path: root/cipher/primegen.c

/* primegen.c - prime number generator
 * Copyright (C) 1998, 2000, 2001, 2002, 2003
 *               2004 Free Software Foundation, Inc.
 *
 * This file is part of Libgcrypt.
 *
 * Libgcrypt is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser general Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * Libgcrypt 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA
 */

#include <config.h>

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

#include "g10lib.h"
#include "mpi.h"
#include "cipher.h"
#include "ath.h"

static gcry_mpi_t gen_prime (unsigned int nbits, int secret, int randomlevel, 
                             int (*extra_check)(void *, gcry_mpi_t),
                             void *extra_check_arg);
static int check_prime( gcry_mpi_t prime, gcry_mpi_t val_2, int rm_rounds,
                        gcry_prime_check_func_t cb_func, void *cb_arg );
static int is_prime (gcry_mpi_t n, int steps, unsigned int *count);
static void m_out_of_n( char *array, int m, int n );

static void (*progress_cb) (void *,const char*,int,int, int );
static void *progress_cb_data;

/* Note: 2 is not included because it can be tested more easily by
   looking at bit 0. The last entry in this list is marked by a zero */
static ushort small_prime_numbers[] = {
    3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43,
    47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97, 101,
    103, 107, 109, 113, 127, 131, 137, 139, 149, 151,
    157, 163, 167, 173, 179, 181, 191, 193, 197, 199,
    211, 223, 227, 229, 233, 239, 241, 251, 257, 263,
    269, 271, 277, 281, 283, 293, 307, 311, 313, 317,
    331, 337, 347, 349, 353, 359, 367, 373, 379, 383,
    389, 397, 401, 409, 419, 421, 431, 433, 439, 443,
    449, 457, 461, 463, 467, 479, 487, 491, 499, 503,
    509, 521, 523, 541, 547, 557, 563, 569, 571, 577,
    587, 593, 599, 601, 607, 613, 617, 619, 631, 641,
    643, 647, 653, 659, 661, 673, 677, 683, 691, 701,
    709, 719, 727, 733, 739, 743, 751, 757, 761, 769,
    773, 787, 797, 809, 811, 821, 823, 827, 829, 839,
    853, 857, 859, 863, 877, 881, 883, 887, 907, 911,
    919, 929, 937, 941, 947, 953, 967, 971, 977, 983,
    991, 997, 1009, 1013, 1019, 1021, 1031, 1033,
    1039, 1049, 1051, 1061, 1063, 1069, 1087, 1091,
    1093, 1097, 1103, 1109, 1117, 1123, 1129, 1151,
    1153, 1163, 1171, 1181, 1187, 1193, 1201, 1213,
    1217, 1223, 1229, 1231, 1237, 1249, 1259, 1277,
    1279, 1283, 1289, 1291, 1297, 1301, 1303, 1307,
    1319, 1321, 1327, 1361, 1367, 1373, 1381, 1399,
    1409, 1423, 1427, 1429, 1433, 1439, 1447, 1451,
    1453, 1459, 1471, 1481, 1483, 1487, 1489, 1493,
    1499, 1511, 1523, 1531, 1543, 1549, 1553, 1559,
    1567, 1571, 1579, 1583, 1597, 1601, 1607, 1609,
    1613, 1619, 1621, 1627, 1637, 1657, 1663, 1667,
    1669, 1693, 1697, 1699, 1709, 1721, 1723, 1733,
    1741, 1747, 1753, 1759, 1777, 1783, 1787, 1789,
    1801, 1811, 1823, 1831, 1847, 1861, 1867, 1871,
    1873, 1877, 1879, 1889, 1901, 1907, 1913, 1931,
    1933, 1949, 1951, 1973, 1979, 1987, 1993, 1997,
    1999, 2003, 2011, 2017, 2027, 2029, 2039, 2053,
    2063, 2069, 2081, 2083, 2087, 2089, 2099, 2111,
    2113, 2129, 2131, 2137, 2141, 2143, 2153, 2161,
    2179, 2203, 2207, 2213, 2221, 2237, 2239, 2243,
    2251, 2267, 2269, 2273, 2281, 2287, 2293, 2297,
    2309, 2311, 2333, 2339, 2341, 2347, 2351, 2357,
    2371, 2377, 2381, 2383, 2389, 2393, 2399, 2411,
    2417, 2423, 2437, 2441, 2447, 2459, 2467, 2473,
    2477, 2503, 2521, 2531, 2539, 2543, 2549, 2551,
    2557, 2579, 2591, 2593, 2609, 2617, 2621, 2633,
    2647, 2657, 2659, 2663, 2671, 2677, 2683, 2687,
    2689, 2693, 2699, 2707, 2711, 2713, 2719, 2729,
    2731, 2741, 2749, 2753, 2767, 2777, 2789, 2791,
    2797, 2801, 2803, 2819, 2833, 2837, 2843, 2851,
    2857, 2861, 2879, 2887, 2897, 2903, 2909, 2917,
    2927, 2939, 2953, 2957, 2963, 2969, 2971, 2999,
    3001, 3011, 3019, 3023, 3037, 3041, 3049, 3061,
    3067, 3079, 3083, 3089, 3109, 3119, 3121, 3137,
    3163, 3167, 3169, 3181, 3187, 3191, 3203, 3209,
    3217, 3221, 3229, 3251, 3253, 3257, 3259, 3271,
    3299, 3301, 3307, 3313, 3319, 3323, 3329, 3331,
    3343, 3347, 3359, 3361, 3371, 3373, 3389, 3391,
    3407, 3413, 3433, 3449, 3457, 3461, 3463, 3467,
    3469, 3491, 3499, 3511, 3517, 3527, 3529, 3533,
    3539, 3541, 3547, 3557, 3559, 3571, 3581, 3583,
    3593, 3607, 3613, 3617, 3623, 3631, 3637, 3643,
    3659, 3671, 3673, 3677, 3691, 3697, 3701, 3709,
    3719, 3727, 3733, 3739, 3761, 3767, 3769, 3779,
    3793, 3797, 3803, 3821, 3823, 3833, 3847, 3851,
    3853, 3863, 3877, 3881, 3889, 3907, 3911, 3917,
    3919, 3923, 3929, 3931, 3943, 3947, 3967, 3989,
    4001, 4003, 4007, 4013, 4019, 4021, 4027, 4049,
    4051, 4057, 4073, 4079, 4091, 4093, 4099, 4111,
    4127, 4129, 4133, 4139, 4153, 4157, 4159, 4177,
    4201, 4211, 4217, 4219, 4229, 4231, 4241, 4243,
    4253, 4259, 4261, 4271, 4273, 4283, 4289, 4297,
    4327, 4337, 4339, 4349, 4357, 4363, 4373, 4391,
    4397, 4409, 4421, 4423, 4441, 4447, 4451, 4457,
    4463, 4481, 4483, 4493, 4507, 4513, 4517, 4519,
    4523, 4547, 4549, 4561, 4567, 4583, 4591, 4597,
    4603, 4621, 4637, 4639, 4643, 4649, 4651, 4657,
    4663, 4673, 4679, 4691, 4703, 4721, 4723, 4729,
    4733, 4751, 4759, 4783, 4787, 4789, 4793, 4799,
    4801, 4813, 4817, 4831, 4861, 4871, 4877, 4889,
    4903, 4909, 4919, 4931, 4933, 4937, 4943, 4951,
    4957, 4967, 4969, 4973, 4987, 4993, 4999,
    0
};
static int no_of_small_prime_numbers = DIM (small_prime_numbers) - 1;



