191 lines
8.1 KiB
ReStructuredText
191 lines
8.1 KiB
ReStructuredText
:mod:`ssl` -- SSL/TLS module
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============================
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.. module:: ssl
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:synopsis: TLS/SSL wrapper for socket objects
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|see_cpython_module| :mod:`python:ssl`.
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This module provides access to Transport Layer Security (previously and
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widely known as “Secure Sockets Layer”) encryption and peer authentication
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facilities for network sockets, both client-side and server-side.
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Functions
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---------
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.. function:: ssl.wrap_socket(sock, server_side=False, key=None, cert=None, cert_reqs=CERT_NONE, cadata=None, server_hostname=None, do_handshake=True)
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Wrap the given *sock* and return a new wrapped-socket object. The implementation
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of this function is to first create an `SSLContext` and then call the `SSLContext.wrap_socket`
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method on that context object. The arguments *sock*, *server_side* and *server_hostname* are
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passed through unchanged to the method call. The argument *do_handshake* is passed through as
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*do_handshake_on_connect*. The remaining arguments have the following behaviour:
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- *cert_reqs* determines whether the peer (server or client) must present a valid certificate.
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Note that for mbedtls based ports, ``ssl.CERT_NONE`` and ``ssl.CERT_OPTIONAL`` will not
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validate any certificate, only ``ssl.CERT_REQUIRED`` will.
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- *cadata* is a bytes object containing the CA certificate chain (in DER format) that will
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validate the peer's certificate. Currently only a single DER-encoded certificate is supported.
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Depending on the underlying module implementation in a particular
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:term:`MicroPython port`, some or all keyword arguments above may be not supported.
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class SSLContext
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----------------
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.. class:: SSLContext(protocol, /)
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Create a new SSLContext instance. The *protocol* argument must be one of the ``PROTOCOL_*``
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constants.
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.. method:: SSLContext.load_cert_chain(certfile, keyfile)
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Load a private key and the corresponding certificate. The *certfile* is a string
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with the file path of the certificate. The *keyfile* is a string with the file path
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of the private key.
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.. admonition:: Difference to CPython
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:class: attention
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MicroPython extension: *certfile* and *keyfile* can be bytes objects instead of
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strings, in which case they are interpreted as the actual certificate/key data.
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.. method:: SSLContext.load_verify_locations(cafile=None, cadata=None)
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Load the CA certificate chain that will validate the peer's certificate.
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*cafile* is the file path of the CA certificates. *cadata* is a bytes object
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containing the CA certificates. Only one of these arguments should be provided.
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.. method:: SSLContext.get_ciphers()
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Get a list of enabled ciphers, returned as a list of strings.
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.. method:: SSLContext.set_ciphers(ciphers)
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Set the available ciphers for sockets created with this context. *ciphers* should be
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a list of strings in the `IANA cipher suite format <https://wiki.mozilla.org/Security/Cipher_Suites>`_ .
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.. method:: SSLContext.wrap_socket(sock, *, server_side=False, do_handshake_on_connect=True, server_hostname=None, client_id=None)
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Takes a `stream` *sock* (usually socket.socket instance of ``SOCK_STREAM`` type),
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and returns an instance of ssl.SSLSocket, wrapping the underlying stream.
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The returned object has the usual `stream` interface methods like
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``read()``, ``write()``, etc.
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- *server_side* selects whether the wrapped socket is on the server or client side.
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A server-side SSL socket should be created from a normal socket returned from
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:meth:`~socket.socket.accept()` on a non-SSL listening server socket.
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- *do_handshake_on_connect* determines whether the handshake is done as part of the ``wrap_socket``
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or whether it is deferred to be done as part of the initial reads or writes
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For blocking sockets doing the handshake immediately is standard. For non-blocking
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sockets (i.e. when the *sock* passed into ``wrap_socket`` is in non-blocking mode)
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the handshake should generally be deferred because otherwise ``wrap_socket`` blocks
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until it completes. Note that in AXTLS the handshake can be deferred until the first
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read or write but it then blocks until completion.
