summary refs log tree commit diff
path: root/crypto/src/tls/TlsProtocol.cs
blob: 9b8039a5e90c49cea59256e829eb592682455d5e (plain) (blame)
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
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
using System;
using System.Collections.Generic;
using System.IO;

using Org.BouncyCastle.Tls.Crypto;
using Org.BouncyCastle.Utilities;
using Org.BouncyCastle.Utilities.IO;

namespace Org.BouncyCastle.Tls
{
    public abstract class TlsProtocol
        : TlsCloseable
    {
        /*
         * Connection States.
         * 
         * NOTE: Redirection of handshake messages to TLS 1.3 handlers assumes CS_START, CS_CLIENT_HELLO
         * are lower than any of the other values.
         */
        protected const short CS_START = 0;
        protected const short CS_CLIENT_HELLO = 1;
        protected const short CS_SERVER_HELLO_RETRY_REQUEST = 2;
        protected const short CS_CLIENT_HELLO_RETRY = 3;
        protected const short CS_SERVER_HELLO = 4;
        protected const short CS_SERVER_ENCRYPTED_EXTENSIONS = 5;
        protected const short CS_SERVER_SUPPLEMENTAL_DATA = 6;
        protected const short CS_SERVER_CERTIFICATE = 7;
        protected const short CS_SERVER_CERTIFICATE_STATUS = 8;
        protected const short CS_SERVER_CERTIFICATE_VERIFY = 9;
        protected const short CS_SERVER_KEY_EXCHANGE = 10;
        protected const short CS_SERVER_CERTIFICATE_REQUEST = 11;
        protected const short CS_SERVER_HELLO_DONE = 12;
        protected const short CS_CLIENT_END_OF_EARLY_DATA = 13;
        protected const short CS_CLIENT_SUPPLEMENTAL_DATA = 14;
        protected const short CS_CLIENT_CERTIFICATE = 15;
        protected const short CS_CLIENT_KEY_EXCHANGE = 16;
        protected const short CS_CLIENT_CERTIFICATE_VERIFY = 17;
        protected const short CS_CLIENT_FINISHED = 18;
        protected const short CS_SERVER_SESSION_TICKET = 19;
        protected const short CS_SERVER_FINISHED = 20;
        protected const short CS_END = 21;

        protected bool IsLegacyConnectionState()
        {
            switch (m_connectionState)
            {
            case CS_START:
            case CS_CLIENT_HELLO:
            case CS_SERVER_HELLO:
            case CS_SERVER_SUPPLEMENTAL_DATA:
            case CS_SERVER_CERTIFICATE:
            case CS_SERVER_CERTIFICATE_STATUS:
            case CS_SERVER_KEY_EXCHANGE:
            case CS_SERVER_CERTIFICATE_REQUEST:
            case CS_SERVER_HELLO_DONE:
            case CS_CLIENT_SUPPLEMENTAL_DATA:
            case CS_CLIENT_CERTIFICATE:
            case CS_CLIENT_KEY_EXCHANGE:
            case CS_CLIENT_CERTIFICATE_VERIFY:
            case CS_CLIENT_FINISHED:
            case CS_SERVER_SESSION_TICKET:
            case CS_SERVER_FINISHED:
            case CS_END:
                return true;

            case CS_SERVER_HELLO_RETRY_REQUEST:
            case CS_CLIENT_HELLO_RETRY:
            case CS_SERVER_ENCRYPTED_EXTENSIONS:
            case CS_SERVER_CERTIFICATE_VERIFY:
            case CS_CLIENT_END_OF_EARLY_DATA:
            default:
                return false;
            }
        }

        protected bool IsTlsV13ConnectionState()
        {
            switch (m_connectionState)
            {
            case CS_START:
            case CS_CLIENT_HELLO:
            case CS_SERVER_HELLO_RETRY_REQUEST:
            case CS_CLIENT_HELLO_RETRY:
            case CS_SERVER_HELLO:
            case CS_SERVER_ENCRYPTED_EXTENSIONS:
            case CS_SERVER_CERTIFICATE_REQUEST:
            case CS_SERVER_CERTIFICATE:
            case CS_SERVER_CERTIFICATE_VERIFY:
            case CS_SERVER_FINISHED:
            case CS_CLIENT_END_OF_EARLY_DATA:
            case CS_CLIENT_CERTIFICATE:
            case CS_CLIENT_CERTIFICATE_VERIFY:
            case CS_CLIENT_FINISHED:
            case CS_END:
                return true;

            case CS_SERVER_SUPPLEMENTAL_DATA:
            case CS_SERVER_CERTIFICATE_STATUS:
            case CS_SERVER_KEY_EXCHANGE:
            case CS_SERVER_HELLO_DONE:
            case CS_CLIENT_SUPPLEMENTAL_DATA:
            case CS_CLIENT_KEY_EXCHANGE:
            case CS_SERVER_SESSION_TICKET:
            default:
                return false;
            }
        }

        /*
         * Different modes to handle the known IV weakness
         */
        protected const short ADS_MODE_1_Nsub1 = 0; // 1/n-1 record splitting
        protected const short ADS_MODE_0_N = 1; // 0/n record splitting
        protected const short ADS_MODE_0_N_FIRSTONLY = 2; // 0/n record splitting on first data fragment only

        /*
         * Queues for data from some protocols.
         */
        private readonly ByteQueue m_applicationDataQueue = new ByteQueue(0);
        private readonly ByteQueue m_alertQueue = new ByteQueue(2);
        private readonly ByteQueue m_handshakeQueue = new ByteQueue(0);
        //private readonly ByteQueue m_heartbeatQueue = new ByteQueue(0);

        internal readonly RecordStream m_recordStream;
        internal readonly object m_recordWriteLock = new object();

        private int m_maxHandshakeMessageSize = -1;

        internal TlsHandshakeHash m_handshakeHash;

        private TlsStream m_tlsStream = null;

        private volatile bool m_closed = false;
        private volatile bool m_failedWithError = false;
        private volatile bool m_appDataReady = false;
        private volatile bool m_appDataSplitEnabled = true;
        private volatile bool m_keyUpdateEnabled = false;
        //private volatile bool m_keyUpdatePendingReceive = false;
        private volatile bool m_keyUpdatePendingSend = false;
        private volatile bool m_resumableHandshake = false;
        private volatile int m_appDataSplitMode = ADS_MODE_1_Nsub1;

        protected TlsSession m_tlsSession = null;
        protected SessionParameters m_sessionParameters = null;
        protected TlsSecret m_sessionMasterSecret = null;

        protected byte[] m_retryCookie = null;
        protected int m_retryGroup = -1;
        protected IDictionary<int, byte[]> m_clientExtensions = null;
        protected IDictionary<int, byte[]> m_serverExtensions = null;

        protected short m_connectionState = CS_START;
        protected bool m_selectedPsk13 = false;
        protected bool m_receivedChangeCipherSpec = false;
        protected bool m_expectSessionTicket = false;

        protected readonly bool m_blocking;
        protected readonly ByteQueueInputStream m_inputBuffers;
        protected readonly ByteQueueOutputStream m_outputBuffer;

        protected TlsProtocol()
        {
            this.m_blocking = false;
            this.m_inputBuffers = new ByteQueueInputStream();
            this.m_outputBuffer = new ByteQueueOutputStream();
            this.m_recordStream = new RecordStream(this, m_inputBuffers, m_outputBuffer);
        }

        public TlsProtocol(Stream stream)
            : this(stream, stream)
        {
        }

        public TlsProtocol(Stream input, Stream output)
        {
            this.m_blocking = true;
            this.m_inputBuffers = null;
            this.m_outputBuffer = null;
            this.m_recordStream = new RecordStream(this, input, output);
        }

        /// <exception cref="IOException"/>
        public virtual void ResumeHandshake()
        {
            if (!m_blocking)
                throw new InvalidOperationException("Cannot use ResumeHandshake() in non-blocking mode!");
            if (!IsHandshaking)
                throw new InvalidOperationException("No handshake in progress");

            BlockForHandshake();
        }

        /// <exception cref="IOException"/>
        protected virtual void CloseConnection()
        {
            m_recordStream.Close();
        }

        protected abstract TlsContext Context { get; }

        internal abstract AbstractTlsContext ContextAdmin { get; }

        protected abstract TlsPeer Peer { get; }

        /// <exception cref="IOException"/>
        protected virtual void HandleAlertMessage(short alertLevel, short alertDescription)
        {
            Peer.NotifyAlertReceived(alertLevel, alertDescription);

            if (alertLevel == AlertLevel.warning)
            {
                HandleAlertWarningMessage(alertDescription);
            }
            else
            {
                HandleFailure();

                throw new TlsFatalAlertReceived(alertDescription);
            }
        }

        /// <exception cref="IOException"/>
        protected virtual void HandleAlertWarningMessage(short alertDescription)
        {
            switch (alertDescription)
            {
            /*
             * RFC 5246 7.2.1. The other party MUST respond with a close_notify alert of its own
             * and close down the connection immediately, discarding any pending writes.
             */
            case AlertDescription.close_notify:
            {
                if (!m_appDataReady)
                    throw new TlsFatalAlert(AlertDescription.handshake_failure);

