aboutsummaryrefslogtreecommitdiff
path: root/lib/vtls/schannel.c
blob: 1f036249bf49954c8ed139f4b44f279c4f6452a9 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
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
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
2238
2239
2240
2241
2242
2243
2244
2245
2246
2247
2248
2249
2250
2251
2252
2253
2254
2255
2256
2257
2258
2259
2260
2261
2262
2263
2264
2265
2266
2267
2268
2269
2270
2271
2272
2273
2274
2275
2276
2277
2278
2279
2280
2281
2282
2283
2284
2285
2286
2287
2288
2289
2290
2291
2292
2293
2294
2295
2296
2297
2298
2299
2300
2301
2302
2303
/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 2012 - 2016, Marc Hoersken, <info@marc-hoersken.de>
 * Copyright (C) 2012, Mark Salisbury, <mark.salisbury@hp.com>
 * Copyright (C) 2012 - 2019, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.haxx.se/docs/copyright.html.
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ***************************************************************************/

/*
 * Source file for all Schannel-specific code for the TLS/SSL layer. No code
 * but vtls.c should ever call or use these functions.
 */

/*
 * Based upon the PolarSSL implementation in polarssl.c and polarssl.h:
 *   Copyright (C) 2010, 2011, Hoi-Ho Chan, <hoiho.chan@gmail.com>
 *
 * Based upon the CyaSSL implementation in cyassl.c and cyassl.h:
 *   Copyright (C) 1998 - 2012, Daniel Stenberg, <daniel@haxx.se>, et al.
 *
 * Thanks for code and inspiration!
 */

#include "curl_setup.h"

#ifdef USE_SCHANNEL

#define EXPOSE_SCHANNEL_INTERNAL_STRUCTS

#ifndef USE_WINDOWS_SSPI
#  error "Can't compile SCHANNEL support without SSPI."
#endif

#include "schannel.h"
#include "vtls.h"
#include "sendf.h"
#include "connect.h" /* for the connect timeout */
#include "strerror.h"
#include "select.h" /* for the socket readyness */
#include "inet_pton.h" /* for IP addr SNI check */
#include "curl_multibyte.h"
#include "warnless.h"
#include "x509asn1.h"
#include "curl_printf.h"
#include "multiif.h"
#include "system_win32.h"

 /* The last #include file should be: */
#include "curl_memory.h"
#include "memdebug.h"

/* ALPN requires version 8.1 of the Windows SDK, which was
   shipped with Visual Studio 2013, aka _MSC_VER 1800:

   https://technet.microsoft.com/en-us/library/hh831771%28v=ws.11%29.aspx
*/
#if defined(_MSC_VER) && (_MSC_VER >= 1800) && !defined(_USING_V110_SDK71_)
#  define HAS_ALPN 1
#endif

#ifndef UNISP_NAME_A
#define UNISP_NAME_A "Microsoft Unified Security Protocol Provider"
#endif

#ifndef UNISP_NAME_W
#define UNISP_NAME_W L"Microsoft Unified Security Protocol Provider"
#endif

#ifndef UNISP_NAME
#ifdef UNICODE
#define UNISP_NAME  UNISP_NAME_W
#else
#define UNISP_NAME  UNISP_NAME_A
#endif
#endif

#if defined(CryptStringToBinary) && defined(CRYPT_STRING_HEX)
#define HAS_CLIENT_CERT_PATH
#endif

#ifdef HAS_CLIENT_CERT_PATH
#ifdef UNICODE
#define CURL_CERT_STORE_PROV_SYSTEM CERT_STORE_PROV_SYSTEM_W
#else
#define CURL_CERT_STORE_PROV_SYSTEM CERT_STORE_PROV_SYSTEM_A
#endif
#endif

#ifndef SP_PROT_SSL2_CLIENT
#define SP_PROT_SSL2_CLIENT             0x00000008
#endif

#ifndef SP_PROT_SSL3_CLIENT
#define SP_PROT_SSL3_CLIENT             0x00000008
#endif

#ifndef SP_PROT_TLS1_CLIENT
#define SP_PROT_TLS1_CLIENT             0x00000080
#endif

#ifndef SP_PROT_TLS1_0_CLIENT
#define SP_PROT_TLS1_0_CLIENT           SP_PROT_TLS1_CLIENT
#endif

#ifndef SP_PROT_TLS1_1_CLIENT
#define SP_PROT_TLS1_1_CLIENT           0x00000200
#endif

#ifndef SP_PROT_TLS1_2_CLIENT
#define SP_PROT_TLS1_2_CLIENT           0x00000800
#endif

#ifndef SECBUFFER_ALERT
#define SECBUFFER_ALERT                 17
#endif

/* Both schannel buffer sizes must be > 0 */
#define CURL_SCHANNEL_BUFFER_INIT_SIZE   4096
#define CURL_SCHANNEL_BUFFER_FREE_SIZE   1024

#define CERT_THUMBPRINT_STR_LEN 40
#define CERT_THUMBPRINT_DATA_LEN 20

/* Uncomment to force verbose output
 * #define infof(x, y, ...) printf(y, __VA_ARGS__)
 * #define failf(x, y, ...) printf(y, __VA_ARGS__)
 */

#ifndef CALG_SHA_256
#  define CALG_SHA_256 0x0000800c
#endif

#define BACKEND connssl->backend

static Curl_recv schannel_recv;
static Curl_send schannel_send;

static CURLcode pkp_pin_peer_pubkey(struct connectdata *conn, int sockindex,
                                    const char *pinnedpubkey);

static void InitSecBuffer(SecBuffer *buffer, unsigned long BufType,
                          void *BufDataPtr, unsigned long BufByteSize)
{
  buffer->cbBuffer = BufByteSize;
  buffer->BufferType = BufType;
  buffer->pvBuffer = BufDataPtr;
}

static void InitSecBufferDesc(SecBufferDesc *desc, SecBuffer *BufArr,
                              unsigned long NumArrElem)
{
  desc->ulVersion = SECBUFFER_VERSION;
  desc->pBuffers = BufArr;
  desc->cBuffers = NumArrElem;
}

static CURLcode
set_ssl_version_min_max(SCHANNEL_CRED *schannel_cred, struct connectdata *conn)
{
  struct Curl_easy *data = conn->data;
  long ssl_version = SSL_CONN_CONFIG(version);
  long ssl_version_max = SSL_CONN_CONFIG(version_max);
  long i = ssl_version;

  switch(ssl_version_max) {
    case CURL_SSLVERSION_MAX_NONE:
    case CURL_SSLVERSION_MAX_DEFAULT:
      ssl_version_max = CURL_SSLVERSION_MAX_TLSv1_2;
      break;
  }
  for(; i <= (ssl_version_max >> 16); ++i) {
    switch(i) {
      case CURL_SSLVERSION_TLSv1_0:
        schannel_cred->grbitEnabledProtocols |= SP_PROT_TLS1_0_CLIENT;
        break;
      case CURL_SSLVERSION_TLSv1_1:
        schannel_cred->grbitEnabledProtocols |= SP_PROT_TLS1_1_CLIENT;
        break;
      case CURL_SSLVERSION_TLSv1_2:
        schannel_cred->grbitEnabledProtocols |= SP_PROT_TLS1_2_CLIENT;
        break;
      case CURL_SSLVERSION_TLSv1_3:
        failf(data, "schannel: TLS 1.3 is not yet supported");
        return CURLE_SSL_CONNECT_ERROR;
    }
  }
  return CURLE_OK;
}

/*longest is 26, buffer is slightly bigger*/
#define LONGEST_ALG_ID 32
#define CIPHEROPTION(X) \
if(strcmp(#X, tmp) == 0) \
  return X

static int
get_alg_id_by_name(char *name)
{
  char tmp[LONGEST_ALG_ID] = { 0 };
  char *nameEnd = strchr(name, ':');
  size_t n = nameEnd ? min((size_t)(nameEnd - name), LONGEST_ALG_ID - 1) : \
    min(strlen(name), LONGEST_ALG_ID - 1);
  strncpy(tmp, name, n);
  tmp[n] = 0;
  CIPHEROPTION(CALG_MD2);
  CIPHEROPTION(CALG_MD4);
  CIPHEROPTION(CALG_MD5);
  CIPHEROPTION(CALG_SHA);
  CIPHEROPTION(CALG_SHA1);
  CIPHEROPTION(CALG_MAC);
  CIPHEROPTION(CALG_RSA_SIGN);
  CIPHEROPTION(CALG_DSS_SIGN);
/*ifdefs for the options that are defined conditionally in wincrypt.h*/
#ifdef CALG_NO_SIGN
  CIPHEROPTION(CALG_NO_SIGN);
#endif
  CIPHEROPTION(CALG_RSA_KEYX);
  CIPHEROPTION(CALG_DES);
#ifdef CALG_3DES_112
  CIPHEROPTION(CALG_3DES_112);
#endif
  CIPHEROPTION(CALG_3DES);
  CIPHEROPTION(CALG_DESX);
  CIPHEROPTION(CALG_RC2);
  CIPHEROPTION(CALG_RC4);
  CIPHEROPTION(CALG_SEAL);
#ifdef CALG_DH_SF
  CIPHEROPTION(CALG_DH_SF);
#endif
  CIPHEROPTION(CALG_DH_EPHEM);
#ifdef CALG_AGREEDKEY_ANY
  CIPHEROPTION(CALG_AGREEDKEY_ANY);
#endif
#ifdef CALG_HUGHES_MD5
  CIPHEROPTION(CALG_HUGHES_MD5);
#endif
  CIPHEROPTION(CALG_SKIPJACK);
#ifdef CALG_TEK
  CIPHEROPTION(CALG_TEK);
#endif
  CIPHEROPTION(CALG_CYLINK_MEK);
  CIPHEROPTION(CALG_SSL3_SHAMD5);
#ifdef CALG_SSL3_MASTER
  CIPHEROPTION(CALG_SSL3_MASTER);
#endif
#ifdef CALG_SCHANNEL_MASTER_HASH
  CIPHEROPTION(CALG_SCHANNEL_MASTER_HASH);
#endif
#ifdef CALG_SCHANNEL_MAC_KEY
  CIPHEROPTION(CALG_SCHANNEL_MAC_KEY);
#endif
#ifdef CALG_SCHANNEL_ENC_KEY
  CIPHEROPTION(CALG_SCHANNEL_ENC_KEY);
#endif
#ifdef CALG_PCT1_MASTER
  CIPHEROPTION(CALG_PCT1_MASTER);
#endif
#ifdef CALG_SSL2_MASTER
  CIPHEROPTION(CALG_SSL2_MASTER);
#endif
#ifdef CALG_TLS1_MASTER
  CIPHEROPTION(CALG_TLS1_MASTER);
#endif
#ifdef CALG_RC5
  CIPHEROPTION(CALG_RC5);
#endif
#ifdef CALG_HMAC
  CIPHEROPTION(CALG_HMAC);
#endif
#if !defined(__W32API_MAJOR_VERSION) || \
    !defined(__W32API_MINOR_VERSION) || \
    defined(__MINGW64_VERSION_MAJOR) || \
    (__W32API_MAJOR_VERSION > 5)     || \
    ((__W32API_MAJOR_VERSION == 5) && (__W32API_MINOR_VERSION > 0))
  /* CALG_TLS1PRF has a syntax error in MinGW's w32api up to version 5.0,
     see https://osdn.net/projects/mingw/ticket/38391 */
  CIPHEROPTION(CALG_TLS1PRF);
#endif
#ifdef CALG_HASH_REPLACE_OWF
  CIPHEROPTION(CALG_HASH_REPLACE_OWF);
#endif
#ifdef CALG_AES_128
  CIPHEROPTION(CALG_AES_128);
#endif
#ifdef CALG_AES_192
  CIPHEROPTION(CALG_AES_192);
#endif
#ifdef CALG_AES_256
  CIPHEROPTION(CALG_AES_256);
#endif
#ifdef CALG_AES
  CIPHEROPTION(CALG_AES);
#endif
#ifdef CALG_SHA_256
  CIPHEROPTION(CALG_SHA_256);
#endif
#ifdef CALG_SHA_384
  CIPHEROPTION(CALG_SHA_384);
#endif
#ifdef CALG_SHA_512
  CIPHEROPTION(CALG_SHA_512);
#endif
#ifdef CALG_ECDH
  CIPHEROPTION(CALG_ECDH);
#endif
#ifdef CALG_ECMQV
  CIPHEROPTION(CALG_ECMQV);
#endif
#ifdef CALG_ECDSA
  CIPHEROPTION(CALG_ECDSA);
#endif
#ifdef CALG_ECDH_EPHEM
  CIPHEROPTION(CALG_ECDH_EPHEM);
#endif
  return 0;
}

