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1# This file is dual licensed under the terms of the Apache License, Version
2# 2.0, and the BSD License. See the LICENSE file in the root of this repository
3# for complete details.
4
5from __future__ import absolute_import, division, print_function
6
7import abc
8
9import six
10
11from cryptography import utils
12from cryptography.exceptions import AlreadyFinalized
13from cryptography.hazmat.bindings._padding import lib
14
15
16@six.add_metaclass(abc.ABCMeta)
17class PaddingContext(object):
18    @abc.abstractmethod
19    def update(self, data):
20        """
21        Pads the provided bytes and returns any available data as bytes.
22        """
23
24    @abc.abstractmethod
25    def finalize(self):
26        """
27        Finalize the padding, returns bytes.
28        """
29
30
31def _byte_padding_check(block_size):
32    if not (0 <= block_size <= 2040):
33        raise ValueError("block_size must be in range(0, 2041).")
34
35    if block_size % 8 != 0:
36        raise ValueError("block_size must be a multiple of 8.")
37
38
39def _byte_padding_update(buffer_, data, block_size):
40    if buffer_ is None:
41        raise AlreadyFinalized("Context was already finalized.")
42
43    utils._check_byteslike("data", data)
44
45    # six.PY2: Only coerce non-bytes objects to avoid triggering bad behavior
46    # of future's newbytes type. Unconditionally call bytes() after Python 2
47    # support is gone.
48    buffer_ += data if isinstance(data, bytes) else bytes(data)
49
50    finished_blocks = len(buffer_) // (block_size // 8)
51
52    result = buffer_[: finished_blocks * (block_size // 8)]
53    buffer_ = buffer_[finished_blocks * (block_size // 8) :]
54
55    return buffer_, result
56
57
58def _byte_padding_pad(buffer_, block_size, paddingfn):
59    if buffer_ is None:
60        raise AlreadyFinalized("Context was already finalized.")
61
62    pad_size = block_size // 8 - len(buffer_)
63    return buffer_ + paddingfn(pad_size)
64
65
66def _byte_unpadding_update(buffer_, data, block_size):
67    if buffer_ is None:
68        raise AlreadyFinalized("Context was already finalized.")
69
70    utils._check_byteslike("data", data)
71
72    # six.PY2: Only coerce non-bytes objects to avoid triggering bad behavior
73    # of future's newbytes type. Unconditionally call bytes() after Python 2
74    # support is gone.
75    buffer_ += data if isinstance(data, bytes) else bytes(data)
76
77    finished_blocks = max(len(buffer_) // (block_size // 8) - 1, 0)
78
79    result = buffer_[: finished_blocks * (block_size // 8)]
80    buffer_ = buffer_[finished_blocks * (block_size // 8) :]
81
82    return buffer_, result
83
84
85def _byte_unpadding_check(buffer_, block_size, checkfn):
86    if buffer_ is None:
87        raise AlreadyFinalized("Context was already finalized.")
88
89    if len(buffer_) != block_size // 8:
90        raise ValueError("Invalid padding bytes.")
91
92    valid = checkfn(buffer_, block_size // 8)
93
94    if not valid:
95        raise ValueError("Invalid padding bytes.")
96
97    pad_size = six.indexbytes(buffer_, -1)
98    return buffer_[:-pad_size]
99
100
101class PKCS7(object):
102    def __init__(self, block_size):
103        _byte_padding_check(block_size)
104        self.block_size = block_size
105
106    def padder(self):
107        return _PKCS7PaddingContext(self.block_size)
108
109    def unpadder(self):
110        return _PKCS7UnpaddingContext(self.block_size)
111
112
113@utils.register_interface(PaddingContext)
114class _PKCS7PaddingContext(object):
115    def __init__(self, block_size):
116        self.block_size = block_size
117        # TODO: more copies than necessary, we should use zero-buffer (#193)
118        self._buffer = b""
119
120    def update(self, data):
121        self._buffer, result = _byte_padding_update(
122            self._buffer, data, self.block_size
123        )
124        return result
125
126    def _padding(self, size):
127        return six.int2byte(size) * size
128
129    def finalize(self):
130        result = _byte_padding_pad(
131            self._buffer, self.block_size, self._padding
132        )
133        self._buffer = None
134        return result
135
136
137@utils.register_interface(PaddingContext)
138class _PKCS7UnpaddingContext(object):
139    def __init__(self, block_size):
140        self.block_size = block_size
141        # TODO: more copies than necessary, we should use zero-buffer (#193)
142        self._buffer = b""
143
144    def update(self, data):
145        self._buffer, result = _byte_unpadding_update(
146            self._buffer, data, self.block_size
147        )
148        return result
149
150    def finalize(self):
151        result = _byte_unpadding_check(
152            self._buffer, self.block_size, lib.Cryptography_check_pkcs7_padding
153        )
154        self._buffer = None
155        return result
156
157
158class ANSIX923(object):
159    def __init__(self, block_size):
160        _byte_padding_check(block_size)
161        self.block_size = block_size
162
163    def padder(self):
164        return _ANSIX923PaddingContext(self.block_size)
165
166    def unpadder(self):
167        return _ANSIX923UnpaddingContext(self.block_size)
168
169
170@utils.register_interface(PaddingContext)
171class _ANSIX923PaddingContext(object):
172    def __init__(self, block_size):
173        self.block_size = block_size
174        # TODO: more copies than necessary, we should use zero-buffer (#193)
175        self._buffer = b""
176
177    def update(self, data):
178        self._buffer, result = _byte_padding_update(
179            self._buffer, data, self.block_size
180        )
181        return result
182
183    def _padding(self, size):
184        return six.int2byte(0) * (size - 1) + six.int2byte(size)
185
186    def finalize(self):
187        result = _byte_padding_pad(
188            self._buffer, self.block_size, self._padding
189        )
190        self._buffer = None
191        return result
192
193
194@utils.register_interface(PaddingContext)
195class _ANSIX923UnpaddingContext(object):
196    def __init__(self, block_size):
197        self.block_size = block_size
198        # TODO: more copies than necessary, we should use zero-buffer (#193)
199        self._buffer = b""
200
201    def update(self, data):
202        self._buffer, result = _byte_unpadding_update(
203            self._buffer, data, self.block_size
204        )
205        return result
206
207    def finalize(self):
208        result = _byte_unpadding_check(
209            self._buffer,
210            self.block_size,
211            lib.Cryptography_check_ansix923_padding,
212        )
213        self._buffer = None
214        return result
215