--- a/Doc/library/ssl.rst +++ b/Doc/library/ssl.rst @@ -28,19 +28,14 @@ probably additional platforms, as long a 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. - -.. warning:: - The ssl module won't validate certificates by default. When used in - client mode, this means you are vulnerable to man-in-the-middle attacks. + 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. - OpenSSL's internal random number generator does not properly handle fork. - 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. 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 @@ -49,23 +44,101 @@ the documents in the "See Also" section 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 :meth:`read` and :meth:`write` methods, along with a method, -:meth:`getpeercert`, to retrieve the certificate of the other side of the -connection, and a method, :meth:`cipher`, to retrieve the cipher being used for -the secure connection. +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. + Functions, Constants, and Exceptions ------------------------------------ .. exception:: SSLError - Raised to signal an error from the underlying SSL implementation. 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:`socket.error`, which in turn is a subtype of - :exc:`IOError`. + 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:`socket.error`, which in turn is a subtype of :exc:`IOError`. The + error code and message of :exc:`SSLError` instances are provided by the + OpenSSL library. + + .. 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:: 2.7.9 + + .. 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:: 2.7.9 + +.. 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:: 2.7.9 + +.. 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:: 2.7.9 -.. function:: wrap_socket (sock, keyfile=None, certfile=None, server_side=False, cert_reqs=CERT_NONE, ssl_version={see docs}, ca_certs=None, do_handshake_on_connect=True, suppress_ragged_eofs=True, ciphers=None) +.. 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:: 2.7.9 + +.. 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:: 2.7.9 + +.. 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:: 2.7.9 + +.. exception:: CertificateError + + Raised to signal an error with a certificate (such as mismatching + hostname). Certificate errors detected by OpenSSL, though, raise + an :exc:`SSLError`. + + +Socket creation +^^^^^^^^^^^^^^^ + +The following function allows for standalone socket creation. Starting from +Python 2.7.9, it can be more flexible to use :meth:`SSLContext.wrap_socket` +instead. + +.. function:: wrap_socket(sock, keyfile=None, certfile=None, server_side=False, cert_reqs=CERT_NONE, ssl_version={see docs}, 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 @@ -85,19 +158,6 @@ Functions, Constants, and Exceptions connection. See the discussion of :ref:`ssl-certificates` for more information on how the certificate is stored in the ``certfile``. - Often the private key is stored in the same file as the certificate; in this - case, only the ``certfile`` parameter need be passed. If the private key is - stored in a separate file, both parameters must be used. If the private key - is stored in the ``certfile``, 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----- - The parameter ``server_side`` is a boolean which identifies whether server-side or client-side behavior is desired from this socket. @@ -127,14 +187,16 @@ Functions, Constants, and Exceptions .. table:: - ======================== ========= ========= ========== ========= - *client* / **server** **SSLv2** **SSLv3** **SSLv23** **TLSv1** - ------------------------ --------- --------- ---------- --------- - *SSLv2* yes no yes no - *SSLv3* no yes yes no - *SSLv23* yes no yes no - *TLSv1* no no yes yes - ======================== ========= ========= ========== ========= + ======================== ========= ========= ========== ========= =========== =========== + *client* / **server** **SSLv2** **SSLv3** **SSLv23** **TLSv1** **TLSv1.1** **TLSv1.2** + ------------------------ --------- --------- ---------- --------- ----------- ----------- + *SSLv2* yes no yes no no no + *SSLv3* no yes yes no no no + *SSLv23* yes no yes no no no + *TLSv1* no no yes yes no no + *TLSv1.1* no no yes no yes no + *TLSv1.2* no no yes no no yes + ======================== ========= ========= ========== ========= =========== =========== .. note:: @@ -161,22 +223,79 @@ Functions, Constants, and Exceptions The parameter ``suppress_ragged_eofs`` specifies how the :meth:`SSLSocket.read` method should signal unexpected EOF from the other end of the connection. If specified as :const:`True` (the default), it returns a - normal EOF in response to unexpected EOF errors raised