ssl.py

# 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:

 get_sigalgs -- return a list of all available TLS signature
 algorithms (requires OpenSSL 3.4 or later)

 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())

 get_server_certificate (addr, ssl_version, ca_certs, timeout) -- Retrieve the
 certificate from the server at the specified
 address and return it as a PEM-encoded string


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_TLS
PROTOCOL_TLS_CLIENT
PROTOCOL_TLS_SERVER
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 sys
import os
from collections import namedtuple
from enum import Enum as _Enum, IntEnum as _IntEnum, IntFlag as _IntFlag
from enum import _simple_enum

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, MemoryBIO, SSLSession
from _ssl import (
 SSLError, SSLZeroReturnError, SSLWantReadError, SSLWantWriteError,
 SSLSyscallError, SSLEOFError, SSLCertVerificationError
 )
from _ssl import txt2obj as _txt2obj, nid2obj as _nid2obj
from _ssl import RAND_status, RAND_add, RAND_bytes
from _ssl import get_sigalgs


from _ssl import (
 HAS_SNI, HAS_ECDH, HAS_NPN, HAS_ALPN, HAS_SSLv2, HAS_SSLv3, HAS_TLSv1,
 HAS_TLSv1_1, HAS_TLSv1_2, HAS_TLSv1_3, HAS_PSK, HAS_PSK_TLS13, HAS_PHA
)
from _ssl import _DEFAULT_CIPHERS, _OPENSSL_API_VERSION

_IntEnum._convert_(
 '_SSLMethod', __name__,
 lambda name: name.startswith('PROTOCOL_') and name != 'PROTOCOL_SSLv23',
 source=_ssl)

_IntFlag._convert_(
 'Options', __name__,
 lambda name: name.startswith('OP_'),
 source=_ssl)

_IntEnum._convert_(
 'AlertDescription', __name__,
 lambda name: name.startswith('ALERT_DESCRIPTION_'),
 source=_ssl)

_IntEnum._convert_(
 'SSLErrorNumber', __name__,
 lambda name: name.startswith('SSL_ERROR_'),
 source=_ssl)

_IntFlag._convert_(
 'VerifyFlags', __name__,
 lambda name: name.startswith('VERIFY_'),
 source=_ssl)

_IntEnum._convert_(
 'VerifyMode', __name__,
 lambda name: name.startswith('CERT_'),
 source=_ssl)

PROTOCOL_SSLv23 = _SSLMethod.PROTOCOL_SSLv23 = _SSLMethod.PROTOCOL_TLS
_PROTOCOL_NAMES = frozendict({
 value: name for name, value in _SSLMethod.__members__.items()})

_SSLv2_IF_EXISTS = getattr(_SSLMethod, 'PROTOCOL_SSLv2', None)


@_simple_enum(_IntEnum)
class TLSVersion:
 MINIMUM_SUPPORTED = _ssl.PROTO_MINIMUM_SUPPORTED
 SSLv3 = _ssl.PROTO_SSLv3
 TLSv1 = _ssl.PROTO_TLSv1
 TLSv1_1 = _ssl.PROTO_TLSv1_1
 TLSv1_2 = _ssl.PROTO_TLSv1_2
 TLSv1_3 = _ssl.PROTO_TLSv1_3
 MAXIMUM_SUPPORTED = _ssl.PROTO_MAXIMUM_SUPPORTED


@_simple_enum(_IntEnum)
class _TLSContentType:
 """Content types (record layer)

 See RFC 8446, section B.1
 """
 CHANGE_CIPHER_SPEC = 20
 ALERT = 21
 HANDSHAKE = 22
 APPLICATION_DATA = 23
 # pseudo content types
 HEADER = 0x100
 INNER_CONTENT_TYPE = 0x101


@_simple_enum(_IntEnum)
class _TLSAlertType:
 """Alert types for TLSContentType.ALERT messages

