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# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import six
from cryptography import utils
from cryptography.hazmat.primitives import interfaces
class PKCS7(object):
def __init__(self, block_size):
if not (0 <= block_size < 256):
raise ValueError("block_size must be in range(0, 256)")
if block_size % 8 != 0:
raise ValueError("block_size must be a multiple of 8")
self.block_size = block_size
def padder(self):
return _PKCS7PaddingContext(self.block_size)
def unpadder(self):
return _PKCS7UnpaddingContext(self.block_size)
@utils.register_interface(interfaces.PaddingContext)
class _PKCS7PaddingContext(object):
def __init__(self, block_size):
self.block_size = block_size
# TODO: O(n ** 2) complexity for repeated concatentation, we should use
# zero-buffer (#193)
self._buffer = b""
def update(self, data):
if self._buffer is None:
raise ValueError("Context was already finalized")
if isinstance(data, six.text_type):
raise TypeError("Unicode-objects must be encoded before padding")
self._buffer += data
finished_blocks = len(self._buffer) // (self.block_size // 8)
result = self._buffer[:finished_blocks * (self.block_size // 8)]
self._buffer = self._buffer[finished_blocks * (self.block_size // 8):]
return result
def finalize(self):
if self._buffer is None:
raise ValueError("Context was already finalized")
pad_size = self.block_size // 8 - len(self._buffer)
result = self._buffer + six.int2byte(pad_size) * pad_size
self._buffer = None
return result
@utils.register_interface(interfaces.PaddingContext)
class _PKCS7UnpaddingContext(object):
def __init__(self, block_size):
self.block_size = block_size
# TODO: O(n ** 2) complexity for repeated concatentation, we should use
# zero-buffer (#193)
self._buffer = b""
def update(self, data):
if self._buffer is None:
raise ValueError("Context was already finalized")
if isinstance(data, six.text_type):
raise TypeError("Unicode-objects must be encoded before unpadding")
self._buffer += data
finished_blocks = max(
len(self._buffer) // (self.block_size // 8) - 1,
0
)
result = self._buffer[:finished_blocks * (self.block_size // 8)]
self._buffer = self._buffer[finished_blocks * (self.block_size // 8):]
return result
def finalize(self):
if self._buffer is None:
raise ValueError("Context was already finalized")
if len(self._buffer) != self.block_size // 8:
raise ValueError("Invalid padding bytes")
pad_size = six.indexbytes(self._buffer, -1)
if not (0 < pad_size <= self.block_size // 8):
raise ValueError("Invalid padding bytes")
mismatch = 0
for b in six.iterbytes(self._buffer[-pad_size:]):
mismatch |= b ^ pad_size
if mismatch != 0:
raise ValueError("Invalid padding bytes")
res = self._buffer[:-pad_size]
self._buffer = None
return res
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