static CURLcode
set_ssl_ciphers(SCHANNEL_CRED *schannel_cred, char *ciphers)
{
  char *startCur = ciphers;
  int algCount = 0;
  static ALG_ID algIds[45]; /*There are 45 listed in the MS headers*/
  while(startCur && (0 != *startCur) && (algCount < 45)) {
    long alg = strtol(startCur, 0, 0);
    if(!alg)
      alg = get_alg_id_by_name(startCur);
    if(alg)
      algIds[algCount++] = alg;
    else
      return CURLE_SSL_CIPHER;
    startCur = strchr(startCur, ':');
    if(startCur)
      startCur++;
  }
    schannel_cred->palgSupportedAlgs = algIds;
  schannel_cred->cSupportedAlgs = algCount;
  return CURLE_OK;
}

#ifdef HAS_CLIENT_CERT_PATH
static CURLcode
get_cert_location(TCHAR *path, DWORD *store_name, TCHAR **store_path,
                  TCHAR **thumbprint)
{
  TCHAR *sep;
  TCHAR *store_path_start;
  size_t store_name_len;

  sep = _tcschr(path, TEXT('\\'));
  if(sep == NULL)
    return CURLE_SSL_CERTPROBLEM;

  store_name_len = sep - path;

  if(_tcsnccmp(path, TEXT("CurrentUser"), store_name_len) == 0)
    *store_name = CERT_SYSTEM_STORE_CURRENT_USER;
  else if(_tcsnccmp(path, TEXT("LocalMachine"), store_name_len) == 0)
    *store_name = CERT_SYSTEM_STORE_LOCAL_MACHINE;
  else if(_tcsnccmp(path, TEXT("CurrentService"), store_name_len) == 0)
    *store_name = CERT_SYSTEM_STORE_CURRENT_SERVICE;
  else if(_tcsnccmp(path, TEXT("Services"), store_name_len) == 0)
    *store_name = CERT_SYSTEM_STORE_SERVICES;
  else if(_tcsnccmp(path, TEXT("Users"), store_name_len) == 0)
    *store_name = CERT_SYSTEM_STORE_USERS;
  else if(_tcsnccmp(path, TEXT("CurrentUserGroupPolicy"),
                    store_name_len) == 0)
    *store_name = CERT_SYSTEM_STORE_CURRENT_USER_GROUP_POLICY;
  else if(_tcsnccmp(path, TEXT("LocalMachineGroupPolicy"),
                    store_name_len) == 0)
    *store_name = CERT_SYSTEM_STORE_LOCAL_MACHINE_GROUP_POLICY;
  else if(_tcsnccmp(path, TEXT("LocalMachineEnterprise"),
                    store_name_len) == 0)
    *store_name = CERT_SYSTEM_STORE_LOCAL_MACHINE_ENTERPRISE;
  else
    return CURLE_SSL_CERTPROBLEM;

  store_path_start = sep + 1;

  sep = _tcschr(store_path_start, TEXT('\\'));
  if(sep == NULL)
    return CURLE_SSL_CERTPROBLEM;

  *sep = TEXT('\0');
  *store_path = _tcsdup(store_path_start);
  *sep = TEXT('\\');
  if(*store_path == NULL)
    return CURLE_OUT_OF_MEMORY;

  *thumbprint = sep + 1;
  if(_tcslen(*thumbprint) != CERT_THUMBPRINT_STR_LEN)
    return CURLE_SSL_CERTPROBLEM;

  return CURLE_OK;
}
#endif

static CURLcode
schannel_connect_step1(struct connectdata *conn, int sockindex)
{
  ssize_t written = -1;
  struct Curl_easy *data = conn->data;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  SecBuffer outbuf;
  SecBufferDesc outbuf_desc;
  SecBuffer inbuf;
  SecBufferDesc inbuf_desc;
#ifdef HAS_ALPN
  unsigned char alpn_buffer[128];
#endif
  SCHANNEL_CRED schannel_cred;
  PCCERT_CONTEXT client_certs[1] = { NULL };
  SECURITY_STATUS sspi_status = SEC_E_OK;
  struct curl_schannel_cred *old_cred = NULL;
  struct in_addr addr;
#ifdef ENABLE_IPV6
  struct in6_addr addr6;
#endif
  TCHAR *host_name;
  CURLcode result;
  char * const hostname = SSL_IS_PROXY() ? conn->http_proxy.host.name :
    conn->host.name;

  DEBUGF(infof(data,
               "schannel: SSL/TLS connection with %s port %hu (step 1/3)\n",
               hostname, conn->remote_port));

  if(Curl_verify_windows_version(5, 1, PLATFORM_WINNT,
                                 VERSION_LESS_THAN_EQUAL)) {
     /* Schannel in Windows XP (OS version 5.1) uses legacy handshakes and
        algorithms that may not be supported by all servers. */
     infof(data, "schannel: Windows version is old and may not be able to "
           "connect to some servers due to lack of SNI, algorithms, etc.\n");
  }

#ifdef HAS_ALPN
  /* ALPN is only supported on Windows 8.1 / Server 2012 R2 and above.
     Also it doesn't seem to be supported for Wine, see curl bug #983. */
  BACKEND->use_alpn = conn->bits.tls_enable_alpn &&
                      !GetProcAddress(GetModuleHandleA("ntdll"),
                                      "wine_get_version") &&
                      Curl_verify_windows_version(6, 3, PLATFORM_WINNT,
                                                  VERSION_GREATER_THAN_EQUAL);
#else
  BACKEND->use_alpn = false;
#endif

#ifdef _WIN32_WCE
#ifdef HAS_MANUAL_VERIFY_API
  /* certificate validation on CE doesn't seem to work right; we'll
   * do it following a more manual process. */
  BACKEND->use_manual_cred_validation = true;
#else
#error "compiler too old to support requisite manual cert verify for Win CE"
#endif
#else
#ifdef HAS_MANUAL_VERIFY_API
  if(SSL_CONN_CONFIG(CAfile)) {
    if(Curl_verify_windows_version(6, 1, PLATFORM_WINNT,
                                   VERSION_GREATER_THAN_EQUAL)) {
      BACKEND->use_manual_cred_validation = true;
    }
    else {
      failf(data, "schannel: this version of Windows is too old to support "
            "certificate verification via CA bundle file.");
      return CURLE_SSL_CACERT_BADFILE;
    }
  }
  else
    BACKEND->use_manual_cred_validation = false;
#else
  if(SSL_CONN_CONFIG(CAfile)) {
    failf(data, "schannel: CA cert support not built in");
    return CURLE_NOT_BUILT_IN;
  }
#endif
#endif

  BACKEND->cred = NULL;

  /* check for an existing re-usable credential handle */
  if(SSL_SET_OPTION(primary.sessionid)) {
    Curl_ssl_sessionid_lock(conn);
    if(!Curl_ssl_getsessionid(conn, (void **)&old_cred, NULL, sockindex)) {
      BACKEND->cred = old_cred;
      DEBUGF(infof(data, "schannel: re-using existing credential handle\n"));

      /* increment the reference counter of the credential/session handle */
      BACKEND->cred->refcount++;
      DEBUGF(infof(data,
                   "schannel: incremented credential handle refcount = %d\n",
                   BACKEND->cred->refcount));
    }
    Curl_ssl_sessionid_unlock(conn);
  }

  if(!BACKEND->cred) {
    /* setup Schannel API options */
    memset(&schannel_cred, 0, sizeof(schannel_cred));
    schannel_cred.dwVersion = SCHANNEL_CRED_VERSION;

    if(conn->ssl_config.verifypeer) {
#ifdef HAS_MANUAL_VERIFY_API
      if(BACKEND->use_manual_cred_validation)
        schannel_cred.dwFlags = SCH_CRED_MANUAL_CRED_VALIDATION;
      else
#endif
        schannel_cred.dwFlags = SCH_CRED_AUTO_CRED_VALIDATION;

      /* TODO s/data->set.ssl.no_revoke/SSL_SET_OPTION(no_revoke)/g */
      if(data->set.ssl.no_revoke) {
        schannel_cred.dwFlags |= SCH_CRED_IGNORE_NO_REVOCATION_CHECK |
          SCH_CRED_IGNORE_REVOCATION_OFFLINE;

        DEBUGF(infof(data, "schannel: disabled server certificate revocation "
                     "checks\n"));
      }
      else {
        schannel_cred.dwFlags |= SCH_CRED_REVOCATION_CHECK_CHAIN;
        DEBUGF(infof(data,
                     "schannel: checking server certificate revocation\n"));
      }
    }
    else {
      schannel_cred.dwFlags = SCH_CRED_MANUAL_CRED_VALIDATION |
        SCH_CRED_IGNORE_NO_REVOCATION_CHECK |
        SCH_CRED_IGNORE_REVOCATION_OFFLINE;
      DEBUGF(infof(data,
                   "schannel: disabled server cert revocation checks\n"));
    }

    if(!conn->ssl_config.verifyhost) {
      schannel_cred.dwFlags |= SCH_CRED_NO_SERVERNAME_CHECK;
      DEBUGF(infof(data, "schannel: verifyhost setting prevents Schannel from "
                   "comparing the supplied target name with the subject "
                   "names in server certificates.\n"));
    }

    switch(conn->ssl_config.version) {
    case CURL_SSLVERSION_DEFAULT:
    case CURL_SSLVERSION_TLSv1:
      schannel_cred.grbitEnabledProtocols = SP_PROT_TLS1_0_CLIENT |
        SP_PROT_TLS1_1_CLIENT |
        SP_PROT_TLS1_2_CLIENT;
      break;
    case CURL_SSLVERSION_TLSv1_0:
    case CURL_SSLVERSION_TLSv1_1:
    case CURL_SSLVERSION_TLSv1_2:
    case CURL_SSLVERSION_TLSv1_3:
      {
        result = set_ssl_version_min_max(&schannel_cred, conn);
        if(result != CURLE_OK)
          return result;
        break;
      }
    case CURL_SSLVERSION_SSLv3:
      schannel_cred.grbitEnabledProtocols = SP_PROT_SSL3_CLIENT;
      break;
    case CURL_SSLVERSION_SSLv2:
      schannel_cred.grbitEnabledProtocols = SP_PROT_SSL2_CLIENT;
      break;
    default:
      failf(data, "Unrecognized parameter passed via CURLOPT_SSLVERSION");
      return CURLE_SSL_CONNECT_ERROR;
    }

    if(SSL_CONN_CONFIG(cipher_list)) {
      result = set_ssl_ciphers(&schannel_cred, SSL_CONN_CONFIG(cipher_list));
      if(CURLE_OK != result) {
        failf(data, "Unable to set ciphers to passed via SSL_CONN_CONFIG");
        return result;
      }
    }


