Table for driving key data extraction.

[u/mdw/catacomb] / bbs-gen.c

/* -*-c-*-
 *
 * $Id: bbs-gen.c,v 1.3 2000/02/12 18:21:02 mdw Exp $
 *
 * Generate Blum integers
 *
 * (c) 1999 Straylight/Edgeware
 */

/*----- Licensing notice --------------------------------------------------* 
 *
 * This file is part of Catacomb.
 *
 * Catacomb is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Library General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 * 
 * Catacomb is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU Library General Public License for more details.
 * 
 * You should have received a copy of the GNU Library General Public
 * License along with Catacomb; if not, write to the Free
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA 02111-1307, USA.
 */

/*----- Revision history --------------------------------------------------* 
 *
 * $Log: bbs-gen.c,v $
 * Revision 1.3  2000/02/12 18:21:02  mdw
 * Overhaul of key management (again).
 *
 * Revision 1.2  1999/12/22 15:52:28  mdw
 * Reworking for new prime-search system.
 *
 * Revision 1.1  1999/12/10 23:14:59  mdw
 * Blum-Blum-Shub generator, and Blum-Goldwasser encryption.
 *
 */

/*----- Header files ------------------------------------------------------*/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#include "bbs.h"
#include "mp.h"
#include "mprand.h"
#include "pgen.h"
#include "strongprime.h"

/*----- Data structures ---------------------------------------------------*/

typedef struct gcdctx {
  mp *q, *jq;
  pfilt p, jp;
  mp *r;
} gcdctx;

/*----- Custom stepper ----------------------------------------------------*/

static int gcdstep(int rq, pgen_event *ev, void *p)
{
  gcdctx *g = p;
  int rc = PGEN_ABORT;
  mp *z = MP_NEW;

  switch (rq) {

    /* --- Set everything up --- */

    case PGEN_BEGIN: {
      mp *p = ev->m;
      if ((p->v[0] & 3) != 3)
	p = mp_add(p, p, g->jp.m);
      rc = pfilt_create(&g->p, p);
      g->q = mp_lsr(MP_NEW, p, 1);
      g->jq = MP_COPY(g->jp.m);
      pfilt_muladd(&g->jp, &g->jp, 2, 0);
      g->jq = mp_lsr(MP_NEW, p, 1);
      mp_drop(p);
    } break;

    /* --- Grind through another iteration --- */

    case PGEN_TRY:
      mp_drop(ev->m);
      rc = pfilt_jump(&g->p, &g->jp);
      g->q = mp_add(g->q, g->q, g->jq);
      break;

    /* --- Finished --- */

    case PGEN_DONE:
      pfilt_destroy(&g->p);
      mp_drop(g->q);
      mp_drop(g->jq);
      return (PGEN_DONE);
  }

  /* --- Step on until everything is OK --- */

  for (;;) {
    if (rc != PGEN_FAIL) {
      mp_gcd(&z, 0, 0, g->r, g->q);
      if (MP_CMP(z, !=, MP_ONE))
	rc = PGEN_FAIL;
    }
    if (rc != PGEN_FAIL)
      break;
    rc = pfilt_jump(&g->p, &g->jp);
    g->q = mp_add(g->q, g->q, g->jq);
  }

  mp_drop(z);
  ev->m = MP_COPY(g->p.m);
  return (rc);
}

/*----- Main code ---------------------------------------------------------*/

/* --- @bbs_gen@ --- *
 *
 * Arguments:	@bbs_param *bp@ = pointer to parameter block
 *		@unsigned nbits@ = number of bits in the modulus
 *		@grand *r@ = pointer to random number source
 *		@unsigned n@ = number of attempts to make
 *		@pgen_proc *event@ = event handler function
 *		@void *ectx@ = argument for event handler
 *
 * Returns:	If it worked OK, @PGEN_DONE@, otherwise @PGEN_ABORT@.
 *
 * Use:		Finds two prime numbers %$p'$% and %$q'$% such that both are
 *		congruent to %$3 \bmod 4$%, and  $(p - 1)/2$% and
 *		%$(q - 1)/2$% have no common factors.  The product %$n = pq$%
 *		is eminently suitable for use as a modulus in a Blum-Blum-
 *		Shub pseudorandom bit generator.
 */

int bbs_gen(bbs_param *bp, unsigned nbits, grand *r, unsigned n,
	    pgen_proc *event, void *ectx)
{
  rabin rb;
  pgen_safejumpctx j;
  gcdctx g;
  unsigned nb = nbits/2;
  mp *x = MP_NEW;

  /* --- Generate @p@ --- */

  if ((x = strongprime_setup("p", x, &j.jq, nb, r, n, event, ectx)) == 0)
    goto fail_x;
  bp->p = pgen("p", MP_NEW, x, event, ectx, n, pgen_safejump, &j,
	       rabin_iters(nb), pgen_test, &rb);
  pfilt_destroy(&j.jq);
  if (!bp->p)
    goto fail_p;

  /* --- Generate @q@ --- */

  nb = nbits - nb;
  if ((x = strongprime_setup("q", x, &g.jp, nb, r, n, event, ectx)) == 0)
    goto fail_q;
  g.r = mp_lsr(MP_NEW, bp->p, 1);
  bp->q = pgen("q", MP_NEW, x, event, ectx, n, gcdstep, &g,
	       rabin_iters(nb), pgen_test, &rb);
  pfilt_destroy(&g.jp);
  mp_drop(g.r);
  if (!bp->q)
    goto fail_q;

  /* --- Compute @n@ --- */

  bp->n = mp_mul(MP_NEW, bp->p, bp->q);
  mp_drop(x);
  return (PGEN_DONE);

  /* --- Tidy up if things went wrong --- */

fail_q:
  mp_drop(bp->p);
fail_p:
  mp_drop(x);
fail_x:
  return (PGEN_ABORT);
}

/*----- That's all, folks -------------------------------------------------*/