/* An object and a list to build up a global pool of primes.  See
   save_pool_prime and get_pool_prime. */
struct primepool_s 
{
  struct primepool_s *next;
  gcry_mpi_t prime;      /* If this is NULL the entry is not used. */
  unsigned int nbits;
  gcry_random_level_t randomlevel;
};
struct primepool_s *primepool;
/* Mutex used to protect access to the primepool.  */
static ath_mutex_t primepool_lock = ATH_MUTEX_INITIALIZER;



/* Save PRIME which has been generated at RANDOMLEVEL for later
   use. Needs to be called while primepool_lock is being hold.  Note
   that PRIME should be considered released after calling this
   function. */
static void
save_pool_prime (gcry_mpi_t prime, gcry_random_level_t randomlevel)
{
  struct primepool_s *item, *item2;
  size_t n;

  for (n=0, item = primepool; item; item = item->next, n++)
    if (!item->prime)
      break;
  if (!item && n > 100)
    {
      /* Remove some of the entries.  Our strategy is removing
         the last third from the list. */
      int i;
      
      for (i=0, item2 = primepool; item2; item2 = item2->next)
        {
          if (i >= n/3*2)
            {
              gcry_mpi_release (item2->prime);
              item2->prime = NULL;
              if (!item)
                item = item2;
            }
        }
    }
  if (!item)
    {
      item = gcry_calloc (1, sizeof *item);
      if (!item)
        {
          /* Out of memory.  Silently giving up. */
          gcry_mpi_release (prime);
          return; 
        }
      item->next = primepool;
      primepool = item;
    }
  item->prime = prime;
  item->nbits = mpi_get_nbits (prime);
  item->randomlevel = randomlevel;
}


/* Return a prime for the prime pool or NULL if none has been found.
   The prime needs to match NBITS and randomlevel. This function needs
   to be called why the primepool_look is being hold. */
static gcry_mpi_t
get_pool_prime (unsigned int nbits, gcry_random_level_t randomlevel)
{
  struct primepool_s *item;

  for (item = primepool; item; item = item->next)
    if (item->prime
        && item->nbits == nbits && item->randomlevel == randomlevel)
      {
        gcry_mpi_t prime = item->prime;
        item->prime = NULL;
        assert (nbits == mpi_get_nbits (prime));
        return prime;
      }
  return NULL;
}






void
_gcry_register_primegen_progress ( void (*cb)(void *,const char*,int,int,int),
                                   void *cb_data )
{
  progress_cb = cb;
  progress_cb_data = cb_data;
}


static void
progress( int c )
{
  if ( progress_cb )
    progress_cb ( progress_cb_data, "primegen", c, 0, 0 );
}


/****************
 * Generate a prime number (stored in secure memory)
 */
gcry_mpi_t
_gcry_generate_secret_prime (unsigned int nbits,
                             int (*extra_check)(void*, gcry_mpi_t),
                             void *extra_check_arg)
{
  gcry_mpi_t prime;

  prime = gen_prime( nbits, 1, 2, extra_check, extra_check_arg);
  progress('\n');
  return prime;
}

gcry_mpi_t
_gcry_generate_public_prime( unsigned int nbits,
                             int (*extra_check)(void*, gcry_mpi_t),
                             void *extra_check_arg)
{
  gcry_mpi_t prime;

  prime = gen_prime( nbits, 0, 2, extra_check, extra_check_arg );
  progress('\n');
  return prime;
}


/* Core prime generation function.  The algorithm used to generate
   practically save primes is due to Lim and Lee as described in the
   CRYPTO '97 proceedings (ISBN3540633847) page 260.

