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cryptography
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hazmat
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primitives
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padding.py
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# This file is dual licensed under the terms of the Apache License, Version # 2.0, and the BSD License. See the LICENSE file in the root of this repository # for complete details. from __future__ import annotations import abc import typing from cryptography import utils from cryptography.exceptions import AlreadyFinalized from cryptography.hazmat.bindings._rust import ( check_ansix923_padding, check_pkcs7_padding, ) class PaddingContext(metaclass=abc.ABCMeta): @abc.abstractmethod def update(self, data: bytes) -> bytes: """ Pads the provided bytes and returns any available data as bytes. """ @abc.abstractmethod def finalize(self) -> bytes: """ Finalize the padding, returns bytes. """ def _byte_padding_check(block_size: int) -> None: if not (0 <= block_size <= 2040): raise ValueError("block_size must be in range(0, 2041).") if block_size % 8 != 0: raise ValueError("block_size must be a multiple of 8.") def _byte_padding_update( buffer_: typing.Optional[bytes], data: bytes, block_size: int ) -> typing.Tuple[bytes, bytes]: if buffer_ is None: raise AlreadyFinalized("Context was already finalized.") utils._check_byteslike("data", data) buffer_ += bytes(data) finished_blocks = len(buffer_) // (block_size // 8) result = buffer_[: finished_blocks * (block_size // 8)] buffer_ = buffer_[finished_blocks * (block_size // 8) :] return buffer_, result def _byte_padding_pad( buffer_: typing.Optional[bytes], block_size: int, paddingfn: typing.Callable[[int], bytes], ) -> bytes: if buffer_ is None: raise AlreadyFinalized("Context was already finalized.") pad_size = block_size // 8 - len(buffer_) return buffer_ + paddingfn(pad_size) def _byte_unpadding_update( buffer_: typing.Optional[bytes], data: bytes, block_size: int ) -> typing.Tuple[bytes, bytes]: if buffer_ is None: raise AlreadyFinalized("Context was already finalized.") utils._check_byteslike("data", data) buffer_ += bytes(data) finished_blocks = max(len(buffer_) // (block_size // 8) - 1, 0) result = buffer_[: finished_blocks * (block_size // 8)] buffer_ = buffer_[finished_blocks * (block_size // 8) :] return buffer_, result def _byte_unpadding_check( buffer_: typing.Optional[bytes], block_size: int, checkfn: typing.Callable[[bytes], int], ) -> bytes: if buffer_ is None: raise AlreadyFinalized("Context was already finalized.") if len(buffer_) != block_size // 8: raise ValueError("Invalid padding bytes.") valid = checkfn(buffer_) if not valid: raise ValueError("Invalid padding bytes.") pad_size = buffer_[-1] return buffer_[:-pad_size] class PKCS7: def __init__(self, block_size: int): _byte_padding_check(block_size) self.block_size = block_size def padder(self) -> PaddingContext: return _PKCS7PaddingContext(self.block_size) def unpadder(self) -> PaddingContext: return _PKCS7UnpaddingContext(self.block_size) class _PKCS7PaddingContext(PaddingContext): _buffer: typing.Optional[bytes] def __init__(self, block_size: int): self.block_size = block_size # TODO: more copies than necessary, we should use zero-buffer (#193) self._buffer = b"" def update(self, data: bytes) -> bytes: self._buffer, result = _byte_padding_update( self._buffer, data, self.block_size ) return result def _padding(self, size: int) -> bytes: return bytes([size]) * size def finalize(self) -> bytes: result = _byte_padding_pad( self._buffer, self.block_size, self._padding ) self._buffer = None return result class _PKCS7UnpaddingContext(PaddingContext): _buffer: typing.Optional[bytes] def __init__(self, block_size: int): self.block_size = block_size # TODO: more copies than necessary, we should use zero-buffer (#193) self._buffer = b"" def update(self, data: bytes) -> bytes: self._buffer, result = _byte_unpadding_update( self._buffer, data, self.block_size ) return result def finalize(self) -> bytes: result = _byte_unpadding_check( self._buffer, self.block_size, check_pkcs7_padding ) self._buffer = None return result class ANSIX923: def __init__(self, block_size: int): _byte_padding_check(block_size) self.block_size = block_size def padder(self) -> PaddingContext: return _ANSIX923PaddingContext(self.block_size) def unpadder(self) -> PaddingContext: return _ANSIX923UnpaddingContext(self.block_size) class _ANSIX923PaddingContext(PaddingContext): _buffer: typing.Optional[bytes] def __init__(self, block_size: int): self.block_size = block_size # TODO: more copies than necessary, we should use zero-buffer (#193) self._buffer = b"" def update(self, data: bytes) -> bytes: self._buffer, result = _byte_padding_update( self._buffer, data, self.block_size ) return result def _padding(self, size: int) -> bytes: return bytes([0]) * (size - 1) + bytes([size]) def finalize(self) -> bytes: result = _byte_padding_pad( self._buffer, self.block_size, self._padding ) self._buffer = None return result class _ANSIX923UnpaddingContext(PaddingContext): _buffer: typing.Optional[bytes] def __init__(self, block_size: int): self.block_size = block_size # TODO: more copies than necessary, we should use zero-buffer (#193) self._buffer = b"" def update(self, data: bytes) -> bytes: self._buffer, result = _byte_unpadding_update( self._buffer, data, self.block_size ) return result def finalize(self) -> bytes: result = _byte_unpadding_check( self._buffer, self.block_size, check_ansix923_padding, ) self._buffer = None return result