#ifdef HAS_CLIENT_CERT_PATH
    /* client certificate */
    if(data->set.ssl.cert) {
      DWORD cert_store_name;
      TCHAR *cert_store_path;
      TCHAR *cert_thumbprint_str;
      CRYPT_HASH_BLOB cert_thumbprint;
      BYTE cert_thumbprint_data[CERT_THUMBPRINT_DATA_LEN];
      HCERTSTORE cert_store;

      TCHAR *cert_path = Curl_convert_UTF8_to_tchar(data->set.ssl.cert);
      if(!cert_path)
        return CURLE_OUT_OF_MEMORY;

      result = get_cert_location(cert_path, &cert_store_name,
                                 &cert_store_path, &cert_thumbprint_str);
      if(result != CURLE_OK) {
        failf(data, "schannel: Failed to get certificate location for %s",
              cert_path);
        Curl_unicodefree(cert_path);
        return result;
      }

      cert_store =
        CertOpenStore(CURL_CERT_STORE_PROV_SYSTEM, 0,
                      (HCRYPTPROV)NULL,
                      CERT_STORE_OPEN_EXISTING_FLAG | cert_store_name,
                      cert_store_path);
      if(!cert_store) {
        failf(data, "schannel: Failed to open cert store %x %s, "
              "last error is %x",
              cert_store_name, cert_store_path, GetLastError());
        free(cert_store_path);
        Curl_unicodefree(cert_path);
        return CURLE_SSL_CERTPROBLEM;
      }
      free(cert_store_path);

      cert_thumbprint.pbData = cert_thumbprint_data;
      cert_thumbprint.cbData = CERT_THUMBPRINT_DATA_LEN;

      if(!CryptStringToBinary(cert_thumbprint_str, CERT_THUMBPRINT_STR_LEN,
                              CRYPT_STRING_HEX,
                              cert_thumbprint_data, &cert_thumbprint.cbData,
                              NULL, NULL)) {
        Curl_unicodefree(cert_path);
        return CURLE_SSL_CERTPROBLEM;
      }

      client_certs[0] = CertFindCertificateInStore(
        cert_store, X509_ASN_ENCODING | PKCS_7_ASN_ENCODING, 0,
        CERT_FIND_HASH, &cert_thumbprint, NULL);

      Curl_unicodefree(cert_path);

      if(client_certs[0]) {
        schannel_cred.cCreds = 1;
        schannel_cred.paCred = client_certs;
      }
      else {
        /* CRYPT_E_NOT_FOUND / E_INVALIDARG */
        return CURLE_SSL_CERTPROBLEM;
      }

      CertCloseStore(cert_store, 0);
    }
#else
    if(data->set.ssl.cert) {
      failf(data, "schannel: client cert support not built in");
      return CURLE_NOT_BUILT_IN;
    }
#endif

    /* allocate memory for the re-usable credential handle */
    BACKEND->cred = (struct curl_schannel_cred *)
      calloc(1, sizeof(struct curl_schannel_cred));
    if(!BACKEND->cred) {
      failf(data, "schannel: unable to allocate memory");

      if(client_certs[0])
        CertFreeCertificateContext(client_certs[0]);

      return CURLE_OUT_OF_MEMORY;
    }
    BACKEND->cred->refcount = 1;

    /* https://msdn.microsoft.com/en-us/library/windows/desktop/aa374716.aspx
       */
    sspi_status =
      s_pSecFn->AcquireCredentialsHandle(NULL, (TCHAR *)UNISP_NAME,
                                         SECPKG_CRED_OUTBOUND, NULL,
                                         &schannel_cred, NULL, NULL,
                                         &BACKEND->cred->cred_handle,
                                         &BACKEND->cred->time_stamp);

    if(client_certs[0])
      CertFreeCertificateContext(client_certs[0]);

    if(sspi_status != SEC_E_OK) {
      char buffer[STRERROR_LEN];
      failf(data, "schannel: AcquireCredentialsHandle failed: %s",
            Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
      Curl_safefree(BACKEND->cred);
      switch(sspi_status) {
        case SEC_E_INSUFFICIENT_MEMORY:
          return CURLE_OUT_OF_MEMORY;
        case SEC_E_NO_CREDENTIALS:
        case SEC_E_SECPKG_NOT_FOUND:
        case SEC_E_NOT_OWNER:
        case SEC_E_UNKNOWN_CREDENTIALS:
        case SEC_E_INTERNAL_ERROR:
        default:
          return CURLE_SSL_CONNECT_ERROR;
      }
    }
  }

  /* Warn if SNI is disabled due to use of an IP address */
  if(Curl_inet_pton(AF_INET, hostname, &addr)
#ifdef ENABLE_IPV6
     || Curl_inet_pton(AF_INET6, hostname, &addr6)
#endif
    ) {
    infof(data, "schannel: using IP address, SNI is not supported by OS.\n");
  }

#ifdef HAS_ALPN
  if(BACKEND->use_alpn) {
    int cur = 0;
    int list_start_index = 0;
    unsigned int *extension_len = NULL;
    unsigned short* list_len = NULL;

    /* The first four bytes will be an unsigned int indicating number
       of bytes of data in the rest of the the buffer. */
    extension_len = (unsigned int *)(&alpn_buffer[cur]);
    cur += sizeof(unsigned int);

    /* The next four bytes are an indicator that this buffer will contain
       ALPN data, as opposed to NPN, for example. */
    *(unsigned int *)&alpn_buffer[cur] =
      SecApplicationProtocolNegotiationExt_ALPN;
    cur += sizeof(unsigned int);

    /* The next two bytes will be an unsigned short indicating the number
       of bytes used to list the preferred protocols. */
    list_len = (unsigned short*)(&alpn_buffer[cur]);
    cur += sizeof(unsigned short);

    list_start_index = cur;

#ifdef USE_NGHTTP2
    if(data->set.httpversion >= CURL_HTTP_VERSION_2) {
      memcpy(&alpn_buffer[cur], NGHTTP2_PROTO_ALPN, NGHTTP2_PROTO_ALPN_LEN);
      cur += NGHTTP2_PROTO_ALPN_LEN;
      infof(data, "schannel: ALPN, offering %s\n", NGHTTP2_PROTO_VERSION_ID);
    }
#endif

    alpn_buffer[cur++] = ALPN_HTTP_1_1_LENGTH;
    memcpy(&alpn_buffer[cur], ALPN_HTTP_1_1, ALPN_HTTP_1_1_LENGTH);
    cur += ALPN_HTTP_1_1_LENGTH;
    infof(data, "schannel: ALPN, offering %s\n", ALPN_HTTP_1_1);

    *list_len = curlx_uitous(cur - list_start_index);
    *extension_len = *list_len + sizeof(unsigned int) + sizeof(unsigned short);

    InitSecBuffer(&inbuf, SECBUFFER_APPLICATION_PROTOCOLS, alpn_buffer, cur);
    InitSecBufferDesc(&inbuf_desc, &inbuf, 1);
  }
  else {
    InitSecBuffer(&inbuf, SECBUFFER_EMPTY, NULL, 0);
    InitSecBufferDesc(&inbuf_desc, &inbuf, 1);
  }
#else /* HAS_ALPN */
  InitSecBuffer(&inbuf, SECBUFFER_EMPTY, NULL, 0);
  InitSecBufferDesc(&inbuf_desc, &inbuf, 1);
#endif

  /* setup output buffer */
  InitSecBuffer(&outbuf, SECBUFFER_EMPTY, NULL, 0);
  InitSecBufferDesc(&outbuf_desc, &outbuf, 1);

  /* setup request flags */
  BACKEND->req_flags = ISC_REQ_SEQUENCE_DETECT | ISC_REQ_REPLAY_DETECT |
    ISC_REQ_CONFIDENTIALITY | ISC_REQ_ALLOCATE_MEMORY |
    ISC_REQ_STREAM;

  /* allocate memory for the security context handle */
  BACKEND->ctxt = (struct curl_schannel_ctxt *)
    calloc(1, sizeof(struct curl_schannel_ctxt));
  if(!BACKEND->ctxt) {
    failf(data, "schannel: unable to allocate memory");
    return CURLE_OUT_OF_MEMORY;
  }

  host_name = Curl_convert_UTF8_to_tchar(hostname);
  if(!host_name)
    return CURLE_OUT_OF_MEMORY;

  /* Schannel InitializeSecurityContext:
     https://msdn.microsoft.com/en-us/library/windows/desktop/aa375924.aspx

     At the moment we don't pass inbuf unless we're using ALPN since we only
     use it for that, and Wine (for which we currently disable ALPN) is giving
     us problems with inbuf regardless. https://github.com/curl/curl/issues/983
  */
  sspi_status = s_pSecFn->InitializeSecurityContext(
    &BACKEND->cred->cred_handle, NULL, host_name, BACKEND->req_flags, 0, 0,
    (BACKEND->use_alpn ? &inbuf_desc : NULL),
    0, &BACKEND->ctxt->ctxt_handle,
    &outbuf_desc, &BACKEND->ret_flags, &BACKEND->ctxt->time_stamp);

  Curl_unicodefree(host_name);

  if(sspi_status != SEC_I_CONTINUE_NEEDED) {
    char buffer[STRERROR_LEN];
    Curl_safefree(BACKEND->ctxt);
    switch(sspi_status) {
      case SEC_E_INSUFFICIENT_MEMORY:
        failf(data, "schannel: initial InitializeSecurityContext failed: %s",
              Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
        return CURLE_OUT_OF_MEMORY;
      case SEC_E_WRONG_PRINCIPAL:
        failf(data, "schannel: SNI or certificate check failed: %s",
              Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
        return CURLE_PEER_FAILED_VERIFICATION;
        /*
      case SEC_E_INVALID_HANDLE:
      case SEC_E_INVALID_TOKEN:
      case SEC_E_LOGON_DENIED:
      case SEC_E_TARGET_UNKNOWN:
      case SEC_E_NO_AUTHENTICATING_AUTHORITY:
      case SEC_E_INTERNAL_ERROR:
      case SEC_E_NO_CREDENTIALS:
      case SEC_E_UNSUPPORTED_FUNCTION:
      case SEC_E_APPLICATION_PROTOCOL_MISMATCH:
        */
      default:
        failf(data, "schannel: initial InitializeSecurityContext failed: %s",
              Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
        return CURLE_SSL_CONNECT_ERROR;
    }
  }