   NEED_Q_FACTOR: If true make sure that at least one factor is of
                  size qbits.  This is for example required for DSA.
   PRIME_GENERATED: Adresss of a variable where the resulting prime
                    number will be stored.
   PBITS: Requested size of the prime number.  At least 48.
   QBITS: One factor of the prime needs to be of this size.  Maybe 0
          if this is not required.  See also MODE.
   G: If not NULL an MPI which will receive a generator for the prime
      for use with Elgamal.
   RET_FACTORS: if not NULL, an array with all factors are stored at
                that address.
   ALL_FACTORS: If set to true all factors of prime-1 are returned.
   RANDOMLEVEL:  How strong should the random numers be.
   FLAGS: Prime generation bit flags. Currently supported:
          GCRY_PRIME_FLAG_SECRET - The prime needs to be kept secret.
   CB_FUNC, CB_ARG:  Callback to be used for extra checks.

 */
static gcry_err_code_t
prime_generate_internal (int need_q_factor,
			 gcry_mpi_t *prime_generated, unsigned int pbits,
			 unsigned int qbits, gcry_mpi_t g,
			 gcry_mpi_t **ret_factors,
			 gcry_random_level_t randomlevel, unsigned int flags,
                         int all_factors,
                         gcry_prime_check_func_t cb_func, void *cb_arg)
{
  gcry_err_code_t err = 0;
  gcry_mpi_t *factors_new = NULL; /* Factors to return to the
				     caller.  */
  gcry_mpi_t *factors = NULL;	/* Current factors.  */
  gcry_random_level_t poolrandomlevel; /* Random level used for pool primes. */
  gcry_mpi_t *pool = NULL;	/* Pool of primes.  */
  int *pool_in_use = NULL;      /* Array with currently used POOL elements. */
  unsigned char *perms = NULL;	/* Permutations of POOL.  */
  gcry_mpi_t q_factor = NULL;	/* Used if QBITS is non-zero.  */
  unsigned int fbits = 0;	/* Length of prime factors.  */
  unsigned int n = 0;		/* Number of factors.  */
  unsigned int m = 0;		/* Number of primes in pool.  */
  gcry_mpi_t q = NULL;		/* First prime factor.  */
  gcry_mpi_t prime = NULL;	/* Prime candidate.  */
  unsigned int nprime = 0;	/* Bits of PRIME.  */
  unsigned int req_qbits;       /* The original QBITS value.  */
  gcry_mpi_t val_2;             /* For check_prime().  */
  int is_locked = 0;            /* Flag to help unlocking the primepool. */
  unsigned int is_secret = (flags & GCRY_PRIME_FLAG_SECRET);
  unsigned int count1 = 0, count2 = 0;
  unsigned int i = 0, j = 0;

  if (pbits < 48)
    return GPG_ERR_INV_ARG;

  /* We won't use a too strong random elvel for the pooled subprimes. */
  poolrandomlevel = (randomlevel > GCRY_STRONG_RANDOM?
                     GCRY_STRONG_RANDOM : randomlevel);


  /* If QBITS is not given, assume a reasonable value. */
  if (!qbits)
    qbits = pbits / 3;

  req_qbits = qbits;

  /* Find number of needed prime factors N.  */
  for (n = 1; (pbits - qbits - 1) / n  >= qbits; n++)
    ;
  n--;

  val_2 = mpi_alloc_set_ui (2);

  if ((! n) || ((need_q_factor) && (n < 2)))
    {
      err = GPG_ERR_INV_ARG;
      goto leave;
    }

  if (need_q_factor)
    {
      n--;  /* Need one factor less because we want a specific Q-FACTOR. */
      fbits = (pbits - 2 * req_qbits -1) / n;
      qbits =  pbits - req_qbits - n * fbits;
    }
  else
    {
      fbits = (pbits - req_qbits -1) / n;
      qbits = pbits - n * fbits;
    }
  
  if (DBG_CIPHER)
    log_debug ("gen prime: pbits=%u qbits=%u fbits=%u/%u n=%d\n",
               pbits, req_qbits, qbits, fbits, n);

  /* Allocate an integer to old the new prime. */
  prime = gcry_mpi_new (pbits);

  /* Generate first prime factor.  */
  q = gen_prime (qbits, is_secret, randomlevel, NULL, NULL);

  /* Generate a specific Q-Factor if requested. */
  if (need_q_factor)
    q_factor = gen_prime (req_qbits, is_secret, randomlevel, NULL, NULL);
  
  /* Allocate an array to hold all factors + 2 for later usage.  */
  factors = gcry_calloc (n + 2, sizeof (*factors));
  if (!factors)
    {
      err = gpg_err_code_from_errno (errno);
      goto leave;
    }

  /* Allocate an array to track pool usage. */
  pool_in_use = gcry_malloc (n * sizeof *pool_in_use);
  if (!pool_in_use)
    {
      err = gpg_err_code_from_errno (errno);
      goto leave;
    }
  for (i=0; i < n; i++)
    pool_in_use[i] = -1;
      
  /* Make a pool of 3n+5 primes (this is an arbitrary value).  We
     require at least 30 primes for are useful selection process. 
     
