summaryrefslogtreecommitdiff
path: root/lib/gnutls_srp.c
blob: e516de88ae918e618654a2311c37361585ceee11 (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
/*
 * Copyright (C) 2001, 2002, 2003, 2004, 2005 Free Software Foundation
 *
 * Author: Nikos Mavrogiannopoulos
 *
 * This file is part of GNUTLS.
 *
 * The GNUTLS library 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.
 *
 * This library 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 library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
 * USA
 *
 */

#include <gnutls_int.h>
#include <gnutls_errors.h>
#include <auth_srp.h>
#include <gnutls_state.h>

#ifdef ENABLE_SRP

#include <gnutls_srp.h>
#include <auth_srp_passwd.h>
#include <gnutls_mpi.h>
#include <gnutls_num.h>
#include <gnutls_helper.h>

#include "debug.h"


/* Here functions for SRP (like g^x mod n) are defined 
 */

int
_gnutls_srp_gx (opaque * text, size_t textsize, opaque ** result,
		mpi_t g, mpi_t prime, gnutls_alloc_function galloc_func)
{
  mpi_t x, e;
  size_t result_size;

  if (_gnutls_mpi_scan_nz (&x, text, &textsize))
    {
      gnutls_assert ();
      return GNUTLS_E_MPI_SCAN_FAILED;
    }

  e = _gnutls_mpi_alloc_like (prime);
  if (e == NULL)
    {
      gnutls_assert ();
      _gnutls_mpi_release (&x);
      return GNUTLS_E_MEMORY_ERROR;
    }

  /* e = g^x mod prime (n) */
  _gnutls_mpi_powm (e, g, x, prime);
  _gnutls_mpi_release (&x);

  _gnutls_mpi_print (NULL, &result_size, e);
  if (result != NULL)
    {
      *result = galloc_func (result_size);
      if ((*result) == NULL)
	return GNUTLS_E_MEMORY_ERROR;

      _gnutls_mpi_print (*result, &result_size, e);
    }

  _gnutls_mpi_release (&e);

  return result_size;

}


/****************
 * Choose a random value b and calculate B = (k* v + g^b) % N.
 * where k == SHA1(N|g)
 * Return: B and if ret_b is not NULL b.
 */
mpi_t
_gnutls_calc_srp_B (mpi_t * ret_b, mpi_t g, mpi_t n, mpi_t v)
{
  mpi_t tmpB = NULL, tmpV = NULL;
  mpi_t b = NULL, B = NULL, k = NULL;
  int bits;


  /* calculate:  B = (k*v + g^b) % N 
   */
  bits = _gnutls_mpi_get_nbits (n);
  b = _gnutls_mpi_snew (bits);
  if (b == NULL)
    {
      gnutls_assert ();
      return NULL;
    }

  tmpV = _gnutls_mpi_alloc_like (n);

  if (tmpV == NULL)
    {
      gnutls_assert ();
      goto error;
    }

  _gnutls_mpi_randomize (b, bits, GCRY_STRONG_RANDOM);

  tmpB = _gnutls_mpi_snew (bits);
  if (tmpB == NULL)
    {
      gnutls_assert ();
      goto error;
    }

  B = _gnutls_mpi_snew (bits);
  if (B == NULL)
    {
      gnutls_assert ();
      goto error;
    }

  k = _gnutls_calc_srp_u (n, g, n);
  if (k == NULL)
    {
      gnutls_assert ();
      goto error;
    }

  _gnutls_mpi_mulm (tmpV, k, v, n);
  _gnutls_mpi_powm (tmpB, g, b, n);

  _gnutls_mpi_addm (B, tmpV, tmpB, n);

  _gnutls_mpi_release (&k);
  _gnutls_mpi_release (&tmpB);
  _gnutls_mpi_release (&tmpV);

  if (ret_b)
    *ret_b = b;
  else
    _gnutls_mpi_release (&b);

  return B;

error:
  _gnutls_mpi_release (&b);
  _gnutls_mpi_release (&B);
  _gnutls_mpi_release (&k);
  _gnutls_mpi_release (&tmpB);
  _gnutls_mpi_release (&tmpV);
  return NULL;