 See RFC 8446, section B.2
 """
 CLOSE_NOTIFY = 0
 UNEXPECTED_MESSAGE = 10
 BAD_RECORD_MAC = 20
 DECRYPTION_FAILED = 21
 RECORD_OVERFLOW = 22
 DECOMPRESSION_FAILURE = 30
 HANDSHAKE_FAILURE = 40
 NO_CERTIFICATE = 41
 BAD_CERTIFICATE = 42
 UNSUPPORTED_CERTIFICATE = 43
 CERTIFICATE_REVOKED = 44
 CERTIFICATE_EXPIRED = 45
 CERTIFICATE_UNKNOWN = 46
 ILLEGAL_PARAMETER = 47
 UNKNOWN_CA = 48
 ACCESS_DENIED = 49
 DECODE_ERROR = 50
 DECRYPT_ERROR = 51
 EXPORT_RESTRICTION = 60
 PROTOCOL_VERSION = 70
 INSUFFICIENT_SECURITY = 71
 INTERNAL_ERROR = 80
 INAPPROPRIATE_FALLBACK = 86
 USER_CANCELED = 90
 NO_RENEGOTIATION = 100
 MISSING_EXTENSION = 109
 UNSUPPORTED_EXTENSION = 110
 CERTIFICATE_UNOBTAINABLE = 111
 UNRECOGNIZED_NAME = 112
 BAD_CERTIFICATE_STATUS_RESPONSE = 113
 BAD_CERTIFICATE_HASH_VALUE = 114
 UNKNOWN_PSK_IDENTITY = 115
 CERTIFICATE_REQUIRED = 116
 NO_APPLICATION_PROTOCOL = 120


@_simple_enum(_IntEnum)
class _TLSMessageType:
 """Message types (handshake protocol)

 See RFC 8446, section B.3
 """
 HELLO_REQUEST = 0
 CLIENT_HELLO = 1
 SERVER_HELLO = 2
 HELLO_VERIFY_REQUEST = 3
 NEWSESSION_TICKET = 4
 END_OF_EARLY_DATA = 5
 HELLO_RETRY_REQUEST = 6
 ENCRYPTED_EXTENSIONS = 8
 CERTIFICATE = 11
 SERVER_KEY_EXCHANGE = 12
 CERTIFICATE_REQUEST = 13
 SERVER_DONE = 14
 CERTIFICATE_VERIFY = 15
 CLIENT_KEY_EXCHANGE = 16
 FINISHED = 20
 CERTIFICATE_URL = 21
 CERTIFICATE_STATUS = 22
 SUPPLEMENTAL_DATA = 23
 KEY_UPDATE = 24
 NEXT_PROTO = 67
 MESSAGE_HASH = 254
 CHANGE_CIPHER_SPEC = 0x0101


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

from socket import socket, SOCK_STREAM, create_connection
from socket import SOL_SOCKET, SO_TYPE, _GLOBAL_DEFAULT_TIMEOUT
import socket as _socket
import base64 # for DER-to-PEM translation
import errno
import warnings


socket_error = OSError # keep that public name in module namespace

CHANNEL_BINDING_TYPES = ['tls-unique']

HAS_NEVER_CHECK_COMMON_NAME = hasattr(_ssl, 'HOSTFLAG_NEVER_CHECK_SUBJECT')


_RESTRICTED_SERVER_CIPHERS = _DEFAULT_CIPHERS

CertificateError = SSLCertVerificationError


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

 - Hostnames are compared lower-case.
 - For IDNA, both dn and hostname must be encoded as IDN A-label (ACE).
 - Partial wildcards like 'www*.example.org', multiple wildcards, sole
 wildcard or wildcards in labels other then the left-most label are not
 supported and a CertificateError is raised.
 - A wildcard must match at least one character.
 """
 if not dn:
 return False

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

 if wildcards > 1:
 raise CertificateError(
 "too many wildcards in certificate DNS name: {!r}.".format(dn))

 dn_leftmost, sep, dn_remainder = dn.partition('.')

 if '*' in dn_remainder:
 # Only match wildcard in leftmost segment.
 raise CertificateError(
 "wildcard can only be present in the leftmost label: "
 "{!r}.".format(dn))

 if not sep:
 # no right side
 raise CertificateError(
 "sole wildcard without additional labels are not support: "
 "{!r}.".format(dn))

 if dn_leftmost != '*':
 # no partial wildcard matching
 raise CertificateError(
 "partial wildcards in leftmost label are not supported: "
 "{!r}.".format(dn))

 hostname_leftmost, sep, hostname_remainder = hostname.partition('.')
 if not hostname_leftmost or not sep:
 # wildcard must match at least one char
 return False
 return dn_remainder.lower() == hostname_remainder.lower()


def _inet_paton(ipname):
 """Try to convert an IP address to packed binary form

 Supports IPv4 addresses on all platforms and IPv6 on platforms with IPv6
 support.
 """
 # inet_aton() also accepts strings like '1', '127.1', some also trailing
 # data like '127.0.0.1 whatever'.
 try:
 addr = _socket.inet_aton(ipname)
 except OSError:
 # not an IPv4 address
 pass
 else:
 if _socket.inet_ntoa(addr) == ipname:
 # only accept injective ipnames
 return addr
 else:
 # refuse for short IPv4 notation and additional trailing data
 raise ValueError(
 "{!r} is not a quad-dotted IPv4 address.".format(ipname)
 )

