kbe/src/lib/python/Doc/library/ssl.rst
ssl --- TLS/SSL wrapper for socket objects.. module:: ssl :synopsis: TLS/SSL wrapper for socket objects
.. moduleauthor:: Bill Janssen [email protected] .. sectionauthor:: Bill Janssen [email protected]
Source code: :source:Lib/ssl.py
.. index:: single: OpenSSL; (use in module ssl)
.. index:: TLS, SSL, Transport Layer Security, Secure Sockets Layer
This module provides access to Transport Layer Security (often known as "Secure Sockets Layer") encryption and peer authentication facilities for network sockets, both client-side and server-side. This module uses the OpenSSL library. It is available on all modern Unix systems, Windows, Mac OS X, and probably additional platforms, as long as OpenSSL is installed on that platform.
.. note::
Some behavior may be platform dependent, since calls are made to the operating system socket APIs. The installed version of OpenSSL may also cause variations in behavior. For example, TLSv1.1 and TLSv1.2 come with openssl version 1.0.1.
.. warning::
Don't use this module without reading the :ref:ssl-security. Doing so
may lead to a false sense of security, as the default settings of the
ssl module are not necessarily appropriate for your application.
This section documents the objects and functions in the ssl module; for more
general information about TLS, SSL, and certificates, the reader is referred to
the documents in the "See Also" section at the bottom.
This module provides a class, :class:ssl.SSLSocket, which is derived from the
:class:socket.socket type, and provides a socket-like wrapper that also
encrypts and decrypts the data going over the socket with SSL. It supports
additional methods such as :meth:getpeercert, which retrieves the
certificate of the other side of the connection, and :meth:cipher,which
retrieves the cipher being used for the secure connection.
For more sophisticated applications, the :class:ssl.SSLContext class
helps manage settings and certificates, which can then be inherited
by SSL sockets created through the :meth:SSLContext.wrap_socket method.
.. versionchanged:: 3.5.3 Updated to support linking with OpenSSL 1.1.0
.. versionchanged:: 3.6
OpenSSL 0.9.8, 1.0.0 and 1.0.1 are deprecated and no longer supported. In the future the ssl module will require at least OpenSSL 1.0.2 or 1.1.0.
Socket creation ^^^^^^^^^^^^^^^
Since Python 3.2 and 2.7.9, it is recommended to use the
:meth:SSLContext.wrap_socket of an :class:SSLContext instance to wrap
sockets as :class:SSLSocket objects. The helper functions
:func:create_default_context returns a new context with secure default
settings. The old :func:wrap_socket function is deprecated since it is
both inefficient and has no support for server name indication (SNI) and
hostname matching.
Client socket example with default context and IPv4/IPv6 dual stack::
import socket
import ssl
hostname = 'www.python.org'
context = ssl.create_default_context()
with socket.create_connection((hostname, 443)) as sock:
with context.wrap_socket(sock, server_hostname=hostname) as ssock:
print(ssock.version())
Client socket example with custom context and IPv4::
hostname = 'www.python.org'
# PROTOCOL_TLS_CLIENT requires valid cert chain and hostname
context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT)
context.load_verify_locations('path/to/cabundle.pem')
with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
with context.wrap_socket(sock, server_hostname=hostname) as ssock:
print(ssock.version())
Server socket example listening on localhost IPv4::
context = ssl.SSLContext(ssl.PROTOCOL_TLS_SERVER)
context.load_cert_chain('/path/to/certchain.pem', '/path/to/private.key')
with socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0) as sock:
sock.bind(('127.0.0.1', 8443))
sock.listen(5)
with context.wrap_socket(sock, server_side=True) as ssock:
conn, addr = ssock.accept()
...
Context creation ^^^^^^^^^^^^^^^^
A convenience function helps create :class:SSLContext objects for common
purposes.
.. function:: create_default_context(purpose=Purpose.SERVER_AUTH, cafile=None, capath=None, cadata=None)
Return a new :class:SSLContext object with default settings for
the given purpose. The settings are chosen by the :mod:ssl module,
and usually represent a higher security level than when calling the
:class:SSLContext constructor directly.
cafile, capath, cadata represent optional CA certificates to
trust for certificate verification, as in
:meth:SSLContext.load_verify_locations. If all three are
:const:None, this function can choose to trust the system's default
CA certificates instead.
The settings are: :data:PROTOCOL_TLS, :data:OP_NO_SSLv2, and
:data:OP_NO_SSLv3 with high encryption cipher suites without RC4 and
without unauthenticated cipher suites. Passing :data:~Purpose.SERVER_AUTH
as purpose sets :data:~SSLContext.verify_mode to :data:CERT_REQUIRED
and either loads CA certificates (when at least one of cafile, capath or
cadata is given) or uses :meth:SSLContext.load_default_certs to load
default CA certificates.
.. note:: The protocol, options, cipher and other settings may change to more restrictive values anytime without prior deprecation. The values represent a fair balance between compatibility and security.
If your application needs specific settings, you should create a
:class:`SSLContext` and apply the settings yourself.
.. note::
If you find that when certain older clients or servers attempt to connect
with a :class:SSLContext created by this function that they get an error
stating "Protocol or cipher suite mismatch", it may be that they only
support SSL3.0 which this function excludes using the
:data:OP_NO_SSLv3. SSL3.0 is widely considered to be completely broken <https://en.wikipedia.org/wiki/POODLE>_. If you still wish to continue to
use this function but still allow SSL 3.0 connections you can re-enable
them using::
ctx = ssl.create_default_context(Purpose.CLIENT_AUTH)
ctx.options &= ~ssl.OP_NO_SSLv3
.. versionadded:: 3.4
.. versionchanged:: 3.4.4
RC4 was dropped from the default cipher string.
.. versionchanged:: 3.6
ChaCha20/Poly1305 was added to the default cipher string.
3DES was dropped from the default cipher string.
Exceptions ^^^^^^^^^^
.. exception:: SSLError
Raised to signal an error from the underlying SSL implementation
(currently provided by the OpenSSL library). This signifies some
problem in the higher-level encryption and authentication layer that's
superimposed on the underlying network connection. This error
is a subtype of :exc:OSError. The error code and message of
:exc:SSLError instances are provided by the OpenSSL library.
.. versionchanged:: 3.3
:exc:SSLError used to be a subtype of :exc:socket.error.
.. attribute:: library
A string mnemonic designating the OpenSSL submodule in which the error
occurred, such as ``SSL``, ``PEM`` or ``X509``. The range of possible
values depends on the OpenSSL version.
.. versionadded:: 3.3
.. attribute:: reason
A string mnemonic designating the reason this error occurred, for
example ``CERTIFICATE_VERIFY_FAILED``. The range of possible
values depends on the OpenSSL version.
.. versionadded:: 3.3
.. exception:: SSLZeroReturnError
A subclass of :exc:SSLError raised when trying to read or write and
the SSL connection has been closed cleanly. Note that this doesn't
mean that the underlying transport (read TCP) has been closed.
.. versionadded:: 3.3
.. exception:: SSLWantReadError
A subclass of :exc:SSLError raised by a :ref:non-blocking SSL socket <ssl-nonblocking> when trying to read or write data, but more data needs
to be received on the underlying TCP transport before the request can be
fulfilled.
.. versionadded:: 3.3
.. exception:: SSLWantWriteError
A subclass of :exc:SSLError raised by a :ref:non-blocking SSL socket <ssl-nonblocking> when trying to read or write data, but more data needs
to be sent on the underlying TCP transport before the request can be
fulfilled.
.. versionadded:: 3.3
.. exception:: SSLSyscallError
A subclass of :exc:SSLError raised when a system error was encountered
while trying to fulfill an operation on a SSL socket. Unfortunately,
there is no easy way to inspect the original errno number.
.. versionadded:: 3.3
.. exception:: SSLEOFError
A subclass of :exc:SSLError raised when the SSL connection has been
terminated abruptly. Generally, you shouldn't try to reuse the underlying
transport when this error is encountered.
.. versionadded:: 3.3
.. exception:: SSLCertVerificationError
A subclass of :exc:SSLError raised when certificate validation has
failed.
.. versionadded:: 3.7
.. attribute:: verify_code
A numeric error number that denotes the verification error.
.. attribute:: verify_message
A human readable string of the verification error.
.. exception:: CertificateError
An alias for :exc:SSLCertVerificationError.
.. versionchanged:: 3.7
The exception is now an alias for :exc:SSLCertVerificationError.
Random generation ^^^^^^^^^^^^^^^^^
.. function:: RAND_bytes(num)
Return num cryptographically strong pseudo-random bytes. Raises an
:class:SSLError if the PRNG has not been seeded with enough data or if the
operation is not supported by the current RAND method. :func:RAND_status
can be used to check the status of the PRNG and :func:RAND_add can be used
to seed the PRNG.
For almost all applications :func:os.urandom is preferable.
Read the Wikipedia article, Cryptographically secure pseudorandom number generator (CSPRNG) <https://en.wikipedia.org/wiki/Cryptographically_secure_pseudorandom_number_generator>_,
to get the requirements of a cryptographically generator.
.. versionadded:: 3.3
.. function:: RAND_pseudo_bytes(num)
Return (bytes, is_cryptographic): bytes are num pseudo-random bytes,
is_cryptographic is True if the bytes generated are cryptographically
strong. Raises an :class:SSLError if the operation is not supported by the
current RAND method.
Generated pseudo-random byte sequences will be unique if they are of sufficient length, but are not necessarily unpredictable. They can be used for non-cryptographic purposes and for certain purposes in cryptographic protocols, but usually not for key generation etc.
For almost all applications :func:os.urandom is preferable.
.. versionadded:: 3.3
.. deprecated:: 3.6
OpenSSL has deprecated :func:`ssl.RAND_pseudo_bytes`, use
:func:`ssl.RAND_bytes` instead.
.. function:: RAND_status()
Return True if the SSL pseudo-random number generator has been seeded
with 'enough' randomness, and False otherwise. You can use
:func:ssl.RAND_egd and :func:ssl.RAND_add to increase the randomness of
the pseudo-random number generator.
.. function:: RAND_egd(path)
If you are running an entropy-gathering daemon (EGD) somewhere, and path is the pathname of a socket connection open to it, this will read 256 bytes of randomness from the socket, and add it to the SSL pseudo-random number generator to increase the security of generated secret keys. This is typically only necessary on systems without better sources of randomness.
See http://egd.sourceforge.net/ or http://prngd.sourceforge.net/ for sources of entropy-gathering daemons.
.. availability:: not available with LibreSSL and OpenSSL > 1.1.0.
.. function:: RAND_add(bytes, entropy)
Mix the given bytes into the SSL pseudo-random number generator. The
parameter entropy (a float) is a lower bound on the entropy contained in
string (so you can always use :const:0.0). See :rfc:1750 for more
information on sources of entropy.
.. versionchanged:: 3.5
Writable :term:bytes-like object is now accepted.
Certificate handling ^^^^^^^^^^^^^^^^^^^^
.. testsetup::
import ssl
.. function:: match_hostname(cert, hostname)
Verify that cert (in decoded format as returned by
:meth:SSLSocket.getpeercert) matches the given hostname. The rules
applied are those for checking the identity of HTTPS servers as outlined
in :rfc:2818, :rfc:5280 and :rfc:6125. In addition to HTTPS, this
function should be suitable for checking the identity of servers in
various SSL-based protocols such as FTPS, IMAPS, POPS and others.
