git.distorted.org.uk Git - u/mdw/catacomb/blob - pgen-safe.c

   1 /* -*-c-*-
   2  *
   3  * $Id: pgen-safe.c,v 1.4 2000/07/03 18:09:27 mdw Exp $
   4  *
   5  * Safe prime generation
   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: pgen-safe.c,v $
  33  * Revision 1.4  2000/07/03 18:09:27  mdw
  34  * Bug fix to the GCD check.  With any luck, this is the last of these to
  35  * need nailing to the wall.
  36  *
  37  * Revision 1.3  2000/06/17 11:52:36  mdw
  38  * Signal a pgen abort if the jump and base share a common factor.
  39  *
  40  * Revision 1.2  2000/02/12 18:21:03  mdw
  41  * Overhaul of key management (again).
  42  *
  43  * Revision 1.1  1999/12/22 16:01:34  mdw
  44  * Find `safe' primes (i.e., %$p = 2q + 1$%).
  45  *
  46  */
  47
  48 /*----- Header files ------------------------------------------------------*/
  49
  50 #include "mp.h"
  51 #include "mprand.h"
  52 #include "pgen.h"
  53
  54 /*----- Main code ---------------------------------------------------------*/
  55
  56 /* --- @pgen_safestep@ --- *
  57  *
  58  * Steps two numbers, %$q$% and %$p = 2q + 1$%, such that neither has any
  59  * small factors.  %$p$% is put in the event block.
  60  */
  61
  62 int pgen_safestep(int rq, pgen_event *ev, void *p)
  63 {
  64   pgen_safestepctx *c = p;
  65   int rc = PGEN_ABORT, qrc = 0;
  66
  67   switch (rq) {
  68
  69     /* --- Set up the contexts --- */
  70
  71     case PGEN_BEGIN: {
  72       mp *p = mp_split(MP_COPY(ev->m));
  73       mp *q;
  74       p->v[0] |= 3;
  75       q = mp_lsr(MP_NEW, p, 1);
  76       rc = pfilt_create(&c->p, p);
  77       qrc = pfilt_create(&c->q, q);
  78       mp_drop(p); mp_drop(q);
  79     } break;
  80
  81     /* --- Step along --- */
  82
  83     case PGEN_TRY:
  84       mp_drop(ev->m);
  85       rc = pfilt_step(&c->p, 4);
  86       qrc = pfilt_step(&c->q, 2);
  87       break;
  88
  89       break;
  90
  91     /* --- Tidy the toys away --- */
  92
  93     case PGEN_DONE:
  94       pfilt_destroy(&c->q);
  95       pfilt_destroy(&c->p);
  96       return (PGEN_DONE);
  97   }
  98
  99   /* --- Continue stepping if necessary --- */
 100
 101   while (rc == PGEN_FAIL || qrc == PGEN_FAIL) {
 102     rc = pfilt_step(&c->p, 4);
 103     qrc = pfilt_step(&c->q, 2);
 104   }
 105
 106   ev->m = MP_COPY(c->p.m);
 107   if (qrc == PGEN_TRY)
 108     rc = PGEN_TRY;
 109   return (rc);
 110 }
 111
 112 /* --- @pgen_safejump@ --- *
 113  *
 114  * Jumps two numbers, %$q$% and %$p = 2q + 1$% such that neither has any
 115  * small factors.
 116  */
 117
 118 int pgen_safejump(int rq, pgen_event *ev, void *p)
 119 {
 120   pgen_safejumpctx *j = p;
 121   int rc = PGEN_ABORT, qrc = 0;
 122
 123   switch (rq) {
 124
 125     /* --- Set up the jump contexts --- *
 126      *
 127      * The jump in @j.q@ is congruent to 2 (mod 4); see @strongprime_setup@.
 128      * If @p@ is initially 1 (mod 4) then add @j.q@.  Then double @j.q@ to
 129      * ensure that the step is 0 (mod 4).  Ensure that @jq@ and @q@ don't
 130      * have any common factors.
 131      */
 132
 133     case PGEN_BEGIN: {
 134       mp *p = ev->m;
 135       mp *q;
 136       mp *g = MP_NEW;
 137       if ((p->v[0] & 3) != 3)
 138         p = mp_add(p, p, j->jq.m);
 139       q = mp_lsr(MP_NEW, p, 1);
 140       mp_gcd(&g, 0, 0, p, j->jq.m);
 141       if (MP_CMP(g, >, MP_ONE)) {
 142         ev->m = p;
 143         mp_drop(q);
 144         mp_drop(g);
 145         return (PGEN_ABORT);
 146       }
 147       mp_drop(g);
 148       rc = pfilt_create(&j->p, p);
 149       pfilt_muladd(&j->jp, &j->jq, 2, 0);
 150       qrc = pfilt_create(&j->q, q);
 151       mp_drop(p);
 152       mp_drop(q);
 153     } break;
 154
 155     /* --- Step on one place --- */
 156
 157     case PGEN_TRY:
 158       mp_drop(ev->m);
 159       rc = pfilt_jump(&j->p, &j->jp);
 160       qrc = pfilt_jump(&j->q, &j->jq);
 161       break;
 162
 163     /* --- Tidy everything up --- */
 164
 165     case PGEN_DONE:
 166       pfilt_destroy(&j->jp);
 167       pfilt_destroy(&j->p);
 168       pfilt_destroy(&j->q);
 169       return (PGEN_DONE);
 170   }
 171
 172   /* --- Step on while @p@ or @q@ have small factors --- */
 173
 174   while (rc == PGEN_FAIL || qrc == PGEN_FAIL) {
 175     rc = pfilt_jump(&j->p, &j->jp);
 176     qrc = pfilt_jump(&j->q, &j->jq);
 177   }
 178   ev->m = MP_COPY(j->p.m);
 179   if (qrc == PGEN_TRY)
 180     rc = PGEN_TRY;
 181   return (rc);
 182 }
 183
 184 /* --- @pgen_safetest@ --- *
 185  *
 186  * Applies Rabin-Miller tests to %$p$% and %$q$%.
 187  */
 188
 189 int pgen_safetest(int rq, pgen_event *ev, void *p)
 190 {
 191   pgen_safetestctx *c = p;
 192   int rc = PGEN_ABORT;
 193
 194   switch (rq) {
 195     case PGEN_BEGIN:
 196       rabin_create(&c->q, c->c.q.m);
 197       rabin_create(&c->p, c->c.p.m);
 198       rc = PGEN_TRY;
 199       break;
 200     case PGEN_TRY: {
 201       mp *m = mprand_range(MP_NEW, c->c.q.m, ev->r, 0);
 202       rc = rabin_test(&c->p, m);
 203       if (rc == PGEN_PASS)
 204         rc = rabin_test(&c->q, m);
 205       mp_drop(m);
 206     } break;
 207     case PGEN_DONE:
 208       rabin_destroy(&c->q);
 209       rabin_destroy(&c->p);
 210       break;
 211   }
 212   return (rc);
 213 }
 214
 215 /*----- That's all, folks -------------------------------------------------*/