[Python-checkins] cpython (3.4): Issue #20913: improve the SSL security considerations to first advocate using
antoine.pitrou
python-checkins at python.org
Sat Mar 22 18:19:45 CET 2014
http://hg.python.org/cpython/rev/8661ffca4581
changeset: 89919:8661ffca4581
branch: 3.4
parent: 89917:869277faf3dc
user: Antoine Pitrou <solipsis at pitrou.net>
date: Sat Mar 22 18:19:11 2014 +0100
summary:
Issue #20913: improve the SSL security considerations to first advocate using create_default_context().
files:
Doc/library/asyncio-eventloop.rst | 2 +
Doc/library/ftplib.rst | 51 +++++++-----------
Doc/library/http.client.rst | 38 +++++++------
Doc/library/imaplib.rst | 29 ++++++----
Doc/library/nntplib.rst | 16 +++--
Doc/library/poplib.rst | 29 ++++++----
Doc/library/smtplib.rst | 27 ++++-----
Doc/library/ssl.rst | 42 +++++++++++++--
8 files changed, 133 insertions(+), 101 deletions(-)
diff --git a/Doc/library/asyncio-eventloop.rst b/Doc/library/asyncio-eventloop.rst
--- a/Doc/library/asyncio-eventloop.rst
+++ b/Doc/library/asyncio-eventloop.rst
@@ -241,6 +241,8 @@
the transport; if *ssl* is :const:`True`, a context with some
unspecified default settings is used.
+ .. seealso:: :ref:`SSL/TLS security considerations <ssl-security>`
+
* *server_hostname*, is only for use together with *ssl*,
and sets or overrides the hostname that the target server's certificate
will be matched against. By default the value of the *host* argument
diff --git a/Doc/library/ftplib.rst b/Doc/library/ftplib.rst
--- a/Doc/library/ftplib.rst
+++ b/Doc/library/ftplib.rst
@@ -80,14 +80,14 @@
:rfc:`4217`.
Connect as usual to port 21 implicitly securing the FTP control connection
before authenticating. Securing the data connection requires the user to
- explicitly ask for it by calling the :meth:`prot_p` method.
- *keyfile* and *certfile* are optional -- they can contain a PEM formatted
- private key and certificate chain file name for the SSL connection.
- *context* parameter is a :class:`ssl.SSLContext` object which allows
- bundling SSL configuration options, certificates and private keys into a
- single (potentially long-lived) structure. *source_address* is a 2-tuple
- ``(host, port)`` for the socket to bind to as its source address before
- connecting.
+ explicitly ask for it by calling the :meth:`prot_p` method. *context*
+ is a :class:`ssl.SSLContext` object which allows bundling SSL configuration
+ options, certificates and private keys into a single (potentially
+ long-lived) structure. Please read :ref:`ssl-security` for best practices.
+
+ *keyfile* and *certfile* are a legacy alternative to *context* -- they
+ can point to PEM-formatted private key and certificate chain files
+ (respectively) for the SSL connection.
.. versionadded:: 3.2
@@ -96,29 +96,18 @@
.. versionchanged:: 3.4
The class now supports hostname check with
- :attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
- :data:`~ssl.HAS_SNI`).
+ :attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
+ :data:`ssl.HAS_SNI`).
- Here's a sample session using the :class:`FTP_TLS` class:
+ Here's a sample session using the :class:`FTP_TLS` class::
- >>> from ftplib import FTP_TLS
- >>> ftps = FTP_TLS('ftp.python.org')
- >>> ftps.login() # login anonymously before securing control channel
- >>> ftps.prot_p() # switch to secure data connection
- >>> ftps.retrlines('LIST') # list directory content securely
- total 9
- drwxr-xr-x 8 root wheel 1024 Jan 3 1994 .
- drwxr-xr-x 8 root wheel 1024 Jan 3 1994 ..
- drwxr-xr-x 2 root wheel 1024 Jan 3 1994 bin
- drwxr-xr-x 2 root wheel 1024 Jan 3 1994 etc
- d-wxrwxr-x 2 ftp wheel 1024 Sep 5 13:43 incoming
- drwxr-xr-x 2 root wheel 1024 Nov 17 1993 lib
- drwxr-xr-x 6 1094 wheel 1024 Sep 13 19:07 pub
- drwxr-xr-x 3 root wheel 1024 Jan 3 1994 usr
- -rw-r--r-- 1 root root 312 Aug 1 1994 welcome.msg
- '226 Transfer complete.'
