394 lines
16 KiB
Python
394 lines
16 KiB
Python
|
# -*- coding: utf-8 -*-
|
||
|
|
#
|
||
|
|
# Cipher/mode_ctr.py : CTR mode
|
||
|
|
#
|
||
|
|
# ===================================================================
|
||
|
|
# The contents of this file are dedicated to the public domain. To
|
||
|
|
# the extent that dedication to the public domain is not available,
|
||
|
|
# everyone is granted a worldwide, perpetual, royalty-free,
|
||
|
|
# non-exclusive license to exercise all rights associated with the
|
||
|
|
# contents of this file for any purpose whatsoever.
|
||
|
|
# No rights are reserved.
|
||
|
|
#
|
||
|
|
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
|
||
|
|
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
|
||
|
|
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
|
||
|
|
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
|
||
|
|
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
|
||
|
|
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
|
||
|
|
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
|
||
|
|
# SOFTWARE.
|
||
|
|
# ===================================================================
|
||
|
|
|
||
|
|
"""
|
||
|
|
Counter (CTR) mode.
|
||
|
|
"""
|
||
|
|
|
||
|
|
__all__ = ['CtrMode']
|
||
|
|
|
||
|
|
import struct
|
||
|
|
|
||
|
|
from Cryptodome.Util._raw_api import (load_pycryptodome_raw_lib, VoidPointer,
|
||
|
|
create_string_buffer, get_raw_buffer,
|
||
|
|
SmartPointer, c_size_t, c_uint8_ptr,
|
||
|
|
is_writeable_buffer)
|
||
|
|
|
||
|
|
from Cryptodome.Random import get_random_bytes
|
||
|
|
from Cryptodome.Util.py3compat import _copy_bytes, is_native_int
|
||
|
|
from Cryptodome.Util.number import long_to_bytes
|
||
|
|
|
||
|
|
raw_ctr_lib = load_pycryptodome_raw_lib("Cryptodome.Cipher._raw_ctr", """
|
||
|
|
int CTR_start_operation(void *cipher,
|
||
|
|
uint8_t initialCounterBlock[],
|
||
|
|
size_t initialCounterBlock_len,
|
||
|
|
size_t prefix_len,
|
||
|
|
unsigned counter_len,
|
||
|
|
unsigned littleEndian,
|
||
|
|
void **pResult);
|
||
|
|
int CTR_encrypt(void *ctrState,
|
||
|
|
const uint8_t *in,
|
||
|
|
uint8_t *out,
|
||
|
|
size_t data_len);
|
||
|
|
int CTR_decrypt(void *ctrState,
|
||
|
|
const uint8_t *in,
|
||
|
|
uint8_t *out,
|
||
|
|
size_t data_len);
|
||
|
|
int CTR_stop_operation(void *ctrState);"""
|
||
|
|
)
|
||
|
|
|
||
|
|
|
||
|
|
class CtrMode(object):
|
||
|
|
"""*CounTeR (CTR)* mode.
|
||
|
|
|
||
|
|
This mode is very similar to ECB, in that
|
||
|
|
encryption of one block is done independently of all other blocks.
|
||
|
|
|
||
|
|
Unlike ECB, the block *position* contributes to the encryption
|
||
|
|
and no information leaks about symbol frequency.
|
||
|
|
|
||
|
|
Each message block is associated to a *counter* which
|
||
|
|
must be unique across all messages that get encrypted
|
||
|
|
with the same key (not just within the same message).
|
||
|
|
The counter is as big as the block size.
|
||
|
|
|
||
|
|
Counters can be generated in several ways. The most
|
||
|
|
straightword one is to choose an *initial counter block*
|
||
|
|
(which can be made public, similarly to the *IV* for the
|
||
|
|
other modes) and increment its lowest **m** bits by one
|
||
|
|
(modulo *2^m*) for each block. In most cases, **m** is
|
||
|
|
chosen to be half the block size.
