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Thomas Wouters47b49bf2007-08-30 22:15:33 +00001:mod:`ssl` --- SSL wrapper for socket objects
Georg Brandl7f01a132009-09-16 15:58:14 +00002=============================================
Thomas Woutersed03b412007-08-28 21:37:11 +00003
4.. module:: ssl
Thomas Wouters47b49bf2007-08-30 22:15:33 +00005 :synopsis: SSL wrapper for socket objects
6
7.. moduleauthor:: Bill Janssen <bill.janssen@gmail.com>
Thomas Wouters47b49bf2007-08-30 22:15:33 +00008.. sectionauthor:: Bill Janssen <bill.janssen@gmail.com>
9
Thomas Woutersed03b412007-08-28 21:37:11 +000010
Thomas Wouters1b7f8912007-09-19 03:06:30 +000011.. index:: single: OpenSSL; (use in module ssl)
12
13.. index:: TLS, SSL, Transport Layer Security, Secure Sockets Layer
14
Georg Brandl7f01a132009-09-16 15:58:14 +000015This module provides access to Transport Layer Security (often known as "Secure
16Sockets Layer") encryption and peer authentication facilities for network
17sockets, both client-side and server-side. This module uses the OpenSSL
18library. It is available on all modern Unix systems, Windows, Mac OS X, and
19probably additional platforms, as long as OpenSSL is installed on that platform.
Thomas Woutersed03b412007-08-28 21:37:11 +000020
21.. note::
22
Georg Brandl7f01a132009-09-16 15:58:14 +000023 Some behavior may be platform dependent, since calls are made to the
24 operating system socket APIs. The installed version of OpenSSL may also
25 cause variations in behavior.
Thomas Woutersed03b412007-08-28 21:37:11 +000026
Georg Brandl7f01a132009-09-16 15:58:14 +000027This section documents the objects and functions in the ``ssl`` module; for more
28general information about TLS, SSL, and certificates, the reader is referred to
29the documents in the "See Also" section at the bottom.
Thomas Woutersed03b412007-08-28 21:37:11 +000030
Georg Brandl7f01a132009-09-16 15:58:14 +000031This module provides a class, :class:`ssl.SSLSocket`, which is derived from the
32:class:`socket.socket` type, and provides a socket-like wrapper that also
33encrypts and decrypts the data going over the socket with SSL. It supports
34additional :meth:`read` and :meth:`write` methods, along with a method,
35:meth:`getpeercert`, to retrieve the certificate of the other side of the
36connection, and a method, :meth:`cipher`, to retrieve the cipher being used for
37the secure connection.
Thomas Woutersed03b412007-08-28 21:37:11 +000038
Antoine Pitrou152efa22010-05-16 18:19:27 +000039For more sophisticated applications, the :class:`ssl.SSLContext` class
40helps manage settings and certificates, which can then be inherited
41by SSL sockets created through the :meth:`SSLContext.wrap_socket` method.
42
43
Thomas Wouters1b7f8912007-09-19 03:06:30 +000044Functions, Constants, and Exceptions
45------------------------------------
46
47.. exception:: SSLError
48
Georg Brandl48310cd2009-01-03 21:18:54 +000049 Raised to signal an error from the underlying SSL implementation. This
Georg Brandl7f01a132009-09-16 15:58:14 +000050 signifies some problem in the higher-level encryption and authentication
51 layer that's superimposed on the underlying network connection. This error
52 is a subtype of :exc:`socket.error`, which in turn is a subtype of
53 :exc:`IOError`.
Thomas Wouters1b7f8912007-09-19 03:06:30 +000054
Antoine Pitrou2d9cb9c2010-04-17 17:40:45 +000055.. 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)
Thomas Wouters1b7f8912007-09-19 03:06:30 +000056
Georg Brandl7f01a132009-09-16 15:58:14 +000057 Takes an instance ``sock`` of :class:`socket.socket`, and returns an instance
58 of :class:`ssl.SSLSocket`, a subtype of :class:`socket.socket`, which wraps
59 the underlying socket in an SSL context. For client-side sockets, the
60 context construction is lazy; if the underlying socket isn't connected yet,
61 the context construction will be performed after :meth:`connect` is called on
62 the socket. For server-side sockets, if the socket has no remote peer, it is
63 assumed to be a listening socket, and the server-side SSL wrapping is
64 automatically performed on client connections accepted via the :meth:`accept`
65 method. :func:`wrap_socket` may raise :exc:`SSLError`.
Thomas Wouters1b7f8912007-09-19 03:06:30 +000066
Georg Brandl7f01a132009-09-16 15:58:14 +000067 The ``keyfile`` and ``certfile`` parameters specify optional files which
68 contain a certificate to be used to identify the local side of the
69 connection. See the discussion of :ref:`ssl-certificates` for more
70 information on how the certificate is stored in the ``certfile``.
Thomas Wouters1b7f8912007-09-19 03:06:30 +000071
Georg Brandl7f01a132009-09-16 15:58:14 +000072 The parameter ``server_side`` is a boolean which identifies whether
73 server-side or client-side behavior is desired from this socket.
Thomas Wouters1b7f8912007-09-19 03:06:30 +000074
Georg Brandl7f01a132009-09-16 15:58:14 +000075 The parameter ``cert_reqs`` specifies whether a certificate is required from
76 the other side of the connection, and whether it will be validated if
77 provided. It must be one of the three values :const:`CERT_NONE`
78 (certificates ignored), :const:`CERT_OPTIONAL` (not required, but validated
79 if provided), or :const:`CERT_REQUIRED` (required and validated). If the
80 value of this parameter is not :const:`CERT_NONE`, then the ``ca_certs``
81 parameter must point to a file of CA certificates.
Thomas Wouters1b7f8912007-09-19 03:06:30 +000082
Georg Brandl7f01a132009-09-16 15:58:14 +000083 The ``ca_certs`` file contains a set of concatenated "certification
84 authority" certificates, which are used to validate certificates passed from
85 the other end of the connection. See the discussion of
86 :ref:`ssl-certificates` for more information about how to arrange the
87 certificates in this file.