:exc:CertificateError is raised on failure. On success, the function
returns nothing::
>>> cert = {'subject': ((('commonName', 'example.com'),),)}
>>> ssl.match_hostname(cert, "example.com")
>>> ssl.match_hostname(cert, "example.org")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/py3k/Lib/ssl.py", line 130, in match_hostname
ssl.CertificateError: hostname 'example.org' doesn't match 'example.com'
.. versionadded:: 3.2
.. versionchanged:: 3.3.3
The function now follows :rfc:6125, section 6.4.3 and does neither
match multiple wildcards (e.g. *.*.com or *a*.example.org) nor
a wildcard inside an internationalized domain names (IDN) fragment.
IDN A-labels such as www*.xn--pthon-kva.org are still supported,
but x*.python.org no longer matches xn--tda.python.org.
.. versionchanged:: 3.5 Matching of IP addresses, when present in the subjectAltName field of the certificate, is now supported.
.. versionchanged:: 3.7 The function is no longer used to TLS connections. Hostname matching is now performed by OpenSSL.
Allow wildcard when it is the leftmost and the only character
in that segment. Partial wildcards like ``www*.example.com`` are no
longer supported.
.. deprecated:: 3.7
.. function:: cert_time_to_seconds(cert_time)
Return the time in seconds since the Epoch, given the cert_time
string representing the "notBefore" or "notAfter" date from a
certificate in "%b %d %H:%M:%S %Y %Z" strptime format (C
locale).
Here's an example:
.. doctest:: newcontext
>>> import ssl
>>> timestamp = ssl.cert_time_to_seconds("Jan 5 09:34:43 2018 GMT")
>>> timestamp # doctest: +SKIP
1515144883
>>> from datetime import datetime
>>> print(datetime.utcfromtimestamp(timestamp)) # doctest: +SKIP
2018-01-05 09:34:43
"notBefore" or "notAfter" dates must use GMT (:rfc:5280).
.. versionchanged:: 3.5 Interpret the input time as a time in UTC as specified by 'GMT' timezone in the input string. Local timezone was used previously. Return an integer (no fractions of a second in the input format)
.. function:: get_server_certificate(addr, ssl_version=PROTOCOL_TLS, ca_certs=None)
Given the address addr of an SSL-protected server, as a (hostname,
port-number) pair, fetches the server's certificate, and returns it as a
PEM-encoded string. If ssl_version is specified, uses that version of
the SSL protocol to attempt to connect to the server. If ca_certs is
specified, it should be a file containing a list of root certificates, the
same format as used for the same parameter in
:meth:SSLContext.wrap_socket. The call will attempt to validate the
server certificate against that set of root certificates, and will fail
if the validation attempt fails.
.. versionchanged:: 3.3 This function is now IPv6-compatible.
.. versionchanged:: 3.5
The default ssl_version is changed from :data:PROTOCOL_SSLv3 to
:data:PROTOCOL_TLS for maximum compatibility with modern servers.
.. function:: DER_cert_to_PEM_cert(DER_cert_bytes)
Given a certificate as a DER-encoded blob of bytes, returns a PEM-encoded string version of the same certificate.
.. function:: PEM_cert_to_DER_cert(PEM_cert_string)
Given a certificate as an ASCII PEM string, returns a DER-encoded sequence of bytes for that same certificate.
.. function:: get_default_verify_paths()
Returns a named tuple with paths to OpenSSL's default cafile and capath.
The paths are the same as used by
:meth:SSLContext.set_default_verify_paths. The return value is a
:term:named tuple DefaultVerifyPaths:
cafile - resolved path to cafile or None if the file doesn't exist,capath - resolved path to capath or None if the directory doesn't exist,openssl_cafile_env - OpenSSL's environment key that points to a cafile,openssl_cafile - hard coded path to a cafile,openssl_capath_env - OpenSSL's environment key that points to a capath,openssl_capath - hard coded path to a capath directory.. availability:: LibreSSL ignores the environment vars
:attr:openssl_cafile_env and :attr:openssl_capath_env.
.. versionadded:: 3.4
.. function:: enum_certificates(store_name)
Retrieve certificates from Windows' system cert store. store_name may be
one of CA, ROOT or MY. Windows may provide additional cert
stores, too.
The function returns a list of (cert_bytes, encoding_type, trust) tuples.
The encoding_type specifies the encoding of cert_bytes. It is either
:const:x509_asn for X.509 ASN.1 data or :const:pkcs_7_asn for
PKCS#7 ASN.1 data. Trust specifies the purpose of the certificate as a set
of OIDS or exactly True if the certificate is trustworthy for all
purposes.
Example::
>>> ssl.enum_certificates("CA")
[(b'data...', 'x509_asn', {'1.3.6.1.5.5.7.3.1', '1.3.6.1.5.5.7.3.2'}),
(b'data...', 'x509_asn', True)]
.. availability:: Windows.
.. versionadded:: 3.4
.. function:: enum_crls(store_name)
Retrieve CRLs from Windows' system cert store. store_name may be
one of CA, ROOT or MY. Windows may provide additional cert
stores, too.
The function returns a list of (cert_bytes, encoding_type, trust) tuples.
The encoding_type specifies the encoding of cert_bytes. It is either
:const:x509_asn for X.509 ASN.1 data or :const:pkcs_7_asn for
PKCS#7 ASN.1 data.
.. availability:: Windows.
.. versionadded:: 3.4
.. function:: wrap_socket(sock, keyfile=None, certfile=None,
server_side=False, cert_reqs=CERT_NONE, ssl_version=PROTOCOL_TLS,
ca_certs=None, do_handshake_on_connect=True,
suppress_ragged_eofs=True, ciphers=None)
Takes an instance sock of :class:socket.socket, and returns an instance
of :class:ssl.SSLSocket, a subtype of :class:socket.socket, which wraps
the underlying socket in an SSL context. sock must be a
:data:~socket.SOCK_STREAM socket; other socket types are unsupported.
Internally, function creates a :class:SSLContext with protocol
ssl_version and :attr:SSLContext.options set to cert_reqs. If
parameters keyfile, certfile, ca_certs or ciphers are set, then
the values are passed to :meth:SSLContext.load_cert_chain,
:meth:SSLContext.load_verify_locations, and
:meth:SSLContext.set_ciphers.
The arguments server_side, do_handshake_on_connect, and
suppress_ragged_eofs have the same meaning as
:meth:SSLContext.wrap_socket.
.. deprecated:: 3.7
Since Python 3.2 and 2.7.9, it is recommended to use the
:meth:`SSLContext.wrap_socket` instead of :func:`wrap_socket`. The
top-level function is limited and creates an insecure client socket
without server name indication or hostname matching.
Constants ^^^^^^^^^
All constants are now :class:enum.IntEnum or :class:enum.IntFlag collections.
.. versionadded:: 3.6
.. data:: CERT_NONE
Possible value for :attr:SSLContext.verify_mode, or the cert_reqs
parameter to :func:wrap_socket. Except for :const:PROTOCOL_TLS_CLIENT,
it is the default mode. With client-side sockets, just about any
cert is accepted. Validation errors, such as untrusted or expired cert,
are ignored and do not abort the TLS/SSL handshake.
In server mode, no certificate is requested from the client, so the client does not send any for client cert authentication.
See the discussion of :ref:ssl-security below.
.. data:: CERT_OPTIONAL
Possible value for :attr:SSLContext.verify_mode, or the cert_reqs
parameter to :func:wrap_socket. In client mode, :const:CERT_OPTIONAL
has the same meaning as :const:CERT_REQUIRED. It is recommended to
use :const:CERT_REQUIRED for client-side sockets instead.
In server mode, a client certificate request is sent to the client. The client may either ignore the request or send a certificate in order perform TLS client cert authentication. If the client chooses to send a certificate, it is verified. Any verification error immediately aborts the TLS handshake.
Use of this setting requires a valid set of CA certificates to
be passed, either to :meth:SSLContext.load_verify_locations or as a
value of the ca_certs parameter to :func:wrap_socket.
.. data:: CERT_REQUIRED
Possible value for :attr:SSLContext.verify_mode, or the cert_reqs
parameter to :func:wrap_socket. In this mode, certificates are
required from the other side of the socket connection; an :class:SSLError
will be raised if no certificate is provided, or if its validation fails.
This mode is not sufficient to verify a certificate in client mode as
it does not match hostnames. :attr:~SSLContext.check_hostname must be
enabled as well to verify the authenticity of a cert.
:const:PROTOCOL_TLS_CLIENT uses :const:CERT_REQUIRED and
enables :attr:~SSLContext.check_hostname by default.
With server socket, this mode provides mandatory TLS client cert authentication. A client certificate request is sent to the client and the client must provide a valid and trusted certificate.
Use of this setting requires a valid set of CA certificates to
be passed, either to :meth:SSLContext.load_verify_locations or as a
value of the ca_certs parameter to :func:wrap_socket.
.. class:: VerifyMode
:class:enum.IntEnum collection of CERT_* constants.
.. versionadded:: 3.6
.. data:: VERIFY_DEFAULT
Possible value for :attr:SSLContext.verify_flags. In this mode, certificate
revocation lists (CRLs) are not checked. By default OpenSSL does neither
require nor verify CRLs.
.. versionadded:: 3.4
.. data:: VERIFY_CRL_CHECK_LEAF
Possible value for :attr:SSLContext.verify_flags. In this mode, only the
peer cert is check but non of the intermediate CA certificates. The mode
requires a valid CRL that is signed by the peer cert's issuer (its direct
ancestor CA). If no proper has been loaded
:attr:SSLContext.load_verify_locations, validation will fail.
.. versionadded:: 3.4
.. data:: VERIFY_CRL_CHECK_CHAIN
Possible value for :attr:SSLContext.verify_flags. In this mode, CRLs of
all certificates in the peer cert chain are checked.
.. versionadded:: 3.4
.. data:: VERIFY_X509_STRICT
Possible value for :attr:SSLContext.verify_flags to disable workarounds
for broken X.509 certificates.
.. versionadded:: 3.4
.. data:: VERIFY_X509_TRUSTED_FIRST
Possible value for :attr:SSLContext.verify_flags. It instructs OpenSSL to
prefer trusted certificates when building the trust chain to validate a
certificate. This flag is enabled by default.
.. versionadded:: 3.4.4
.. class:: VerifyFlags
:class:enum.IntFlag collection of VERIFY_* constants.
.. versionadded:: 3.6
.. data:: PROTOCOL_TLS
Selects the highest protocol version that both the client and server support. Despite the name, this option can select both "SSL" and "TLS" protocols.
.. versionadded:: 3.6
.. data:: PROTOCOL_TLS_CLIENT
Auto-negotiate the highest protocol version like :data:PROTOCOL_TLS,
but only support client-side :class:SSLSocket connections. The protocol
enables :data:CERT_REQUIRED and :attr:~SSLContext.check_hostname by
default.
.. versionadded:: 3.6
.. data:: PROTOCOL_TLS_SERVER
Auto-negotiate the highest protocol version like :data:PROTOCOL_TLS,
but only support server-side :class:SSLSocket connections.
.. versionadded:: 3.6
.. data:: PROTOCOL_SSLv23
Alias for data:PROTOCOL_TLS.
.. deprecated:: 3.6
Use :data:`PROTOCOL_TLS` instead.
.. data:: PROTOCOL_SSLv2
Selects SSL version 2 as the channel encryption protocol.
This protocol is not available if OpenSSL is compiled with the
OPENSSL_NO_SSL2 flag.
.. warning::
SSL version 2 is insecure. Its use is highly discouraged.
.. deprecated:: 3.6
OpenSSL has removed support for SSLv2.