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- *server_hostname* is for use as a client, and sets the hostname to check against the received
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server certificate. It also sets the name for Server Name Indication (SNI), allowing the server
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to present the proper certificate.
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- *client_id* is a MicroPython-specific extension argument used only when implementing a DTLS
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Server. See :ref:`dtls` for details.
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.. warning::
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Some implementations of ``ssl`` module do NOT validate server certificates,
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which makes an SSL connection established prone to man-in-the-middle attacks.
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CPython's ``wrap_socket`` returns an ``SSLSocket`` object which has methods typical
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for sockets, such as ``send``, ``recv``, etc. MicroPython's ``wrap_socket``
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returns an object more similar to CPython's ``SSLObject`` which does not have
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these socket methods.
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.. attribute:: SSLContext.verify_mode
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Set or get the behaviour for verification of peer certificates. Must be one of the
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``CERT_*`` constants.
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.. note::
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``ssl.CERT_REQUIRED`` requires the device's date/time to be properly set, e.g. using
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`mpremote rtc --set <mpremote_command_rtc>` or ``ntptime``, and ``server_hostname``
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must be specified when on the client side.
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Exceptions
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----------
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.. data:: ssl.SSLError
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This exception does NOT exist. Instead its base class, OSError, is used.
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.. _dtls:
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DTLS support
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------------
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.. admonition:: Difference to CPython
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:class: attention
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This is a MicroPython extension.
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On most ports, this module supports DTLS in client and server mode via the
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`PROTOCOL_DTLS_CLIENT` and `PROTOCOL_DTLS_SERVER` constants that can be used as
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the ``protocol`` argument of `SSLContext`.
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In this case the underlying socket is expected to behave as a datagram socket (i.e.
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like the socket opened with ``socket.socket`` with ``socket.AF_INET`` as ``af`` and
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``socket.SOCK_DGRAM`` as ``type``).
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DTLS is only supported on ports that use mbedTLS, and it is enabled by default
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in most configurations but can be manually disabled by defining
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``MICROPY_PY_SSL_DTLS`` to 0.
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DTLS server support
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^^^^^^^^^^^^^^^^^^^
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MicroPython's DTLS server support is configured with "Hello Verify" as required
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for DTLS 1.2. This is transparent for DTLS clients, but there are relevant
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considerations when implementing a DTLS server in MicroPython:
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- The server should pass an additional argument *client_id* when calling
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`SSLContext.wrap_socket()`. This ID must be a `bytes` object (or similar) with
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a transport-specific identifier representing the client.
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The simplest approach is to convert the tuple of ``(client_ip, client_port)``
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returned from ``socket.recv_from()`` into a byte string, i.e.::
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_, client_addr = sock.recvfrom(1, socket.MSG_PEEK)
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sock.connect(client_addr) # Connect back to the client
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sock = ssl_ctx.wrap_socket(sock, server_side=True,
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client_id=repr(client_addr).encode())
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- The first time a client connects, the server call to ``wrap_socket`` will fail
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with a `OSError` error "Hello Verify Required". This is because the DTLS
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"Hello Verify" cookie is not yet known by the client. If the same client
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connects a second time then ``wrap_socket`` will succeed.
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- DTLS cookies for "Hello Verify" are associated with the `SSLContext` object,
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so the same `SSLContext` object should be used to wrap a subsequent connection
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from the same client. The cookie implementation includes a timeout and has
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constant memory use regardless of how many clients connect, so it's OK to
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reuse the same `SSLContext` object for the lifetime of the server.
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Constants
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---------
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.. data:: ssl.PROTOCOL_TLS_CLIENT
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ssl.PROTOCOL_TLS_SERVER
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ssl.PROTOCOL_DTLS_CLIENT (when DTLS support is enabled)
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ssl.PROTOCOL_DTLS_SERVER (when DTLS support is enabled)
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Supported values for the *protocol* parameter.
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.. data:: ssl.CERT_NONE
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ssl.CERT_OPTIONAL
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ssl.CERT_REQUIRED
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Supported values for *cert_reqs* parameter, and the :attr:`SSLContext.verify_mode`
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attribute.
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