Merge branch 'master' of https://github.com/pyca/cryptography into verify

Conflicts:
	tests/hazmat/primitives/test_hashes.py
	tests/hazmat/primitives/test_hmac.py

7 files changed, 53 insertions, 15 deletions

diff --git a/docs/hazmat/backends/index.rst b/docs/hazmat/backends/index.rst
index a89cf0d5..06951281 100644
--- a/docs/hazmat/backends/index.rst
+++ b/docs/hazmat/backends/index.rst
@@ -1,17 +1,10 @@
 .. hazmat::
 
-Bindings
+Backends
 ========
 
-.. toctree::
-    :maxdepth: 1
-
-    openssl
-    interfaces
-
-
-Getting a Backend Provider
-~~~~~~~~~~~~~~~~~~~~~~~~~~
+Getting a Backend
+-----------------
 
 .. currentmodule:: cryptography.hazmat.backends
 
@@ -19,8 +12,7 @@ Getting a Backend Provider
 the widest number of supported cryptographic algorithms as well as supporting
 platform specific implementations.
 
-You can get the default backend by calling
-:func:`~default_backend`.
+You can get the default backend by calling :func:`~default_backend`.
 
 The default backend will change over time as we implement new backends and
 the libraries we use in those backends changes.
@@ -32,3 +24,11 @@ the libraries we use in those backends changes.
         :class:`~interfaces.CipherBackend`, :class:`~interfaces.HashBackend`, and
         :class:`~interfaces.HMACBackend`.
 
+Individual Backends
+-------------------
+
+.. toctree::
+    :maxdepth: 1
+
+    openssl
+    interfaces
diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst
index b524943d..5b6cd64d 100644
--- a/docs/hazmat/backends/interfaces.rst
+++ b/docs/hazmat/backends/interfaces.rst
@@ -126,6 +126,17 @@ A specific ``backend`` may provide one or more of these interfaces.
     A backend with methods for using cryptographic hash functions as message
     authentication codes.
 
+    .. method:: hmac_supported(algorithm)
+
+        Check if the specified ``algorithm`` is supported by this backend.
+
+        :param algorithm: An instance of a
+            :class:`~cryptography.hazmat.primitives.interfaces.HashAlgorithm`
+            provider.
+
+        :returns: ``True`` if the specified ``algorithm`` is supported for HMAC
+            by this backend, otherwise ``False``.
+
     .. method:: create_hmac_ctx(algorithm)
 
         Create a
diff --git a/docs/hazmat/backends/openssl.rst b/docs/hazmat/backends/openssl.rst
index 12fbff04..5e51c75e 100644
--- a/docs/hazmat/backends/openssl.rst
+++ b/docs/hazmat/backends/openssl.rst
@@ -1,7 +1,7 @@
 .. hazmat::
 
-OpenSSL
-=======
+OpenSSL Backend
+===============
 
 These are `CFFI`_ bindings to the `OpenSSL`_ C library.
 
diff --git a/docs/hazmat/primitives/cryptographic-hashes.rst b/docs/hazmat/primitives/cryptographic-hashes.rst
index f6a3f7a1..f00dd3f5 100644
--- a/docs/hazmat/primitives/cryptographic-hashes.rst
+++ b/docs/hazmat/primitives/cryptographic-hashes.rst
@@ -28,6 +28,9 @@ Message Digests
         >>> digest.finalize()
         'l\xa1=R\xcap\xc8\x83\xe0\xf0\xbb\x10\x1eBZ\x89\xe8bM\xe5\x1d\xb2\xd29%\x93\xafj\x84\x11\x80\x90'
 
+    If the backend doesn't support the requested ``algorithm`` an
+    :class:`~cryptography.exceptions.UnsupportedAlgorithm` will be raised.
+
     Keep in mind that attacks against cryptographic hashes only get stronger
     with time, and that often algorithms that were once thought to be strong,
     become broken. Because of this it's important to include a plan for
diff --git a/docs/hazmat/primitives/hmac.rst b/docs/hazmat/primitives/hmac.rst
index 0c19f20c..b8f94fd2 100644
--- a/docs/hazmat/primitives/hmac.rst
+++ b/docs/hazmat/primitives/hmac.rst
@@ -34,6 +34,8 @@ message.
         >>> h.finalize()
         '#F\xdaI\x8b"e\xc4\xf1\xbb\x9a\x8fc\xff\xf5\xdex.\xbc\xcd/+\x8a\x86\x1d\x84\'\xc3\xa6\x1d\xd8J'
 
+    If the backend doesn't support the requested ``algorithm`` an
+    :class:`~cryptography.exceptions.UnsupportedAlgorithm` will be raised.
 
     :param key: Secret key as ``bytes``.
     :param algorithm: A
diff --git a/docs/hazmat/primitives/interfaces.rst b/docs/hazmat/primitives/interfaces.rst
index 11cff51a..361b723e 100644
--- a/docs/hazmat/primitives/interfaces.rst
+++ b/docs/hazmat/primitives/interfaces.rst
@@ -36,6 +36,17 @@ Symmetric Ciphers
         The number of bits in the key being used.
 
 
+.. class:: BlockCipherAlgorithm
+
+    A block cipher algorithm.
+
+    .. attribute:: block_size
+
+        :type: int
+
+        The number of bits in a block.
+
+
 Cipher Modes
 ------------
 
diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index f4d0457a..30896a05 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -61,7 +61,7 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_.
             provider.
 
         If the backend doesn't support the requested combination of ``cipher``
-        and ``mode`` an :class:`cryptography.exceptions.UnsupportedAlgorithm`
+        and ``mode`` an :class:`~cryptography.exceptions.UnsupportedAlgorithm`
         will be raised.
 
     .. method:: decryptor()
@@ -352,6 +352,16 @@ Modes
                                         Do not reuse an ``initialization_vector``
                                         with a given ``key``.
 
+    .. note::
+
+        Cryptography will emit a 128-bit tag when finalizing encryption.
+        You can shorten a tag by truncating it to the desired length, but this
+        is **not recommended** as it lowers the security margins of the
+        authentication (`NIST SP-800-38D`_ recommends 96-bits or greater).
+        If you must shorten the tag the minimum allowed length is 4 bytes
+        (32-bits). Applications **must** verify the tag is the expected length
+        to guarantee the expected security margin.
+
     :param bytes tag: The tag bytes to verify during decryption. When encrypting
                       this must be None.
 
@@ -390,3 +400,4 @@ 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
+.. _`NIST SP-800-38D`: http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf