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ssl – SSL/TLS module

This module implements a subset of the corresponding CPython module, as described below. For more information, refer to the original CPython documentation: ssl.

This module provides access to Transport Layer Security (previously and widely known as “Secure Sockets Layer”) encryption and peer authentication facilities for network sockets, both client-side and server-side.

Functions

ssl.wrap_socket(sock, server_side=False, keyfile=None, certfile=None, cert_reqs=CERT_NONE, cadata=None, server_hostname=None, do_handshake=True)

Takes a stream sock (usually socket.socket instance of SOCK_STREAM type), and returns an instance of ssl.SSLSocket, which wraps the underlying stream in an SSL context. Returned object has the usual stream interface methods like read(), write(), etc. A server-side SSL socket should be created from a normal socket returned from accept() on a non-SSL listening server socket.

  • do_handshake determines whether the handshake is done as part of the wrap_socket or whether it is deferred to be done as part of the initial reads or writes (there is no do_handshake method as in CPython). For blocking sockets doing the handshake immediately is standard. For non-blocking sockets (i.e. when the sock passed into wrap_socket is in non-blocking mode) the handshake should generally be deferred because otherwise wrap_socket blocks until it completes. Note that in AXTLS the handshake can be deferred until the first read or write but it then blocks until completion.

  • cert_reqs determines whether the peer (server or client) must present a valid certificate. Note that for mbedtls based ports, ssl.CERT_NONE and ssl.CERT_OPTIONAL will not validate any certificate, only ssl.CERT_REQUIRED will.

  • cadata is a bytes object containing the CA certificate chain (in DER format) that will validate the peer’s certificate. Currently only a single DER-encoded certificate is supported.

  • server_hostname is for use as a client, and sets the hostname to check against the received server certificate. It also sets the name for Server Name Indication (SNI), allowing the server to present the proper certificate.

Depending on the underlying module implementation in a particular MicroPython port, some or all keyword arguments above may be not supported.

Warning

Some implementations of ssl module do NOT validate server certificates, which makes an SSL connection established prone to man-in-the-middle attacks.

CPython’s wrap_socket returns an SSLSocket object which has methods typical for sockets, such as send, recv, etc. MicroPython’s wrap_socket returns an object more similar to CPython’s SSLObject which does not have these socket methods.

Exceptions

ssl.SSLError

This exception does NOT exist. Instead its base class, OSError, is used.

Constants

ssl.CERT_NONE
ssl.CERT_OPTIONAL
ssl.CERT_REQUIRED

Supported values for cert_reqs parameter.