from the underlying - socket; if :const:`False`, it will raise the exceptions back to the caller. + 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. .. versionchanged:: 2.7 New optional argument *ciphers*. + +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 in Python 2.7.9 are: :data:`PROTOCOL_SSLv23`, + :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 has problematic security due to a number of + poor implementations and it's reliance on MD5 within the protocol. If you + 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:: 2.7.9 + + +Random generation +^^^^^^^^^^^^^^^^^ + .. function:: RAND_status() Returns ``True`` if the SSL pseudo-random number generator has been seeded with - 'enough' randomness, and False otherwise. You can use :func:`ssl.RAND_egd` + '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`` + 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 @@ -187,28 +306,66 @@ Functions, Constants, and Exceptions .. function:: RAND_add(bytes, entropy) - Mixes the given ``bytes`` into the SSL pseudo-random number generator. The - parameter ``entropy`` (a float) is a lower bound on the entropy contained in + Mixes 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. -.. function:: cert_time_to_seconds(timestring) +Certificate handling +^^^^^^^^^^^^^^^^^^^^ + +.. 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` and :rfc:`6125`, except that IP addresses are not currently + supported. 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. - Returns a floating-point value containing a normal seconds-after-the-epoch - time value, given the time-string representing the "notBefore" or "notAfter" - date from a certificate. + :exc:`CertificateError` is raised on failure. On success, the function + returns nothing:: - Here's an example:: + >>> 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:: 2.7.9 + - >>> import ssl - >>> ssl.cert_time_to_seconds("May 9 00:00:00 2007 GMT") - 1178694000.0 - >>> import time - >>> time.ctime(ssl.cert_time_to_seconds("May 9 00:00:00 2007 GMT")) - 'Wed May 9 00:00:00 2007' - >>> +.. 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 -.. function:: get_server_certificate (addr, ssl_version=PROTOCOL_SSLv3, ca_certs=None) + >>> import ssl + >>> timestamp = ssl.cert_time_to_seconds("Jan 5 09:34:43 2018 GMT") + >>> timestamp + 1515144883 + >>> from datetime import datetime + >>> print(datetime.utcfromtimestamp(timestamp)) + 2018-01-05 09:34:43 + + "notBefore" or "notAfter" dates must use GMT (:rfc:`5280`). + + .. versionchanged:: 2.7.9 + 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_SSLv23, 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 @@ -219,36 +376,144 @@ Functions, Constants, and Exceptions will attempt to validate the server certificate against that set of root certificates, and will fail if the validation attempt fails. -.. function:: DER_cert_to_PEM_cert (DER_cert_bytes) + .. versionchanged:: 2.7.9 + + This function is now IPv6-compatible, and the default *ssl_version* is + changed from :data:`PROTOCOL_SSLv3` to :data:`PROTOCOL_SSLv23` 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) +.. 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``: + + * :attr:`cafile` - resolved path to cafile or None if the file doesn't exist, + * :attr:`capath` - resolved path to capath or None if the directory doesn't exist, + * :attr:`openssl_cafile_env` - OpenSSL's environment key that points to a cafile, + * :attr:`openssl_cafile` - hard coded path to a cafile, + * :attr:`openssl_capath_env` - OpenSSL's environment key that points to a capath, + * :attr:`openssl_capath` - hard coded path to a capath directory + + .. versionadded:: 2.7.9 + +.. 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:: 2.7.9 + +.. 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:: 2.7.9 + + +Constants +^^^^^^^^^ + .. data:: CERT_NONE - Value to pass to the ``cert_reqs`` parameter to :func:`sslobject` when no - certificates will be required or validated from the other side of the socket - connection. + Possible value for :attr:`SSLContext.verify_mode`, or the ``cert_reqs`` + parameter to :func:`wrap_socket`. In this mode (the default), no + certificates will be required from the other side of the socket connection. + If a certificate is received from the other end, no attempt to validate it + is made. + + See the discussion of :ref:`ssl-security` below. .. data:: CERT_OPTIONAL - Value to pass to the ``cert_reqs`` parameter to :func:`sslobject` when no - certificates will be required from the other side of the socket connection, - but if they are provided, will be validated. Note that use of this setting - requires a valid certificate validation file also be passed as a value of the - ``ca_certs`` parameter. + Possible value for :attr:`SSLContext.verify_mode`, or the ``cert_reqs`` + parameter to :func:`wrap_socket`. In this mode no certificates will be + required from the other side of the socket connection; but if they + are provided, validation will be attempted and an :class:`SSLError` + will be raised on failure. + + 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 - Value to pass to the ``cert_reqs`` parameter to :func:`sslobject` when - certificates will be required from the other side of the socket connection. - Note that use of this setting requires a valid certificate validation file - also be passed as a value of the ``ca_certs`` parameter. + 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. + + 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:: 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:: 2.7.9 + +.. 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:: 2.7.9 + +.. 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:: 2.7.9 + +.. data:: VERIFY_X509_STRICT + + Possible value for :attr:`SSLContext.verify_flags` to disable workarounds + for broken X.509 certificates. + + .. versionadded:: 2.7.9 .. data:: PROTOCOL_SSLv2 @@ -275,9 +540,136 @@ Functions, Constants, and Exceptions .. data:: PROTOCOL_TLSv1 - Selects TLS version 1 as the channel encryption protocol. This is the most + Selects TLS version 1.0 as the channel encryption protocol. + +.. data:: PROTOCOL_TLSv1_1 + + Selects TLS version 1.1 as the channel encryption protocol. + Available only with openssl version 1.0.1+. + + .. versionadded:: 2.7.9 + +.. 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. + sides can speak it. Available only with openssl version 1.0.1+. + + .. versionadded:: 2.7.9 + +.. 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:: 2.7.9 + +.. data:: OP_NO_SSLv2 + + Prevents an SSLv2 connection. This option is only applicable in + conjunction with :const:`PROTOCOL_SSLv23`. It prevents the peers from + choosing SSLv2 as the protocol version. + + .. versionadded:: 2.7.9 + +.. data:: OP_NO_SSLv3 + + Prevents an SSLv3 connection. This option is only applicable in + conjunction with :const:`PROTOCOL_SSLv23`. It prevents the peers from + choosing SSLv3 as the protocol version. + + .. versionadded:: 2.7.9 + +.. data:: OP_NO_TLSv1 + + Prevents a TLSv1 connection. This option is only applicable in + conjunction with :const:`PROTOCOL_SSLv23`. It prevents the peers from + choosing TLSv1 as the protocol version. + + .. versionadded:: 2.7.9 + +.. data:: OP_NO_TLSv1_1 + + Prevents a TLSv1.1 connection. This option is only applicable in conjunction + with :const:`PROTOCOL_SSLv23`. It prevents the peers from choosing TLSv1.1 as + the protocol version. Available only with openssl version 1.0.1+. + + .. versionadded:: 2.7.9 + +.. data:: OP_NO_TLSv1_2 + + Prevents a TLSv1.2 connection. This option is only applicable in conjunction + with :const:`PROTOCOL_SSLv23`. It prevents the peers from choosing TLSv1.2 as + the protocol version. Available only with openssl version 1.0.1+. + + .. versionadded:: 2.7.9 + +.. 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:: 2.7.9 + +.. 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:: 2.7.9 + +.. 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:: 2.7.9 + +.. 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:: 2.7.9 + +.. data:: HAS_ECDH + + Whether the OpenSSL library has built-in support for Elliptic Curve-based + Diffie-Hellman key exchange. This should be true unless the feature was + explicitly disabled by the distributor. + + .. versionadded:: 2.7.9 + +.. data:: HAS_SNI + + Whether the OpenSSL library has built-in support for the *Server Name + Indication* extension to the SSLv3 and TLSv1 protocols (as defined in + :rfc:`4366`). When true, you can use the *server_hostname* argument to + :meth:`SSLContext.wrap_socket`. + + .. versionadded:: 2.7.9 + +.. data:: HAS_NPN + + Whether the OpenSSL library has built-in support for *Next Protocol + Negotiation* as described in the `NPN draft specification + <http://tools.ietf.org/html/draft-agl-tls-nextprotoneg>`_. When true, + you can use the :meth:`SSLContext.set_npn_protocols` method to advertise + which protocols you want to support. + + .. versionadded:: 2.7.9 + +.. 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:: 2.7.9 .. data:: OPENSSL_VERSION @@ -309,9 +701,40 @@ Functions, Constants, and Exceptions .. versionadded:: 2.7 +.. data:: ALERT_DESCRIPTION_HANDSHAKE_FAILURE + ALERT_DESCRIPTION_INTERNAL_ERROR + ALERT_DESCRIPTION_* -SSLSocket Objects ------------------ + Alert Descriptions from :rfc:`5246` and others. The `IANA TLS Alert Registry + <http://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:: 2.7.9 + +.. 