From 0ab3e44b0512a6cbab845a65759a21787bf15d27 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Fri, 22 Nov 2013 12:52:18 -0800
Subject: Raise a correct error when content isn't padded correctly

---
 cryptography/exceptions.py                      |  4 ++++
 cryptography/hazmat/bindings/openssl/backend.py | 22 ++++++++++++++++++++--
 cryptography/hazmat/bindings/openssl/err.py     |  7 +++++++
 tests/hazmat/primitives/test_block.py           | 20 +++++++++++++++++++-
 4 files changed, 50 insertions(+), 3 deletions(-)

diff --git a/cryptography/exceptions.py b/cryptography/exceptions.py
index c2e71493..a39674f9 100644
--- a/cryptography/exceptions.py
+++ b/cryptography/exceptions.py
@@ -18,3 +18,7 @@ class UnsupportedAlgorithm(Exception):
 
 class AlreadyFinalized(Exception):
     pass
+
+
+class IncorrectPadding(Exception):
+    pass
diff --git a/cryptography/hazmat/bindings/openssl/backend.py b/cryptography/hazmat/bindings/openssl/backend.py
index db4d18e7..0071da5d 100644
--- a/cryptography/hazmat/bindings/openssl/backend.py
+++ b/cryptography/hazmat/bindings/openssl/backend.py
@@ -19,7 +19,7 @@ import sys
 import cffi
 
 from cryptography import utils
-from cryptography.exceptions import UnsupportedAlgorithm
+from cryptography.exceptions import UnsupportedAlgorithm, IncorrectPadding
 from cryptography.hazmat.bindings.interfaces import (
     CipherBackend, HashBackend, HMACBackend
 )
@@ -193,6 +193,22 @@ class Backend(object):
     def create_symmetric_decryption_ctx(self, cipher, mode):
         return _CipherContext(self, cipher, mode, _CipherContext._DECRYPT)
 
+    def _handle_error(self):
+        code = self.lib.ERR_get_error()
+        assert code != 0
+        lib = self.lib.ERR_GET_LIB(code)
+        func = self.lib.ERR_GET_FUNC(code)
+        reason = self.lib.ERR_GET_REASON(code)
+
+        if lib == self.lib.ERR_LIB_EVP:
+            if func == self.lib.EVP_F_EVP_ENCRYPTFINAL_EX:
+                if reason == self.lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH:
+                    raise IncorrectPadding
+            elif func == self.lib.EVP_F_EVP_DECRYPTFINAL_EX:
+                if reason == self.lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH:
+                    raise IncorrectPadding
+        assert False
+
 
 class GetCipherByName(object):
     def __init__(self, fmt):
@@ -268,7 +284,9 @@ class _CipherContext(object):
         buf = self._backend.ffi.new("unsigned char[]", self._cipher.block_size)
         outlen = self._backend.ffi.new("int *")
         res = self._backend.lib.EVP_CipherFinal_ex(self._ctx, buf, outlen)
-        assert res != 0
+        if res == 0:
+            self._backend._handle_error()
+
         res = self._backend.lib.EVP_CIPHER_CTX_cleanup(self._ctx)
         assert res == 1
         return self._backend.ffi.buffer(buf)[:outlen[0]]
diff --git a/cryptography/hazmat/bindings/openssl/err.py b/cryptography/hazmat/bindings/openssl/err.py
index 6a36dee0..3dac6948 100644
--- a/cryptography/hazmat/bindings/openssl/err.py
+++ b/cryptography/hazmat/bindings/openssl/err.py
@@ -21,6 +21,13 @@ struct ERR_string_data_st {
     const char *string;
 };
 typedef struct ERR_string_data_st ERR_STRING_DATA;
+
+static const int ERR_LIB_EVP;
+
+static const int EVP_F_EVP_ENCRYPTFINAL_EX;
+static const int EVP_F_EVP_DECRYPTFINAL_EX;
+
+static const int EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH;
 """
 
 FUNCTIONS = """
diff --git a/tests/hazmat/primitives/test_block.py b/tests/hazmat/primitives/test_block.py
index 9460c53d..4c756203 100644
--- a/tests/hazmat/primitives/test_block.py
+++ b/tests/hazmat/primitives/test_block.py
@@ -18,7 +18,9 @@ import binascii
 import pytest
 
 from cryptography import utils
-from cryptography.exceptions import UnsupportedAlgorithm, AlreadyFinalized
+from cryptography.exceptions import (
+    UnsupportedAlgorithm, AlreadyFinalized, IncorrectPadding
+)
 from cryptography.hazmat.primitives import interfaces
 from cryptography.hazmat.primitives.ciphers import (
     Cipher, algorithms, modes
@@ -108,3 +110,19 @@ class TestCipherContext(object):
 