  DEBUGF(infof(data, "schannel: sending initial handshake data: "
               "sending %lu bytes...\n", outbuf.cbBuffer));

  /* send initial handshake data which is now stored in output buffer */
  result = Curl_write_plain(conn, conn->sock[sockindex], outbuf.pvBuffer,
                            outbuf.cbBuffer, &written);
  s_pSecFn->FreeContextBuffer(outbuf.pvBuffer);
  if((result != CURLE_OK) || (outbuf.cbBuffer != (size_t) written)) {
    failf(data, "schannel: failed to send initial handshake data: "
          "sent %zd of %lu bytes", written, outbuf.cbBuffer);
    return CURLE_SSL_CONNECT_ERROR;
  }

  DEBUGF(infof(data, "schannel: sent initial handshake data: "
               "sent %zd bytes\n", written));

  BACKEND->recv_unrecoverable_err = CURLE_OK;
  BACKEND->recv_sspi_close_notify = false;
  BACKEND->recv_connection_closed = false;
  BACKEND->encdata_is_incomplete = false;

  /* continue to second handshake step */
  connssl->connecting_state = ssl_connect_2;

  return CURLE_OK;
}

static CURLcode
schannel_connect_step2(struct connectdata *conn, int sockindex)
{
  int i;
  ssize_t nread = -1, written = -1;
  struct Curl_easy *data = conn->data;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  unsigned char *reallocated_buffer;
  size_t reallocated_length;
  SecBuffer outbuf[3];
  SecBufferDesc outbuf_desc;
  SecBuffer inbuf[2];
  SecBufferDesc inbuf_desc;
  SECURITY_STATUS sspi_status = SEC_E_OK;
  TCHAR *host_name;
  CURLcode result;
  bool doread;
  char * const hostname = SSL_IS_PROXY() ? conn->http_proxy.host.name :
    conn->host.name;
  const char *pubkey_ptr;

  doread = (connssl->connecting_state != ssl_connect_2_writing) ? TRUE : FALSE;

  DEBUGF(infof(data,
               "schannel: SSL/TLS connection with %s port %hu (step 2/3)\n",
               hostname, conn->remote_port));

  if(!BACKEND->cred || !BACKEND->ctxt)
    return CURLE_SSL_CONNECT_ERROR;

  /* buffer to store previously received and decrypted data */
  if(BACKEND->decdata_buffer == NULL) {
    BACKEND->decdata_offset = 0;
    BACKEND->decdata_length = CURL_SCHANNEL_BUFFER_INIT_SIZE;
    BACKEND->decdata_buffer = malloc(BACKEND->decdata_length);
    if(BACKEND->decdata_buffer == NULL) {
      failf(data, "schannel: unable to allocate memory");
      return CURLE_OUT_OF_MEMORY;
    }
  }

  /* buffer to store previously received and encrypted data */
  if(BACKEND->encdata_buffer == NULL) {
    BACKEND->encdata_is_incomplete = false;
    BACKEND->encdata_offset = 0;
    BACKEND->encdata_length = CURL_SCHANNEL_BUFFER_INIT_SIZE;
    BACKEND->encdata_buffer = malloc(BACKEND->encdata_length);
    if(BACKEND->encdata_buffer == NULL) {
      failf(data, "schannel: unable to allocate memory");
      return CURLE_OUT_OF_MEMORY;
    }
  }

  /* if we need a bigger buffer to read a full message, increase buffer now */
  if(BACKEND->encdata_length - BACKEND->encdata_offset <
     CURL_SCHANNEL_BUFFER_FREE_SIZE) {
    /* increase internal encrypted data buffer */
    reallocated_length = BACKEND->encdata_offset +
      CURL_SCHANNEL_BUFFER_FREE_SIZE;
    reallocated_buffer = realloc(BACKEND->encdata_buffer,
                                 reallocated_length);

    if(reallocated_buffer == NULL) {
      failf(data, "schannel: unable to re-allocate memory");
      return CURLE_OUT_OF_MEMORY;
    }
    else {
      BACKEND->encdata_buffer = reallocated_buffer;
      BACKEND->encdata_length = reallocated_length;
    }
  }

  for(;;) {
    if(doread) {
      /* read encrypted handshake data from socket */
      result = Curl_read_plain(conn->sock[sockindex],
                               (char *) (BACKEND->encdata_buffer +
                                         BACKEND->encdata_offset),
                               BACKEND->encdata_length -
                               BACKEND->encdata_offset,
                               &nread);
      if(result == CURLE_AGAIN) {
        if(connssl->connecting_state != ssl_connect_2_writing)
          connssl->connecting_state = ssl_connect_2_reading;
        DEBUGF(infof(data, "schannel: failed to receive handshake, "
                     "need more data\n"));
        return CURLE_OK;
      }
      else if((result != CURLE_OK) || (nread == 0)) {
        failf(data, "schannel: failed to receive handshake, "
              "SSL/TLS connection failed");
        return CURLE_SSL_CONNECT_ERROR;
      }

      /* increase encrypted data buffer offset */
      BACKEND->encdata_offset += nread;
      BACKEND->encdata_is_incomplete = false;
      DEBUGF(infof(data, "schannel: encrypted data got %zd\n", nread));
    }

    DEBUGF(infof(data,
                 "schannel: encrypted data buffer: offset %zu length %zu\n",
                 BACKEND->encdata_offset, BACKEND->encdata_length));

    /* setup input buffers */
    InitSecBuffer(&inbuf[0], SECBUFFER_TOKEN, malloc(BACKEND->encdata_offset),
                  curlx_uztoul(BACKEND->encdata_offset));
    InitSecBuffer(&inbuf[1], SECBUFFER_EMPTY, NULL, 0);
    InitSecBufferDesc(&inbuf_desc, inbuf, 2);

    /* setup output buffers */
    InitSecBuffer(&outbuf[0], SECBUFFER_TOKEN, NULL, 0);
    InitSecBuffer(&outbuf[1], SECBUFFER_ALERT, NULL, 0);
    InitSecBuffer(&outbuf[2], SECBUFFER_EMPTY, NULL, 0);
    InitSecBufferDesc(&outbuf_desc, outbuf, 3);

    if(inbuf[0].pvBuffer == NULL) {
      failf(data, "schannel: unable to allocate memory");
      return CURLE_OUT_OF_MEMORY;
    }

    /* copy received handshake data into input buffer */
    memcpy(inbuf[0].pvBuffer, BACKEND->encdata_buffer,
           BACKEND->encdata_offset);

    host_name = Curl_convert_UTF8_to_tchar(hostname);
    if(!host_name)
      return CURLE_OUT_OF_MEMORY;

    /* https://msdn.microsoft.com/en-us/library/windows/desktop/aa375924.aspx
       */
    sspi_status = s_pSecFn->InitializeSecurityContext(
      &BACKEND->cred->cred_handle, &BACKEND->ctxt->ctxt_handle,
      host_name, BACKEND->req_flags, 0, 0, &inbuf_desc, 0, NULL,
      &outbuf_desc, &BACKEND->ret_flags, &BACKEND->ctxt->time_stamp);

    Curl_unicodefree(host_name);

    /* free buffer for received handshake data */
    Curl_safefree(inbuf[0].pvBuffer);

    /* check if the handshake was incomplete */
    if(sspi_status == SEC_E_INCOMPLETE_MESSAGE) {
      BACKEND->encdata_is_incomplete = true;
      connssl->connecting_state = ssl_connect_2_reading;
      DEBUGF(infof(data,
                   "schannel: received incomplete message, need more data\n"));
      return CURLE_OK;
    }

    /* If the server has requested a client certificate, attempt to continue
       the handshake without one. This will allow connections to servers which
       request a client certificate but do not require it. */
    if(sspi_status == SEC_I_INCOMPLETE_CREDENTIALS &&
       !(BACKEND->req_flags & ISC_REQ_USE_SUPPLIED_CREDS)) {
      BACKEND->req_flags |= ISC_REQ_USE_SUPPLIED_CREDS;
      connssl->connecting_state = ssl_connect_2_writing;
      DEBUGF(infof(data,
                   "schannel: a client certificate has been requested\n"));
      return CURLE_OK;
    }

    /* check if the handshake needs to be continued */
    if(sspi_status == SEC_I_CONTINUE_NEEDED || sspi_status == SEC_E_OK) {
      for(i = 0; i < 3; i++) {
        /* search for handshake tokens that need to be send */
        if(outbuf[i].BufferType == SECBUFFER_TOKEN && outbuf[i].cbBuffer > 0) {
          DEBUGF(infof(data, "schannel: sending next handshake data: "
                       "sending %lu bytes...\n", outbuf[i].cbBuffer));

          /* send handshake token to server */
          result = Curl_write_plain(conn, conn->sock[sockindex],
                                    outbuf[i].pvBuffer, outbuf[i].cbBuffer,
                                    &written);
          if((result != CURLE_OK) ||
             (outbuf[i].cbBuffer != (size_t) written)) {
            failf(data, "schannel: failed to send next handshake data: "
                  "sent %zd of %lu bytes", written, outbuf[i].cbBuffer);
            return CURLE_SSL_CONNECT_ERROR;
          }
        }

        /* free obsolete buffer */
        if(outbuf[i].pvBuffer != NULL) {
          s_pSecFn->FreeContextBuffer(outbuf[i].pvBuffer);
        }
      }
    }
    else {
      char buffer[STRERROR_LEN];
      switch(sspi_status) {
        case SEC_E_INSUFFICIENT_MEMORY:
          failf(data, "schannel: next InitializeSecurityContext failed: %s",
                Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
          return CURLE_OUT_OF_MEMORY;
        case SEC_E_WRONG_PRINCIPAL:
          failf(data, "schannel: SNI or certificate check failed: %s",
                Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
          return CURLE_PEER_FAILED_VERIFICATION;
          /*
        case SEC_E_INVALID_HANDLE:
        case SEC_E_INVALID_TOKEN:
        case SEC_E_LOGON_DENIED:
        case SEC_E_TARGET_UNKNOWN:
        case SEC_E_NO_AUTHENTICATING_AUTHORITY:
        case SEC_E_INTERNAL_ERROR:
        case SEC_E_NO_CREDENTIALS:
        case SEC_E_UNSUPPORTED_FUNCTION:
        case SEC_E_APPLICATION_PROTOCOL_MISMATCH:
          */
        default:
          failf(data, "schannel: next InitializeSecurityContext failed: %s",
                Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
          return CURLE_SSL_CONNECT_ERROR;
      }
    }

    /* check if there was additional remaining encrypted data */
    if(inbuf[1].BufferType == SECBUFFER_EXTRA && inbuf[1].cbBuffer > 0) {
      DEBUGF(infof(data, "schannel: encrypted data length: %lu\n",
                   inbuf[1].cbBuffer));
      /*
        There are two cases where we could be getting extra data here:
        1) If we're renegotiating a connection and the handshake is already
        complete (from the server perspective), it can encrypted app data
        (not handshake data) in an extra buffer at this point.
        2) (sspi_status == SEC_I_CONTINUE_NEEDED) We are negotiating a
        connection and this extra data is part of the handshake.
        We should process the data immediately; waiting for the socket to
        be ready may fail since the server is done sending handshake data.
      */
      /* check if the remaining data is less than the total amount
         and therefore begins after the already processed data */
      if(BACKEND->encdata_offset > inbuf[1].cbBuffer) {
        memmove(BACKEND->encdata_buffer,
                (BACKEND->encdata_buffer + BACKEND->encdata_offset) -
                inbuf[1].cbBuffer, inbuf[1].cbBuffer);
        BACKEND->encdata_offset = inbuf[1].cbBuffer;
        if(sspi_status == SEC_I_CONTINUE_NEEDED) {
          doread = FALSE;
          continue;
        }
      }
    }
    else {
      BACKEND->encdata_offset = 0;
    }
    break;
  }

