[u/mdw/catacomb] / bbs.h

/* -*-c-*-
 *
 * $Id: bbs.h,v 1.6 2001/02/03 16:07:33 mdw Exp $
 *
 * The Blum-Blum-Shub random bit generator
 *
 * (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.h,v $
 * Revision 1.6  2001/02/03 16:07:33  mdw
 * Give generic random objects separate namespaces for their supported misc
 * ops.
 *
 * Revision 1.5  2000/07/01 11:20:24  mdw
 * New functions for freeing public and private keys.  Remove bad type name
 * `bbs_param'.
 *
 * Revision 1.4  2000/06/17 10:45:48  mdw
 * Minor changes for key fetching.  Typesetting fixes.
 *
 * Revision 1.3  2000/02/12 18:21:02  mdw
 * Overhaul of key management (again).
 *
 * Revision 1.2  1999/12/22 15:52:08  mdw
 * Rename `bbs_params' to `bbs_param' for consistency.
 *
 * Revision 1.1  1999/12/10 23:14:59  mdw
 * Blum-Blum-Shub generator, and Blum-Goldwasser encryption.
 *
 */

/*----- Notes on the BBS generator ----------------------------------------*
 *
 * The Blum-Blum-Shub generator takes the least significant bits from the
 * sequence %$x_i = x_{i - 1}^2 \bmod n$%, where %$n = pq$% is the product of
 * two primes %$p$% and %$q$%, each of which are congruent to %$3 \bmod 4$%.
 * For maximum period of the generator, %$(p - 1)/2$% and %$(q - 1)/1$%
 * should be coprime.  It is safe to use the least significant
 * %$\log \log n$% bits of each step in the sequence -- an adversary must
 * factor the modulus before being able to work forwards or backwards.  The
 * output of the generator cannot be distinguished from a (uniform,
 * independent) random sequence of bits using any polynomial-time test.  This
 * is by far the strongest pseudorandom number generator provided in
 * Catacomb, and by far the slowest too.  For normal use, the standard
 * Catacomb @rand@ generator should be more than adequate.
 */

#ifndef CATACOMB_BBS_H
#define CATACOMB_BBS_H

#ifdef __cplusplus
  extern "C" {
#endif

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

#include <mLib/bits.h>

#ifndef CATACOMB_GRAND_H
#  include "grand.h"
#endif

#ifndef CATACOMB_KEY_H
#  include "key.h"
#endif

#ifndef CATACOMB_MP_H
#  include "mp.h"
#endif

#ifndef CATACOMB_MPBARRETT_H
#  include "mpbarrett.h"
#endif

#ifndef CATACOMB_PGEN_H
#  include "pgen.h"
#endif

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

/* --- Basic generator state --- */

typedef struct bbs {
  mpbarrett mb;                         /* Barrett reduction context */
  mp *x;                                /* Current quadratic residue */
  unsigned k;                           /* Number of bits from each step */
  unsigned b;                           /* Number of bits in reservoir */
  mpw r;                                /* Reservoir of output bits */
} bbs;

/* --- Parameters --- */

typedef struct bbs_pub {
  mp *n;
} bbs_pub;

typedef struct bbs_priv {
  mp *p, *q;                            /* Prime factors (3 mod 4) */
  mp *n;                                /* Product @pq@ -- a Blum integer */
} bbs_priv;

/*----- Key fetching ------------------------------------------------------*/

extern const key_fetchdef bbs_pubfetch[];
#define BBS_PUBFETCHSZ 3

extern const key_fetchdef bbs_privfetch[];
#define BBS_PRIVFETCHSZ 7

/* --- @bbs_pubfree@, @bbs_privfree@ --- *
 *
 * Arguments:   @bbs_pub *bp@, @bbs_priv *bp@ = pointer to key block
 *
 * Returns:     ---
 *
 * Use:         Frees a BBS key block.
 */

extern void bbs_pubfree(bbs_pub */*bp*/);
extern void bbs_privfree(bbs_priv */*bp*/);

/*----- The basic generator -----------------------------------------------*/

/* --- @bbs_create@ --- *
 *
 * Arguments:   @bbs *b@ = pointer to BBS generator state to initialize
 *              @mp *m@ = modulus (must be a Blum integer)
 *              @mp *x@ = initial seed for generator
 *
 * Returns:     ---
 *
 * Use:         Initializes a BBS generator.  The generator is stepped once
 *              after initialization, as for @bbs_seed@.
 */

extern void bbs_create(bbs */*b*/, mp */*m*/, mp */*x*/);

