summaryrefslogtreecommitdiffstats
path: root/Lib/ssl.py
blob: f0ecbc7e7f5f000b2ede2f33aa85dcdd43787e4b (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
# Wrapper module for _ssl, providing some additional facilities
# implemented in Python.  Written by Bill Janssen.

"""This module provides some more Pythonic support for SSL.

Object types:

  SSLSocket -- subtype of socket.socket which does SSL over the socket

Exceptions:

  SSLError -- exception raised for I/O errors

Functions:

  cert_time_to_seconds -- convert time string used for certificate
                          notBefore and notAfter functions to integer
                          seconds past the Epoch (the time values
                          returned from time.time())

  fetch_server_certificate (HOST, PORT) -- fetch the certificate provided
                          by the server running on HOST at port PORT.  No
                          validation of the certificate is performed.

Integer constants:

SSL_ERROR_ZERO_RETURN
SSL_ERROR_WANT_READ
SSL_ERROR_WANT_WRITE
SSL_ERROR_WANT_X509_LOOKUP
SSL_ERROR_SYSCALL
SSL_ERROR_SSL
SSL_ERROR_WANT_CONNECT

SSL_ERROR_EOF
SSL_ERROR_INVALID_ERROR_CODE

The following group define certificate requirements that one side is
allowing/requiring from the other side:

CERT_NONE - no certificates from the other side are required (or will
            be looked at if provided)
CERT_OPTIONAL - certificates are not required, but if provided will be
                validated, and if validation fails, the connection will
                also fail
CERT_REQUIRED - certificates are required, and will be validated, and
                if validation fails, the connection will also fail

The following constants identify various SSL protocol variants:

PROTOCOL_SSLv2
PROTOCOL_SSLv3
PROTOCOL_SSLv23
PROTOCOL_TLSv1
PROTOCOL_TLSv1_1
PROTOCOL_TLSv1_2

The following constants identify various SSL alert message descriptions as per
http://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-6

ALERT_DESCRIPTION_CLOSE_NOTIFY
ALERT_DESCRIPTION_UNEXPECTED_MESSAGE
ALERT_DESCRIPTION_BAD_RECORD_MAC
ALERT_DESCRIPTION_RECORD_OVERFLOW
ALERT_DESCRIPTION_DECOMPRESSION_FAILURE
ALERT_DESCRIPTION_HANDSHAKE_FAILURE
ALERT_DESCRIPTION_BAD_CERTIFICATE
ALERT_DESCRIPTION_UNSUPPORTED_CERTIFICATE
ALERT_DESCRIPTION_CERTIFICATE_REVOKED
ALERT_DESCRIPTION_CERTIFICATE_EXPIRED
ALERT_DESCRIPTION_CERTIFICATE_UNKNOWN
ALERT_DESCRIPTION_ILLEGAL_PARAMETER
ALERT_DESCRIPTION_UNKNOWN_CA
ALERT_DESCRIPTION_ACCESS_DENIED
ALERT_DESCRIPTION_DECODE_ERROR
ALERT_DESCRIPTION_DECRYPT_ERROR
ALERT_DESCRIPTION_PROTOCOL_VERSION
ALERT_DESCRIPTION_INSUFFICIENT_SECURITY
ALERT_DESCRIPTION_INTERNAL_ERROR
ALERT_DESCRIPTION_USER_CANCELLED
ALERT_DESCRIPTION_NO_RENEGOTIATION
ALERT_DESCRIPTION_UNSUPPORTED_EXTENSION
ALERT_DESCRIPTION_CERTIFICATE_UNOBTAINABLE
ALERT_DESCRIPTION_UNRECOGNIZED_NAME
ALERT_DESCRIPTION_BAD_CERTIFICATE_STATUS_RESPONSE
ALERT_DESCRIPTION_BAD_CERTIFICATE_HASH_VALUE
ALERT_DESCRIPTION_UNKNOWN_PSK_IDENTITY
"""

import textwrap
import re
import sys
import os
from collections import namedtuple
from enum import Enum as _Enum, IntEnum as _IntEnum

