Issue #20913: improve the SSL security considerations to first advocate using create_default_context().
This commit is contained in:
Antoine Pitrou
commit
0a0a9ade4f
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@ -241,6 +241,8 @@ Creating connections
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the transport; if *ssl* is :const:`True`, a context with some
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unspecified default settings is used.
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.. seealso:: :ref:`SSL/TLS security considerations <ssl-security>`
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* *server_hostname*, is only for use together with *ssl*,
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and sets or overrides the hostname that the target server's certificate
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will be matched against. By default the value of the *host* argument
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@ -80,14 +80,14 @@ The module defines the following items:
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:rfc:`4217`.
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Connect as usual to port 21 implicitly securing the FTP control connection
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before authenticating. Securing the data connection requires the user to
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explicitly ask for it by calling the :meth:`prot_p` method.
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*keyfile* and *certfile* are optional -- they can contain a PEM formatted
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private key and certificate chain file name for the SSL connection.
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*context* parameter is a :class:`ssl.SSLContext` object which allows
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bundling SSL configuration options, certificates and private keys into a
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single (potentially long-lived) structure. *source_address* is a 2-tuple
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``(host, port)`` for the socket to bind to as its source address before
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connecting.
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explicitly ask for it by calling the :meth:`prot_p` method. *context*
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is a :class:`ssl.SSLContext` object which allows bundling SSL configuration
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options, certificates and private keys into a single (potentially
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long-lived) structure. Please read :ref:`ssl-security` for best practices.
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*keyfile* and *certfile* are a legacy alternative to *context* -- they
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can point to PEM-formatted private key and certificate chain files
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(respectively) for the SSL connection.
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.. versionadded:: 3.2
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@ -96,29 +96,18 @@ The module defines the following items:
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.. versionchanged:: 3.4
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The class now supports hostname check with
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:attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
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:data:`~ssl.HAS_SNI`).
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:attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
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:data:`ssl.HAS_SNI`).
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Here's a sample session using the :class:`FTP_TLS` class:
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Here's a sample session using the :class:`FTP_TLS` class::
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>>> from ftplib import FTP_TLS
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>>> ftps = FTP_TLS('ftp.python.org')
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>>> ftps.login() # login anonymously before securing control channel
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>>> ftps.prot_p() # switch to secure data connection
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>>> ftps.retrlines('LIST') # list directory content securely
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total 9
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drwxr-xr-x 8 root wheel 1024 Jan 3 1994 .
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drwxr-xr-x 8 root wheel 1024 Jan 3 1994 ..
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drwxr-xr-x 2 root wheel 1024 Jan 3 1994 bin
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drwxr-xr-x 2 root wheel 1024 Jan 3 1994 etc
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d-wxrwxr-x 2 ftp wheel 1024 Sep 5 13:43 incoming
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drwxr-xr-x 2 root wheel 1024 Nov 17 1993 lib
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drwxr-xr-x 6 1094 wheel 1024 Sep 13 19:07 pub
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drwxr-xr-x 3 root wheel 1024 Jan 3 1994 usr
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-rw-r--r-- 1 root root 312 Aug 1 1994 welcome.msg
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'226 Transfer complete.'
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>>> ftps.quit()
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>>>
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>>> ftps = FTP_TLS('ftp.pureftpd.org')
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>>> ftps.login()
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'230 Anonymous user logged in'
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>>> ftps.prot_p()
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'200 Data protection level set to "private"'
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>>> ftps.nlst()
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['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']
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.. exception:: error_reply
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@ -434,8 +423,8 @@ FTP_TLS Objects
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.. versionchanged:: 3.4
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The method now supports hostname check with
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:attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
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:data:`~ssl.HAS_SNI`).
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:attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
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:data:`ssl.HAS_SNI`).
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.. method:: FTP_TLS.ccc()
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@ -43,10 +43,10 @@ The module provides the following classes:
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For example, the following calls all create instances that connect to the server
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at the same host and port::
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>>> h1 = http.client.HTTPConnection('www.cwi.nl')
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>>> h2 = http.client.HTTPConnection('www.cwi.nl:80')
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>>> h3 = http.client.HTTPConnection('www.cwi.nl', 80)
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>>> h3 = http.client.HTTPConnection('www.cwi.nl', 80, timeout=10)
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>>> h1 = http.client.HTTPConnection('www.python.org')
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>>> h2 = http.client.HTTPConnection('www.python.org:80')
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>>> h3 = http.client.HTTPConnection('www.python.org', 80)
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>>> h4 = http.client.HTTPConnection('www.python.org', 80, timeout=10)
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.. versionchanged:: 3.2
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*source_address* was added.
