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

   1 /* -*-c-*-
   2  *
   3  * $Id: bbs-gen.c,v 1.3 2000/02/12 18:21:02 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 1.3  2000/02/12 18:21:02  mdw
  34  * Overhaul of key management (again).
  35  *
  36  * Revision 1.2  1999/12/22 15:52:28  mdw
  37  * Reworking for new prime-search system.
  38  *
  39  * Revision 1.1  1999/12/10 23:14:59  mdw
  40  * Blum-Blum-Shub generator, and Blum-Goldwasser encryption.
  41  *
  42  */
  43
  44 /*----- Header files ------------------------------------------------------*/
  45
  46 #include <stdio.h>
  47 #include <stdlib.h>
  48 #include <string.h>
  49
  50 #include "bbs.h"
  51 #include "mp.h"
  52 #include "mprand.h"
  53 #include "pgen.h"
  54 #include "strongprime.h"
  55
  56 /*----- Data structures ---------------------------------------------------*/
  57
  58 typedef struct gcdctx {
  59   mp *q, *jq;
  60   pfilt p, jp;
  61   mp *r;
  62 } gcdctx;
  63
  64 /*----- Custom stepper ----------------------------------------------------*/
  65
  66 static int gcdstep(int rq, pgen_event *ev, void *p)
  67 {
  68   gcdctx *g = p;
  69   int rc = PGEN_ABORT;
  70   mp *z = MP_NEW;
  71
  72   switch (rq) {
  73
  74     /* --- Set everything up --- */
  75
  76     case PGEN_BEGIN: {
  77       mp *p = ev->m;
  78       if ((p->v[0] & 3) != 3)
  79         p = mp_add(p, p, g->jp.m);
  80       rc = pfilt_create(&g->p, p);
  81       g->q = mp_lsr(MP_NEW, p, 1);
  82       g->jq = MP_COPY(g->jp.m);
  83       pfilt_muladd(&g->jp, &g->jp, 2, 0);
  84       g->jq = mp_lsr(MP_NEW, p, 1);
  85       mp_drop(p);
  86     } break;
  87
  88     /* --- Grind through another iteration --- */
  89
  90     case PGEN_TRY:
  91       mp_drop(ev->m);
  92       rc = pfilt_jump(&g->p, &g->jp);
  93       g->q = mp_add(g->q, g->q, g->jq);
  94       break;
  95
  96     /* --- Finished --- */
  97
  98     case PGEN_DONE:
  99       pfilt_destroy(&g->p);
 100       mp_drop(g->q);
 101       mp_drop(g->jq);
 102       return (PGEN_DONE);
 103   }
 104
 105   /* --- Step on until everything is OK --- */
 106
 107   for (;;) {
 108     if (rc != PGEN_FAIL) {
 109       mp_gcd(&z, 0, 0, g->r, g->q);
 110       if (MP_CMP(z, !=, MP_ONE))
 111         rc = PGEN_FAIL;
 112     }
 113     if (rc != PGEN_FAIL)
 114       break;
 115     rc = pfilt_jump(&g->p, &g->jp);
 116     g->q = mp_add(g->q, g->q, g->jq);
 117   }
 118
 119   mp_drop(z);
 120   ev->m = MP_COPY(g->p.m);
 121   return (rc);
 122 }
 123
 124 /*----- Main code ---------------------------------------------------------*/
 125
 126 /* --- @bbs_gen@ --- *
 127  *
 128  * Arguments:   @bbs_param *bp@ = pointer to parameter block
 129  *              @unsigned nbits@ = number of bits in the modulus
 130  *              @grand *r@ = pointer to random number source
 131  *              @unsigned n@ = number of attempts to make
 132  *              @pgen_proc *event@ = event handler function
 133  *              @void *ectx@ = argument for event handler
 134  *
 135  * Returns:     If it worked OK, @PGEN_DONE@, otherwise @PGEN_ABORT@.
 136  *
 137  * Use:         Finds two prime numbers %$p'$% and %$q'$% such that both are
 138  *              congruent to %$3 \bmod 4$%, and  $(p - 1)/2$% and
 139  *              %$(q - 1)/2$% have no common factors.  The product %$n = pq$%
 140  *              is eminently suitable for use as a modulus in a Blum-Blum-
 141  *              Shub pseudorandom bit generator.
 142  */
 143
 144 int bbs_gen(bbs_param *bp, unsigned nbits, grand *r, unsigned n,
 145             pgen_proc *event, void *ectx)
 146 {
 147   rabin rb;
 148   pgen_safejumpctx j;
 149   gcdctx g;
 150   unsigned nb = nbits/2;
 151   mp *x = MP_NEW;
 152
 153   /* --- Generate @p@ --- */
 154
 155   if ((x = strongprime_setup("p", x, &j.jq, nb, r, n, event, ectx)) == 0)
 156     goto fail_x;
 157   bp->p = pgen("p", MP_NEW, x, event, ectx, n, pgen_safejump, &j,
 158                rabin_iters(nb), pgen_test, &rb);
 159   pfilt_destroy(&j.jq);
 160   if (!bp->p)
 161     goto fail_p;
 162
 163   /* --- Generate @q@ --- */
 164
 165   nb = nbits - nb;
 166   if ((x = strongprime_setup("q", x, &g.jp, nb, r, n, event, ectx)) == 0)
 167     goto fail_q;
 168   g.r = mp_lsr(MP_NEW, bp->p, 1);
 169   bp->q = pgen("q", MP_NEW, x, event, ectx, n, gcdstep, &g,
 170                rabin_iters(nb), pgen_test, &rb);
 171   pfilt_destroy(&g.jp);
 172   mp_drop(g.r);
 173   if (!bp->q)
 174     goto fail_q;
 175
 176   /* --- Compute @n@ --- */
 177
 178   bp->n = mp_mul(MP_NEW, bp->p, bp->q);
 179   mp_drop(x);
 180   return (PGEN_DONE);
 181
 182   /* --- Tidy up if things went wrong --- */
 183
 184 fail_q:
 185   mp_drop(bp->p);
 186 fail_p:
 187   mp_drop(x);
 188 fail_x:
 189   return (PGEN_ABORT);
 190 }
 191
 192 /*----- That's all, folks -------------------------------------------------*/