Thomas Wouters1b7f8912007-09-19 03:06:30 +000088
Georg Brandl7f01a132009-09-16 15:58:14 +000089 The parameter ``ssl_version`` specifies which version of the SSL protocol to
90 use. Typically, the server chooses a particular protocol version, and the
91 client must adapt to the server's choice. Most of the versions are not
92 interoperable with the other versions. If not specified, for client-side
93 operation, the default SSL version is SSLv3; for server-side operation,
94 SSLv23. These version selections provide the most compatibility with other
95 versions.
Thomas Wouters1b7f8912007-09-19 03:06:30 +000096
Georg Brandl7f01a132009-09-16 15:58:14 +000097 Here's a table showing which versions in a client (down the side) can connect
98 to which versions in a server (along the top):
Thomas Wouters1b7f8912007-09-19 03:06:30 +000099
100 .. table::
101
102 ======================== ========= ========= ========== =========
103 *client* / **server** **SSLv2** **SSLv3** **SSLv23** **TLSv1**
Christian Heimes255f53b2007-12-08 15:33:56 +0000104 ------------------------ --------- --------- ---------- ---------
Antoine Pitrou2d9cb9c2010-04-17 17:40:45 +0000105 *SSLv2* yes no yes no
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000106 *SSLv3* yes yes yes no
107 *SSLv23* yes no yes no
108 *TLSv1* no no yes yes
109 ======================== ========= ========= ========== =========
110
Antoine Pitrou2d9cb9c2010-04-17 17:40:45 +0000111 .. note::
112
Benjamin Petersond7c3ed52010-06-27 22:32:30 +0000113 Which connections succeed will vary depending on the version of
114 OpenSSL. For instance, in some older versions of OpenSSL (such
115 as 0.9.7l on OS X 10.4), an SSLv2 client could not connect to an
116 SSLv23 server. Another example: beginning with OpenSSL 1.0.0,
117 an SSLv23 client will not actually attempt SSLv2 connections
118 unless you explicitly enable SSLv2 ciphers; for example, you
119 might specify ``"ALL"`` or ``"SSLv2"`` as the *ciphers* parameter
120 to enable them.
Antoine Pitrou2d9cb9c2010-04-17 17:40:45 +0000121
Benjamin Petersond7c3ed52010-06-27 22:32:30 +0000122 The *ciphers* parameter sets the available ciphers for this SSL object.
Antoine Pitrou2d9cb9c2010-04-17 17:40:45 +0000123 It should be a string in the `OpenSSL cipher list format
124 <http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT>`_.
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000125
Bill Janssen48dc27c2007-12-05 03:38:10 +0000126 The parameter ``do_handshake_on_connect`` specifies whether to do the SSL
127 handshake automatically after doing a :meth:`socket.connect`, or whether the
Georg Brandl7f01a132009-09-16 15:58:14 +0000128 application program will call it explicitly, by invoking the
129 :meth:`SSLSocket.do_handshake` method. Calling
130 :meth:`SSLSocket.do_handshake` explicitly gives the program control over the
131 blocking behavior of the socket I/O involved in the handshake.
Bill Janssen48dc27c2007-12-05 03:38:10 +0000132
Georg Brandl7f01a132009-09-16 15:58:14 +0000133 The parameter ``suppress_ragged_eofs`` specifies how the
134 :meth:`SSLSocket.read` method should signal unexpected EOF from the other end
135 of the connection. If specified as :const:`True` (the default), it returns a
136 normal EOF in response to unexpected EOF errors raised from the underlying
137 socket; if :const:`False`, it will raise the exceptions back to the caller.
Bill Janssen48dc27c2007-12-05 03:38:10 +0000138
Ezio Melotti4d5195b2010-04-20 10:57:44 +0000139 .. versionchanged:: 3.2
Antoine Pitrou2d9cb9c2010-04-17 17:40:45 +0000140 New optional argument *ciphers*.
141
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000142.. function:: RAND_status()
143
Georg Brandl7f01a132009-09-16 15:58:14 +0000144 Returns True if the SSL pseudo-random number generator has been seeded with
145 'enough' randomness, and False otherwise. You can use :func:`ssl.RAND_egd`
146 and :func:`ssl.RAND_add` to increase the randomness of the pseudo-random
147 number generator.
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000148
149.. function:: RAND_egd(path)
150
151 If you are running an entropy-gathering daemon (EGD) somewhere, and ``path``
Georg Brandl7f01a132009-09-16 15:58:14 +0000152 is the pathname of a socket connection open to it, this will read 256 bytes
153 of randomness from the socket, and add it to the SSL pseudo-random number
154 generator to increase the security of generated secret keys. This is
155 typically only necessary on systems without better sources of randomness.
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000156
Georg Brandl7f01a132009-09-16 15:58:14 +0000157 See http://egd.sourceforge.net/ or http://prngd.sourceforge.net/ for sources
158 of entropy-gathering daemons.
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000159
160.. function:: RAND_add(bytes, entropy)
161
Georg Brandl7f01a132009-09-16 15:58:14 +0000162 Mixes the given ``bytes`` into the SSL pseudo-random number generator. The
163 parameter ``entropy`` (a float) is a lower bound on the entropy contained in
164 string (so you can always use :const:`0.0`). See :rfc:`1750` for more
165 information on sources of entropy.
Thomas Woutersed03b412007-08-28 21:37:11 +0000166
167.. function:: cert_time_to_seconds(timestring)
168
Georg Brandl7f01a132009-09-16 15:58:14 +0000169 Returns a floating-point value containing a normal seconds-after-the-epoch
170 time value, given the time-string representing the "notBefore" or "notAfter"
171 date from a certificate.