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@ -64,23 +64,27 @@ The module provides the following classes:
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A subclass of :class:`HTTPConnection` that uses SSL for communication with
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secure servers. Default port is ``443``. If *context* is specified, it
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must be a :class:`ssl.SSLContext` instance describing the various SSL
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options. If *context* is specified and has a :attr:`~ssl.SSLContext.verify_mode`
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of either :data:`~ssl.CERT_OPTIONAL` or :data:`~ssl.CERT_REQUIRED`, then
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by default *host* is matched against the host name(s) allowed by the
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server's certificate. If you want to change that behaviour, you can
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explicitly set *check_hostname* to False.
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options.
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*key_file* and *cert_file* are deprecated, please use
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:meth:`ssl.SSLContext.load_cert_chain` instead.
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:meth:`ssl.SSLContext.load_cert_chain` instead, or let
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:func:`ssl.create_default_context` select the system's trusted CA
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certificates for you.
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If you access arbitrary hosts on the Internet, it is recommended to
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require certificate checking and feed the *context* with a set of
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trusted CA certificates::
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The recommended way to connect to HTTPS hosts on the Internet is as
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follows::
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context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
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context.verify_mode = ssl.CERT_REQUIRED
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context.load_verify_locations('/etc/pki/tls/certs/ca-bundle.crt')
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h = client.HTTPSConnection('svn.python.org', 443, context=context)
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context = ssl.create_default_context()
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h = client.HTTPSConnection('www.python.org', 443, context=context)
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Please read :ref:`ssl-security` for more information on best practices.
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.. note::
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If *context* is specified and has a :attr:`~ssl.SSLContext.verify_mode`
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of either :data:`~ssl.CERT_OPTIONAL` or :data:`~ssl.CERT_REQUIRED`, then
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by default *host* is matched against the host name(s) allowed by the
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server's certificate. If you want to change that behaviour, you can
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explicitly set *check_hostname* to False.
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.. versionchanged:: 3.2
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*source_address*, *context* and *check_hostname* were added.
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@ -69,21 +69,25 @@ There's also a subclass for secure connections:
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This is a subclass derived from :class:`IMAP4` that connects over an SSL
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encrypted socket (to use this class you need a socket module that was compiled
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with SSL support). If *host* is not specified, ``''`` (the local host) is used.
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If *port* is omitted, the standard IMAP4-over-SSL port (993) is used. *keyfile*
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and *certfile* are also optional - they can contain a PEM formatted private key
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and certificate chain file for the SSL connection. *ssl_context* parameter is a
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:class:`ssl.SSLContext` object which allows bundling SSL configuration
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options, certificates and private keys into a single (potentially long-lived)
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structure. Note that the *keyfile*/*certfile* parameters are mutually exclusive with *ssl_context*,
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a :class:`ValueError` is raised if *keyfile*/*certfile* is provided along with *ssl_context*.
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If *port* is omitted, the standard IMAP4-over-SSL port (993) is used.
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*ssl_context* is a :class:`ssl.SSLContext` object which allows bundling
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SSL configuration options, certificates and private keys into a single
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(potentially long-lived) structure. Please read :ref:`ssl-security` for
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best practices.
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*keyfile* and *certfile* are a legacy alternative to *ssl_context* - they
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can point to PEM-formatted private key and certificate chain files for
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the SSL connection. Note that the *keyfile*/*certfile* parameters are
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mutually exclusive with *ssl_context*, a :class:`ValueError` is raised
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if *keyfile*/*certfile* is provided along with *ssl_context*.
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.. versionchanged:: 3.3
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*ssl_context* parameter added.
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.. versionchanged:: 3.4
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The class now supports hostname check with
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:attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
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:data:`~ssl.HAS_SNI`).
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:attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
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:data:`ssl.HAS_SNI`).
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The second subclass allows for connections created by a child process:
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@ -437,14 +441,15 @@ An :class:`IMAP4` instance has the following methods:
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Send a ``STARTTLS`` command. The *ssl_context* argument is optional
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and should be a :class:`ssl.SSLContext` object. This will enable
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encryption on the IMAP connection.