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:: 2.7.9 + +.. 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:: 2.7.9 + + +SSL Sockets +----------- SSL sockets provide the following methods of :ref:`socket-objects`: @@ -334,37 +757,64 @@ SSL sockets provide the following method 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. +the specification of normal, OS-level sockets. See especially the +:ref:`notes on non-blocking sockets <ssl-nonblocking>`. SSL sockets also have the following additional methods and attributes: +.. method:: SSLSocket.do_handshake() + + Perform the SSL setup handshake. + + .. versionchanged:: 2.7.9 + + The handshake method also performs :func:`match_hostname` when the + :attr:`~SSLContext.check_hostname` attribute of the socket's + :attr:`~SSLSocket.context` is true. + .. method:: SSLSocket.getpeercert(binary_form=False) If there is no certificate for the peer on the other end of the connection, - returns ``None``. + 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 the keys ``subject`` (the principal for - which the certificate was issued), and ``notAfter`` (the time after which the - certificate should not be trusted). The certificate was already validated, - so the ``notBefore`` and ``issuer`` fields are not returned. 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. + 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:: - The "subject" field is a tuple containing the sequence of relative - distinguished names (RDNs) given in the certificate's data structure for the - principal, and each RDN is a sequence of name-value pairs:: + {'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', 'hostmaster@eff.org'),)), + 'subjectAltName': (('DNS', '*.eff.org'), ('DNS', 'eff.org')), + 'version': 3} - {'notAfter': 'Feb 16 16:54:50 2013 GMT', - 'subject': ((('countryName', u'US'),), - (('stateOrProvinceName', u'Delaware'),), - (('localityName', u'Wilmington'),), - (('organizationName', u'Python Software Foundation'),), - (('organizationalUnitName', u'SSL'),), - (('commonName', u'somemachine.python.org'),))} + .. 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 @@ -380,40 +830,388 @@ SSL sockets also have the following addi :const:`None` if you used :const:`CERT_NONE` (rather than :const:`CERT_OPTIONAL` or :const:`CERT_REQUIRED`). + .. versionchanged:: 2.7.9 + The returned dictionary includes additional items such as ``issuer`` and + ``notBefore``. Additionall :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.do_handshake() +.. method:: SSLSocket.compression() + + Return the compression algorithm being used as a string, or ``None`` + if the connection isn't compressed. - Perform a TLS/SSL handshake. If this is used with a non-blocking socket, it - may raise :exc:`SSLError` with an ``arg[0]`` of :const:`SSL_ERROR_WANT_READ` - or :const:`SSL_ERROR_WANT_WRITE`, in which case it must be called again until - it completes successfully. For example, to simulate the behavior of a - blocking socket, one might write:: + If the higher-level protocol supports its own compression mechanism, + you can use :data:`OP_NO_COMPRESSION` to disable SSL-level compression. + + .. versionadded:: 2.7.9 + +.. 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. - while True: - try: - s.do_handshake() - break - except ssl.SSLError as err: - if err.args[0] == ssl.SSL_ERROR_WANT_READ: - select.select([s], [], []) - elif err.args[0] == ssl.SSL_ERROR_WANT_WRITE: - select.select([], [s], []) - else: - raise + 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:: 2.7.9 + +.. method:: SSLSocket.selected_npn_protocol() + + Returns the 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:: 2.7.9 .. 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 - socket instance returned should always be used for further communication with - the other side of the connection, rather than the original socket instance - (which may not function properly after the unwrap). + returned socket should always be used for further communication with the + other side of the connection, rather than the original socket. + +.. attribute:: SSLSocket.context + + The :class:`SSLContext` object this SSL socket is tied to. If the SSL + socket was created using the top-level :func:`wrap_socket` function + (rather than :meth:`SSLContext.wrap_socket`), this is a custom context + object created for this SSL socket. + + .. versionadded:: 2.7.9 + + +SSL Contexts +------------ + +.. versionadded:: 2.7.9 + +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) + + Create a new SSL context. You must pass *protocol* which must be one + of the ``PROTOCOL_*`` constants defined in this module. + :data:`PROTOCOL_SSLv23` is currently recommended for maximum + interoperability. + + .. seealso:: + :func:`create_default_context` lets the :mod:`ssl` module choose + security settings for a given purpose. + + +: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} + + +.. 