                HandleClose(false);
                break;
            }
            case AlertDescription.no_certificate:
            {
                throw new TlsFatalAlert(AlertDescription.unexpected_message);
            }
            case AlertDescription.no_renegotiation:
            {
                // TODO[reneg] Give peer the option to tolerate this
                throw new TlsFatalAlert(AlertDescription.handshake_failure);
            }
            }
        }

        /// <exception cref="IOException"/>
        protected virtual void HandleChangeCipherSpecMessage()
        {
        }

        /// <exception cref="IOException"/>
        protected virtual void HandleClose(bool user_canceled)
        {
            if (!m_closed)
            {
                this.m_closed = true;

                if (!m_appDataReady)
                {
                    CleanupHandshake();

                    if (user_canceled)
                    {
                        RaiseAlertWarning(AlertDescription.user_canceled, "User canceled handshake");
                    }
                }

                RaiseAlertWarning(AlertDescription.close_notify, "Connection closed");

                CloseConnection();

                TlsUtilities.NotifyConnectionClosed(Peer);
            }
        }

        /// <exception cref="IOException"/>
        protected virtual void HandleException(short alertDescription, string message, Exception e)
        {
            // TODO[tls-port] Can we support interrupted IO on .NET?
            //if ((m_appDataReady || IsResumableHandshake()) && (e is InterruptedIOException))
            //    return;

            if (!m_closed)
            {
                RaiseAlertFatal(alertDescription, message, e);

                HandleFailure();
            }
        }

        /// <exception cref="IOException"/>
        protected virtual void HandleFailure()
        {
            this.m_closed = true;
            this.m_failedWithError = true;

            /*
             * RFC 2246 7.2.1. The session becomes unresumable if any connection is terminated
             * without proper close_notify messages with level equal to warning.
             */
            // TODO This isn't quite in the right place. Also, as of TLS 1.1 the above is obsolete.
            InvalidateSession();

            if (!m_appDataReady)
            {
                CleanupHandshake();
            }

            CloseConnection();

            TlsUtilities.NotifyConnectionClosed(Peer);
        }

        /// <exception cref="IOException"/>
        protected abstract void HandleHandshakeMessage(short type, HandshakeMessageInput buf);

        /// <exception cref="IOException"/>
        protected virtual void ApplyMaxFragmentLengthExtension(short maxFragmentLength)
        {
            if (maxFragmentLength >= 0)
            {
                if (!MaxFragmentLength.IsValid(maxFragmentLength))
                    throw new TlsFatalAlert(AlertDescription.internal_error);

                int plainTextLimit = 1 << (8 + maxFragmentLength);
                m_recordStream.SetPlaintextLimit(plainTextLimit);
            }
        }

        /// <exception cref="IOException"/>
        protected virtual void CheckReceivedChangeCipherSpec(bool expected)
        {
            if (expected != m_receivedChangeCipherSpec)
                throw new TlsFatalAlert(AlertDescription.unexpected_message);
        }

        /// <exception cref="IOException"/>
        protected virtual void BlockForHandshake()
        {
            while (m_connectionState != CS_END)
            {
                if (IsClosed)
                {
                    // NOTE: Any close during the handshake should have raised an exception.
                    throw new TlsFatalAlert(AlertDescription.internal_error);
                }

                SafeReadRecord();
            }
        }

        /// <exception cref="IOException"/>
        protected virtual void BeginHandshake()
        {
            AbstractTlsContext context = ContextAdmin;
            TlsPeer peer = Peer;

            this.m_maxHandshakeMessageSize = System.Math.Max(1024, peer.GetMaxHandshakeMessageSize());

            this.m_handshakeHash = new DeferredHash(context);
            this.m_connectionState = CS_START;
            this.m_selectedPsk13 = false;

            context.HandshakeBeginning(peer);

            SecurityParameters securityParameters = context.SecurityParameters;

            securityParameters.m_extendedPadding = peer.ShouldUseExtendedPadding();
        }

        protected virtual void CleanupHandshake()
        {
            TlsContext context = Context;
            if (null != context)
            {
                SecurityParameters securityParameters = context.SecurityParameters;
                if (null != securityParameters)
                {
                    securityParameters.Clear();
                }
            }

            this.m_tlsSession = null;
            this.m_sessionParameters = null;
            this.m_sessionMasterSecret = null;

            this.m_retryCookie = null;
            this.m_retryGroup = -1;
            this.m_clientExtensions = null;
            this.m_serverExtensions = null;

            this.m_selectedPsk13 = false;
            this.m_receivedChangeCipherSpec = false;
            this.m_expectSessionTicket = false;
        }

        /// <exception cref="IOException"/>
        protected virtual void CompleteHandshake()
        {
            try
            {
                AbstractTlsContext context = ContextAdmin;
                SecurityParameters securityParameters = context.SecurityParameters;

                if (!context.IsHandshaking ||
                    null == securityParameters.LocalVerifyData ||
                    null == securityParameters.PeerVerifyData)
                {
                    throw new TlsFatalAlert(AlertDescription.internal_error);
                }

                m_recordStream.FinaliseHandshake();
                this.m_connectionState = CS_END;

                // TODO Prefer to set to null, but would need guards elsewhere
                this.m_handshakeHash = new DeferredHash(context);

                m_alertQueue.Shrink();
                m_handshakeQueue.Shrink();

                ProtocolVersion negotiatedVersion = securityParameters.NegotiatedVersion;

                this.m_appDataSplitEnabled = !TlsUtilities.IsTlsV11(negotiatedVersion);
                this.m_appDataReady = true;

                this.m_keyUpdateEnabled = TlsUtilities.IsTlsV13(negotiatedVersion);

                if (m_blocking)
                {
                    this.m_tlsStream = new TlsStream(this);
                }

                if (m_sessionParameters == null)
                {
                    this.m_sessionMasterSecret = securityParameters.MasterSecret;

                    this.m_sessionParameters = new SessionParameters.Builder()
                        .SetCipherSuite(securityParameters.CipherSuite)
                        .SetExtendedMasterSecret(securityParameters.IsExtendedMasterSecret)
                        .SetLocalCertificate(securityParameters.LocalCertificate)
                        .SetMasterSecret(context.Crypto.AdoptSecret(m_sessionMasterSecret))
                        .SetNegotiatedVersion(securityParameters.NegotiatedVersion)
                        .SetPeerCertificate(securityParameters.PeerCertificate)
                        .SetPskIdentity(securityParameters.PskIdentity)
                        .SetSrpIdentity(securityParameters.SrpIdentity)
                        // TODO Consider filtering extensions that aren't relevant to resumed sessions
                        .SetServerExtensions(m_serverExtensions)
                        .Build();

                    this.m_tlsSession = TlsUtilities.ImportSession(securityParameters.SessionID, m_sessionParameters);
                }
                else
                {
                    securityParameters.m_localCertificate = m_sessionParameters.LocalCertificate;
                    securityParameters.m_peerCertificate = m_sessionParameters.PeerCertificate;
                    securityParameters.m_pskIdentity = m_sessionParameters.PskIdentity;
                    securityParameters.m_srpIdentity = m_sessionParameters.SrpIdentity;
                }

                context.HandshakeComplete(Peer, m_tlsSession);
            }
            finally
            {
                CleanupHandshake();
            }
        }

        /// <exception cref="IOException"/>
        internal void ProcessRecord(short protocol, byte[] buf, int off, int len)
        {
            /*
             * Have a look at the protocol type, and add it to the correct queue.
             */
            switch (protocol)
            {
            case ContentType.alert:
            {
                m_alertQueue.AddData(buf, off, len);
                ProcessAlertQueue();
                break;
            }
            case ContentType.application_data:
            {
                if (!m_appDataReady)
                    throw new TlsFatalAlert(AlertDescription.unexpected_message);

                m_applicationDataQueue.AddData(buf, off, len);
                ProcessApplicationDataQueue();
                break;
            }
            case ContentType.change_cipher_spec:
            {
                ProcessChangeCipherSpec(buf, off, len);
                break;
            }
            case ContentType.handshake:
            {
                if (m_handshakeQueue.Available > 0)
                {
                    m_handshakeQueue.AddData(buf, off, len);
                    ProcessHandshakeQueue(m_handshakeQueue);
                }
                else
                {
                    ByteQueue tmpQueue = new ByteQueue(buf, off, len);
                    ProcessHandshakeQueue(tmpQueue);
                    int remaining = tmpQueue.Available;
                    if (remaining > 0)
                    {
                        m_handshakeQueue.AddData(buf, off + len - remaining, remaining);
                    }
                }
                break;
            }
            //case ContentType.heartbeat:
            //{
            //    if (!m_appDataReady)
            //        throw new TlsFatalAlert(AlertDescription.unexpected_message);

