Contributing ============ Process ------- As an open source project, ``cryptography`` welcomes contributions of all forms. These can include: * Bug reports and feature requests * Pull requests for both code and documentation * Patch reviews You can file bugs and submit pull requests on `GitHub`_. To discuss larger changes you can start a conversation on `our mailing list`_. Because cryptography is so complex, and the implications of getting it wrong so devastating, ``cryptography`` has a strict code review policy: * Patches must *never* be pushed directly to ``master``, all changes (even the most trivial typo fixes!) must be submitted as a pull request. * A committer may *never* merge their own pull request, a second party must merge their changes. If multiple people work on a pull request, it must be merged by someone who did not work on it. * A patch which breaks tests, or introduces regressions by changing or removing existing tests should not be merged. Tests must always be passing on ``master``. * If somehow the tests get into a failing state on ``master`` (such as by a backwards incompatible release of a dependency) no pull requests may be merged until this is rectified. * All merged patches must have 100% test coverage. * New features and significant bug fixes should be documented in the :doc:`/changelog`. The purpose of these policies is to minimize the chances we merge a change which jeopardizes our users' security. If you believe you've identified a security issue in ``cryptography``, please follow the directions on the :doc:`security page `. Code ---- When in doubt, refer to `PEP 8`_ for Python code. Every code file must start with the boilerplate notice of the Apache License. Additionally, every Python code file must contain .. code-block:: python from __future__ import absolute_import, division, print_function API Considerations ~~~~~~~~~~~~~~~~~~ Most projects' APIs are designed with a philosophy of "make easy things easy, and make hard things possible". One of the perils of writing cryptographic code is that secure code looks just like insecure code, and its results are almost always indistinguishable. As a result ``cryptography`` has, as a design philosophy: "make it hard to do insecure things". Here are a few strategies for API design which should be both followed, and should inspire other API choices: If it is necessary to compare a user provided value with a computed value (for example, verifying a signature), there should be an API provided which performs the verification in a secure way (for example, using a constant time comparison), rather than requiring the user to perform the comparison themselves. If it is incorrect to ignore the result of a method, it should raise an exception, and not return a boolean ``True``/``False`` flag. For example, a method to verify a signature should raise ``InvalidSignature``, and not return whether the signature was valid. .. code-block:: python # This is bad. def verify(sig): # ... return is_valid # Good! def verify(sig): # ... if not is_valid: raise InvalidSignature Every recipe should include a version or algorithmic marker of some sort in its output in order to allow transparent upgrading of the algorithms in use, as the algorithms or parameters needed to achieve a given security margin evolve. APIs at the :doc:`/hazmat/primitives/index` layer should always take an explicit backend, APIs at the recipes layer should automatically use the :func:`~cryptography.hazmat.backends.default_backend`, but optionally allow specifying a different backend. C bindings ~~~~~~~~~~ When binding C code with ``cffi`` we have our own style guide, it's pretty simple. Don't name parameters: .. code-block:: c // Good long f(long); // Bad long f(long x); ...unless they're inside a struct: .. code-block:: c struct my_struct { char *name; int number; ...; }; Include ``void`` if the function takes no arguments: .. code-block:: c // Good long f(void); // Bad long f(); Wrap lines at 80 characters like so: .. code-block:: c // Pretend this went to 80 characters long f(long, long, int *) Include a space after commas between parameters: .. code-block:: c // Good long f(int, char *) // Bad long f(int,char *) Values set by ``#define`` should be assigned the appropriate type. If you see this: .. code-block:: c #define SOME_INTEGER_LITERAL 0x0; #define SOME_UNSIGNED_INTEGER_LITERAL 