summaryrefslogtreecommitdiff
path: root/lib/cipher.c
blob: 28eafbe1883cb91d7b052bbff277bfcbd543b96b (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
/*
 * Copyright (C) 2000-2013 Free Software Foundation, Inc.
 * Copyright (C) 2013 Nikos Mavrogiannopoulos
 * Copyright (C) 2017-2018 Red Hat, Inc.
 *
 * Author: Nikos Mavrogiannopoulos
 *
 * This file is part of GnuTLS.
 *
 * The GnuTLS 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 program.  If not, see <https://www.gnu.org/licenses/>
 *
 */

/* Some high level functions to be used in the record encryption are
 * included here.
 */

#include "gnutls_int.h"
#include "errors.h"
#include "cipher.h"
#include "algorithms.h"
#include "hash_int.h"
#include "cipher_int.h"
#include "debug.h"
#include "num.h"
#include "datum.h"
#include "kx.h"
#include "record.h"
#include "constate.h"
#include "mbuffers.h"
#include <state.h>
#include <random.h>

#include <nettle/memxor.h>

static int encrypt_packet(gnutls_session_t session,
			    uint8_t * cipher_data, int cipher_size,
			    gnutls_datum_t * plain,
			    size_t min_pad,
			    content_type_t _type,
			    record_parameters_st * params);

static int decrypt_packet(gnutls_session_t session,
			    gnutls_datum_t * ciphertext,
			    gnutls_datum_t * plain,
			    content_type_t type,
			    record_parameters_st * params,
			    uint64_t sequence);

static int
decrypt_packet_tls13(gnutls_session_t session,
		     gnutls_datum_t * ciphertext,
		     gnutls_datum_t * plain,
		     content_type_t *type, record_parameters_st * params,
		     uint64_t sequence);

static int
encrypt_packet_tls13(gnutls_session_t session,
		     uint8_t *cipher_data, size_t cipher_size,
		     gnutls_datum_t *plain,
		     size_t pad_size,
		     uint8_t type,
		     record_parameters_st *params);

/* returns ciphertext which contains the headers too. This also
 * calculates the size in the header field.
 *
 */
int
_gnutls_encrypt(gnutls_session_t session,
		const uint8_t *data, size_t data_size,
		size_t min_pad,
		mbuffer_st *bufel,
		content_type_t type, record_parameters_st *params)
{
	gnutls_datum_t plaintext;
	const version_entry_st *vers =
		(session->internals.hsk_flags & HSK_EARLY_DATA_IN_FLIGHT) &&
		!IS_SERVER(session) ?
		session->internals.resumed_security_parameters.pversion :
		get_version(session);
	int ret;

	plaintext.data = (uint8_t *) data;
	plaintext.size = data_size;

	if (vers && vers->tls13_sem) {
		/* it fills the header, as it is included in the authenticated
		 * data of the AEAD cipher. */
		ret =
		    encrypt_packet_tls13(session,
					 _mbuffer_get_udata_ptr(bufel),
					 _mbuffer_get_udata_size(bufel),
					 &plaintext, min_pad, type,
					 params);
		if (ret < 0)
			return gnutls_assert_val(ret);
	} else {
		ret =
		    encrypt_packet(session,
				   _mbuffer_get_udata_ptr(bufel),
				   _mbuffer_get_udata_size
				   (bufel), &plaintext, min_pad, type,
				   params);
		if (ret < 0)
			return gnutls_assert_val(ret);

	}

	if (IS_DTLS(session))
		_gnutls_write_uint16(ret,
				     ((uint8_t *)
				      _mbuffer_get_uhead_ptr(bufel)) + 11);
	else
		_gnutls_write_uint16(ret,
				     ((uint8_t *)
				      _mbuffer_get_uhead_ptr(bufel)) + 3);