  /* check if the handshake needs to be continued */
  if(sspi_status == SEC_I_CONTINUE_NEEDED) {
    connssl->connecting_state = ssl_connect_2_reading;
    return CURLE_OK;
  }

  /* check if the handshake is complete */
  if(sspi_status == SEC_E_OK) {
    connssl->connecting_state = ssl_connect_3;
    DEBUGF(infof(data, "schannel: SSL/TLS handshake complete\n"));
  }

  pubkey_ptr = SSL_IS_PROXY() ?
    data->set.str[STRING_SSL_PINNEDPUBLICKEY_PROXY] :
    data->set.str[STRING_SSL_PINNEDPUBLICKEY_ORIG];
  if(pubkey_ptr) {
    result = pkp_pin_peer_pubkey(conn, sockindex, pubkey_ptr);
    if(result) {
      failf(data, "SSL: public key does not match pinned public key!");
      return result;
    }
  }

#ifdef HAS_MANUAL_VERIFY_API
  if(conn->ssl_config.verifypeer && BACKEND->use_manual_cred_validation) {
    return Curl_verify_certificate(conn, sockindex);
  }
#endif

  return CURLE_OK;
}

static bool
valid_cert_encoding(const CERT_CONTEXT *cert_context)
{
  return (cert_context != NULL) &&
    ((cert_context->dwCertEncodingType & X509_ASN_ENCODING) != 0) &&
    (cert_context->pbCertEncoded != NULL) &&
    (cert_context->cbCertEncoded > 0);
}

typedef bool(*Read_crt_func)(const CERT_CONTEXT *ccert_context, void *arg);

static void
traverse_cert_store(const CERT_CONTEXT *context, Read_crt_func func,
                    void *arg)
{
  const CERT_CONTEXT *current_context = NULL;
  bool should_continue = true;
  while(should_continue &&
        (current_context = CertEnumCertificatesInStore(
          context->hCertStore,
          current_context)) != NULL)
    should_continue = func(current_context, arg);

  if(current_context)
    CertFreeCertificateContext(current_context);
}

static bool
cert_counter_callback(const CERT_CONTEXT *ccert_context, void *certs_count)
{
  if(valid_cert_encoding(ccert_context))
    (*(int *)certs_count)++;
  return true;
}

struct Adder_args
{
  struct connectdata *conn;
  CURLcode result;
  int idx;
};

static bool
add_cert_to_certinfo(const CERT_CONTEXT *ccert_context, void *raw_arg)
{
  struct Adder_args *args = (struct Adder_args*)raw_arg;
  args->result = CURLE_OK;
  if(valid_cert_encoding(ccert_context)) {
    const char *beg = (const char *) ccert_context->pbCertEncoded;
    const char *end = beg + ccert_context->cbCertEncoded;
    args->result = Curl_extract_certinfo(args->conn, (args->idx)++, beg, end);
  }
  return args->result == CURLE_OK;
}

static CURLcode
schannel_connect_step3(struct connectdata *conn, int sockindex)
{
  CURLcode result = CURLE_OK;
  struct Curl_easy *data = conn->data;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  SECURITY_STATUS sspi_status = SEC_E_OK;
  CERT_CONTEXT *ccert_context = NULL;
#ifdef DEBUGBUILD
  const char * const hostname = SSL_IS_PROXY() ? conn->http_proxy.host.name :
    conn->host.name;
#endif
#ifdef HAS_ALPN
  SecPkgContext_ApplicationProtocol alpn_result;
#endif

  DEBUGASSERT(ssl_connect_3 == connssl->connecting_state);

  DEBUGF(infof(data,
               "schannel: SSL/TLS connection with %s port %hu (step 3/3)\n",
               hostname, conn->remote_port));

  if(!BACKEND->cred)
    return CURLE_SSL_CONNECT_ERROR;

  /* check if the required context attributes are met */
  if(BACKEND->ret_flags != BACKEND->req_flags) {
    if(!(BACKEND->ret_flags & ISC_RET_SEQUENCE_DETECT))
      failf(data, "schannel: failed to setup sequence detection");
    if(!(BACKEND->ret_flags & ISC_RET_REPLAY_DETECT))
      failf(data, "schannel: failed to setup replay detection");
    if(!(BACKEND->ret_flags & ISC_RET_CONFIDENTIALITY))
      failf(data, "schannel: failed to setup confidentiality");
    if(!(BACKEND->ret_flags & ISC_RET_ALLOCATED_MEMORY))
      failf(data, "schannel: failed to setup memory allocation");
    if(!(BACKEND->ret_flags & ISC_RET_STREAM))
      failf(data, "schannel: failed to setup stream orientation");
    return CURLE_SSL_CONNECT_ERROR;
  }

#ifdef HAS_ALPN
  if(BACKEND->use_alpn) {
    sspi_status = s_pSecFn->QueryContextAttributes(&BACKEND->ctxt->ctxt_handle,
      SECPKG_ATTR_APPLICATION_PROTOCOL, &alpn_result);

    if(sspi_status != SEC_E_OK) {
      failf(data, "schannel: failed to retrieve ALPN result");
      return CURLE_SSL_CONNECT_ERROR;
    }

    if(alpn_result.ProtoNegoStatus ==
       SecApplicationProtocolNegotiationStatus_Success) {

      infof(data, "schannel: ALPN, server accepted to use %.*s\n",
        alpn_result.ProtocolIdSize, alpn_result.ProtocolId);

#ifdef USE_NGHTTP2
      if(alpn_result.ProtocolIdSize == NGHTTP2_PROTO_VERSION_ID_LEN &&
         !memcmp(NGHTTP2_PROTO_VERSION_ID, alpn_result.ProtocolId,
          NGHTTP2_PROTO_VERSION_ID_LEN)) {
        conn->negnpn = CURL_HTTP_VERSION_2;
      }
      else
#endif
      if(alpn_result.ProtocolIdSize == ALPN_HTTP_1_1_LENGTH &&
         !memcmp(ALPN_HTTP_1_1, alpn_result.ProtocolId,
           ALPN_HTTP_1_1_LENGTH)) {
        conn->negnpn = CURL_HTTP_VERSION_1_1;
      }
    }
    else
      infof(data, "ALPN, server did not agree to a protocol\n");
    Curl_multiuse_state(conn, conn->negnpn == CURL_HTTP_VERSION_2 ?
                        BUNDLE_MULTIPLEX : BUNDLE_NO_MULTIUSE);
  }
#endif

  /* save the current session data for possible re-use */
  if(SSL_SET_OPTION(primary.sessionid)) {
    bool incache;
    struct curl_schannel_cred *old_cred = NULL;

    Curl_ssl_sessionid_lock(conn);
    incache = !(Curl_ssl_getsessionid(conn, (void **)&old_cred, NULL,
                                      sockindex));
    if(incache) {
      if(old_cred != BACKEND->cred) {
        DEBUGF(infof(data,
                     "schannel: old credential handle is stale, removing\n"));
        /* we're not taking old_cred ownership here, no refcount++ is needed */
        Curl_ssl_delsessionid(conn, (void *)old_cred);
        incache = FALSE;
      }
    }
    if(!incache) {
      result = Curl_ssl_addsessionid(conn, (void *)BACKEND->cred,
                                     sizeof(struct curl_schannel_cred),
                                     sockindex);
      if(result) {
        Curl_ssl_sessionid_unlock(conn);
        failf(data, "schannel: failed to store credential handle");
        return result;
      }
      else {
        /* this cred session is now also referenced by sessionid cache */
        BACKEND->cred->refcount++;
        DEBUGF(infof(data,
                     "schannel: stored credential handle in session cache\n"));
      }
    }
    Curl_ssl_sessionid_unlock(conn);
  }

  if(data->set.ssl.certinfo) {
    int certs_count = 0;
    sspi_status = s_pSecFn->QueryContextAttributes(&BACKEND->ctxt->ctxt_handle,
      SECPKG_ATTR_REMOTE_CERT_CONTEXT, &ccert_context);

    if((sspi_status != SEC_E_OK) || (ccert_context == NULL)) {
      failf(data, "schannel: failed to retrieve remote cert context");
      return CURLE_PEER_FAILED_VERIFICATION;
    }

    traverse_cert_store(ccert_context, cert_counter_callback, &certs_count);

    result = Curl_ssl_init_certinfo(data, certs_count);
    if(!result) {
      struct Adder_args args;
      args.conn = conn;
      args.idx = 0;
      traverse_cert_store(ccert_context, add_cert_to_certinfo, &args);
      result = args.result;
    }
    CertFreeCertificateContext(ccert_context);
    if(result)
      return result;
  }

  connssl->connecting_state = ssl_connect_done;

  return CURLE_OK;
}

static CURLcode
schannel_connect_common(struct connectdata *conn, int sockindex,
                        bool nonblocking, bool *done)
{
  CURLcode result;
  struct Curl_easy *data = conn->data;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  curl_socket_t sockfd = conn->sock[sockindex];
  time_t timeout_ms;
  int what;

  /* check if the connection has already been established */
  if(ssl_connection_complete == connssl->state) {
    *done = TRUE;
    return CURLE_OK;
  }

  if(ssl_connect_1 == connssl->connecting_state) {
    /* check out how much more time we're allowed */
    timeout_ms = Curl_timeleft(data, NULL, TRUE);

    if(timeout_ms < 0) {
      /* no need to continue if time already is up */
      failf(data, "SSL/TLS connection timeout");
      return CURLE_OPERATION_TIMEDOUT;
    }

    result = schannel_connect_step1(conn, sockindex);
    if(result)
      return result;
  }

  while(ssl_connect_2 == connssl->connecting_state ||
        ssl_connect_2_reading == connssl->connecting_state ||
        ssl_connect_2_writing == connssl->connecting_state) {

    /* check out how much more time we're allowed */
    timeout_ms = Curl_timeleft(data, NULL, TRUE);

    if(timeout_ms < 0) {
      /* no need to continue if time already is up */
      failf(data, "SSL/TLS connection timeout");
      return CURLE_OPERATION_TIMEDOUT;
    }

    /* if ssl is expecting something, check if it's available. */
    if(connssl->connecting_state == ssl_connect_2_reading
       || connssl->connecting_state == ssl_connect_2_writing) {

      curl_socket_t writefd = ssl_connect_2_writing ==
        connssl->connecting_state ? sockfd : CURL_SOCKET_BAD;
      curl_socket_t readfd = ssl_connect_2_reading ==
        connssl->connecting_state ? sockfd : CURL_SOCKET_BAD;

      what = Curl_socket_check(readfd, CURL_SOCKET_BAD, writefd,
                               nonblocking ? 0 : timeout_ms);
      if(what < 0) {
        /* fatal error */
        failf(data, "select/poll on SSL/TLS socket, errno: %d", SOCKERRNO);
        return CURLE_SSL_CONNECT_ERROR;
      }
      else if(0 == what) {
        if(nonblocking) {
          *done = FALSE;
          return CURLE_OK;
        }
        else {
          /* timeout */
          failf(data, "SSL/TLS connection timeout");
          return CURLE_OPERATION_TIMEDOUT;
        }
      }
      /* socket is readable or writable */
    }