}

/* This calculates the SHA1(A | B)
 * A and B will be left-padded with zeros to fill n_size.
 */
mpi_t
_gnutls_calc_srp_u (mpi_t A, mpi_t B, mpi_t n)
{
  size_t b_size, a_size;
  opaque *holder, hd[MAX_HASH_SIZE];
  size_t holder_size, hash_size, n_size;
  GNUTLS_HASH_HANDLE td;
  int ret;
  mpi_t res;

  /* get the size of n in bytes */
  _gnutls_mpi_print (NULL, &n_size, n);

  _gnutls_mpi_print (NULL, &a_size, A);
  _gnutls_mpi_print (NULL, &b_size, B);

  if (a_size > n_size || b_size > n_size)
    {
      gnutls_assert ();
      return NULL;		/* internal error */
    }

  holder_size = n_size + n_size;

  holder = gnutls_calloc (1, holder_size);
  if (holder == NULL)
    return NULL;

  _gnutls_mpi_print (&holder[n_size - a_size], &a_size, A);
  _gnutls_mpi_print (&holder[n_size + n_size - b_size], &b_size, B);

  td = _gnutls_hash_init (GNUTLS_MAC_SHA1);
  if (td == NULL)
    {
      gnutls_free (holder);
      gnutls_assert ();
      return NULL;
    }
  _gnutls_hash (td, holder, holder_size);
  _gnutls_hash_deinit (td, hd);

  /* convert the bytes of hd to integer
   */
  hash_size = 20;		/* SHA */
  ret = _gnutls_mpi_scan_nz (&res, hd, &hash_size);
  gnutls_free (holder);

  if (ret < 0)
    {
      gnutls_assert ();
      return NULL;
    }

  return res;
}

/* S = (A * v^u) ^ b % N 
 * this is our shared key (server premaster secret)
 */
mpi_t
_gnutls_calc_srp_S1 (mpi_t A, mpi_t b, mpi_t u, mpi_t v, mpi_t n)
{
  mpi_t tmp1 = NULL, tmp2 = NULL;
  mpi_t S = NULL;

  S = _gnutls_mpi_alloc_like (n);
  if (S == NULL)
    return NULL;

  tmp1 = _gnutls_mpi_alloc_like (n);
  tmp2 = _gnutls_mpi_alloc_like (n);

  if (tmp1 == NULL || tmp2 == NULL)
    goto freeall;

  _gnutls_mpi_powm (tmp1, v, u, n);
  _gnutls_mpi_mulm (tmp2, A, tmp1, n);
  _gnutls_mpi_powm (S, tmp2, b, n);

  _gnutls_mpi_release (&tmp1);
  _gnutls_mpi_release (&tmp2);

  return S;

freeall:
  _gnutls_mpi_release (&tmp1);
  _gnutls_mpi_release (&tmp2);
  return NULL;
}

/* A = g^a % N 
 * returns A and a (which is random)
 */
mpi_t
_gnutls_calc_srp_A (mpi_t * a, mpi_t g, mpi_t n)
{
  mpi_t tmpa;
  mpi_t A;
  int bits;

  bits = _gnutls_mpi_get_nbits (n);
  tmpa = _gnutls_mpi_snew (bits);
  if (tmpa == NULL)
    {
      gnutls_assert ();
      return NULL;
    }

  _gnutls_mpi_randomize (tmpa, bits, GCRY_STRONG_RANDOM);

  A = _gnutls_mpi_snew (bits);
  if (A == NULL)
    {
      gnutls_assert ();
      _gnutls_mpi_release (&tmpa);
      return NULL;
    }
  _gnutls_mpi_powm (A, g, tmpa, n);

  if (a != NULL)
    *a = tmpa;
  else
    _gnutls_mpi_release (&tmpa);

  return A;
}

/* generate x = SHA(s | SHA(U | ":" | p))
 * The output is exactly 20 bytes
 */
int
_gnutls_calc_srp_sha (const char *username, const char *password,
		      opaque * salt, int salt_size, size_t * size,
		      void *digest)
{
  GNUTLS_HASH_HANDLE td;
  opaque res[MAX_HASH_SIZE];

  *size = 20;

  td = _gnutls_hash_init (GNUTLS_MAC_SHA1);
  if (td == NULL)
    {
      return GNUTLS_E_MEMORY_ERROR;
    }
  _gnutls_hash (td, username, strlen (username));
  _gnutls_hash (td, ":", 1);
  _gnutls_hash (td, password, strlen (password));