import _ssl             # if we can't import it, let the error propagate

from _ssl import OPENSSL_VERSION_NUMBER, OPENSSL_VERSION_INFO, OPENSSL_VERSION
from _ssl import _SSLContext
from _ssl import (
    SSLError, SSLZeroReturnError, SSLWantReadError, SSLWantWriteError,
    SSLSyscallError, SSLEOFError,
    )
from _ssl import CERT_NONE, CERT_OPTIONAL, CERT_REQUIRED
from _ssl import (VERIFY_DEFAULT, VERIFY_CRL_CHECK_LEAF, VERIFY_CRL_CHECK_CHAIN,
    VERIFY_X509_STRICT)
from _ssl import txt2obj as _txt2obj, nid2obj as _nid2obj
from _ssl import RAND_status, RAND_egd, RAND_add, RAND_bytes, RAND_pseudo_bytes

def _import_symbols(prefix):
    for n in dir(_ssl):
        if n.startswith(prefix):
            globals()[n] = getattr(_ssl, n)

_import_symbols('OP_')
_import_symbols('ALERT_DESCRIPTION_')
_import_symbols('SSL_ERROR_')

from _ssl import HAS_SNI, HAS_ECDH, HAS_NPN

from _ssl import _OPENSSL_API_VERSION

_SSLMethod = _IntEnum('_SSLMethod',
                      {name: value for name, value in vars(_ssl).items()
                       if name.startswith('PROTOCOL_')})
globals().update(_SSLMethod.__members__)

_PROTOCOL_NAMES = {value: name for name, value in _SSLMethod.__members__.items()}

try:
    _SSLv2_IF_EXISTS = PROTOCOL_SSLv2
except NameError:
    _SSLv2_IF_EXISTS = None

if sys.platform == "win32":
    from _ssl import enum_certificates, enum_crls

from socket import socket, AF_INET, SOCK_STREAM, create_connection
from socket import SOL_SOCKET, SO_TYPE
import base64        # for DER-to-PEM translation
import errno


socket_error = OSError  # keep that public name in module namespace

if _ssl.HAS_TLS_UNIQUE:
    CHANNEL_BINDING_TYPES = ['tls-unique']
else:
    CHANNEL_BINDING_TYPES = []

# Disable weak or insecure ciphers by default
# (OpenSSL's default setting is 'DEFAULT:!aNULL:!eNULL')
# Enable a better set of ciphers by default
# This list has been explicitly chosen to:
#   * Prefer cipher suites that offer perfect forward secrecy (DHE/ECDHE)
#   * Prefer ECDHE over DHE for better performance
#   * Prefer any AES-GCM over any AES-CBC for better performance and security
#   * Then Use HIGH cipher suites as a fallback
#   * Then Use 3DES as fallback which is secure but slow
#   * Finally use RC4 as a fallback which is problematic but needed for
#     compatibility some times.
#   * Disable NULL authentication, NULL encryption, and MD5 MACs for security
#     reasons
_DEFAULT_CIPHERS = (
    'ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+HIGH:'
    'DH+HIGH:ECDH+3DES:DH+3DES:RSA+AESGCM:RSA+AES:RSA+HIGH:RSA+3DES:ECDH+RC4:'
    'DH+RC4:RSA+RC4:!aNULL:!eNULL:!MD5'
)

# Restricted and more secure ciphers for the server side
# This list has been explicitly chosen to:
#   * Prefer cipher suites that offer perfect forward secrecy (DHE/ECDHE)
#   * Prefer ECDHE over DHE for better performance
#   * Prefer any AES-GCM over any AES-CBC for better performance and security
#   * Then Use HIGH cipher suites as a fallback
#   * Then Use 3DES as fallback which is secure but slow
#   * Disable NULL authentication, NULL encryption, MD5 MACs, DSS, and RC4 for
#     security reasons
_RESTRICTED_SERVER_CIPHERS = (
    'ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+HIGH:'
    'DH+HIGH:ECDH+3DES:DH+3DES:RSA+AESGCM:RSA+AES:RSA+HIGH:RSA+3DES:!aNULL:'
    '!eNULL:!MD5:!DSS:!RC4'
)


class CertificateError(ValueError):
    pass


def _dnsname_match(dn, hostname, max_wildcards=1):
    """Matching according to RFC 6125, section 6.4.3

    http://tools.ietf.org/html/rfc6125#section-6.4.3
    """
    pats = []
    if not dn:
        return False

    leftmost, *remainder = dn.split(r'.')

