Frequently asked questions
I cannot suppress the deprecation warning that
cryptography emits on import
If your pytest setup follows the best practices of failing on
emitted warnings (
filterwarnings = error), you may ignore it
by adding the following line at the end of the list:
ignore:Python 2 is no longer supported by the Python core team. Support for it is now deprecated in cryptography, and will be removed in a future release.:UserWarning
is not possible here because specifying it triggers
import cryptography internally that emits the warning before
the ignore rule even kicks in.
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
pip install cryptography again, please see the Installation
cryptography compare to NaCl (Networking and Cryptography Library)?
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
If you prefer NaCl’s design, we highly recommend PyNaCl, which is also maintained by the PyCA team.
If you’ve done cryptographic work in Python before you have likely encountered
other libraries in Python such as M2Crypto, PyCrypto, or PyOpenSSL. In
cryptography we wanted to address a few issues we observed in the
cryptography require Rust?
cryptography uses OpenSSL (see: Use of OpenSSL) for its cryptographic operations. OpenSSL is
the de facto standard for cryptographic libraries and provides high performance
along with various certifications that may be relevant to developers. However,
it is written in C and lacks memory safety. We want
cryptography to be
as secure as possible while retaining the advantages of OpenSSL, so we’ve
chosen to rewrite non-cryptographic operations (such as ASN.1 parsing) in a
high performance memory safe language: Rust.
cryptography produces a
fatal error: 'openssl/opensslv.h' file not found error
cryptography provides wheels which include a statically linked copy of
OpenSSL. If you see this error it is likely because your copy of
pip is too
old to find our wheel files. Upgrade your
pip install -U pip
and then try to install
Users on unusual CPU architectures will need to compile
themselves. Please view our Installation documentation.
cryptography raised an
InternalError and I’m not sure what to do?
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
Please file an issue with instructions on how to reproduce it.
-Werror=sign-conversion: No option
-Wsign-conversion during installation
The compiler you are using is too old and not supported by
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
gcc and then install
CC=/path/to/newer/gcc pip install cryptography.
Installing cryptography with OpenSSL 0.9.8, 1.0.0, 1.0.1, 1.0.2, 1.1.0 fails
The OpenSSL project has dropped support for the 0.9.8, 1.0.0, 1.0.1, 1.0.2,
and 1.1.0 release series. Since they are no longer receiving security patches
cryptography is also dropping support for them. To fix this
issue you should upgrade to a newer version of OpenSSL (1.1.1 or later). This
may require you to upgrade to a newer operating system.
cryptography fails with
error: Can not find Rust compiler
cryptography from source requires you have Rust installed
and available on your
PATH. You may be able to fix this
by upgrading to a newer version of
pip which will install a pre-compiled
cryptography wheel. If not, you’ll need to install Rust. Follow the
instructions to ensure you install a recent Rust
Rust is only required during the build phase of
cryptography, you do not
need to have Rust installed after you’ve built
cryptography. This is the
same as the C compiler toolchain which is also required to build
cryptography, but not afterwards.
I’m getting errors installing or importing
cryptography on AWS Lambda
Why are there no wheels for my Python3.x version?
Our Python3 wheels are
abi3 wheels. This means they support multiple
versions of Python. The
abi3 wheel can be used with any version of Python
greater than or equal to the version it specifies. Recent versions of
will automatically install
Why can’t I import my PEM file?
PEM is a format (defined by several RFCs, but originally RFC 1421) for encoding keys, certificates and others cryptographic data into a regular form. The data is encoded as base64 and wrapped with a header and footer.
If you are having trouble importing PEM files, make sure your file fits the following rules:
has a one-line header like this:
-----BEGIN [FILE TYPE]-----(where
PRIVATE KEY, etc.)
has a one-line footer like this:
-----END [FILE TYPE]-----
all lines, except for the final one, must consist of exactly 64 characters.
For example, this is a PEM file for a RSA Public Key:
-----BEGIN PUBLIC KEY----- MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA7CsKFSzq20NLb2VQDXma 9DsDXtKADv0ziI5hT1KG6Bex5seE9pUoEcUxNv4uXo2jzAUgyRweRl/DLU8SoN8+ WWd6YWik4GZvNv7j0z28h9Q5jRySxy4dmElFtIRHGiKhqd1Z06z4AzrmKEzgxkOk LJjY9cvwD+iXjpK2oJwNNyavvjb5YZq6V60RhpyNtKpMh2+zRLgIk9sROEPQeYfK 22zj2CnGBMg5Gm2uPOsGDltl/I/Fdh1aO3X4i1GXwCuPf1kSAg6lPJD0batftkSG v0X0heUaV0j1HSNlBWamT4IR9+iJfKJHekOqvHQBcaCu7Ja4kXzx6GZ3M2j/Ja3A 2QIDAQAB -----END PUBLIC KEY-----
What happened to the backend argument?
cryptography stopped requiring the use of
backend arguments in
version 3.1 and deprecated their use in version 36.0. If you are on an older
version that requires these arguments please view the appropriate documentation
version or upgrade to the latest release.
Note that for forward compatibility
backend is still silently accepted by
functions that previously required it, but it is ignored and no longer
Will you upload wheels for my non-x86 non-ARM64 CPU architecture?
Maybe! But there’s some pre-requisites. For us to build wheels and upload them to PyPI, we consider it necessary to run our tests for that architecture as a part of our CI (i.e. for every commit). If we don’t run the tests, it’s hard to have confidence that everything works – particularly with cryptography, which frequently employs per-architecture assembly code.
For us to add something to CI we need a provider which offers builds on that architecture, which integrate into our workflows, has sufficient capacity, and performs well enough not to regress the contributor experience. We don’t think this is an insurmountable bar, but it’s also not one that can be cleared lightly.
If you are interested in helping support a new CPU architecture, we encourage you to reach out, discuss, and contribute that support. We will attempt to be supportive, but we cannot commit to doing the work ourselves.