            //    // TODO[RFC 6520]
            //    m_heartbeatQueue.addData(buf, off, len);
            //    ProcessHeartbeatQueue();
            //    break;
            //}
            default:
                throw new TlsFatalAlert(AlertDescription.unexpected_message);
            }
        }

        /// <exception cref="IOException"/>
        private void ProcessHandshakeQueue(ByteQueue queue)
        {
            /*
             * We need the first 4 bytes, they contain type and length of the message.
             */
            while (queue.Available >= 4)
            {
                int header = queue.ReadInt32();

                short type = (short)((uint)header >> 24);
                if (!HandshakeType.IsRecognized(type))
                {
                    throw new TlsFatalAlert(AlertDescription.unexpected_message,
                        "Handshake message of unrecognized type: " + type);
                }

                int length = header & 0x00FFFFFF;
                if (length > m_maxHandshakeMessageSize)
                {
                    throw new TlsFatalAlert(AlertDescription.internal_error,
                        "Handshake message length exceeds the maximum: " + HandshakeType.GetText(type) + ", " + length
                            + " > " + m_maxHandshakeMessageSize);
                }

                int totalLength = 4 + length;
                if (queue.Available < totalLength)
                {
                    // Not enough bytes in the buffer to read the full message.
                    break;
                }

                /*
                 * Check ChangeCipherSpec status
                 */
                switch (type)
                {
                case HandshakeType.hello_request:
                    break;

                default:
                {
                    ProtocolVersion negotiatedVersion = Context.ServerVersion;
                    if (null != negotiatedVersion && TlsUtilities.IsTlsV13(negotiatedVersion))
                        break;

                    CheckReceivedChangeCipherSpec(HandshakeType.finished == type);
                    break;
                }
                }

                HandshakeMessageInput buf = queue.ReadHandshakeMessage(totalLength);

                switch (type)
                {
                /*
                 * These message types aren't included in the transcript.
                 */
                case HandshakeType.hello_request:
                case HandshakeType.key_update:
                    break;

                /*
                 * Not included in the transcript for (D)TLS 1.3+
                 */
                case HandshakeType.new_session_ticket:
                {
                    ProtocolVersion negotiatedVersion = Context.ServerVersion;
                    if (null != negotiatedVersion && !TlsUtilities.IsTlsV13(negotiatedVersion))
                    {
                        buf.UpdateHash(m_handshakeHash);
                    }

                    break;
                }

                /*
                 * These message types are deferred to the handler to explicitly update the transcript.
                 */
                case HandshakeType.certificate_verify:
                case HandshakeType.client_hello:
                case HandshakeType.finished:
                case HandshakeType.server_hello:
                    break;

                /*
                 * For all others we automatically update the transcript immediately. 
                 */
                default:
                {
                    buf.UpdateHash(m_handshakeHash);
                    break;
                }
                }

                buf.Seek(4L, SeekOrigin.Current);

                HandleHandshakeMessage(type, buf);
            }
        }

        private void ProcessApplicationDataQueue()
        {
            /*
             * There is nothing we need to do here.
             * 
             * This function could be used for callbacks when application data arrives in the future.
             */
        }

        /// <exception cref="IOException"/>
        private void ProcessAlertQueue()
        {
            while (m_alertQueue.Available >= 2)
            {
                /*
                 * An alert is always 2 bytes. Read the alert.
                 */
                byte[] alert = m_alertQueue.RemoveData(2, 0);
                short alertLevel = alert[0];
                short alertDescription = alert[1];

                HandleAlertMessage(alertLevel, alertDescription);
            }
        }

        /// <summary>This method is called, when a change cipher spec message is received.</summary>
        /// <exception cref="IOException">If the message has an invalid content or the handshake is not in the correct
        /// state.</exception>
        private void ProcessChangeCipherSpec(byte[] buf, int off, int len)
        {
            ProtocolVersion negotiatedVersion = Context.ServerVersion;
            if (null == negotiatedVersion || TlsUtilities.IsTlsV13(negotiatedVersion))
            {
                // See RFC 8446 D.4.
                throw new TlsFatalAlert(AlertDescription.unexpected_message);
            }

            for (int i = 0; i < len; ++i)
            {
                short message = TlsUtilities.ReadUint8(buf, off + i);

                if (message != ChangeCipherSpec.change_cipher_spec)
                    throw new TlsFatalAlert(AlertDescription.decode_error);

                if (this.m_receivedChangeCipherSpec
                    || m_alertQueue.Available > 0
                    || m_handshakeQueue.Available > 0)
                {
                    throw new TlsFatalAlert(AlertDescription.unexpected_message);
                }

                m_recordStream.NotifyChangeCipherSpecReceived();

                this.m_receivedChangeCipherSpec = true;

                HandleChangeCipherSpecMessage();
            }
        }

        public virtual int ApplicationDataAvailable
        {
            get { return m_applicationDataQueue.Available; }
        }

        /// <summary>Read data from the network.</summary>
        /// <remarks>
        /// The method will return immediately, if there is still some data left in the buffer, or block until some
        /// application data has been read from the network.
        /// </remarks>
        /// <param name="buffer">The buffer where the data will be copied to.</param>
        /// <param name="offset">The position where the data will be placed in the buffer.</param>
        /// <param name="count">The maximum number of bytes to read.</param>
        /// <returns>The number of bytes read.</returns>
        /// <exception cref="IOException">If something goes wrong during reading data.</exception>
        public virtual int ReadApplicationData(byte[] buffer, int offset, int count)
        {
            Streams.ValidateBufferArguments(buffer, offset, count);

#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
            return ReadApplicationData(buffer.AsSpan(offset, count));
#else
            if (!m_appDataReady)
                throw new InvalidOperationException("Cannot read application data until initial handshake completed.");

            while (m_applicationDataQueue.Available < 1)
            {
                if (this.m_closed)
                {
                    if (this.m_failedWithError)
                        throw new IOException("Cannot read application data on failed TLS connection");

                    return 0;
                }

                /*
                 * NOTE: Only called more than once when empty records are received, so no special
                 * InterruptedIOException handling is necessary.
                 */
                SafeReadRecord();
            }

            if (count > 0)
            {
                count = System.Math.Min(count, m_applicationDataQueue.Available);
                m_applicationDataQueue.RemoveData(buffer, offset, count, 0);
            }
            return count;
#endif
        }

#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
        public virtual int ReadApplicationData(Span<byte> buffer)
        {
            if (!m_appDataReady)
                throw new InvalidOperationException("Cannot read application data until initial handshake completed.");

            while (m_applicationDataQueue.Available < 1)
            {
                if (this.m_closed)
                {
                    if (this.m_failedWithError)
                        throw new IOException("Cannot read application data on failed TLS connection");

                    return 0;
                }

                /*
                 * NOTE: Only called more than once when empty records are received, so no special
                 * InterruptedIOException handling is necessary.
                 */
                SafeReadRecord();
            }

            int count = buffer.Length;
            if (count > 0)
            {
                count = System.Math.Min(count, m_applicationDataQueue.Available);
                m_applicationDataQueue.RemoveData(buffer[..count], 0);
            }
            return count;
        }
#endif

        /// <exception cref="IOException"/>
        protected virtual RecordPreview SafePreviewRecordHeader(byte[] recordHeader)
        {
            try
            {
                return m_recordStream.PreviewRecordHeader(recordHeader);
            }
            catch (TlsFatalAlert e)
            {
                HandleException(e.AlertDescription, "Failed to read record", e);
                throw;
            }
            catch (IOException e)
            {
                HandleException(AlertDescription.internal_error, "Failed to read record", e);
                throw;
            }
            catch (Exception e)
            {
                HandleException(AlertDescription.internal_error, "Failed to read record", e);
                throw new TlsFatalAlert(AlertDescription.internal_error, e);
            }
        }

        /// <exception cref="IOException"/>
        protected virtual void SafeReadRecord()
        {
            try
            {
                if (m_recordStream.ReadRecord())
                    return;

                if (!m_appDataReady)
                    throw new TlsFatalAlert(AlertDescription.handshake_failure);

                if (!Peer.RequiresCloseNotify())
                {
                    HandleClose(false);
                    return;
                }
            }
            catch (TlsFatalAlertReceived)
            {
                // Connection failure already handled at source
                throw;
            }
            catch (TlsFatalAlert e)
            {
                HandleException(e.AlertDescription, "Failed to read record", e);
                throw;
            }
            catch (IOException e)
            {
                HandleException(AlertDescription.internal_error, "Failed to read record", e);
                throw;
            }
            catch (Exception e)
            {
                HandleException(AlertDescription.internal_error, "Failed to read record", e);
                throw new TlsFatalAlert(AlertDescription.internal_error, e);
            }

