Added support for padding ANSI X.923
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index a203a16..60d46d5 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -6,6 +6,8 @@
.. note:: This version is not yet released and is under active development.
+* Added support for padding ANSI X.923 with
+ :class:`~cryptography.hazmat.primitives.padding.ANSIX923`.
* Deprecated support for OpenSSL 0.9.8. Support will be removed in
``cryptography`` 1.4.
diff --git a/docs/hazmat/primitives/padding.rst b/docs/hazmat/primitives/padding.rst
index a60f5ac..37e4252 100644
--- a/docs/hazmat/primitives/padding.rst
+++ b/docs/hazmat/primitives/padding.rst
@@ -54,6 +54,47 @@
provider.
+.. class:: ANSIX923(block_size)
+
+ ANSI X.923 padding works by appending ``N-1`` bytes with the value of ``0``
+ and a last byte with the value of ``chr(N)``, where ``N`` is the number of
+ bytes required to make the final block of data the same size as the block
+ size. A simple example of padding is:
+
+ .. doctest::
+
+ >>> padder = padding.ANSIX923(128).padder()
+ >>> padded_data = padder.update(b"11111111111111112222222222")
+ >>> padded_data
+ '1111111111111111'
+ >>> padded_data += padder.finalize()
+ >>> padded_data
+ '11111111111111112222222222\x00\x00\x00\x00\x00\x06'
+ >>> unpadder = padding.ANSIX923(128).unpadder()
+ >>> data = unpadder.update(padded_data)
+ >>> data
+ '1111111111111111'
+ >>> data + unpadder.finalize()
+ '11111111111111112222222222'
+
+ :param block_size: The size of the block in bits that the data is being
+ padded to.
+ :raises ValueError: Raised if block size is not a multiple of 8 or is not
+ between 0 and 256.
+
+ .. method:: padder()
+
+ :returns: A padding
+ :class:`~cryptography.hazmat.primitives.padding.PaddingContext`
+ provider
+
+ .. method:: unpadder()
+
+ :returns: An unpadding
+ :class:`~cryptography.hazmat.primitives.padding.PaddingContext`
+ provider.
+
+
.. class:: PaddingContext
When calling ``padder()`` or ``unpadder()`` the result will conform to the
diff --git a/src/cryptography/hazmat/primitives/padding.py b/src/cryptography/hazmat/primitives/padding.py
index f6491eb..72ebff2 100644
--- a/src/cryptography/hazmat/primitives/padding.py
+++ b/src/cryptography/hazmat/primitives/padding.py
@@ -68,12 +68,15 @@
return result
+ def _padding(self, size):
+ return six.int2byte(size) * size
+
def finalize(self):
if self._buffer is None:
raise AlreadyFinalized("Context was already finalized.")
pad_size = self.block_size // 8 - len(self._buffer)
- result = self._buffer + six.int2byte(pad_size) * pad_size
+ result = self._buffer + self._padding(pad_size)
self._buffer = None
return result
@@ -104,6 +107,11 @@
return result
+ def _check_padding(self):
+ return lib.Cryptography_check_pkcs7_padding(
+ self._buffer, self.block_size // 8
+ )
+
def finalize(self):
if self._buffer is None:
raise AlreadyFinalized("Context was already finalized.")
@@ -111,9 +119,7 @@
if len(self._buffer) != self.block_size // 8:
raise ValueError("Invalid padding bytes.")
- valid = lib.Cryptography_check_pkcs7_padding(
- self._buffer, self.block_size // 8
- )
+ valid = self._check_padding()
if not valid:
raise ValueError("Invalid padding bytes.")
@@ -122,3 +128,26 @@
res = self._buffer[:-pad_size]
self._buffer = None
return res
+
+
+class ANSIX923(PKCS7):
+
+ def padder(self):
+ return _ANSIX923PaddingContext(self.block_size)
+
+ def unpadder(self):
+ return _ANSIX923UnpaddingContext(self.block_size)
+
+
+@utils.register_interface(PaddingContext)
+class _ANSIX923PaddingContext(_PKCS7PaddingContext):
+
+ def _padding(self, size):
+ return six.int2byte(0) * (size - 1) + six.int2byte(size)
+
+
+@utils.register_interface(PaddingContext)
+class _ANSIX923UnpaddingContext(_PKCS7UnpaddingContext):
+
+ def _check_padding(self):
+ return True
diff --git a/tests/hazmat/primitives/test_padding.py b/tests/hazmat/primitives/test_padding.py
index 392ea73..9da8ea7 100644
--- a/tests/hazmat/primitives/test_padding.py
+++ b/tests/hazmat/primitives/test_padding.py
@@ -99,3 +99,51 @@
unpadder.update(b"")
with pytest.raises(AlreadyFinalized):
unpadder.finalize()
+
+
+class TestANSIX923(object):
+ @pytest.mark.parametrize(("size", "unpadded", "padded"), [
+ (
+ 128,
+ b"1111111111",
+ b"1111111111\x00\x00\x00\x00\x00\x06",
+ ),
+ (
+ 128,
+ b"111111111111111122222222222222",
+ b"111111111111111122222222222222\x00\x02",
+ ),
+ (
+ 128,
+ b"1" * 16,
+ b"1" * 16 + b"\x00" * 15 + b"\x10",
+ ),
+ (
+ 128,
+ b"1" * 17,
+ b"1" * 17 + b"\x00" * 14 + b"\x0F",
+ )
+ ])
+ def test_pad(self, size, unpadded, padded):
+ padder = padding.ANSIX923(size).padder()
+ result = padder.update(unpadded)
+ result += padder.finalize()
+ assert result == padded
+
+ @pytest.mark.parametrize(("size", "unpadded", "padded"), [
+ (
+ 128,
+ b"1111111111",
+ b"1111111111\x00\x00\x00\x00\x00\x06",
+ ),
+ (
+ 128,
+ b"111111111111111122222222222222",
+ b"111111111111111122222222222222\x00\x02",
+ ),
+ ])
+ def test_unpad(self, size, unpadded, padded):
+ unpadder = padding.ANSIX923(size).unpadder()
+ result = unpadder.update(padded)
+ result += unpadder.finalize()
+ assert result == unpadded
diff --git a/tests/hypothesis/test_padding.py b/tests/hypothesis/test_padding.py
index 21c9a23..29d726f 100644
--- a/tests/hypothesis/test_padding.py
+++ b/tests/hypothesis/test_padding.py
@@ -5,7 +5,7 @@
from hypothesis import given
from hypothesis.strategies import binary, integers
-from cryptography.hazmat.primitives.padding import PKCS7
+from cryptography.hazmat.primitives.padding import ANSIX923, PKCS7
@given(integers(min_value=1, max_value=31), binary())
@@ -19,3 +19,14 @@
padded = padder.update(data) + padder.finalize()
assert unpadder.update(padded) + unpadder.finalize() == data
+
+
+@given(integers(min_value=1, max_value=31), binary())
+def test_ansix923(block_size, data):
+ a = ANSIX923(block_size=block_size * 8)
+ padder = a.padder()
+ unpadder = a.unpadder()
+
+ padded = padder.update(data) + padder.finalize()
+
+ assert unpadder.update(padded) + unpadder.finalize() == data