Thomas Woutersed03b412007-08-28 21:37:11 +0000172
173 Here's an example::
174
175 >>> import ssl
176 >>> ssl.cert_time_to_seconds("May 9 00:00:00 2007 GMT")
177 1178694000.0
178 >>> import time
179 >>> time.ctime(ssl.cert_time_to_seconds("May 9 00:00:00 2007 GMT"))
180 'Wed May 9 00:00:00 2007'
Georg Brandl48310cd2009-01-03 21:18:54 +0000181 >>>
Thomas Woutersed03b412007-08-28 21:37:11 +0000182
Georg Brandl7f01a132009-09-16 15:58:14 +0000183.. function:: get_server_certificate(addr, ssl_version=PROTOCOL_SSLv3, ca_certs=None)
Thomas Woutersed03b412007-08-28 21:37:11 +0000184
Georg Brandl7f01a132009-09-16 15:58:14 +0000185 Given the address ``addr`` of an SSL-protected server, as a (*hostname*,
186 *port-number*) pair, fetches the server's certificate, and returns it as a
187 PEM-encoded string. If ``ssl_version`` is specified, uses that version of
188 the SSL protocol to attempt to connect to the server. If ``ca_certs`` is
189 specified, it should be a file containing a list of root certificates, the
190 same format as used for the same parameter in :func:`wrap_socket`. The call
191 will attempt to validate the server certificate against that set of root
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000192 certificates, and will fail if the validation attempt fails.
193
Georg Brandl7f01a132009-09-16 15:58:14 +0000194.. function:: DER_cert_to_PEM_cert(DER_cert_bytes)
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000195
196 Given a certificate as a DER-encoded blob of bytes, returns a PEM-encoded
197 string version of the same certificate.
198
Georg Brandl7f01a132009-09-16 15:58:14 +0000199.. function:: PEM_cert_to_DER_cert(PEM_cert_string)
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000200
Georg Brandl7f01a132009-09-16 15:58:14 +0000201 Given a certificate as an ASCII PEM string, returns a DER-encoded sequence of
202 bytes for that same certificate.
Thomas Woutersed03b412007-08-28 21:37:11 +0000203
204.. data:: CERT_NONE
205
Antoine Pitrou152efa22010-05-16 18:19:27 +0000206 Possible value for :attr:`SSLContext.verify_mode`, or the ``cert_reqs``
207 parameter to :func:`wrap_socket`. In this mode (the default), no
208 certificates will be required from the other side of the socket connection.
209 If a certificate is received from the other end, no attempt to validate it
210 is made.
211
212 See the discussion of :ref:`ssl-security` below.
Thomas Woutersed03b412007-08-28 21:37:11 +0000213
214.. data:: CERT_OPTIONAL
215
Antoine Pitrou152efa22010-05-16 18:19:27 +0000216 Possible value for :attr:`SSLContext.verify_mode`, or the ``cert_reqs``
217 parameter to :func:`wrap_socket`. In this mode no certificates will be
218 required from the other side of the socket connection; but if they
219 are provided, validation will be attempted and an :class:`SSLError`
220 will be raised on failure.
221
222 Use of this setting requires a valid set of CA certificates to
223 be passed, either to :meth:`SSLContext.load_verify_locations` or as a
224 value of the ``ca_certs`` parameter to :func:`wrap_socket`.
Thomas Woutersed03b412007-08-28 21:37:11 +0000225
226.. data:: CERT_REQUIRED
227
Antoine Pitrou152efa22010-05-16 18:19:27 +0000228 Possible value for :attr:`SSLContext.verify_mode`, or the ``cert_reqs``
229 parameter to :func:`wrap_socket`. In this mode, certificates are
230 required from the other side of the socket connection; an :class:`SSLError`
231 will be raised if no certificate is provided, or if its validation fails.
232
233 Use of this setting requires a valid set of CA certificates to
234 be passed, either to :meth:`SSLContext.load_verify_locations` or as a
235 value of the ``ca_certs`` parameter to :func:`wrap_socket`.
Thomas Woutersed03b412007-08-28 21:37:11 +0000236
237.. data:: PROTOCOL_SSLv2
238
239 Selects SSL version 2 as the channel encryption protocol.
240
Antoine Pitrou8eac60d2010-05-16 14:19:41 +0000241 .. warning::
242
243 SSL version 2 is insecure. Its use is highly discouraged.
244
Thomas Woutersed03b412007-08-28 21:37:11 +0000245.. data:: PROTOCOL_SSLv23
246
Georg Brandl7f01a132009-09-16 15:58:14 +0000247 Selects SSL version 2 or 3 as the channel encryption protocol. This is a
248 setting to use with servers for maximum compatibility with the other end of
249 an SSL connection, but it may cause the specific ciphers chosen for the
250 encryption to be of fairly low quality.
Thomas Woutersed03b412007-08-28 21:37:11 +0000251
252.. data:: PROTOCOL_SSLv3
253
Georg Brandl7f01a132009-09-16 15:58:14 +0000254 Selects SSL version 3 as the channel encryption protocol. For clients, this
255 is the maximally compatible SSL variant.
Thomas Woutersed03b412007-08-28 21:37:11 +0000256
257.. data:: PROTOCOL_TLSv1
258
Georg Brandl7f01a132009-09-16 15:58:14 +0000259 Selects TLS version 1 as the channel encryption protocol. This is the most
260 modern version, and probably the best choice for maximum protection, if both
261 sides can speak it.
Thomas Woutersed03b412007-08-28 21:37:11 +0000262
Antoine Pitroub5218772010-05-21 09:56:06 +0000263.. data:: OP_ALL
264
265 Enables workarounds for various bugs present in other SSL implementations.
266 This option is set by default.
267
268 .. versionadded:: 3.2
269
270.. data:: OP_NO_SSLv2
271
272 Prevents an SSLv2 connection. This option is only applicable in
273 conjunction with :const:`PROTOCOL_SSLv23`. It prevents the peers from
274 choosing SSLv2 as the protocol version.
275
276 .. versionadded:: 3.2
277
278.. data:: OP_NO_SSLv3
279
280 Prevents an SSLv3 connection. This option is only applicable in
281 conjunction with :const:`PROTOCOL_SSLv23`. It prevents the peers from
282 choosing SSLv3 as the protocol version.
283
284 .. versionadded:: 3.2
285
286.. data:: OP_NO_TLSv1
287
288 Prevents a TLSv1 connection. This option is only applicable in
289 conjunction with :const:`PROTOCOL_SSLv23`. It prevents the peers from
290 choosing TLSv1 as the protocol version.