            HandleFailure();

            throw new TlsNoCloseNotifyException();
        }

        /// <exception cref="IOException"/>
        protected virtual bool SafeReadFullRecord(byte[] input, int inputOff, int inputLen)
        {
            try
            {
                return m_recordStream.ReadFullRecord(input, inputOff, inputLen);
            }
            catch (TlsFatalAlert e)
            {
                HandleException(e.AlertDescription, "Failed to process record", e);
                throw;
            }
            catch (IOException e)
            {
                HandleException(AlertDescription.internal_error, "Failed to process record", e);
                throw;
            }
            catch (Exception e)
            {
                HandleException(AlertDescription.internal_error, "Failed to process record", e);
                throw new TlsFatalAlert(AlertDescription.internal_error, e);
            }
        }

        /// <exception cref="IOException"/>
        protected virtual void SafeWriteRecord(short type, byte[] buf, int offset, int len)
        {
            try
            {
                m_recordStream.WriteRecord(type, buf, offset, len);
            }
            catch (TlsFatalAlert e)
            {
                HandleException(e.AlertDescription, "Failed to write record", e);
                throw;
            }
            catch (IOException e)
            {
                HandleException(AlertDescription.internal_error, "Failed to write record", e);
                throw;
            }
            catch (Exception e)
            {
                HandleException(AlertDescription.internal_error, "Failed to write record", e);
                throw new TlsFatalAlert(AlertDescription.internal_error, e);
            }
        }

#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
        /// <exception cref="IOException"/>
        protected virtual void SafeWriteRecord(short type, ReadOnlySpan<byte> buffer)
        {
            try
            {
                m_recordStream.WriteRecord(type, buffer);
            }
            catch (TlsFatalAlert e)
            {
                HandleException(e.AlertDescription, "Failed to write record", e);
                throw;
            }
            catch (IOException e)
            {
                HandleException(AlertDescription.internal_error, "Failed to write record", e);
                throw;
            }
            catch (Exception e)
            {
                HandleException(AlertDescription.internal_error, "Failed to write record", e);
                throw new TlsFatalAlert(AlertDescription.internal_error, e);
            }
        }
#endif

        /// <summary>Write some application data.</summary>
        /// <remarks>
        /// Fragmentation is handled internally. Usable in both blocking/non-blocking modes.<br/><br/>
        /// In blocking mode, the output will be automatically sent via the underlying transport. In non-blocking mode,
        /// call <see cref="ReadOutput(byte[], int, int)"/> to get the output bytes to send to the peer.<br/><br/>
        /// This method must not be called until after the initial handshake is complete. Attempting to call it earlier
        /// will result in an <see cref="InvalidOperationException"/>.
        /// </remarks>
        /// <param name="buffer">The buffer containing application data to send.</param>
        /// <param name="offset">The offset at which the application data begins</param>
        /// <param name="count">The number of bytes of application data.</param>
        /// <exception cref="InvalidOperationException">If called before the initial handshake has completed.
        /// </exception>
        /// <exception cref="IOException">If connection is already closed, or for encryption or transport errors.
        /// </exception>
        public virtual void WriteApplicationData(byte[] buffer, int offset, int count)
        {
            Streams.ValidateBufferArguments(buffer, offset, count);

#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
            WriteApplicationData(buffer.AsSpan(offset, count));
#else
            if (!m_appDataReady)
                throw new InvalidOperationException(
                    "Cannot write application data until initial handshake completed.");

            lock (m_recordWriteLock)
            {
                while (count > 0)
                {
                    if (m_closed)
                        throw new IOException("Cannot write application data on closed/failed TLS connection");

                    /*
                     * RFC 5246 6.2.1. Zero-length fragments of Application data MAY be sent as they are
                     * potentially useful as a traffic analysis countermeasure.
                     * 
                     * NOTE: Actually, implementations appear to have settled on 1/n-1 record splitting.
                     */
                    if (m_appDataSplitEnabled)
                    {
                        /*
                         * Protect against known IV attack!
                         * 
                         * DO NOT REMOVE THIS CODE, EXCEPT YOU KNOW EXACTLY WHAT YOU ARE DOING HERE.
                         */
                        switch (m_appDataSplitMode)
                        {
                        case ADS_MODE_0_N_FIRSTONLY:
                        {
                            this.m_appDataSplitEnabled = false;
                            SafeWriteRecord(ContentType.application_data, TlsUtilities.EmptyBytes, 0, 0);
                            break;
                        }
                        case ADS_MODE_0_N:
                        {
                            SafeWriteRecord(ContentType.application_data, TlsUtilities.EmptyBytes, 0, 0);
                            break;
                        }
                        case ADS_MODE_1_Nsub1:
                        default:
                        {
                            if (count > 1)
                            {
                                SafeWriteRecord(ContentType.application_data, buffer, offset, 1);
                                ++offset;
                                --count;
                            }
                            break;
                        }
                        }
                    }
                    else if (m_keyUpdateEnabled)
                    {
                        if (m_keyUpdatePendingSend)
                        {
                            Send13KeyUpdate(false);
                        }
                        else if (m_recordStream.NeedsKeyUpdate())
                        {
                            Send13KeyUpdate(true);
                        }
                    }

                    // Fragment data according to the current fragment limit.
                    int toWrite = System.Math.Min(count, m_recordStream.PlaintextLimit);
                    SafeWriteRecord(ContentType.application_data, buffer, offset, toWrite);
                    offset += toWrite;
                    count -= toWrite;
                }
            }
#endif
        }

#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
        public virtual void WriteApplicationData(ReadOnlySpan<byte> buffer)
        {
            if (!m_appDataReady)
                throw new InvalidOperationException(
                    "Cannot write application data until initial handshake completed.");

            lock (m_recordWriteLock)
            {
                while (!buffer.IsEmpty)
                {
                    if (m_closed)
                        throw new IOException("Cannot write application data on closed/failed TLS connection");

                    /*
                     * RFC 5246 6.2.1. Zero-length fragments of Application data MAY be sent as they are
                     * potentially useful as a traffic analysis countermeasure.
                     * 
                     * NOTE: Actually, implementations appear to have settled on 1/n-1 record splitting.
                     */
                    if (m_appDataSplitEnabled)
                    {
                        /*
                         * Protect against known IV attack!
                         * 
                         * DO NOT REMOVE THIS CODE, EXCEPT YOU KNOW EXACTLY WHAT YOU ARE DOING HERE.
                         */
                        switch (m_appDataSplitMode)
                        {
                        case ADS_MODE_0_N_FIRSTONLY:
                        {
                            this.m_appDataSplitEnabled = false;
                            SafeWriteRecord(ContentType.application_data, TlsUtilities.EmptyBytes, 0, 0);
                            break;
                        }
                        case ADS_MODE_0_N:
                        {
                            SafeWriteRecord(ContentType.application_data, TlsUtilities.EmptyBytes, 0, 0);
                            break;
                        }
                        case ADS_MODE_1_Nsub1:
                        default:
                        {
                            if (buffer.Length > 1)
                            {
                                SafeWriteRecord(ContentType.application_data, buffer[..1]);
                                buffer = buffer[1..];
                            }
                            break;
                        }
                        }
                    }
                    else if (m_keyUpdateEnabled)
                    {
                        if (m_keyUpdatePendingSend)
                        {
                            Send13KeyUpdate(false);
                        }
                        else if (m_recordStream.NeedsKeyUpdate())
                        {
                            Send13KeyUpdate(true);
                        }
                    }

                    // Fragment data according to the current fragment limit.
                    int toWrite = System.Math.Min(buffer.Length, m_recordStream.PlaintextLimit);
                    SafeWriteRecord(ContentType.application_data, buffer[..toWrite]);
                    buffer = buffer[toWrite..];
                }
            }
        }
#endif

        public virtual int AppDataSplitMode
        {
            get { return m_appDataSplitMode; }
            set
            {
                if (value < ADS_MODE_1_Nsub1 || value > ADS_MODE_0_N_FIRSTONLY)
                    throw new InvalidOperationException("Illegal appDataSplitMode mode: " + value);

                this.m_appDataSplitMode = value;
            }
        }

        public virtual bool IsResumableHandshake
        {
            get { return m_resumableHandshake; }
            set { this.m_resumableHandshake = value; }
        }

