from __future__ import absolute_import
import errno
import warnings
import hmac
from binascii import hexlify, unhexlify
from hashlib import md5, sha1, sha256
from ..exceptions import SSLError, InsecurePlatformWarning, SNIMissingWarning
SSLContext = None
HAS_SNI = False
create_default_context = None
IS_PYOPENSSL = False
# Maps the length of a digest to a possible hash function producing this digest
HASHFUNC_MAP = {
32: md5,
40: sha1,
64: sha256,
}
def _const_compare_digest_backport(a, b):
"""
Compare two digests of equal length in constant time.
The digests must be of type str/bytes.
Returns True if the digests match, and False otherwise.
"""
result = abs(len(a) - len(b))
for l, r in zip(bytearray(a), bytearray(b)):
result |= l ^ r
return result == 0
_const_compare_digest = getattr(hmac, 'compare_digest',
_const_compare_digest_backport)
try: # Test for SSL features
import ssl
from ssl import wrap_socket, CERT_NONE, PROTOCOL_SSLv23
from ssl import HAS_SNI # Has SNI?
except ImportError:
pass
try:
from ssl import OP_NO_SSLv2, OP_NO_SSLv3, OP_NO_COMPRESSION
except ImportError:
OP_NO_SSLv2, OP_NO_SSLv3 = 0x1000000, 0x2000000
OP_NO_COMPRESSION = 0x20000
# A secure default.
# Sources for more information on TLS ciphers:
#
# - https://wiki.mozilla.org/Security/Server_Side_TLS
# - https://www.ssllabs.com/projects/best-practices/index.html
# - https://hynek.me/articles/hardening-your-web-servers-ssl-ciphers/
#
# The general intent is:
# - 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,
# - use 3DES as fallback which is secure but slow,
# - disable NULL authentication, MD5 MACs and DSS 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:!aNULL:'
'!eNULL:!MD5'
)
try:
from ssl import SSLContext # Modern SSL?
except ImportError:
import sys
class SSLContext(object): # Platform-specific: Python 2 & 3.1
supports_set_ciphers = ((2, 7) <= sys.version_info < (3,) or
(3, 2) <= sys.version_info)
def __init__(self, protocol_version):
self.protocol = protocol_version
# Use default values from a real SSLContext
self.check_hostname = False
self.verify_mode = ssl.CERT_NONE
self.ca_certs = None
self.options = 0
self.certfile = None
self.keyfile = None
self.ciphers = None
def load_cert_chain(self, certfile, keyfile):
self.certfile = certfile
self.keyfile = keyfile
def load_verify_locations(self, cafile=None, capath=None):
self.ca_certs = cafile
if capath is not None:
raise SSLError("CA directories not supported in older Pythons")
def set_ciphers(self, cipher_suite):
if not self.supports_set_ciphers:
raise TypeError(
'Your version of Python does not support setting '
'a custom cipher suite. Please upgrade to Python '
'2.7, 3.2, or later if you need this functionality.'
)
self.ciphers = cipher_suite
def wrap_socket(self, socket, server_hostname=None, server_side=False):
warnings.warn(
'A true SSLContext object is not available. This prevents '
'urllib3 from configuring SSL appropriately and may cause '
'certain SSL connections to fail. You can upgrade to a newer '
'version of Python to solve this. For more information, see '
'https://urllib3.readthedocs.io/en/latest/security.html'
'#insecureplatformwarning.',
InsecurePlatformWarning
)
kwargs = {
'keyfile': self.keyfile,
'certfile': self.certfile,
'ca_certs': self.ca_certs,
'cert_reqs': self.verify_mode,
'ssl_version': self.protocol,
'server_side': server_side,
}
if self.supports_set_ciphers: # Platform-specific: Python 2.7+
return wrap_socket(socket, ciphers=self.ciphers, **kwargs)
else: # Platform-specific: Python 2.6
return wrap_socket(socket, **kwargs)
def assert_fingerprint(cert, fingerprint):
"""
Checks if given fingerprint matches the supplied certificate.
:param cert:
Certificate as bytes object.
:param fingerprint:
Fingerprint as string of hexdigits, can be interspersed by colons.
"""
fingerprint = fingerprint.replace(':', '').lower()
digest_length = len(fingerprint)
hashfunc = HASHFUNC_MAP.get(digest_length)
if not hashfunc:
raise SSLError(
'Fingerprint of invalid length: {0}'.format(fingerprint))
# We need encode() here for py32; works on py2 and p33.
fingerprint_bytes = unhexlify(fingerprint.encode())
cert_digest = hashfunc(cert).digest()
if not _const_compare_digest(cert_digest, fingerprint_bytes):
raise SSLError('Fingerprints did not match. Expected "{0}", got "{1}".'
.format(fingerprint, hexlify(cert_digest)))
def resolve_cert_reqs(candidate):
"""
Resolves the argument to a numeric constant, which can be passed to
the wrap_socket function/method from the ssl module.
Defaults to :data:`ssl.CERT_NONE`.
If given a string it is assumed to be the name of the constant in the
:mod:`ssl` module or its abbrevation.