.. data:: PROTOCOL_SSLv3
Selects SSL version 3 as the channel encryption protocol.
This protocol is not be available if OpenSSL is compiled with the
OPENSSL_NO_SSLv3 flag.
.. warning::
SSL version 3 is insecure. Its use is highly discouraged.
.. deprecated:: 3.6
OpenSSL has deprecated all version specific protocols. Use the default
protocol :data:`PROTOCOL_TLS` with flags like :data:`OP_NO_SSLv3` instead.
.. data:: PROTOCOL_TLSv1
Selects TLS version 1.0 as the channel encryption protocol.
.. deprecated:: 3.6
OpenSSL has deprecated all version specific protocols. Use the default
protocol :data:`PROTOCOL_TLS` with flags like :data:`OP_NO_SSLv3` instead.
.. data:: PROTOCOL_TLSv1_1
Selects TLS version 1.1 as the channel encryption protocol. Available only with openssl version 1.0.1+.
.. versionadded:: 3.4
.. deprecated:: 3.6
OpenSSL has deprecated all version specific protocols. Use the default
protocol :data:`PROTOCOL_TLS` with flags like :data:`OP_NO_SSLv3` instead.
.. data:: PROTOCOL_TLSv1_2
Selects TLS version 1.2 as the channel encryption protocol. This is the most modern version, and probably the best choice for maximum protection, if both sides can speak it. Available only with openssl version 1.0.1+.
.. versionadded:: 3.4
.. deprecated:: 3.6
OpenSSL has deprecated all version specific protocols. Use the default
protocol :data:`PROTOCOL_TLS` with flags like :data:`OP_NO_SSLv3` instead.
.. data:: OP_ALL
Enables workarounds for various bugs present in other SSL implementations.
This option is set by default. It does not necessarily set the same
flags as OpenSSL's SSL_OP_ALL constant.
.. versionadded:: 3.2
.. data:: OP_NO_SSLv2
Prevents an SSLv2 connection. This option is only applicable in
conjunction with :const:PROTOCOL_TLS. It prevents the peers from
choosing SSLv2 as the protocol version.
.. versionadded:: 3.2
.. deprecated:: 3.6
SSLv2 is deprecated
.. data:: OP_NO_SSLv3
Prevents an SSLv3 connection. This option is only applicable in
conjunction with :const:PROTOCOL_TLS. It prevents the peers from
choosing SSLv3 as the protocol version.
.. versionadded:: 3.2
.. deprecated:: 3.6
SSLv3 is deprecated
.. data:: OP_NO_TLSv1
Prevents a TLSv1 connection. This option is only applicable in
conjunction with :const:PROTOCOL_TLS. It prevents the peers from
choosing TLSv1 as the protocol version.
.. versionadded:: 3.2
.. deprecated:: 3.7
The option is deprecated since OpenSSL 1.1.0, use the new
:attr:SSLContext.minimum_version and
:attr:SSLContext.maximum_version instead.
.. data:: OP_NO_TLSv1_1
Prevents a TLSv1.1 connection. This option is only applicable in conjunction
with :const:PROTOCOL_TLS. It prevents the peers from choosing TLSv1.1 as
the protocol version. Available only with openssl version 1.0.1+.
.. versionadded:: 3.4
.. deprecated:: 3.7 The option is deprecated since OpenSSL 1.1.0.
.. data:: OP_NO_TLSv1_2
Prevents a TLSv1.2 connection. This option is only applicable in conjunction
with :const:PROTOCOL_TLS. It prevents the peers from choosing TLSv1.2 as
the protocol version. Available only with openssl version 1.0.1+.
.. versionadded:: 3.4
.. deprecated:: 3.7 The option is deprecated since OpenSSL 1.1.0.
.. data:: OP_NO_TLSv1_3
Prevents a TLSv1.3 connection. This option is only applicable in conjunction
with :const:PROTOCOL_TLS. It prevents the peers from choosing TLSv1.3 as
the protocol version. TLS 1.3 is available with OpenSSL 1.1.1 or later.
When Python has been compiled against an older version of OpenSSL, the
flag defaults to 0.
.. versionadded:: 3.7
.. deprecated:: 3.7 The option is deprecated since OpenSSL 1.1.0. It was added to 2.7.15, 3.6.3 and 3.7.0 for backwards compatibility with OpenSSL 1.0.2.
.. data:: OP_NO_RENEGOTIATION
Disable all renegotiation in TLSv1.2 and earlier. Do not send HelloRequest messages, and ignore renegotiation requests via ClientHello.
This option is only available with OpenSSL 1.1.0h and later.
.. versionadded:: 3.7
.. data:: OP_CIPHER_SERVER_PREFERENCE
Use the server's cipher ordering preference, rather than the client's. This option has no effect on client sockets and SSLv2 server sockets.
.. versionadded:: 3.3
.. data:: OP_SINGLE_DH_USE
Prevents re-use of the same DH key for distinct SSL sessions. This improves forward secrecy but requires more computational resources. This option only applies to server sockets.
.. versionadded:: 3.3
.. data:: OP_SINGLE_ECDH_USE
Prevents re-use of the same ECDH key for distinct SSL sessions. This improves forward secrecy but requires more computational resources. This option only applies to server sockets.
.. versionadded:: 3.3
.. data:: OP_ENABLE_MIDDLEBOX_COMPAT
Send dummy Change Cipher Spec (CCS) messages in TLS 1.3 handshake to make a TLS 1.3 connection look more like a TLS 1.2 connection.
This option is only available with OpenSSL 1.1.1 and later.
.. versionadded:: 3.8
.. data:: OP_NO_COMPRESSION
Disable compression on the SSL channel. This is useful if the application protocol supports its own compression scheme.
This option is only available with OpenSSL 1.0.0 and later.
.. versionadded:: 3.3
.. class:: Options
:class:enum.IntFlag collection of OP_* constants.
.. data:: OP_NO_TICKET
Prevent client side from requesting a session ticket.
.. versionadded:: 3.6
.. data:: HAS_ALPN
Whether the OpenSSL library has built-in support for the Application-Layer
Protocol Negotiation TLS extension as described in :rfc:7301.
.. versionadded:: 3.5
.. data:: HAS_NEVER_CHECK_COMMON_NAME
Whether the OpenSSL library has built-in support not checking subject
common name and :attr:SSLContext.hostname_checks_common_name is
writeable.
.. versionadded:: 3.7
.. data:: HAS_ECDH
Whether the OpenSSL library has built-in support for the Elliptic Curve-based Diffie-Hellman key exchange. This should be true unless the feature was explicitly disabled by the distributor.
.. versionadded:: 3.3
.. data:: HAS_SNI
Whether the OpenSSL library has built-in support for the Server Name
Indication extension (as defined in :rfc:6066).
.. versionadded:: 3.2
.. data:: HAS_NPN
Whether the OpenSSL library has built-in support for the Next Protocol
Negotiation as described in the Application Layer Protocol Negotiation <https://en.wikipedia.org/wiki/Application-Layer_Protocol_Negotiation>_.
When true, you can use the :meth:SSLContext.set_npn_protocols method to advertise
which protocols you want to support.
.. versionadded:: 3.3
.. data:: HAS_SSLv2
Whether the OpenSSL library has built-in support for the SSL 2.0 protocol.
.. versionadded:: 3.7
.. data:: HAS_SSLv3
Whether the OpenSSL library has built-in support for the SSL 3.0 protocol.
.. versionadded:: 3.7
.. data:: HAS_TLSv1
Whether the OpenSSL library has built-in support for the TLS 1.0 protocol.
.. versionadded:: 3.7
.. data:: HAS_TLSv1_1
Whether the OpenSSL library has built-in support for the TLS 1.1 protocol.
.. versionadded:: 3.7
.. data:: HAS_TLSv1_2
Whether the OpenSSL library has built-in support for the TLS 1.2 protocol.
.. versionadded:: 3.7
.. data:: HAS_TLSv1_3
Whether the OpenSSL library has built-in support for the TLS 1.3 protocol.
.. versionadded:: 3.7
.. data:: CHANNEL_BINDING_TYPES
List of supported TLS channel binding types. Strings in this list
can be used as arguments to :meth:SSLSocket.get_channel_binding.
.. versionadded:: 3.3
.. data:: OPENSSL_VERSION
The version string of the OpenSSL library loaded by the interpreter::
>>> ssl.OPENSSL_VERSION
'OpenSSL 1.0.2k 26 Jan 2017'
.. versionadded:: 3.2
.. data:: OPENSSL_VERSION_INFO
A tuple of five integers representing version information about the OpenSSL library::
>>> ssl.OPENSSL_VERSION_INFO
(1, 0, 2, 11, 15)
.. versionadded:: 3.2
.. data:: OPENSSL_VERSION_NUMBER
The raw version number of the OpenSSL library, as a single integer::
>>> ssl.OPENSSL_VERSION_NUMBER
268443839
>>> hex(ssl.OPENSSL_VERSION_NUMBER)
'0x100020bf'
.. versionadded:: 3.2
.. data:: ALERT_DESCRIPTION_HANDSHAKE_FAILURE ALERT_DESCRIPTION_INTERNAL_ERROR ALERT_DESCRIPTION_*
Alert Descriptions from :rfc:5246 and others. The IANA TLS Alert Registry <https://www.iana.org/assignments/tls-parameters/tls-parameters.xml#tls-parameters-6>_
contains this list and references to the RFCs where their meaning is defined.
Used as the return value of the callback function in
:meth:SSLContext.set_servername_callback.
.. versionadded:: 3.4
.. class:: AlertDescription
:class:enum.IntEnum collection of ALERT_DESCRIPTION_* constants.
.. versionadded:: 3.6
.. data:: Purpose.SERVER_AUTH
Option for :func:create_default_context and
:meth:SSLContext.load_default_certs. This value indicates that the
context may be used to authenticate Web servers (therefore, it will
be used to create client-side sockets).
.. versionadded:: 3.4
.. data:: Purpose.CLIENT_AUTH
Option for :func:create_default_context and
:meth:SSLContext.load_default_certs. This value indicates that the
context may be used to authenticate Web clients (therefore, it will
be used to create server-side sockets).
.. versionadded:: 3.4
.. class:: SSLErrorNumber
:class:enum.IntEnum collection of SSL_ERROR_* constants.
.. versionadded:: 3.6
.. class:: TLSVersion
:class:enum.IntEnum collection of SSL and TLS versions for
:attr:SSLContext.maximum_version and :attr:SSLContext.minimum_version.
.. versionadded:: 3.7
.. attribute:: TLSVersion.MINIMUM_SUPPORTED .. attribute:: TLSVersion.MAXIMUM_SUPPORTED
The minimum or maximum supported SSL or TLS version. These are magic constants. Their values don't reflect the lowest and highest available TLS/SSL versions.
.. attribute:: TLSVersion.SSLv3 .. attribute:: TLSVersion.TLSv1 .. attribute:: TLSVersion.TLSv1_1 .. attribute:: TLSVersion.TLSv1_2 .. attribute:: TLSVersion.TLSv1_3
SSL 3.0 to TLS 1.3.
