summaryrefslogtreecommitdiffabout
path: root/pwmanager/libcrypt/cipher/primegen.c
blob: afd435e78a5f7f64eb7d35bf3a7a697ae27cebbd (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
/* 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
 *
 * ***********************************************************************
 * The algorithm used to generate practically save primes is due to
 * Lim and Lee as described in the CRYPTO '97 proceedings (ISBN3540633847)
 * page 260.
 */

#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"

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,
                        gcry_prime_check_func_t cb_func, void *cb_arg );
static int is_prime( gcry_mpi_t n, int steps, 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;

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;
}


/****************
 * We do not need to use the strongest RNG because we gain no extra
 * security from it - The prime number is public and we could also
 * offer the factors for those who are willing to check that it is
 * indeed a strong prime.  With ALL_FACTORS set to true all afcors of
 * prime-1 are returned in FACTORS.
 *
 * mode 0: Standard
 *	1: Make sure that at least one factor is of size qbits.
 */
static gcry_err_code_t
prime_generate_internal (int mode,
			 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_mpi_t *pool = NULL;	/* Pool of primes.  */
  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().  */
  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;

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

  req_qbits = qbits;

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

  val_2 = mpi_alloc_set_ui (2);

  if ((! n) || ((mode == 1) && (n < 2)))
    {
      err = GPG_ERR_INV_ARG;
      goto leave;
    }

  if (mode == 1)
    {
      n--;
      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);

  prime = gcry_mpi_new (pbits);

  /* Generate first prime factor.  */
  q = gen_prime (qbits, is_secret, randomlevel, NULL, NULL);
  
  if (mode == 1)
    q_factor = gen_prime (req_qbits, is_secret, randomlevel, NULL, NULL);
  
  /* Allocate an array to hold the factors + 2 for later usage.  */
  factors = gcry_calloc (n + 2, sizeof (*factors));
  if (!factors)
    {
      err = gpg_err_code_from_errno (errno);
      goto leave;
    }
      
  /* Make a pool of 3n+5 primes (this is an arbitrary value).  */
  m = n * 3 + 5;
  if (mode == 1) /* Need some more (for e.g. DSA).  */
    m += 5;
  if (m < 25)
    m = 25;
  pool = gcry_calloc (m , sizeof (*pool));
  if (! pool)
    {
      err = gpg_err_code_from_errno (errno);
      goto leave;
    }

  /* Permutate over the pool of primes.  */
  do
    {
    next_try:
      if (! perms)
        {
          /* Allocate new 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;
            }
          for(i = 0; i < n; i++)
            {
              perms[i] = 1;
              pool[i] = gen_prime (fbits, is_secret,
                                   randomlevel, NULL, NULL);
              factors[i] = pool[i];
            }
        }
      else
        {
          m_out_of_n (perms, n, m);
          for (i = j = 0; (i < m) && (j < n); i++)
            if (perms[i])
              {
                if(! pool[i])
                  pool[i] = gen_prime (fbits, 0, 1, NULL, NULL);
                factors[j++] = pool[i];
              }
          if (i == n)
            {
              gcry_free (perms);
              perms = NULL;
              progress ('!');
              goto next_try;	/* Allocate new primes.  */
            }
        }

	/* 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 (mode == 1)
	  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, 0, 0, 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, 0, 0, NULL, NULL);
		goto next_try;
	      }
	  }
	else
	  count2 = 0;
    }
  while (! ((nprime == pbits) && check_prime (prime, val_2, cb_func, cb_arg)));

  if (DBG_CIPHER)
    {
      progress ('\n');
      log_mpidump ("prime    : ", prime);
      log_mpidump ("factor  q: ", q);
      if (mode == 1)
        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 (mode == 1)
        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 (mode == 1)
            factors_new[i++] = mpi_copy (q_factor);
          for(j=0; j < n; j++)
            factors_new[i++] = mpi_copy (factors[j]);
        }
      else
        {
          i = 0;
          if (mode == 1)
            {
              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 (mode == 1)
        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)
    {
      for(i = 0; i < m; i++)
	mpi_free (pool[i]);
      gcry_free (pool);
    }
  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, &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 x, step;
  unsigned 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
 */
static int
check_prime( gcry_mpi_t prime, gcry_mpi_t val_2,
             gcry_prime_check_func_t cb_func, void *cb_arg)
{
  int i;
  unsigned int x;
  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, 5, &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, 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 );

  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;
}


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;

  if( m == 1 )
    { 
      /* Special case. */
      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:
  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, &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. */

  if (! check_prime (x, val_2, 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);
    }
}