0x0001U; #define SOME_STRING_LITERAL "hello"; ...it should be added to the bindings like so: .. code-block:: c static const int SOME_INTEGER_LITERAL; static const unsigned int SOME_UNSIGNED_INTEGER_LITERAL; static const char *const SOME_STRING_LITERAL; Documentation ------------- All features should be documented with prose. Docstrings should be written like this: .. code-block:: python def some_function(some_arg): """ Does some things. :param some_arg: Some argument. """ So, specifically: * Always use three double quotes. * Put the three double quotes on their own line. * No blank line at the end. * Use Sphinx parameter/attribute documentation `syntax`_. Because of the inherent challenges in implementing correct cryptographic systems, we want to make our documentation point people in the right directions as much as possible. To that end: * When documenting a generic interface, use a strong algorithm in examples. (e.g. when showing a hashing example, don't use :class:`~cryptography.hazmat.primitives.hashes.MD5`) * When giving prescriptive advice, always provide references and supporting material. * When there is real disagreement between cryptographic experts, represent both sides of the argument and describe the trade-offs clearly. When documenting a new module in the ``hazmat`` package, its documentation should begin with the "Hazardous Materials" warning: .. code-block:: rest .. hazmat:: When referring to a hypothetical individual (such as "a person receiving an encrypted message") use gender neutral pronouns (they/them/their). Development Environment ----------------------- Working on ``cryptography`` requires the installation of a small number of development dependencies. These are listed in ``dev-requirements.txt`` and they can be installed in a `virtualenv`_ using `pip`_. Once you've installed the dependencies, install ``cryptography`` in ``editable`` mode. For example: .. code-block:: console $ # Create a virtualenv and activate it $ pip install --requirement dev-requirements.txt $ pip install --editable . You are now ready to run the tests and build the documentation. Running Tests ~~~~~~~~~~~~~ ``cryptography`` unit tests are found in the ``tests/`` directory and are designed to be run using `pytest`_. `pytest`_ will discover the tests automatically, so all you have to do is: .. code-block:: console $ py.test ... 62746 passed in 220.43 seconds This runs the tests with the default Python interpreter. You can also verify that the tests pass on other supported Python interpreters. For this we use `tox`_, which will automatically create a `virtualenv`_ for each supported Python version and run the tests. For example: .. code-block:: console $ tox ... ERROR: py26: InterpreterNotFound: python2.6 py27: commands succeeded ERROR: pypy: InterpreterNotFound: pypy ERROR: py32: InterpreterNotFound: python3.2 py33: commands succeeded docs: commands succeeded pep8: commands succeeded You may not have all the required Python versions installed, in which case you will see one or more ``InterpreterNotFound`` errors. Explicit Backend Selection ~~~~~~~~~~~~~~~~~~~~~~~~~~ While testing you may want to run tests against a subset of the backends that cryptography supports. Explicit backend selection can be done via the ``--backend`` flag. This flag should be passed to ``py.test`` with a comma delimited list of backend names. To use it with ``tox`` you must pass it as ``tox -- --backend=openssl``. Building Documentation ~~~~~~~~~~~~~~~~~~~~~~ ``cryptography`` documentation is stored in the ``docs/`` directory. It is written in `reStructured Text`_ and rendered using `Sphinx`_. Use `tox`_ to build the documentation. For example: .. code-block:: console $ tox -e docs ... docs: commands succeeded congratulations :) The HTML documentation index can now be found at ``docs/_build/html/index.html``. .. _`GitHub`: https://github.com/pyca/cryptography .. _`our mailing list`: https://mail.python.org/mailman/listinfo/cryptography-dev .. _`PEP 8`: http://www.peps.io/8/ .. _`syntax`: http://sphinx-doc.org/domains.html#info-field-lists .. _`pytest`: https://pypi.python.org/pypi/pytest .. _`tox`: https://pypi.python.org/pypi/tox .. _`virtualenv`: https://pypi.python.org/pypi/virtualenv .. _`pip`: https://pypi.python.org/pypi/pip .. _`sphinx`: https://pypi.python.org/pypi/Sphinx .. _`reStructured Text`: http://sphinx-doc.org/rest.html