.. class:: SSLSocket(socket.socket)
SSL sockets provide the following methods of :ref:socket-objects:
~socket.socket.accept()~socket.socket.bind()~socket.socket.close()~socket.socket.connect()~socket.socket.detach()~socket.socket.fileno()~socket.socket.getpeername(), :meth:~socket.socket.getsockname()~socket.socket.getsockopt(), :meth:~socket.socket.setsockopt()~socket.socket.gettimeout(), :meth:~socket.socket.settimeout(),
:meth:~socket.socket.setblocking()~socket.socket.listen()~socket.socket.makefile()~socket.socket.recv(), :meth:~socket.socket.recv_into()
(but passing a non-zero flags argument is not allowed)~socket.socket.send(), :meth:~socket.socket.sendall() (with
the same limitation)~socket.socket.sendfile() (but :mod:os.sendfile will be used
for plain-text sockets only, else :meth:~socket.socket.send() will be used)~socket.socket.shutdown()However, since the SSL (and TLS) protocol has its own framing atop
of TCP, the SSL sockets abstraction can, in certain respects, diverge from
the specification of normal, OS-level sockets. See especially the
:ref:notes on non-blocking sockets <ssl-nonblocking>.
Instances of :class:SSLSocket must be created using the
:meth:SSLContext.wrap_socket method.
.. versionchanged:: 3.5
The :meth:sendfile method was added.
.. versionchanged:: 3.5
The :meth:shutdown does not reset the socket timeout each time bytes
are received or sent. The socket timeout is now to maximum total duration
of the shutdown.
.. deprecated:: 3.6
It is deprecated to create a :class:SSLSocket instance directly, use
:meth:SSLContext.wrap_socket to wrap a socket.
.. versionchanged:: 3.7
:class:SSLSocket instances must to created with
:meth:~SSLContext.wrap_socket. In earlier versions, it was possible
to create instances directly. This was never documented or officially
supported.
SSL sockets also have the following additional methods and attributes:
.. method:: SSLSocket.read(len=1024, buffer=None)
Read up to len bytes of data from the SSL socket and return the result as
a bytes instance. If buffer is specified, then read into the buffer
instead, and return the number of bytes read.
Raise :exc:SSLWantReadError or :exc:SSLWantWriteError if the socket is
:ref:non-blocking <ssl-nonblocking> and the read would block.
As at any time a re-negotiation is possible, a call to :meth:read can also
cause write operations.
.. versionchanged:: 3.5 The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration to read up to len bytes.
.. deprecated:: 3.6
Use :meth:~SSLSocket.recv instead of :meth:~SSLSocket.read.
.. method:: SSLSocket.write(buf)
Write buf to the SSL socket and return the number of bytes written. The buf argument must be an object supporting the buffer interface.
Raise :exc:SSLWantReadError or :exc:SSLWantWriteError if the socket is
:ref:non-blocking <ssl-nonblocking> and the write would block.
As at any time a re-negotiation is possible, a call to :meth:write can
also cause read operations.
.. versionchanged:: 3.5 The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration to write buf.
.. deprecated:: 3.6
Use :meth:~SSLSocket.send instead of :meth:~SSLSocket.write.
.. note::
The :meth:~SSLSocket.read and :meth:~SSLSocket.write methods are the
low-level methods that read and write unencrypted, application-level data
and decrypt/encrypt it to encrypted, wire-level data. These methods
require an active SSL connection, i.e. the handshake was completed and
:meth:SSLSocket.unwrap was not called.
Normally you should use the socket API methods like
:meth:~socket.socket.recv and :meth:~socket.socket.send instead of these
methods.
.. method:: SSLSocket.do_handshake()
Perform the SSL setup handshake.
.. versionchanged:: 3.4
The handshake method also performs :func:match_hostname when the
:attr:~SSLContext.check_hostname attribute of the socket's
:attr:~SSLSocket.context is true.
.. versionchanged:: 3.5 The socket timeout is no more reset each time bytes are received or sent. The socket timeout is now to maximum total duration of the handshake.
.. versionchanged:: 3.7
Hostname or IP address is matched by OpenSSL during handshake. The
function :func:match_hostname is no longer used. In case OpenSSL
refuses a hostname or IP address, the handshake is aborted early and
a TLS alert message is send to the peer.
.. method:: SSLSocket.getpeercert(binary_form=False)
If there is no certificate for the peer on the other end of the connection,
return None. If the SSL handshake hasn't been done yet, raise
:exc:ValueError.
If the binary_form parameter is :const:False, and a certificate was
received from the peer, this method returns a :class:dict instance. If the
certificate was not validated, the dict is empty. If the certificate was
validated, it returns a dict with several keys, amongst them subject
(the principal for which the certificate was issued) and issuer
(the principal issuing the certificate). If a certificate contains an
instance of the Subject Alternative Name extension (see :rfc:3280),
there will also be a subjectAltName key in the dictionary.
The subject and issuer fields are tuples containing the sequence
of relative distinguished names (RDNs) given in the certificate's data
structure for the respective fields, and each RDN is a sequence of
name-value pairs. Here is a real-world example::
{'issuer': ((('countryName', 'IL'),),
(('organizationName', 'StartCom Ltd.'),),
(('organizationalUnitName',
'Secure Digital Certificate Signing'),),
(('commonName',
'StartCom Class 2 Primary Intermediate Server CA'),)),
'notAfter': 'Nov 22 08:15:19 2013 GMT',
'notBefore': 'Nov 21 03:09:52 2011 GMT',
'serialNumber': '95F0',
'subject': ((('description', '571208-SLe257oHY9fVQ07Z'),),
(('countryName', 'US'),),
(('stateOrProvinceName', 'California'),),
(('localityName', 'San Francisco'),),
(('organizationName', 'Electronic Frontier Foundation, Inc.'),),
(('commonName', '*.eff.org'),),
(('emailAddress', '[email protected]'),)),
'subjectAltName': (('DNS', '*.eff.org'), ('DNS', 'eff.org')),
'version': 3}
.. note::
To validate a certificate for a particular service, you can use the
:func:`match_hostname` function.
If the binary_form parameter is :const:True, and a certificate was
provided, this method returns the DER-encoded form of the entire certificate
as a sequence of bytes, or :const:None if the peer did not provide a
certificate. Whether the peer provides a certificate depends on the SSL
socket's role:
for a client SSL socket, the server will always provide a certificate, regardless of whether validation was required;
for a server SSL socket, the client will only provide a certificate
when requested by the server; therefore :meth:getpeercert will return
:const:None if you used :const:CERT_NONE (rather than
:const:CERT_OPTIONAL or :const:CERT_REQUIRED).
.. versionchanged:: 3.2
The returned dictionary includes additional items such as issuer
and notBefore.
.. versionchanged:: 3.4
:exc:ValueError is raised when the handshake isn't done.
The returned dictionary includes additional X509v3 extension items
such as crlDistributionPoints, caIssuers and OCSP URIs.
.. method:: SSLSocket.cipher()
Returns a three-value tuple containing the name of the cipher being used, the
version of the SSL protocol that defines its use, and the number of secret
bits being used. If no connection has been established, returns None.
.. method:: SSLSocket.shared_ciphers()
Return the list of ciphers shared by the client during the handshake. Each
entry of the returned list is a three-value tuple containing the name of the
cipher, the version of the SSL protocol that defines its use, and the number
of secret bits the cipher uses. :meth:~SSLSocket.shared_ciphers returns
None if no connection has been established or the socket is a client
socket.
.. versionadded:: 3.5
.. method:: SSLSocket.compression()
Return the compression algorithm being used as a string, or None
if the connection isn't compressed.
If the higher-level protocol supports its own compression mechanism,
you can use :data:OP_NO_COMPRESSION to disable SSL-level compression.
.. versionadded:: 3.3
.. method:: SSLSocket.get_channel_binding(cb_type="tls-unique")
Get channel binding data for current connection, as a bytes object. Returns
None if not connected or the handshake has not been completed.
The cb_type parameter allow selection of the desired channel binding
type. Valid channel binding types are listed in the
:data:CHANNEL_BINDING_TYPES list. Currently only the 'tls-unique' channel
binding, defined by :rfc:5929, is supported. :exc:ValueError will be
raised if an unsupported channel binding type is requested.
.. versionadded:: 3.3
.. method:: SSLSocket.selected_alpn_protocol()
Return the protocol that was selected during the TLS handshake. If
:meth:SSLContext.set_alpn_protocols was not called, if the other party does
not support ALPN, if this socket does not support any of the client's
proposed protocols, or if the handshake has not happened yet, None is
returned.
.. versionadded:: 3.5
.. method:: SSLSocket.selected_npn_protocol()
Return the higher-level protocol that was selected during the TLS/SSL
handshake. If :meth:SSLContext.set_npn_protocols was not called, or
if the other party does not support NPN, or if the handshake has not yet
happened, this will return None.
.. versionadded:: 3.3
.. method:: SSLSocket.unwrap()
Performs the SSL shutdown handshake, which removes the TLS layer from the underlying socket, and returns the underlying socket object. This can be used to go from encrypted operation over a connection to unencrypted. The returned socket should always be used for further communication with the other side of the connection, rather than the original socket.
.. method:: SSLSocket.verify_client_post_handshake()
Requests post-handshake authentication (PHA) from a TLS 1.3 client. PHA
can only be initiated for a TLS 1.3 connection from a server-side socket,
after the initial TLS handshake and with PHA enabled on both sides, see
:attr:SSLContext.post_handshake_auth.
The method does not perform a cert exchange immediately. The server-side sends a CertificateRequest during the next write event and expects the client to respond with a certificate on the next read event.
If any precondition isn't met (e.g. not TLS 1.3, PHA not enabled), an
:exc:SSLError is raised.
.. note::
Only available with OpenSSL 1.1.1 and TLS 1.3 enabled. Without TLS 1.3
support, the method raises :exc:NotImplementedError.
.. versionadded:: 3.7.1
.. method:: SSLSocket.version()
Return the actual SSL protocol version negotiated by the connection
as a string, or None is no secure connection is established.
As of this writing, possible return values include "SSLv2",
"SSLv3", "TLSv1", "TLSv1.1" and "TLSv1.2".
Recent OpenSSL versions may define more return values.
.. versionadded:: 3.5
.. method:: SSLSocket.pending()
Returns the number of already decrypted bytes available for read, pending on the connection.
.. attribute:: SSLSocket.context
The :class:SSLContext object this SSL socket is tied to. If the SSL
socket was created using the deprecated :func:wrap_socket function
(rather than :meth:SSLContext.wrap_socket), this is a custom context
object created for this SSL socket.
.. versionadded:: 3.2
.. attribute:: SSLSocket.server_side
A boolean which is True for server-side sockets and False for
client-side sockets.
.. versionadded:: 3.2
.. attribute:: SSLSocket.server_hostname
Hostname of the server: :class:str type, or None for server-side
socket or if the hostname was not specified in the constructor.
.. versionadded:: 3.2
.. versionchanged:: 3.7
The attribute is now always ASCII text. When server_hostname is
an internationalized domain name (IDN), this attribute now stores the
A-label form ("xn--pythn-mua.org"), rather than the U-label form
("pythön.org").
.. attribute:: SSLSocket.session
The :class:SSLSession for this SSL connection. The session is available
for client and server side sockets after the TLS handshake has been
performed. For client sockets the session can be set before
:meth:~SSLSocket.do_handshake has been called to reuse a session.
.. versionadded:: 3.6
.. attribute:: SSLSocket.session_reused
.. versionadded:: 3.6
.. versionadded:: 3.2
An SSL context holds various data longer-lived than single SSL connections, such as SSL configuration options, certificate(s) and private key(s). It also manages a cache of SSL sessions for server-side sockets, in order to speed up repeated connections from the same clients.