 try:
 return _socket.inet_pton(_socket.AF_INET6, ipname)
 except OSError:
 raise ValueError("{!r} is neither an IPv4 nor an IP6 "
 "address.".format(ipname))
 except AttributeError:
 # AF_INET6 not available
 pass

 raise ValueError("{!r} is not an IPv4 address.".format(ipname))


def _ipaddress_match(cert_ipaddress, host_ip):
 """Exact matching of IP addresses.

 RFC 6125 explicitly doesn't define an algorithm for this
 (section 1.7.2 - "Out of Scope").
 """
 # OpenSSL may add a trailing newline to a subjectAltName's IP address,
 # commonly with IPv6 addresses. Strip off trailing \n.
 ip = _inet_paton(cert_ipaddress.rstrip())
 return ip == host_ip


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."""
 _windows_cert_stores = ("CA", "ROOT")

 sslsocket_class = None # SSLSocket is assigned later.
 sslobject_class = None # SSLObject is assigned later.

 def __new__(cls, protocol=None, *args, **kwargs):
 if protocol is None:
 warnings.warn(
 "ssl.SSLContext() without protocol argument is deprecated.",
 category=DeprecationWarning,
 stacklevel=2
 )
 protocol = PROTOCOL_TLS
 self = _SSLContext.__new__(cls, protocol)
 return self

 def _encode_hostname(self, hostname):
 if hostname is None:
 return None
 elif isinstance(hostname, str):
 return hostname.encode('idna').decode('ascii')
 else:
 return hostname.decode('ascii')

 def wrap_socket(self, sock, server_side=False,
 do_handshake_on_connect=True,
 suppress_ragged_eofs=True,
 server_hostname=None, session=None):
 # SSLSocket class handles server_hostname encoding before it calls
 # ctx._wrap_socket()
 return self.sslsocket_class._create(
 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,
 session=session
 )

 def wrap_bio(self, incoming, outgoing, server_side=False,
 server_hostname=None, session=None):
 # Need to encode server_hostname here because _wrap_bio() can only
 # handle ASCII str.
 return self.sslobject_class._create(
 incoming, outgoing, server_side=server_side,
 server_hostname=self._encode_hostname(server_hostname),
 session=session, context=self,
 )

 def set_npn_protocols(self, npn_protocols):
 warnings.warn(
 "ssl NPN is deprecated, use ALPN instead",
 DeprecationWarning,
 stacklevel=2
 )
 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 set_servername_callback(self, server_name_callback):
 if server_name_callback is None:
 self.sni_callback = None
 else:
 if not callable(server_name_callback):
 raise TypeError("not a callable object")

 def shim_cb(sslobj, servername, sslctx):
 servername = self._encode_hostname(servername)
 return server_name_callback(sslobj, servername, sslctx)

 self.sni_callback = shim_cb

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

 self._set_alpn_protocols(protos)

 def _load_windows_store_certs(self, storename, purpose):
 try:
 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:
 try:
 self.load_verify_locations(cadata=cert)
 except SSLError as exc:
 warnings.warn(f"Bad certificate in Windows certificate store: {exc!s}")
 except PermissionError:
 warnings.warn("unable to enumerate Windows certificate store")

 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)
 self.set_default_verify_paths()

 if hasattr(_SSLContext, 'minimum_version'):
 @property
 def minimum_version(self):
 return TLSVersion(super().minimum_version)

 @minimum_version.setter
 def minimum_version(self, value):
 if value == TLSVersion.SSLv3:
 self.options &= ~Options.OP_NO_SSLv3
 super(SSLContext, SSLContext).minimum_version.__set__(self, value)

 @property
 def maximum_version(self):
 return TLSVersion(super().maximum_version)

 @maximum_version.setter
 def maximum_version(self, value):
 super(SSLContext, SSLContext).maximum_version.__set__(self, value)

 @property
 def options(self):
 return Options(super().options)

 @options.setter
 def options(self, value):
 super(SSLContext, SSLContext).options.__set__(self, value)

 if hasattr(_ssl, 'HOSTFLAG_NEVER_CHECK_SUBJECT'):
 @property
 def hostname_checks_common_name(self):
 ncs = self._host_flags & _ssl.HOSTFLAG_NEVER_CHECK_SUBJECT
 return ncs != _ssl.HOSTFLAG_NEVER_CHECK_SUBJECT

