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aws-encryption-sdk
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   :target: https://pypi.python.org/pypi/aws-encryption-sdk
   :alt: Latest Version

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   :target: https://aws-encryption-sdk-python.readthedocs.io/en/stable/
   :alt: Documentation Status

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   :target: https://travis-ci.org/awslabs/aws-encryption-sdk-python

The AWS Encryption SDK for Python provides a fully compliant, native Python implementation of the `AWS Encryption SDK`_.

The latest full documentation can be found at `Read the Docs`_.

Find us on `GitHub`_.

***************
Getting Started
***************
Required Prerequisites
======================

* Python 2.7+ or 3.4+
* cryptography >= 1.8.1
* boto3
* attrs

Installation
============

.. note::

   If you have not already installed `cryptography`_, you might need to install additional prerequisites as
   detailed in the `cryptography installation guide`_ for your operating system.

   .. code::

       $ pip install aws-encryption-sdk

Concepts
========
There are four main concepts that you need to understand to use this library:

Cryptographic Materials Managers
--------------------------------
Cryptographic materials managers (CMMs) are resources that collect cryptographic materials and prepare them for
use by the Encryption SDK core logic.

An example of a CMM is the default CMM, which is automatically generated anywhere a caller provides a master
key provider. The default CMM collects encrypted data keys from all master keys referenced by the master key
provider.

An example of a more advanced CMM is the caching CMM, which caches cryptographic materials provided by another CMM.

Master Key Providers
--------------------
Master key providers are resources that provide master keys.
An example of a master key provider is `AWS KMS`_.

To encrypt data in this client, a ``MasterKeyProvider`` object must contain at least one ``MasterKey`` object.

``MasterKeyProvider`` objects can also contain other ``MasterKeyProvider`` objects.

Master Keys
-----------
Master keys generate, encrypt, and decrypt data keys.
An example of a master key is a `KMS customer master key (CMK)`_.

Data Keys
---------
Data keys are the encryption keys that are used to encrypt your data. If your algorithm suite
uses a key derivation function, the data key is used to generate the key that directly encrypts the data.

*****
Usage
*****
To use this client, you (the caller) must provide an instance of either a master key provider
or a CMM. The examples in this readme use the ``KMSMasterKeyProvider`` class.

KMSMasterKeyProvider
====================
Because the ``KMSMasterKeyProvider`` uses the `boto3 SDK`_ to interact with `AWS KMS`_, it requires AWS Credentials.
To provide these credentials, use the `standard means by which boto3 locates credentials`_ or provide a
pre-existing instance of a ``botocore session`` to the ``KMSMasterKeyProvider``.
This latter option can be useful if you have an alternate way to store your AWS credentials or
you want to reuse an existing instance of a botocore session in order to decrease startup costs.

.. code:: python

    import aws_encryption_sdk
    import botocore.session

    kms_key_provider = aws_encryption_sdk.KMSMasterKeyProvider()

    existing_botocore_session = botocore.session.Session()
    kms_key_provider = aws_encryption_sdk.KMSMasterKeyProvider(botocore_session=existing_botocore_session)


You can pre-load the ``KMSMasterKeyProvider`` with one or more CMKs.
To encrypt data, you must configure the ``KMSMasterKeyProvider`` with as least one CMK.
If you configure the the ``KMSMasterKeyProvider`` with multiple CMKs, the `final message`_
will include a copy of the data key encrypted by each configured CMK.

.. code:: python

    import aws_encryption_sdk

    kms_key_provider = aws_encryption_sdk.KMSMasterKeyProvider(key_ids=[
        'arn:aws:kms:us-east-1:2222222222222:key/22222222-2222-2222-2222-222222222222',
        'arn:aws:kms:us-east-1:3333333333333:key/33333333-3333-3333-3333-333333333333'
    ])

You can add CMKs from multiple regions to the ``KMSMasterKeyProvider``.

.. code:: python

    import aws_encryption_sdk

    kms_key_provider = aws_encryption_sdk.KMSMasterKeyProvider(key_ids=[
        'arn:aws:kms:us-east-1:2222222222222:key/22222222-2222-2222-2222-222222222222',
        'arn:aws:kms:us-west-2:3333333333333:key/33333333-3333-3333-3333-333333333333',
        'arn:aws:kms:ap-northeast-1:4444444444444:key/44444444-4444-4444-4444-444444444444'
    ])


Encryption and Decryption
=========================
After you create an instance of a ``MasterKeyProvider``, you can use either of the two
high-level ``encrypt``/``decrypt`` functions to encrypt and decrypt your data.