    wildcards = leftmost.count('*')
    if wildcards > max_wildcards:
        # Issue #17980: avoid denials of service by refusing more
        # than one wildcard per fragment.  A survery of established
        # policy among SSL implementations showed it to be a
        # reasonable choice.
        raise CertificateError(
            "too many wildcards in certificate DNS name: " + repr(dn))

    # speed up common case w/o wildcards
    if not wildcards:
        return dn.lower() == hostname.lower()

    # RFC 6125, section 6.4.3, subitem 1.
    # The client SHOULD NOT attempt to match a presented identifier in which
    # the wildcard character comprises a label other than the left-most label.
    if leftmost == '*':
        # When '*' is a fragment by itself, it matches a non-empty dotless
        # fragment.
        pats.append('[^.]+')
    elif leftmost.startswith('xn--') or hostname.startswith('xn--'):
        # RFC 6125, section 6.4.3, subitem 3.
        # The client SHOULD NOT attempt to match a presented identifier
        # where the wildcard character is embedded within an A-label or
        # U-label of an internationalized domain name.
        pats.append(re.escape(leftmost))
    else:
        # Otherwise, '*' matches any dotless string, e.g. www*
        pats.append(re.escape(leftmost).replace(r'\*', '[^.]*'))

    # add the remaining fragments, ignore any wildcards
    for frag in remainder:
        pats.append(re.escape(frag))

    pat = re.compile(r'\A' + r'\.'.join(pats) + r'\Z', re.IGNORECASE)
    return pat.match(hostname)


def match_hostname(cert, hostname):
    """Verify that *cert* (in decoded format as returned by
    SSLSocket.getpeercert()) matches the *hostname*.  RFC 2818 and RFC 6125
    rules are followed, but IP addresses are not accepted for *hostname*.

    CertificateError is raised on failure. On success, the function
    returns nothing.
    """
    if not cert:
        raise ValueError("empty or no certificate, match_hostname needs a "
                         "SSL socket or SSL context with either "
                         "CERT_OPTIONAL or CERT_REQUIRED")
    dnsnames = []
    san = cert.get('subjectAltName', ())
    for key, value in san:
        if key == 'DNS':
            if _dnsname_match(value, hostname):
                return
            dnsnames.append(value)
    if not dnsnames:
        # The subject is only checked when there is no dNSName entry
        # in subjectAltName
        for sub in cert.get('subject', ()):
            for key, value in sub:
                # XXX according to RFC 2818, the most specific Common Name
                # must be used.
                if key == 'commonName':
                    if _dnsname_match(value, hostname):
                        return
                    dnsnames.append(value)
    if len(dnsnames) > 1:
        raise CertificateError("hostname %r "
            "doesn't match either of %s"
            % (hostname, ', '.join(map(repr, dnsnames))))
    elif len(dnsnames) == 1:
        raise CertificateError("hostname %r "
            "doesn't match %r"
            % (hostname, dnsnames[0]))
    else:
        raise CertificateError("no appropriate commonName or "
            "subjectAltName fields were found")


DefaultVerifyPaths = namedtuple("DefaultVerifyPaths",
    "cafile capath openssl_cafile_env openssl_cafile openssl_capath_env "
    "openssl_capath")

def get_default_verify_paths():
    """Return paths to default cafile and capath.
    """
    parts = _ssl.get_default_verify_paths()

    # environment vars shadow paths
    cafile = os.environ.get(parts[0], parts[1])
    capath = os.environ.get(parts[2], parts[3])

    return DefaultVerifyPaths(cafile if os.path.isfile(cafile) else None,
                              capath if os.path.isdir(capath) else None,
                              *parts)


class _ASN1Object(namedtuple("_ASN1Object", "nid shortname longname oid")):
    """ASN.1 object identifier lookup
    """
    __slots__ = ()

    def __new__(cls, oid):
        return super().__new__(cls, *_txt2obj(oid, name=False))

    @classmethod
    def fromnid(cls, nid):
        """Create _ASN1Object from OpenSSL numeric ID
        """
        return super().__new__(cls, *_nid2obj(nid))

    @classmethod
    def fromname(cls, name):
        """Create _ASN1Object from short name, long name or OID
        """
        return super().__new__(cls, *_txt2obj(name, name=True))


class Purpose(_ASN1Object, _Enum):
    """SSLContext purpose flags with X509v3 Extended Key Usage objects
    """
    SERVER_AUTH = '1.3.6.1.5.5.7.3.1'
    CLIENT_AUTH = '1.3.6.1.5.5.7.3.2'


class SSLContext(_SSLContext):
    """An SSLContext holds various SSL-related configuration options and
    data, such as certificates and possibly a private key."""