 @hostname_checks_common_name.setter
 def hostname_checks_common_name(self, value):
 if value:
 self._host_flags &= ~_ssl.HOSTFLAG_NEVER_CHECK_SUBJECT
 else:
 self._host_flags |= _ssl.HOSTFLAG_NEVER_CHECK_SUBJECT
 else:
 @property
 def hostname_checks_common_name(self):
 return True

 @property
 def _msg_callback(self):
 """TLS message callback

 The message callback provides a debugging hook to analyze TLS
 connections. The callback is called for any TLS protocol message
 (header, handshake, alert, and more), but not for application data.
 Due to technical limitations, the callback can't be used to filter
 traffic or to abort a connection. Any exception raised in the
 callback is delayed until the handshake, read, or write operation
 has been performed.

 def msg_cb(conn, direction, version, content_type, msg_type, data):
 pass

 conn
 :class:`SSLSocket` or :class:`SSLObject` instance
 direction
 ``read`` or ``write``
 version
 :class:`TLSVersion` enum member or int for unknown version. For a
 frame header, it's the header version.
 content_type
 :class:`_TLSContentType` enum member or int for unsupported
 content type.
 msg_type
 Either a :class:`_TLSContentType` enum number for a header
 message, a :class:`_TLSAlertType` enum member for an alert
 message, a :class:`_TLSMessageType` enum member for other
 messages, or int for unsupported message types.
 data
 Raw, decrypted message content as bytes
 """
 inner = super()._msg_callback
 if inner is not None:
 return inner.user_function
 else:
 return None

 @_msg_callback.setter
 def _msg_callback(self, callback):
 if callback is None:
 super(SSLContext, SSLContext)._msg_callback.__set__(self, None)
 return

 if not hasattr(callback, '__call__'):
 raise TypeError(f"{callback} is not callable.")

 def inner(conn, direction, version, content_type, msg_type, data):
 try:
 version = TLSVersion(version)
 except ValueError:
 pass

 try:
 content_type = _TLSContentType(content_type)
 except ValueError:
 pass

 if content_type == _TLSContentType.HEADER:
 msg_enum = _TLSContentType
 elif content_type == _TLSContentType.ALERT:
 msg_enum = _TLSAlertType
 else:
 msg_enum = _TLSMessageType
 try:
 msg_type = msg_enum(msg_type)
 except ValueError:
 pass

 return callback(conn, direction, version,
 content_type, msg_type, data)

 inner.user_function = callback

 super(SSLContext, SSLContext)._msg_callback.__set__(self, inner)

 @property
 def protocol(self):
 return _SSLMethod(super().protocol)

 @property
 def verify_flags(self):
 return VerifyFlags(super().verify_flags)

 @verify_flags.setter
 def verify_flags(self, value):
 super(SSLContext, SSLContext).verify_flags.__set__(self, value)

 @property
 def verify_mode(self):
 value = super().verify_mode
 try:
 return VerifyMode(value)
 except ValueError:
 return value

 @verify_mode.setter
 def verify_mode(self, value):
 super(SSLContext, SSLContext).verify_mode.__set__(self, value)


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)

 # SSLContext sets OP_NO_SSLv2, OP_NO_SSLv3, OP_NO_COMPRESSION,
 # OP_CIPHER_SERVER_PREFERENCE, OP_SINGLE_DH_USE and OP_SINGLE_ECDH_USE
 # by default.
 if purpose == Purpose.SERVER_AUTH:
 # verify certs and host name in client mode
 context = SSLContext(PROTOCOL_TLS_CLIENT)
 context.verify_mode = CERT_REQUIRED
 context.check_hostname = True
 elif purpose == Purpose.CLIENT_AUTH:
 context = SSLContext(PROTOCOL_TLS_SERVER)
 else:
 raise ValueError(purpose)

 # `VERIFY_X509_PARTIAL_CHAIN` makes OpenSSL's chain building behave more
 # like RFC 3280 and 5280, which specify that chain building stops with the
 # first trust anchor, even if that anchor is not self-signed.
 #
 # `VERIFY_X509_STRICT` makes OpenSSL more conservative about the
 # certificates it accepts, including "disabling workarounds for
 # some broken certificates."
 context.verify_flags |= (_ssl.VERIFY_X509_PARTIAL_CHAIN |
 _ssl.VERIFY_X509_STRICT)