.. class:: SSLContext(protocol=PROTOCOL_TLS)
Create a new SSL context. You may pass protocol which must be one
of the PROTOCOL_* constants defined in this module. The parameter
specifies which version of the SSL protocol to use. Typically, the
server chooses a particular protocol version, and the client must adapt
to the server's choice. Most of the versions are not interoperable
with the other versions. If not specified, the default is
:data:PROTOCOL_TLS; it provides the most compatibility with other
versions.
Here's a table showing which versions in a client (down the side) can connect to which versions in a server (along the top):
.. table::
======================== ============ ============ ============= ========= =========== ===========
*client* / **server** **SSLv2** **SSLv3** **TLS** [3]_ **TLSv1** **TLSv1.1** **TLSv1.2**
------------------------ ------------ ------------ ------------- --------- ----------- -----------
*SSLv2* yes no no [1]_ no no no
*SSLv3* no yes no [2]_ no no no
*TLS* (*SSLv23*) [3]_ no [1]_ no [2]_ yes yes yes yes
*TLSv1* no no yes yes no no
*TLSv1.1* no no yes no yes no
*TLSv1.2* no no yes no no yes
======================== ============ ============ ============= ========= =========== ===========
.. rubric:: Footnotes
.. [1] :class:SSLContext disables SSLv2 with :data:OP_NO_SSLv2 by default.
.. [2] :class:SSLContext disables SSLv3 with :data:OP_NO_SSLv3 by default.
.. [3] TLS 1.3 protocol will be available with :data:PROTOCOL_TLS in
OpenSSL >= 1.1.1. There is no dedicated PROTOCOL constant for just
TLS 1.3.
.. seealso::
:func:create_default_context lets the :mod:ssl module choose
security settings for a given purpose.
.. versionchanged:: 3.6
The context is created with secure default values. The options
:data:`OP_NO_COMPRESSION`, :data:`OP_CIPHER_SERVER_PREFERENCE`,
:data:`OP_SINGLE_DH_USE`, :data:`OP_SINGLE_ECDH_USE`,
:data:`OP_NO_SSLv2` (except for :data:`PROTOCOL_SSLv2`),
and :data:`OP_NO_SSLv3` (except for :data:`PROTOCOL_SSLv3`) are
set by default. The initial cipher suite list contains only ``HIGH``
ciphers, no ``NULL`` ciphers and no ``MD5`` ciphers (except for
:data:`PROTOCOL_SSLv2`).
:class:SSLContext objects have the following methods and attributes:
.. method:: SSLContext.cert_store_stats()
Get statistics about quantities of loaded X.509 certificates, count of X.509 certificates flagged as CA certificates and certificate revocation lists as dictionary.
Example for a context with one CA cert and one other cert::
>>> context.cert_store_stats()
{'crl': 0, 'x509_ca': 1, 'x509': 2}
.. versionadded:: 3.4
.. method:: SSLContext.load_cert_chain(certfile, keyfile=None, password=None)
Load a private key and the corresponding certificate. The certfile
string must be the path to a single file in PEM format containing the
certificate as well as any number of CA certificates needed to establish
the certificate's authenticity. The keyfile string, if present, must
point to a file containing the private key in. Otherwise the private
key will be taken from certfile as well. See the discussion of
:ref:ssl-certificates for more information on how the certificate
is stored in the certfile.
The password argument may be a function to call to get the password for decrypting the private key. It will only be called if the private key is encrypted and a password is necessary. It will be called with no arguments, and it should return a string, bytes, or bytearray. If the return value is a string it will be encoded as UTF-8 before using it to decrypt the key. Alternatively a string, bytes, or bytearray value may be supplied directly as the password argument. It will be ignored if the private key is not encrypted and no password is needed.
If the password argument is not specified and a password is required, OpenSSL's built-in password prompting mechanism will be used to interactively prompt the user for a password.
An :class:SSLError is raised if the private key doesn't
match with the certificate.
.. versionchanged:: 3.3 New optional argument password.
.. method:: SSLContext.load_default_certs(purpose=Purpose.SERVER_AUTH)
Load a set of default "certification authority" (CA) certificates from
default locations. On Windows it loads CA certs from the CA and
ROOT system stores. On other systems it calls
:meth:SSLContext.set_default_verify_paths. In the future the method may
load CA certificates from other locations, too.
The purpose flag specifies what kind of CA certificates are loaded. The
default settings :data:Purpose.SERVER_AUTH loads certificates, that are
flagged and trusted for TLS web server authentication (client side
sockets). :data:Purpose.CLIENT_AUTH loads CA certificates for client
certificate verification on the server side.
.. versionadded:: 3.4
.. method:: SSLContext.load_verify_locations(cafile=None, capath=None, cadata=None)
Load a set of "certification authority" (CA) certificates used to validate
other peers' certificates when :data:verify_mode is other than
:data:CERT_NONE. At least one of cafile or capath must be specified.
This method can also load certification revocation lists (CRLs) in PEM or
DER format. In order to make use of CRLs, :attr:SSLContext.verify_flags
must be configured properly.
The cafile string, if present, is the path to a file of concatenated
CA certificates in PEM format. See the discussion of
:ref:ssl-certificates for more information about how to arrange the
certificates in this file.
The capath string, if present, is
the path to a directory containing several CA certificates in PEM format,
following an OpenSSL specific layout <https://www.openssl.org/docs/manmaster/man3/SSL_CTX_load_verify_locations.html>_.
The cadata object, if present, is either an ASCII string of one or more
PEM-encoded certificates or a :term:bytes-like object of DER-encoded
certificates. Like with capath extra lines around PEM-encoded
certificates are ignored but at least one certificate must be present.
.. versionchanged:: 3.4 New optional argument cadata
.. method:: SSLContext.get_ca_certs(binary_form=False)
Get a list of loaded "certification authority" (CA) certificates. If the
binary_form parameter is :const:False each list
entry is a dict like the output of :meth:SSLSocket.getpeercert. Otherwise
the method returns a list of DER-encoded certificates. The returned list
does not contain certificates from capath unless a certificate was
requested and loaded by a SSL connection.
.. note:: Certificates in a capath directory aren't loaded unless they have been used at least once.
.. versionadded:: 3.4
.. method:: SSLContext.get_ciphers()
Get a list of enabled ciphers. The list is in order of cipher priority.
See :meth:SSLContext.set_ciphers.
Example::
>>> ctx = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
>>> ctx.set_ciphers('ECDHE+AESGCM:!ECDSA')
>>> ctx.get_ciphers() # OpenSSL 1.0.x
[{'alg_bits': 256,
'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(256) Mac=AEAD',
'id': 50380848,
'name': 'ECDHE-RSA-AES256-GCM-SHA384',
'protocol': 'TLSv1/SSLv3',
'strength_bits': 256},
{'alg_bits': 128,
'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(128) Mac=AEAD',
'id': 50380847,
'name': 'ECDHE-RSA-AES128-GCM-SHA256',
'protocol': 'TLSv1/SSLv3',
'strength_bits': 128}]
On OpenSSL 1.1 and newer the cipher dict contains additional fields::
>>> ctx.get_ciphers() # OpenSSL 1.1+
[{'aead': True,
'alg_bits': 256,
'auth': 'auth-rsa',
'description': 'ECDHE-RSA-AES256-GCM-SHA384 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(256) Mac=AEAD',
'digest': None,
'id': 50380848,
'kea': 'kx-ecdhe',
'name': 'ECDHE-RSA-AES256-GCM-SHA384',
'protocol': 'TLSv1.2',
'strength_bits': 256,
'symmetric': 'aes-256-gcm'},
{'aead': True,
'alg_bits': 128,
'auth': 'auth-rsa',
'description': 'ECDHE-RSA-AES128-GCM-SHA256 TLSv1.2 Kx=ECDH Au=RSA '
'Enc=AESGCM(128) Mac=AEAD',
'digest': None,
'id': 50380847,
'kea': 'kx-ecdhe',
'name': 'ECDHE-RSA-AES128-GCM-SHA256',
'protocol': 'TLSv1.2',
'strength_bits': 128,
'symmetric': 'aes-128-gcm'}]
.. availability:: OpenSSL 1.0.2+.
.. versionadded:: 3.6
.. method:: SSLContext.set_default_verify_paths()
Load a set of default "certification authority" (CA) certificates from a filesystem path defined when building the OpenSSL library. Unfortunately, there's no easy way to know whether this method succeeds: no error is returned if no certificates are to be found. When the OpenSSL library is provided as part of the operating system, though, it is likely to be configured properly.
.. method:: SSLContext.set_ciphers(ciphers)
Set the available ciphers for sockets created with this context.
It should be a string in the OpenSSL cipher list format <https://www.openssl.org/docs/manmaster/man1/ciphers.html>_.
If no cipher can be selected (because compile-time options or other
configuration forbids use of all the specified ciphers), an
:class:SSLError will be raised.
.. note::
when connected, the :meth:SSLSocket.cipher method of SSL sockets will
give the currently selected cipher.
OpenSSL 1.1.1 has TLS 1.3 cipher suites enabled by default. The suites
cannot be disabled with :meth:`~SSLContext.set_ciphers`.
.. method:: SSLContext.set_alpn_protocols(protocols)
Specify which protocols the socket should advertise during the SSL/TLS
handshake. It should be a list of ASCII strings, like ['http/1.1', 'spdy/2'], ordered by preference. The selection of a protocol will happen
during the handshake, and will play out according to :rfc:7301. After a
successful handshake, the :meth:SSLSocket.selected_alpn_protocol method will
return the agreed-upon protocol.
This method will raise :exc:NotImplementedError if :data:HAS_ALPN is
False.
OpenSSL 1.1.0 to 1.1.0e will abort the handshake and raise :exc:SSLError
when both sides support ALPN but cannot agree on a protocol. 1.1.0f+
behaves like 1.0.2, :meth:SSLSocket.selected_alpn_protocol returns None.
.. versionadded:: 3.5
.. method:: SSLContext.set_npn_protocols(protocols)
Specify which protocols the socket should advertise during the SSL/TLS
handshake. It should be a list of strings, like ['http/1.1', 'spdy/2'],
ordered by preference. The selection of a protocol will happen during the
handshake, and will play out according to the Application Layer Protocol Negotiation <https://en.wikipedia.org/wiki/Application-Layer_Protocol_Negotiation>_. After a
successful handshake, the :meth:SSLSocket.selected_npn_protocol method will
return the agreed-upon protocol.
This method will raise :exc:NotImplementedError if :data:HAS_NPN is
False.
.. versionadded:: 3.3
.. attribute:: SSLContext.sni_callback
Register a callback function that will be called after the TLS Client Hello
handshake message has been received by the SSL/TLS server when the TLS client
specifies a server name indication. The server name indication mechanism
is specified in :rfc:6066 section 3 - Server Name Indication.
Only one callback can be set per SSLContext. If sni_callback
is set to None then the callback is disabled. Calling this function a
subsequent time will disable the previously registered callback.
The callback function will be called with three
arguments; the first being the :class:ssl.SSLSocket, the second is a string
that represents the server name that the client is intending to communicate
(or :const:None if the TLS Client Hello does not contain a server name)
and the third argument is the original :class:SSLContext. The server name
argument is text. For internationalized domain name, the server
name is an IDN A-label ("xn--pythn-mua.org").
A typical use of this callback is to change the :class:ssl.SSLSocket's
:attr:SSLSocket.context attribute to a new object of type
:class:SSLContext representing a certificate chain that matches the server
name.
Due to the early negotiation phase of the TLS connection, only limited
methods and attributes are usable like
:meth:SSLSocket.selected_alpn_protocol and :attr:SSLSocket.context.