     FIXME: We need to do some reseacrh on the best formula for sizing
     the pool.
  */
  m = n * 3 + 5;
  if (need_q_factor) /* Need some more in this case. */
    m += 5;
  if (m < 30)
    m = 30;
  pool = gcry_calloc (m , sizeof (*pool));
  if (! pool)
    {
      err = gpg_err_code_from_errno (errno);
      goto leave;
    }

  /* Permutate over the pool of primes until we find a prime of the
     requested length.  */
  do
    {
    next_try:
      for (i=0; i < n; i++)
        pool_in_use[i] = -1;

      if (!perms)
        {
          /* Allocate new primes.  This is done right at the beginning
             of the loop and if we have later run out of primes. */
          for (i = 0; i < m; i++)
            {
              mpi_free (pool[i]);
              pool[i] = NULL;
            }

          /* Init m_out_of_n().  */
          perms = gcry_calloc (1, m);
          if (!perms)
            {
              err = gpg_err_code_from_errno (errno);
              goto leave;
            }

          if (ath_mutex_lock (&primepool_lock))
            {
              err = GPG_ERR_INTERNAL;
              goto leave;
            }
          is_locked = 1;
          for (i = 0; i < n; i++)
            {
              perms[i] = 1; 
              /* At a maximum we use strong random for the factors.
                 This saves us a lot of entropy. Given that Q and
                 possible Q-factor are also used in the final prime
                 this should be acceptable.  We also don't allocate in
                 secure memory to save on that scare resource too.  If
                 Q has been allocated in secure memory, the final
                 prime will be saved there anyway.  This is because
                 our MPI routines take care of that.  GnuPG has worked
                 this way ever since.  */
              pool[i] = NULL;
              if (is_locked)
                {
                  pool[i] = get_pool_prime (fbits, poolrandomlevel);
                  if (!pool[i])
                    {
                      if (ath_mutex_unlock (&primepool_lock))
                        {
                          err = GPG_ERR_INTERNAL;
                          goto leave;
                        }
                      is_locked = 0;
                    }
                }
              if (!pool[i])
                pool[i] = gen_prime (fbits, 0, poolrandomlevel, NULL, NULL);
              pool_in_use[i] = i;
              factors[i] = pool[i];
            }
          if (is_locked && ath_mutex_unlock (&primepool_lock))
            {
              err = GPG_ERR_INTERNAL;
              goto leave;
            }
          is_locked = 0;
        }
      else
        {
          /* Get next permutation. */
          m_out_of_n ( (char*)perms, n, m);
          if (ath_mutex_lock (&primepool_lock))
            {
              err = GPG_ERR_INTERNAL;
              goto leave;
            }
          is_locked = 1;
          for (i = j = 0; (i < m) && (j < n); i++)
            if (perms[i])
              {
                /* If the subprime has not yet beed generated do it now. */
                if (!pool[i] && is_locked)
                  {
                    pool[i] = get_pool_prime (fbits, poolrandomlevel);
                    if (!pool[i])
                      {
                        if (ath_mutex_unlock (&primepool_lock))
                          {
                            err = GPG_ERR_INTERNAL;
                            goto leave;
                          }
                        is_locked = 0;
                      }
                  }
                if (!pool[i])
                  pool[i] = gen_prime (fbits, 0, poolrandomlevel, NULL, NULL);
                pool_in_use[j] = i;
                factors[j++] = pool[i];
              }
          if (is_locked && ath_mutex_unlock (&primepool_lock))
            {
              err = GPG_ERR_INTERNAL;
              goto leave;
            }
          is_locked = 0;
          if (i == n)
            {
              /* Ran out of permutations: Allocate new primes.  */
              gcry_free (perms);
              perms = NULL;
              progress ('!');
              goto next_try;	
            }
        }

	/* Generate next prime candidate:
	   p = 2 * q [ * q_factor] * factor_0 * factor_1 * ... * factor_n + 1. 
         */
	mpi_set (prime, q);
	mpi_mul_ui (prime, prime, 2);
	if (need_q_factor)
	  mpi_mul (prime, prime, q_factor);
	for(i = 0; i < n; i++)
	  mpi_mul (prime, prime, factors[i]);
	mpi_add_ui (prime, prime, 1);
	nprime = mpi_get_nbits (prime);

	if (nprime < pbits)
	  {
	    if (++count1 > 20)
	      {
		count1 = 0;
		qbits++;
		progress('>');
		mpi_free (q);
		q = gen_prime (qbits, is_secret, randomlevel, NULL, NULL);
		goto next_try;
	      }
	  }
	else
	  count1 = 0;
        