 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)
 # OpenSSL 1.1.1 keylog file
 keylogfile = os.environ.get('SSLKEYLOGFILE')
 if keylogfile and not sys.flags.ignore_environment:
 context.keylog_filename = keylogfile
 return context

def _create_unverified_context(protocol=None, *, cert_reqs=CERT_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)

 # SSLContext sets OP_NO_SSLv2, OP_NO_SSLv3, OP_NO_COMPRESSION,
 # OP_CIPHER_SERVER_PREFERENCE, OP_SINGLE_DH_USE and OP_SINGLE_ECDH_USE
 # by default.
 if purpose == Purpose.SERVER_AUTH:
 # verify certs and host name in client mode
 if protocol is None:
 protocol = PROTOCOL_TLS_CLIENT
 elif purpose == Purpose.CLIENT_AUTH:
 if protocol is None:
 protocol = PROTOCOL_TLS_SERVER
 else:
 raise ValueError(purpose)

 context = SSLContext(protocol)
 context.check_hostname = check_hostname
 if cert_reqs is not None:
 context.verify_mode = cert_reqs

 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)
 # OpenSSL 1.1.1 keylog file
 keylogfile = os.environ.get('SSLKEYLOGFILE')
 if keylogfile and not sys.flags.ignore_environment:
 context.keylog_filename = keylogfile
 return context

# Used by http.client if no context is explicitly passed.
_create_default_https_context = create_default_context


# Backwards compatibility alias, even though it's not a public name.
_create_stdlib_context = _create_unverified_context


class SSLObject:
 """This class implements an interface on top of a low-level SSL object as
 implemented by OpenSSL. This object captures the state of an SSL connection
 but does not provide any network IO itself. IO needs to be performed
 through separate "BIO" objects which are OpenSSL's IO abstraction layer.

 This class does not have a public constructor. Instances are returned by
 ``SSLContext.wrap_bio``. This class is typically used by framework authors
 that want to implement asynchronous IO for SSL through memory buffers.

 When compared to ``SSLSocket``, this object lacks the following features:

 * Any form of network IO, including methods such as ``recv`` and ``send``.
 * The ``do_handshake_on_connect`` and ``suppress_ragged_eofs`` machinery.
 """
 def __init__(self, *args, **kwargs):
 raise TypeError(
 f"{self.__class__.__name__} does not have a public "
 f"constructor. Instances are returned by SSLContext.wrap_bio()."
 )

 @classmethod
 def _create(cls, incoming, outgoing, server_side=False,
 server_hostname=None, session=None, context=None):
 self = cls.__new__(cls)
 sslobj = context._wrap_bio(
 incoming, outgoing, server_side=server_side,
 server_hostname=server_hostname,
 owner=self, session=session
 )
 self._sslobj = sslobj
 return self

 @property
 def context(self):
 """The SSLContext that is currently in use."""
 return self._sslobj.context

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

 @property
 def session(self):
 """The SSLSession for client socket."""
 return self._sslobj.session

 @session.setter
 def session(self, session):
 self._sslobj.session = session

 @property
 def session_reused(self):
 """Was the client session reused during handshake"""
 return self._sslobj.session_reused

 @property
 def server_side(self):
 """Whether this is a server-side socket."""
 return self._sslobj.server_side

 @property
 def server_hostname(self):
 """The currently set server hostname (for SNI), or ``None`` if no
 server hostname is set."""
 return self._sslobj.server_hostname

 def read(self, len=1024, buffer=None):
 """Read up to 'len' bytes from the SSL object and return them.

 If 'buffer' is provided, read into this buffer and return the number of
 bytes read.
 """
 if buffer is not None:
 v = self._sslobj.read(len, buffer)
 else:
 v = self._sslobj.read(len)
 return v

 def write(self, data):
 """Write 'data' to the SSL object and return the number of bytes
 written.

 The 'data' argument must support the buffer interface.
 """
 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.
 """
 return self._sslobj.getpeercert(binary_form)

 def get_verified_chain(self):
 """Returns verified certificate chain provided by the other
 end of the SSL channel as a list of DER-encoded bytes.