|
||
|
|
|
||
|
|
See `NIST SP800-38A`_, Section 6.5 (for the mode) and
|
||
|
|
Appendix B (for how to manage the *initial counter block*).
|
||
|
|
|
||
|
|
.. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
|
||
|
|
|
||
|
|
:undocumented: __init__
|
||
|
|
"""
|
||
|
|
|
||
|
|
def __init__(self, block_cipher, initial_counter_block,
|
||
|
|
prefix_len, counter_len, little_endian):
|
||
|
|
"""Create a new block cipher, configured in CTR mode.
|
||
|
|
|
||
|
|
:Parameters:
|
||
|
|
block_cipher : C pointer
|
||
|
|
A smart pointer to the low-level block cipher instance.
|
||
|
|
|
||
|
|
initial_counter_block : bytes/bytearray/memoryview
|
||
|
|
The initial plaintext to use to generate the key stream.
|
||
|
|
|
||
|
|
It is as large as the cipher block, and it embeds
|
||
|
|
the initial value of the counter.
|
||
|
|
|
||
|
|
This value must not be reused.
|
||
|
|
It shall contain a nonce or a random component.
|
||
|
|
Reusing the *initial counter block* for encryptions
|
||
|
|
performed with the same key compromises confidentiality.
|
||
|
|
|
||
|
|
prefix_len : integer
|
||
|
|
The amount of bytes at the beginning of the counter block
|
||
|
|
that never change.
|
||
|
|
|
||
|
|
counter_len : integer
|
||
|
|
The length in bytes of the counter embedded in the counter
|
||
|
|
block.
|
||
|
|
|
||
|
|
little_endian : boolean
|
||
|
|
True if the counter in the counter block is an integer encoded
|
||
|
|
in little endian mode. If False, it is big endian.
|
||
|
|
"""
|
||
|
|
|
||
|
|
if len(initial_counter_block) == prefix_len + counter_len:
|
||
|
|
self.nonce = _copy_bytes(None, prefix_len, initial_counter_block)
|
||
|
|
"""Nonce; not available if there is a fixed suffix"""
|
||
|
|
|
||
|
|
self._state = VoidPointer()
|
||
|
|
result = raw_ctr_lib.CTR_start_operation(block_cipher.get(),
|
||
|
|
c_uint8_ptr(initial_counter_block),
|
||
|
|
c_size_t(len(initial_counter_block)),
|
||
|
|
c_size_t(prefix_len),
|
||
|
|
counter_len,
|
||
|
|
little_endian,
|
||
|
|
self._state.address_of())
|
||
|
|
if result:
|
||
|
|
raise ValueError("Error %X while instantiating the CTR mode"
|
||
|
|
% result)
|
||
|
|
|
||
|
|
# Ensure that object disposal of this Python object will (eventually)
|
||
|
|
# free the memory allocated by the raw library for the cipher mode
|
||
|
|
self._state = SmartPointer(self._state.get(),
|
||
|
|
raw_ctr_lib.CTR_stop_operation)
|
||
|
|
|
||
|
|
# Memory allocated for the underlying block cipher is now owed
|
||
|
|
# by the cipher mode
|
||
|
|
block_cipher.release()
|
||
|
|
|
||
|
|
self.block_size = len(initial_counter_block)
|
||
|
|
"""The block size of the underlying cipher, in bytes."""
|
||
|
|
|
||
|
|
self._next = ["encrypt", "decrypt"]
|
||
|
|
|
||
|
|
def encrypt(self, plaintext, output=None):
|
||
|
|
"""Encrypt data with the key and the parameters set at initialization.
|
||
|
|
|
||
|
|
A cipher object is stateful: once you have encrypted a message
|
||
|
|
you cannot encrypt (or decrypt) another message using the same
|
||
|
|
object.
|
||
|
|
|
||
|
|
The data to encrypt can be broken up in two or
|
||
|
|
more pieces and `encrypt` can be called multiple times.