/* --- @bbs_destroy@ --- *
 *
 * Arguments:   @bbs *b@ = pointer to BBS generator state
 *
 * Returns:     ---
 *
 * Use:         Destroys a generator state when it's no longer wanted.
 */

extern void bbs_destroy(bbs */*b*/);

/* --- @bbs_step@ --- *
 *
 * Arguments:   @bbs *b@ = pointer to BBS generator state
 *
 * Returns:     ---
 *
 * Use:         Steps the generator once.  This isn't too useful in client
 *              code.
 */

extern void bbs_step(bbs */*b*/);

/* --- @bbs_set@ --- *
 *
 * Arguments:   @bbs *b@ = pointer to BBS generator state
 *              @mp *x@ = new residue to set
 *
 * Returns:     ---
 *
 * Use:         Sets a new quadratic residue.  The generator is stepped once.
 */

extern void bbs_set(bbs */*b*/, mp */*x*/);

/* --- @bbs_seed@ --- *
 *
 * Arguments:   @bbs *b@ = pointer to BBS generator state
 *              @mp *x@ = new seed to set
 *
 * Returns      ---
 *
 * Use:         Sets a new seed.  The generator is stepped until the residue
 *              has clearly wrapped around.
 */

extern void bbs_seed(bbs */*b*/, mp */*x*/);

/* --- @bbs_bits@ --- *
 *
 * Arguments:   @bbs *b@ = pointer to BBS generator state
 *              @unsigned bits@ = number of bits wanted
 *
 * Returns:     Bits extracted from the BBS generator.
 *
 * Use:         Extracts a requested number of bits from the BBS generator.
 */

extern uint32 bbs_bits(bbs */*b*/, unsigned /*bits*/);

/* --- @bbs_wrap@ --- *
 *
 * Arguments:   @bbs *b@ = pointer to BBS generator state
 *
 * Returns:     ---
 *
 * Use:         Steps the generator if any of the reservoir bits are used.
 *              This can be used to `wrap up' after a Blum-Goldwasser
 *              encryption, for example, producing the final value to be sent
 *              along with the ciphertext.
 *
 *              If a generator is seeded, %$b$% bits are extracted, and then
 *              @bbs_wrap@ is called, the generator will have been stepped
 *              %$\lceil b/k \rceil$% times.
 */

extern void bbs_wrap(bbs */*b*/);

/*----- Large forwards and backwards jumps --------------------------------*/

/* --- @bbs_ff@ --- *
 *
 * Arguments:   @bbs *b@ = pointer to a BBS generator state
 *              @bbs_priv *bp@ = pointer to BBS modulus factors
 *              @unsigned long n@ = number of steps to make
 *
 * Returns:     ---
 *
 * Use:         `Fast-forwards' a Blum-Blum-Shub generator by @n@ steps.
 *              Requires the factorization of the Blum modulus to do this
 *              efficiently.
 */

extern void bbs_ff(bbs */*b*/, bbs_priv */*bp*/, unsigned long /*n*/);

/* --- @bbs_rew@ --- *
 *
 * Arguments:   @bbs *b@ = pointer to a BBS generator state
 *              @bbs_priv *bp@ = pointer to BBS modulus factors
 *              @unsigned long n@ = number of steps to make
 *
 * Returns:     ---
 *
 * Use:         `Rewinds' a Blum-Blum-Shub generator by @n@ steps.
 *              Requires the factorization of the Blum modulus to do this
 *              at all.
 */

extern void bbs_rew(bbs */*b*/, bbs_priv */*bp*/, unsigned long /*n*/);

/*----- Parameter generation ----------------------------------------------*/

/* --- @bbs_gen@ --- *
 *
 * Arguments:   @bbs_priv *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.
 */

extern int bbs_gen(bbs_priv */*bp*/, unsigned /*nbits*/, grand */*r*/,
                   unsigned /*n*/, pgen_proc */*event*/, void */*ectx*/);

/*----- Generic random number generator interface -------------------------*/

/* --- @bbs_rand@ --- *
 *
 * Arguments:   @mp *m@ = modulus
 *              @mp *x@ = initial seed
 *
 * Returns:     Pointer to a generic generator.
 *
 * Use:         Constructs a generic generator interface over a
 *              Blum-Blum-Shub generator.
 */

extern grand *bbs_rand(mp */*m*/, mp */*x*/);

/* --- Blum-Blum-Shub-specific misc op codes --- */

enum {
  BBS_SET = GRAND_SPECIFIC('B')         /* @mp *x@ */
};

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

#ifdef __cplusplus
  }
#endif

#endif