291
292 .. versionadded:: 3.2
293
Antoine Pitrou04f6a322010-04-05 21:40:07 +0000294.. data:: OPENSSL_VERSION
295
296 The version string of the OpenSSL library loaded by the interpreter::
297
298 >>> ssl.OPENSSL_VERSION
299 'OpenSSL 0.9.8k 25 Mar 2009'
300
Antoine Pitrou43a94c312010-04-05 21:44:48 +0000301 .. versionadded:: 3.2
Antoine Pitrou04f6a322010-04-05 21:40:07 +0000302
303.. data:: OPENSSL_VERSION_INFO
304
305 A tuple of five integers representing version information about the
306 OpenSSL library::
307
308 >>> ssl.OPENSSL_VERSION_INFO
309 (0, 9, 8, 11, 15)
310
Antoine Pitrou43a94c312010-04-05 21:44:48 +0000311 .. versionadded:: 3.2
Antoine Pitrou04f6a322010-04-05 21:40:07 +0000312
313.. data:: OPENSSL_VERSION_NUMBER
314
315 The raw version number of the OpenSSL library, as a single integer::
316
317 >>> ssl.OPENSSL_VERSION_NUMBER
Antoine Pitrou43a94c312010-04-05 21:44:48 +0000318 9470143
Antoine Pitrou04f6a322010-04-05 21:40:07 +0000319 >>> hex(ssl.OPENSSL_VERSION_NUMBER)
Antoine Pitrou43a94c312010-04-05 21:44:48 +0000320 '0x9080bf'
Antoine Pitrou04f6a322010-04-05 21:40:07 +0000321
Antoine Pitrou43a94c312010-04-05 21:44:48 +0000322 .. versionadded:: 3.2
Antoine Pitrou04f6a322010-04-05 21:40:07 +0000323
Thomas Woutersed03b412007-08-28 21:37:11 +0000324
Antoine Pitrou152efa22010-05-16 18:19:27 +0000325SSL Sockets
326-----------
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000327
Antoine Pitrou792ff3e2010-09-19 13:19:21 +0000328SSL sockets provide the basic interface of :ref:`socket-objects`. However,
329not all functionality is supported (for example, passing a non-zero ``flags``
330argument to :meth:`recv()` is not allowed).
331
332SSL sockets also have the following additional methods and attributes:
333
Bill Janssen48dc27c2007-12-05 03:38:10 +0000334.. method:: SSLSocket.read(nbytes=1024, buffer=None)
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000335
336 Reads up to ``nbytes`` bytes from the SSL-encrypted channel and returns them.
Georg Brandl7f01a132009-09-16 15:58:14 +0000337 If the ``buffer`` is specified, it will attempt to read into the buffer the
338 minimum of the size of the buffer and ``nbytes``, if that is specified. If
339 no buffer is specified, an immutable buffer is allocated and returned with
340 the data read from the socket.
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000341
342.. method:: SSLSocket.write(data)
343
Georg Brandl7f01a132009-09-16 15:58:14 +0000344 Writes the ``data`` to the other side of the connection, using the SSL
345 channel to encrypt. Returns the number of bytes written.
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000346
Bill Janssen48dc27c2007-12-05 03:38:10 +0000347.. method:: SSLSocket.do_handshake()
348
Georg Brandl7f01a132009-09-16 15:58:14 +0000349 Performs the SSL setup handshake. If the socket is non-blocking, this method
350 may raise :exc:`SSLError` with the value of the exception instance's
351 ``args[0]`` being either :const:`SSL_ERROR_WANT_READ` or
352 :const:`SSL_ERROR_WANT_WRITE`, and should be called again until it stops
353 raising those exceptions. Here's an example of how to do that::
Bill Janssen48dc27c2007-12-05 03:38:10 +0000354
355 while True:
356 try:
357 sock.do_handshake()
358 break
359 except ssl.SSLError as err:
360 if err.args[0] == ssl.SSL_ERROR_WANT_READ:
361 select.select([sock], [], [])
362 elif err.args[0] == ssl.SSL_ERROR_WANT_WRITE:
363 select.select([], [sock], [])
364 else:
365 raise
366
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000367.. method:: SSLSocket.getpeercert(binary_form=False)
368
Georg Brandl7f01a132009-09-16 15:58:14 +0000369 If there is no certificate for the peer on the other end of the connection,
370 returns ``None``.
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000371
Georg Brandl7f01a132009-09-16 15:58:14 +0000372 If the parameter ``binary_form`` is :const:`False`, and a certificate was
373 received from the peer, this method returns a :class:`dict` instance. If the
374 certificate was not validated, the dict is empty. If the certificate was
375 validated, it returns a dict with the keys ``subject`` (the principal for
376 which the certificate was issued), and ``notAfter`` (the time after which the
377 certificate should not be trusted). The certificate was already validated,
378 so the ``notBefore`` and ``issuer`` fields are not returned. If a
379 certificate contains an instance of the *Subject Alternative Name* extension
380 (see :rfc:`3280`), there will also be a ``subjectAltName`` key in the
381 dictionary.
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000382
383 The "subject" field is a tuple containing the sequence of relative
Georg Brandl7f01a132009-09-16 15:58:14 +0000384 distinguished names (RDNs) given in the certificate's data structure for the
385 principal, and each RDN is a sequence of name-value pairs::
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000386
387 {'notAfter': 'Feb 16 16:54:50 2013 GMT',
Ezio Melotti985e24d2009-09-13 07:54:02 +0000388 'subject': ((('countryName', 'US'),),
389 (('stateOrProvinceName', 'Delaware'),),
390 (('localityName', 'Wilmington'),),
391 (('organizationName', 'Python Software Foundation'),),
392 (('organizationalUnitName', 'SSL'),),
393 (('commonName', 'somemachine.python.org'),))}
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000394
Georg Brandl7f01a132009-09-16 15:58:14 +0000395 If the ``binary_form`` parameter is :const:`True`, and a certificate was
396 provided, this method returns the DER-encoded form of the entire certificate
397 as a sequence of bytes, or :const:`None` if the peer did not provide a
398 certificate. This return value is independent of validation; if validation
399 was required (:const:`CERT_OPTIONAL` or :const:`CERT_REQUIRED`), it will have
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000400 been validated, but if :const:`CERT_NONE` was used to establish the
401 connection, the certificate, if present, will not have been validated.
