Frequently asked questions

cryptography failed to install!

If you are having issues installing cryptography the first troubleshooting step is to upgrade pip and then try to install again. For most users this will take the form of pip install -U pip, but on Windows you should do python -m pip install -U pip. If you are still seeing errors after upgrading and trying pip install cryptography again, please see the Installation documentation.

How does cryptography compare to NaCl (Networking and Cryptography Library)?

While cryptography and NaCl both share the goal of making cryptography easier, and safer, to use for developers, cryptography is designed to be a general purpose library, interoperable with existing systems, while NaCl features a collection of hand selected algorithms.

cryptography’s recipes layer has similar goals to NaCl.

If you prefer NaCl’s design, we highly recommend PyNaCl.

Why use cryptography?

If you’ve done cryptographic work in Python before you have likely encountered other libraries in Python such as M2Crypto, PyCrypto, or PyOpenSSL. In building cryptography we wanted to address a few issues we observed in the legacy libraries:

  • Extremely error prone APIs and insecure defaults.
  • Use of poor implementations of algorithms (i.e. ones with known side-channel attacks).
  • Lack of maintenance.
  • Lack of high level APIs.
  • Lack of PyPy and Python 3 support.
  • Absence of algorithms such as AES-GCM and HKDF.

Compiling cryptography on macOS produces a fatal error: 'openssl/aes.h' file not found error

This happens because macOS 10.11 no longer includes a copy of OpenSSL. cryptography now provides wheels which include a statically linked copy of OpenSSL. You’re seeing this error because your copy of pip is too old to find our wheel files. Upgrade your copy of pip with pip install -U pip and then try install cryptography again.

If you are using PyPy, we do not currently ship cryptography wheels for PyPy. You will need to install your own copy of OpenSSL – we recommend using Homebrew.

Starting cryptography using mod_wsgi produces an InternalError during a call in _register_osrandom_engine

Upgrade to the latest cryptography and this issue should be resolved.

cryptography raised an InternalError and I’m not sure what to do?

Frequently InternalError is raised when there are errors on the OpenSSL error stack that were placed there by other libraries that are also using OpenSSL. Try removing the other libraries and see if the problem persists. If you have no other libraries using OpenSSL in your process, or they do not appear to be at fault, it’s possible that this is a bug in cryptography. Please file an issue with instructions on how to reproduce it.

Installing cryptography fails with ImportError: No module named setuptools_ext

Your cffi package is out of date. pip install -U cffi to update it.

error: -Werror=sign-conversion: No option -Wsign-conversion during installation

The compiler you are using is too old and not supported by cryptography. Please upgrade to a more recent version. If you are running OpenBSD 6.1 or earlier the default compiler is extremely old. Use pkg_add to install a newer gcc and then install cryptography using CC=/path/to/newer/gcc pip install cryptography.

Installing cryptography fails with Invalid environment marker: python_version < '3'

Your pip and/or setuptools are outdated. Please upgrade to the latest versions with pip install -U pip setuptools (or on Windows python -m pip install -U pip setuptools).

Installing cryptography with OpenSSL 0.9.8 or 1.0.0 fails

The OpenSSL project has dropped support for the 0.9.8 and 1.0.0 release series. Since they are no longer receiving security patches from upstream, cryptography is also dropping support for them. To fix this issue you should upgrade to a newer version of OpenSSL (1.0.1 or later). This may require you to upgrade to a newer operating system.