	_mbuffer_set_udata_size(bufel, ret);
	_mbuffer_set_uhead_size(bufel, 0);

	return _mbuffer_get_udata_size(bufel);
}

/* Decrypts the given data.
 * Returns the decrypted data length.
 *
 * The output is preallocated with the maximum allowed data size.
 */
int
_gnutls_decrypt(gnutls_session_t session,
		gnutls_datum_t *ciphertext,
		gnutls_datum_t *output,
		content_type_t *type,
		record_parameters_st *params,
		uint64_t sequence)
{
	int ret;
	const version_entry_st *vers = get_version(session);

	if (ciphertext->size == 0)
		return 0;

	if (vers && vers->tls13_sem)
		ret =
		    decrypt_packet_tls13(session, ciphertext,
					 output, type, params,
					 sequence);
	else
		ret =
		    decrypt_packet(session, ciphertext,
				   output, *type, params,
				   sequence);
	if (ret < 0)
		return gnutls_assert_val(ret);

	return ret;
}


inline static int
calc_enc_length_block(gnutls_session_t session,
		      const version_entry_st * ver,
		      int data_size,
		      int hash_size, uint8_t * pad,
		      unsigned auth_cipher,
		      uint16_t blocksize,
		      unsigned etm)
{
	/* pad is the LH pad the user wants us to add. Besides
	 * this LH pad, we only add minimal padding
	 */
	unsigned int pre_length = data_size + *pad;
	unsigned int length, new_pad;

	if (etm == 0)
		pre_length += hash_size;

	new_pad = (uint8_t) (blocksize - (pre_length % blocksize)) + *pad;

	if (new_pad > 255)
		new_pad -= blocksize;
	*pad = new_pad;

	length = data_size + hash_size + *pad;

	if (_gnutls_version_has_explicit_iv(ver))
		length += blocksize;	/* for the IV */

	return length;
}

inline static int
calc_enc_length_stream(gnutls_session_t session, int data_size,
		       int hash_size, unsigned auth_cipher,
		       unsigned exp_iv_size)
{
	unsigned int length;

	length = data_size + hash_size;
	if (auth_cipher)
		length += exp_iv_size;

	return length;
}

/* generates the authentication data (data to be hashed only
 * and are not to be sent). Returns their size.
 */
int
_gnutls_make_preamble(uint64_t uint64_data, uint8_t type, unsigned int length,
		      const version_entry_st * ver, uint8_t preamble[MAX_PREAMBLE_SIZE])
{
	uint8_t *p = preamble;
	uint16_t c_length;

	c_length = _gnutls_conv_uint16(length);

	_gnutls_write_uint64(uint64_data, p);
	p += 8;
	*p = type;
	p++;
#ifdef ENABLE_SSL3
	if (ver->id != GNUTLS_SSL3)
#endif
	{	/* TLS protocols */
		*p = ver->major;
		p++;
		*p = ver->minor;
		p++;
	}
	memcpy(p, &c_length, 2);
	p += 2;
	return p - preamble;
}

/* This is the actual encryption
 * Encrypts the given plaintext datum, and puts the result to cipher_data,
 * which has cipher_size size.
 * return the actual encrypted data length.
 */
static int
encrypt_packet(gnutls_session_t session,
			 uint8_t * cipher_data, int cipher_size,
			 gnutls_datum_t * plain,
			 size_t min_pad,
			 content_type_t type,
			 record_parameters_st * params)
{
	uint8_t pad;
	int length, ret;
	uint8_t preamble[MAX_PREAMBLE_SIZE];
	int preamble_size;
	int tag_size =
	    _gnutls_auth_cipher_tag_len(&params->write.ctx.tls12);
	int blocksize = _gnutls_cipher_get_block_size(params->cipher);
	unsigned algo_type = _gnutls_cipher_type(params->cipher);
	uint8_t *data_ptr, *full_cipher_ptr;
	const version_entry_st *ver = get_version(session);
	int explicit_iv = _gnutls_version_has_explicit_iv(ver);
	int auth_cipher =
	    _gnutls_auth_cipher_is_aead(&params->write.ctx.tls12);
	uint8_t nonce[MAX_CIPHER_IV_SIZE];
	unsigned imp_iv_size = 0, exp_iv_size = 0;
	bool etm = 0;

	if (unlikely(ver == NULL))
		return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

	if (algo_type == CIPHER_BLOCK && params->etm != 0)
		etm = 1;