402
403.. method:: SSLSocket.cipher()
404
Georg Brandl7f01a132009-09-16 15:58:14 +0000405 Returns a three-value tuple containing the name of the cipher being used, the
406 version of the SSL protocol that defines its use, and the number of secret
407 bits being used. If no connection has been established, returns ``None``.
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000408
409
Benjamin Peterson4aeec042008-08-19 21:42:13 +0000410.. method:: SSLSocket.unwrap()
411
Georg Brandl7f01a132009-09-16 15:58:14 +0000412 Performs the SSL shutdown handshake, which removes the TLS layer from the
413 underlying socket, and returns the underlying socket object. This can be
414 used to go from encrypted operation over a connection to unencrypted. The
415 returned socket should always be used for further communication with the
416 other side of the connection, rather than the original socket.
Benjamin Peterson4aeec042008-08-19 21:42:13 +0000417
Antoine Pitrou152efa22010-05-16 18:19:27 +0000418
Antoine Pitrouec883db2010-05-24 21:20:20 +0000419.. attribute:: SSLSocket.context
420
421 The :class:`SSLContext` object this SSL socket is tied to. If the SSL
422 socket was created using the top-level :func:`wrap_socket` function
423 (rather than :meth:`SSLContext.wrap_socket`), this is a custom context
424 object created for this SSL socket.
425
426 .. versionadded:: 3.2
427
428
Antoine Pitrou152efa22010-05-16 18:19:27 +0000429SSL Contexts
430------------
431
Antoine Pitroucafaad42010-05-24 15:58:43 +0000432.. versionadded:: 3.2
433
Antoine Pitrou152efa22010-05-16 18:19:27 +0000434.. class:: SSLContext(protocol)
435
436 An object holding various data longer-lived than single SSL connections,
437 such as SSL configuration options, certificate(s) and private key(s).
438 You must pass *protocol* which must be one of the ``PROTOCOL_*`` constants
439 defined in this module. :data:`PROTOCOL_SSLv23` is recommended for
440 maximum interoperability.
441
442:class:`SSLContext` objects have the following methods and attributes:
443
444.. method:: SSLContext.load_cert_chain(certfile, keyfile=None)
445
446 Load a private key and the corresponding certificate. The *certfile*
447 string must be the path to a single file in PEM format containing the
448 certificate as well as any number of CA certificates needed to establish
449 the certificate's authenticity. The *keyfile* string, if present, must
450 point to a file containing the private key in. Otherwise the private
451 key will be taken from *certfile* as well. See the discussion of
452 :ref:`ssl-certificates` for more information on how the certificate
453 is stored in the *certfile*.
454
455 An :class:`SSLError` is raised if the private key doesn't
456 match with the certificate.
457
458.. method:: SSLContext.load_verify_locations(cafile=None, capath=None)
459
460 Load a set of "certification authority" (CA) certificates used to validate
461 other peers' certificates when :data:`verify_mode` is other than
462 :data:`CERT_NONE`. At least one of *cafile* or *capath* must be specified.
463
464 The *cafile* string, if present, is the path to a file of concatenated
465 CA certificates in PEM format. See the discussion of
466 :ref:`ssl-certificates` for more information about how to arrange the
467 certificates in this file.
468
469 The *capath* string, if present, is
470 the path to a directory containing several CA certificates in PEM format,
471 following an `OpenSSL specific layout
472 <http://www.openssl.org/docs/ssl/SSL_CTX_load_verify_locations.html>`_.
473
474.. method:: SSLContext.set_ciphers(ciphers)
475
476 Set the available ciphers for sockets created with this context.
477 It should be a string in the `OpenSSL cipher list format
478 <http://www.openssl.org/docs/apps/ciphers.html#CIPHER_LIST_FORMAT>`_.
479 If no cipher can be selected (because compile-time options or other
480 configuration forbids use of all the specified ciphers), an
481 :class:`SSLError` will be raised.
482
483 .. note::
484 when connected, the :meth:`SSLSocket.cipher` method of SSL sockets will
485 give the currently selected cipher.
486
487.. method:: SSLContext.wrap_socket(sock, server_side=False, do_handshake_on_connect=True, suppress_ragged_eofs=True)
488
489 Wrap an existing Python socket *sock* and return an :class:`SSLSocket`
490 object. The SSL socket is tied to the context, its settings and
491 certificates. The parameters *server_side*, *do_handshake_on_connect*
492 and *suppress_ragged_eofs* have the same meaning as in the top-level
493 :func:`wrap_socket` function.
494
Antoine Pitroub5218772010-05-21 09:56:06 +0000495.. attribute:: SSLContext.options
496
497 An integer representing the set of SSL options enabled on this context.
498 The default value is :data:`OP_ALL`, but you can specify other options
499 such as :data:`OP_NO_SSLv2` by ORing them together.
500
501 .. note::
502 With versions of OpenSSL older than 0.9.8m, it is only possible
503 to set options, not to clear them. Attempting to clear an option
504 (by resetting the corresponding bits) will raise a ``ValueError``.
505
Antoine Pitrou152efa22010-05-16 18:19:27 +0000506.. attribute:: SSLContext.protocol
507
508 The protocol version chosen when constructing the context. This attribute
509 is read-only.
510
511.. attribute:: SSLContext.verify_mode
512
513 Whether to try to verify other peers' certificates and how to behave
514 if verification fails. This attribute must be one of
515 :data:`CERT_NONE`, :data:`CERT_OPTIONAL` or :data:`CERT_REQUIRED`.
516
517
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000518.. index:: single: certificates
519
520.. index:: single: X509 certificate
521
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000522.. _ssl-certificates:
523
Thomas Woutersed03b412007-08-28 21:37:11 +0000524Certificates
525------------
526
Georg Brandl7f01a132009-09-16 15:58:14 +0000527Certificates in general are part of a public-key / private-key system. In this
528system, each *principal*, (which may be a machine, or a person, or an
529organization) is assigned a unique two-part encryption key. One part of the key
530is public, and is called the *public key*; the other part is kept secret, and is
531called the *private key*. The two parts are related, in that if you encrypt a
532message with one of the parts, you can decrypt it with the other part, and
533**only** with the other part.
