289 lines
10 KiB
Python
289 lines
10 KiB
Python
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# -*- coding: utf-8 -*-
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#
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# Cipher/AES.py : AES
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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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"""AES symmetric cipher
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AES `(Advanced Encryption Standard)`__ is a symmetric block cipher standardized
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by NIST_ . It has a fixed data block size of 16 bytes.
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Its keys can be 128, 192, or 256 bits long.
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AES is very fast and secure, and it is the de facto standard for symmetric
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encryption.
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As an example, encryption can be done as follows:
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>>> from Crypto.Cipher import AES
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>>>
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>>> key = b'Sixteen byte key'
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>>> cipher = AES.new(key, AES.MODE_CFB)
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>>> msg = cipher.iv + cipher.encrypt(b'Attack at dawn')
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A more complicated example is based on CCM, (see `MODE_CCM`) an `AEAD`_ mode
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that provides both confidentiality and authentication for a message.
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The CCM mode optionally allows the header of the message to remain in the clear,
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whilst still being authenticated. The encryption is done as follows:
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>>> from Crypto.Cipher import AES
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>>> from Crypto.Random import get_random_bytes
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>>>
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>>>
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>>> hdr = b'To your eyes only'
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>>> plaintext = b'Attack at dawn'
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>>> key = b'Sixteen byte key'
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>>> cipher = AES.new(key, AES.MODE_CCM, nonce)
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>>> cipher.update(hdr)
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>>> msg = cipher.nonce, hdr, cipher.encrypt(plaintext), cipher.digest()
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We assume that the tuple ``msg`` is transmitted to the receiver:
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>>> nonce, hdr, ciphertext, mac = msg
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>>> key = b'Sixteen byte key'
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>>> cipher = AES.new(key, AES.MODE_CCM, nonce)
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>>> cipher.update(hdr)
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>>> plaintext = cipher.decrypt(ciphertext)
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>>> try:
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>>> cipher.verify(mac)
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>>> print "The message is authentic: hdr=%s, pt=%s" % (hdr, plaintext)
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>>> except ValueError:
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>>> print "Key incorrect or message corrupted"
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.. __: http://en.wikipedia.org/wiki/Advanced_Encryption_Standard
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.. _NIST: http://csrc.nist.gov/publications/fips/fips197/fips-197.pdf
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.. _AEAD: http://blog.cryptographyengineering.com/2012/05/how-to-choose-authenticated-encryption.html
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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._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_cpuid_lib = load_pycryptodome_raw_lib("Crypto.Util._cpuid",
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"int have_aes_ni(void);")
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_cproto = """
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int AES_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 AES_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 AES_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 AES_stop_operation(void *state);
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"""
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_raw_aes_lib = load_pycryptodome_raw_lib("Crypto.Cipher._raw_aes",
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_cproto)
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_raw_aesni_lib = None
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try:
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if _raw_cpuid_lib.have_aes_ni() == 1:
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_raw_aesni_lib = load_pycryptodome_raw_lib("Crypto.Cipher._raw_aesni",
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_cproto.replace("AES",
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"AESNI"))
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except OSError:
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pass
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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
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base cipher. It will absorb named parameters in the process."""
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use_aesni = dict_parameters.pop("use_aesni", True)
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try:
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key = dict_parameters.pop("key")
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except KeyError:
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raise TypeError("Missing 'key' parameter")
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expect_byte_string(key)
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if len(key) not in key_size:
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raise ValueError("Incorrect AES key length (%d bytes)" % len(key))
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if use_aesni and _raw_aesni_lib:
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start_operation = _raw_aesni_lib.AESNI_start_operation
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stop_operation = _raw_aesni_lib.AESNI_stop_operation
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else:
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start_operation = _raw_aes_lib.AES_start_operation
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stop_operation = _raw_aes_lib.AES_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 AES 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 AES 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 (*AES-128*), 24 (*AES-192*), or 32 (*AES-256*)
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bytes long.
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Only in `MODE_SIV`, it needs to be 32, 48, or 64 bytes long.
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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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If in doubt, use `MODE_EAX`.
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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`, it must be 16 bytes long for encryption
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and 18 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 16 bytes long.
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In not provided, a random byte string is used (you must then
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read its value with the ``iv`` attribute).
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nonce : byte string
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(*Only* `MODE_CCM`, `MODE_EAX`, `MODE_GCM`, `MODE_SIV`, `MODE_OCB`,
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`MODE_CTR`).
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A value that must never be reused for any other encryption done
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with this key.
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For `MODE_CCM`, its length must be in the range ``[7..13]``.
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Bear in mind that with CCM there is a trade-off between nonce
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length and maximum message size.
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For `MODE_OCB`, its length must be in the range ``[1..15]``.
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For `MODE_CTR`, its length must be in the range ``[0..15]``.
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For the other modes, there are no restrictions on its length.
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The recommended length depends on the mode: 8 bytes for `MODE_CTR`,
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11 bytes for `MODE_CCM`, 15 bytes for `MODE_OCB` and 16 bytes
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for the remaining modes.
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In not provided, a random byte string of the recommended
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length is used (you must then read its value with the ``nonce`` attribute).
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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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mac_len : integer
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(*Only* `MODE_EAX`, `MODE_GCM`, `MODE_OCB`, `MODE_CCM`)
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Length of the authentication tag, in bytes.
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It must be even and in the range ``[4..16]``.
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The recommended value (and the default, if not specified) is 16.
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msg_len : integer
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(*Only* `MODE_CCM`). Length of the message to (de)cipher.
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If not specified, ``encrypt`` must be called with the entire message.
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Similarly, ``decrypt`` can only be called once.
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assoc_len : integer
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(*Only* `MODE_CCM`). Length of the associated data.
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If not specified, all associated data is buffered internally,
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which may represent a problem for very large messages.
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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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use_aesni : boolean
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Use Intel AES-NI hardware extensions if available.
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:Return: an AES object, of the applicable mode:
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- CBC_ mode
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- CCM_ 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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- GCM_ mode
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- OCB_ mode
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- OFB_ mode
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- OpenPgp_ mode
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- SIV_ mode
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.. _CBC: Crypto.Cipher._mode_cbc.CbcMode-class.html
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.. _CCM: Crypto.Cipher._mode_ccm.CcmMode-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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.. _GCM: Crypto.Cipher._mode_gcm.GcmMode-class.html
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.. _OCB: Crypto.Cipher._mode_ocb.OcbMode-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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.. _SIV: Crypto.Cipher._mode_siv.SivMode-class.html
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"""
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kwargs["add_aes_modes"] = True
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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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#: Counter with CBC-MAC (CCM) Mode. See `Crypto.Cipher._mode_ccm.CcmMode`.
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MODE_CCM = 8
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#: EAX Mode. See `Crypto.Cipher._mode_eax.EaxMode`.
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MODE_EAX = 9
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#: Syntethic Initialization Vector (SIV). See `Crypto.Cipher._mode_siv.SivMode`.
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MODE_SIV = 10
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#: Galois Counter Mode (GCM). See `Crypto.Cipher._mode_gcm.GcmMode`.
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MODE_GCM = 11
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#: Offset Code Book (OCB). See `Crypto.Cipher._mode_ocb.OcbMode`.
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MODE_OCB = 12
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#: Size of a data block (in bytes)
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block_size = 16
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#: Size of a key (in bytes)
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key_size = (16, 24, 32)
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