	_gnutls_hard_log("ENC[%p]: cipher: %s, MAC: %s, Epoch: %u\n",
			 session, _gnutls_cipher_get_name(params->cipher),
			 _gnutls_mac_get_name(params->mac),
			 (unsigned int) params->epoch);

	/* Calculate the encrypted length (padding etc.)
	 */
	if (algo_type == CIPHER_BLOCK) {
		/* Call gnutls_rnd() once. Get data used for the IV
		 */
		ret = gnutls_rnd(GNUTLS_RND_NONCE, nonce, blocksize);
		if (ret < 0)
			return gnutls_assert_val(ret);

		pad = min_pad;

		length =
		    calc_enc_length_block(session, ver, plain->size,
					  tag_size, &pad, auth_cipher,
					  blocksize, etm);
	} else { /* AEAD + STREAM */
		imp_iv_size = _gnutls_cipher_get_implicit_iv_size(params->cipher);
		exp_iv_size = _gnutls_cipher_get_explicit_iv_size(params->cipher);

		pad = 0;
		length =
		    calc_enc_length_stream(session, plain->size,
					   tag_size, auth_cipher,
					   exp_iv_size);
	}

	if (length < 0)
		return gnutls_assert_val(length);

	/* copy the encrypted data to cipher_data.
	 */
	if (cipher_size < length)
		return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

	data_ptr = cipher_data;
	full_cipher_ptr = data_ptr;

	if (algo_type == CIPHER_BLOCK || algo_type == CIPHER_STREAM) {
		if (algo_type == CIPHER_BLOCK && explicit_iv != 0) {
			/* copy the random IV.
			 */
			memcpy(data_ptr, nonce, blocksize);
			ret = _gnutls_auth_cipher_setiv(&params->write.
						  ctx.tls12, data_ptr,
						  blocksize);
			if (ret < 0)
				return gnutls_assert_val(ret);

			/*data_ptr += blocksize;*/
			cipher_data += blocksize;
		}
	} else { /* AEAD */
		if ((params->cipher->flags & GNUTLS_CIPHER_FLAG_XOR_NONCE) == 0) {
			/* Values in AEAD are pretty fixed in TLS 1.2 for 128-bit block
			 */
			 if (params->write.iv_size != imp_iv_size)
				return
				    gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

			/* Instead of generating a new nonce on every packet, we use the
			 * write.sequence_number (It is a MAY on RFC 5288), and safer
			 * as it will never reuse a value.
			 */
			memcpy(nonce, params->write.iv,
			       params->write.iv_size);
			_gnutls_write_uint64(params->write.sequence_number, &nonce[imp_iv_size]);

			memcpy(data_ptr, &nonce[imp_iv_size],
			       exp_iv_size);

			/*data_ptr += exp_iv_size;*/
			cipher_data += exp_iv_size;
		} else { /* XOR nonce with IV */
			if (unlikely(params->write.iv_size != 12 || imp_iv_size != 12 || exp_iv_size != 0))
				return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

			memset(nonce, 0, 4);
			_gnutls_write_uint64(params->write.sequence_number, &nonce[4]);

			memxor(nonce, params->write.iv, 12);
		}
	}

	if (etm)
		ret = length-tag_size;
	else
		ret = plain->size;

	preamble_size =
	    _gnutls_make_preamble(params->write.sequence_number,
				  type, ret, ver, preamble);

	if (algo_type == CIPHER_BLOCK || algo_type == CIPHER_STREAM) {
		/* add the authenticated data */
		ret =
		    _gnutls_auth_cipher_add_auth(&params->write.ctx.tls12,
					 preamble, preamble_size);
		if (ret < 0)
			return gnutls_assert_val(ret);

		if (etm && explicit_iv) {
			/* In EtM we need to hash the IV as well */
			ret =
			    _gnutls_auth_cipher_add_auth(&params->write.ctx.tls12,
						 full_cipher_ptr, blocksize);
			if (ret < 0)
				return gnutls_assert_val(ret);
		}