        /// <exception cref="IOException"/>
        internal void WriteHandshakeMessage(byte[] buf, int off, int len)
        {
            if (len < 4)
                throw new TlsFatalAlert(AlertDescription.internal_error);

            short type = TlsUtilities.ReadUint8(buf, off);
            switch (type)
            {
            /*
             * These message types aren't included in the transcript.
             */
            case HandshakeType.hello_request:
            case HandshakeType.key_update:
                break;

            /*
             * Not included in the transcript for (D)TLS 1.3+
             */
            case HandshakeType.new_session_ticket:
            {
                ProtocolVersion negotiatedVersion = Context.ServerVersion;
                if (null != negotiatedVersion && !TlsUtilities.IsTlsV13(negotiatedVersion))
                {
                    m_handshakeHash.Update(buf, off, len);
                }

                break;
            }

            /*
             * These message types are deferred to the writer to explicitly update the transcript.
             */
            case HandshakeType.client_hello:
                break;

            /*
             * For all others we automatically update the transcript. 
             */
            default:
            {
                m_handshakeHash.Update(buf, off, len);
                break;
            }
            }

            int total = 0;
            do
            {
                // Fragment data according to the current fragment limit.
                int toWrite = System.Math.Min(len - total, m_recordStream.PlaintextLimit);
                SafeWriteRecord(ContentType.handshake, buf, off + total, toWrite);
                total += toWrite;
            }
            while (total < len);
        }

        /// <summary>The secure bidirectional stream for this connection</summary>
        /// <remarks>Only allowed in blocking mode.</remarks>
        public virtual Stream Stream
        {
            get
            {
                if (!m_blocking)
                    throw new InvalidOperationException(
                        "Cannot use Stream in non-blocking mode! Use OfferInput()/OfferOutput() instead.");

                return this.m_tlsStream;
            }
        }

        /// <summary>Should be called in non-blocking mode when the input data reaches EOF.</summary>
        /// <exception cref="IOException"/>
        public virtual void CloseInput()
        {
            if (m_blocking)
                throw new InvalidOperationException("Cannot use CloseInput() in blocking mode!");

            if (m_closed)
                return;

            if (m_inputBuffers.Available > 0)
                throw new EndOfStreamException();

            if (!m_appDataReady)
                throw new TlsFatalAlert(AlertDescription.handshake_failure);

            if (!Peer.RequiresCloseNotify())
            {
                HandleClose(false);
                return;
            }

            HandleFailure();

            throw new TlsNoCloseNotifyException();
        }

        /// <exception cref="IOException"/>
        public virtual RecordPreview PreviewInputRecord(byte[] recordHeader)
        {
            if (m_blocking)
                throw new InvalidOperationException("Cannot use PreviewInputRecord() in blocking mode!");
            if (m_inputBuffers.Available != 0)
                throw new InvalidOperationException("Can only use PreviewInputRecord() for record-aligned input.");
            if (m_closed)
                throw new IOException("Connection is closed, cannot accept any more input");

            return SafePreviewRecordHeader(recordHeader);
        }

        public virtual int PreviewOutputRecord()
        {
            if (m_blocking)
                throw new InvalidOperationException("Cannot use PreviewOutputRecord() in blocking mode!");

            ByteQueue buffer = m_outputBuffer.Buffer;
            int available = buffer.Available;
            if (available < 1)
                return 0;

            if (available >= RecordFormat.FragmentOffset)
            {
                int length = buffer.ReadUint16(RecordFormat.LengthOffset);
                int recordSize = RecordFormat.FragmentOffset + length;

                if (available >= recordSize)
                    return recordSize;
            }

            throw new InvalidOperationException("Can only use PreviewOutputRecord() for record-aligned output.");
        }

        /// <exception cref="IOException"/>
        public virtual RecordPreview PreviewOutputRecord(int applicationDataSize)
        {
            if (!m_appDataReady)
                throw new InvalidOperationException(
                    "Cannot use PreviewOutputRecord() until initial handshake completed.");
            if (m_blocking)
                throw new InvalidOperationException("Cannot use PreviewOutputRecord() in blocking mode!");
            if (m_outputBuffer.Buffer.Available != 0)
                throw new InvalidOperationException("Can only use PreviewOutputRecord() for record-aligned output.");
            if (m_closed)
                throw new IOException("Connection is closed, cannot produce any more output");

            if (applicationDataSize < 1)
                return new RecordPreview(0, 0);

            if (m_appDataSplitEnabled)
            {
                switch (m_appDataSplitMode)
                {
                case ADS_MODE_0_N_FIRSTONLY:
                case ADS_MODE_0_N:
                {
                    RecordPreview a = m_recordStream.PreviewOutputRecord(0);
                    RecordPreview b = m_recordStream.PreviewOutputRecord(applicationDataSize);
                    return RecordPreview.CombineAppData(a, b);
                }
                case ADS_MODE_1_Nsub1:
                default:
                {
                    RecordPreview a = m_recordStream.PreviewOutputRecord(1);
                    if (applicationDataSize > 1)
                    {
                        RecordPreview b = m_recordStream.PreviewOutputRecord(applicationDataSize - 1);
                        a = RecordPreview.CombineAppData(a, b);
                    }
                    return a;
                }
                }
            }
            else
            {
                RecordPreview a = m_recordStream.PreviewOutputRecord(applicationDataSize);
                if (m_keyUpdateEnabled && (m_keyUpdatePendingSend || m_recordStream.NeedsKeyUpdate()))
                {
                    int keyUpdateLength = HandshakeMessageOutput.GetLength(1);
                    int recordSize = m_recordStream.PreviewOutputRecordSize(keyUpdateLength);
                    a = RecordPreview.ExtendRecordSize(a, recordSize);
                }
                return a;
            }
        }

        /// <summary>Equivalent to <code>OfferInput(input, 0, input.Length)</code>.</summary>
        /// <param name="input">The input buffer to offer.</param>
        /// <exception cref="IOException"/>
        /// <seealso cref="OfferInput(byte[], int, int)"/>
        public virtual void OfferInput(byte[] input)
        {
            OfferInput(input, 0, input.Length);
        }

        /// <summary>Offer input from an arbitrary source.</summary>
        /// <remarks>Only allowed in non-blocking mode.<br/><br/>
        /// This method will decrypt and process all records that are fully available. If only part of a record is
        /// available, the buffer will be retained until the remainder of the record is offered.<br/><br/>
        /// If any records containing application data were processed, the decrypted data can be obtained using
        /// <see cref="ReadInput(byte[], int, int)"/>. If any records containing protocol data were processed, a
        /// response may have been generated. You should always check to see if there is any available output after
        /// calling this method by calling <see cref="GetAvailableOutputBytes"/>.
        /// </remarks>
        /// <param name="input">The input buffer to offer.</param>
        /// <param name="inputOff">The offset within the input buffer that input begins.</param>
        /// <param name="inputLen">The number of bytes of input being offered.</param>
        /// <exception cref="IOException">If an error occurs while decrypting or processing a record.</exception>
        public virtual void OfferInput(byte[] input, int inputOff, int inputLen)
        {
            if (m_blocking)
                throw new InvalidOperationException("Cannot use OfferInput() in blocking mode! Use Stream instead.");
            if (m_closed)
                throw new IOException("Connection is closed, cannot accept any more input");

            // Fast path if the input is arriving one record at a time
            if (m_inputBuffers.Available == 0 && SafeReadFullRecord(input, inputOff, inputLen))
            {
                if (m_closed)
                {
                    if (!m_appDataReady)
                    {
                        // NOTE: Any close during the handshake should have raised an exception.
                        throw new TlsFatalAlert(AlertDescription.internal_error);
                    }
                }
                return;
            }

            m_inputBuffers.AddBytes(input, inputOff, inputLen);

            // loop while there are enough bytes to read the length of the next record
            while (m_inputBuffers.Available >= RecordFormat.FragmentOffset)
            {
                byte[] recordHeader = new byte[RecordFormat.FragmentOffset];
                if (RecordFormat.FragmentOffset != m_inputBuffers.Peek(recordHeader))
                    throw new TlsFatalAlert(AlertDescription.internal_error);

                RecordPreview preview = SafePreviewRecordHeader(recordHeader);
                if (m_inputBuffers.Available < preview.RecordSize)
                {
                    // not enough bytes to read a whole record
                    break;
                }

                // NOTE: This is actually reading from inputBuffers, so InterruptedIOException shouldn't be possible
                SafeReadRecord();

                if (m_closed)
                {
                    if (!m_appDataReady)
                    {
                        // NOTE: Any close during the handshake should have raised an exception.
                        throw new TlsFatalAlert(AlertDescription.internal_error);
                    }
                    break;
                }
            }
        }

        public virtual int ApplicationDataLimit
        {
            get { return m_recordStream.PlaintextLimit; }
        }