:meth:SSLSocket.getpeercert, :meth:SSLSocket.getpeercert,
:meth:SSLSocket.cipher and :meth:SSLSocket.compress methods require that
the TLS connection has progressed beyond the TLS Client Hello and therefore
will not contain return meaningful values nor can they be called safely.
The sni_callback function must return None to allow the
TLS negotiation to continue. If a TLS failure is required, a constant
:const:ALERT_DESCRIPTION_* <ALERT_DESCRIPTION_INTERNAL_ERROR> can be
returned. Other return values will result in a TLS fatal error with
:const:ALERT_DESCRIPTION_INTERNAL_ERROR.
If an exception is raised from the sni_callback function the TLS
connection will terminate with a fatal TLS alert message
:const:ALERT_DESCRIPTION_HANDSHAKE_FAILURE.
This method will raise :exc:NotImplementedError if the OpenSSL library
had OPENSSL_NO_TLSEXT defined when it was built.
.. versionadded:: 3.7
.. attribute:: SSLContext.set_servername_callback(server_name_callback)
This is a legacy API retained for backwards compatibility. When possible,
you should use :attr:sni_callback instead. The given server_name_callback
is similar to sni_callback, except that when the server hostname is an
IDN-encoded internationalized domain name, the server_name_callback
receives a decoded U-label ("pythön.org").
If there is an decoding error on the server name, the TLS connection will
terminate with an :const:ALERT_DESCRIPTION_INTERNAL_ERROR fatal TLS
alert message to the client.
.. versionadded:: 3.4
.. method:: SSLContext.load_dh_params(dhfile)
Load the key generation parameters for Diffie-Hellman (DH) key exchange. Using DH key exchange improves forward secrecy at the expense of computational resources (both on the server and on the client). The dhfile parameter should be the path to a file containing DH parameters in PEM format.
This setting doesn't apply to client sockets. You can also use the
:data:OP_SINGLE_DH_USE option to further improve security.
.. versionadded:: 3.3
.. method:: SSLContext.set_ecdh_curve(curve_name)
Set the curve name for Elliptic Curve-based Diffie-Hellman (ECDH) key
exchange. ECDH is significantly faster than regular DH while arguably
as secure. The curve_name parameter should be a string describing
a well-known elliptic curve, for example prime256v1 for a widely
supported curve.
This setting doesn't apply to client sockets. You can also use the
:data:OP_SINGLE_ECDH_USE option to further improve security.
This method is not available if :data:HAS_ECDH is False.
.. versionadded:: 3.3
.. seealso::
SSL/TLS & Perfect Forward Secrecy <https://vincent.bernat.im/en/blog/2011-ssl-perfect-forward-secrecy>_
Vincent Bernat.
.. method:: SSLContext.wrap_socket(sock, server_side=False,
do_handshake_on_connect=True, suppress_ragged_eofs=True,
server_hostname=None, session=None)
Wrap an existing Python socket sock and return an instance of
:attr:SSLContext.sslsocket_class (default :class:SSLSocket). The
returned SSL socket is tied to the context, its settings and certificates.
sock must be a :data:~socket.SOCK_STREAM socket; other
socket types are unsupported.
The parameter server_side is a boolean which identifies whether
server-side or client-side behavior is desired from this socket.
For client-side sockets, the context construction is lazy; if the
underlying socket isn't connected yet, the context construction will be
performed after :meth:connect is called on the socket. For
server-side sockets, if the socket has no remote peer, it is assumed
to be a listening socket, and the server-side SSL wrapping is
automatically performed on client connections accepted via the
:meth:accept method. The method may raise :exc:SSLError.
On client connections, the optional parameter server_hostname specifies
the hostname of the service which we are connecting to. This allows a
single server to host multiple SSL-based services with distinct certificates,
quite similarly to HTTP virtual hosts. Specifying server_hostname will
raise a :exc:ValueError if server_side is true.
The parameter do_handshake_on_connect specifies whether to do the SSL
handshake automatically after doing a :meth:socket.connect, or whether the
application program will call it explicitly, by invoking the
:meth:SSLSocket.do_handshake method. Calling
:meth:SSLSocket.do_handshake explicitly gives the program control over the
blocking behavior of the socket I/O involved in the handshake.
The parameter suppress_ragged_eofs specifies how the
:meth:SSLSocket.recv method should signal unexpected EOF from the other end
of the connection. If specified as :const:True (the default), it returns a
normal EOF (an empty bytes object) in response to unexpected EOF errors
raised from the underlying socket; if :const:False, it will raise the
exceptions back to the caller.
session, see :attr:~SSLSocket.session.
.. versionchanged:: 3.5 Always allow a server_hostname to be passed, even if OpenSSL does not have SNI.
.. versionchanged:: 3.6 session argument was added.
.. versionchanged:: 3.7
The method returns on instance of :attr:`SSLContext.sslsocket_class`
instead of hard-coded :class:`SSLSocket`.
.. attribute:: SSLContext.sslsocket_class
The return type of :meth:SSLContext.wrap_sockets, defaults to
:class:SSLSocket. The attribute can be overridden on instance of class
in order to return a custom subclass of :class:SSLSocket.
.. versionadded:: 3.7
.. method:: SSLContext.wrap_bio(incoming, outgoing, server_side=False,
server_hostname=None, session=None)
Wrap the BIO objects incoming and outgoing and return an instance of
attr:SSLContext.sslobject_class (default :class:SSLObject). The SSL
routines will read input data from the incoming BIO and write data to the
outgoing BIO.
The server_side, server_hostname and session parameters have the
same meaning as in :meth:SSLContext.wrap_socket.
.. versionchanged:: 3.6 session argument was added.
.. versionchanged:: 3.7
The method returns on instance of :attr:SSLContext.sslobject_class
instead of hard-coded :class:SSLObject.
.. attribute:: SSLContext.sslobject_class
The return type of :meth:SSLContext.wrap_bio, defaults to
:class:SSLObject. The attribute can be overridden on instance of class
in order to return a custom subclass of :class:SSLObject.
.. versionadded:: 3.7
.. method:: SSLContext.session_stats()
Get statistics about the SSL sessions created or managed by this context.
A dictionary is returned which maps the names of each piece of information <https://www.openssl.org/docs/man1.1.0/ssl/SSL_CTX_sess_number.html>_ to their
numeric values. For example, here is the total number of hits and misses
in the session cache since the context was created::
>>> stats = context.session_stats()
>>> stats['hits'], stats['misses']
(0, 0)
.. attribute:: SSLContext.check_hostname
Whether to match the peer cert's hostname with :func:match_hostname in
:meth:SSLSocket.do_handshake. The context's
:attr:~SSLContext.verify_mode must be set to :data:CERT_OPTIONAL or
:data:CERT_REQUIRED, and you must pass server_hostname to
:meth:~SSLContext.wrap_socket in order to match the hostname. Enabling
hostname checking automatically sets :attr:~SSLContext.verify_mode from
:data:CERT_NONE to :data:CERT_REQUIRED. It cannot be set back to
:data:CERT_NONE as long as hostname checking is enabled.
Example::
import socket, ssl
context = ssl.SSLContext()
context.verify_mode = ssl.CERT_REQUIRED
context.check_hostname = True
context.load_default_certs()
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
ssl_sock = context.wrap_socket(s, server_hostname='www.verisign.com')
ssl_sock.connect(('www.verisign.com', 443))
.. versionadded:: 3.4
.. versionchanged:: 3.7
:attr:`~SSLContext.verify_mode` is now automatically changed
to :data:`CERT_REQUIRED` when hostname checking is enabled and
:attr:`~SSLContext.verify_mode` is :data:`CERT_NONE`. Previously
the same operation would have failed with a :exc:`ValueError`.
.. note::
This features requires OpenSSL 0.9.8f or newer.
.. attribute:: SSLContext.maximum_version
A :class:TLSVersion enum member representing the highest supported
TLS version. The value defaults to :attr:TLSVersion.MAXIMUM_SUPPORTED.
The attribute is read-only for protocols other than :attr:PROTOCOL_TLS,
:attr:PROTOCOL_TLS_CLIENT, and :attr:PROTOCOL_TLS_SERVER.
The attributes :attr:~SSLContext.maximum_version,
:attr:~SSLContext.minimum_version and
:attr:SSLContext.options all affect the supported SSL
and TLS versions of the context. The implementation does not prevent
invalid combination. For example a context with
:attr:OP_NO_TLSv1_2 in :attr:~SSLContext.options and
:attr:~SSLContext.maximum_version set to :attr:TLSVersion.TLSv1_2
will not be able to establish a TLS 1.2 connection.
.. note::
This attribute is not available unless the ssl module is compiled
with OpenSSL 1.1.0g or newer.
.. versionadded:: 3.7
.. attribute:: SSLContext.minimum_version
Like :attr:SSLContext.maximum_version except it is the lowest
supported version or :attr:TLSVersion.MINIMUM_SUPPORTED.
.. note::
This attribute is not available unless the ssl module is compiled
with OpenSSL 1.1.0g or newer.
.. versionadded:: 3.7
.. attribute:: SSLContext.options
An integer representing the set of SSL options enabled on this context.
The default value is :data:OP_ALL, but you can specify other options
such as :data:OP_NO_SSLv2 by ORing them together.
.. note::
With versions of OpenSSL older than 0.9.8m, it is only possible
to set options, not to clear them. Attempting to clear an option
(by resetting the corresponding bits) will raise a :exc:ValueError.
.. versionchanged:: 3.6
:attr:SSLContext.options returns :class:Options flags:
>>> ssl.create_default_context().options # doctest: +SKIP
<Options.OP_ALL|OP_NO_SSLv3|OP_NO_SSLv2|OP_NO_COMPRESSION: 2197947391>
.. attribute:: SSLContext.post_handshake_auth
Enable TLS 1.3 post-handshake client authentication. Post-handshake auth is disabled by default and a server can only request a TLS client certificate during the initial handshake. When enabled, a server may request a TLS client certificate at any time after the handshake.
When enabled on client-side sockets, the client signals the server that it supports post-handshake authentication.
When enabled on server-side sockets, :attr:SSLContext.verify_mode must
be set to :data:CERT_OPTIONAL or :data:CERT_REQUIRED, too. The
actual client cert exchange is delayed until
:meth:SSLSocket.verify_client_post_handshake is called and some I/O is
performed.
.. note:: Only available with OpenSSL 1.1.1 and TLS 1.3 enabled. Without TLS 1.3 support, the property value is None and can't be modified
.. versionadded:: 3.7.1
.. attribute:: SSLContext.protocol
The protocol version chosen when constructing the context. This attribute is read-only.
.. attribute:: SSLContext.hostname_checks_common_name
Whether :attr:~SSLContext.check_hostname falls back to verify the cert's
subject common name in the absence of a subject alternative name
extension (default: true).
.. note:: Only writeable with OpenSSL 1.1.0 or higher.
.. versionadded:: 3.7
.. attribute:: SSLContext.verify_flags
The flags for certificate verification operations. You can set flags like
:data:VERIFY_CRL_CHECK_LEAF by ORing them together. By default OpenSSL
does neither require nor verify certificate revocation lists (CRLs).
Available only with openssl version 0.9.8+.
.. versionadded:: 3.4
.. versionchanged:: 3.6
:attr:SSLContext.verify_flags returns :class:VerifyFlags flags:
>>> ssl.create_default_context().verify_flags # doctest: +SKIP
<VerifyFlags.VERIFY_X509_TRUSTED_FIRST: 32768>
.. attribute:: SSLContext.verify_mode
Whether to try to verify other peers' certificates and how to behave
if verification fails. This attribute must be one of
:data:CERT_NONE, :data:CERT_OPTIONAL or :data:CERT_REQUIRED.