		/* Actual encryption.
		 */
		ret =
		    _gnutls_auth_cipher_encrypt2_tag(&params->write.ctx.tls12,
						     plain->data,
						     plain->size, cipher_data,
						     cipher_size, pad);
		if (ret < 0)
			return gnutls_assert_val(ret);
	} else { /* AEAD */
		ret = _gnutls_aead_cipher_encrypt(&params->write.ctx.tls12.cipher,
						  nonce, imp_iv_size + exp_iv_size,
						  preamble, preamble_size,
						  tag_size,
						  plain->data, plain->size,
						  cipher_data, cipher_size);
		if (ret < 0)
			return gnutls_assert_val(ret);
	}

	return length;
}

static int
encrypt_packet_tls13(gnutls_session_t session,
		     uint8_t *cipher_data, size_t cipher_size,
		     gnutls_datum_t *plain,
		     size_t pad_size,
		     uint8_t type,
		     record_parameters_st *params)
{
	int ret;
	unsigned int tag_size = params->write.aead_tag_size;
	const version_entry_st *ver = get_version(session);
	uint8_t nonce[MAX_CIPHER_IV_SIZE];
	unsigned iv_size = 0;
	ssize_t max, total;
	uint8_t aad[5];
	giovec_t auth_iov[1];
	giovec_t iov[2];

	if (unlikely(ver == NULL))
		return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

	_gnutls_hard_log("ENC[%p]: cipher: %s, MAC: %s, Epoch: %u\n",
			 session, _gnutls_cipher_get_name(params->cipher),
			 _gnutls_mac_get_name(params->mac),
			 (unsigned int) params->epoch);

	iv_size = params->write.iv_size;

	if (params->cipher->id == GNUTLS_CIPHER_NULL) {
		if (cipher_size < plain->size+1)
			return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);
		memcpy(cipher_data, plain->data, plain->size);
		return plain->size;
	}

	if (unlikely(iv_size < 8))
		return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

	memset(nonce, 0, iv_size - 8);
	_gnutls_write_uint64(params->write.sequence_number, &nonce[iv_size-8]);
	memxor(nonce, params->write.iv, iv_size);

	max = MAX_RECORD_SEND_SIZE(session);

	/* make TLS 1.3 form of data */
	total = plain->size + 1 + pad_size;

	/* check whether padding would exceed max */
	if (total > max) {
		if (unlikely(max < (ssize_t)plain->size+1))
			return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

		pad_size = max - plain->size - 1;
		total = max;
	}

	/* create authenticated data header */
	aad[0] = GNUTLS_APPLICATION_DATA;
	aad[1] = 0x03;
	aad[2] = 0x03;
	_gnutls_write_uint16(total+tag_size, &aad[3]);

	auth_iov[0].iov_base = aad;
	auth_iov[0].iov_len = sizeof(aad);

	iov[0].iov_base = plain->data;
	iov[0].iov_len = plain->size;

	if (pad_size || (session->internals.flags & GNUTLS_SAFE_PADDING_CHECK)) {
		uint8_t *pad = gnutls_calloc(1, 1+pad_size);
		if (pad == NULL)
			return gnutls_assert_val(GNUTLS_E_MEMORY_ERROR);

		pad[0] = type;

		iov[1].iov_base = pad;
		iov[1].iov_len = 1+pad_size;

		ret = gnutls_aead_cipher_encryptv(&params->write.ctx.aead,
						  nonce, iv_size,
						  auth_iov, 1,
						  tag_size,
						  iov, 2,
						  cipher_data, &cipher_size);
		gnutls_free(pad);
	} else {
		iov[1].iov_base = &type;
		iov[1].iov_len = 1;

		ret = gnutls_aead_cipher_encryptv(&params->write.ctx.aead,
						  nonce, iv_size,
						  auth_iov, 1,
						  tag_size,
						  iov, 2,
						  cipher_data, &cipher_size);
	}

	if (ret < 0)
		return gnutls_assert_val(ret);

