[u/mdw/catacomb] / bbs.h

/* -*-c-*-
 *
 * $Id$
 *
 * 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.
 */

/*----- 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,rew}{,n}@ --- *
 *
 * Arguments:	@bbs *b@ = pointer to a BBS generator state
 *		@const bbs_priv *bp@ = pointer to BBS modulus factors
 *		@mp *n@, @unsigned long n@ = number of steps to make
 *
 * Returns:	---
 *
 * Use:		`Fast-forwards' or rewinds a Blum-Blum-Shub generator by @n@
 *		steps.  The @...n@ versions take an @unsigned long@ argument;
 *		the non-@...n@ versions a multiprecision integer.  If @n@ is
 *		negative then the generator is stepped in the reverse
 *		direction.
 */

extern void bbs_ff(bbs */*b*/, const bbs_priv */*bp*/, mp */*n*/);
extern void bbs_ffn(bbs */*b*/, const bbs_priv */*bp*/, unsigned long /*n*/);
extern void bbs_rew(bbs */*b*/, const bbs_priv */*bp*/, mp */*n*/);
extern void bbs_rewn(bbs */*b*/, const 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@ */
  BBS_STEP,				/* @void@ */
  BBS_STEPSZ,				/* @void@ */
  BBS_BITS,				/* @unsigned bits, uint32 *w@ */
  BBS_WRAP,				/* @void@ */
  BBS_FF,				/* @bbs_priv *p, mp *n@ */
  BBS_FFN,				/* @bbs_priv *p, unsigned long n@ */
  BBS_REW,				/* @bbs_priv *p, mp *n@ */
  BBS_REWN,				/* @bbs_priv *p, unsigned long n@ */
  BBS_MOD,				/* @mp **n@ */
  BBS_STATE				/* @mp **x@ */
};