|
||
|
|
|
||
|
|
That is, the statement:
|
||
|
|
|
||
|
|
>>> c.encrypt(a) + c.encrypt(b)
|
||
|
|
|
||
|
|
is equivalent to:
|
||
|
|
|
||
|
|
>>> c.encrypt(a+b)
|
||
|
|
|
||
|
|
This function does not add any padding to the plaintext.
|
||
|
|
|
||
|
|
:Parameters:
|
||
|
|
plaintext : bytes/bytearray/memoryview
|
||
|
|
The piece of data to encrypt.
|
||
|
|
It can be of any length.
|
||
|
|
:Keywords:
|
||
|
|
output : bytearray/memoryview
|
||
|
|
The location where the ciphertext must be written to.
|
||
|
|
If ``None``, the ciphertext is returned.
|
||
|
|
:Return:
|
||
|
|
If ``output`` is ``None``, the ciphertext is returned as ``bytes``.
|
||
|
|
Otherwise, ``None``.
|
||
|
|
"""
|
||
|
|
|
||
|
|
if "encrypt" not in self._next:
|
||
|
|
raise TypeError("encrypt() cannot be called after decrypt()")
|
||
|
|
self._next = ["encrypt"]
|
||
|
|
|
||
|
|
if output is None:
|
||
|
|
ciphertext = create_string_buffer(len(plaintext))
|
||
|
|
else:
|
||
|
|
ciphertext = output
|
||
|
|
|
||
|
|
if not is_writeable_buffer(output):
|
||
|
|
raise TypeError("output must be a bytearray or a writeable memoryview")
|
||
|
|
|
||
|
|
if len(plaintext) != len(output):
|
||
|
|
raise ValueError("output must have the same length as the input"
|
||
|
|
" (%d bytes)" % len(plaintext))
|
||
|
|
|
||
|
|
result = raw_ctr_lib.CTR_encrypt(self._state.get(),
|
||
|
|
c_uint8_ptr(plaintext),
|
||
|
|
c_uint8_ptr(ciphertext),
|
||
|
|
c_size_t(len(plaintext)))
|
||
|
|
if result:
|
||
|
|
if result == 0x60002:
|
||
|
|
raise OverflowError("The counter has wrapped around in"
|
||
|
|
" CTR mode")
|
||
|
|
raise ValueError("Error %X while encrypting in CTR mode" % result)
|
||
|
|
|
||
|
|
if output is None:
|
||
|
|
return get_raw_buffer(ciphertext)
|
||
|
|
else:
|
||
|
|
return None
|
||
|
|
|
||
|
|
def decrypt(self, ciphertext, output=None):
|
||
|
|
"""Decrypt data with the key and the parameters set at initialization.
|
||
|
|
|
||
|
|
A cipher object is stateful: once you have decrypted a message
|
||
|
|
you cannot decrypt (or encrypt) another message with the same
|
||
|
|
object.
|
||
|
|
|
||
|
|
The data to decrypt can be broken up in two or
|
||
|
|
more pieces and `decrypt` can be called multiple times.
|
||
|
|
|
||
|
|
That is, the statement:
|
||
|
|
|
||
|
|
>>> c.decrypt(a) + c.decrypt(b)
|
||
|
|
|
||
|
|
is equivalent to:
|
||
|
|
|
||
|
|
>>> c.decrypt(a+b)
|
||
|
|
|
||
|
|
This function does not remove any padding from the plaintext.
|
||
|
|
|
||
|
|
:Parameters:
|
||
|
|
ciphertext : bytes/bytearray/memoryview
|
||
|
|
The piece of data to decrypt.
|
||
|
|
It can be of any length.
|
||
|
|
:Keywords:
|
||
|
|
output : bytearray/memoryview
|
||
|
|
The location where the plaintext must be written to.
|
||
|
|
If ``None``, the plaintext is returned.