Thomas Woutersed03b412007-08-28 21:37:11 +0000534
Georg Brandl7f01a132009-09-16 15:58:14 +0000535A certificate contains information about two principals. It contains the name
536of a *subject*, and the subject's public key. It also contains a statement by a
537second principal, the *issuer*, that the subject is who he claims to be, and
538that this is indeed the subject's public key. The issuer's statement is signed
539with the issuer's private key, which only the issuer knows. However, anyone can
540verify the issuer's statement by finding the issuer's public key, decrypting the
541statement with it, and comparing it to the other information in the certificate.
542The certificate also contains information about the time period over which it is
543valid. This is expressed as two fields, called "notBefore" and "notAfter".
Thomas Woutersed03b412007-08-28 21:37:11 +0000544
Georg Brandl7f01a132009-09-16 15:58:14 +0000545In the Python use of certificates, a client or server can use a certificate to
546prove who they are. The other side of a network connection can also be required
547to produce a certificate, and that certificate can be validated to the
548satisfaction of the client or server that requires such validation. The
549connection attempt can be set to raise an exception if the validation fails.
550Validation is done automatically, by the underlying OpenSSL framework; the
551application need not concern itself with its mechanics. But the application
552does usually need to provide sets of certificates to allow this process to take
553place.
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000554
Georg Brandl7f01a132009-09-16 15:58:14 +0000555Python uses files to contain certificates. They should be formatted as "PEM"
556(see :rfc:`1422`), which is a base-64 encoded form wrapped with a header line
557and a footer line::
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000558
559 -----BEGIN CERTIFICATE-----
560 ... (certificate in base64 PEM encoding) ...
561 -----END CERTIFICATE-----
562
Antoine Pitrou152efa22010-05-16 18:19:27 +0000563Certificate chains
564^^^^^^^^^^^^^^^^^^
565
Georg Brandl7f01a132009-09-16 15:58:14 +0000566The Python files which contain certificates can contain a sequence of
567certificates, sometimes called a *certificate chain*. This chain should start
568with the specific certificate for the principal who "is" the client or server,
569and then the certificate for the issuer of that certificate, and then the
570certificate for the issuer of *that* certificate, and so on up the chain till
571you get to a certificate which is *self-signed*, that is, a certificate which
572has the same subject and issuer, sometimes called a *root certificate*. The
573certificates should just be concatenated together in the certificate file. For
574example, suppose we had a three certificate chain, from our server certificate
575to the certificate of the certification authority that signed our server
576certificate, to the root certificate of the agency which issued the
577certification authority's certificate::
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000578
579 -----BEGIN CERTIFICATE-----
580 ... (certificate for your server)...
581 -----END CERTIFICATE-----
582 -----BEGIN CERTIFICATE-----
583 ... (the certificate for the CA)...
584 -----END CERTIFICATE-----
585 -----BEGIN CERTIFICATE-----
586 ... (the root certificate for the CA's issuer)...
587 -----END CERTIFICATE-----
588
Antoine Pitrou152efa22010-05-16 18:19:27 +0000589CA certificates
590^^^^^^^^^^^^^^^
591
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000592If you are going to require validation of the other side of the connection's
593certificate, you need to provide a "CA certs" file, filled with the certificate
Georg Brandl7f01a132009-09-16 15:58:14 +0000594chains for each issuer you are willing to trust. Again, this file just contains
595these chains concatenated together. For validation, Python will use the first
596chain it finds in the file which matches. Some "standard" root certificates are
597available from various certification authorities: `CACert.org
598<http://www.cacert.org/index.php?id=3>`_, `Thawte
599<http://www.thawte.com/roots/>`_, `Verisign
600<http://www.verisign.com/support/roots.html>`_, `Positive SSL
601<http://www.PositiveSSL.com/ssl-certificate-support/cert_installation/UTN-USERFirst-Hardware.crt>`_
602(used by python.org), `Equifax and GeoTrust
603<http://www.geotrust.com/resources/root_certificates/index.asp>`_.
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000604
Georg Brandl7f01a132009-09-16 15:58:14 +0000605In general, if you are using SSL3 or TLS1, you don't need to put the full chain
606in your "CA certs" file; you only need the root certificates, and the remote
607peer is supposed to furnish the other certificates necessary to chain from its
608certificate to a root certificate. See :rfc:`4158` for more discussion of the
609way in which certification chains can be built.
Thomas Woutersed03b412007-08-28 21:37:11 +0000610
Antoine Pitrou152efa22010-05-16 18:19:27 +0000611Combined key and certificate
612^^^^^^^^^^^^^^^^^^^^^^^^^^^^
613
614Often the private key is stored in the same file as the certificate; in this
615case, only the ``certfile`` parameter to :meth:`SSLContext.load_cert_chain`
616and :func:`wrap_socket` needs to be passed. If the private key is stored
617with the certificate, it should come before the first certificate in
618the certificate chain::
619
620 -----BEGIN RSA PRIVATE KEY-----
621 ... (private key in base64 encoding) ...
622 -----END RSA PRIVATE KEY-----
623 -----BEGIN CERTIFICATE-----
624 ... (certificate in base64 PEM encoding) ...
625 -----END CERTIFICATE-----
626
627Self-signed certificates
628^^^^^^^^^^^^^^^^^^^^^^^^
629
Georg Brandl7f01a132009-09-16 15:58:14 +0000630If you are going to create a server that provides SSL-encrypted connection
631services, you will need to acquire a certificate for that service. There are
632many ways of acquiring appropriate certificates, such as buying one from a
633certification authority. Another common practice is to generate a self-signed
634certificate. The simplest way to do this is with the OpenSSL package, using
635something like the following::
Thomas Woutersed03b412007-08-28 21:37:11 +0000636
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000637 % openssl req -new -x509 -days 365 -nodes -out cert.pem -keyout cert.pem
638 Generating a 1024 bit RSA private key
639 .......++++++
640 .............................++++++
641 writing new private key to 'cert.pem'
642 -----
643 You are about to be asked to enter information that will be incorporated
644 into your certificate request.