  _gnutls_hash_deinit (td, res);

  td = _gnutls_hash_init (GNUTLS_MAC_SHA1);
  if (td == NULL)
    {
      return GNUTLS_E_MEMORY_ERROR;
    }

  _gnutls_hash (td, salt, salt_size);
  _gnutls_hash (td, res, 20);	/* 20 bytes is the output of sha1 */

  _gnutls_hash_deinit (td, digest);

  return 0;
}

int
_gnutls_calc_srp_x (char *username, char *password, opaque * salt,
		    size_t salt_size, size_t * size, void *digest)
{

  return _gnutls_calc_srp_sha (username, password, salt,
			       salt_size, size, digest);
}


/* S = (B - k*g^x) ^ (a + u * x) % N
 * this is our shared key (client premaster secret)
 */
mpi_t
_gnutls_calc_srp_S2 (mpi_t B, mpi_t g, mpi_t x, mpi_t a, mpi_t u, mpi_t n)
{
  mpi_t S = NULL, tmp1 = NULL, tmp2 = NULL;
  mpi_t tmp4 = NULL, tmp3 = NULL, k = NULL;

  S = _gnutls_mpi_alloc_like (n);
  if (S == NULL)
    return NULL;

  tmp1 = _gnutls_mpi_alloc_like (n);
  tmp2 = _gnutls_mpi_alloc_like (n);
  tmp3 = _gnutls_mpi_alloc_like (n);
  if (tmp1 == NULL || tmp2 == NULL || tmp3 == NULL)
    {
      goto freeall;
    }

  k = _gnutls_calc_srp_u (n, g, n);
  if (k == NULL)
    {
      gnutls_assert ();
      goto freeall;
    }

  _gnutls_mpi_powm (tmp1, g, x, n);	/* g^x */
  _gnutls_mpi_mulm (tmp3, tmp1, k, n);	/* k*g^x mod n */
  _gnutls_mpi_subm (tmp2, B, tmp3, n);

  tmp4 = _gnutls_mpi_alloc_like (n);
  if (tmp4 == NULL)
    goto freeall;

  _gnutls_mpi_mul (tmp1, u, x);
  _gnutls_mpi_add (tmp4, a, tmp1);
  _gnutls_mpi_powm (S, tmp2, tmp4, n);

  _gnutls_mpi_release (&tmp1);
  _gnutls_mpi_release (&tmp2);
  _gnutls_mpi_release (&tmp3);
  _gnutls_mpi_release (&tmp4);
  _gnutls_mpi_release (&k);

  return S;

freeall:
  _gnutls_mpi_release (&k);
  _gnutls_mpi_release (&tmp1);
  _gnutls_mpi_release (&tmp2);
  _gnutls_mpi_release (&tmp3);
  _gnutls_mpi_release (&tmp4);
  _gnutls_mpi_release (&S);
  return NULL;
}

/**
  * gnutls_srp_free_client_credentials - Used to free an allocated gnutls_srp_client_credentials_t structure
  * @sc: is an #gnutls_srp_client_credentials_t structure.
  *
  * This structure is complex enough to manipulate directly thus
  * this helper function is provided in order to free (deallocate) it.
  *
  **/
void
gnutls_srp_free_client_credentials (gnutls_srp_client_credentials_t sc)
{
  gnutls_free (sc->username);
  gnutls_free (sc->password);
  gnutls_free (sc);
}

/**
  * gnutls_srp_allocate_client_credentials - Used to allocate an gnutls_srp_server_credentials_t structure
  * @sc: is a pointer to an #gnutls_srp_server_credentials_t structure.
  *
  * This structure is complex enough to manipulate directly thus
  * this helper function is provided in order to allocate it.
  *
  * Returns 0 on success.
  **/
int
gnutls_srp_allocate_client_credentials (gnutls_srp_client_credentials_t * sc)
{
  *sc = gnutls_calloc (1, sizeof (srp_client_credentials_st));

  if (*sc == NULL)
    return GNUTLS_E_MEMORY_ERROR;