    __slots__ = ('protocol', '__weakref__')
    _windows_cert_stores = ("CA", "ROOT")

    def __new__(cls, protocol, *args, **kwargs):
        self = _SSLContext.__new__(cls, protocol)
        if protocol != _SSLv2_IF_EXISTS:
            self.set_ciphers(_DEFAULT_CIPHERS)
        return self

    def __init__(self, protocol):
        self.protocol = protocol

    def wrap_socket(self, sock, server_side=False,
                    do_handshake_on_connect=True,
                    suppress_ragged_eofs=True,
                    server_hostname=None):
        return SSLSocket(sock=sock, server_side=server_side,
                         do_handshake_on_connect=do_handshake_on_connect,
                         suppress_ragged_eofs=suppress_ragged_eofs,
                         server_hostname=server_hostname,
                         _context=self)

    def set_npn_protocols(self, npn_protocols):
        protos = bytearray()
        for protocol in npn_protocols:
            b = bytes(protocol, 'ascii')
            if len(b) == 0 or len(b) > 255:
                raise SSLError('NPN protocols must be 1 to 255 in length')
            protos.append(len(b))
            protos.extend(b)

        self._set_npn_protocols(protos)

    def _load_windows_store_certs(self, storename, purpose):
        certs = bytearray()
        for cert, encoding, trust in enum_certificates(storename):
            # CA certs are never PKCS#7 encoded
            if encoding == "x509_asn":
                if trust is True or purpose.oid in trust:
                    certs.extend(cert)
        self.load_verify_locations(cadata=certs)
        return certs

    def load_default_certs(self, purpose=Purpose.SERVER_AUTH):
        if not isinstance(purpose, _ASN1Object):
            raise TypeError(purpose)
        if sys.platform == "win32":
            for storename in self._windows_cert_stores:
                self._load_windows_store_certs(storename, purpose)
        else:
            self.set_default_verify_paths()


def create_default_context(purpose=Purpose.SERVER_AUTH, *, cafile=None,
                           capath=None, cadata=None):
    """Create a SSLContext object with default settings.

    NOTE: The protocol and settings may change anytime without prior
          deprecation. The values represent a fair balance between maximum
          compatibility and security.
    """
    if not isinstance(purpose, _ASN1Object):
        raise TypeError(purpose)

    context = SSLContext(PROTOCOL_SSLv23)

    # SSLv2 considered harmful.
    context.options |= OP_NO_SSLv2

    # SSLv3 has problematic security and is only required for really old
    # clients such as IE6 on Windows XP
    context.options |= OP_NO_SSLv3

    # disable compression to prevent CRIME attacks (OpenSSL 1.0+)
    context.options |= getattr(_ssl, "OP_NO_COMPRESSION", 0)

    if purpose == Purpose.SERVER_AUTH:
        # verify certs and host name in client mode
        context.verify_mode = CERT_REQUIRED
        context.check_hostname = True
    elif purpose == Purpose.CLIENT_AUTH:
        # Prefer the server's ciphers by default so that we get stronger
        # encryption
        context.options |= getattr(_ssl, "OP_CIPHER_SERVER_PREFERENCE", 0)

        # Use single use keys in order to improve forward secrecy
        context.options |= getattr(_ssl, "OP_SINGLE_DH_USE", 0)
        context.options |= getattr(_ssl, "OP_SINGLE_ECDH_USE", 0)

        # disallow ciphers with known vulnerabilities
        context.set_ciphers(_RESTRICTED_SERVER_CIPHERS)

    if cafile or capath or cadata:
        context.load_verify_locations(cafile, capath, cadata)
    elif context.verify_mode != CERT_NONE:
        # no explicit cafile, capath or cadata but the verify mode is
        # CERT_OPTIONAL or CERT_REQUIRED. Let's try to load default system
        # root CA certificates for the given purpose. This may fail silently.
        context.load_default_certs(purpose)
    return context


def _create_stdlib_context(protocol=PROTOCOL_SSLv23, *, cert_reqs=None,
                           check_hostname=False, purpose=Purpose.SERVER_AUTH,
                           certfile=None, keyfile=None,
                           cafile=None, capath=None, cadata=None):
    """Create a SSLContext object for Python stdlib modules