 If certificate verification was disabled method acts the same as
 ``SSLSocket.get_unverified_chain``.
 """
 chain = self._sslobj.get_verified_chain()

 if chain is None:
 return []

 return [cert.public_bytes(_ssl.ENCODING_DER) for cert in chain]

 def get_unverified_chain(self):
 """Returns raw certificate chain provided by the other
 end of the SSL channel as a list of DER-encoded bytes.
 """
 chain = self._sslobj.get_unverified_chain()

 if chain is None:
 return []

 return [cert.public_bytes(_ssl.ENCODING_DER) for cert in chain]

 def selected_npn_protocol(self):
 """Return the currently selected NPN protocol as a string, or ``None``
 if a next protocol was not negotiated or if NPN is not supported by one
 of the peers."""
 warnings.warn(
 "ssl NPN is deprecated, use ALPN instead",
 DeprecationWarning,
 stacklevel=2
 )

 def selected_alpn_protocol(self):
 """Return the currently selected ALPN protocol as a string, or ``None``
 if a next protocol was not negotiated or if ALPN is not supported by one
 of the peers."""
 return self._sslobj.selected_alpn_protocol()

 def cipher(self):
 """Return the currently selected cipher as a 3-tuple ``(name,
 ssl_version, secret_bits)``."""
 return self._sslobj.cipher()

 def group(self):
 """Return the currently selected key agreement group name."""
 return self._sslobj.group()

 def client_sigalg(self):
 """Return the selected client authentication signature algorithm."""
 return self._sslobj.client_sigalg()

 def server_sigalg(self):
 """Return the selected server handshake signature algorithm."""
 return self._sslobj.server_sigalg()

 def shared_ciphers(self):
 """Return a list of ciphers shared by the client during the handshake or
 None if this is not a valid server connection.
 """
 return self._sslobj.shared_ciphers()

 def compression(self):
 """Return the current compression algorithm in use, or ``None`` if
 compression was not negotiated or not supported by one of the peers."""
 return self._sslobj.compression()

 def pending(self):
 """Return the number of bytes that can be read immediately."""
 return self._sslobj.pending()

 def do_handshake(self):
 """Start the SSL/TLS handshake."""
 self._sslobj.do_handshake()

 def unwrap(self):
 """Start the SSL shutdown handshake."""
 return self._sslobj.shutdown()

 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)."""
 return self._sslobj.get_channel_binding(cb_type)

 def version(self):
 """Return a string identifying the protocol version used by the
 current SSL channel. """
 return self._sslobj.version()

 def verify_client_post_handshake(self):
 return self._sslobj.verify_client_post_handshake()


def _sslcopydoc(func):
 """Copy docstring from SSLObject to SSLSocket"""
 func.__doc__ = getattr(SSLObject, func.__name__).__doc__
 return func


class _GiveupOnSSLSendfile(Exception):
 pass


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, *args, **kwargs):
 raise TypeError(
 f"{self.__class__.__name__} does not have a public "
 f"constructor. Instances are returned by "
 f"SSLContext.wrap_socket()."
 )

 @classmethod
 def _create(cls, sock, server_side=False, do_handshake_on_connect=True,
 suppress_ragged_eofs=True, server_hostname=None,
 context=None, session=None):
 if sock.getsockopt(SOL_SOCKET, SO_TYPE) != SOCK_STREAM:
 raise NotImplementedError("only stream sockets are supported")
 if server_side:
 if server_hostname:
 raise ValueError("server_hostname can only be specified "
 "in client mode")
 if session is not None:
 raise ValueError("session can only be specified in "
 "client mode")
 if context.check_hostname and not server_hostname:
 raise ValueError("check_hostname requires server_hostname")

 sock_timeout = sock.gettimeout()
 kwargs = dict(
 family=sock.family, type=sock.type, proto=sock.proto,
 fileno=sock.fileno()
 )
 self = cls.__new__(cls, **kwargs)
 super(SSLSocket, self).__init__(**kwargs)
 sock.detach()
 # Now SSLSocket is responsible for closing the file descriptor.
 try:
 self._context = context
 self._session = session
 self._closed = False
 self._sslobj = None
 self.server_side = server_side
 self.server_hostname = context._encode_hostname(server_hostname)
 self.do_handshake_on_connect = do_handshake_on_connect
 self.suppress_ragged_eofs = suppress_ragged_eofs