645 What you are about to enter is what is called a Distinguished Name or a DN.
646 There are quite a few fields but you can leave some blank
647 For some fields there will be a default value,
648 If you enter '.', the field will be left blank.
649 -----
650 Country Name (2 letter code) [AU]:US
651 State or Province Name (full name) [Some-State]:MyState
652 Locality Name (eg, city) []:Some City
653 Organization Name (eg, company) [Internet Widgits Pty Ltd]:My Organization, Inc.
654 Organizational Unit Name (eg, section) []:My Group
655 Common Name (eg, YOUR name) []:myserver.mygroup.myorganization.com
656 Email Address []:ops@myserver.mygroup.myorganization.com
657 %
Thomas Woutersed03b412007-08-28 21:37:11 +0000658
Georg Brandl7f01a132009-09-16 15:58:14 +0000659The disadvantage of a self-signed certificate is that it is its own root
660certificate, and no one else will have it in their cache of known (and trusted)
661root certificates.
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000662
663
Thomas Woutersed03b412007-08-28 21:37:11 +0000664Examples
665--------
666
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000667Testing for SSL support
668^^^^^^^^^^^^^^^^^^^^^^^
669
Georg Brandl7f01a132009-09-16 15:58:14 +0000670To test for the presence of SSL support in a Python installation, user code
671should use the following idiom::
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000672
673 try:
674 import ssl
675 except ImportError:
676 pass
677 else:
678 [ do something that requires SSL support ]
679
680Client-side operation
681^^^^^^^^^^^^^^^^^^^^^
682
Georg Brandl7f01a132009-09-16 15:58:14 +0000683This example connects to an SSL server, prints the server's address and
684certificate, sends some bytes, and reads part of the response::
Thomas Woutersed03b412007-08-28 21:37:11 +0000685
686 import socket, ssl, pprint
687
688 s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000689
690 # require a certificate from the server
691 ssl_sock = ssl.wrap_socket(s,
692 ca_certs="/etc/ca_certs_file",
693 cert_reqs=ssl.CERT_REQUIRED)
Thomas Woutersed03b412007-08-28 21:37:11 +0000694
695 ssl_sock.connect(('www.verisign.com', 443))
696
Georg Brandl6911e3c2007-09-04 07:15:32 +0000697 print(repr(ssl_sock.getpeername()))
698 pprint.pprint(ssl_sock.getpeercert())
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000699 print(pprint.pformat(ssl_sock.getpeercert()))
Thomas Woutersed03b412007-08-28 21:37:11 +0000700
Georg Brandl24420152008-05-26 16:32:26 +0000701 # Set a simple HTTP request -- use http.client in actual code.
Antoine Pitrou152efa22010-05-16 18:19:27 +0000702 ssl_sock.write(b"GET / HTTP/1.0\r\nHost: www.verisign.com\r\n\r\n")
Thomas Woutersed03b412007-08-28 21:37:11 +0000703
704 # Read a chunk of data. Will not necessarily
705 # read all the data returned by the server.
706 data = ssl_sock.read()
707
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000708 # note that closing the SSLSocket will also close the underlying socket
Thomas Woutersed03b412007-08-28 21:37:11 +0000709 ssl_sock.close()
710
Georg Brandl7f01a132009-09-16 15:58:14 +0000711As of September 6, 2007, the certificate printed by this program looked like
712this::
Thomas Woutersed03b412007-08-28 21:37:11 +0000713
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000714 {'notAfter': 'May 8 23:59:59 2009 GMT',
Ezio Melotti985e24d2009-09-13 07:54:02 +0000715 'subject': ((('serialNumber', '2497886'),),
716 (('1.3.6.1.4.1.311.60.2.1.3', 'US'),),
717 (('1.3.6.1.4.1.311.60.2.1.2', 'Delaware'),),
718 (('countryName', 'US'),),
719 (('postalCode', '94043'),),
720 (('stateOrProvinceName', 'California'),),
721 (('localityName', 'Mountain View'),),
722 (('streetAddress', '487 East Middlefield Road'),),
723 (('organizationName', 'VeriSign, Inc.'),),
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000724 (('organizationalUnitName',
Ezio Melotti985e24d2009-09-13 07:54:02 +0000725 'Production Security Services'),),
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000726 (('organizationalUnitName',
Ezio Melotti985e24d2009-09-13 07:54:02 +0000727 'Terms of use at www.verisign.com/rpa (c)06'),),
728 (('commonName', 'www.verisign.com'),))}
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000729
730which is a fairly poorly-formed ``subject`` field.
Thomas Woutersed03b412007-08-28 21:37:11 +0000731
Antoine Pitrou152efa22010-05-16 18:19:27 +0000732This other example first creates an SSL context, instructs it to verify
733certificates sent by peers, and feeds it a set of recognized certificate
734authorities (CA)::
735
736 >>> context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
737 >>> context.verify_mode = ssl.CERT_OPTIONAL
738 >>> context.load_verify_locations("/etc/ssl/certs/ca-bundle.crt")
739
740(it is assumed your operating system places a bundle of all CA certificates
741in ``/etc/ssl/certs/ca-bundle.crt``; if not, you'll get an error and have
742to adjust the location)
743
744When you use the context to connect to a server, :const:`CERT_OPTIONAL`
745validates the server certificate: it ensures that the server certificate
746was signed with one of the CA certificates, and checks the signature for
747correctness::
748
749 >>> conn = context.wrap_socket(socket.socket(socket.AF_INET))
750 >>> conn.connect(("linuxfr.org", 443))
751
752You should then fetch the certificate and check its fields for conformity.
753Here, the ``commonName`` field in the ``subject`` matches the desired HTTPS
754host ``linuxfr.org``::
755
756 >>> pprint.pprint(conn.getpeercert())
757 {'notAfter': 'Jun 26 21:41:46 2011 GMT',
758 'subject': ((('commonName', 'linuxfr.org'),),),
759 'subjectAltName': (('DNS', 'linuxfr.org'), ('othername', '<unsupported>'))}
760
761Now that you are assured of its authenticity, you can proceed to talk with
762the server::
763
764 >>> conn.write(b"HEAD / HTTP/1.0\r\nHost: linuxfr.org\r\n\r\n")
765 38
766 >>> pprint.pprint(conn.read().split(b"\r\n"))
767 [b'HTTP/1.1 302 Found',
768 b'Date: Sun, 16 May 2010 13:43:28 GMT',
769 b'Server: Apache/2.2',
770 b'Location: https://linuxfr.org/pub/',
771 b'Vary: Accept-Encoding',
772 b'Connection: close',
773 b'Content-Type: text/html; charset=iso-8859-1',
774 b'',
775 b'']
776
777
778See the discussion of :ref:`ssl-security` below.
