diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/conf.py | 1 | ||||
| -rw-r--r-- | docs/contributing.rst | 44 | ||||
| -rw-r--r-- | docs/exceptions.rst | 12 | ||||
| -rw-r--r-- | docs/glossary.rst | 11 | ||||
| -rw-r--r-- | docs/hazmat/bindings/interfaces.rst | 4 | ||||
| -rw-r--r-- | docs/hazmat/bindings/openssl.rst | 2 | ||||
| -rw-r--r-- | docs/hazmat/primitives/constant-time.rst | 38 | ||||
| -rw-r--r-- | docs/hazmat/primitives/index.rst | 1 | ||||
| -rw-r--r-- | docs/hazmat/primitives/symmetric-encryption.rst | 84 | ||||
| -rw-r--r-- | docs/index.rst | 21 |
10 files changed, 202 insertions, 16 deletions
diff --git a/docs/conf.py b/docs/conf.py index 77050e72..5092e4d3 100644 --- a/docs/conf.py +++ b/docs/conf.py @@ -257,6 +257,5 @@ texinfo_documents = [ # How to display URL addresses: 'footnote', 'no', or 'inline'. #texinfo_show_urls = 'footnote' - # Example configuration for intersphinx: refer to the Python standard library. intersphinx_mapping = {'http://docs.python.org/': None} diff --git a/docs/contributing.rst b/docs/contributing.rst index 97f31e0b..a8010a9a 100644 --- a/docs/contributing.rst +++ b/docs/contributing.rst @@ -28,6 +28,7 @@ devastating, ``cryptography`` has a strict code review policy: * 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. The purpose of these policies is to minimize the chances we merge a change which jeopardizes our users' security. @@ -47,8 +48,42 @@ Additionally, every Python code file must contain 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 code that is secure looks just like code that isn't, and produces +results that are also difficult to distinguish. 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 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 + +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.bindings.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. @@ -141,6 +176,9 @@ should begin with the "Hazardous Materials" warning: .. hazmat:: +When referring to a hypothetical individual (such as "a person receiving an +encrypted message") use gender neutral pronouns (they/them/their). + Development Environment ----------------------- @@ -158,7 +196,7 @@ dependencies, install ``cryptography`` in ``editable`` mode. For example: 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 @@ -192,7 +230,7 @@ You may not have all the required Python versions installed, in which case you will see one or more ``InterpreterNotFound`` errors. Building Documentation ----------------------- +~~~~~~~~~~~~~~~~~~~~~~ ``cryptography`` documentation is stored in the ``docs/`` directory. It is written in `reStructured Text`_ and rendered using `Sphinx`_. diff --git a/docs/exceptions.rst b/docs/exceptions.rst index c6f5a7cc..087066b8 100644 --- a/docs/exceptions.rst +++ b/docs/exceptions.rst @@ -8,6 +8,18 @@ Exceptions This is raised when a context is used after being finalized. +.. class:: NotYetFinalized + + This is raised when the AEAD tag property is accessed on a context + before it is finalized. + + +.. class:: AlreadyUpdated + + This is raised when additional data is added to a context after update + has already been called. + + .. class:: UnsupportedAlgorithm This is raised when a backend doesn't support the requested algorithm (or diff --git a/docs/glossary.rst b/docs/glossary.rst index b6f2d06f..63e0a6ce 100644 --- a/docs/glossary.rst +++ b/docs/glossary.rst @@ -28,3 +28,14 @@ Glossary asymmetric cryptography Cryptographic operations where encryption and decryption use different keys. There are separate encryption and decryption keys. + + authentication + The process of verifying that a message was created by a specific + individual (or program). Like encryption, authentication can be either + symmetric or asymmetric. Authentication is necessary for effective + encryption. + + Ciphertext indistinguishability + This is a property of encryption systems whereby two encrypted messages + aren't distinguishable without knowing the encryption key. This is + considered a basic, necessary property for a working encryption system. diff --git a/docs/hazmat/bindings/interfaces.rst b/docs/hazmat/bindings/interfaces.rst index c55d86dc..711c82c2 100644 --- a/docs/hazmat/bindings/interfaces.rst +++ b/docs/hazmat/bindings/interfaces.rst @@ -69,6 +69,8 @@ A specific ``backend`` may provide one or more of these interfaces. :returns: :class:`~cryptography.hazmat.primitives.interfaces.CipherContext` + :raises ValueError: When tag is not None in an AEAD mode + .. method:: create_symmetric_decryption_ctx(cipher, mode) @@ -86,6 +88,8 @@ A specific ``backend`` may provide one or more of these interfaces. :returns: :class:`~cryptography.hazmat.primitives.interfaces.CipherContext` + :raises