|
||
|
|
:Return:
|
||
|
|
If ``output`` is ``None``, the plaintext is returned as ``bytes``.
|
||
|
|
Otherwise, ``None``.
|
||
|
|
"""
|
||
|
|
|
||
|
|
if "decrypt" not in self._next:
|
||
|
|
raise TypeError("decrypt() cannot be called after encrypt()")
|
||
|
|
self._next = ["decrypt"]
|
||
|
|
|
||
|
|
if output is None:
|
||
|
|
plaintext = create_string_buffer(len(ciphertext))
|
||
|
|
else:
|
||
|
|
plaintext = output
|
||
|
|
|
||
|
|
if not is_writeable_buffer(output):
|
||
|
|
raise TypeError("output must be a bytearray or a writeable memoryview")
|
||
|
|
|
||
|
|
if len(ciphertext) != len(output):
|
||
|
|
raise ValueError("output must have the same length as the input"
|
||
|
|
" (%d bytes)" % len(plaintext))
|
||
|
|
|
||
|
|
result = raw_ctr_lib.CTR_decrypt(self._state.get(),
|
||
|
|
c_uint8_ptr(ciphertext),
|
||
|
|
c_uint8_ptr(plaintext),
|
||
|
|
c_size_t(len(ciphertext)))
|
||
|
|
if result:
|
||
|
|
if result == 0x60002:
|
||
|
|
raise OverflowError("The counter has wrapped around in"
|
||
|
|
" CTR mode")
|
||
|
|
raise ValueError("Error %X while decrypting in CTR mode" % result)
|
||
|
|
|
||
|
|
if output is None:
|
||
|
|
return get_raw_buffer(plaintext)
|
||
|
|
else:
|
||
|
|
return None
|
||
|
|
|
||
|
|
|
||
|
|
def _create_ctr_cipher(factory, **kwargs):
|
||
|
|
"""Instantiate a cipher object that performs CTR encryption/decryption.
|
||
|
|
|
||
|
|
:Parameters:
|
||
|
|
factory : module
|
||
|
|
The underlying block cipher, a module from ``Cryptodome.Cipher``.
|
||
|
|
|
||
|
|
:Keywords:
|
||
|
|
nonce : bytes/bytearray/memoryview
|
||
|
|
The fixed part at the beginning of the counter block - the rest is
|
||
|
|
the counter number that gets increased when processing the next block.
|
||
|
|
The nonce must be such that no two messages are encrypted under the
|
||
|
|
same key and the same nonce.
|
||
|
|
|
||
|
|
The nonce must be shorter than the block size (it can have
|
||
|
|
zero length; the counter is then as long as the block).
|
||
|
|
|
||
|
|
If this parameter is not present, a random nonce will be created with
|
||
|
|
length equal to half the block size. No random nonce shorter than
|
||
|
|
64 bits will be created though - you must really think through all
|
||
|
|
security consequences of using such a short block size.
|
||
|
|
|
||
|
|
initial_value : posive integer or bytes/bytearray/memoryview
|
||
|
|
The initial value for the counter. If not present, the cipher will
|
||
|
|
start counting from 0. The value is incremented by one for each block.
|
||
|
|
The counter number is encoded in big endian mode.
|
||
|
|
|
||
|
|
counter : object
|
||
|
|
Instance of ``Cryptodome.Util.Counter``, which allows full customization
|
||
|
|
of the counter block. This parameter is incompatible to both ``nonce``
|
||
|
|
and ``initial_value``.
|
||
|
|
|
||
|
|
Any other keyword will be passed to the underlying block cipher.
|
||
|
|
See the relevant documentation for details (at least ``key`` will need
|
||
|
|
to be present).