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

#ifdef __cplusplus
  }
#endif

#endif
Commit	Line	Data
2c52abe6	1	/* --c--
2c52abe6	2	*
2cc3d1d0	3	* $Id$
2c52abe6	4	*
	5	* The Blum-Blum-Shub random bit generator
	6	*
	7	* (c) 1999 Straylight/Edgeware
	8	*/
	9
45c0fd36	10	/----- Licensing notice --------------------------------------------------
2c52abe6	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.
45c0fd36	18	*
2c52abe6	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.
45c0fd36	23	*
2c52abe6	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
2c52abe6	30	/----- Notes on the BBS generator ----------------------------------------
	31	*
	32	* The Blum-Blum-Shub generator takes the least significant bits from the
	33	* sequence %$x_i = x_{i - 1}^2 \bmod n$%, where %$n = pq$% is the product of
	34	* two primes %$p$% and %$q$%, each of which are congruent to %$3 \bmod 4$%.
	35	* For maximum period of the generator, %$(p - 1)/2$% and %$(q - 1)/1$%
05cac080	36	* should be coprime. It is safe to use the least significant
	37	* %$\log \log n$% bits of each step in the sequence -- an adversary must
	38	* factor the modulus before being able to work forwards or backwards. The
	39	* output of the generator cannot be distinguished from a (uniform,
	40	* independent) random sequence of bits using any polynomial-time test. This
	41	* is by far the strongest pseudorandom number generator provided in
	42	* Catacomb, and by far the slowest too. For normal use, the standard
	43	* Catacomb @rand@ generator should be more than adequate.
2c52abe6	44	*/
	45
	46	#ifndef CATACOMB_BBS_H
	47	#define CATACOMB_BBS_H
	48
	49	#ifdef __cplusplus
	50	extern "C" {
	51	#endif
	52
	53	/----- Header files ------------------------------------------------------/
	54
	55	#include <mLib/bits.h>
	56
	57	#ifndef CATACOMB_GRAND_H
	58	# include "grand.h"
	59	#endif
	60
05cac080	61	#ifndef CATACOMB_KEY_H
	62	# include "key.h"
	63	#endif
	64
2c52abe6	65	#ifndef CATACOMB_MP_H
	66	# include "mp.h"
	67	#endif
	68
	69	#ifndef CATACOMB_MPBARRETT_H
	70	# include "mpbarrett.h"
	71	#endif
	72
4f743df5	73	#ifndef CATACOMB_PGEN_H
	74	# include "pgen.h"
	75	#endif
	76
2c52abe6	77	/----- Data structures ---------------------------------------------------/
	78
	79	/* --- Basic generator state --- */
	80
	81	typedef struct bbs {
	82	mpbarrett mb; /* Barrett reduction context */
	83	mp x; / Current quadratic residue */
	84	unsigned k; /* Number of bits from each step */
	85	unsigned b; /* Number of bits in reservoir */
	86	mpw r; /* Reservoir of output bits */
	87	} bbs;
	88
	89	/* --- Parameters --- */
	90
05cac080	91	typedef struct bbs_pub {
	92	mp *n;
	93	} bbs_pub;
	94
9083376e	95	typedef struct bbs_priv {
2c52abe6	96	mp p, q; /* Prime factors (3 mod 4) */
2c52abe6	97	mp n; / Product @pq@ -- a Blum integer */
9083376e	98	} bbs_priv;
05cac080	99
	100	/----- Key fetching ------------------------------------------------------/
	101
	102	extern const key_fetchdef bbs_pubfetch[];
	103	#define BBS_PUBFETCHSZ 3
	104
	105	extern const key_fetchdef bbs_privfetch[];
	106	#define BBS_PRIVFETCHSZ 7
2c52abe6	107
9083376e	108	/* --- @bbs_pubfree@, @bbs_privfree@ --- *
	109	*
	110	* Arguments: @bbs_pub bp@, @bbs_priv bp@ = pointer to key block
	111	*
	112	* Returns: ---
	113	*
	114	* Use: Frees a BBS key block.
	115	*/
	116
	117	extern void bbs_pubfree(bbs_pub /bp*/);
	118	extern void bbs_privfree(bbs_priv /bp*/);
	119
2c52abe6	120	/----- The basic generator -----------------------------------------------/
	121
	122	/* --- @bbs_create@ --- *
	123	*
	124	* Arguments: @bbs *b@ = pointer to BBS generator state to initialize
	125	* @mp *m@ = modulus (must be a Blum integer)
	126	* @mp *x@ = initial seed for generator
	127	*
	128	* Returns: ---
	129	*
	130	* Use: Initializes a BBS generator. The generator is stepped once
	131	* after initialization, as for @bbs_seed@.
	132	*/
	133
	134	extern void bbs_create(bbs /b/, mp /m/, mp /x*/);
	135
	136	/* --- @bbs_destroy@ --- *
	137	*
	138	* Arguments: @bbs *b@ = pointer to BBS generator state
	139	*
	140	* Returns: ---
	141	*
	142	* Use: Destroys a generator state when it's no longer wanted.
	143	*/
	144
	145	extern void bbs_destroy(bbs /b*/);
	146
	147	/* --- @bbs_step@ --- *
	148	*
	149	* Arguments: @bbs *b@ = pointer to BBS generator state
	150	*
	151	* Returns: ---
	152	*
	153	* Use: Steps the generator once. This isn't too useful in client
	154	* code.
	155	*/
	156
	157	extern void bbs_step(bbs /b*/);
	158
	159	/* --- @bbs_set@ --- *
	160	*
	161	* Arguments: @bbs *b@ = pointer to BBS generator state
	162	* @mp *x@ = new residue to set
	163	*
	164	* Returns: ---