	if (nprime > pbits)
	  {
	    if (++count2 > 20)
	      {
		count2 = 0;
		qbits--;
		progress('<');
		mpi_free (q);
		q = gen_prime (qbits, is_secret, randomlevel, NULL, NULL);
		goto next_try;
	      }
	  }
	else
	  count2 = 0;
    }
  while (! ((nprime == pbits) && check_prime (prime, val_2, 5,
                                              cb_func, cb_arg)));

  if (DBG_CIPHER)
    {
      progress ('\n');
      log_mpidump ("prime    : ", prime);
      log_mpidump ("factor  q: ", q);
      if (need_q_factor)
        log_mpidump ("factor q0: ", q_factor);
      for (i = 0; i < n; i++)
        log_mpidump ("factor pi: ", factors[i]);
      log_debug ("bit sizes: prime=%u, q=%u",
                 mpi_get_nbits (prime), mpi_get_nbits (q));
      if (need_q_factor)
        log_debug (", q0=%u", mpi_get_nbits (q_factor));
      for (i = 0; i < n; i++)
        log_debug (", p%d=%u", i, mpi_get_nbits (factors[i]));
      progress('\n');
    }

  if (ret_factors)
    {
      /* Caller wants the factors.  */
      factors_new = gcry_calloc (n + 4, sizeof (*factors_new));
      if (! factors_new)
        {
          err = gpg_err_code_from_errno (errno);
          goto leave;
        }

      if (all_factors)
        {
          i = 0;
          factors_new[i++] = gcry_mpi_set_ui (NULL, 2);
          factors_new[i++] = mpi_copy (q);
          if (need_q_factor)
            factors_new[i++] = mpi_copy (q_factor);
          for(j=0; j < n; j++)
            factors_new[i++] = mpi_copy (factors[j]);
        }
      else
        {
          i = 0;
          if (need_q_factor)
            {
              factors_new[i++] = mpi_copy (q_factor);
              for (; i <= n; i++)
                factors_new[i] = mpi_copy (factors[i]);
            }
          else
            for (; i < n; i++ )
              factors_new[i] = mpi_copy (factors[i]);
        }
    }
  
  if (g)
    {
      /* Create a generator (start with 3).  */
      gcry_mpi_t tmp = mpi_alloc (mpi_get_nlimbs (prime));
      gcry_mpi_t b = mpi_alloc (mpi_get_nlimbs (prime));
      gcry_mpi_t pmin1 = mpi_alloc (mpi_get_nlimbs (prime));
      
      if (need_q_factor)
        err = GPG_ERR_NOT_IMPLEMENTED;
      else
        {
          factors[n] = q;
          factors[n + 1] = mpi_alloc_set_ui (2);
          mpi_sub_ui (pmin1, prime, 1);
          mpi_set_ui (g, 2);
          do
            {
              mpi_add_ui (g, g, 1);
              if (DBG_CIPHER)
                {
                  log_debug ("checking g:");
                  gcry_mpi_dump (g);
                  log_printf ("\n");
                }
              else
                progress('^');
              for (i = 0; i < n + 2; i++)
                {
                  mpi_fdiv_q (tmp, pmin1, factors[i]);
                  /* No mpi_pow(), but it is okay to use this with mod
                     prime.  */
                  gcry_mpi_powm (b, g, tmp, prime);
                  if (! mpi_cmp_ui (b, 1))
                    break;
                }
              if (DBG_CIPHER)
                progress('\n');
            } 
          while (i < n + 2);

          mpi_free (factors[n+1]);
          mpi_free (tmp);
          mpi_free (b);
          mpi_free (pmin1);
        }
    }
  
  if (! DBG_CIPHER)
    progress ('\n');


 leave:
  if (pool)
    {
      is_locked = !ath_mutex_lock (&primepool_lock);
      for(i = 0; i < m; i++)
        {
          if (pool[i])
            {
              for (j=0; j < n; j++)
                if (pool_in_use[j] == i)
                  break;
              if (j == n && is_locked)
                {
                  /* This pooled subprime has not been used. */
                  save_pool_prime (pool[i], poolrandomlevel);
                }
              else
                mpi_free (pool[i]);
            }
        }
      if (is_locked && ath_mutex_unlock (&primepool_lock))
        err = GPG_ERR_INTERNAL;
      is_locked = 0;
      gcry_free (pool);
    }
  gcry_free (pool_in_use);
  if (factors)
    gcry_free (factors);  /* Factors are shallow copies.  */
  if (perms)
    gcry_free (perms);

  mpi_free (val_2);
  mpi_free (q);
  mpi_free (q_factor);

  if (! err)
    {
      *prime_generated = prime;
      if (ret_factors)
	*ret_factors = factors_new;
    }
  else
    {
      if (factors_new)
	{
	  for (i = 0; factors_new[i]; i++)
	    mpi_free (factors_new[i]);
	  gcry_free (factors_new);
	}
      mpi_free (prime);
    }

  return err;
}



gcry_mpi_t
_gcry_generate_elg_prime (int mode, unsigned pbits, unsigned qbits,
			  gcry_mpi_t g, gcry_mpi_t **ret_factors)
{
  gcry_err_code_t err = GPG_ERR_NO_ERROR;
  gcry_mpi_t prime = NULL;
  
  err = prime_generate_internal ((mode == 1), &prime, pbits, qbits, g,
				 ret_factors, GCRY_WEAK_RANDOM, 0, 0,
                                 NULL, NULL);

  return prime;
}

static gcry_mpi_t
gen_prime (unsigned int nbits, int secret, int randomlevel, 
           int (*extra_check)(void *, gcry_mpi_t), void *extra_check_arg)
{
  gcry_mpi_t prime, ptest, pminus1, val_2, val_3, result;
  int i;
  unsigned int x, step;
  unsigned int count1, count2;
  int *mods;
  
