# Frequently asked questions

## I cannot suppress the deprecation warning that `cryptography` emits on import

Hint

The deprecation warning emitted on import does not inherit `DeprecationWarning` but inherits `UserWarning` instead.

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

Note: Using `cryptography.utils.CryptographyDeprecationWarning` is not possible here because specifying it triggers `import cryptography` internally that emits the warning before the ignore rule even kicks in.

Ref: https://github.com/pytest-dev/pytest/issues/7524

The same applies when you use `filterwarnings()` in your code or invoke CPython with `-W` command line option.

## `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, which is also maintained by the PyCA team.

## 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`.

## Installing `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` with `pip install -U pip` and then try to install `cryptography` again.

Users on PyPy, unusual CPU architectures, or distributions of Linux using `musl` (like Alpine) will need to compile `cryptography` themselves. Please view our Installation documentation.

## `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.

## 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, 1.0.0, 1.0.1, 1.0.2 fails

The OpenSSL project has dropped support for the 0.9.8, 1.0.0, 1.0.1, and 1.0.2 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 (1.1.0 or later). This may require you to upgrade to a newer operating system.

## Installing `cryptography` fails with `error: Can not find Rust compiler`

Building `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 version.

For the current release only you can temporarily bypass the requirement to have Rust installed by setting the `CRYPTOGRAPHY_DONT_BUILD_RUST` environment variable. Note that this option will be removed in the next release and not having Rust available will be a hard error.

## 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 `pip` will automatically install `abi3` wheels.

## 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 `[FILE TYPE]` is `CERTIFICATE`, `PUBLIC KEY`, `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-----