|
||
|
|
"""
|
||
|
|
|
||
|
|
cipher_state = factory._create_base_cipher(kwargs)
|
||
|
|
|
||
|
|
counter = kwargs.pop("counter", None)
|
||
|
|
nonce = kwargs.pop("nonce", None)
|
||
|
|
initial_value = kwargs.pop("initial_value", None)
|
||
|
|
if kwargs:
|
||
|
|
raise TypeError("Invalid parameters for CTR mode: %s" % str(kwargs))
|
||
|
|
|
||
|
|
if counter is not None and (nonce, initial_value) != (None, None):
|
||
|
|
raise TypeError("'counter' and 'nonce'/'initial_value'"
|
||
|
|
" are mutually exclusive")
|
||
|
|
|
||
|
|
if counter is None:
|
||
|
|
# Cryptodome.Util.Counter is not used
|
||
|
|
if nonce is None:
|
||
|
|
if factory.block_size < 16:
|
||
|
|
raise TypeError("Impossible to create a safe nonce for short"
|
||
|
|
" block sizes")
|
||
|
|
nonce = get_random_bytes(factory.block_size // 2)
|
||
|
|
else:
|
||
|
|
if len(nonce) >= factory.block_size:
|
||
|
|
raise ValueError("Nonce is too long")
|
||
|
|
|
||
|
|
# What is not nonce is counter
|
||
|
|
counter_len = factory.block_size - len(nonce)
|
||
|
|
|
||
|
|
if initial_value is None:
|
||
|
|
initial_value = 0
|
||
|
|
|
||
|
|
if is_native_int(initial_value):
|
||
|
|
if (1 << (counter_len * 8)) - 1 < initial_value:
|
||
|
|
raise ValueError("Initial counter value is too large")
|
||
|
|
initial_counter_block = nonce + long_to_bytes(initial_value, counter_len)
|
||
|
|
else:
|
||
|
|
if len(initial_value) != counter_len:
|
||
|
|
raise ValueError("Incorrect length for counter byte string (%d bytes, expected %d)" %
|
||
|
|
(len(initial_value), counter_len))
|
||
|
|
initial_counter_block = nonce + initial_value
|
||
|
|
|
||
|
|
return CtrMode(cipher_state,
|
||
|
|
initial_counter_block,
|
||
|
|
len(nonce), # prefix
|
||
|
|
counter_len,
|
||
|
|
False) # little_endian
|
||
|
|
|
||
|
|
# Cryptodome.Util.Counter is used
|
||
|
|
|
||
|
|
# 'counter' used to be a callable object, but now it is
|
||
|
|
# just a dictionary for backward compatibility.
|
||
|
|
_counter = dict(counter)
|
||
|
|
try:
|
||
|
|
counter_len = _counter.pop("counter_len")
|
||
|
|
prefix = _counter.pop("prefix")
|
||
|
|
suffix = _counter.pop("suffix")
|
||
|
|
initial_value = _counter.pop("initial_value")
|
||
|
|
little_endian = _counter.pop("little_endian")
|
||
|
|
except KeyError:
|
||
|
|
raise TypeError("Incorrect counter object"
|
||
|
|
" (use Cryptodome.Util.Counter.new)")
|
||
|
|
|
||
|
|
# Compute initial counter block
|
||
|
|
words = []
|
||
|
|
while initial_value > 0:
|
||
|
|
words.append(struct.pack('B', initial_value & 255))
|
||
|
|
initial_value >>= 8
|
||
|
|
words += [b'\x00'] * max(0, counter_len - len(words))
|
||
|
|
if not little_endian:
|
||
|
|
words.reverse()
|
||
|
|
initial_counter_block = prefix + b"".join(words) + suffix
|
||
|
|
|
||
|
|
if len(initial_counter_block) != factory.block_size:
|
||
|
|
raise ValueError("Size of the counter block (%d bytes) must match"
|
||
|
|
" block size (%d)" % (len(initial_counter_block),
|
||
|
|
factory.block_size))
|
||
|
|
|
||
|
|
return CtrMode(cipher_state, initial_counter_block,
|
||
|
|
len(prefix), counter_len, little_endian)
|