237 lines
8.6 KiB
Python
237 lines
8.6 KiB
Python
# -*- coding: utf-8 -*-
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#
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# Cipher/DES3.py : DES3
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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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"""Triple DES symmetric cipher
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`Triple DES`__ (or TDES or TDEA or 3DES) is a symmetric block cipher
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standardized by NIST_. It has a fixed data block size of 8 bytes.
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TDES consists of the concatenation of 3 simple Single `DES` ciphers
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(encryption - decryption - encryption), where each stage uses an
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indipendent sub-key.
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A TDES key is therefore 24 (8+8+8) bytes long. However, like Single DES,
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only 7 out of 8 bits are actually used: the remaining ones are parity
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bits (which practically all TDES implementations ignore).
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Theoreticaly, Triple DES achieves up to 112 bits of effective security.
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Triple DES can also operate with a 16 bytes key (Option 2, also termed 2TDES),
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in which case subkey *K1* equals subkey *K2*. The effective security
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is as low as `90 bits`_.
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Thi implementation checks and enforces the condition *K1 != K2 != K3*
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(Option 3), as it degrades Triple DES to Single DES.
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*Use AES, not TDES. This module is provided for legacy purposes only.**
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As an example, encryption can be done as follows:
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>>> from Crypto.Cipher import DES3
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>>> from Crypto.Random import get_random_bytes
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>>>
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>>> # When generating a Triple DES key you must check that
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>>> # subkey1 != subkey2 and subkey2 != subkey3
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>>> while True:
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>>> try:
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>>> key = DES3.adjust_key_parity(get_random_bytes(24))
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>>> break
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>>> except ValueError
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>>> pass
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>>>
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>>> cipher = DES3.new(key, DES3.MODE_CFB)
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>>> plaintext = b'We are no longer the knights who say ni!'
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>>> msg = cipher.nonce + cipher.encrypt(plaintext)
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.. __: http://en.wikipedia.org/wiki/Triple_DES
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.. _NIST: http://csrc.nist.gov/publications/nistpubs/800-67-Rev1/SP-800-67-Rev1.pdf
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.. _90 bits: http://people.scs.carleton.ca/~paulv/papers/Euro90.pdf
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:undocumented: __package__
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"""
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import sys
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from Crypto.Cipher import _create_cipher
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from Crypto.Util.py3compat import byte_string, b, bchr, bord
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from Crypto.Util._raw_api import (load_pycryptodome_raw_lib,
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VoidPointer, SmartPointer,
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c_size_t, expect_byte_string)
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_raw_des3_lib = load_pycryptodome_raw_lib(
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"Crypto.Cipher._raw_des3",
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"""
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int DES3_start_operation(const uint8_t key[],
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size_t key_len,
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void **pResult);
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int DES3_encrypt(const void *state,
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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 DES3_decrypt(const void *state,
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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 DES3_stop_operation(void *state);
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""")
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def adjust_key_parity(key_in):
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"""Return the TDES key with parity bits correctly set"""
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def parity_byte(key_byte):
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parity = 1
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for i in range(1, 8):
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parity ^= (key_byte >> i) & 1
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return (key_byte & 0xFE) | parity
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if len(key_in) not in key_size:
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raise ValueError("Not a valid TDES key")
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key_out = b("").join([ bchr(parity_byte(bord(x)) )for x in key_in ])
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if key_out[:8] == key_out[8:16] or key_out[-16:-8] == key_out[-8:]:
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raise ValueError("Triple DES key degenerates to single DES")
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return key_out
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def _create_base_cipher(dict_parameters):
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"""This method instantiates and returns a handle to a low-level base cipher.
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It will absorb named parameters in the process."""
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try:
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key_in = dict_parameters.pop("key")
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except KeyError:
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raise TypeError("Missing 'key' parameter")
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key = adjust_key_parity(key_in)
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start_operation = _raw_des3_lib.DES3_start_operation
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stop_operation = _raw_des3_lib.DES3_stop_operation
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cipher = VoidPointer()
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result = start_operation(key,
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c_size_t(len(key)),
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cipher.address_of())
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if result:
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raise ValueError("Error %X while instantiating the TDES cipher"
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% result)
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return SmartPointer(cipher.get(), stop_operation)
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def new(key, mode, *args, **kwargs):
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"""Create a new TDES cipher
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:Parameters:
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key : byte string
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The secret key to use in the symmetric cipher.
