179 lines
6.4 KiB
Python
179 lines
6.4 KiB
Python
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# -*- coding: utf-8 -*-
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#
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# Cipher/mode_ecb.py : ECB mode
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#
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# ===================================================================
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# The contents of this file are dedicated to the public domain. To
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# the extent that dedication to the public domain is not available,
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# everyone is granted a worldwide, perpetual, royalty-free,
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# non-exclusive license to exercise all rights associated with the
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# contents of this file for any purpose whatsoever.
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# No rights are reserved.
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#
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# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
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# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
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# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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# SOFTWARE.
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# ===================================================================
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"""
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Electronic Code Book (ECB) mode.
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"""
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__all__ = [ 'EcbMode' ]
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from Crypto.Util._raw_api import (load_pycryptodome_raw_lib,
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VoidPointer, create_string_buffer,
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get_raw_buffer, SmartPointer,
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c_size_t, expect_byte_string)
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raw_ecb_lib = load_pycryptodome_raw_lib("Crypto.Cipher._raw_ecb", """
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int ECB_start_operation(void *cipher,
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void **pResult);
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int ECB_encrypt(void *ecbState,
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const uint8_t *in,
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uint8_t *out,
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size_t data_len);
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int ECB_decrypt(void *ecbState,
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const uint8_t *in,
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uint8_t *out,
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size_t data_len);
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int ECB_stop_operation(void *state);
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"""
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)
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class EcbMode(object):
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"""*Electronic Code Book (ECB)*.
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This is the simplest encryption mode. Each of the plaintext blocks
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is directly encrypted into a ciphertext block, independently of
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any other block.
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This mode is dangerous because it exposes frequency of symbols
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in your plaintext. Other modes (e.g. *CBC*) should be used instead.
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See `NIST SP800-38A`_ , Section 6.1.
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.. _`NIST SP800-38A` : http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
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:undocumented: __init__
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"""
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def __init__(self, block_cipher):
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"""Create a new block cipher, configured in ECB mode.
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:Parameters:
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block_cipher : C pointer
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A smart pointer to the low-level block cipher instance.
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"""
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self._state = VoidPointer()
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result = raw_ecb_lib.ECB_start_operation(block_cipher.get(),
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self._state.address_of())
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if result:
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raise ValueError("Error %d while instatiating the ECB mode"
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% result)
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# Ensure that object disposal of this Python object will (eventually)
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# free the memory allocated by the raw library for the cipher
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# mode
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self._state = SmartPointer(self._state.get(),
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raw_ecb_lib.ECB_stop_operation)
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# Memory allocated for the underlying block cipher is now owned
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# by the cipher mode
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block_cipher.release()
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def encrypt(self, plaintext):
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"""Encrypt data with the key set at initialization.
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The data to encrypt can be broken up in two or
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more pieces and `encrypt` can be called multiple times.
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That is, the statement:
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>>> c.encrypt(a) + c.encrypt(b)
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is equivalent to:
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>>> c.encrypt(a+b)
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This function does not add any padding to the plaintext.
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:Parameters:
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plaintext : byte string
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The piece of data to encrypt.
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The length must be multiple of the cipher block length.
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:Return:
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the encrypted data, as a byte string.
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It is as long as *plaintext*.
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"""
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expect_byte_string(plaintext)
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ciphertext = create_string_buffer(len(plaintext))
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result = raw_ecb_lib.ECB_encrypt(self._state.get(),
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plaintext,
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ciphertext,
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c_size_t(len(plaintext)))
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if result:
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raise ValueError("Error %d while encrypting in ECB mode" % result)
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return get_raw_buffer(ciphertext)
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def decrypt(self, ciphertext):
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"""Decrypt data with the key set at initialization.
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The data to decrypt can be broken up in two or
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more pieces and `decrypt` can be called multiple times.
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That is, the statement:
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>>> c.decrypt(a) + c.decrypt(b)
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is equivalent to:
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>>> c.decrypt(a+b)
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This function does not remove any padding from the plaintext.
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:Parameters:
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ciphertext : byte string
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The piece of data to decrypt.
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The length must be multiple of the cipher block length.
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:Return:
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the decrypted data (byte string).
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It is as long as *ciphertext*.
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"""
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expect_byte_string(ciphertext)
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plaintext = create_string_buffer(len(ciphertext))
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result = raw_ecb_lib.ECB_decrypt(self._state.get(),
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ciphertext,
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plaintext,
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c_size_t(len(ciphertext)))
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if result:
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raise ValueError("Error %d while decrypting in ECB mode" % result)
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return get_raw_buffer(plaintext)
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def _create_ecb_cipher(factory, **kwargs):
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"""Instantiate a cipher object that performs ECB encryption/decryption.
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:Parameters:
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factory : module
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The underlying block cipher, a module from ``Crypto.Cipher``.
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All keywords are passed to the underlying block cipher.
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See the relevant documentation for details (at least ``key`` will need
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to be present"""
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cipher_state = factory._create_base_cipher(kwargs)
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if kwargs:
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raise TypeError("Unknown parameters for ECB: %s" % str(kwargs))
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return EcbMode(cipher_state)
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