Merge branch 'master' into fernet

5 files changed, 123 insertions, 6 deletions

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