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It must be 16 or 24 bytes long. The parity bits will be ignored.
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The condition K1 != K2 != K3 must hold.
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mode : a *MODE_** constant
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The chaining mode to use for encryption or decryption.
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:Keywords:
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iv : byte string
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(*Only* `MODE_CBC`, `MODE_CFB`, `MODE_OFB`, `MODE_OPENPGP`).
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The initialization vector to use for encryption or decryption.
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For `MODE_OPENPGP`, IV must be 8 bytes long for encryption
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and 10 bytes for decryption (in the latter case, it is
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actually the *encrypted* IV which was prefixed to the ciphertext).
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For all other modes, it must be 8 bytes long.
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If not provided, a random byte string will be generated (you can read
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it back via the ``iv`` attribute).
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nonce : byte string
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(*Only* `MODE_EAX` and `MODE_CTR`)
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A value that must never be reused for any other encryption.
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For `MODE_CTR`, its length must be in the range ``[0..7]``.
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For `MODE_EAX`, there are no restrictions, but it is recommended to
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use at least 16 bytes.
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If not provided for `MODE_EAX`, a random 16 byte string is generated
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(you can read it back via the ``nonce`` attribute).
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mac_len : integer
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(*Only* `MODE_EAX`). Length of the authentication tag, in bytes.
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It must be no larger than 8 (which is the default).
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segment_size : integer
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(*Only* `MODE_CFB`).The number of **bits** the plaintext and ciphertext
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are segmented in. It must be a multiple of 8.
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If not specified, it will be assumed to be 8.
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initial_value : integer
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(*Only* `MODE_CTR`). The initial value for the counter within
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the counter block. By default it is 0.
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:Attention: it is important that all 8 byte subkeys are different,
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otherwise TDES would degrade to single `DES`.
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:Raise ValueError:
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when the key degrades to Single DES.
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:Return: a DES cipher object, of the applicable mode:
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- CBC_ mode
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- CFB_ mode
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- CTR_ mode
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- EAX_ mode
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- ECB_ mode
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- OFB_ mode
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- OpenPgp_ mode
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.. _CBC: Crypto.Cipher._mode_cbc.CbcMode-class.html
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.. _CFB: Crypto.Cipher._mode_cfb.CfbMode-class.html
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.. _CTR: Crypto.Cipher._mode_ctr.CtrMode-class.html
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.. _EAX: Crypto.Cipher._mode_eax.EaxMode-class.html
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.. _ECB: Crypto.Cipher._mode_ecb.EcbMode-class.html
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.. _OFB: Crypto.Cipher._mode_ofb.OfbMode-class.html
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.. _OpenPgp: Crypto.Cipher._mode_openpgp.OpenPgpMode-class.html
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"""
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return _create_cipher(sys.modules[__name__], key, mode, *args, **kwargs)
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#: Electronic Code Book (ECB). See `Crypto.Cipher._mode_ecb.EcbMode`.
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MODE_ECB = 1
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#: Cipher-Block Chaining (CBC). See `Crypto.Cipher._mode_cbc.CbcMode`.
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MODE_CBC = 2
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#: Cipher FeedBack (CFB). See `Crypto.Cipher._mode_cfb.CfbMode`.
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MODE_CFB = 3
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#: Output FeedBack (OFB). See `Crypto.Cipher._mode_ofb.OfbMode`.
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MODE_OFB = 5
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#: CounTer Mode (CTR). See `Crypto.Cipher._mode_ctr.CtrMode`.
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MODE_CTR = 6
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#: OpenPGP Mode. See `Crypto.Cipher._mode_openpgp.OpenPgpMode`.
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MODE_OPENPGP = 7
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#: EAX Mode. See `Crypto.Cipher._mode_eax.EaxMode`.
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MODE_EAX = 9
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#: Size of a data block (in bytes)
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block_size = 8
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#: Size of a key (in bytes)
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key_size = (16, 24)
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