         with pytest.raises(UnsupportedAlgorithm):
             cipher.decryptor()
+
+    def test_incorrectly_padded(self, backend):
+        cipher = Cipher(
+            algorithms.AES(b"\x00" * 16),
+            modes.CBC(b"\x00" * 16),
+            backend
+        )
+        encryptor = cipher.encryptor()
+        encryptor.update(b"1")
+        with pytest.raises(IncorrectPadding):
+            encryptor.finalize()
+
+        decryptor = cipher.decryptor()
+        decryptor.update(b"1")
+        with pytest.raises(IncorrectPadding):
+            decryptor.finalize()
-- 
cgit v1.2.3


From 797dd83d81915d5bab8791e513fcb26051870eb7 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Fri, 22 Nov 2013 13:08:58 -0800
Subject: Documentation!

---
 docs/hazmat/primitives/symmetric-encryption.rst | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index eef359d6..35b0d9a8 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -75,6 +75,15 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_.
     everything into the context. Once that is done call ``finalize()`` to
     finish the operation and obtain the remainder of the data.
 
+    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
+    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
+    about this.
+
     .. method:: update(data)
 
         :param bytes data: The data you wish to pass into the context.
@@ -90,6 +99,13 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_.
     .. method:: finalize()
 
         :return bytes: Returns the remainder of the data.
+        :raises cryptography.exceptions.IncorrectPadding: This is raised when
+                                                          the data provided
+                                                          isn't correctly
+                                                          padded to be a
+                                                          multiple of the
+                                                          algorithm's block
+                                                          size.
 
         Once ``finalize`` is called this object can no longer be used and
         :meth:`update` and :meth:`finalize` will raise
-- 
cgit v1.2.3


From f1569b6abbba6920ca343c62721098e0ce8c7f9c Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Fri, 22 Nov 2013 13:09:38 -0800
Subject: One more documentation

---
 docs/exceptions.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/docs/exceptions.rst b/docs/exceptions.rst
index ab1b28fe..b0435b0c 100644
--- a/docs/exceptions.rst
+++ b/docs/exceptions.rst
@@ -13,3 +13,7 @@ Exceptions
     This is raised when a backend doesn't support the requested algorithm (or
     combination of algorithms).
 
+
+.. class:: IncorrectPadding
+
+    This is raised when a block cipher's content isn't correctly padded.
-- 
cgit v1.2.3


From d203710bba3f2eb15a2e2db38a20305540af2eea Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Fri, 22 Nov 2013 13:12:02 -0800
Subject: Better, but still not covered

---
 cryptography/hazmat/bindings/openssl/backend.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/cryptography/hazmat/bindings/openssl/backend.py b/cryptography/hazmat/bindings/openssl/backend.py
index 0071da5d..99f11f45 100644
--- a/cryptography/hazmat/bindings/openssl/backend.py
+++ b/cryptography/hazmat/bindings/openssl/backend.py
@@ -207,7 +207,9 @@ class Backend(object):
             elif func == self.lib.EVP_F_EVP_DECRYPTFINAL_EX:
                 if reason == self.lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH:
                     raise IncorrectPadding
-        assert False
+        raise SystemError(
+            "Unknown error code from OpenSSL, you should probably file a bug"
+        )
 
 
 class GetCipherByName(object):
-- 
cgit v1.2.3


From 3edffe25ab91702842a7553b028d50086c58eef1 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Fri, 22 Nov 2013 14:31:52 -0800
Subject: include the error message

---
 cryptography/hazmat/bindings/openssl/backend.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/cryptography/hazmat/bindings/openssl/backend.py b/cryptography/hazmat/bindings/openssl/backend.py
index 99f11f45..ae951717 100644
--- a/cryptography/hazmat/bindings/openssl/backend.py
+++ b/cryptography/hazmat/bindings/openssl/backend.py
@@ -207,8 +207,11 @@ class Backend(object):
             elif func == self.lib.EVP_F_EVP_DECRYPTFINAL_EX:
                 if reason == self.lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH:
                     raise IncorrectPadding
+
+        message = self.ffi.string(self.lib.ERR_reason_error_string(code))
         raise SystemError(
-            "Unknown error code from OpenSSL, you should probably file a bug"
+            "Unknown error code from OpenSSL, you should probably file a bug. "
+            "Cause: %s" % message
         )
 
 
-- 
cgit v1.2.3


From e247d0be584c52e25694918ad2345dadde3fefa9 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Fri, 22 Nov 2013 16:24:06 -0800
Subject: Coverage