    All Python stdlib modules shall use this function to create SSLContext
    objects in order to keep common settings in one place. The configuration
    is less restrict than create_default_context()'s to increase backward
    compatibility.
    """
    if not isinstance(purpose, _ASN1Object):
        raise TypeError(purpose)

    context = SSLContext(protocol)
    # SSLv2 considered harmful.
    context.options |= OP_NO_SSLv2

    if cert_reqs is not None:
        context.verify_mode = cert_reqs
    context.check_hostname = check_hostname

    if keyfile and not certfile:
        raise ValueError("certfile must be specified")
    if certfile or keyfile:
        context.load_cert_chain(certfile, keyfile)

    # load CA root certs
    if cafile or capath or cadata:
        context.load_verify_locations(cafile, capath, cadata)
    elif context.verify_mode != CERT_NONE:
        # no explicit cafile, capath or cadata but the verify mode is
        # CERT_OPTIONAL or CERT_REQUIRED. Let's try to load default system
        # root CA certificates for the given purpose. This may fail silently.
        context.load_default_certs(purpose)

    return context

class SSLSocket(socket):
    """This class implements a subtype of socket.socket that wraps
    the underlying OS socket in an SSL context when necessary, and
    provides read and write methods over that channel."""

    def __init__(self, sock=None, keyfile=None, certfile=None,
                 server_side=False, cert_reqs=CERT_NONE,
                 ssl_version=PROTOCOL_SSLv23, ca_certs=None,
                 do_handshake_on_connect=True,
                 family=AF_INET, type=SOCK_STREAM, proto=0, fileno=None,
                 suppress_ragged_eofs=True, npn_protocols=None, ciphers=None,
                 server_hostname=None,
                 _context=None):

        if _context:
            self._context = _context
        else:
            if server_side and not certfile:
                raise ValueError("certfile must be specified for server-side "
                                 "operations")
            if keyfile and not certfile:
                raise ValueError("certfile must be specified")
            if certfile and not keyfile:
                keyfile = certfile
            self._context = SSLContext(ssl_version)
            self._context.verify_mode = cert_reqs
            if ca_certs:
                self._context.load_verify_locations(ca_certs)
            if certfile:
                self._context.load_cert_chain(certfile, keyfile)
            if npn_protocols:
                self._context.set_npn_protocols(npn_protocols)
            if ciphers:
                self._context.set_ciphers(ciphers)
            self.keyfile = keyfile
            self.certfile = certfile
            self.cert_reqs = cert_reqs
            self.ssl_version = ssl_version
            self.ca_certs = ca_certs
            self.ciphers = ciphers
        # Can't use sock.type as other flags (such as SOCK_NONBLOCK) get
        # mixed in.
        if sock.getsockopt(SOL_SOCKET, SO_TYPE) != SOCK_STREAM:
            raise NotImplementedError("only stream sockets are supported")
        if server_side and server_hostname:
            raise ValueError("server_hostname can only be specified "
                             "in client mode")
        if self._context.check_hostname and not server_hostname:
            if HAS_SNI:
                raise ValueError("check_hostname requires server_hostname")
            else:
                raise ValueError("check_hostname requires server_hostname, "
                                 "but it's not supported by your OpenSSL "
                                 "library")
        self.server_side = server_side
        self.server_hostname = server_hostname
        self.do_handshake_on_connect = do_handshake_on_connect
        self.suppress_ragged_eofs = suppress_ragged_eofs
        if sock is not None:
            socket.__init__(self,
                            family=sock.family,
                            type=sock.type,
                            proto=sock.proto,
                            fileno=sock.fileno())
            self.settimeout(sock.gettimeout())
            sock.detach()
        elif fileno is not None:
            socket.__init__(self, fileno=fileno)
        else:
            socket.__init__(self, family=family, type=type, proto=proto)