    /* Run transaction, and return to the caller if it failed or if
     * this connection is part of a multi handle and this loop would
     * execute again. This permits the owner of a multi handle to
     * abort a connection attempt before step2 has completed while
     * ensuring that a client using select() or epoll() will always
     * have a valid fdset to wait on.
     */
    result = schannel_connect_step2(conn, sockindex);
    if(result || (nonblocking &&
                  (ssl_connect_2 == connssl->connecting_state ||
                   ssl_connect_2_reading == connssl->connecting_state ||
                   ssl_connect_2_writing == connssl->connecting_state)))
      return result;

  } /* repeat step2 until all transactions are done. */

  if(ssl_connect_3 == connssl->connecting_state) {
    result = schannel_connect_step3(conn, sockindex);
    if(result)
      return result;
  }

  if(ssl_connect_done == connssl->connecting_state) {
    connssl->state = ssl_connection_complete;
    conn->recv[sockindex] = schannel_recv;
    conn->send[sockindex] = schannel_send;

#ifdef SECPKG_ATTR_ENDPOINT_BINDINGS
    /* When SSPI is used in combination with Schannel
     * we need the Schannel context to create the Schannel
     * binding to pass the IIS extended protection checks.
     * Available on Windows 7 or later.
     */
    conn->sslContext = &BACKEND->ctxt->ctxt_handle;
#endif

    *done = TRUE;
  }
  else
    *done = FALSE;

  /* reset our connection state machine */
  connssl->connecting_state = ssl_connect_1;

  return CURLE_OK;
}

static ssize_t
schannel_send(struct connectdata *conn, int sockindex,
              const void *buf, size_t len, CURLcode *err)
{
  ssize_t written = -1;
  size_t data_len = 0;
  unsigned char *data = NULL;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  SecBuffer outbuf[4];
  SecBufferDesc outbuf_desc;
  SECURITY_STATUS sspi_status = SEC_E_OK;
  CURLcode result;

  /* check if the maximum stream sizes were queried */
  if(BACKEND->stream_sizes.cbMaximumMessage == 0) {
    sspi_status = s_pSecFn->QueryContextAttributes(
      &BACKEND->ctxt->ctxt_handle,
      SECPKG_ATTR_STREAM_SIZES,
      &BACKEND->stream_sizes);
    if(sspi_status != SEC_E_OK) {
      *err = CURLE_SEND_ERROR;
      return -1;
    }
  }

  /* check if the buffer is longer than the maximum message length */
  if(len > BACKEND->stream_sizes.cbMaximumMessage) {
    len = BACKEND->stream_sizes.cbMaximumMessage;
  }

  /* calculate the complete message length and allocate a buffer for it */
  data_len = BACKEND->stream_sizes.cbHeader + len +
    BACKEND->stream_sizes.cbTrailer;
  data = (unsigned char *) malloc(data_len);
  if(data == NULL) {
    *err = CURLE_OUT_OF_MEMORY;
    return -1;
  }

  /* setup output buffers (header, data, trailer, empty) */
  InitSecBuffer(&outbuf[0], SECBUFFER_STREAM_HEADER,
                data, BACKEND->stream_sizes.cbHeader);
  InitSecBuffer(&outbuf[1], SECBUFFER_DATA,
                data + BACKEND->stream_sizes.cbHeader, curlx_uztoul(len));
  InitSecBuffer(&outbuf[2], SECBUFFER_STREAM_TRAILER,
                data + BACKEND->stream_sizes.cbHeader + len,
                BACKEND->stream_sizes.cbTrailer);
  InitSecBuffer(&outbuf[3], SECBUFFER_EMPTY, NULL, 0);
  InitSecBufferDesc(&outbuf_desc, outbuf, 4);

  /* copy data into output buffer */
  memcpy(outbuf[1].pvBuffer, buf, len);

  /* https://msdn.microsoft.com/en-us/library/windows/desktop/aa375390.aspx */
  sspi_status = s_pSecFn->EncryptMessage(&BACKEND->ctxt->ctxt_handle, 0,
                                         &outbuf_desc, 0);

  /* check if the message was encrypted */
  if(sspi_status == SEC_E_OK) {
    written = 0;

    /* send the encrypted message including header, data and trailer */
    len = outbuf[0].cbBuffer + outbuf[1].cbBuffer + outbuf[2].cbBuffer;

    /*
      It's important to send the full message which includes the header,
      encrypted payload, and trailer.  Until the client receives all the
      data a coherent message has not been delivered and the client
      can't read any of it.

      If we wanted to buffer the unwritten encrypted bytes, we would
      tell the client that all data it has requested to be sent has been
      sent. The unwritten encrypted bytes would be the first bytes to
      send on the next invocation.
      Here's the catch with this - if we tell the client that all the
      bytes have been sent, will the client call this method again to
      send the buffered data?  Looking at who calls this function, it
      seems the answer is NO.
    */

    /* send entire message or fail */
    while(len > (size_t)written) {
      ssize_t this_write;
      time_t timeleft;
      int what;

      this_write = 0;

      timeleft = Curl_timeleft(conn->data, NULL, FALSE);
      if(timeleft < 0) {
        /* we already got the timeout */
        failf(conn->data, "schannel: timed out sending data "
              "(bytes sent: %zd)", written);
        *err = CURLE_OPERATION_TIMEDOUT;
        written = -1;
        break;
      }

      what = SOCKET_WRITABLE(conn->sock[sockindex], timeleft);
      if(what < 0) {
        /* fatal error */
        failf(conn->data, "select/poll on SSL socket, errno: %d", SOCKERRNO);
        *err = CURLE_SEND_ERROR;
        written = -1;
        break;
      }
      else if(0 == what) {
        failf(conn->data, "schannel: timed out sending data "
              "(bytes sent: %zd)", written);
        *err = CURLE_OPERATION_TIMEDOUT;
        written = -1;
        break;
      }
      /* socket is writable */

      result = Curl_write_plain(conn, conn->sock[sockindex], data + written,
                                len - written, &this_write);
      if(result == CURLE_AGAIN)
        continue;
      else if(result != CURLE_OK) {
        *err = result;
        written = -1;
        break;
      }

      written += this_write;
    }
  }
  else if(sspi_status == SEC_E_INSUFFICIENT_MEMORY) {
    *err = CURLE_OUT_OF_MEMORY;
  }
  else{
    *err = CURLE_SEND_ERROR;
  }

  Curl_safefree(data);

  if(len == (size_t)written)
    /* Encrypted message including header, data and trailer entirely sent.
       The return value is the number of unencrypted bytes that were sent. */
    written = outbuf[1].cbBuffer;

  return written;
}

static ssize_t
schannel_recv(struct connectdata *conn, int sockindex,
              char *buf, size_t len, CURLcode *err)
{
  size_t size = 0;
  ssize_t nread = -1;
  struct Curl_easy *data = conn->data;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  unsigned char *reallocated_buffer;
  size_t reallocated_length;
  bool done = FALSE;
  SecBuffer inbuf[4];
  SecBufferDesc inbuf_desc;
  SECURITY_STATUS sspi_status = SEC_E_OK;
  /* we want the length of the encrypted buffer to be at least large enough
     that it can hold all the bytes requested and some TLS record overhead. */
  size_t min_encdata_length = len + CURL_SCHANNEL_BUFFER_FREE_SIZE;

  /****************************************************************************
   * Don't return or set BACKEND->recv_unrecoverable_err unless in the cleanup.
   * The pattern for return error is set *err, optional infof, goto cleanup.
   *
   * Our priority is to always return as much decrypted data to the caller as
   * possible, even if an error occurs. The state of the decrypted buffer must
   * always be valid. Transfer of decrypted data to the caller's buffer is
   * handled in the cleanup.
   */

  DEBUGF(infof(data, "schannel: client wants to read %zu bytes\n", len));
  *err = CURLE_OK;

  if(len && len <= BACKEND->decdata_offset) {
    infof(data, "schannel: enough decrypted data is already available\n");
    goto cleanup;
  }
  else if(BACKEND->recv_unrecoverable_err) {
    *err = BACKEND->recv_unrecoverable_err;
    infof(data, "schannel: an unrecoverable error occurred in a prior call\n");
    goto cleanup;
  }
  else if(BACKEND->recv_sspi_close_notify) {
    /* once a server has indicated shutdown there is no more encrypted data */
    infof(data, "schannel: server indicated shutdown in a prior call\n");
    goto cleanup;
  }
  else if(!len) {
    /* It's debatable what to return when !len. Regardless we can't return
    immediately because there may be data to decrypt (in the case we want to
    decrypt all encrypted cached data) so handle !len later in cleanup.
    */
    ; /* do nothing */
  }
  else if(!BACKEND->recv_connection_closed) {
    /* increase enc buffer in order to fit the requested amount of data */
    size = BACKEND->encdata_length - BACKEND->encdata_offset;
    if(size < CURL_SCHANNEL_BUFFER_FREE_SIZE ||
       BACKEND->encdata_length < min_encdata_length) {
      reallocated_length = BACKEND->encdata_offset +
                           CURL_SCHANNEL_BUFFER_FREE_SIZE;
      if(reallocated_length < min_encdata_length) {
        reallocated_length = min_encdata_length;
      }
      reallocated_buffer = realloc(BACKEND->encdata_buffer,
                                   reallocated_length);
      if(reallocated_buffer == NULL) {
        *err = CURLE_OUT_OF_MEMORY;
        failf(data, "schannel: unable to re-allocate memory");
        goto cleanup;
      }

      BACKEND->encdata_buffer = reallocated_buffer;
      BACKEND->encdata_length = reallocated_length;
      size = BACKEND->encdata_length - BACKEND->encdata_offset;
      DEBUGF(infof(data, "schannel: encdata_buffer resized %zu\n",
                   BACKEND->encdata_length));
    }

    DEBUGF(infof(data,
                 "schannel: encrypted data buffer: offset %zu length %zu\n",
                 BACKEND->encdata_offset, BACKEND->encdata_length));

    /* read encrypted data from socket */
    *err = Curl_read_plain(conn->sock[sockindex],
                           (char *)(BACKEND->encdata_buffer +
                                    BACKEND->encdata_offset),
                           size, &nread);
    if(*err) {
      nread = -1;
      if(*err == CURLE_AGAIN)
        DEBUGF(infof(data,
                     "schannel: Curl_read_plain returned CURLE_AGAIN\n"));
      else if(*err == CURLE_RECV_ERROR)
        infof(data, "schannel: Curl_read_plain returned CURLE_RECV_ERROR\n");
      else
        infof(data, "schannel: Curl_read_plain returned error %d\n", *err);
    }
    else if(nread == 0) {
      BACKEND->recv_connection_closed = true;
      DEBUGF(infof(data, "schannel: server closed the connection\n"));
    }
    else if(nread > 0) {
      BACKEND->encdata_offset += (size_t)nread;
      BACKEND->encdata_is_incomplete = false;
      DEBUGF(infof(data, "schannel: encrypted data got %zd\n", nread));
    }
  }