ValueError: When tag is None in an AEAD mode + .. class:: HashBackend diff --git a/docs/hazmat/bindings/openssl.rst b/docs/hazmat/bindings/openssl.rst index 194eeb92..d6bfa672 100644 --- a/docs/hazmat/bindings/openssl.rst +++ b/docs/hazmat/bindings/openssl.rst @@ -21,5 +21,5 @@ These are `CFFI`_ bindings to the `OpenSSL`_ C library. and access constants. -.. _`CFFI`: http://cffi.readthedocs.org/ +.. _`CFFI`: https://cffi.readthedocs.org/ .. _`OpenSSL`: https://www.openssl.org/ diff --git a/docs/hazmat/primitives/constant-time.rst b/docs/hazmat/primitives/constant-time.rst new file mode 100644 index 00000000..632e7c68 --- /dev/null +++ b/docs/hazmat/primitives/constant-time.rst @@ -0,0 +1,38 @@ +.. hazmat:: + +Constant time functions +======================= + +.. currentmodule:: cryptography.hazmat.primitives.constant_time + +This module contains functions for operating with secret data in a way that +does not leak information about that data through how long it takes to perform +the operation. These functions should be used whenever operating on secret data +along with data that is user supplied. + +An example would be comparing a HMAC signature received from a client to the +one generated by the server code for authentication purposes. + +For more information about this sort of issue, see `Coda Hale's blog post`_ +about the timing attacks on KeyCzar and Java's ``MessageDigest.isEqual()``. + + +.. function:: bytes_eq(a, b) + + Compare ``a`` and ``b`` to one another in constant time if they are of the + same length. + + .. doctest:: + + >>> from cryptography.hazmat.primitives import constant_time + >>> constant_time.bytes_eq(b"foo", b"foo") + True + >>> constant_time.bytes_eq(b"foo", b"bar") + False + + :param a bytes: The left-hand side. + :param b bytes: The right-hand side. + :returns boolean: True if ``a`` has the same bytes as ``b``. + + +.. _`Coda Hale's blog post`: http://codahale.com/a-lesson-in-timing-attacks/ diff --git a/docs/hazmat/primitives/index.rst b/docs/hazmat/primitives/index.rst index 614c414a..b115fdbc 100644 --- a/docs/hazmat/primitives/index.rst +++ b/docs/hazmat/primitives/index.rst @@ -10,4 +10,5 @@ Primitives hmac symmetric-encryption padding + constant-time interfaces diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst index 4ab91408..ef6f0871 100644 --- a/docs/hazmat/primitives/symmetric-encryption.rst +++ b/docs/hazmat/primitives/symmetric-encryption.rst @@ -12,9 +12,6 @@ Symmetric Encryption key = binascii.unhexlify(b"0" * 32) iv = binascii.unhexlify(b"0" * 32) - from cryptography.hazmat.bindings import default_backend - backend = default_backend() - Symmetric encryption is a way to encrypt (hide the plaintext value) material where the sender and receiver both use the same key. Note that symmetric @@ -37,6 +34,8 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_. .. doctest:: >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes + >>> from cryptography.hazmat.bindings import default_backend + >>> backend = default_backend() >>> cipher = Cipher(algorithms.AES(key), modes.CBC(iv), backend=backend) >>> encryptor = cipher.encryptor() >>> ct = encryptor.update(b"a secret message") + encryptor.finalize() @@ -89,7 +88,7 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_. Block ciphers require that plaintext or ciphertext always be a multiple of their block size, because of that **padding** is often required to make a message the correct size. ``CipherContext`` will not automatically apply - any padding; you'll need to add your own. For block ciphers the reccomended + any padding; you'll need to add your own. For block ciphers the recommended padding is :class:`cryptography.hazmat.primitives.padding.PKCS7`. If you are using a stream cipher mode (such as :class:`cryptography.hazmat.primitives.modes.CTR`) you don't have to worry @@ -118,6 +117,36 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_. :meth:`update` and :meth:`finalize` will raise :class:`~cryptography.exceptions.AlreadyFinalized`. +.. class:: AEADCipherContext + + When calling ``encryptor()`` or ``decryptor()`` on a ``Cipher`` object + with an AEAD mode you will receive a return object conforming to the + ``AEADCipherContext`` interface (in addition to the ``CipherContext`` + interface). If it is an encryption context it will additionally be an + ``AEADEncryptionContext`` interface. ``AEADCipherContext`` contains an + additional method ``authenticate_additional_data`` for adding additional + authenticated but unencrypted data. You should call this before calls to + ``update``. When you are done call ``finalize()`` to finish the operation. + + .. method:: authenticate_additional_data(data) + + :param