        # See if we are connected
        try:
            self.getpeername()
        except OSError as e:
            if e.errno != errno.ENOTCONN:
                raise
            connected = False
        else:
            connected = True

        self._closed = False
        self._sslobj = None
        self._connected = connected
        if connected:
            # create the SSL object
            try:
                self._sslobj = self._context._wrap_socket(self, server_side,
                                                         server_hostname)
                if do_handshake_on_connect:
                    timeout = self.gettimeout()
                    if timeout == 0.0:
                        # non-blocking
                        raise ValueError("do_handshake_on_connect should not be specified for non-blocking sockets")
                    self.do_handshake()

            except (OSError, ValueError):
                self.close()
                raise

    @property
    def context(self):
        return self._context

    @context.setter
    def context(self, ctx):
        self._context = ctx
        self._sslobj.context = ctx

    def dup(self):
        raise NotImplemented("Can't dup() %s instances" %
                             self.__class__.__name__)

    def _checkClosed(self, msg=None):
        # raise an exception here if you wish to check for spurious closes
        pass

    def _check_connected(self):
        if not self._connected:
            # getpeername() will raise ENOTCONN if the socket is really
            # not connected; note that we can be connected even without
            # _connected being set, e.g. if connect() first returned
            # EAGAIN.
            self.getpeername()

    def read(self, len=0, buffer=None):
        """Read up to LEN bytes and return them.
        Return zero-length string on EOF."""

        self._checkClosed()
        if not self._sslobj:
            raise ValueError("Read on closed or unwrapped SSL socket.")
        try:
            if buffer is not None:
                v = self._sslobj.read(len, buffer)
            else:
                v = self._sslobj.read(len or 1024)
            return v
        except SSLError as x:
            if x.args[0] == SSL_ERROR_EOF and self.suppress_ragged_eofs:
                if buffer is not None:
                    return 0
                else:
                    return b''
            else:
                raise

    def write(self, data):
        """Write DATA to the underlying SSL channel.  Returns
        number of bytes of DATA actually transmitted."""

        self._checkClosed()
        if not self._sslobj:
            raise ValueError("Write on closed or unwrapped SSL socket.")
        return self._sslobj.write(data)

    def getpeercert(self, binary_form=False):
        """Returns a formatted version of the data in the
        certificate provided by the other end of the SSL channel.
        Return None if no certificate was provided, {} if a
        certificate was provided, but not validated."""

        self._checkClosed()
        self._check_connected()
        return self._sslobj.peer_certificate(binary_form)

    def selected_npn_protocol(self):
        self._checkClosed()
        if not self._sslobj or not _ssl.HAS_NPN:
            return None
        else:
            return self._sslobj.selected_npn_protocol()

    def cipher(self):
        self._checkClosed()
        if not self._sslobj:
            return None
        else:
            return self._sslobj.cipher()

    def compression(self):
        self._checkClosed()
        if not self._sslobj:
            return None
        else:
            return self._sslobj.compression()

    def send(self, data, flags=0):
        self._checkClosed()
        if self._sslobj:
            if flags != 0:
                raise ValueError(
                    "non-zero flags not allowed in calls to send() on %s" %
                    self.__class__)
            return self._sslobj.write(data)
        else:
            return socket.send(self, data, flags)

    def sendto(self, data, flags_or_addr, addr=None):
        self._checkClosed()
        if self._sslobj:
            raise ValueError("sendto not allowed on instances of %s" %
                             self.__class__)
        elif addr is None:
            return socket.sendto(self, data, flags_or_addr)
        else:
            return socket.sendto(self, data, flags_or_addr, addr)

    def sendmsg(self, *args, **kwargs):
        # Ensure programs don't send data unencrypted if they try to
        # use this method.
        raise NotImplementedError("sendmsg not allowed on instances of %s" %
                                  self.__class__)

    def sendall(self, data, flags=0):
        self._checkClosed()
        if self._sslobj:
            if flags != 0:
                raise ValueError(
                    "non-zero flags not allowed in calls to sendall() on %s" %
                    self.__class__)
            amount = len(data)
            count = 0
            while (count < amount):
                v = self.send(data[count:])
                count += v
            return amount
        else:
            return socket.sendall(self, data, flags)

    def sendfile(self, file, offset=0, count=None):
        """Send a file, possibly by using os.sendfile() if this is a
        clear-text socket.  Return the total number of bytes sent.
        """
        if self._sslobj is None:
            # os.sendfile() works with plain sockets only
            return super().sendfile(file, offset, count)
        else:
            return self._sendfile_use_send(file, offset, count)

    def recv(self, buflen=1024, flags=0):
        self._checkClosed()
        if self._sslobj:
            if flags != 0:
                raise ValueError(
                    "non-zero flags not allowed in calls to recv() on %s" %
                    self.__class__)
            return self.read(buflen)
        else:
            return socket.recv(self, buflen, flags)