  DEBUGF(infof(data,
               "schannel: encrypted data buffer: offset %zu length %zu\n",
               BACKEND->encdata_offset, BACKEND->encdata_length));

  /* decrypt loop */
  while(BACKEND->encdata_offset > 0 && sspi_status == SEC_E_OK &&
        (!len || BACKEND->decdata_offset < len ||
         BACKEND->recv_connection_closed)) {
    /* prepare data buffer for DecryptMessage call */
    InitSecBuffer(&inbuf[0], SECBUFFER_DATA, BACKEND->encdata_buffer,
                  curlx_uztoul(BACKEND->encdata_offset));

    /* we need 3 more empty input buffers for possible output */
    InitSecBuffer(&inbuf[1], SECBUFFER_EMPTY, NULL, 0);
    InitSecBuffer(&inbuf[2], SECBUFFER_EMPTY, NULL, 0);
    InitSecBuffer(&inbuf[3], SECBUFFER_EMPTY, NULL, 0);
    InitSecBufferDesc(&inbuf_desc, inbuf, 4);

    /* https://msdn.microsoft.com/en-us/library/windows/desktop/aa375348.aspx
       */
    sspi_status = s_pSecFn->DecryptMessage(&BACKEND->ctxt->ctxt_handle,
                                           &inbuf_desc, 0, NULL);

    /* check if everything went fine (server may want to renegotiate
       or shutdown the connection context) */
    if(sspi_status == SEC_E_OK || sspi_status == SEC_I_RENEGOTIATE ||
       sspi_status == SEC_I_CONTEXT_EXPIRED) {
      /* check for successfully decrypted data, even before actual
         renegotiation or shutdown of the connection context */
      if(inbuf[1].BufferType == SECBUFFER_DATA) {
        DEBUGF(infof(data, "schannel: decrypted data length: %lu\n",
                     inbuf[1].cbBuffer));

        /* increase buffer in order to fit the received amount of data */
        size = inbuf[1].cbBuffer > CURL_SCHANNEL_BUFFER_FREE_SIZE ?
               inbuf[1].cbBuffer : CURL_SCHANNEL_BUFFER_FREE_SIZE;
        if(BACKEND->decdata_length - BACKEND->decdata_offset < size ||
           BACKEND->decdata_length < len) {
          /* increase internal decrypted data buffer */
          reallocated_length = BACKEND->decdata_offset + size;
          /* make sure that the requested amount of data fits */
          if(reallocated_length < len) {
            reallocated_length = len;
          }
          reallocated_buffer = realloc(BACKEND->decdata_buffer,
                                       reallocated_length);
          if(reallocated_buffer == NULL) {
            *err = CURLE_OUT_OF_MEMORY;
            failf(data, "schannel: unable to re-allocate memory");
            goto cleanup;
          }
          BACKEND->decdata_buffer = reallocated_buffer;
          BACKEND->decdata_length = reallocated_length;
        }

        /* copy decrypted data to internal buffer */
        size = inbuf[1].cbBuffer;
        if(size) {
          memcpy(BACKEND->decdata_buffer + BACKEND->decdata_offset,
                 inbuf[1].pvBuffer, size);
          BACKEND->decdata_offset += size;
        }

        DEBUGF(infof(data, "schannel: decrypted data added: %zu\n", size));
        DEBUGF(infof(data,
                     "schannel: decrypted cached: offset %zu length %zu\n",
                     BACKEND->decdata_offset, BACKEND->decdata_length));
      }

      /* check for remaining encrypted data */
      if(inbuf[3].BufferType == SECBUFFER_EXTRA && inbuf[3].cbBuffer > 0) {
        DEBUGF(infof(data, "schannel: encrypted data length: %lu\n",
                     inbuf[3].cbBuffer));

        /* check if the remaining data is less than the total amount
         * and therefore begins after the already processed data
         */
        if(BACKEND->encdata_offset > inbuf[3].cbBuffer) {
          /* move remaining encrypted data forward to the beginning of
             buffer */
          memmove(BACKEND->encdata_buffer,
                  (BACKEND->encdata_buffer + BACKEND->encdata_offset) -
                  inbuf[3].cbBuffer, inbuf[3].cbBuffer);
          BACKEND->encdata_offset = inbuf[3].cbBuffer;
        }

        DEBUGF(infof(data,
                     "schannel: encrypted cached: offset %zu length %zu\n",
                     BACKEND->encdata_offset, BACKEND->encdata_length));
      }
      else {
        /* reset encrypted buffer offset, because there is no data remaining */
        BACKEND->encdata_offset = 0;
      }

      /* check if server wants to renegotiate the connection context */
      if(sspi_status == SEC_I_RENEGOTIATE) {
        infof(data, "schannel: remote party requests renegotiation\n");
        if(*err && *err != CURLE_AGAIN) {
          infof(data, "schannel: can't renogotiate, an error is pending\n");
          goto cleanup;
        }
        if(BACKEND->encdata_offset) {
          *err = CURLE_RECV_ERROR;
          infof(data, "schannel: can't renogotiate, "
                      "encrypted data available\n");
          goto cleanup;
        }
        /* begin renegotiation */
        infof(data, "schannel: renegotiating SSL/TLS connection\n");
        connssl->state = ssl_connection_negotiating;
        connssl->connecting_state = ssl_connect_2_writing;
        *err = schannel_connect_common(conn, sockindex, FALSE, &done);
        if(*err) {
          infof(data, "schannel: renegotiation failed\n");
          goto cleanup;
        }
        /* now retry receiving data */
        sspi_status = SEC_E_OK;
        infof(data, "schannel: SSL/TLS connection renegotiated\n");
        continue;
      }
      /* check if the server closed the connection */
      else if(sspi_status == SEC_I_CONTEXT_EXPIRED) {
        /* In Windows 2000 SEC_I_CONTEXT_EXPIRED (close_notify) is not
           returned so we have to work around that in cleanup. */
        BACKEND->recv_sspi_close_notify = true;
        if(!BACKEND->recv_connection_closed) {
          BACKEND->recv_connection_closed = true;
          infof(data, "schannel: server closed the connection\n");
        }
        goto cleanup;
      }
    }
    else if(sspi_status == SEC_E_INCOMPLETE_MESSAGE) {
      BACKEND->encdata_is_incomplete = true;
      if(!*err)
        *err = CURLE_AGAIN;
      infof(data, "schannel: failed to decrypt data, need more data\n");
      goto cleanup;
    }
    else {
      char buffer[STRERROR_LEN];
      *err = CURLE_RECV_ERROR;
      infof(data, "schannel: failed to read data from server: %s\n",
            Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
      goto cleanup;
    }
  }

  DEBUGF(infof(data,
               "schannel: encrypted data buffer: offset %zu length %zu\n",
               BACKEND->encdata_offset, BACKEND->encdata_length));

  DEBUGF(infof(data,
               "schannel: decrypted data buffer: offset %zu length %zu\n",
               BACKEND->decdata_offset, BACKEND->decdata_length));

cleanup:
  /* Warning- there is no guarantee the encdata state is valid at this point */
  DEBUGF(infof(data, "schannel: schannel_recv cleanup\n"));

  /* Error if the connection has closed without a close_notify.
  Behavior here is a matter of debate. We don't want to be vulnerable to a
  truncation attack however there's some browser precedent for ignoring the
  close_notify for compatibility reasons.
  Additionally, Windows 2000 (v5.0) is a special case since it seems it doesn't
  return close_notify. In that case if the connection was closed we assume it
  was graceful (close_notify) since there doesn't seem to be a way to tell.
  */
  if(len && !BACKEND->decdata_offset && BACKEND->recv_connection_closed &&
     !BACKEND->recv_sspi_close_notify) {
    bool isWin2k = Curl_verify_windows_version(5, 0, PLATFORM_WINNT,
                                               VERSION_EQUAL);

    if(isWin2k && sspi_status == SEC_E_OK)
      BACKEND->recv_sspi_close_notify = true;
    else {
      *err = CURLE_RECV_ERROR;
      infof(data, "schannel: server closed abruptly (missing close_notify)\n");
    }
  }

  /* Any error other than CURLE_AGAIN is an unrecoverable error. */
  if(*err && *err != CURLE_AGAIN)
      BACKEND->recv_unrecoverable_err = *err;

  size = len < BACKEND->decdata_offset ? len : BACKEND->decdata_offset;
  if(size) {
    memcpy(buf, BACKEND->decdata_buffer, size);
    memmove(BACKEND->decdata_buffer, BACKEND->decdata_buffer + size,
            BACKEND->decdata_offset - size);
    BACKEND->decdata_offset -= size;
    DEBUGF(infof(data, "schannel: decrypted data returned %zu\n", size));
    DEBUGF(infof(data,
                 "schannel: decrypted data buffer: offset %zu length %zu\n",
                 BACKEND->decdata_offset, BACKEND->decdata_length));
    *err = CURLE_OK;
    return (ssize_t)size;
  }

  if(!*err && !BACKEND->recv_connection_closed)
      *err = CURLE_AGAIN;

  /* It's debatable what to return when !len. We could return whatever error we
  got from decryption but instead we override here so the return is consistent.
  */
  if(!len)
    *err = CURLE_OK;

  return *err ? -1 : 0;
}

static CURLcode Curl_schannel_connect_nonblocking(struct connectdata *conn,
                                                  int sockindex, bool *done)
{
  return schannel_connect_common(conn, sockindex, TRUE, done);
}

static CURLcode Curl_schannel_connect(struct connectdata *conn, int sockindex)
{
  CURLcode result;
  bool done = FALSE;

  result = schannel_connect_common(conn, sockindex, FALSE, &done);
  if(result)
    return result;

  DEBUGASSERT(done);

  return CURLE_OK;
}

static bool Curl_schannel_data_pending(const struct connectdata *conn,
                                       int sockindex)
{
  const struct ssl_connect_data *connssl = &conn->ssl[sockindex];

  if(connssl->use) /* SSL/TLS is in use */
    return (BACKEND->decdata_offset > 0 ||
            (BACKEND->encdata_offset > 0 && !BACKEND->encdata_is_incomplete));
  else
    return FALSE;
}

static void Curl_schannel_close(struct connectdata *conn, int sockindex)
{
  if(conn->ssl[sockindex].use)
    /* if the SSL/TLS channel hasn't been shut down yet, do that now. */
    Curl_ssl_shutdown(conn, sockindex);
}

static void Curl_schannel_session_free(void *ptr)
{
  /* this is expected to be called under sessionid lock */
  struct curl_schannel_cred *cred = ptr;

  cred->refcount--;
  if(cred->refcount == 0) {
    s_pSecFn->FreeCredentialsHandle(&cred->cred_handle);
    Curl_safefree(cred);
  }
}

static int Curl_schannel_shutdown(struct connectdata *conn, int sockindex)
{
  /* See https://msdn.microsoft.com/en-us/library/windows/desktop/aa380138.aspx
   * Shutting Down an Schannel Connection
   */
  struct Curl_easy *data = conn->data;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  char * const hostname = SSL_IS_PROXY() ? conn->http_proxy.host.name :
    conn->host.name;