	return cipher_size;
}


/* Deciphers the ciphertext packet, and puts the result to plain.
 * Returns the actual plaintext packet size.
 */
static int
decrypt_packet(gnutls_session_t session,
		gnutls_datum_t * ciphertext,
		gnutls_datum_t * plain,
		content_type_t type, record_parameters_st * params,
		uint64_t sequence)
{
	uint8_t tag[MAX_HASH_SIZE];
	uint8_t nonce[MAX_CIPHER_IV_SIZE];
	const uint8_t *tag_ptr = NULL;
	unsigned int pad = 0;
	int length, length_to_decrypt;
	uint16_t blocksize;
	int ret;
	uint8_t preamble[MAX_PREAMBLE_SIZE];
	unsigned int preamble_size = 0;
	const version_entry_st *ver = get_version(session);
	unsigned int tag_size =
	    _gnutls_auth_cipher_tag_len(&params->read.ctx.tls12);
	unsigned int explicit_iv = _gnutls_version_has_explicit_iv(ver);
	unsigned imp_iv_size, exp_iv_size;
	unsigned cipher_type = _gnutls_cipher_type(params->cipher);
	bool etm = 0;

	if (unlikely(ver == NULL))
		return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

	imp_iv_size = _gnutls_cipher_get_implicit_iv_size(params->cipher);
	exp_iv_size = _gnutls_cipher_get_explicit_iv_size(params->cipher);
	blocksize = _gnutls_cipher_get_block_size(params->cipher);

	if (params->etm !=0 && cipher_type == CIPHER_BLOCK)
		etm = 1;

	/* if EtM mode and not AEAD */
	if (etm) {
		if (unlikely(ciphertext->size < tag_size))
			return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

		preamble_size = _gnutls_make_preamble(sequence,
						      type, ciphertext->size-tag_size,
						      ver, preamble);

		ret = _gnutls_auth_cipher_add_auth(&params->read.
						   ctx.tls12, preamble,
						   preamble_size);
		if (unlikely(ret < 0))
			return gnutls_assert_val(ret);

		ret = _gnutls_auth_cipher_add_auth(&params->read.
						   ctx.tls12,
						   ciphertext->data,
						   ciphertext->size-tag_size);
		if (unlikely(ret < 0))
			return gnutls_assert_val(ret);

		ret = _gnutls_auth_cipher_tag(&params->read.ctx.tls12, tag, tag_size);
		if (unlikely(ret < 0))
			return gnutls_assert_val(ret);

		if (unlikely(gnutls_memcmp(tag, &ciphertext->data[ciphertext->size-tag_size], tag_size) != 0)) {
			/* HMAC was not the same. */
			return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
		}
	}

	/* actual decryption (inplace)
	 */
	switch (cipher_type) {
	case CIPHER_AEAD:
		/* The way AEAD ciphers are defined in RFC5246, it allows
		 * only stream ciphers.
		 */
		if (unlikely(_gnutls_auth_cipher_is_aead(&params->read.
						   ctx.tls12) == 0))
			return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);


		if (unlikely(ciphertext->size < (tag_size + exp_iv_size)))
			return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);

		if ((params->cipher->flags & GNUTLS_CIPHER_FLAG_XOR_NONCE) == 0) {
			/* Values in AEAD are pretty fixed in TLS 1.2 for 128-bit block
			 */
			 if (unlikely(params->read.iv_size != 4))
				return
				    gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);

			memcpy(nonce, params->read.iv,
			       imp_iv_size);

			memcpy(&nonce[imp_iv_size],
			       ciphertext->data, exp_iv_size);

			ciphertext->data += exp_iv_size;
			ciphertext->size -= exp_iv_size;
		} else { /* XOR nonce with IV */
			if (unlikely(params->read.iv_size != 12 || imp_iv_size != 12 || exp_iv_size != 0))
				return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);

			memset(nonce, 0, 4);
			_gnutls_write_uint64(sequence, &nonce[4]);

			memxor(nonce, params->read.iv, 12);
		}

		length =
		    ciphertext->size - tag_size;

		length_to_decrypt = ciphertext->size;