        /// <summary>Gets the amount of received application data.</summary>
        /// <remarks>A call to <see cref="ReadInput(byte[], int, int)"/> is guaranteed to be able to return at least
        /// this much data.<br/><br/>
        /// Only allowed in non-blocking mode.
        /// </remarks>
        /// <returns>The number of bytes of available application data.</returns>
        public virtual int GetAvailableInputBytes()
        {
            if (m_blocking)
                throw new InvalidOperationException("Cannot use GetAvailableInputBytes() in blocking mode!");

            return ApplicationDataAvailable;
        }

        /// <summary>Retrieves received application data.</summary>
        /// <remarks>
        /// Use <see cref="GetAvailableInputBytes"/> to check how much application data is currently available. This
        /// method functions similarly to <see cref="Stream.Read(byte[], int, int)"/>, except that it never blocks. If
        /// no data is available, nothing will be copied and zero will be returned.<br/><br/>
        /// Only allowed in non-blocking mode.
        /// </remarks>
        /// <param name="buf">The buffer to hold the application data.</param>
        /// <param name="off">The start offset in the buffer at which the data is written.</param>
        /// <param name="len">The maximum number of bytes to read.</param>
        /// <returns>The total number of bytes copied to the buffer. May be less than the length specified if the
        /// length was greater than the amount of available data.</returns>
        public virtual int ReadInput(byte[] buf, int off, int len)
        {
            if (m_blocking)
                throw new InvalidOperationException("Cannot use ReadInput() in blocking mode! Use Stream instead.");

            len = System.Math.Min(len, ApplicationDataAvailable);
            if (len < 1)
                return 0;

            m_applicationDataQueue.RemoveData(buf, off, len, 0);
            return len;
        }

        /// <summary>Gets the amount of encrypted data available to be sent.</summary>
        /// <remarks>
        /// A call to <see cref="ReadOutput(byte[], int, int)"/> is guaranteed to be able to return at least this much
        /// data. Only allowed in non-blocking mode.
        /// </remarks>
        /// <returns>The number of bytes of available encrypted data.</returns>
        public virtual int GetAvailableOutputBytes()
        {
            if (m_blocking)
                throw new InvalidOperationException("Cannot use GetAvailableOutputBytes() in blocking mode! Use Stream instead.");

            return m_outputBuffer.Buffer.Available;
        }

        /// <summary>Retrieves encrypted data to be sent.</summary>
        /// <remarks>
        /// Use <see cref="GetAvailableOutputBytes"/> to check how much encrypted data is currently available. This
        /// method functions similarly to <see cref="Stream.Read(byte[], int, int)"/>, except that it never blocks. If
        /// no data is available, nothing will be copied and zero will be returned. Only allowed in non-blocking mode.
        /// </remarks>
        /// <param name="buffer">The buffer to hold the encrypted data.</param>
        /// <param name="offset">The start offset in the buffer at which the data is written.</param>
        /// <param name="length">The maximum number of bytes to read.</param>
        /// <returns>The total number of bytes copied to the buffer. May be less than the length specified if the
        /// length was greater than the amount of available data.</returns>
        public virtual int ReadOutput(byte[] buffer, int offset, int length)
        {
            if (m_blocking)
                throw new InvalidOperationException("Cannot use ReadOutput() in blocking mode! Use 'Stream() instead.");

            int bytesToRead = System.Math.Min(GetAvailableOutputBytes(), length);
            m_outputBuffer.Buffer.RemoveData(buffer, offset, bytesToRead, 0);
            return bytesToRead;
        }

        protected virtual bool EstablishSession(TlsSession sessionToResume)
        {
            this.m_tlsSession = null;
            this.m_sessionParameters = null;
            this.m_sessionMasterSecret = null;

            if (null == sessionToResume || !sessionToResume.IsResumable)
                return false;

            SessionParameters sessionParameters = sessionToResume.ExportSessionParameters();
            if (null == sessionParameters)
                return false;

            ProtocolVersion sessionVersion = sessionParameters.NegotiatedVersion;
            if (null == sessionVersion || !sessionVersion.IsTls)
                return false;

            bool isEms = sessionParameters.IsExtendedMasterSecret;
            if (sessionVersion.IsSsl)
            {
                if (isEms)
                    return false;
            }
            else if (!TlsUtilities.IsExtendedMasterSecretOptional(sessionVersion))
            {
                if (!isEms)
                    return false;
            }

            TlsSecret sessionMasterSecret = TlsUtilities.GetSessionMasterSecret(Context.Crypto,
                sessionParameters.MasterSecret);
            if (null == sessionMasterSecret)
                return false;

            this.m_tlsSession = sessionToResume;
            this.m_sessionParameters = sessionParameters;
            this.m_sessionMasterSecret = sessionMasterSecret;

            return true;
        }

        protected virtual void CancelSession()
        {
            if (m_sessionMasterSecret != null)
            {
                m_sessionMasterSecret.Destroy();
                this.m_sessionMasterSecret = null;
            }

            if (m_sessionParameters != null)
            {
                m_sessionParameters.Clear();
                this.m_sessionParameters = null;
            }

            this.m_tlsSession = null;
        }

        protected virtual void InvalidateSession()
        {
            if (m_tlsSession != null)
            {
                m_tlsSession.Invalidate();
            }

            CancelSession();
        }

        /// <exception cref="IOException"/>
        protected virtual void ProcessFinishedMessage(MemoryStream buf)
        {
            TlsContext context = Context;
            SecurityParameters securityParameters = context.SecurityParameters;
            bool isServerContext = context.IsServer;

#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
            Span<byte> verify_data = stackalloc byte[securityParameters.VerifyDataLength];
            TlsUtilities.ReadFully(verify_data, buf);
#else
            byte[] verify_data = TlsUtilities.ReadFully(securityParameters.VerifyDataLength, buf);
#endif

            AssertEmpty(buf);

            byte[] expected_verify_data = TlsUtilities.CalculateVerifyData(context, m_handshakeHash, !isServerContext);

            /*
             * Compare both checksums.
             */
            if (!Arrays.FixedTimeEquals(expected_verify_data, verify_data))
            {
                /*
                 * Wrong checksum in the finished message.
                 */
                throw new TlsFatalAlert(AlertDescription.decrypt_error);
            }

            securityParameters.m_peerVerifyData = expected_verify_data;

            if (!securityParameters.IsResumedSession || securityParameters.IsExtendedMasterSecret)
            {
                if (null == securityParameters.LocalVerifyData)
                {
                    securityParameters.m_tlsUnique = expected_verify_data;
                }
            }
        }

        /// <exception cref="IOException"/>
        protected virtual void Process13FinishedMessage(MemoryStream buf)
        {
            TlsContext context = Context;
            SecurityParameters securityParameters = context.SecurityParameters;
            bool isServerContext = context.IsServer;

#if NETCOREAPP2_1_OR_GREATER || NETSTANDARD2_1_OR_GREATER
            Span<byte> verify_data = stackalloc byte[securityParameters.VerifyDataLength];
            TlsUtilities.ReadFully(verify_data, buf);
#else
            byte[] verify_data = TlsUtilities.ReadFully(securityParameters.VerifyDataLength, buf);
#endif

            AssertEmpty(buf);

            byte[] expected_verify_data = TlsUtilities.CalculateVerifyData(context, m_handshakeHash, !isServerContext);

            /*
             * Compare both checksums.
             */
            if (!Arrays.FixedTimeEquals(expected_verify_data, verify_data))
            {
                /*
                 * Wrong checksum in the finished message.
                 */
                throw new TlsFatalAlert(AlertDescription.decrypt_error);
            }

            securityParameters.m_peerVerifyData = expected_verify_data;
            securityParameters.m_tlsUnique = null;
        }

        /// <exception cref="IOException"/>
        protected virtual void RaiseAlertFatal(short alertDescription, string message, Exception cause)
        {
            Peer.NotifyAlertRaised(AlertLevel.fatal, alertDescription, message, cause);

            byte[] alert = new byte[]{ (byte)AlertLevel.fatal, (byte)alertDescription };

            try
            {
                m_recordStream.WriteRecord(ContentType.alert, alert, 0, 2);
            }
            catch (Exception)
            {
                // We are already processing an exception, so just ignore this
            }
        }

        /// <exception cref="IOException"/>
        protected virtual void RaiseAlertWarning(short alertDescription, string message)
        {
            Peer.NotifyAlertRaised(AlertLevel.warning, alertDescription, message, null);

            byte[] alert = new byte[]{ (byte)AlertLevel.warning, (byte)alertDescription };