bytes data: The data you wish to authenticate but not encrypt. + :raises: :class:`~cryptography.exceptions.AlreadyFinalized` + +.. class:: AEADEncryptionContext + + When creating an encryption context using ``encryptor()`` on a ``Cipher`` + object with an AEAD mode you will receive a return object conforming to the + ``AEADEncryptionContext`` interface (as well as ``AEADCipherContext``). + This interface provides one additional attribute ``tag``. ``tag`` can only + be obtained after ``finalize()``. + + .. attribute:: tag + + :return bytes: Returns the tag value as bytes. + :raises: :class:`~cryptography.exceptions.NotYetFinalized` if called + before the context is finalized. + .. _symmetric-encryption-algorithms: Algorithms @@ -200,8 +229,9 @@ Weak Ciphers .. doctest:: >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes + >>> from cryptography.hazmat.bindings import default_backend >>> algorithm = algorithms.ARC4(key) - >>> cipher = Cipher(algorithm, mode=None, backend=backend) + >>> cipher = Cipher(algorithm, mode=None, backend=default_backend()) >>> encryptor = cipher.encryptor() >>> ct = encryptor.update(b"a secret message") >>> decryptor = cipher.decryptor() @@ -295,6 +325,49 @@ Modes reuse an ``initialization_vector`` with a given ``key``. +.. class:: GCM(initialization_vector, tag=None) + + .. danger:: + + When using this mode you MUST not use the decrypted data until + :meth:`~cryptography.hazmat.primitives.interfaces.CipherContext.finalize` + has been called. GCM provides NO guarantees of ciphertext integrity + until decryption is complete. + + GCM (Galois Counter Mode) is a mode of operation for block ciphers. An + AEAD (authenticated encryption with additional data) mode is a type of + block cipher mode that encrypts the message as well as authenticating it + (and optionally additional data that is not encrypted) simultaneously. + Additional means of verifying integrity (like + :doc:`HMAC </hazmat/primitives/hmac>`) are not necessary. + + :param bytes initialization_vector: Must be random bytes. They do not need + to be kept secret (they can be included + in a transmitted message). NIST + `recommends 96-bit IV length`_ for + performance critical situations, but it + can be up to 2\ :sup:`64` - 1 bits. + Do not reuse an ``initialization_vector`` + with a given ``key``. + + :param bytes tag: The tag bytes to verify during decryption. When encrypting + this must be None. + + .. doctest:: + + >>> from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes + >>> from cryptography.hazmat.bindings import default_backend + >>> cipher = Cipher(algorithms.AES(key), modes.GCM(iv), backend=default_backend()) + >>> encryptor = cipher.encryptor() + >>> encryptor.authenticate_additional_data(b"authenticated but not encrypted payload") + >>> ct = encryptor.update(b"a secret message") + encryptor.finalize() + >>> tag = encryptor.tag + >>> cipher = Cipher(algorithms.AES(key), modes.GCM(iv, tag), backend) + >>> decryptor = cipher.decryptor() + >>> decryptor.authenticate_additional_data(b"authenticated but not encrypted payload") + >>> decryptor.update(ct) + decryptor.finalize() + 'a secret message' + Insecure Modes -------------- @@ -314,3 +387,4 @@ Insecure Modes .. _`described by Colin Percival`: http://www.daemonology.net/blog/2009-06-11-cryptographic-right-answers.html +.. _`recommends 96-bit IV length`: http://csrc.nist.gov/groups/ST/toolkit/BCM/documents/proposedmodes/gcm/gcm-spec.pdf diff --git a/docs/index.rst b/docs/index.rst index b9bf1735..0b023276 100644 --- a/docs/index.rst +++ b/docs/index.rst @@ -1,18 +1,27 @@ Welcome to ``cryptography`` =========================== -.. warning:: +``cryptography`` is a Python library which exposes cryptographic recipes and +primitives. We hope it'll be your one-stop-shop for all your cryptographic +needs in Python. - ``cryptography`` is very young, and very incomplete. +Installing +---------- -``cryptography`` is a Python library which exposes cryptographic recipes and -primitives. +We don't yet have a release on PyPI, for now you can install ``cryptography`` +directly from Github: + +.. code-block:: console + + $ pip install git+https://github.com/pyca/cryptography Why a new crypto library for Python? ------------------------------------ -We wanted to address a few issues with existing cryptography libraries in -Python: +If you've done cryptographic work in Python before, you've probably seen some +other libraries in Python, such as *M2Crypto*, *PyCrypto*, or *PyOpenSSL*. In +building ``cryptography`` we wanted to address a few issues we observed in the +existing libraries: * Lack of PyPy and Python 3 support. * Lack of maintenance. |