(So you can specify `REQUIRED` instead of `CERT_REQUIRED`.
If it's neither `None` nor a string we assume it is already the numeric
constant which can directly be passed to wrap_socket.
"""
if candidate is None:
return CERT_NONE
if isinstance(candidate, str):
res = getattr(ssl, candidate, None)
if res is None:
res = getattr(ssl, 'CERT_' + candidate)
return res
return candidate
def resolve_ssl_version(candidate):
"""
like resolve_cert_reqs
"""
if candidate is None:
return PROTOCOL_SSLv23
if isinstance(candidate, str):
res = getattr(ssl, candidate, None)
if res is None:
res = getattr(ssl, 'PROTOCOL_' + candidate)
return res
return candidate
def create_urllib3_context(ssl_version=None, cert_reqs=None,
options=None, ciphers=None):
"""All arguments have the same meaning as ``ssl_wrap_socket``.
By default, this function does a lot of the same work that
``ssl.create_default_context`` does on Python 3.4+. It:
- Disables SSLv2, SSLv3, and compression
- Sets a restricted set of server ciphers
If you wish to enable SSLv3, you can do::
from urllib3.util import ssl_
context = ssl_.create_urllib3_context()
context.options &= ~ssl_.OP_NO_SSLv3
You can do the same to enable compression (substituting ``COMPRESSION``
for ``SSLv3`` in the last line above).
:param ssl_version:
The desired protocol version to use. This will default to
PROTOCOL_SSLv23 which will negotiate the highest protocol that both
the server and your installation of OpenSSL support.
:param cert_reqs:
Whether to require the certificate verification. This defaults to
``ssl.CERT_REQUIRED``.
:param options:
Specific OpenSSL options. These default to ``ssl.OP_NO_SSLv2``,
``ssl.OP_NO_SSLv3``, ``ssl.OP_NO_COMPRESSION``.
:param ciphers:
Which cipher suites to allow the server to select.
:returns:
Constructed SSLContext object with specified options
:rtype: SSLContext
"""
context = SSLContext(ssl_version or ssl.PROTOCOL_SSLv23)
# Setting the default here, as we may have no ssl module on import
cert_reqs = ssl.CERT_REQUIRED if cert_reqs is None else cert_reqs
if options is None:
options = 0
# SSLv2 is easily broken and is considered harmful and dangerous
options |= OP_NO_SSLv2
# SSLv3 has several problems and is now dangerous
options |= OP_NO_SSLv3
# Disable compression to prevent CRIME attacks for OpenSSL 1.0+
# (issue #309)
options |= OP_NO_COMPRESSION
context.options |= options
if getattr(context, 'supports_set_ciphers', True): # Platform-specific: Python 2.6
context.set_ciphers(ciphers or DEFAULT_CIPHERS)
context.verify_mode = cert_reqs
if getattr(context, 'check_hostname', None) is not None: # Platform-specific: Python 3.2
# We do our own verification, including fingerprints and alternative
# hostnames. So disable it here
context.check_hostname = False
return context
def ssl_wrap_socket(sock, keyfile=None, certfile=None, cert_reqs=None,
ca_certs=None, server_hostname=None,
ssl_version=None, ciphers=None, ssl_context=None,
ca_cert_dir=None):
"""
All arguments except for server_hostname, ssl_context, and ca_cert_dir have
the same meaning as they do when using :func:`ssl.wrap_socket`.
:param server_hostname:
When SNI is supported, the expected hostname of the certificate
:param ssl_context:
A pre-made :class:`SSLContext` object. If none is provided, one will
be created using :func:`create_urllib3_context`.
:param ciphers:
A string of ciphers we wish the client to support. This is not
supported on Python 2.6 as the ssl module does not support it.
:param ca_cert_dir:
A directory containing CA certificates in multiple separate files, as
supported by OpenSSL's -CApath flag or the capath argument to
SSLContext.load_verify_locations().
"""
context = ssl_context
if context is None:
context = create_urllib3_context(ssl_version, cert_reqs,
ciphers=ciphers)
if ca_certs or ca_cert_dir:
try:
context.load_verify_locations(ca_certs, ca_cert_dir)
except IOError as e: # Platform-specific: Python 2.6, 2.7, 3.2
raise SSLError(e)
# Py33 raises FileNotFoundError which subclasses OSError
# These are not equivalent unless we check the errno attribute
except OSError as e: # Platform-specific: Python 3.3 and beyond
if e.errno == errno.ENOENT:
raise SSLError(e)
raise
if certfile:
context.load_cert_chain(certfile, keyfile)
if HAS_SNI: # Platform-specific: OpenSSL with enabled SNI
return context.wrap_socket(sock, server_hostname=server_hostname)
warnings.warn(
'An HTTPS request has been made, but the SNI (Subject Name '
'Indication) extension to TLS is not available on this platform. '
'This may cause the server to present an incorrect TLS '
'certificate, which can cause validation failures. You can upgrade to '
'a newer version of Python to solve this. For more information, see '
'https://urllib3.readthedocs.io/en/latest/security.html'
'#snimissingwarning.',
SNIMissingWarning
)
return context.wrap_socket(sock)