		/* Pass the type, version, length and plain through
		 * MAC.
		 */
		preamble_size =
		    _gnutls_make_preamble(sequence, type,
					  length, ver, preamble);


		if (unlikely
		    ((unsigned) length_to_decrypt > plain->size)) {
			_gnutls_audit_log(session,
					  "Received %u bytes, while expecting less than %u\n",
					  (unsigned int) length_to_decrypt,
					  (unsigned int) plain->size);
			return
			    gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
		}

		ret = _gnutls_aead_cipher_decrypt(&params->read.ctx.tls12.cipher,
						  nonce, exp_iv_size + imp_iv_size,
						  preamble, preamble_size,
						  tag_size,
						  ciphertext->data, length_to_decrypt,
						  plain->data, plain->size);
		if (unlikely(ret < 0))
			return gnutls_assert_val(ret);

		return length;

		break;
	case CIPHER_STREAM:
		if (unlikely(ciphertext->size < tag_size))
			return
			    gnutls_assert_val
			    (GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

		length_to_decrypt = ciphertext->size;
		length = ciphertext->size - tag_size;
		tag_ptr = plain->data + length;

		/* Pass the type, version, length and plain through
		 * MAC.
		 */
		preamble_size =
		    _gnutls_make_preamble(sequence, type,
					  length, ver, preamble);

		ret =
		    _gnutls_auth_cipher_add_auth(&params->read.
						 ctx.tls12, preamble,
						 preamble_size);
		if (unlikely(ret < 0))
			return gnutls_assert_val(ret);

		if (unlikely
		    ((unsigned) length_to_decrypt > plain->size)) {
			_gnutls_audit_log(session,
					  "Received %u bytes, while expecting less than %u\n",
					  (unsigned int) length_to_decrypt,
					  (unsigned int) plain->size);
			return
			    gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
		}

		ret =
		    _gnutls_auth_cipher_decrypt2(&params->read.
						 ctx.tls12,
						 ciphertext->data,
						 length_to_decrypt,
						 plain->data,
						 plain->size);

		if (unlikely(ret < 0))
			return gnutls_assert_val(ret);

		ret =
		    _gnutls_auth_cipher_tag(&params->read.ctx.tls12, tag,
					    tag_size);
		if (unlikely(ret < 0))
			return gnutls_assert_val(ret);

		if (unlikely
		    (gnutls_memcmp(tag, tag_ptr, tag_size) != 0)) {
			return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
		}

		break;
	case CIPHER_BLOCK:
		if (unlikely(ciphertext->size < blocksize))
			return
			    gnutls_assert_val
			    (GNUTLS_E_UNEXPECTED_PACKET_LENGTH);

		if (etm == 0) {
			if (unlikely(ciphertext->size % blocksize != 0))
				return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
		} else {
			if (unlikely((ciphertext->size - tag_size) % blocksize != 0))
				return gnutls_assert_val(GNUTLS_E_UNEXPECTED_PACKET_LENGTH);
		}

		/* ignore the IV in TLS 1.1+
		 */
		if (explicit_iv) {
			ret = _gnutls_auth_cipher_setiv(&params->read.
						  ctx.tls12,
						  ciphertext->data,
						  blocksize);
			if (ret < 0)
				return gnutls_assert_val(ret);

			memcpy(nonce, ciphertext->data, blocksize);
			ciphertext->size -= blocksize;
			ciphertext->data += blocksize;
		}

		if (unlikely(ciphertext->size < tag_size + 1))
			return
			    gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);

		/* we don't use the auth_cipher interface here, since
		 * TLS with block ciphers is impossible to be used under such
		 * an API. (the length of plaintext is required to calculate
		 * auth_data, but it is not available before decryption).
		 */
		if (unlikely(ciphertext->size > plain->size))
			return
			    gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);

		if (etm == 0) {
			ret =
			    _gnutls_cipher_decrypt2(&params->read.ctx.tls12.
						    cipher, ciphertext->data,
						    ciphertext->size,
						    plain->data,
						    plain->size);
			if (unlikely(ret < 0))
				return gnutls_assert_val(ret);