779
780
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000781Server-side operation
782^^^^^^^^^^^^^^^^^^^^^
783
Antoine Pitrou152efa22010-05-16 18:19:27 +0000784For server operation, typically you'll need to have a server certificate, and
785private key, each in a file. You'll first create a context holding the key
786and the certificate, so that clients can check your authenticity. Then
787you'll open a socket, bind it to a port, call :meth:`listen` on it, and start
788waiting for clients to connect::
Thomas Woutersed03b412007-08-28 21:37:11 +0000789
790 import socket, ssl
791
Antoine Pitrou152efa22010-05-16 18:19:27 +0000792 context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
793 context.load_cert_chain(certfile="mycertfile", keyfile="mykeyfile")
794
Thomas Woutersed03b412007-08-28 21:37:11 +0000795 bindsocket = socket.socket()
796 bindsocket.bind(('myaddr.mydomain.com', 10023))
797 bindsocket.listen(5)
798
Antoine Pitrou152efa22010-05-16 18:19:27 +0000799When a client connects, you'll call :meth:`accept` on the socket to get the
800new socket from the other end, and use the context's :meth:`SSLContext.wrap_socket`
801method to create a server-side SSL socket for the connection::
Thomas Woutersed03b412007-08-28 21:37:11 +0000802
803 while True:
804 newsocket, fromaddr = bindsocket.accept()
Antoine Pitrou152efa22010-05-16 18:19:27 +0000805 connstream = context.wrap_socket(newsocket, server_side=True)
806 try:
807 deal_with_client(connstream)
808 finally:
809 connstream.close()
Thomas Woutersed03b412007-08-28 21:37:11 +0000810
Antoine Pitrou152efa22010-05-16 18:19:27 +0000811Then you'll read data from the ``connstream`` and do something with it till you
Georg Brandl7f01a132009-09-16 15:58:14 +0000812are finished with the client (or the client is finished with you)::
Thomas Woutersed03b412007-08-28 21:37:11 +0000813
814 def deal_with_client(connstream):
Thomas Woutersed03b412007-08-28 21:37:11 +0000815 data = connstream.read()
Antoine Pitrou152efa22010-05-16 18:19:27 +0000816 # empty data means the client is finished with us
Thomas Woutersed03b412007-08-28 21:37:11 +0000817 while data:
818 if not do_something(connstream, data):
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000819 # we'll assume do_something returns False
820 # when we're finished with client
Thomas Woutersed03b412007-08-28 21:37:11 +0000821 break
822 data = connstream.read()
823 # finished with client
Thomas Woutersed03b412007-08-28 21:37:11 +0000824
Antoine Pitrou152efa22010-05-16 18:19:27 +0000825And go back to listening for new client connections (of course, a real server
826would probably handle each client connection in a separate thread, or put
827the sockets in non-blocking mode and use an event loop).
828
829
830.. _ssl-security:
831
832Security considerations
833-----------------------
834
835Verifying certificates
836^^^^^^^^^^^^^^^^^^^^^^
837
838:const:`CERT_NONE` is the default. Since it does not authenticate the other
839peer, it can be insecure, especially in client mode where most of time you
840would like to ensure the authenticity of the server you're talking to.
841Therefore, when in client mode, it is highly recommended to use
842:const:`CERT_REQUIRED`. However, it is in itself not sufficient; you also
843have to check that the server certificate (obtained with
844:meth:`SSLSocket.getpeercert`) matches the desired service. The exact way
845of doing so depends on the higher-level protocol used; for example, with
846HTTPS, you'll check that the host name in the URL matches either the
847``commonName`` field in the ``subjectName``, or one of the ``DNS`` fields
848in the ``subjectAltName``.
849
850In server mode, if you want to authenticate your clients using the SSL layer
851(rather than using a higher-level authentication mechanism), you'll also have
852to specify :const:`CERT_REQUIRED` and similarly check the client certificate.
853
854 .. note::
855
856 In client mode, :const:`CERT_OPTIONAL` and :const:`CERT_REQUIRED` are
857 equivalent unless anonymous ciphers are enabled (they are disabled
858 by default).
Thomas Woutersed03b412007-08-28 21:37:11 +0000859
Antoine Pitroub5218772010-05-21 09:56:06 +0000860Protocol versions
861^^^^^^^^^^^^^^^^^
862
863SSL version 2 is considered insecure and is therefore dangerous to use. If
864you want maximum compatibility between clients and servers, it is recommended
865to use :const:`PROTOCOL_SSLv23` as the protocol version and then disable
866SSLv2 explicitly using the :data:`SSLContext.options` attribute::
867
868 context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
869 context.options |= ssl.OP_NO_SSLv2
870
871The SSL context created above will allow SSLv3 and TLSv1 connections, but
872not SSLv2.
873
Georg Brandl48310cd2009-01-03 21:18:54 +0000874
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000875.. seealso::
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000876
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000877 Class :class:`socket.socket`
878 Documentation of underlying :mod:`socket` class
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000879
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000880 `Introducing SSL and Certificates using OpenSSL <http://old.pseudonym.org/ssl/wwwj-index.html>`_
881 Frederick J. Hirsch
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000882
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000883 `RFC 1422: Privacy Enhancement for Internet Electronic Mail: Part II: Certificate-Based Key Management <http://www.ietf.org/rfc/rfc1422>`_
884 Steve Kent
Thomas Wouters47b49bf2007-08-30 22:15:33 +0000885
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000886 `RFC 1750: Randomness Recommendations for Security <http://www.ietf.org/rfc/rfc1750>`_
887 D. Eastlake et. al.
Thomas Wouters89d996e2007-09-08 17:39:28 +0000888
Thomas Wouters1b7f8912007-09-19 03:06:30 +0000889 `RFC 3280: Internet X.509 Public Key Infrastructure Certificate and CRL Profile <http://www.ietf.org/rfc/rfc3280>`_
890 Housley et. al.