  return 0;
}

/**
  * gnutls_srp_set_client_credentials - Used to set the username/password, in a gnutls_srp_client_credentials_t structure
  * @res: is an #gnutls_srp_client_credentials_t structure.
  * @username: is the user's userid
  * @password: is the user's password
  *
  * This function sets the username and password, in a gnutls_srp_client_credentials_t structure.
  * Those will be used in SRP authentication. @username and @password should be ASCII
  * strings or UTF-8 strings prepared using the "SASLprep" profile of "stringprep".
  *
  * Returns 0 on success.
  **/
int
gnutls_srp_set_client_credentials (gnutls_srp_client_credentials_t res,
				   const char *username, const char *password)
{

  if (username == NULL || password == NULL)
    {
      gnutls_assert ();
      return GNUTLS_E_INVALID_REQUEST;
    }

  res->username = gnutls_strdup (username);
  if (res->username == NULL)
    return GNUTLS_E_MEMORY_ERROR;

  res->password = gnutls_strdup (password);
  if (res->password == NULL)
    {
      gnutls_free (res->username);
      return GNUTLS_E_MEMORY_ERROR;
    }

  return 0;
}

/**
  * gnutls_srp_free_server_credentials - Used to free an allocated gnutls_srp_server_credentials_t structure
  * @sc: is an #gnutls_srp_server_credentials_t structure.
  *
  * This structure is complex enough to manipulate directly thus
  * this helper function is provided in order to free (deallocate) it.
  *
  **/
void
gnutls_srp_free_server_credentials (gnutls_srp_server_credentials_t sc)
{
  gnutls_free (sc->password_file);
  gnutls_free (sc->password_conf_file);

  gnutls_free (sc);
}

/**
  * gnutls_srp_allocate_server_credentials - Used to allocate an gnutls_srp_server_credentials_t structure
  * @sc: is a pointer to an #gnutls_srp_server_credentials_t structure.
  *
  * This structure is complex enough to manipulate directly thus
  * this helper function is provided in order to allocate it.
  * 
  * Returns 0 on success.
  **/
int
gnutls_srp_allocate_server_credentials (gnutls_srp_server_credentials_t * sc)
{
  *sc = gnutls_calloc (1, sizeof (srp_server_cred_st));

  if (*sc == NULL)
    return GNUTLS_E_MEMORY_ERROR;

  return 0;
}

/**
  * gnutls_srp_set_server_credentials_file - Used to set the password files, in a gnutls_srp_server_credentials_t structure
  * @res: is an #gnutls_srp_server_credentials_t structure.
  * @password_file: is the SRP password file (tpasswd)
  * @password_conf_file: is the SRP password conf file (tpasswd.conf)
  *
  * This function sets the password files, in a gnutls_srp_server_credentials_t structure.
  * Those password files hold usernames and verifiers and will be used for SRP authentication.
  *
  * Returns 0 on success.
  *
  **/
int
gnutls_srp_set_server_credentials_file (gnutls_srp_server_credentials_t
					res, const char *password_file,
					const char *password_conf_file)
{

  if (password_file == NULL || password_conf_file == NULL)
    {
      gnutls_assert ();
      return GNUTLS_E_INVALID_REQUEST;
    }

  /* Check if the files can be opened */
  if (_gnutls_file_exists (password_file) != 0)
    {
      gnutls_assert ();
      return GNUTLS_E_FILE_ERROR;
    }

  if (_gnutls_file_exists (password_conf_file) != 0)
    {
      gnutls_assert ();
      return GNUTLS_E_FILE_ERROR;
    }

  res->password_file = gnutls_strdup (password_file);
  if (res->password_file == NULL)
    {
      gnutls_assert ();
      return GNUTLS_E_MEMORY_ERROR;
    }

  res->password_conf_file = gnutls_strdup (password_conf_file);
  if (res->password_conf_file == NULL)
    {
      gnutls_assert ();
      gnutls_free (res->password_file);
      res->password_file = NULL;
      return GNUTLS_E_MEMORY_ERROR;
    }

