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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 

IS_PYOPENSSL = False 

IS_SECURETRANSPORT = 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 TLS 1.3 cipher suites 

# - prefer cipher suites that offer perfect forward secrecy (DHE/ECDHE), 

# - prefer ECDHE over DHE for better performance, 

# - prefer any AES-GCM and ChaCha20 over any AES-CBC for better performance and 

# security, 

# - prefer AES-GCM over ChaCha20 because hardware-accelerated AES is common, 

# - disable NULL authentication, MD5 MACs and DSS for security reasons. 

DEFAULT_CIPHERS = ':'.join([ 

'TLS13-AES-256-GCM-SHA384', 

'TLS13-CHACHA20-POLY1305-SHA256', 

'TLS13-AES-128-GCM-SHA256', 

'ECDH+AESGCM', 

'ECDH+CHACHA20', 

'DH+AESGCM', 

'DH+CHACHA20', 

'ECDH+AES256', 

'DH+AES256', 

'ECDH+AES128', 

'DH+AES', 

'RSA+AESGCM', 

'RSA+AES', 

'!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/advanced-usage.html' 

'#ssl-warnings', 

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: 

# Note: This branch of code and all the variables in it are no longer 

# used by urllib3 itself. We should consider deprecating and removing 

# this code. 

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 

elif getattr(context, 'load_default_certs', None) is not None: 

# try to load OS default certs; works well on Windows (require Python3.4+) 

context.load_default_certs() 

 

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/advanced-usage.html' 

'#ssl-warnings', 

SNIMissingWarning 

) 

return context.wrap_socket(sock)