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. + +.. 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. + +.. 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 + <http://www.openssl.org/docs/ssl/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 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. + +.. 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. + +.. 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 + <http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT>`_. + 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. + +.. 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 `NPN draft specification + <http://tools.ietf.org/html/draft-agl-tls-nextprotoneg>`_. 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. + +.. method:: SSLContext.set_servername_callback(server_name_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 *server_name_callback* + is ``None`` then the callback is disabled. Calling this function a + subsequent time will disable the previously registered callback. + + The callback function, *server_name_callback*, 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 the IDNA decoded server name. + + 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_npn_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 *server_name_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 there is an IDNA 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. + + If an exception is raised from the *server_name_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. + +.. method:: SSLContext.load_dh_params(dhfile) + + Load the key generation parameters for Diffie-Helman (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. + +.. 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. + + .. seealso:: + `SSL/TLS & Perfect Forward Secrecy <http://vincent.bernat.im/en/blog/2011-ssl-perfect-forward-secrecy.html>`_ + Vincent Bernat. + +.. method:: SSLContext.wrap_socket(sock, server_side=False, \ + do_handshake_on_connect=True, suppress_ragged_eofs=True, \ + server_hostname=None) + + Wrap an existing Python socket *sock* and return an :class:`SSLSocket` + object. *sock* must be a :data:`~socket.SOCK_STREAM` socket; other socket + types are unsupported. + + The returned SSL socket is tied to the context, its settings and + certificates. The parameters *server_side*, *do_handshake_on_connect* + and *suppress_ragged_eofs* have the same meaning as in the top-level + :func:`wrap_socket` function. + + 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 the OpenSSL library doesn't have support + for it (that is, if :data:`HAS_SNI` is :const:`False`). Specifying + *server_hostname* will also raise a :exc:`ValueError` if *server_side* + is true. + +.. 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 + <http://www.openssl.org/docs/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) + +.. method:: SSLContext.get_ca_certs(binary_form=False) + + Returns a list of dicts with information of loaded CA certs. If the + optional argument is true, returns a DER-encoded copy of the CA + certificate. + + .. note:: + Certificates in a capath directory aren't loaded unless they have + been used at least once. + +.. attribute:: SSLContext.check_hostname + + Wether 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. + + Example:: + + import socket, ssl + + context = ssl.SSLContext(ssl.PROTOCOL_TLSv1) + 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)) + + .. note:: + + This features requires OpenSSL 0.9.8f or newer. + +.. 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 ``ValueError``. + +.. attribute:: SSLContext.protocol + + The protocol version chosen when constructing the context. This attribute + is read-only. + +.. 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+. + +.. 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`. + .. index:: single: certificates @@ -460,6 +1258,9 @@ and a footer line:: ... (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, @@ -483,24 +1284,35 @@ certification authority's 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. +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 +^^^^^^^^^^^^^^^^^^^^^^^^^^^^ -Some "standard" root certificates are available from various certification -authorities: `Thawte <http://www.thawte.com/roots/>`_, `Verisign -<http://www.verisign.com/support/roots.html>`_, `Positive SSL -<http://www.PositiveSSL.com/ssl-certificate-support/cert_installation/UTN-USERFirst-Hardware.crt>`_ -(used by python.org), `Equifax and