- >>> ftps.quit()
- >>>
+ >>> ftps = FTP_TLS('ftp.pureftpd.org')
+ >>> ftps.login()
+ '230 Anonymous user logged in'
+ >>> ftps.prot_p()
+ '200 Data protection level set to "private"'
+ >>> ftps.nlst()
+ ['6jack', 'OpenBSD', 'antilink', 'blogbench', 'bsdcam', 'clockspeed', 'djbdns-jedi', 'docs', 'eaccelerator-jedi', 'favicon.ico', 'francotone', 'fugu', 'ignore', 'libpuzzle', 'metalog', 'minidentd', 'misc', 'mysql-udf-global-user-variables', 'php-jenkins-hash', 'php-skein-hash', 'php-webdav', 'phpaudit', 'phpbench', 'pincaster', 'ping', 'posto', 'pub', 'public', 'public_keys', 'pure-ftpd', 'qscan', 'qtc', 'sharedance', 'skycache', 'sound', 'tmp', 'ucarp']
.. exception:: error_reply
@@ -434,8 +423,8 @@
.. versionchanged:: 3.4
The method now supports hostname check with
- :attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
- :data:`~ssl.HAS_SNI`).
+ :attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
+ :data:`ssl.HAS_SNI`).
.. method:: FTP_TLS.ccc()
diff --git a/Doc/library/http.client.rst b/Doc/library/http.client.rst
--- a/Doc/library/http.client.rst
+++ b/Doc/library/http.client.rst
@@ -43,10 +43,10 @@
For example, the following calls all create instances that connect to the server
at the same host and port::
- >>> h1 = http.client.HTTPConnection('www.cwi.nl')
- >>> h2 = http.client.HTTPConnection('www.cwi.nl:80')
- >>> h3 = http.client.HTTPConnection('www.cwi.nl', 80)
- >>> h3 = http.client.HTTPConnection('www.cwi.nl', 80, timeout=10)
+ >>> h1 = http.client.HTTPConnection('www.python.org')
+ >>> h2 = http.client.HTTPConnection('www.python.org:80')
+ >>> h3 = http.client.HTTPConnection('www.python.org', 80)
+ >>> h4 = http.client.HTTPConnection('www.python.org', 80, timeout=10)
.. versionchanged:: 3.2
*source_address* was added.
@@ -64,23 +64,27 @@
A subclass of :class:`HTTPConnection` that uses SSL for communication with
secure servers. Default port is ``443``. If *context* is specified, it
must be a :class:`ssl.SSLContext` instance describing the various SSL
- options. If *context* is specified and has a :attr:`~ssl.SSLContext.verify_mode`
- of either :data:`~ssl.CERT_OPTIONAL` or :data:`~ssl.CERT_REQUIRED`, then
- by default *host* is matched against the host name(s) allowed by the
- server's certificate. If you want to change that behaviour, you can
- explicitly set *check_hostname* to False.
+ options.
*key_file* and *cert_file* are deprecated, please use
- :meth:`ssl.SSLContext.load_cert_chain` instead.
+ :meth:`ssl.SSLContext.load_cert_chain` instead, or let
+ :func:`ssl.create_default_context` select the system's trusted CA
+ certificates for you.
- If you access arbitrary hosts on the Internet, it is recommended to
- require certificate checking and feed the *context* with a set of
- trusted CA certificates::
+ The recommended way to connect to HTTPS hosts on the Internet is as
+ follows::
- context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
- context.verify_mode = ssl.CERT_REQUIRED
- context.load_verify_locations('/etc/pki/tls/certs/ca-bundle.crt')
- h = client.HTTPSConnection('svn.python.org', 443, context=context)
+ context = ssl.create_default_context()
+ h = client.HTTPSConnection('www.python.org', 443, context=context)
+
+ Please read :ref:`ssl-security` for more information on best practices.
+
+ .. note::
+ If *context* is specified and has a :attr:`~ssl.SSLContext.verify_mode`
+ of either :data:`~ssl.CERT_OPTIONAL` or :data:`~ssl.CERT_REQUIRED`, then
+ by default *host* is matched against the host name(s) allowed by the
+ server's certificate. If you want to change that behaviour, you can
+ explicitly set *check_hostname* to False.
.. versionchanged:: 3.2
*source_address*, *context* and *check_hostname* were added.
diff --git a/Doc/library/imaplib.rst b/Doc/library/imaplib.rst
--- a/Doc/library/imaplib.rst
+++ b/Doc/library/imaplib.rst
@@ -69,21 +69,25 @@
This is a subclass derived from :class:`IMAP4` that connects over an SSL
encrypted socket (to use this class you need a socket module that was compiled
with SSL support). If *host* is not specified, ``''`` (the local host) is used.