.. versionchanged:: 3.6
:attr:SSLContext.verify_mode returns :class:VerifyMode enum:
>>> ssl.create_default_context().verify_mode
<VerifyMode.CERT_REQUIRED: 2>
.. index:: single: certificates
.. index:: single: X509 certificate
.. _ssl-certificates:
Certificates in general are part of a public-key / private-key system. In this system, each principal, (which may be a machine, or a person, or an organization) is assigned a unique two-part encryption key. One part of the key is public, and is called the public key; the other part is kept secret, and is called the private key. The two parts are related, in that if you encrypt a message with one of the parts, you can decrypt it with the other part, and only with the other part.
A certificate contains information about two principals. It contains the name of a subject, and the subject's public key. It also contains a statement by a second principal, the issuer, that the subject is who they claim to be, and that this is indeed the subject's public key. The issuer's statement is signed with the issuer's private key, which only the issuer knows. However, anyone can verify the issuer's statement by finding the issuer's public key, decrypting the statement with it, and comparing it to the other information in the certificate. The certificate also contains information about the time period over which it is valid. This is expressed as two fields, called "notBefore" and "notAfter".
In the Python use of certificates, a client or server can use a certificate to prove who they are. The other side of a network connection can also be required to produce a certificate, and that certificate can be validated to the satisfaction of the client or server that requires such validation. The connection attempt can be set to raise an exception if the validation fails. Validation is done automatically, by the underlying OpenSSL framework; the application need not concern itself with its mechanics. But the application does usually need to provide sets of certificates to allow this process to take place.
Python uses files to contain certificates. They should be formatted as "PEM"
(see :rfc:1422), which is a base-64 encoded form wrapped with a header line
and a footer line::
-----BEGIN CERTIFICATE-----
... (certificate in base64 PEM encoding) ...
-----END CERTIFICATE-----
Certificate chains ^^^^^^^^^^^^^^^^^^
The Python files which contain certificates can contain a sequence of certificates, sometimes called a certificate chain. This chain should start with the specific certificate for the principal who "is" the client or server, and then the certificate for the issuer of that certificate, and then the certificate for the issuer of that certificate, and so on up the chain till you get to a certificate which is self-signed, that is, a certificate which has the same subject and issuer, sometimes called a root certificate. The certificates should just be concatenated together in the certificate file. For example, suppose we had a three certificate chain, from our server certificate to the certificate of the certification authority that signed our server certificate, to the root certificate of the agency which issued the certification authority's certificate::
-----BEGIN CERTIFICATE-----
... (certificate for your server)...
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
... (the certificate for the CA)...
-----END CERTIFICATE-----
-----BEGIN CERTIFICATE-----
... (the root certificate for the CA's issuer)...
-----END CERTIFICATE-----
CA certificates ^^^^^^^^^^^^^^^
If you are going to require validation of the other side of the connection's
certificate, you need to provide a "CA certs" file, filled with the certificate
chains for each issuer you are willing to trust. Again, this file just contains
these chains concatenated together. For validation, Python will use the first
chain it finds in the file which matches. The platform's certificates file can
be used by calling :meth:SSLContext.load_default_certs, this is done
automatically with :func:.create_default_context.
Combined key and certificate ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Often the private key is stored in the same file as the certificate; in this
case, only the certfile parameter to :meth:SSLContext.load_cert_chain
and :func:wrap_socket needs to be passed. If the private key is stored
with the certificate, it should come before the first certificate in
the certificate chain::
-----BEGIN RSA PRIVATE KEY----- ... (private key in base64 encoding) ... -----END RSA PRIVATE KEY----- -----BEGIN CERTIFICATE----- ... (certificate in base64 PEM encoding) ... -----END CERTIFICATE-----
Self-signed certificates ^^^^^^^^^^^^^^^^^^^^^^^^
If you are going to create a server that provides SSL-encrypted connection services, you will need to acquire a certificate for that service. There are many ways of acquiring appropriate certificates, such as buying one from a certification authority. Another common practice is to generate a self-signed certificate. The simplest way to do this is with the OpenSSL package, using something like the following::
Country Name (2 letter code) [AU]:US State or Province Name (full name) [Some-State]:MyState Locality Name (eg, city) []:Some City Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Organization, Inc. Organizational Unit Name (eg, section) []:My Group Common Name (eg, YOUR name) []:myserver.mygroup.myorganization.com Email Address []:[email protected] %
The disadvantage of a self-signed certificate is that it is its own root certificate, and no one else will have it in their cache of known (and trusted) root certificates.
Testing for SSL support ^^^^^^^^^^^^^^^^^^^^^^^
To test for the presence of SSL support in a Python installation, user code should use the following idiom::
try: import ssl except ImportError: pass else: ... # do something that requires SSL support
Client-side operation ^^^^^^^^^^^^^^^^^^^^^
This example creates a SSL context with the recommended security settings for client sockets, including automatic certificate verification::
context = ssl.create_default_context()
If you prefer to tune security settings yourself, you might create a context from scratch (but beware that you might not get the settings right)::
context = ssl.SSLContext() context.verify_mode = ssl.CERT_REQUIRED context.check_hostname = True context.load_verify_locations("/etc/ssl/certs/ca-bundle.crt")
(this snippet assumes your operating system places a bundle of all CA
certificates in /etc/ssl/certs/ca-bundle.crt; if not, you'll get an
error and have to adjust the location)
When you use the context to connect to a server, :const:CERT_REQUIRED
validates the server certificate: it ensures that the server certificate
was signed with one of the CA certificates, and checks the signature for
correctness::
conn = context.wrap_socket(socket.socket(socket.AF_INET), ... server_hostname="www.python.org") conn.connect(("www.python.org", 443))
You may then fetch the certificate::
cert = conn.getpeercert()
Visual inspection shows that the certificate does identify the desired service
(that is, the HTTPS host www.python.org)::
pprint.pprint(cert) {'OCSP': ('http://ocsp.digicert.com',), 'caIssuers': ('http://cacerts.digicert.com/DigiCertSHA2ExtendedValidationServerCA.crt',), 'crlDistributionPoints': ('http://crl3.digicert.com/sha2-ev-server-g1.crl', 'http://crl4.digicert.com/sha2-ev-server-g1.crl'), 'issuer': ((('countryName', 'US'),), (('organizationName', 'DigiCert Inc'),), (('organizationalUnitName', 'www.digicert.com'),), (('commonName', 'DigiCert SHA2 Extended Validation Server CA'),)), 'notAfter': 'Sep 9 12:00:00 2016 GMT', 'notBefore': 'Sep 5 00:00:00 2014 GMT', 'serialNumber': '01BB6F00122B177F36CAB49CEA8B6B26', 'subject': ((('businessCategory', 'Private Organization'),), (('1.3.6.1.4.1.311.60.2.1.3', 'US'),), (('1.3.6.1.4.1.311.60.2.1.2', 'Delaware'),), (('serialNumber', '3359300'),), (('streetAddress', '16 Allen Rd'),), (('postalCode', '03894-4801'),), (('countryName', 'US'),), (('stateOrProvinceName', 'NH'),), (('localityName', 'Wolfeboro,'),), (('organizationName', 'Python Software Foundation'),), (('commonName', 'www.python.org'),)), 'subjectAltName': (('DNS', 'www.python.org'), ('DNS', 'python.org'), ('DNS', 'pypi.org'), ('DNS', 'docs.python.org'), ('DNS', 'testpypi.org'), ('DNS', 'bugs.python.org'), ('DNS', 'wiki.python.org'), ('DNS', 'hg.python.org'), ('DNS', 'mail.python.org'), ('DNS', 'packaging.python.org'), ('DNS', 'pythonhosted.org'), ('DNS', 'www.pythonhosted.org'), ('DNS', 'test.pythonhosted.org'), ('DNS', 'us.pycon.org'), ('DNS', 'id.python.org')), 'version': 3}
Now the SSL channel is established and the certificate verified, you can proceed to talk with the server::
conn.sendall(b"HEAD / HTTP/1.0\r\nHost: linuxfr.org\r\n\r\n") pprint.pprint(conn.recv(1024).split(b"\r\n")) [b'HTTP/1.1 200 OK', b'Date: Sat, 18 Oct 2014 18:27:20 GMT', b'Server: nginx', b'Content-Type: text/html; charset=utf-8', b'X-Frame-Options: SAMEORIGIN', b'Content-Length: 45679', b'Accept-Ranges: bytes', b'Via: 1.1 varnish', b'Age: 2188', b'X-Served-By: cache-lcy1134-LCY', b'X-Cache: HIT', b'X-Cache-Hits: 11', b'Vary: Cookie', b'Strict-Transport-Security: max-age=63072000; includeSubDomains', b'Connection: close', b'', b'']
See the discussion of :ref:ssl-security below.
Server-side operation ^^^^^^^^^^^^^^^^^^^^^
For server operation, typically you'll need to have a server certificate, and
private key, each in a file. You'll first create a context holding the key
and the certificate, so that clients can check your authenticity. Then
you'll open a socket, bind it to a port, call :meth:listen on it, and start
waiting for clients to connect::
import socket, ssl
context = ssl.create_default_context(ssl.Purpose.CLIENT_AUTH) context.load_cert_chain(certfile="mycertfile", keyfile="mykeyfile")
bindsocket = socket.socket() bindsocket.bind(('myaddr.mydomain.com', 10023)) bindsocket.listen(5)
When a client connects, you'll call :meth:accept on the socket to get the
new socket from the other end, and use the context's :meth:SSLContext.wrap_socket
method to create a server-side SSL socket for the connection::
while True: newsocket, fromaddr = bindsocket.accept() connstream = context.wrap_socket(newsocket, server_side=True) try: deal_with_client(connstream) finally: connstream.shutdown(socket.SHUT_RDWR) connstream.close()
Then you'll read data from the connstream and do something with it till you
are finished with the client (or the client is finished with you)::
def deal_with_client(connstream): data = connstream.recv(1024) # empty data means the client is finished with us while data: if not do_something(connstream, data): # we'll assume do_something returns False # when we're finished with client break data = connstream.recv(1024) # finished with client
And go back to listening for new client connections (of course, a real server
would probably handle each client connection in a separate thread, or put
the sockets in :ref:non-blocking mode <ssl-nonblocking> and use an event loop).
.. _ssl-nonblocking:
SSL sockets behave slightly different than regular sockets in non-blocking mode. When working with non-blocking sockets, there are thus several things you need to be aware of:
Most :class:SSLSocket methods will raise either
:exc:SSLWantWriteError or :exc:SSLWantReadError instead of
:exc:BlockingIOError if an I/O operation would
block. :exc:SSLWantReadError will be raised if a read operation on
the underlying socket is necessary, and :exc:SSLWantWriteError for
a write operation on the underlying socket. Note that attempts to
write to an SSL socket may require reading from the underlying
socket first, and attempts to read from the SSL socket may require
a prior write to the underlying socket.
.. versionchanged:: 3.5
In earlier Python versions, the :meth:!SSLSocket.send method
returned zero instead of raising :exc:SSLWantWriteError or
:exc:SSLWantReadError.
Calling :func:~select.select tells you that the OS-level socket can be
read from (or written to), but it does not imply that there is sufficient
data at the upper SSL layer. For example, only part of an SSL frame might
have arrived. Therefore, you must be ready to handle :meth:SSLSocket.recv
and :meth:SSLSocket.send failures, and retry after another call to
:func:~select.select.
