Add verify function to hmac and hashes.

8 files changed, 90 insertions, 6 deletions

diff --git a/cryptography/exceptions.py b/cryptography/exceptions.py
index e9d88199..44363c24 100644
--- a/cryptography/exceptions.py
+++ b/cryptography/exceptions.py
@@ -30,3 +30,7 @@ class NotYetFinalized(Exception):
 
 class InvalidTag(Exception):
     pass
+
+
+class InvalidSignature(Exception):
+    pass
diff --git a/cryptography/hazmat/primitives/hashes.py b/cryptography/hazmat/primitives/hashes.py
index bee188b3..b3c626d4 100644
--- a/cryptography/hazmat/primitives/hashes.py
+++ b/cryptography/hazmat/primitives/hashes.py
@@ -16,8 +16,8 @@ from __future__ import absolute_import, division, print_function
 import six
 
 from cryptography import utils
-from cryptography.exceptions import AlreadyFinalized
-from cryptography.hazmat.primitives import interfaces
+from cryptography.exceptions import AlreadyFinalized, InvalidSignature
+from cryptography.hazmat.primitives import constant_time, interfaces
 
 
 @utils.register_interface(interfaces.HashContext)
@@ -55,6 +55,13 @@ class Hash(object):
         self._ctx = None
         return digest
 
+    def verify(self, sig):
+        if isinstance(sig, six.text_type):
+            raise TypeError("Unicode-objects must be encoded before verifying")
+        digest = self.finalize()
+        if not constant_time.bytes_eq(digest, sig):
+            raise InvalidSignature("Signature did not match digest.")
+
 
 @utils.register_interface(interfaces.HashAlgorithm)
 class SHA1(object):
diff --git a/cryptography/hazmat/primitives/hmac.py b/cryptography/hazmat/primitives/hmac.py
index 618bccc5..8ade84aa 100644
--- a/cryptography/hazmat/primitives/hmac.py
+++ b/cryptography/hazmat/primitives/hmac.py
@@ -16,8 +16,8 @@ from __future__ import absolute_import, division, print_function
 import six
 
 from cryptography import utils
-from cryptography.exceptions import AlreadyFinalized
-from cryptography.hazmat.primitives import interfaces
+from cryptography.exceptions import AlreadyFinalized, InvalidSignature
+from cryptography.hazmat.primitives import constant_time, interfaces
 
 
 @utils.register_interface(interfaces.HashContext)
@@ -57,3 +57,10 @@ class HMAC(object):
         digest = self._ctx.finalize()
         self._ctx = None
         return digest
+
+    def verify(self, sig):
+        if isinstance(sig, six.text_type):
+            raise TypeError("Unicode-objects must be encoded before verifying")
+        digest = self.finalize()
+        if not constant_time.bytes_eq(digest, sig):
+            raise InvalidSignature("Signature did not match digest.")
diff --git a/cryptography/hazmat/primitives/interfaces.py b/cryptography/hazmat/primitives/interfaces.py
index e3f4f586..76dc9339 100644
--- a/cryptography/hazmat/primitives/interfaces.py
+++ b/cryptography/hazmat/primitives/interfaces.py
@@ -152,3 +152,9 @@ class HashContext(six.with_metaclass(abc.ABCMeta)):
         """
         return a HashContext that is a copy of the current context.
         """
+
+    @abc.abstractmethod
+    def verify(self, sig):
+        """
+        compare digest to sig and raise exception if not equal.
+        """
diff --git a/docs/hazmat/primitives/cryptographic-hashes.rst b/docs/hazmat/primitives/cryptographic-hashes.rst
index 90ca198a..02c7b5e1 100644
--- a/docs/hazmat/primitives/cryptographic-hashes.rst
+++ b/docs/hazmat/primitives/cryptographic-hashes.rst
@@ -67,6 +67,13 @@ Message Digests
 
         :return bytes: The message digest as bytes.
 