- If *port* is omitted, the standard IMAP4-over-SSL port (993) is used. *keyfile*
- and *certfile* are also optional - they can contain a PEM formatted private key
- and certificate chain file for the SSL connection. *ssl_context* parameter is a
- :class:`ssl.SSLContext` object which allows bundling SSL configuration
- options, certificates and private keys into a single (potentially long-lived)
- structure. Note that the *keyfile*/*certfile* parameters are mutually exclusive with *ssl_context*,
- a :class:`ValueError` is raised if *keyfile*/*certfile* is provided along with *ssl_context*.
+ If *port* is omitted, the standard IMAP4-over-SSL port (993) is used.
+ *ssl_context* is a :class:`ssl.SSLContext` object which allows bundling
+ SSL configuration options, certificates and private keys into a single
+ (potentially long-lived) structure. Please read :ref:`ssl-security` for
+ best practices.
+
+ *keyfile* and *certfile* are a legacy alternative to *ssl_context* - they
+ can point to PEM-formatted private key and certificate chain files for
+ the SSL connection. Note that the *keyfile*/*certfile* parameters are
+ mutually exclusive with *ssl_context*, a :class:`ValueError` is raised
+ if *keyfile*/*certfile* is provided along with *ssl_context*.
.. versionchanged:: 3.3
*ssl_context* parameter added.
.. versionchanged:: 3.4
The class now supports hostname check with
- :attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
- :data:`~ssl.HAS_SNI`).
+ :attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
+ :data:`ssl.HAS_SNI`).
The second subclass allows for connections created by a child process:
@@ -437,14 +441,15 @@
Send a ``STARTTLS`` command. The *ssl_context* argument is optional
and should be a :class:`ssl.SSLContext` object. This will enable
- encryption on the IMAP connection.
+ encryption on the IMAP connection. Please read :ref:`ssl-security` for
+ best practices.
.. versionadded:: 3.2
.. versionchanged:: 3.4
The method now supports hostname check with
- :attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
- :data:`~ssl.HAS_SNI`).
+ :attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
+ :data:`ssl.HAS_SNI`).
.. method:: IMAP4.status(mailbox, names)
diff --git a/Doc/library/nntplib.rst b/Doc/library/nntplib.rst
--- a/Doc/library/nntplib.rst
+++ b/Doc/library/nntplib.rst
@@ -94,6 +94,7 @@
port *port*. :class:`NNTP_SSL` objects have the same methods as
:class:`NNTP` objects. If *port* is omitted, port 563 (NNTPS) is used.
*ssl_context* is also optional, and is a :class:`~ssl.SSLContext` object.
+ Please read :ref:`ssl-security` for best practices.
All other parameters behave the same as for :class:`NNTP`.
Note that SSL-on-563 is discouraged per :rfc:`4642`, in favor of
@@ -104,8 +105,8 @@
.. versionchanged:: 3.4
The class now supports hostname check with
- :attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
- :data:`~ssl.HAS_SNI`).
+ :attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
+ :data:`ssl.HAS_SNI`).
.. exception:: NNTPError
@@ -234,9 +235,10 @@
.. method:: NNTP.starttls(ssl_context=None)
- Send a ``STARTTLS`` command. The *ssl_context* argument is optional
- and should be a :class:`ssl.SSLContext` object. This will enable
- encryption on the NNTP connection.
+ Send a ``STARTTLS`` command. This will enable encryption on the NNTP
+ connection. The *ssl_context* argument is optional and should be a
+ :class:`ssl.SSLContext` object. Please read :ref:`ssl-security` for best
+ practices.
Note that this may not be done after authentication information has
been transmitted, and authentication occurs by default if possible during a
@@ -247,8 +249,8 @@
.. versionchanged:: 3.4
The method now supports hostname check with
- :attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
- :data:`~ssl.HAS_SNI`).
+ :attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
+ :data:`ssl.HAS_SNI`).
.. method:: NNTP.newgroups(date, *, file=None)
diff --git a/Doc/library/poplib.rst b/Doc/library/poplib.rst
--- a/Doc/library/poplib.rst
+++ b/Doc/library/poplib.rst
@@ -43,20 +43,23 @@
This is a subclass of :class:`POP3` that connects to the server over an SSL
encrypted socket. If *port* is not specified, 995, the standard POP3-over-SSL
- port is used. *keyfile* and *certfile* are also optional - they can contain a
- PEM formatted private key and certificate chain file for the SSL connection.
- *timeout* works as in the :class:`POP3` constructor. *context* parameter is a
- :class:`ssl.SSLContext` object which allows bundling SSL configuration
- options, certificates and private keys into a single (potentially long-lived)
- structure.
+ port is used. *timeout* works as in the :class:`POP3` constructor.
+ *context* is an optional :class:`ssl.SSLContext` object which allows
+ bundling SSL configuration options, certificates and private keys into a
+ single (potentially long-lived) structure. Please read :ref:`ssl-security`
+ for best practices.