.. code:: python

    import aws_encryption_sdk

    kms_key_provider = aws_encryption_sdk.KMSMasterKeyProvider(key_ids=[
        'arn:aws:kms:us-east-1:2222222222222:key/22222222-2222-2222-2222-222222222222',
        'arn:aws:kms:us-east-1:3333333333333:key/33333333-3333-3333-3333-333333333333'
    ])
    my_plaintext = 'This is some super secret data!  Yup, sure is!'

    my_ciphertext, encryptor_header = aws_encryption_sdk.encrypt(
        source=my_plaintext,
        key_provider=kms_key_provider
    )

    decrypted_plaintext, decryptor_header = aws_encryption_sdk.decrypt(
        source=my_ciphertext,
        key_provider=kms_key_provider
    )

    assert my_plaintext == decrypted_plaintext
    assert encryptor_header.encryption_context == decryptor_header.encryption_context

You can provide an `encryption context`_: a form of additional authenticating information.

.. code:: python

    import aws_encryption_sdk

    kms_key_provider = aws_encryption_sdk.KMSMasterKeyProvider(key_ids=[
        'arn:aws:kms:us-east-1:2222222222222:key/22222222-2222-2222-2222-222222222222',
        'arn:aws:kms:us-east-1:3333333333333:key/33333333-3333-3333-3333-333333333333'
    ])
    my_plaintext = 'This is some super secret data!  Yup, sure is!'

    my_ciphertext, encryptor_header = aws_encryption_sdk.encrypt(
        source=my_plaintext,
        key_provider=kms_key_provider,
        encryption_context={
            'not really': 'a secret',
            'but adds': 'some authentication'
        }
    )

    decrypted_plaintext, decryptor_header = aws_encryption_sdk.decrypt(
        source=my_ciphertext,
        key_provider=kms_key_provider
    )

    assert my_plaintext == decrypted_plaintext
    assert encryptor_header.encryption_context == decryptor_header.encryption_context


Streaming
=========
If you are handling large files or simply do not want to put the entire plaintext or ciphertext in
memory at once, you can use this library's streaming clients directly. The streaming clients are
file-like objects, and behave exactly as you would expect a Python file object to behave,
offering context manager and iteration support.

.. code:: python

    import aws_encryption_sdk
    import filecmp

    kms_key_provider = aws_encryption_sdk.KMSMasterKeyProvider(key_ids=[
        'arn:aws:kms:us-east-1:2222222222222:key/22222222-2222-2222-2222-222222222222',
        'arn:aws:kms:us-east-1:3333333333333:key/33333333-3333-3333-3333-333333333333'
    ])
    plaintext_filename = 'my-secret-data.dat'
    ciphertext_filename = 'my-encrypted-data.ct'

    with open(plaintext_filename, 'rb') as pt_file, open(ciphertext_filename, 'wb') as ct_file:
        with aws_encryption_sdk.stream(
            mode='e',
            source=pt_file,
            key_provider=kms_key_provider
        ) as encryptor:
            for chunk in encryptor:
                ct_file.write(chunk)

    new_plaintext_filename = 'my-decrypted-data.dat'

    with open(ciphertext_filename, 'rb') as ct_file, open(new_plaintext_filename, 'wb') as pt_file:
        with aws_encryption_sdk.stream(
            mode='d',
            source=ct_file,
            key_provider=kms_key_provider
        ) as decryptor:
            for chunk in decryptor:
                pt_file.write(chunk)

    assert filecmp.cmp(plaintext_filename, new_plaintext_filename)
    assert encryptor.header.encryption_context == decryptor.header.encryption_context

Performance Considerations
==========================
Adjusting the frame size can significantly improve the performance of encrypt/decrypt operations with this library.

Processing each frame in a framed message involves a certain amount of overhead.  If you are encrypting a large file,
increasing the frame size can offer potentially significant performance gains.  We recommend that you tune these values
to your use-case in order to obtain peak performance.


.. _AWS Encryption SDK: https://docs.aws.amazon.com/encryption-sdk/latest/developer-guide/introduction.html
.. _cryptography: https://cryptography.io/en/latest/
.. _cryptography installation guide: https://cryptography.io/en/latest/installation/
.. _Read the Docs: http://aws-encryption-sdk-python.readthedocs.io/en/latest/
.. _GitHub: https://github.com/awslabs/aws-encryption-sdk-python/
.. _AWS KMS: https://docs.aws.amazon.com/kms/latest/developerguide/overview.html
.. _KMS customer master key (CMK): https://docs.aws.amazon.com/kms/latest/developerguide/concepts.html#master_keys
.. _boto3 SDK: https://boto3.readthedocs.io/en/latest/
.. _standard means by which boto3 locates credentials: https://boto3.readthedocs.io/en/latest/guide/configuration.html
.. _final message: https://docs.aws.amazon.com/encryption-sdk/latest/developer-guide/message-format.html
.. _encryption context: https://docs.aws.amazon.com/kms/latest/developerguide/concepts.html#encrypt_context