GeoTrust -<http://www.geotrust.com/resources/root_certificates/index.asp>`_. +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:: -In general, if you are using SSL3 or TLS1, you don't need to put the full chain -in your "CA certs" file; you only need the root certificates, and the remote -peer is supposed to furnish the other certificates necessary to chain from its -certificate to a root certificate. See :rfc:`4158` for more discussion of the -way in which certification chains can be built. + -----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 @@ -555,87 +1367,156 @@ should use the following idiom:: Client-side operation ^^^^^^^^^^^^^^^^^^^^^ -This example connects to an SSL server, prints the server's address and -certificate, sends some bytes, and reads part of the response:: +This example connects to an SSL server and prints the server's certificate:: import socket, ssl, pprint s = socket.socket(socket.AF_INET, socket.SOCK_STREAM) - # require a certificate from the server ssl_sock = ssl.wrap_socket(s, ca_certs="/etc/ca_certs_file", cert_reqs=ssl.CERT_REQUIRED) - ssl_sock.connect(('www.verisign.com', 443)) - print repr(ssl_sock.getpeername()) - print ssl_sock.cipher() - print pprint.pformat(ssl_sock.getpeercert()) - - # Set a simple HTTP request -- use httplib in actual code. - ssl_sock.write("""GET / HTTP/1.0\r - Host: www.verisign.com\r

\r

""") - - # Read a chunk of data. Will not necessarily - # read all the data returned by the server. - data = ssl_sock.read() - + pprint.pprint(ssl_sock.getpeercert()) # note that closing the SSLSocket will also close the underlying socket ssl_sock.close() -As of September 6, 2007, the certificate printed by this program looked like +As of January 6, 2012, the certificate printed by this program looks like this:: - {'notAfter': 'May 8 23:59:59 2009 GMT', - 'subject': ((('serialNumber', u'2497886'),), - (('1.3.6.1.4.1.311.60.2.1.3', u'US'),), - (('1.3.6.1.4.1.311.60.2.1.2', u'Delaware'),), - (('countryName', u'US'),), - (('postalCode', u'94043'),), - (('stateOrProvinceName', u'California'),), - (('localityName', u'Mountain View'),), - (('streetAddress', u'487 East Middlefield Road'),), - (('organizationName', u'VeriSign, Inc.'),), - (('organizationalUnitName', - u'Production Security Services'),), - (('organizationalUnitName', - u'Terms of use at www.verisign.com/rpa (c)06'),), - (('commonName', u'www.verisign.com'),))} + {'issuer': ((('countryName', 'US'),), + (('organizationName', 'VeriSign, Inc.'),), + (('organizationalUnitName', 'VeriSign Trust Network'),), + (('organizationalUnitName', + 'Terms of use at https://www.verisign.com/rpa (c)06'),), + (('commonName', + 'VeriSign Class 3 Extended Validation SSL SGC CA'),)), + 'notAfter': 'May 25 23:59:59 2012 GMT', + 'notBefore': 'May 26 00:00:00 2010 GMT', + 'serialNumber': '53D2BEF924A7245E83CA01E46CAA2477', + 'subject': ((('1.3.6.1.4.1.311.60.2.1.3', 'US'),), + (('1.3.6.1.4.1.311.60.2.1.2', 'Delaware'),), + (('businessCategory', 'V1.0, Clause 5.(b)'),), + (('serialNumber', '2497886'),), + (('countryName', 'US'),), + (('postalCode', '94043'),), + (('stateOrProvinceName', 'California'),), + (('localityName', 'Mountain View'),), + (('streetAddress', '487 East Middlefield Road'),), + (('organizationName', 'VeriSign, Inc.'),), + (('organizationalUnitName', ' Production Security Services'),), + (('commonName', 'www.verisign.com'),)), + 'subjectAltName': (('DNS', 'www.verisign.com'), + ('DNS', 'verisign.com'), + ('DNS', 'www.verisign.net'), + ('DNS', 'verisign.net'), + ('DNS', 'www.verisign.mobi'), + ('DNS', 'verisign.mobi'), + ('DNS', 'www.verisign.eu'), + ('DNS', 'verisign.eu')), + 'version': 3} + +This other example first creates an SSL context, instructs it to verify +certificates sent by peers, and feeds it a set of recognized certificate +authorities (CA):: + + >>> context = ssl.SSLContext(ssl.PROTOCOL_SSLv23) + >>> context.verify_mode = ssl.CERT_REQUIRED + >>> context.load_verify_locations("/etc/ssl/certs/ca-bundle.crt") + +(it is assumed 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:: -which is a fairly poorly-formed ``subject`` field. + >>> conn = context.wrap_socket(socket.socket(socket.AF_INET)) + >>> conn.connect(("linuxfr.org", 443)) + +You should then fetch the certificate and check its fields for conformity:: + + >>> cert = conn.getpeercert() + >>> ssl.match_hostname(cert, "linuxfr.org") + +Visual inspection shows that the certificate does identify the desired service +(that is, the HTTPS host ``linuxfr.org``):: + + >>> pprint.pprint(cert) + {'issuer': ((('organizationName', 'CAcert Inc.'),), + (('organizationalUnitName', 'http://www.CAcert.org'),), + (('commonName', 'CAcert Class 3 Root'),)), + 'notAfter': 'Jun 7 21:02:24 2013 GMT', + 'notBefore': 'Jun 8 21:02:24 2011 GMT', + 'serialNumber': 'D3E9', + 'subject': ((('commonName', 'linuxfr.org'),),), + 'subjectAltName': (('DNS', 'linuxfr.org'), + ('othername', '<unsupported>'), + ('DNS', 'linuxfr.org'), + ('othername', '<unsupported>'), + ('DNS', 'dev.linuxfr.org'), + ('othername', '<unsupported>'), + ('DNS', 'prod.linuxfr.org'), + ('othername', '<unsupported>'), + ('DNS', 'alpha.linuxfr.org'), + ('othername', '<unsupported>'), + ('DNS', '*.linuxfr.org'), + ('othername', '<unsupported>')), + 'version': 3} + +Now that you are assured of its authenticity, you can proceed to talk with +the server:: + + >>> conn.sendall(b"HEAD / HTTP/1.0\r