 # See if we are connected
 try:
 self.getpeername()
 except OSError as e:
 if e.errno != errno.ENOTCONN:
 raise
 connected = False
 blocking = self.getblocking()
 self.setblocking(False)
 try:
 # We are not connected so this is not supposed to block, but
 # testing revealed otherwise on macOS and Windows so we do
 # the non-blocking dance regardless. Our raise when any data
 # is found means consuming the data is harmless.
 notconn_pre_handshake_data = self.recv(1)
 except OSError as e:
 # EINVAL occurs for recv(1) on non-connected on unix sockets.
 if e.errno in (errno.ENOTCONN, errno.EINVAL):
 pass
 elif sys.platform == 'cygwin' and e.errno == errno.EAGAIN:
 # EAGAIN occurs on Cygwin.
 pass
 else:
 raise
 notconn_pre_handshake_data = b''
 self.setblocking(blocking)
 if notconn_pre_handshake_data:
 # This prevents pending data sent to the socket before it was
 # closed from escaping to the caller who could otherwise
 # presume it came through a successful TLS connection.
 reason = "Closed before TLS handshake with data in recv buffer."
 notconn_pre_handshake_data_error = SSLError(e.errno, reason)
 # Add the SSLError attributes that _ssl.c always adds.
 notconn_pre_handshake_data_error.reason = reason
 notconn_pre_handshake_data_error.library = None
 try:
 raise notconn_pre_handshake_data_error
 finally:
 # Explicitly break the reference cycle.
 notconn_pre_handshake_data_error = None
 else:
 connected = True

 self.settimeout(sock_timeout) # Must come after setblocking() calls.
 self._connected = connected
 if connected:
 # create the SSL object
 self._sslobj = self._context._wrap_socket(
 self, server_side, self.server_hostname,
 owner=self, session=self._session,
 )
 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:
 try:
 self.close()
 except OSError:
 pass
 raise
 return self

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

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

 @property
 @_sslcopydoc
 def session(self):
 if self._sslobj is not None:
 return self._sslobj.session

 @session.setter
 def session(self, session):
 self._session = session
 if self._sslobj is not None:
 self._sslobj.session = session

 @property
 @_sslcopydoc
 def session_reused(self):
 if self._sslobj is not None:
 return self._sslobj.session_reused

 def dup(self):
 raise NotImplementedError("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=1024, buffer=None):
 """Read up to LEN bytes and return them.
 Return zero-length string on EOF."""

 self._checkClosed()
 if self._sslobj is None:
 raise ValueError("Read on closed or unwrapped SSL socket.")
 try:
 if buffer is not None:
 return self._sslobj.read(len, buffer)
 else:
 return self._sslobj.read(len)
 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 self._sslobj is None:
 raise ValueError("Write on closed or unwrapped SSL socket.")
 return self._sslobj.write(data)

 @_sslcopydoc
 def getpeercert(self, binary_form=False):
 self._checkClosed()
 self._check_connected()
 return self._sslobj.getpeercert(binary_form)

 @_sslcopydoc
 def get_verified_chain(self):
 chain = self._sslobj.get_verified_chain()

 if chain is None:
 return []

 return [cert.public_bytes(_ssl.ENCODING_DER) for cert in chain]

 @_sslcopydoc
 def get_unverified_chain(self):
 chain = self._sslobj.get_unverified_chain()

 if chain is None:
 return []

 return [cert.public_bytes(_ssl.ENCODING_DER) for cert in chain]

 @_sslcopydoc
 def selected_npn_protocol(self):
 self._checkClosed()
 warnings.warn(
 "ssl NPN is deprecated, use ALPN instead",
 DeprecationWarning,
 stacklevel=2
 )
 return None

 @_sslcopydoc
 def selected_alpn_protocol(self):
 self._checkClosed()
 if self._sslobj is None or not _ssl.HAS_ALPN:
 return None
 else:
 return self._sslobj.selected_alpn_protocol()

 @_sslcopydoc
 def cipher(self):
 self._checkClosed()
 if self._sslobj is None:
 return None
 else:
 return self._sslobj.cipher()

 @_sslcopydoc
 def group(self):
 self._checkClosed()
 if self._sslobj is None:
 return None
 else:
 return self._sslobj.group()

 @_sslcopydoc
 def client_sigalg(self):
 self._checkClosed()
 if self._sslobj is None:
 return None
 else:
 return self._sslobj.client_sigalg()

 @_sslcopydoc
 def server_sigalg(self):
 self._checkClosed()
 if self._sslobj is None:
 return None
 else:
 return self._sslobj.server_sigalg()

 @_sslcopydoc
 def shared_ciphers(self):
 self._checkClosed()
 if self._sslobj is None:
 return None
 else:
 return self._sslobj.shared_ciphers()