+    .. method:: verify(sig)
+
+        Finalize the current context and securely compare digest to sig.
+
+        :raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize`
+        :raises cryptography.exceptions.InvalidSignature: If sig does not match digest
+
 
 .. _cryptographic-hash-algorithms:
 
diff --git a/docs/hazmat/primitives/hmac.rst b/docs/hazmat/primitives/hmac.rst
index 0c0d0220..b556bd6a 100644
--- a/docs/hazmat/primitives/hmac.rst
+++ b/docs/hazmat/primitives/hmac.rst
@@ -69,3 +69,10 @@ message.
 
         :return bytes: The message digest as bytes.
         :raises cryptography.exceptions.AlreadyFinalized:
+
+    .. method:: verify(sig)
+
+        Finalize the current context and securely compare digest to sig.
+
+        :raises cryptography.exceptions.AlreadyFinalized: See :meth:`finalize`
+        :raises cryptography.exceptions.InvalidSignature: If sig does not match digest
diff --git a/tests/hazmat/primitives/test_hashes.py b/tests/hazmat/primitives/test_hashes.py
index ff42e8f4..cd58b065 100644
--- a/tests/hazmat/primitives/test_hashes.py
+++ b/tests/hazmat/primitives/test_hashes.py
@@ -19,7 +19,7 @@ import pytest
 
 import six
 
-from cryptography.exceptions import AlreadyFinalized
+from cryptography.exceptions import AlreadyFinalized, InvalidSignature
 from cryptography.hazmat.primitives import hashes
 
 from .utils import generate_base_hash_test
@@ -57,6 +57,29 @@ class TestHashContext(object):
         with pytest.raises(AlreadyFinalized):
             h.finalize()
 
+    def test_verify(self, backend):
+        h = hashes.Hash(hashes.SHA1(), backend=backend)
+        digest = h.finalize()
+
+        h = hashes.Hash(hashes.SHA1(), backend=backend)
+        h.verify(digest)
+
+        with pytest.raises(AlreadyFinalized):
+            h.verify(b'')
+
+    def test_invalid_verify(self, backend):
+        h = hashes.Hash(hashes.SHA1(), backend=backend)
+        with pytest.raises(InvalidSignature):
+            h.verify(b'')
+
+        with pytest.raises(AlreadyFinalized):
+            h.verify(b'')
+
+    def test_verify_reject_unicode(self, backend):
+        h = hashes.Hash(hashes.SHA1(), backend=backend)
+        with pytest.raises(TypeError):
+            h.verify(six.u(''))
+
 
 class TestSHA1(object):
     test_SHA1 = generate_base_hash_test(
diff --git a/tests/hazmat/primitives/test_hmac.py b/tests/hazmat/primitives/test_hmac.py
index 992bcb1a..48360185 100644
--- a/tests/hazmat/primitives/test_hmac.py
+++ b/tests/hazmat/primitives/test_hmac.py
@@ -19,7 +19,7 @@ import pytest
 
 import six
 
-from cryptography.exceptions import AlreadyFinalized
+from cryptography.exceptions import AlreadyFinalized, InvalidSignature
 from cryptography.hazmat.primitives import hashes, hmac
 
 from .utils import generate_base_hmac_test
@@ -63,3 +63,26 @@ class TestHMAC(object):
 
         with pytest.raises(AlreadyFinalized):
             h.finalize()
+
+    def test_verify(self, backend):
+        h = hmac.HMAC(b'', hashes.SHA1(), backend=backend)
+        digest = h.finalize()
+
+        h = hmac.HMAC(b'', hashes.SHA1(), backend=backend)
+        h.verify(digest)
+
+        with pytest.raises(AlreadyFinalized):
+            h.verify(b'')
+
+    def test_invalid_verify(self, backend):
+        h = hmac.HMAC(b'', hashes.SHA1(), backend=backend)
+        with pytest.raises(InvalidSignature):
+            h.verify(b'')
+
+        with pytest.raises(AlreadyFinalized):
+            h.verify(b'')
+
+    def test_verify_reject_unicode(self, backend):
+        h = hmac.HMAC(b'', hashes.SHA1(), backend=backend)
+        with pytest.raises(TypeError):
+            h.verify(six.u(''))