/*   if (  DBG_CIPHER ) */
/*     log_debug ("generate a prime of %u bits ", nbits ); */

  if (nbits < 16)
    log_fatal ("can't generate a prime with less than %d bits\n", 16);

  mods = gcry_xmalloc( no_of_small_prime_numbers * sizeof *mods );
  /* Make nbits fit into gcry_mpi_t implementation. */
  val_2  = mpi_alloc_set_ui( 2 );
  val_3 = mpi_alloc_set_ui( 3);
  prime  = secret? gcry_mpi_snew ( nbits ): gcry_mpi_new ( nbits );
  result = mpi_alloc_like( prime );
  pminus1= mpi_alloc_like( prime );
  ptest  = mpi_alloc_like( prime );
  count1 = count2 = 0;
  for (;;)
    {  /* try forvever */
      int dotcount=0;
      
      /* generate a random number */
      gcry_mpi_randomize( prime, nbits, randomlevel );
      
      /* Set high order bit to 1, set low order bit to 1.  If we are
         generating a secret prime we are most probably doing that
         for RSA, to make sure that the modulus does have the
         requested key size we set the 2 high order bits. */
      mpi_set_highbit (prime, nbits-1);
      if (secret)
        mpi_set_bit (prime, nbits-2);
      mpi_set_bit(prime, 0);
      
      /* Calculate all remainders. */
      for (i=0; (x = small_prime_numbers[i]); i++ )
        mods[i] = mpi_fdiv_r_ui(NULL, prime, x);
      
      /* Now try some primes starting with prime. */
      for(step=0; step < 20000; step += 2 ) 
        {
          /* Check against all the small primes we have in mods. */
          count1++;
          for (i=0; (x = small_prime_numbers[i]); i++ ) 
            {
              while ( mods[i] + step >= x )
                mods[i] -= x;
              if ( !(mods[i] + step) )
                break;
	    }
          if ( x )
            continue;   /* Found a multiple of an already known prime. */
          
          mpi_add_ui( ptest, prime, step );

          /* Do a fast Fermat test now. */
          count2++;
          mpi_sub_ui( pminus1, ptest, 1);
          gcry_mpi_powm( result, val_2, pminus1, ptest );
          if ( !mpi_cmp_ui( result, 1 ) )
            { 
              /* Not composite, perform stronger tests */
              if (is_prime(ptest, 5, &count2 ))
                {
                  if (!mpi_test_bit( ptest, nbits-1-secret ))
                    {
                      progress('\n');
                      log_debug ("overflow in prime generation\n");
                      break; /* Stop loop, continue with a new prime. */
                    }

                  if (extra_check && extra_check (extra_check_arg, ptest))
                    { 
                      /* The extra check told us that this prime is
                         not of the caller's taste. */
                      progress ('/');
                    }
                  else
                    { 
                      /* Got it. */
                      mpi_free(val_2);
                      mpi_free(val_3);
                      mpi_free(result);
                      mpi_free(pminus1);
                      mpi_free(prime);
                      gcry_free(mods);
                      return ptest; 
                    }
                }
	    }
          if (++dotcount == 10 )
            {
              progress('.');
              dotcount = 0;
	    }
	}
      progress(':'); /* restart with a new random value */
    }
}

/****************
 * Returns: true if this may be a prime
 * RM_ROUNDS gives the number of Rabin-Miller tests to run.
 */
static int
check_prime( gcry_mpi_t prime, gcry_mpi_t val_2, int rm_rounds,
             gcry_prime_check_func_t cb_func, void *cb_arg)
{
  int i;
  unsigned int x;
  unsigned int count=0;

  /* Check against small primes. */
  for (i=0; (x = small_prime_numbers[i]); i++ )
    {
      if ( mpi_divisible_ui( prime, x ) )
        return 0;
    }

  /* A quick Fermat test. */
  {
    gcry_mpi_t result = mpi_alloc_like( prime );
    gcry_mpi_t pminus1 = mpi_alloc_like( prime );
    mpi_sub_ui( pminus1, prime, 1);
    gcry_mpi_powm( result, val_2, pminus1, prime );
    mpi_free( pminus1 );
    if ( mpi_cmp_ui( result, 1 ) )
      { 
        /* Is composite. */
        mpi_free( result );
        progress('.');
        return 0;
      }
    mpi_free( result );
  }

  if (!cb_func || cb_func (cb_arg, GCRY_PRIME_CHECK_AT_MAYBE_PRIME, prime))
    {
      /* Perform stronger tests. */
      if ( is_prime( prime, rm_rounds, &count ) )
        {
          if (!cb_func
              || cb_func (cb_arg, GCRY_PRIME_CHECK_AT_GOT_PRIME, prime))
            return 1; /* Probably a prime. */
        }
    }
  progress('.');
  return 0;
}