 @_sslcopydoc
 def compression(self):
 self._checkClosed()
 if self._sslobj is None:
 return None
 else:
 return self._sslobj.compression()

 def send(self, data, flags=0):
 self._checkClosed()
 if self._sslobj is not None:
 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 super().send(data, flags)

 def sendto(self, data, flags_or_addr, addr=None):
 self._checkClosed()
 if self._sslobj is not None:
 raise ValueError("sendto not allowed on instances of %s" %
 self.__class__)
 elif addr is None:
 return super().sendto(data, flags_or_addr)
 else:
 return super().sendto(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 is not None:
 if flags != 0:
 raise ValueError(
 "non-zero flags not allowed in calls to sendall() on %s" %
 self.__class__)
 count = 0
 with memoryview(data) as view, view.cast("B") as byte_view:
 amount = len(byte_view)
 while count < amount:
 v = self.send(byte_view[count:])
 count += v
 else:
 return super().sendall(data, flags)

 def sendfile(self, file, offset=0, count=None):
 """Send a file, possibly by using an efficient sendfile() call if
 the system supports it. Return the total number of bytes sent.
 """
 if self._sslobj is None:
 return super().sendfile(file, offset, count)

 if not self._sslobj.uses_ktls_for_send():
 return self._sendfile_use_send(file, offset, count)

 sendfile = getattr(self._sslobj, "sendfile", None)
 if sendfile is None:
 return self._sendfile_use_send(file, offset, count)

 try:
 return self._sendfile_zerocopy(
 sendfile, _GiveupOnSSLSendfile, file, offset, count,
 )
 except _GiveupOnSSLSendfile:
 return self._sendfile_use_send(file, offset, count)

 def recv(self, buflen=1024, flags=0):
 self._checkClosed()
 if self._sslobj is not None:
 if flags != 0:
 raise ValueError(
 "non-zero flags not allowed in calls to recv() on %s" %
 self.__class__)
 return self.read(buflen)
 else:
 return super().recv(buflen, flags)

 def recv_into(self, buffer, nbytes=None, flags=0):
 self._checkClosed()
 if nbytes is None:
 if buffer is not None:
 with memoryview(buffer) as view:
 nbytes = view.nbytes
 if not nbytes:
 nbytes = 1024
 else:
 nbytes = 1024
 if self._sslobj is not None:
 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 super().recv_into(buffer, nbytes, flags)

 def recvfrom(self, buflen=1024, flags=0):
 self._checkClosed()
 if self._sslobj is not None:
 raise ValueError("recvfrom not allowed on instances of %s" %
 self.__class__)
 else:
 return super().recvfrom(buflen, flags)

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

 @_sslcopydoc
 def pending(self):
 self._checkClosed()
 if self._sslobj is not None:
 return self._sslobj.pending()
 else:
 return 0

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

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

 @_sslcopydoc
 def verify_client_post_handshake(self):
 if self._sslobj:
 return self._sslobj.verify_client_post_handshake()
 else:
 raise ValueError("No SSL wrapper around " + str(self))

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

 @_sslcopydoc
 def do_handshake(self, block=False):
 self._check_connected()
 timeout = self.gettimeout()
 try:
 if timeout == 0.0 and block:
 self.settimeout(None)
 self._sslobj.do_handshake()
 finally:
 self.settimeout(timeout)

 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 or self._sslobj is not None:
 raise ValueError("attempt to connect already-connected SSLSocket!")
 self._sslobj = self.context._wrap_socket(
 self, False, self.server_hostname,
 owner=self, session=self._session
 )
 try:
 if connect_ex:
 rc = super().connect_ex(addr)
 else:
 rc = None
 super().connect(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 = super().accept()
 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

 @_sslcopydoc
 def get_channel_binding(self, cb_type="tls-unique"):
 if self._sslobj is not None:
 return self._sslobj.get_channel_binding(cb_type)
 else:
 if cb_type not in CHANNEL_BINDING_TYPES:
 raise ValueError(
 "{0} channel binding type not implemented".format(cb_type)
 )
 return None

 @_sslcopydoc
 def version(self):
 if self._sslobj is not None:
 return self._sslobj.version()
 else:
 return None


# Python does not support forward declaration of types.
SSLContext.sslsocket_class = SSLSocket
SSLContext.sslobject_class = SSLObject


# 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.b64encode(der_cert_bytes, wrapcol=64), 'ASCII')
 return f'{PEM_HEADER}\n{f}\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_TLS_CLIENT,
 ca_certs=None, timeout=_GLOBAL_DEFAULT_TIMEOUT):
 """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.
 If 'timeout' 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, timeout=timeout) as sock:
 with context.wrap_socket(sock, server_hostname=host) 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>')