Conversely, since the SSL layer has its own framing, a SSL socket may
still have data available for reading without :func:~select.select
being aware of it. Therefore, you should first call
:meth:SSLSocket.recv to drain any potentially available data, and then
only block on a :func:~select.select call if still necessary.
(of course, similar provisions apply when using other primitives such as
:func:~select.poll, or those in the :mod:selectors module)
The SSL handshake itself will be non-blocking: the
:meth:SSLSocket.do_handshake method has to be retried until it returns
successfully. Here is a synopsis using :func:~select.select to wait for
the socket's readiness::
while True: try: sock.do_handshake() break except ssl.SSLWantReadError: select.select([sock], [], []) except ssl.SSLWantWriteError: select.select([], [sock], [])
.. seealso::
The :mod:asyncio module supports :ref:non-blocking SSL sockets <ssl-nonblocking> and provides a
higher level API. It polls for events using the :mod:selectors module and
handles :exc:SSLWantWriteError, :exc:SSLWantReadError and
:exc:BlockingIOError exceptions. It runs the SSL handshake asynchronously
as well.
.. versionadded:: 3.5
Ever since the SSL module was introduced in Python 2.6, the :class:SSLSocket
class has provided two related but distinct areas of functionality:
The network IO API is identical to that provided by :class:socket.socket,
from which :class:SSLSocket also inherits. This allows an SSL socket to be
used as a drop-in replacement for a regular socket, making it very easy to add
SSL support to an existing application.
Combining SSL protocol handling and network IO usually works well, but there
are some cases where it doesn't. An example is async IO frameworks that want to
use a different IO multiplexing model than the "select/poll on a file
descriptor" (readiness based) model that is assumed by :class:socket.socket
and by the internal OpenSSL socket IO routines. This is mostly relevant for
platforms like Windows where this model is not efficient. For this purpose, a
reduced scope variant of :class:SSLSocket called :class:SSLObject is
provided.
.. class:: SSLObject
A reduced-scope variant of :class:SSLSocket representing an SSL protocol
instance that does not contain any network IO methods. This class is
typically used by framework authors that want to implement asynchronous IO
for SSL through memory buffers.
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 has no public constructor. An :class:SSLObject instance
must be created using the :meth:~SSLContext.wrap_bio method. This
method will create the :class:SSLObject instance and bind it to a
pair of BIOs. The incoming BIO is used to pass data from Python to the
SSL protocol instance, while the outgoing BIO is used to pass data the
other way around.
The following methods are available:
~SSLSocket.context~SSLSocket.server_side~SSLSocket.server_hostname~SSLSocket.session~SSLSocket.session_reused~SSLSocket.read~SSLSocket.write~SSLSocket.getpeercert~SSLSocket.selected_npn_protocol~SSLSocket.cipher~SSLSocket.shared_ciphers~SSLSocket.compression~SSLSocket.pending~SSLSocket.do_handshake~SSLSocket.unwrap~SSLSocket.get_channel_bindingWhen compared to :class:SSLSocket, this object lacks the following
features:
Any form of network IO; recv() and send() read and write only to
the underlying :class:MemoryBIO buffers.
There is no do_handshake_on_connect machinery. You must always manually
call :meth:~SSLSocket.do_handshake to start the handshake.
There is no handling of suppress_ragged_eofs. All end-of-file conditions
that are in violation of the protocol are reported via the
:exc:SSLEOFError exception.
The method :meth:~SSLSocket.unwrap call does not return anything,
unlike for an SSL socket where it returns the underlying socket.
The server_name_callback callback passed to
:meth:SSLContext.set_servername_callback will get an :class:SSLObject
instance instead of a :class:SSLSocket instance as its first parameter.
Some notes related to the use of :class:SSLObject:
All IO on an :class:SSLObject is :ref:non-blocking <ssl-nonblocking>.
This means that for example :meth:~SSLSocket.read will raise an
:exc:SSLWantReadError if it needs more data than the incoming BIO has
available.
There is no module-level wrap_bio() call like there is for
:meth:~SSLContext.wrap_socket. An :class:SSLObject is always created
via an :class:SSLContext.
.. versionchanged:: 3.7
:class:SSLObject instances must to created with
:meth:~SSLContext.wrap_bio. In earlier versions, it was possible to
create instances directly. This was never documented or officially
supported.
An SSLObject communicates with the outside world using memory buffers. The
class :class:MemoryBIO provides a memory buffer that can be used for this
purpose. It wraps an OpenSSL memory BIO (Basic IO) object:
.. class:: MemoryBIO
A memory buffer that can be used to pass data between Python and an SSL protocol instance.
.. attribute:: MemoryBIO.pending
Return the number of bytes currently in the memory buffer.
.. attribute:: MemoryBIO.eof
A boolean indicating whether the memory BIO is current at the end-of-file
position.
.. method:: MemoryBIO.read(n=-1)
Read up to *n* bytes from the memory buffer. If *n* is not specified or
negative, all bytes are returned.
.. method:: MemoryBIO.write(buf)
Write the bytes from *buf* to the memory BIO. The *buf* argument must be an
object supporting the buffer protocol.
The return value is the number of bytes written, which is always equal to
the length of *buf*.
.. method:: MemoryBIO.write_eof()
Write an EOF marker to the memory BIO. After this method has been called, it
is illegal to call :meth:`~MemoryBIO.write`. The attribute :attr:`eof` will
become true after all data currently in the buffer has been read.
.. versionadded:: 3.6
.. class:: SSLSession
Session object used by :attr:~SSLSocket.session.
.. attribute:: id .. attribute:: time .. attribute:: timeout .. attribute:: ticket_lifetime_hint .. attribute:: has_ticket
.. _ssl-security:
Best defaults ^^^^^^^^^^^^^
For client use, if you don't have any special requirements for your
security policy, it is highly recommended that you use the
:func:create_default_context function to create your SSL context.
It will load the system's trusted CA certificates, enable certificate
validation and hostname checking, and try to choose reasonably secure
protocol and cipher settings.
For example, here is how you would use the :class:smtplib.SMTP class to
create a trusted, secure connection to a SMTP server::
import ssl, smtplib smtp = smtplib.SMTP("mail.python.org", port=587) context = ssl.create_default_context() smtp.starttls(context=context) (220, b'2.0.0 Ready to start TLS')
If a client certificate is needed for the connection, it can be added with
:meth:SSLContext.load_cert_chain.
By contrast, if you create the SSL context by calling the :class:SSLContext
constructor yourself, it will not have certificate validation nor hostname
checking enabled by default. If you do so, please read the paragraphs below
to achieve a good security level.
Manual settings ^^^^^^^^^^^^^^^
Verifying certificates ''''''''''''''''''''''
When calling the :class:SSLContext constructor directly,
:const:CERT_NONE is the default. Since it does not authenticate the other
peer, it can be insecure, especially in client mode where most of time you
would like to ensure the authenticity of the server you're talking to.
Therefore, when in client mode, it is highly recommended to use
:const:CERT_REQUIRED. However, it is in itself not sufficient; you also
have to check that the server certificate, which can be obtained by calling
:meth:SSLSocket.getpeercert, matches the desired service. For many
protocols and applications, the service can be identified by the hostname;
in this case, the :func:match_hostname function can be used. This common
check is automatically performed when :attr:SSLContext.check_hostname is
enabled.
.. versionchanged:: 3.7
Hostname matchings is now performed by OpenSSL. Python no longer uses
:func:match_hostname.
In server mode, if you want to authenticate your clients using the SSL layer
(rather than using a higher-level authentication mechanism), you'll also have
to specify :const:CERT_REQUIRED and similarly check the client certificate.
Protocol versions '''''''''''''''''
SSL versions 2 and 3 are considered insecure and are therefore dangerous to
use. If you want maximum compatibility between clients and servers, it is
recommended to use :const:PROTOCOL_TLS_CLIENT or
:const:PROTOCOL_TLS_SERVER as the protocol version. SSLv2 and SSLv3 are
disabled by default.
::
client_context = ssl.SSLContext(ssl.PROTOCOL_TLS_CLIENT) client_context.options |= ssl.OP_NO_TLSv1 client_context.options |= ssl.OP_NO_TLSv1_1
The SSL context created above will only allow TLSv1.2 and later (if
supported by your system) connections to a server. :const:PROTOCOL_TLS_CLIENT
implies certificate validation and hostname checks by default. You have to
load certificates into the context.
Cipher selection ''''''''''''''''
If you have advanced security requirements, fine-tuning of the ciphers
enabled when negotiating a SSL session is possible through the
:meth:SSLContext.set_ciphers method. Starting from Python 3.2.3, the
ssl module disables certain weak ciphers by default, but you may want
to further restrict the cipher choice. Be sure to read OpenSSL's documentation
about the cipher list format <https://www.openssl.org/docs/manmaster/man1/ciphers.html#CIPHER-LIST-FORMAT>_.
If you want to check which ciphers are enabled by a given cipher list, use
:meth:SSLContext.get_ciphers or the openssl ciphers command on your
system.
Multi-processing ^^^^^^^^^^^^^^^^
If using this module as part of a multi-processed application (using,
for example the :mod:multiprocessing or :mod:concurrent.futures modules),
be aware that OpenSSL's internal random number generator does not properly
handle forked processes. Applications must change the PRNG state of the
parent process if they use any SSL feature with :func:os.fork. Any
successful call of :func:~ssl.RAND_add, :func:~ssl.RAND_bytes or
:func:~ssl.RAND_pseudo_bytes is sufficient.
.. _ssl-tlsv1_3:
.. versionadded:: 3.7
Python has provisional and experimental support for TLS 1.3 with OpenSSL 1.1.1. The new protocol behaves slightly differently than previous version of TLS/SSL. Some new TLS 1.3 features are not yet available.
SSLContext.set_ciphers cannot enable or disable any TLS 1.3
ciphers yet, but :meth:SSLContext.get_ciphers returns them.SSLSocket.session and :class:SSLSession
are not compatible with TLS 1.3... _ssl-libressl:
LibreSSL is a fork of OpenSSL 1.0.1. The ssl module has limited support for LibreSSL. Some features are not available when the ssl module is compiled with LibreSSL.
SSLContext.set_npn_protocols and
:meth:SSLSocket.selected_npn_protocol are not available.SSLContext.set_default_verify_paths ignores the env vars
:envvar:SSL_CERT_FILE and :envvar:SSL_CERT_PATH although
:func:get_default_verify_paths still reports them... seealso::
Class :class:socket.socket
Documentation of underlying :mod:socket class
SSL/TLS Strong Encryption: An Introduction <https://httpd.apache.org/docs/trunk/en/ssl/ssl_intro.html>_
Intro from the Apache HTTP Server documentation
:rfc:RFC 1422: Privacy Enhancement for Internet Electronic Mail: Part II: Certificate-Based Key Management <1422>
Steve Kent
:rfc:RFC 4086: Randomness Requirements for Security <4086>
Donald E., Jeffrey I. Schiller
:rfc:RFC 5280: Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile <5280>
D. Cooper
:rfc:RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2 <5246>
T. Dierks et. al.
:rfc:RFC 6066: Transport Layer Security (TLS) Extensions <6066>
D. Eastlake
IANA TLS: Transport Layer Security (TLS) Parameters <https://www.iana.org/assignments/tls-parameters/tls-parameters.xml>_
IANA
:rfc:RFC 7525: Recommendations for Secure Use of Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) <7525>
IETF
Mozilla's Server Side TLS recommendations <https://wiki.mozilla.org/Security/Server_Side_TLS>_
Mozilla