---
 cryptography/hazmat/bindings/openssl/backend.py | 6 +++---
 tests/hazmat/bindings/test_openssl.py           | 4 ++++
 2 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/cryptography/hazmat/bindings/openssl/backend.py b/cryptography/hazmat/bindings/openssl/backend.py
index ae951717..77ecf277 100644
--- a/cryptography/hazmat/bindings/openssl/backend.py
+++ b/cryptography/hazmat/bindings/openssl/backend.py
@@ -199,7 +199,9 @@ class Backend(object):
         lib = self.lib.ERR_GET_LIB(code)
         func = self.lib.ERR_GET_FUNC(code)
         reason = self.lib.ERR_GET_REASON(code)
+        return self._handle_error_code(lib, func, reason)
 
+    def _handle_error_code(self, lib, func, reason):
         if lib == self.lib.ERR_LIB_EVP:
             if func == self.lib.EVP_F_EVP_ENCRYPTFINAL_EX:
                 if reason == self.lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH:
@@ -208,10 +210,8 @@ class Backend(object):
                 if reason == self.lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH:
                     raise IncorrectPadding
 
-        message = self.ffi.string(self.lib.ERR_reason_error_string(code))
         raise SystemError(
-            "Unknown error code from OpenSSL, you should probably file a bug. "
-            "Cause: %s" % message
+            "Unknown error code from OpenSSL, you should probably file a bug."
         )
 
 
diff --git a/tests/hazmat/bindings/test_openssl.py b/tests/hazmat/bindings/test_openssl.py
index 9f27aab7..7ad1ea75 100644
--- a/tests/hazmat/bindings/test_openssl.py
+++ b/tests/hazmat/bindings/test_openssl.py
@@ -70,3 +70,7 @@ class TestOpenSSL(object):
         )
         with pytest.raises(UnsupportedAlgorithm):
             cipher.encryptor()
+
+    def test_handle_unknown_error(self):
+        with pytest.raises(SystemError):
+            backend._handle_error_code(0, 0, 0)
-- 
cgit v1.2.3


From bae899ad36bcb99dbec94aaf026ef1650f2b1242 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Fri, 22 Nov 2013 16:54:55 -0800
Subject: Change teh exception

---
 cryptography/exceptions.py                      |  4 ----
 cryptography/hazmat/bindings/openssl/backend.py |  6 +++---
 docs/exceptions.rst                             |  5 -----
 docs/hazmat/primitives/padding.rst              |  8 +++++++-
 docs/hazmat/primitives/symmetric-encryption.rst | 10 +++-------
 tests/hazmat/primitives/test_block.py           |  8 +++-----
 6 files changed, 16 insertions(+), 25 deletions(-)

diff --git a/cryptography/exceptions.py b/cryptography/exceptions.py
index a39674f9..c2e71493 100644
--- a/cryptography/exceptions.py
+++ b/cryptography/exceptions.py
@@ -18,7 +18,3 @@ class UnsupportedAlgorithm(Exception):
 
 class AlreadyFinalized(Exception):
     pass
-
-
-class IncorrectPadding(Exception):
-    pass
diff --git a/cryptography/hazmat/bindings/openssl/backend.py b/cryptography/hazmat/bindings/openssl/backend.py
index 77ecf277..b2599d22 100644
--- a/cryptography/hazmat/bindings/openssl/backend.py
+++ b/cryptography/hazmat/bindings/openssl/backend.py
@@ -19,7 +19,7 @@ import sys
 import cffi
 
 from cryptography import utils
-from cryptography.exceptions import UnsupportedAlgorithm, IncorrectPadding
+from cryptography.exceptions import UnsupportedAlgorithm
 from cryptography.hazmat.bindings.interfaces import (
     CipherBackend, HashBackend, HMACBackend
 )
@@ -205,10 +205,10 @@ class Backend(object):
         if lib == self.lib.ERR_LIB_EVP:
             if func == self.lib.EVP_F_EVP_ENCRYPTFINAL_EX:
                 if reason == self.lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH:
-                    raise IncorrectPadding
+                    raise ValueError
             elif func == self.lib.EVP_F_EVP_DECRYPTFINAL_EX:
                 if reason == self.lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH:
-                    raise IncorrectPadding
+                    raise ValueError
 
         raise SystemError(
             "Unknown error code from OpenSSL, you should probably file a bug."
diff --git a/docs/exceptions.rst b/docs/exceptions.rst
index b0435b0c..c6f5a7cc 100644
--- a/docs/exceptions.rst
+++ b/docs/exceptions.rst
@@ -12,8 +12,3 @@ Exceptions
 