  DEBUGASSERT(data);

  infof(data, "schannel: shutting down SSL/TLS connection with %s port %hu\n",
        hostname, conn->remote_port);

  if(BACKEND->cred && BACKEND->ctxt) {
    SecBufferDesc BuffDesc;
    SecBuffer Buffer;
    SECURITY_STATUS sspi_status;
    SecBuffer outbuf;
    SecBufferDesc outbuf_desc;
    CURLcode result;
    TCHAR *host_name;
    DWORD dwshut = SCHANNEL_SHUTDOWN;

    InitSecBuffer(&Buffer, SECBUFFER_TOKEN, &dwshut, sizeof(dwshut));
    InitSecBufferDesc(&BuffDesc, &Buffer, 1);

    sspi_status = s_pSecFn->ApplyControlToken(&BACKEND->ctxt->ctxt_handle,
                                              &BuffDesc);

    if(sspi_status != SEC_E_OK) {
      char buffer[STRERROR_LEN];
      failf(data, "schannel: ApplyControlToken failure: %s",
            Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
    }

    host_name = Curl_convert_UTF8_to_tchar(hostname);
    if(!host_name)
      return CURLE_OUT_OF_MEMORY;

    /* setup output buffer */
    InitSecBuffer(&outbuf, SECBUFFER_EMPTY, NULL, 0);
    InitSecBufferDesc(&outbuf_desc, &outbuf, 1);

    sspi_status = s_pSecFn->InitializeSecurityContext(
      &BACKEND->cred->cred_handle,
      &BACKEND->ctxt->ctxt_handle,
      host_name,
      BACKEND->req_flags,
      0,
      0,
      NULL,
      0,
      &BACKEND->ctxt->ctxt_handle,
      &outbuf_desc,
      &BACKEND->ret_flags,
      &BACKEND->ctxt->time_stamp);

    Curl_unicodefree(host_name);

    if((sspi_status == SEC_E_OK) || (sspi_status == SEC_I_CONTEXT_EXPIRED)) {
      /* send close message which is in output buffer */
      ssize_t written;
      result = Curl_write_plain(conn, conn->sock[sockindex], outbuf.pvBuffer,
                                outbuf.cbBuffer, &written);

      s_pSecFn->FreeContextBuffer(outbuf.pvBuffer);
      if((result != CURLE_OK) || (outbuf.cbBuffer != (size_t) written)) {
        infof(data, "schannel: failed to send close msg: %s"
              " (bytes written: %zd)\n", curl_easy_strerror(result), written);
      }
    }
  }

  /* free SSPI Schannel API security context handle */
  if(BACKEND->ctxt) {
    DEBUGF(infof(data, "schannel: clear security context handle\n"));
    s_pSecFn->DeleteSecurityContext(&BACKEND->ctxt->ctxt_handle);
    Curl_safefree(BACKEND->ctxt);
  }

  /* free SSPI Schannel API credential handle */
  if(BACKEND->cred) {
    /*
     * When this function is called from Curl_schannel_close() the connection
     * might not have an associated transfer so the check for conn->data is
     * necessary.
     */
    Curl_ssl_sessionid_lock(conn);
    Curl_schannel_session_free(BACKEND->cred);
    Curl_ssl_sessionid_unlock(conn);
    BACKEND->cred = NULL;
  }

  /* free internal buffer for received encrypted data */
  if(BACKEND->encdata_buffer != NULL) {
    Curl_safefree(BACKEND->encdata_buffer);
    BACKEND->encdata_length = 0;
    BACKEND->encdata_offset = 0;
    BACKEND->encdata_is_incomplete = false;
  }

  /* free internal buffer for received decrypted data */
  if(BACKEND->decdata_buffer != NULL) {
    Curl_safefree(BACKEND->decdata_buffer);
    BACKEND->decdata_length = 0;
    BACKEND->decdata_offset = 0;
  }

  return CURLE_OK;
}

static int Curl_schannel_init(void)
{
  return (Curl_sspi_global_init() == CURLE_OK ? 1 : 0);
}

static void Curl_schannel_cleanup(void)
{
  Curl_sspi_global_cleanup();
}

static size_t Curl_schannel_version(char *buffer, size_t size)
{
  size = msnprintf(buffer, size, "Schannel");

  return size;
}

static CURLcode Curl_schannel_random(struct Curl_easy *data UNUSED_PARAM,
                                     unsigned char *entropy, size_t length)
{
  HCRYPTPROV hCryptProv = 0;

  (void)data;

  if(!CryptAcquireContext(&hCryptProv, NULL, NULL, PROV_RSA_FULL,
                          CRYPT_VERIFYCONTEXT | CRYPT_SILENT))
    return CURLE_FAILED_INIT;

  if(!CryptGenRandom(hCryptProv, (DWORD)length, entropy)) {
    CryptReleaseContext(hCryptProv, 0UL);
    return CURLE_FAILED_INIT;
  }

  CryptReleaseContext(hCryptProv, 0UL);
  return CURLE_OK;
}

static CURLcode pkp_pin_peer_pubkey(struct connectdata *conn, int sockindex,
                                    const char *pinnedpubkey)
{
  SECURITY_STATUS sspi_status;
  struct Curl_easy *data = conn->data;
  struct ssl_connect_data *connssl = &conn->ssl[sockindex];
  CERT_CONTEXT *pCertContextServer = NULL;
  const char *x509_der;
  DWORD x509_der_len;
  curl_X509certificate x509_parsed;
  curl_asn1Element *pubkey;

  /* Result is returned to caller */
  CURLcode result = CURLE_SSL_PINNEDPUBKEYNOTMATCH;

  /* if a path wasn't specified, don't pin */
  if(!pinnedpubkey)
    return CURLE_OK;

  do {
    sspi_status =
      s_pSecFn->QueryContextAttributes(&BACKEND->ctxt->ctxt_handle,
                                       SECPKG_ATTR_REMOTE_CERT_CONTEXT,
                                       &pCertContextServer);

    if((sspi_status != SEC_E_OK) || (pCertContextServer == NULL)) {
      char buffer[STRERROR_LEN];
      failf(data, "schannel: Failed to read remote certificate context: %s",
            Curl_sspi_strerror(sspi_status, buffer, sizeof(buffer)));
      break; /* failed */
    }


    if(!(((pCertContextServer->dwCertEncodingType & X509_ASN_ENCODING) != 0) &&
       (pCertContextServer->cbCertEncoded > 0)))
      break;

    x509_der = (const char *)pCertContextServer->pbCertEncoded;
    x509_der_len = pCertContextServer->cbCertEncoded;
    memset(&x509_parsed, 0, sizeof(x509_parsed));
    if(Curl_parseX509(&x509_parsed, x509_der, x509_der + x509_der_len))
      break;

    pubkey = &x509_parsed.subjectPublicKeyInfo;
    if(!pubkey->header || pubkey->end <= pubkey->header) {
      failf(data, "SSL: failed retrieving public key from server certificate");
      break;
    }

    result = Curl_pin_peer_pubkey(data,
                                  pinnedpubkey,
                                  (const unsigned char *)pubkey->header,
                                  (size_t)(pubkey->end - pubkey->header));
    if(result) {
      failf(data, "SSL: public key does not match pinned public key!");
    }
  } while(0);

  if(pCertContextServer)
    CertFreeCertificateContext(pCertContextServer);

  return result;
}

static void Curl_schannel_checksum(const unsigned char *input,
                                   size_t inputlen,
                                   unsigned char *checksum,
                                   size_t checksumlen,
                                   DWORD provType,
                                   const unsigned int algId)
{
  HCRYPTPROV hProv = 0;
  HCRYPTHASH hHash = 0;
  DWORD cbHashSize = 0;
  DWORD dwHashSizeLen = (DWORD)sizeof(cbHashSize);
  DWORD dwChecksumLen = (DWORD)checksumlen;

  /* since this can fail in multiple ways, zero memory first so we never
   * return old data
   */
  memset(checksum, 0, checksumlen);

  if(!CryptAcquireContext(&hProv, NULL, NULL, provType,
                          CRYPT_VERIFYCONTEXT))
    return; /* failed */

  do {
    if(!CryptCreateHash(hProv, algId, 0, 0, &hHash))
      break; /* failed */

    /* workaround for original MinGW, should be (const BYTE*) */
    if(!CryptHashData(hHash, (BYTE*)input, (DWORD)inputlen, 0))
      break; /* failed */

    /* get hash size */
    if(!CryptGetHashParam(hHash, HP_HASHSIZE, (BYTE *)&cbHashSize,
                          &dwHashSizeLen, 0))
      break; /* failed */

    /* check hash size */
    if(checksumlen < cbHashSize)
      break; /* failed */

    if(CryptGetHashParam(hHash, HP_HASHVAL, checksum, &dwChecksumLen, 0))
      break; /* failed */
  } while(0);

  if(hHash)
    CryptDestroyHash(hHash);

  if(hProv)
    CryptReleaseContext(hProv, 0);
}

static CURLcode Curl_schannel_md5sum(unsigned char *input,
                                     size_t inputlen,
                                     unsigned char *md5sum,
                                     size_t md5len)
{
  Curl_schannel_checksum(input, inputlen, md5sum, md5len,
                         PROV_RSA_FULL, CALG_MD5);
  return CURLE_OK;
}

static CURLcode Curl_schannel_sha256sum(const unsigned char *input,
                                    size_t inputlen,
                                    unsigned char *sha256sum,
                                    size_t sha256len)
{
  Curl_schannel_checksum(input, inputlen, sha256sum, sha256len,
                         PROV_RSA_AES, CALG_SHA_256);
  return CURLE_OK;
}

static void *Curl_schannel_get_internals(struct ssl_connect_data *connssl,
                                         CURLINFO info UNUSED_PARAM)
{
  (void)info;
  return &BACKEND->ctxt->ctxt_handle;
}

const struct Curl_ssl Curl_ssl_schannel = {
  { CURLSSLBACKEND_SCHANNEL, "schannel" }, /* info */

  SSLSUPP_CERTINFO |
  SSLSUPP_PINNEDPUBKEY,

  sizeof(struct ssl_backend_data),

  Curl_schannel_init,                /* init */
  Curl_schannel_cleanup,             /* cleanup */
  Curl_schannel_version,             /* version */
  Curl_none_check_cxn,               /* check_cxn */
  Curl_schannel_shutdown,            /* shutdown */
  Curl_schannel_data_pending,        /* data_pending */
  Curl_schannel_random,              /* random */
  Curl_none_cert_status_request,     /* cert_status_request */
  Curl_schannel_connect,             /* connect */
  Curl_schannel_connect_nonblocking, /* connect_nonblocking */
  Curl_schannel_get_internals,       /* get_internals */
  Curl_schannel_close,               /* close_one */
  Curl_none_close_all,               /* close_all */
  Curl_schannel_session_free,        /* session_free */
  Curl_none_set_engine,              /* set_engine */
  Curl_none_set_engine_default,      /* set_engine_default */
  Curl_none_engines_list,            /* engines_list */
  Curl_none_false_start,             /* false_start */
  Curl_schannel_md5sum,              /* md5sum */
  Curl_schannel_sha256sum            /* sha256sum */
};

#endif /* USE_SCHANNEL */