/*
 * Return true if n is probably a prime
 */
static int
is_prime (gcry_mpi_t n, int steps, unsigned int *count)
{
  gcry_mpi_t x = mpi_alloc( mpi_get_nlimbs( n ) );
  gcry_mpi_t y = mpi_alloc( mpi_get_nlimbs( n ) );
  gcry_mpi_t z = mpi_alloc( mpi_get_nlimbs( n ) );
  gcry_mpi_t nminus1 = mpi_alloc( mpi_get_nlimbs( n ) );
  gcry_mpi_t a2 = mpi_alloc_set_ui( 2 );
  gcry_mpi_t q;
  unsigned i, j, k;
  int rc = 0;
  unsigned nbits = mpi_get_nbits( n );

  if (steps < 5) /* Make sure that we do at least 5 rounds. */
    steps = 5; 

  mpi_sub_ui( nminus1, n, 1 );

  /* Find q and k, so that n = 1 + 2^k * q . */
  q = mpi_copy ( nminus1 );
  k = mpi_trailing_zeros ( q );
  mpi_tdiv_q_2exp (q, q, k);

  for (i=0 ; i < steps; i++ )
    {
      ++*count;
      if( !i )
        {
          mpi_set_ui( x, 2 );
        }
      else
        {
          gcry_mpi_randomize( x, nbits, GCRY_WEAK_RANDOM );

          /* Make sure that the number is smaller than the prime and
             keep the randomness of the high bit. */
          if ( mpi_test_bit ( x, nbits-2) )
            {
              mpi_set_highbit ( x, nbits-2); /* Clear all higher bits. */
            }
          else
            {
              mpi_set_highbit( x, nbits-2 );
              mpi_clear_bit( x, nbits-2 );
            }
          assert ( mpi_cmp( x, nminus1 ) < 0 && mpi_cmp_ui( x, 1 ) > 0 );
	}
      gcry_mpi_powm ( y, x, q, n);
      if ( mpi_cmp_ui(y, 1) && mpi_cmp( y, nminus1 ) )
        {
          for ( j=1; j < k && mpi_cmp( y, nminus1 ); j++ )
            {
              gcry_mpi_powm(y, y, a2, n);
              if( !mpi_cmp_ui( y, 1 ) )
                goto leave; /* Not a prime. */
            }
          if (mpi_cmp( y, nminus1 ) )
            goto leave; /* Not a prime. */
	}
      progress('+');
    }
  rc = 1; /* May be a prime. */

 leave:
  mpi_free( x );
  mpi_free( y );
  mpi_free( z );
  mpi_free( nminus1 );
  mpi_free( q );
  mpi_free( a2 );

  return rc;
}


/* Given ARRAY of size N with M elements set to true produce a
   modified array with the next permutation of M elements.  Note, that
   ARRAY is used in a one-bit-per-byte approach.  To detected the last
   permutation it is useful to intialize the array with the first M
   element set to true and use this test:
       m_out_of_n (array, m, n);
       for (i = j = 0; i < n && j < m; i++)
         if (array[i])
           j++;
       if (j == m)
         goto ready;
     
   This code is based on the algorithm 452 from the "Collected
   Algorithms From ACM, Volume II" by C. N. Liu and D. T. Tang.
*/
static void
m_out_of_n ( char *array, int m, int n )
{
  int i=0, i1=0, j=0, jp=0,  j1=0, k1=0, k2=0;

  if( !m || m >= n )
    return;

  /* Need to handle this simple case separately. */
  if( m == 1 )
    { 
      for (i=0; i < n; i++ )
        {
          if ( array[i] )
            {
              array[i++] = 0;
              if( i >= n )
                i = 0;
              array[i] = 1;
              return;
            }
        }
      BUG();
    }


  for (j=1; j < n; j++ )
    {
      if ( array[n-1] == array[n-j-1])
        continue;
      j1 = j;
      break;
    }

  if ( (m & 1) )
    {
      /* M is odd. */
      if( array[n-1] )
        {
          if( j1 & 1 )
            {
              k1 = n - j1;
              k2 = k1+2;
              if( k2 > n )
                k2 = n;
              goto leave;
            }
          goto scan;
        }
      k2 = n - j1 - 1;
      if( k2 == 0 )
        {
          k1 = i;
          k2 = n - j1;
        }
      else if( array[k2] && array[k2-1] )
        k1 = n;
      else
        k1 = k2 + 1;
    }
  else 
    {
      /* M is even. */
      if( !array[n-1] )
        {
          k1 = n - j1;
          k2 = k1 + 1;
          goto leave;
        }
        
      if( !(j1 & 1) )
        {
          k1 = n - j1;
          k2 = k1+2;
          if( k2 > n )
            k2 = n;
          goto leave;
        }
    scan:
      jp = n - j1 - 1;
      for (i=1; i <= jp; i++ ) 
        {
          i1 = jp + 2 - i;
          if( array[i1-1]  )
            {
              if( array[i1-2] )
                {
                  k1 = i1 - 1;
                  k2 = n - j1;
		}
              else
                {
                  k1 = i1 - 1;
                  k2 = n + 1 - j1;
                }
              goto leave;
            }
        }
      k1 = 1;
      k2 = n + 1 - m;
    }
 leave:
  /* Now complement the two selected bits. */
  array[k1-1] = !array[k1-1];
  array[k2-1] = !array[k2-1];
}