     This is raised when a backend doesn't support the requested algorithm (or
     combination of algorithms).
-
-
-.. class:: IncorrectPadding
-
-    This is raised when a block cipher's content isn't correctly padded.
diff --git a/docs/hazmat/primitives/padding.rst b/docs/hazmat/primitives/padding.rst
index aebb4d4d..4d79ac8f 100644
--- a/docs/hazmat/primitives/padding.rst
+++ b/docs/hazmat/primitives/padding.rst
@@ -25,8 +25,14 @@ multiple of the block size.
         >>> padder = padding.PKCS7(128).padder()
         >>> padder.update(b"1111111111")
         ''
-        >>> padder.finalize()
+        >>> padded_data = padder.finalize()
+        >>> padded_data
         '1111111111\x06\x06\x06\x06\x06\x06'
+        >>> unpadder = padding.PKCS7(128).unpadder()
+        >>> unpadder.update(padded_data)
+        ''
+        >>> unpadder.finalize()
+        '1111111111'
 
     :param block_size: The size of the block in bits that the data is being
                        padded to.
diff --git a/docs/hazmat/primitives/symmetric-encryption.rst b/docs/hazmat/primitives/symmetric-encryption.rst
index 35b0d9a8..732af33c 100644
--- a/docs/hazmat/primitives/symmetric-encryption.rst
+++ b/docs/hazmat/primitives/symmetric-encryption.rst
@@ -99,13 +99,9 @@ an "encrypt-then-MAC" formulation as `described by Colin Percival`_.
     .. method:: finalize()
 
         :return bytes: Returns the remainder of the data.
-        :raises cryptography.exceptions.IncorrectPadding: This is raised when
-                                                          the data provided
-                                                          isn't correctly
-                                                          padded to be a
-                                                          multiple of the
-                                                          algorithm's block
-                                                          size.
+        :raises ValueError: This is raised when the data provided isn't
+                            correctly padded to be a multiple of the
+                            algorithm's block size.
 
         Once ``finalize`` is called this object can no longer be used and
         :meth:`update` and :meth:`finalize` will raise
diff --git a/tests/hazmat/primitives/test_block.py b/tests/hazmat/primitives/test_block.py
index 4c756203..ea40127e 100644
--- a/tests/hazmat/primitives/test_block.py
+++ b/tests/hazmat/primitives/test_block.py
@@ -18,9 +18,7 @@ import binascii
 import pytest
 
 from cryptography import utils
-from cryptography.exceptions import (
-    UnsupportedAlgorithm, AlreadyFinalized, IncorrectPadding
-)
+from cryptography.exceptions import UnsupportedAlgorithm, AlreadyFinalized
 from cryptography.hazmat.primitives import interfaces
 from cryptography.hazmat.primitives.ciphers import (
     Cipher, algorithms, modes
@@ -119,10 +117,10 @@ class TestCipherContext(object):
         )
         encryptor = cipher.encryptor()
         encryptor.update(b"1")
-        with pytest.raises(IncorrectPadding):
+        with pytest.raises(ValueError):
             encryptor.finalize()
 
         decryptor = cipher.decryptor()
         decryptor.update(b"1")
-        with pytest.raises(IncorrectPadding):
+        with pytest.raises(ValueError):
             decryptor.finalize()
-- 
cgit v1.2.3


From b7e8990aabb46ac6c0511530d7a67f69e08f1788 Mon Sep 17 00:00:00 2001
From: Alex Gaynor <alex.gaynor@gmail.com>
Date: Fri, 22 Nov 2013 16:58:34 -0800
Subject: Useful error message

---
 cryptography/hazmat/bindings/openssl/backend.py | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/cryptography/hazmat/bindings/openssl/backend.py b/cryptography/hazmat/bindings/openssl/backend.py
index b2599d22..9f8ea939 100644
--- a/cryptography/hazmat/bindings/openssl/backend.py
+++ b/cryptography/hazmat/bindings/openssl/backend.py
@@ -205,10 +205,16 @@ class Backend(object):
         if lib == self.lib.ERR_LIB_EVP:
             if func == self.lib.EVP_F_EVP_ENCRYPTFINAL_EX:
                 if reason == self.lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH:
-                    raise ValueError
+                    raise ValueError(
+                        "The length of the provided data is not a multiple of "
+                        "the block length"
+                    )
             elif func == self.lib.EVP_F_EVP_DECRYPTFINAL_EX:
                 if reason == self.lib.EVP_R_DATA_NOT_MULTIPLE_OF_BLOCK_LENGTH:
-                    raise ValueError
+                    raise ValueError(
+                        "The length of the provided data is not a multiple of "
+                        "the block length"
+                    )
 
         raise SystemError(
             "Unknown error code from OpenSSL, you should probably file a bug."
-- 
cgit v1.2.3