    def recv_into(self, buffer, nbytes=None, flags=0):
        self._checkClosed()
        if buffer and (nbytes is None):
            nbytes = len(buffer)
        elif nbytes is None:
            nbytes = 1024
        if self._sslobj:
            if flags != 0:
                raise ValueError(
                  "non-zero flags not allowed in calls to recv_into() on %s" %
                  self.__class__)
            return self.read(nbytes, buffer)
        else:
            return socket.recv_into(self, buffer, nbytes, flags)

    def recvfrom(self, buflen=1024, flags=0):
        self._checkClosed()
        if self._sslobj:
            raise ValueError("recvfrom not allowed on instances of %s" %
                             self.__class__)
        else:
            return socket.recvfrom(self, buflen, flags)

    def recvfrom_into(self, buffer, nbytes=None, flags=0):
        self._checkClosed()
        if self._sslobj:
            raise ValueError("recvfrom_into not allowed on instances of %s" %
                             self.__class__)
        else:
            return socket.recvfrom_into(self, buffer, nbytes, flags)

    def recvmsg(self, *args, **kwargs):
        raise NotImplementedError("recvmsg not allowed on instances of %s" %
                                  self.__class__)

    def recvmsg_into(self, *args, **kwargs):
        raise NotImplementedError("recvmsg_into not allowed on instances of "
                                  "%s" % self.__class__)

    def pending(self):
        self._checkClosed()
        if self._sslobj:
            return self._sslobj.pending()
        else:
            return 0

    def shutdown(self, how):
        self._checkClosed()
        self._sslobj = None
        socket.shutdown(self, how)

    def unwrap(self):
        if self._sslobj:
            s = self._sslobj.shutdown()
            self._sslobj = None
            return s
        else:
            raise ValueError("No SSL wrapper around " + str(self))

    def _real_close(self):
        self._sslobj = None
        socket._real_close(self)

    def do_handshake(self, block=False):
        """Perform a TLS/SSL handshake."""
        self._check_connected()
        timeout = self.gettimeout()
        try:
            if timeout == 0.0 and block:
                self.settimeout(None)
            self._sslobj.do_handshake()
        finally:
            self.settimeout(timeout)

        if self.context.check_hostname:
            if not self.server_hostname:
                raise ValueError("check_hostname needs server_hostname "
                                 "argument")
            match_hostname(self.getpeercert(), self.server_hostname)

    def _real_connect(self, addr, connect_ex):
        if self.server_side:
            raise ValueError("can't connect in server-side mode")
        # Here we assume that the socket is client-side, and not
        # connected at the time of the call.  We connect it, then wrap it.
        if self._connected:
            raise ValueError("attempt to connect already-connected SSLSocket!")
        self._sslobj = self.context._wrap_socket(self, False, self.server_hostname)
        try:
            if connect_ex:
                rc = socket.connect_ex(self, addr)
            else:
                rc = None
                socket.connect(self, addr)
            if not rc:
                self._connected = True
                if self.do_handshake_on_connect:
                    self.do_handshake()
            return rc
        except (OSError, ValueError):
            self._sslobj = None
            raise

    def connect(self, addr):
        """Connects to remote ADDR, and then wraps the connection in
        an SSL channel."""
        self._real_connect(addr, False)

    def connect_ex(self, addr):
        """Connects to remote ADDR, and then wraps the connection in
        an SSL channel."""
        return self._real_connect(addr, True)

    def accept(self):
        """Accepts a new connection from a remote client, and returns
        a tuple containing that new connection wrapped with a server-side
        SSL channel, and the address of the remote client."""

        newsock, addr = socket.accept(self)
        newsock = self.context.wrap_socket(newsock,
                    do_handshake_on_connect=self.do_handshake_on_connect,
                    suppress_ragged_eofs=self.suppress_ragged_eofs,
                    server_side=True)
        return newsock, addr

    def get_channel_binding(self, cb_type="tls-unique"):
        """Get channel binding data for current connection.  Raise ValueError
        if the requested `cb_type` is not supported.  Return bytes of the data
        or None if the data is not available (e.g. before the handshake).
        """
        if cb_type not in CHANNEL_BINDING_TYPES:
            raise ValueError("Unsupported channel binding type")
        if cb_type != "tls-unique":
            raise NotImplementedError(
                            "{0} channel binding type not implemented"
                            .format(cb_type))
        if self._sslobj is None:
            return None
        return self._sslobj.tls_unique_cb()