/* Generate a new prime number of PRIME_BITS bits and store it in
   PRIME.  If FACTOR_BITS is non-zero, one of the prime factors of
   (prime - 1) / 2 must be FACTOR_BITS bits long.  If FACTORS is
   non-zero, allocate a new, NULL-terminated array holding the prime
   factors and store it in FACTORS.  FLAGS might be used to influence
   the prime number generation process.  */
gcry_error_t
gcry_prime_generate (gcry_mpi_t *prime, unsigned int prime_bits,
		     unsigned int factor_bits, gcry_mpi_t **factors,
		     gcry_prime_check_func_t cb_func, void *cb_arg,
		     gcry_random_level_t random_level,
		     unsigned int flags)
{
  gcry_err_code_t err = GPG_ERR_NO_ERROR;
  gcry_mpi_t *factors_generated = NULL;
  gcry_mpi_t prime_generated = NULL;
  unsigned int mode = 0;

  if (!prime)
    return gpg_error (GPG_ERR_INV_ARG);
  *prime = NULL; 

  if (flags & GCRY_PRIME_FLAG_SPECIAL_FACTOR)
    mode = 1;

  /* Generate.  */
  err = prime_generate_internal ((mode==1), &prime_generated, prime_bits,
				 factor_bits, NULL,
                                 factors? &factors_generated : NULL,
				 random_level, flags, 1,
                                 cb_func, cb_arg);

  if (! err)
    if (cb_func)
      {
	/* Additional check. */
	if ( !cb_func (cb_arg, GCRY_PRIME_CHECK_AT_FINISH, prime_generated))
	  {
	    /* Failed, deallocate resources.  */
	    unsigned int i;

	    mpi_free (prime_generated);
            if (factors)
              {
                for (i = 0; factors_generated[i]; i++)
                  mpi_free (factors_generated[i]);
                gcry_free (factors_generated);
              }
	    err = GPG_ERR_GENERAL; 
	  }
      }

  if (! err)
    {
      if (factors)
        *factors = factors_generated;
      *prime = prime_generated;
    }

  return gcry_error (err);
}

/* Check wether the number X is prime.  */
gcry_error_t
gcry_prime_check (gcry_mpi_t x, unsigned int flags)
{
  gcry_err_code_t err = GPG_ERR_NO_ERROR;
  gcry_mpi_t val_2 = mpi_alloc_set_ui (2); /* Used by the Fermat test. */

  (void)flags;

  /* We use 64 rounds because the prime we are going to test is not
     guaranteed to be a random one. */
  if (! check_prime (x, val_2, 64, NULL, NULL))
    err = GPG_ERR_NO_PRIME;

  mpi_free (val_2);

  return gcry_error (err);
}

/* Find a generator for PRIME where the factorization of (prime-1) is
   in the NULL terminated array FACTORS. Return the generator as a
   newly allocated MPI in R_G.  If START_G is not NULL, use this as s
   atart for the search. Returns 0 on success.*/
gcry_error_t
gcry_prime_group_generator (gcry_mpi_t *r_g,
                            gcry_mpi_t prime, gcry_mpi_t *factors,
                            gcry_mpi_t start_g)
{
  gcry_mpi_t tmp = gcry_mpi_new (0);
  gcry_mpi_t b = gcry_mpi_new (0);
  gcry_mpi_t pmin1 = gcry_mpi_new (0);
  gcry_mpi_t g = start_g? gcry_mpi_copy (start_g) : gcry_mpi_set_ui (NULL, 3);
  int first = 1;
  int i, n;

  if (!factors || !r_g || !prime)
    return gpg_error (GPG_ERR_INV_ARG);
  *r_g = NULL; 

  for (n=0; factors[n]; n++)
    ;
  if (n < 2)
    return gpg_error (GPG_ERR_INV_ARG);

  /* Extra sanity check - usually disabled. */  
/*   mpi_set (tmp, factors[0]); */
/*   for(i = 1; i < n; i++) */
/*     mpi_mul (tmp, tmp, factors[i]); */
/*   mpi_add_ui (tmp, tmp, 1); */
/*   if (mpi_cmp (prime, tmp)) */
/*     return gpg_error (GPG_ERR_INV_ARG); */
  
  gcry_mpi_sub_ui (pmin1, prime, 1);      
  do         
    {
      if (first)
        first = 0;
      else
        gcry_mpi_add_ui (g, g, 1);
      
      if (DBG_CIPHER)
        {
          log_debug ("checking g:");
          gcry_mpi_dump (g);
          log_debug ("\n");
        }
      else
        progress('^');
      
      for (i = 0; i < n; i++)
        {
          mpi_fdiv_q (tmp, pmin1, factors[i]);
          gcry_mpi_powm (b, g, tmp, prime);
          if (! mpi_cmp_ui (b, 1))
            break;
        }
      if (DBG_CIPHER)
        progress('\n');
    }
  while (i < n);
  
  gcry_mpi_release (tmp);
  gcry_mpi_release (b); 
  gcry_mpi_release (pmin1); 
  *r_g = g; 

  return 0; 
}

/* Convenience function to release the factors array. */
void
gcry_prime_release_factors (gcry_mpi_t *factors)
{
  if (factors)
    {
      int i;
      
      for (i=0; factors[i]; i++)
        mpi_free (factors[i]);
      gcry_free (factors);
    }
}