Host: linuxfr.org\r

\r

") + >>> pprint.pprint(conn.recv(1024).split(b"\r

")) + [b'HTTP/1.1 302 Found', + b'Date: Sun, 16 May 2010 13:43:28 GMT', + b'Server: Apache/2.2', + b'Location: https://linuxfr.org/pub/', + b'Vary: Accept-Encoding', + b'Connection: close', + b'Content-Type: text/html; charset=iso-8859-1', + b'', + b''] + +See the discussion of :ref:`ssl-security` below. + Server-side operation ^^^^^^^^^^^^^^^^^^^^^ -For server operation, typically you'd need to have a server certificate, and -private key, each in a file. You'd open a socket, bind it to a port, call -:meth:`listen` on it, then start waiting for clients to connect:: +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.SSLContext(ssl.PROTOCOL_SSLv23) + context.load_cert_chain(certfile="mycertfile", keyfile="mykeyfile") + bindsocket = socket.socket() bindsocket.bind(('myaddr.mydomain.com', 10023)) bindsocket.listen(5) -When one did, you'd call :meth:`accept` on the socket to get the new socket from -the other end, and use :func:`wrap_socket` to create a server-side SSL context -for it:: +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 = ssl.wrap_socket(newsocket, - server_side=True, - certfile="mycertfile", - keyfile="mykeyfile", - ssl_version=ssl.PROTOCOL_TLSv1) + connstream = context.wrap_socket(newsocket, server_side=True) try: deal_with_client(connstream) finally: connstream.shutdown(socket.SHUT_RDWR) connstream.close() -Then you'd read data from the ``connstream`` and do something with it till you +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): @@ -649,7 +1530,138 @@ are finished with the client (or the cli data = connstream.read() # finished with client -And go back to listening for new client connections. +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 non-blocking mode and use an event loop). + + +.. _ssl-nonblocking: + +Notes on non-blocking sockets +----------------------------- + +When working with non-blocking sockets, there are several things you need +to be aware of: + +- 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], []) + + +.. _ssl-security: + +Security considerations +----------------------- + +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. + +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. + +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. + + .. note:: + + In client mode, :const:`CERT_OPTIONAL` and :const:`CERT_REQUIRED` are + equivalent unless anonymous ciphers are enabled (they are disabled + by default). + +Protocol versions +''''''''''''''''' + +SSL version 2 is considered insecure and is therefore dangerous to use. If +you want maximum compatibility between clients and servers, it is recommended +to use :const:`PROTOCOL_SSLv23` as the protocol version and then disable +SSLv2 explicitly using the :data:`SSLContext.options` attribute:: + + context = ssl.SSLContext(ssl.PROTOCOL_SSLv23) + context.options |= ssl.OP_NO_SSLv2 + +The SSL context created above will allow SSLv3 and TLSv1 (and later, if +supported by your system) connections, but not SSLv2. + +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 2.7.9, 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 <http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT>`_. +If you want to check which ciphers are enabled by a given cipher list, use 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. .. seealso:: @@ -668,3 +1680,15 @@ And go back to listening for new client `RFC 3280: Internet X.509 Public Key Infrastructure Certificate and CRL Profile <http://www.ietf.org/rfc/rfc3280>`_ Housley et. al. + + `RFC 4366: Transport Layer Security (TLS) Extensions <http://www.ietf.org/rfc/rfc4366>`_ + Blake-Wilson et. al. + + `RFC 5246: The Transport Layer Security (TLS) Protocol Version 1.2 <http://www.ietf.org/rfc/rfc5246>`_ + T. Dierks et. al. + + `RFC 6066: Transport Layer Security (TLS) Extensions <http://www.ietf.org/rfc/rfc6066>`_ + D. Eastlake + + `IANA TLS: Transport Layer Security (TLS) Parameters <http://www.iana.org/assignments/tls-parameters/tls-parameters.xml>`_ + IANA