            SafeWriteRecord(ContentType.alert, alert, 0, 2);
        }


        /// <exception cref="IOException"/>
        protected virtual void Receive13KeyUpdate(MemoryStream buf)
        {
            // TODO[tls13] This is interesting enough to notify the TlsPeer for possible logging/vetting

            if (!(m_appDataReady && m_keyUpdateEnabled))
                throw new TlsFatalAlert(AlertDescription.unexpected_message);

            short requestUpdate = TlsUtilities.ReadUint8(buf);

            AssertEmpty(buf);

            if (!KeyUpdateRequest.IsValid(requestUpdate))
                throw new TlsFatalAlert(AlertDescription.illegal_parameter);

            bool updateRequested = (KeyUpdateRequest.update_requested == requestUpdate);

            TlsUtilities.Update13TrafficSecretPeer(Context);
            m_recordStream.NotifyKeyUpdateReceived();

            //this.m_keyUpdatePendingReceive &= updateRequested;
            this.m_keyUpdatePendingSend |= updateRequested;
        }

        /// <exception cref="IOException"/>
        protected virtual void SendCertificateMessage(Certificate certificate, Stream endPointHash)
        {
            TlsContext context = Context;
            SecurityParameters securityParameters = context.SecurityParameters;
            if (null != securityParameters.LocalCertificate)
                throw new TlsFatalAlert(AlertDescription.internal_error);

            if (null == certificate)
            {
                certificate = Certificate.EmptyChain;
            }

            if (certificate.IsEmpty && !context.IsServer && securityParameters.NegotiatedVersion.IsSsl)
            {
                string message = "SSLv3 client didn't provide credentials";
                RaiseAlertWarning(AlertDescription.no_certificate, message);
            }
            else
            {
                HandshakeMessageOutput message = new HandshakeMessageOutput(HandshakeType.certificate);
                certificate.Encode(context, message, endPointHash);
                message.Send(this);
            }

            securityParameters.m_localCertificate = certificate;
        }

        /// <exception cref="IOException"/>
        protected virtual void Send13CertificateMessage(Certificate certificate)
        {
            if (null == certificate)
                throw new TlsFatalAlert(AlertDescription.internal_error);

            TlsContext context = Context;
            SecurityParameters securityParameters = context.SecurityParameters;
            if (null != securityParameters.LocalCertificate)
                throw new TlsFatalAlert(AlertDescription.internal_error);

            HandshakeMessageOutput message = new HandshakeMessageOutput(HandshakeType.certificate);
            certificate.Encode(context, message, null);
            message.Send(this);

            securityParameters.m_localCertificate = certificate;
        }

        /// <exception cref="IOException"/>
        protected virtual void Send13CertificateVerifyMessage(DigitallySigned certificateVerify)
        {
            HandshakeMessageOutput message = new HandshakeMessageOutput(HandshakeType.certificate_verify);
            certificateVerify.Encode(message);
            message.Send(this);
        }

        /// <exception cref="IOException"/>
        protected virtual void SendChangeCipherSpec()
        {
            SendChangeCipherSpecMessage();
            m_recordStream.EnablePendingCipherWrite();
        }

        /// <exception cref="IOException"/>
        protected virtual void SendChangeCipherSpecMessage()
        {
            byte[] message = new byte[]{ 1 };
            SafeWriteRecord(ContentType.change_cipher_spec, message, 0, message.Length);
        }

        /// <exception cref="IOException"/>
        protected virtual void SendFinishedMessage()
        {
            TlsContext context = Context;
            SecurityParameters securityParameters = context.SecurityParameters;
            bool isServerContext = context.IsServer;

            byte[] verify_data = TlsUtilities.CalculateVerifyData(context, m_handshakeHash, isServerContext);

            securityParameters.m_localVerifyData = verify_data;

            if (!securityParameters.IsResumedSession || securityParameters.IsExtendedMasterSecret)
            {
                if (null == securityParameters.PeerVerifyData)
                {
                    securityParameters.m_tlsUnique = verify_data;
                }
            }

            HandshakeMessageOutput.Send(this, HandshakeType.finished, verify_data);
        }

        /// <exception cref="IOException"/>
        protected virtual void Send13FinishedMessage()
        {
            TlsContext context = Context;
            SecurityParameters securityParameters = context.SecurityParameters;
            bool isServerContext = context.IsServer;

            byte[] verify_data = TlsUtilities.CalculateVerifyData(context, m_handshakeHash, isServerContext);

            securityParameters.m_localVerifyData = verify_data;
            securityParameters.m_tlsUnique = null;

            HandshakeMessageOutput.Send(this, HandshakeType.finished, verify_data);
        }

        /// <exception cref="IOException"/>
        protected virtual void Send13KeyUpdate(bool updateRequested)
        {
            // TODO[tls13] This is interesting enough to notify the TlsPeer for possible logging/vetting

            if (!(m_appDataReady && m_keyUpdateEnabled))
                throw new TlsFatalAlert(AlertDescription.internal_error);

            short requestUpdate = updateRequested
                ? KeyUpdateRequest.update_requested
                : KeyUpdateRequest.update_not_requested;

            HandshakeMessageOutput.Send(this, HandshakeType.key_update, TlsUtilities.EncodeUint8(requestUpdate));

            TlsUtilities.Update13TrafficSecretLocal(Context);
            m_recordStream.NotifyKeyUpdateSent();

            //this.m_keyUpdatePendingReceive |= updateRequested;
            this.m_keyUpdatePendingSend &= updateRequested;
        }

        /// <exception cref="IOException"/>
        protected virtual void SendSupplementalDataMessage(IList<SupplementalDataEntry> supplementalData)
        {
            HandshakeMessageOutput message = new HandshakeMessageOutput(HandshakeType.supplemental_data);
            WriteSupplementalData(message, supplementalData);
            message.Send(this);
        }

        public virtual void Close()
        {
            HandleClose(true);
        }

        public virtual void Flush()
        {
        }

        internal bool IsApplicationDataReady
        {
            get { return m_appDataReady; }
        }

        public virtual bool IsClosed
        {
            get { return m_closed; }
        }

        public virtual bool IsConnected
        {
            get
            {
                if (m_closed)
                    return false;

                AbstractTlsContext context = ContextAdmin;

                return null != context && context.IsConnected;
            }
        }

        public virtual bool IsHandshaking
        {
            get
            {
                if (m_closed)
                    return false;

                AbstractTlsContext context = ContextAdmin;

                return null != context && context.IsHandshaking;
            }
        }

        /// <exception cref="IOException"/>
        [Obsolete("Will be removed")]
        protected virtual short ProcessMaxFragmentLengthExtension(IDictionary<int, byte[]> clientExtensions,
            IDictionary<int, byte[]> serverExtensions, short alertDescription)
        {
            return TlsUtilities.ProcessMaxFragmentLengthExtension(clientExtensions, serverExtensions, alertDescription);
        }

        /// <exception cref="IOException"/>
        protected virtual void RefuseRenegotiation()
        {
            /*
             * RFC 5746 4.5 SSLv3 clients [..] SHOULD use a fatal handshake_failure alert.
             */
            if (TlsUtilities.IsSsl(Context))
                throw new TlsFatalAlert(AlertDescription.handshake_failure);

            RaiseAlertWarning(AlertDescription.no_renegotiation, "Renegotiation not supported");
        }

        /// <summary>Make sure the <see cref="Stream"/> 'buf' is now empty. Fail otherwise.</summary>
        /// <param name="buf">The <see cref="Stream"/> to check.</param>
        /// <exception cref="IOException"/>
        internal static void AssertEmpty(MemoryStream buf)
        {
            if (buf.Position < buf.Length)
                throw new TlsFatalAlert(AlertDescription.decode_error);
        }

        internal static byte[] CreateRandomBlock(bool useGmtUnixTime, TlsContext context)
        {
            byte[] result = context.NonceGenerator.GenerateNonce(32);

            if (useGmtUnixTime)
            {
                TlsUtilities.WriteGmtUnixTime(result, 0);
            }

            return result;
        }

        /// <exception cref="IOException"/>
        internal static byte[] CreateRenegotiationInfo(byte[] renegotiated_connection)
        {
            return TlsUtilities.EncodeOpaque8(renegotiated_connection);
        }

        /// <exception cref="IOException"/>
        internal static void EstablishMasterSecret(TlsContext context, TlsKeyExchange keyExchange)
        {
            TlsSecret preMasterSecret = keyExchange.GeneratePreMasterSecret();
            if (preMasterSecret == null)
                throw new TlsFatalAlert(AlertDescription.internal_error);

            try
            {
                context.SecurityParameters.m_masterSecret = TlsUtilities.CalculateMasterSecret(context,
                    preMasterSecret);
            }
            finally
            {
                /*
                 * RFC 2246 8.1. The pre_master_secret should be deleted from memory once the
                 * master_secret has been computed.
                 */
                preMasterSecret.Destroy();
            }
        }