			ret = cbc_mac_verify(session, params, preamble, type,
					     sequence, plain->data, ciphertext->size,
					     tag_size);
			if (unlikely(ret < 0))
				return gnutls_assert_val(ret);

			length = ret;
		} else { /* EtM */
			ret =
			    _gnutls_cipher_decrypt2(&params->read.ctx.tls12.
						    cipher, ciphertext->data,
						    ciphertext->size - tag_size,
						    plain->data,
						    plain->size);
			if (unlikely(ret < 0))
				return gnutls_assert_val(ret);

			pad = plain->data[ciphertext->size - tag_size - 1]; /* pad */
			length = ciphertext->size - tag_size - pad - 1;

			if (unlikely(length < 0))
				return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
		}
		break;
	default:
		return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
	}


	return length;
}

static int
decrypt_packet_tls13(gnutls_session_t session,
		     gnutls_datum_t *ciphertext,
		     gnutls_datum_t *plain,
		     content_type_t *type, record_parameters_st *params,
		     uint64_t sequence)
{
	uint8_t nonce[MAX_CIPHER_IV_SIZE];
	size_t length, length_to_decrypt;
	int ret;
	const version_entry_st *ver = get_version(session);
	unsigned int tag_size = params->read.aead_tag_size;
	unsigned iv_size;
	unsigned j;
	volatile unsigned length_set;
	uint8_t aad[5];

	if (unlikely(ver == NULL))
		return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

	if (params->cipher->id == GNUTLS_CIPHER_NULL) {
		if (plain->size < ciphertext->size)
			return gnutls_assert_val(GNUTLS_E_INTERNAL_ERROR);

		length = ciphertext->size;
		memcpy(plain->data, ciphertext->data, length);

		return length;
	}

	iv_size = _gnutls_cipher_get_iv_size(params->cipher);

	/* The way AEAD ciphers are defined in RFC5246, it allows
	 * only stream ciphers.
	 */
	if (unlikely(ciphertext->size < tag_size))
		return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);

	if (unlikely(params->read.iv_size != iv_size || iv_size < 8))
		return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);

	memset(nonce, 0, iv_size - 8);
	_gnutls_write_uint64(sequence, &nonce[iv_size-8]);
	memxor(nonce, params->read.iv, params->read.iv_size);

	length =
	    ciphertext->size - tag_size;

	length_to_decrypt = ciphertext->size;

	if (unlikely
	    ((unsigned) length_to_decrypt > plain->size)) {
			_gnutls_audit_log(session,
				  "Received %u bytes, while expecting less than %u\n",
				  (unsigned int) length_to_decrypt,
				  (unsigned int) plain->size);
		return
		    gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);
	}

	aad[0] = GNUTLS_APPLICATION_DATA;
	aad[1] = 0x03;
	aad[2] = 0x03;
	_gnutls_write_uint16(ciphertext->size, &aad[3]);

	ret = gnutls_aead_cipher_decrypt(&params->read.ctx.aead,
					 nonce, iv_size,
					 aad, sizeof(aad),
					 tag_size,
					 ciphertext->data, length_to_decrypt,
					 plain->data, &length);
	if (unlikely(ret < 0))
		return gnutls_assert_val(ret);

	/* 1 octet for content type */
	if (length > max_decrypted_size(session) + 1) {
		_gnutls_audit_log
		    (session, "Received packet with illegal length: %u\n",
		     (unsigned int) length);

		return gnutls_assert_val(GNUTLS_E_RECORD_OVERFLOW);
	}

	length_set = 0;

	/* now figure the actual data size. We intentionally iterate through all data,
	 * to avoid leaking the padding length due to timing differences in processing.
	 */
	for (j=length;j>0;j--) {
		if (plain->data[j-1]!=0 && length_set == 0) {
			*type = plain->data[j-1];
			length = j-1;
			length_set = 1;
			if (!(session->internals.flags & GNUTLS_SAFE_PADDING_CHECK))
				break;
		}
	}

	if (!length_set)
		return gnutls_assert_val(GNUTLS_E_DECRYPTION_FAILED);

	return length;
}