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encryption on the IMAP connection. Please read :ref:`ssl-security` for
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best practices.
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.. versionadded:: 3.2
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.. versionchanged:: 3.4
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The method now supports hostname check with
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:attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
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:data:`~ssl.HAS_SNI`).
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:attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
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:data:`ssl.HAS_SNI`).
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.. method:: IMAP4.status(mailbox, names)
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@ -94,6 +94,7 @@ The module itself defines the following classes:
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port *port*. :class:`NNTP_SSL` objects have the same methods as
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:class:`NNTP` objects. If *port* is omitted, port 563 (NNTPS) is used.
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*ssl_context* is also optional, and is a :class:`~ssl.SSLContext` object.
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Please read :ref:`ssl-security` for best practices.
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All other parameters behave the same as for :class:`NNTP`.
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Note that SSL-on-563 is discouraged per :rfc:`4642`, in favor of
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@ -104,8 +105,8 @@ The module itself defines the following classes:
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.. versionchanged:: 3.4
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The class now supports hostname check with
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:attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
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:data:`~ssl.HAS_SNI`).
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:attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
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:data:`ssl.HAS_SNI`).
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.. exception:: NNTPError
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@ -234,9 +235,10 @@ tuples or objects that the method normally returns will be empty.
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.. method:: NNTP.starttls(ssl_context=None)
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Send a ``STARTTLS`` command. The *ssl_context* argument is optional
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and should be a :class:`ssl.SSLContext` object. This will enable
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encryption on the NNTP connection.
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Send a ``STARTTLS`` command. This will enable encryption on the NNTP
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connection. The *ssl_context* argument is optional and should be a
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:class:`ssl.SSLContext` object. Please read :ref:`ssl-security` for best
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practices.
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Note that this may not be done after authentication information has
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been transmitted, and authentication occurs by default if possible during a
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@ -247,8 +249,8 @@ tuples or objects that the method normally returns will be empty.
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.. versionchanged:: 3.4
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The method now supports hostname check with
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:attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
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:data:`~ssl.HAS_SNI`).
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:attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
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:data:`ssl.HAS_SNI`).
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.. method:: NNTP.newgroups(date, *, file=None)
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@ -43,20 +43,23 @@ The :mod:`poplib` module provides two classes:
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This is a subclass of :class:`POP3` that connects to the server over an SSL
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encrypted socket. If *port* is not specified, 995, the standard POP3-over-SSL
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port is used. *keyfile* and *certfile* are also optional - they can contain a
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PEM formatted private key and certificate chain file for the SSL connection.
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*timeout* works as in the :class:`POP3` constructor. *context* parameter is a
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:class:`ssl.SSLContext` object which allows bundling SSL configuration
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options, certificates and private keys into a single (potentially long-lived)
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structure.
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port is used. *timeout* works as in the :class:`POP3` constructor.
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*context* is an optional :class:`ssl.SSLContext` object which allows
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bundling SSL configuration options, certificates and private keys into a
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single (potentially long-lived) structure. Please read :ref:`ssl-security`
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for best practices.
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|
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*keyfile* and *certfile* are a legacy alternative to *context* - they can
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point to PEM-formatted private key and certificate chain files,
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respectively, for the SSL connection.
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|
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.. versionchanged:: 3.2
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*context* parameter added.
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.. versionchanged:: 3.4
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The class now supports hostname check with
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:attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
|
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:data:`~ssl.HAS_SNI`).
|
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:attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
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:data:`ssl.HAS_SNI`).
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One exception is defined as an attribute of the :mod:`poplib` module:
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@ -198,10 +201,12 @@ An :class:`POP3` instance has the following methods:
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*context* parameter is a :class:`ssl.SSLContext` object which allows
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bundling SSL configuration options, certificates and private keys into
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a single (potentially long-lived) structure. This method supports
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hostname checking via :attr:`SSLContext.check_hostname`
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:attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
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:data:`~ssl.HAS_SNI`).
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a single (potentially long-lived) structure. Please read :ref:`ssl-security`
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for best practices.
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|
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This method supports hostname checking via
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:attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
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:data:`ssl.HAS_SNI`).
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.. versionadded:: 3.4
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@ -69,20 +69,15 @@ Protocol) and :rfc:`1869` (SMTP Service Extensions).
