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class InvalidPaddingError(Exception):
pass
class Padding:
"""Base class for padding and unpadding."""
def __init__(self, block_size):
self.block_size = block_size
def pad(self, value):
raise NotImplementedError('Subclasses must implement this!')
def unpad(self, value):
raise NotImplementedError('Subclasses must implement this!')
class PKCS5Padding(Padding):
"""Provide PKCS5 padding and unpadding."""
def pad(self, value):
if not isinstance(value, bytes):
value = value.encode()
padding_length = (self.block_size - len(value) % self.block_size)
padding_sequence = padding_length * bytes((padding_length,))
value_with_padding = value + padding_sequence
return value_with_padding
def unpad(self, value):
# Perform some input validations.
# In case of error, we throw a generic InvalidPaddingError()
if not value or len(value) < self.block_size:
# PKCS5 padded output will always be at least 1 block size
raise InvalidPaddingError()
if len(value) % self.block_size != 0:
# PKCS5 padded output will be a multiple of the block size
raise InvalidPaddingError()
if isinstance(value, bytes):
padding_length = value[-1]
if isinstance(value, str):
padding_length = ord(value[-1])
if padding_length == 0 or padding_length > self.block_size:
raise InvalidPaddingError()
def convert_byte_or_char_to_number(x):
return ord(x) if isinstance(x, str) else x
if any([padding_length != convert_byte_or_char_to_number(x)
for x in value[-padding_length:]]):
raise InvalidPaddingError()
value_without_padding = value[0:-padding_length]
return value_without_padding
class OneAndZeroesPadding(Padding):
"""Provide the one and zeroes padding and unpadding.
This mechanism pads with 0x80 followed by zero bytes.
For unpadding it strips off all trailing zero bytes and the 0x80 byte.
"""
BYTE_80 = 0x80
BYTE_00 = 0x00
def pad(self, value):
if not isinstance(value, bytes):
value = value.encode()
padding_length = (self.block_size - len(value) % self.block_size)
one_part_bytes = bytes((self.BYTE_80,))
zeroes_part_bytes = (padding_length - 1) * bytes((self.BYTE_00,))
padding_sequence = one_part_bytes + zeroes_part_bytes
value_with_padding = value + padding_sequence
return value_with_padding
def unpad(self, value):
value_without_padding = value.rstrip(bytes((self.BYTE_00,)))
value_without_padding = value_without_padding.rstrip(
bytes((self.BYTE_80,)))
return value_without_padding
class ZeroesPadding(Padding):
"""Provide zeroes padding and unpadding.
This mechanism pads with 0x00 except the last byte equals
to the padding length. For unpadding it reads the last byte
and strips off that many bytes.
"""
BYTE_00 = 0x00
def pad(self, value):
if not isinstance(value, bytes):
value = value.encode()
padding_length = (self.block_size - len(value) % self.block_size)
zeroes_part_bytes = (padding_length - 1) * bytes((self.BYTE_00,))
last_part_bytes = bytes((padding_length,))
padding_sequence = zeroes_part_bytes + last_part_bytes
value_with_padding = value + padding_sequence
return value_with_padding
def unpad(self, value):
if isinstance(value, bytes):
padding_length = value[-1]
if isinstance(value, str):
padding_length = ord(value[-1])
value_without_padding = value[0:-padding_length]
return value_without_padding
class NaivePadding(Padding):
"""Naive padding and unpadding using '*'.
The class is provided only for backwards compatibility.
"""
CHARACTER = b'*'
def pad(self, value):
num_of_bytes = (self.block_size - len(value) % self.block_size)
value_with_padding = value + num_of_bytes * self.CHARACTER
return value_with_padding
def unpad(self, value):
value_without_padding = value.rstrip(self.CHARACTER)
return value_without_padding
PADDING_MECHANISM = {
'pkcs5': PKCS5Padding,
'oneandzeroes': OneAndZeroesPadding,
'zeroes': ZeroesPadding,
'naive': NaivePadding
}
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