	165	*
	166	* Use: Sets a new quadratic residue. The generator is stepped once.
	167	*/
	168
	169	extern void bbs_set(bbs /b/, mp /x/);
	170
	171	/* --- @bbs_seed@ --- *
	172	*
	173	* Arguments: @bbs *b@ = pointer to BBS generator state
	174	* @mp *x@ = new seed to set
	175	*
	176	* Returns ---
	177	*
	178	* Use: Sets a new seed. The generator is stepped until the residue
	179	* has clearly wrapped around.
	180	*/
	181
	182	extern void bbs_seed(bbs /b/, mp /x/);
	183
184	/* --- @bbs_bits@ --- *
185	*
186	* Arguments: @bbs *b@ = pointer to BBS generator state
187	* @unsigned bits@ = number of bits wanted
188	*
189	* Returns: Bits extracted from the BBS generator.
190	*
191	* Use: Extracts a requested number of bits from the BBS generator.
192	*/
193
194	extern uint32 bbs_bits(bbs /b/, unsigned /bits*/);
195
196	/* --- @bbs_wrap@ --- *
197	*
198	* Arguments: @bbs *b@ = pointer to BBS generator state
199	*
200	* Returns: ---
201	*
202	* Use: Steps the generator if any of the reservoir bits are used.
203	* This can be used to `wrap up' after a Blum-Goldwasser
204	* encryption, for example, producing the final value to be sent
205	* along with the ciphertext.
206	*
207	* If a generator is seeded, %$b$% bits are extracted, and then
208	* @bbs_wrap@ is called, the generator will have been stepped
05cac080	209	* %$\lceil b/k \rceil$% times.
2c52abe6	210	*/
	211
	212	extern void bbs_wrap(bbs /b*/);
	213
	214	/----- Large forwards and backwards jumps --------------------------------/
	215
2cc3d1d0	216	/* --- @bbs_{ff,rew}{,n}@ --- *
2c52abe6	217	*
2c52abe6	218	* Arguments: @bbs *b@ = pointer to a BBS generator state
2cc3d1d0	219	* @const bbs_priv *bp@ = pointer to BBS modulus factors
2cc3d1d0	220	* @mp *n@, @unsigned long n@ = number of steps to make
2c52abe6	221	*
	222	* Returns: ---
	223	*
2cc3d1d0	224	* Use: `Fast-forwards' or rewinds a Blum-Blum-Shub generator by @n@
	225	* steps. The @...n@ versions take an @unsigned long@ argument;
	226	* the non-@...n@ versions a multiprecision integer. If @n@ is
	227	* negative then the generator is stepped in the reverse
45c0fd36	228	* direction.
2c52abe6	229	*/
2c52abe6	230
2cc3d1d0	231	extern void bbs_ff(bbs /b/, const bbs_priv /bp/, mp /n*/);
	232	extern void bbs_ffn(bbs /b/, const bbs_priv /bp/, unsigned long /n/);
	233	extern void bbs_rew(bbs /b/, const bbs_priv /bp/, mp /n*/);
	234	extern void bbs_rewn(bbs /b/, const bbs_priv /bp/, unsigned long /n/);
2c52abe6	235
	236	/----- Parameter generation ----------------------------------------------/
	237
	238	/* --- @bbs_gen@ --- *
	239	*
9083376e	240	* Arguments: @bbs_priv *bp@ = pointer to parameter block
052b36d0	241	* @unsigned nbits@ = number of bits in the modulus
	242	* @grand *r@ = pointer to random number source
	243	* @unsigned n@ = number of attempts to make
4f743df5	244	* @pgen_proc *event@ = event handler function
4f743df5	245	* @void *ectx@ = argument for event handler
2c52abe6	246	*
4f743df5	247	* Returns: If it worked OK, @PGEN_DONE@, otherwise @PGEN_ABORT@.
2c52abe6	248	*
2c52abe6	249	* Use: Finds two prime numbers %$p'$% and %$q'$% such that both are
45c0fd36	250	* congruent to %$3 \bmod 4$%, and $(p - 1)/2$% and
2c52abe6	251	* %$(q - 1)/2$% have no common factors. The product %$n = pq$%
	252	* is eminently suitable for use as a modulus in a Blum-Blum-
	253	* Shub pseudorandom bit generator.
	254	*/
	255
9083376e	256	extern int bbs_gen(bbs_priv /bp/, unsigned /nbits/, grand /r/,
052b36d0	257	unsigned /n/, pgen_proc /event/, void /ectx/);
2c52abe6	258
	259	/----- Generic random number generator interface -------------------------/
	260
	261	/* --- @bbs_rand@ --- *
	262	*
45c0fd36	263	* Arguments: @mp *m@ = modulus
2c52abe6	264	* @mp *x@ = initial seed
2c52abe6	265	*
45c0fd36	266	* Returns: Pointer to a generic generator.
2c52abe6	267	*
45c0fd36	268	* Use: Constructs a generic generator interface over a
2c52abe6	269	* Blum-Blum-Shub generator.
	270	*/
	271
	272	extern grand bbs_rand(mp /m/, mp /x*/);
	273
	274	/* --- Blum-Blum-Shub-specific misc op codes --- */
	275
	276	enum {
2cc3d1d0	277	BBS_SET = GRAND_SPECIFIC('B'), /* @mp x@ /
	278	BBS_STEP, /* @void@ */
	279	BBS_STEPSZ, /* @void@ */
	280	BBS_BITS, /* @unsigned bits, uint32 w@ /
	281	BBS_WRAP, /* @void@ */
	282	BBS_FF, /* @bbs_priv p, mp n@ */
	283	BBS_FFN, /* @bbs_priv p, unsigned long n@ /
	284	BBS_REW, /* @bbs_priv p, mp n@ */
	285	BBS_REWN, /* @bbs_priv p, unsigned long n@ /
	286	BBS_MOD, /* @mp *n@ /
	287	BBS_STATE /* @mp *x@ /
2c52abe6	288	};
	289
	290	/----- That's all, folks -------------------------------------------------/
	291
	292	#ifdef __cplusplus
	293	}
	294	#endif
	295
	296	#endif