        /// <exception cref="IOException"/>
        internal static IDictionary<int, byte[]> ReadExtensions(MemoryStream input)
        {
            if (input.Position >= input.Length)
                return null;

            byte[] extBytes = TlsUtilities.ReadOpaque16(input);

            AssertEmpty(input);

            return ReadExtensionsData(extBytes);
        }

        /// <exception cref="IOException"/>
        internal static IDictionary<int, byte[]> ReadExtensionsData(byte[] extBytes)
        {
            // Int32 -> byte[]
            var extensions = new Dictionary<int, byte[]>();

            if (extBytes.Length > 0)
            {
                MemoryStream buf = new MemoryStream(extBytes, false);

                do
                {
                    int extension_type = TlsUtilities.ReadUint16(buf);
                    byte[] extension_data = TlsUtilities.ReadOpaque16(buf);

                    /*
                     * RFC 3546 2.3 There MUST NOT be more than one extension of the same type.
                     */
                    if (extensions.ContainsKey(extension_type))
                        throw new TlsFatalAlert(AlertDescription.illegal_parameter,
                            "Repeated extension: " + ExtensionType.GetText(extension_type));

                    extensions.Add(extension_type, extension_data);
                }
                while (buf.Position < buf.Length);
            }

            return extensions;
        }

        /// <exception cref="IOException"/>
        internal static IDictionary<int, byte[]> ReadExtensionsData13(int handshakeType, byte[] extBytes)
        {
            // Int32 -> byte[]
            var extensions = new Dictionary<int, byte[]>();

            if (extBytes.Length > 0)
            {
                MemoryStream buf = new MemoryStream(extBytes, false);

                do
                {
                    int extension_type = TlsUtilities.ReadUint16(buf);

                    if (!TlsUtilities.IsPermittedExtensionType13(handshakeType, extension_type))
                    {
                        throw new TlsFatalAlert(AlertDescription.illegal_parameter,
                            "Invalid extension: " + ExtensionType.GetText(extension_type));
                    }

                    byte[] extension_data = TlsUtilities.ReadOpaque16(buf);

                    /*
                     * RFC 3546 2.3 There MUST NOT be more than one extension of the same type.
                     */
                    if (extensions.ContainsKey(extension_type))
                        throw new TlsFatalAlert(AlertDescription.illegal_parameter,
                            "Repeated extension: " + ExtensionType.GetText(extension_type));

                    extensions.Add(extension_type, extension_data);
                }
                while (buf.Position < buf.Length);
            }

            return extensions;
        }

        /// <exception cref="IOException"/>
        internal static IDictionary<int, byte[]> ReadExtensionsDataClientHello(byte[] extBytes)
        {
            /*
             * TODO[tls13] We are currently allowing any extensions to appear in ClientHello. It is
             * somewhat complicated to restrict what can appear based on the specific set of versions
             * the client is offering, and anyway could be fragile since clients may take a
             * "kitchen sink" approach to adding extensions independently of the offered versions.
             */

            // Int32 -> byte[]
            var extensions = new Dictionary<int, byte[]>();

            if (extBytes.Length > 0)
            {
                MemoryStream buf = new MemoryStream(extBytes, false);

                int extension_type;
                bool pre_shared_key_found = false;

                do
                {
                    extension_type = TlsUtilities.ReadUint16(buf);
                    byte[] extension_data = TlsUtilities.ReadOpaque16(buf);

                    /*
                     * RFC 3546 2.3 There MUST NOT be more than one extension of the same type.
                     */
                    if (extensions.ContainsKey(extension_type))
                        throw new TlsFatalAlert(AlertDescription.illegal_parameter,
                            "Repeated extension: " + ExtensionType.GetText(extension_type));

                    extensions.Add(extension_type, extension_data);

                    pre_shared_key_found |= (ExtensionType.pre_shared_key == extension_type);
                }
                while (buf.Position < buf.Length);

                if (pre_shared_key_found && (ExtensionType.pre_shared_key != extension_type))
                    throw new TlsFatalAlert(AlertDescription.illegal_parameter,
                        "'pre_shared_key' MUST be last in ClientHello");
            }

            return extensions;
        }

        /// <exception cref="IOException"/>
        internal static IList<SupplementalDataEntry> ReadSupplementalDataMessage(MemoryStream input)
        {
            byte[] supp_data = TlsUtilities.ReadOpaque24(input, 1);

            AssertEmpty(input);

            MemoryStream buf = new MemoryStream(supp_data, false);

            var supplementalData = new List<SupplementalDataEntry>();

            while (buf.Position < buf.Length)
            {
                int supp_data_type = TlsUtilities.ReadUint16(buf);
                byte[] data = TlsUtilities.ReadOpaque16(buf);

                supplementalData.Add(new SupplementalDataEntry(supp_data_type, data));
            }

            return supplementalData;
        }

        /// <exception cref="IOException"/>
        internal static void WriteExtensions(Stream output, IDictionary<int, byte[]> extensions)
        {
            WriteExtensions(output, extensions, 0);
        }

        /// <exception cref="IOException"/>
        internal static void WriteExtensions(Stream output, IDictionary<int, byte[]> extensions, int bindersSize)
        {
            if (null == extensions || extensions.Count < 1)
                return;

            byte[] extBytes = WriteExtensionsData(extensions, bindersSize);

            int lengthWithBinders = extBytes.Length + bindersSize;
            TlsUtilities.CheckUint16(lengthWithBinders);
            TlsUtilities.WriteUint16(lengthWithBinders, output);
            output.Write(extBytes, 0, extBytes.Length);
        }

        /// <exception cref="IOException"/>
        internal static byte[] WriteExtensionsData(IDictionary<int, byte[]> extensions)
        {
            return WriteExtensionsData(extensions, 0);
        }

        /// <exception cref="IOException"/>
        internal static byte[] WriteExtensionsData(IDictionary<int, byte[]> extensions, int bindersSize)
        {
            MemoryStream buf = new MemoryStream();
            WriteExtensionsData(extensions, buf, bindersSize);
            return buf.ToArray();
        }

        /// <exception cref="IOException"/>
        internal static void WriteExtensionsData(IDictionary<int, byte[]> extensions, MemoryStream buf)
        {
            WriteExtensionsData(extensions, buf, 0);
        }

        /// <exception cref="IOException"/>
        internal static void WriteExtensionsData(IDictionary<int, byte[]> extensions, MemoryStream buf, int bindersSize)
        {
            /*
             * NOTE: There are reports of servers that don't accept a zero-length extension as the last
             * one, so we write out any zero-length ones first as a best-effort workaround.
             */
            WriteSelectedExtensions(buf, extensions, true);
            WriteSelectedExtensions(buf, extensions, false);
            WritePreSharedKeyExtension(buf, extensions, bindersSize);
        }

        /// <exception cref="IOException"/>
        internal static void WritePreSharedKeyExtension(MemoryStream buf, IDictionary<int, byte[]> extensions,
            int bindersSize)
        {
            if (extensions.TryGetValue(ExtensionType.pre_shared_key, out var extension_data))
            {
                TlsUtilities.CheckUint16(ExtensionType.pre_shared_key);
                TlsUtilities.WriteUint16(ExtensionType.pre_shared_key, buf);

                int lengthWithBinders = extension_data.Length + bindersSize;
                TlsUtilities.CheckUint16(lengthWithBinders);
                TlsUtilities.WriteUint16(lengthWithBinders, buf);
                buf.Write(extension_data, 0, extension_data.Length);
            }
        }

        /// <exception cref="IOException"/>
        internal static void WriteSelectedExtensions(Stream output, IDictionary<int, byte[]> extensions,
            bool selectEmpty)
        {
            foreach (var extension in extensions)
            {
                int extension_type = extension.Key;

                // NOTE: Must be last; handled by 'WritePreSharedKeyExtension'
                if (ExtensionType.pre_shared_key == extension_type)
                    continue;

                byte[] extension_data = extension.Value;

                if (selectEmpty == (extension_data.Length == 0))
                {
                    TlsUtilities.CheckUint16(extension_type);
                    TlsUtilities.WriteUint16(extension_type, output);
                    TlsUtilities.WriteOpaque16(extension_data, output);
                }
            }
        }

        /// <exception cref="IOException"/>
        internal static void WriteSupplementalData(Stream output, IList<SupplementalDataEntry> supplementalData)
        {
            MemoryStream buf = new MemoryStream();

            foreach (SupplementalDataEntry entry in supplementalData)
            {
                int supp_data_type = entry.DataType;
                TlsUtilities.CheckUint16(supp_data_type);
                TlsUtilities.WriteUint16(supp_data_type, buf);
                TlsUtilities.WriteOpaque16(entry.Data, buf);
            }

            byte[] supp_data = buf.ToArray();

            TlsUtilities.WriteOpaque24(supp_data, output);
        }
    }
}