  1999/12/22 15:52:28  mdw
  34  * Reworking for new prime-search system.
  35  *
  36  * Revision 1.1  1999/12/10 23:14:59  mdw
  37  * Blum-Blum-Shub generator, and Blum-Goldwasser encryption.
  38  *
  39  */
  40
  41 /*----- Header files ------------------------------------------------------*/
  42
  43 #include <stdio.h>
  44 #include <stdlib.h>
  45 #include <string.h>
  46
  47 #include "bbs.h"
  48 #include "mp.h"
  49 #include "mprand.h"
  50 #include "pgen.h"
  51
  52 /*----- Data structures ---------------------------------------------------*/
  53
  54 typedef struct gcdctx {
  55   mp *q;
  56   mp *r;
  57   pfilt p;
  58 } gcdctx;
  59
  60 /*----- Custom stepper ----------------------------------------------------*/
  61
  62 static int gcdstep(int rq, pgen_event *ev, void *p)
  63 {
  64   gcdctx *g = p;
  65   int rc = PGEN_ABORT;
  66   mp *z = MP_NEW;
  67
  68   switch (rq) {
  69     case PGEN_BEGIN: {
  70       mp *p = ev->m = mp_split(ev->m);
  71       p->v[0] |= 3;
  72       g->q = mp_lsr(MP_NEW, p, 1);
  73       rc = pfilt_create(&g->p, p);
  74     } break;
  75     case PGEN_TRY:
  76       g->q = mp_add(g->q, g->q, MP_FOUR);
  77       rc = pfilt_step(&g->p, 4);
  78       break;
  79     case PGEN_DONE:
  80       pfilt_destroy(&g->p);
  81       mp_drop(g->q);
  82       return (PGEN_DONE);
  83   }
  84   for (;;) {
  85     if (rc != PGEN_FAIL) {
  86       mp_gcd(&z, 0, 0, g->r, g->q);
  87       if (MP_CMP(z, !=, MP_ONE))
  88         rc = PGEN_FAIL;
  89     }
  90     if (rc != PGEN_FAIL)
  91       break;
  92     g->q = mp_add(g->q, g->q, MP_FOUR);
  93     rc = pfilt_step(&g->p, 4);
  94   }
  95
  96   mp_drop(z);
  97   mp_drop(ev->m);
  98   ev->m = MP_COPY(g->p.m);
  99   return (rc);
 100 }
 101
 102 /*----- Main code ---------------------------------------------------------*/
 103
 104 /* --- @bbs_gen@ --- *
 105  *
 106  * Arguments:   @bbs_param *bp@ = pointer to parameter block
 107  *              @mp *p, *q@ = initial numbers to search from
 108  *              @size_t n@ = number of attempts to make
 109  *              @pgen_proc *event@ = event handler function
 110  *              @void *ectx@ = argument for event handler
 111  *
 112  * Returns:     If it worked OK, @PGEN_DONE@, otherwise @PGEN_ABORT@.
 113  *
 114  * Use:         Finds two prime numbers %$p'$% and %$q'$% such that both are
 115  *              congruent to %$3 \bmod 4$%, and  $(p - 1)/2$% and
 116  *              %$(q - 1)/2$% have no common factors.  The product %$n = pq$%
 117  *              is eminently suitable for use as a modulus in a Blum-Blum-
 118  *              Shub pseudorandom bit generator.
 119  */
 120
 121 int bbs_gen(bbs_param *bp, mp *p, mp *q, size_t n,
 122             pgen_proc *event, void *ectx)
 123 {
 124   rabin r;
 125   pgen_safestepctx c;
 126   gcdctx g;
 127
 128   /* --- Generate @p@ --- */
 129
 130   if ((bp->p = pgen("p", MP_NEW, p, event, ectx, n, pgen_safestep, &c,
 131                     rabin_iters(mp_bits(p)), pgen_test, &r)) == 0)
 132     goto fail_p;
 133
 134   /* --- Generate @q@ --- */
 135
 136   g.r = mp_lsr(MP_NEW, bp->p, 1);
 137   if ((bp->q = pgen("q", MP_NEW, q, event, ectx, n, gcdstep, &g,
 138                     rabin_iters(mp_bits(q)), pgen_test, &r)) == 0)
 139     goto fail_q;
 140
 141   /* --- Compute @n@ --- */
 142
 143   bp->n = mp_mul(MP_NEW, bp->p, bp->q);
 144   mp_drop(g.r);
 145   return (PGEN_DONE);
 146
 147   /* --- Tidy up if things went wrong --- */
 148
 149 fail_q:
 150   mp_drop(g.r);
 151   mp_drop(bp->p);
 152 fail_p:
 153   return (PGEN_ABORT);
 154 }
 155
 156 /*----- That's all, folks -------------------------------------------------*/