+
+ *keyfile* and *certfile* are a legacy alternative to *context* - they can
+ point to PEM-formatted private key and certificate chain files,
+ respectively, for the SSL connection.
.. versionchanged:: 3.2
*context* parameter added.
.. versionchanged:: 3.4
The class now supports hostname check with
- :attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
- :data:`~ssl.HAS_SNI`).
+ :attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
+ :data:`ssl.HAS_SNI`).
One exception is defined as an attribute of the :mod:`poplib` module:
@@ -198,10 +201,12 @@
*context* parameter is a :class:`ssl.SSLContext` object which allows
bundling SSL configuration options, certificates and private keys into
- a single (potentially long-lived) structure. This method supports
- hostname checking via :attr:`SSLContext.check_hostname`
- :attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
- :data:`~ssl.HAS_SNI`).
+ a single (potentially long-lived) structure. Please read :ref:`ssl-security`
+ for best practices.
+
+ This method supports hostname checking via
+ :attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
+ :data:`ssl.HAS_SNI`).
.. versionadded:: 3.4
diff --git a/Doc/library/smtplib.rst b/Doc/library/smtplib.rst
--- a/Doc/library/smtplib.rst
+++ b/Doc/library/smtplib.rst
@@ -69,20 +69,15 @@
required from the beginning of the connection and using :meth:`starttls` is
not appropriate. If *host* is not specified, the local host is used. If
*port* is zero, the standard SMTP-over-SSL port (465) is used. The optional
- arguments *local_hostname* and *source_address* have the same meaning as
- they do in the :class:`SMTP` class. *keyfile* and *certfile* are also
- optional, and can contain a PEM formatted private key and certificate chain
- file for the SSL connection. *context* also optional, can contain a
- SSLContext, and is an alternative to keyfile and certfile; If it is
- specified both keyfile and certfile must be None. The optional *timeout*
- parameter specifies a timeout in seconds for blocking operations like the
- connection attempt (if not specified, the global default timeout setting
- will be used). The optional source_address parameter allows to bind to some
- specific source address in a machine with multiple network interfaces,
- and/or to some specific source tcp port. It takes a 2-tuple (host, port),
- for the socket to bind to as its source address before connecting. If
- omitted (or if host or port are ``''`` and/or 0 respectively) the OS default
- behavior will be used.
+ arguments *local_hostname*, *timeout* and *source_address* have the same
+ meaning as they do in the :class:`SMTP` class. *context*, also optional,
+ can contain a :class:`~ssl.SSLContext` and allows to configure various
+ aspects of the secure connection. Please read :ref:`ssl-security` for
+ best practices.
+
+ *keyfile* and *certfile* are a legacy alternative to *context*, and can
+ point to a PEM formatted private key and certificate chain file for the
+ SSL connection.
.. versionchanged:: 3.3
*context* was added.
@@ -92,8 +87,8 @@
.. versionchanged:: 3.4
The class now supports hostname check with
- :attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
- :data:`~ssl.HAS_SNI`).
+ :attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
+ :data:`ssl.HAS_SNI`).
.. class:: LMTP(host='', port=LMTP_PORT, local_hostname=None, source_address=None)
diff --git a/Doc/library/ssl.rst b/Doc/library/ssl.rst
--- a/Doc/library/ssl.rst
+++ b/Doc/library/ssl.rst
@@ -1542,7 +1542,7 @@
import socket, ssl
- context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
+ context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
context.load_cert_chain(certfile="mycertfile", keyfile="mykeyfile")
bindsocket = socket.socket()
@@ -1619,9 +1619,39 @@
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 try to choose reasonably secure protocol and cipher settings.
+
+For example, here is how you would use the :class:`smtplib.SMTP` class to
+create a trusted, secure connection to a SMTP server::
+
+ >>> import ssl, smtplib
+ >>> smtp = smtplib.SMTP("mail.python.org", port=587)
+ >>> context = ssl.create_default_context()
+ >>> smtp.starttls(context=context)
+ (220, b'2.0.0 Ready to start TLS')
+
+If a client certificate is needed for the connection, it can be added with
+:meth:`SSLContext.load_cert_chain`.
+
+By contrast, if you create the SSL context by calling the :class:`SSLContext`
+constructor yourself, it will not have certificate validation 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 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.
@@ -1645,7 +1675,7 @@
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
@@ -1655,11 +1685,11 @@
context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
context.options |= ssl.OP_NO_SSLv2
-The SSL context created above will allow SSLv3 and TLSv1 connections, but
-not 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
--
Repository URL: http://hg.python.org/cpython
More information about the Python-checkins
mailing list