File Encryptor
==============

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This is a library used by MetaDisk to convergently encrypt and decrypt
files. It contains helper methods to encrypt and decrypt files inline
(without using extra space) and to stream decryption.

Installation
------------

You can easily install ``file-encryptor`` using pip:

::

    pip install file_encryptor

Usage
-----

Here’s an example to encrypt a file inline using convergent encryption:

.. code:: python

    import file_encryptor.convergence

    key = convergence.encrypt_inline_file("/path/to/file", None)

You can also specify a passphrase:

.. code:: python

    import file_encryptor.convergence

    key = convergence.encrypt_inline_file("/path/to/file", "rainbow dinosaur secret")

To decrypt a file inline, you need the key that was returned by the
encrypt method:

.. code:: python

    import file_encryptor.convergence

    key = convergence.encrypt_inline_file("/path/to/file", "rainbow dinosaur secret")

    convergence.decrypt_inline_file("/path/to/file", key)

The reason why you cannot use the passphrase directly is because the key
is derived from both the passphrase and the SHA-256 of the original
file.

For streaming applications, you can decrypt a file with a generator:

.. code:: python

    for chunk in convergence.decrypt_generator("/path/to/file", key):
        do_something_with_chunk(chunk)

Cryptoconcerns
--------------

The key generation mechanism is the following:

.. code:: python

    key = HMAC-SHA256(passphrase, hex(SHA256(file-contents)))

If no passphrase is given, a default is used.

The file itself is encrypted using AES128-CTR, from pycrypto. We’re not
specifying any IV, thinking that for convergent encryption that is the
right thing to do.

Testing
-------

To run tests, execute the following command in the project root:

::

    python setup.py test -a "--doctest-modules --pep8 -v tests/"

To run tests with detailed coverage output, execute:

::

    coverage run setup.py test -a "--doctest-modules --pep8 -v tests/"
    coverage report -m --include="file_encryptor/*"

.. |Build Status| image:: https://travis-ci.org/Storj/file-encryptor.svg
   :target: https://travis-ci.org/Storj/file-encryptor
.. |Coverage Status| image:: https://coveralls.io/repos/Storj/file-encryptor/badge.png?branch=master
   :target: https://coveralls.io/r/Storj/file-encryptor?branch=master
.. |PyPI version| image:: https://badge.fury.io/py/file_encryptor.svg
   :target: http://badge.fury.io/py/file_encryptor