    def version(self):
        """
        Return a string identifying the protocol version used by the
        current SSL channel, or None if there is no established channel.
        """
        if self._sslobj is None:
            return None
        return self._sslobj.version()


def wrap_socket(sock, keyfile=None, certfile=None,
                server_side=False, cert_reqs=CERT_NONE,
                ssl_version=PROTOCOL_SSLv23, ca_certs=None,
                do_handshake_on_connect=True,
                suppress_ragged_eofs=True,
                ciphers=None):

    return SSLSocket(sock=sock, keyfile=keyfile, certfile=certfile,
                     server_side=server_side, cert_reqs=cert_reqs,
                     ssl_version=ssl_version, ca_certs=ca_certs,
                     do_handshake_on_connect=do_handshake_on_connect,
                     suppress_ragged_eofs=suppress_ragged_eofs,
                     ciphers=ciphers)

# some utility functions

def cert_time_to_seconds(cert_time):
    """Return the time in seconds since the Epoch, given the timestring
    representing the "notBefore" or "notAfter" date from a certificate
    in ``"%b %d %H:%M:%S %Y %Z"`` strptime format (C locale).

    "notBefore" or "notAfter" dates must use UTC (RFC 5280).

    Month is one of: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
    UTC should be specified as GMT (see ASN1_TIME_print())
    """
    from time import strptime
    from calendar import timegm

    months = (
        "Jan","Feb","Mar","Apr","May","Jun",
        "Jul","Aug","Sep","Oct","Nov","Dec"
    )
    time_format = ' %d %H:%M:%S %Y GMT' # NOTE: no month, fixed GMT
    try:
        month_number = months.index(cert_time[:3].title()) + 1
    except ValueError:
        raise ValueError('time data %r does not match '
                         'format "%%b%s"' % (cert_time, time_format))
    else:
        # found valid month
        tt = strptime(cert_time[3:], time_format)
        # return an integer, the previous mktime()-based implementation
        # returned a float (fractional seconds are always zero here).
        return timegm((tt[0], month_number) + tt[2:6])

PEM_HEADER = "-----BEGIN CERTIFICATE-----"
PEM_FOOTER = "-----END CERTIFICATE-----"

def DER_cert_to_PEM_cert(der_cert_bytes):
    """Takes a certificate in binary DER format and returns the
    PEM version of it as a string."""

    f = str(base64.standard_b64encode(der_cert_bytes), 'ASCII', 'strict')
    return (PEM_HEADER + '\n' +
            textwrap.fill(f, 64) + '\n' +
            PEM_FOOTER + '\n')

def PEM_cert_to_DER_cert(pem_cert_string):
    """Takes a certificate in ASCII PEM format and returns the
    DER-encoded version of it as a byte sequence"""

    if not pem_cert_string.startswith(PEM_HEADER):
        raise ValueError("Invalid PEM encoding; must start with %s"
                         % PEM_HEADER)
    if not pem_cert_string.strip().endswith(PEM_FOOTER):
        raise ValueError("Invalid PEM encoding; must end with %s"
                         % PEM_FOOTER)
    d = pem_cert_string.strip()[len(PEM_HEADER):-len(PEM_FOOTER)]
    return base64.decodebytes(d.encode('ASCII', 'strict'))

def get_server_certificate(addr, ssl_version=PROTOCOL_SSLv23, ca_certs=None):
    """Retrieve the certificate from the server at the specified address,
    and return it as a PEM-encoded string.
    If 'ca_certs' is specified, validate the server cert against it.
    If 'ssl_version' is specified, use it in the connection attempt."""

    host, port = addr
    if ca_certs is not None:
        cert_reqs = CERT_REQUIRED
    else:
        cert_reqs = CERT_NONE
    context = _create_stdlib_context(ssl_version,
                                     cert_reqs=cert_reqs,
                                     cafile=ca_certs)
    with  create_connection(addr) as sock:
        with context.wrap_socket(sock) as sslsock:
            dercert = sslsock.getpeercert(True)
    return DER_cert_to_PEM_cert(dercert)

def get_protocol_name(protocol_code):
    return _PROTOCOL_NAMES.get(protocol_code, '<unknown>')