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required from the beginning of the connection and using :meth:`starttls` is
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not appropriate. If *host* is not specified, the local host is used. If
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*port* is zero, the standard SMTP-over-SSL port (465) is used. The optional
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arguments *local_hostname* and *source_address* have the same meaning as
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they do in the :class:`SMTP` class. *keyfile* and *certfile* are also
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optional, and can contain a PEM formatted private key and certificate chain
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file for the SSL connection. *context* also optional, can contain a
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SSLContext, and is an alternative to keyfile and certfile; If it is
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specified both keyfile and certfile must be None. The optional *timeout*
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parameter specifies a timeout in seconds for blocking operations like the
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connection attempt (if not specified, the global default timeout setting
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will be used). The optional source_address parameter allows to bind to some
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specific source address in a machine with multiple network interfaces,
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and/or to some specific source tcp port. It takes a 2-tuple (host, port),
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for the socket to bind to as its source address before connecting. If
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omitted (or if host or port are ``''`` and/or 0 respectively) the OS default
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behavior will be used.
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arguments *local_hostname*, *timeout* and *source_address* have the same
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meaning as they do in the :class:`SMTP` class. *context*, also optional,
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can contain a :class:`~ssl.SSLContext` and allows to configure various
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aspects of the secure connection. Please read :ref:`ssl-security` for
|
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best practices.
|
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|
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*keyfile* and *certfile* are a legacy alternative to *context*, and can
|
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point to a PEM formatted private key and certificate chain file for the
|
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SSL connection.
|
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|
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.. versionchanged:: 3.3
|
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*context* was added.
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|
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@ -92,8 +87,8 @@ Protocol) and :rfc:`1869` (SMTP Service Extensions).
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|
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.. versionchanged:: 3.4
|
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The class now supports hostname check with
|
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:attr:`SSLContext.check_hostname` and *Server Name Indicator* (see
|
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:data:`~ssl.HAS_SNI`).
|
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:attr:`ssl.SSLContext.check_hostname` and *Server Name Indication* (see
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:data:`ssl.HAS_SNI`).
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.. class:: LMTP(host='', port=LMTP_PORT, local_hostname=None, source_address=None)
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|
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@ -1542,7 +1542,7 @@ waiting for clients to connect::
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import socket, ssl
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context = ssl.SSLContext(ssl.PROTOCOL_TLSv1)
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context = ssl.SSLContext(ssl.PROTOCOL_SSLv23)
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context.load_cert_chain(certfile="mycertfile", keyfile="mykeyfile")
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bindsocket = socket.socket()
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@ -1619,9 +1619,39 @@ to be aware of:
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Security considerations
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-----------------------
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Verifying certificates
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^^^^^^^^^^^^^^^^^^^^^^
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Best defaults
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^^^^^^^^^^^^^
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For **client use**, if you don't have any special requirements for your
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security policy, it is highly recommended that you use the
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:func:`create_default_context` function to create your SSL context.
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It will load the system's trusted CA certificates, enable certificate
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validation, and try to choose reasonably secure protocol and cipher settings.
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For example, here is how you would use the :class:`smtplib.SMTP` class to
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create a trusted, secure connection to a SMTP server::
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>>> import ssl, smtplib
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>>> smtp = smtplib.SMTP("mail.python.org", port=587)
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>>> context = ssl.create_default_context()
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>>> smtp.starttls(context=context)
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(220, b'2.0.0 Ready to start TLS')
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If a client certificate is needed for the connection, it can be added with
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:meth:`SSLContext.load_cert_chain`.
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By contrast, if you create the SSL context by calling the :class:`SSLContext`
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constructor yourself, it will not have certificate validation enabled by
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default. If you do so, please read the paragraphs below to achieve a good
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security level.
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Manual settings
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^^^^^^^^^^^^^^^
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Verifying certificates
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''''''''''''''''''''''
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When calling the the :class:`SSLContext` constructor directly,
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:const:`CERT_NONE` is the default. Since it does not authenticate the other
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peer, it can be insecure, especially in client mode where most of time you
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would like to ensure the authenticity of the server you're talking to.
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@ -1645,7 +1675,7 @@ to specify :const:`CERT_REQUIRED` and similarly check the client certificate.
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|||
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 @@ 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 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
|
||||
|
|
|
|||
Loading…
Reference in New Issue