This is a “Hazardous Materials” module. You should ONLY use it if you’re 100% absolutely sure that you know what you’re doing because this module is full of land mines, dragons, and dinosaurs with laser guns.

OpenSSL binding

These are CFFI bindings to the OpenSSL C library. Cryptography supports OpenSSL version 1.0.1 and greater.

class cryptography.hazmat.bindings.openssl.binding.Binding

This is the exposed API for the OpenSSL bindings. It has two public attributes:


This is a cffi.FFI instance. It can be used to allocate and otherwise manipulate OpenSSL structures.


This is a cffi library. It can be used to call OpenSSL functions, and access constants.

classmethod init_static_locks()

Enables the best available locking callback for OpenSSL. See Threading.


cryptography enables OpenSSLs thread safety facilities in two different ways depending on the configuration of your system. Normally the locking callbacks provided by your Python implementation specifically for OpenSSL will be used. However, if you have linked cryptography to a different version of OpenSSL than that used by your Python implementation we enable an alternative locking callback. This version is implemented in Python and so may result in lower performance in some situations. In particular parallelism is reduced because it has to acquire the GIL whenever any lock operations occur within OpenSSL.