  return 0;
}


/**
  * gnutls_srp_set_server_credentials_function - Used to set a callback to retrieve the user's SRP credentials
  * @cred: is a #gnutls_srp_server_credentials_t structure.
  * @func: is the callback function
  *
  * This function can be used to set a callback to retrieve the user's SRP credentials.
  * The callback's function form is:
  * int (*callback)(gnutls_session_t, const char* username,
  *  gnutls_datum_t* salt, gnutls_datum_t *verifier, gnutls_datum_t* g,
  *  gnutls_datum_t* n);
  *
  * @username contains the actual username. 
  * The @salt, @verifier, @generator and @prime must be filled
  * in using the gnutls_malloc(). For convenience @prime and @generator 
  * may also be one of the static parameters defined in extra.h.
  *
  * In case the callback returned a negative number then gnutls will
  * assume that the username does not exist.
  *
  * In order to prevent attackers from guessing valid usernames,
  * if a user does not exist, g and n values should be filled in
  * using a random user's parameters. In that case the callback must
  * return the special value (1).
  *
  * The callback function will only be called once per handshake.
  * The callback function should return 0 on success, while
  * -1 indicates an error.
  *
  **/
void
gnutls_srp_set_server_credentials_function (gnutls_srp_server_credentials_t
					    cred,
					    gnutls_srp_server_credentials_function
					    * func)
{
  cred->pwd_callback = func;
}

/**
  * gnutls_srp_set_client_credentials_function - Used to set a callback to retrieve the username and password
  * @cred: is a #gnutls_srp_server_credentials_t structure.
  * @func: is the callback function
  *
  * This function can be used to set a callback to retrieve the username and
  * password for client SRP authentication.
  * The callback's function form is:
  * int (*callback)(gnutls_session_t, char** username,
  *  char** password);
  *
  * The @username and @password must be allocated using gnutls_malloc().
  * @username and @password should be ASCII strings or UTF-8 strings 
  * prepared using the "SASLprep" profile of "stringprep".
  *
  * The callback function will be called once per handshake before the
  * initial hello message is sent.
  * 
  * The callback should not return a negative error code the second
  * time called, since the handshake procedure will be aborted.
  *
  * The callback function should return 0 on success.
  * -1 indicates an error.
  *
  **/
void
gnutls_srp_set_client_credentials_function (gnutls_srp_client_credentials_t
					    cred,
					    gnutls_srp_client_credentials_function
					    * func)
{
  cred->get_function = func;
}


/**
  * gnutls_srp_server_get_username - This function returns the username of the peer
  * @session: is a gnutls session
  *
  * This function will return the username of the peer. This should only be
  * called in case of SRP authentication and in case of a server.
  * Returns NULL in case of an error.
  *
  **/
const char *
gnutls_srp_server_get_username (gnutls_session_t session)
{
  srp_server_auth_info_t info;

  CHECK_AUTH (GNUTLS_CRD_SRP, NULL);

  info = _gnutls_get_auth_info (session);
  if (info == NULL)
    return NULL;
  return info->username;
}

/**
  * gnutls_srp_verifier - Used to calculate an SRP verifier
  * @username: is the user's name
  * @password: is the user's password
  * @salt: should be some randomly generated bytes
  * @generator: is the generator of the group
  * @prime: is the group's prime
  * @res: where the verifier will be stored.
  *
  * This function will create an SRP verifier, as specified in RFC2945.
  * The @prime and @generator should be one of the static parameters defined
  * in gnutls/extra.h or may be generated using the GCRYPT functions
  * gcry_prime_generate() and gcry_prime_group_generator().
  * The verifier will be allocated with @malloc and will be stored in @res using 
  * binary format.
  *
  **/
int
gnutls_srp_verifier (const char *username, const char *password,
		     const gnutls_datum_t * salt,
		     const gnutls_datum_t * generator,
		     const gnutls_datum_t * prime, gnutls_datum_t * res)
{
  mpi_t _n, _g;
  int ret;
  size_t digest_size = 20, size;
  opaque digest[20];

  ret = _gnutls_calc_srp_sha (username, password, salt->data,
			      salt->size, &digest_size, digest);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }

  size = prime->size;
  if (_gnutls_mpi_scan_nz (&_n, prime->data, &size))
    {
      gnutls_assert ();
      return GNUTLS_E_MPI_SCAN_FAILED;
    }

  size = generator->size;
  if (_gnutls_mpi_scan_nz (&_g, generator->data, &size))
    {
      gnutls_assert ();
      return GNUTLS_E_MPI_SCAN_FAILED;
    }

  ret = _gnutls_srp_gx (digest, 20, &res->data, _g, _n, malloc);
  if (ret < 0)
    {
      gnutls_assert ();
      return ret;
    }
  res->size = ret;

  return 0;
}

#endif /* ENABLE_SRP */