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lib/python3.5/site-packages/Crypto/Cipher/DES.py

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+# -*- coding: utf-8 -*-
+#
+#  Cipher/DES.py : DES
+#
+# ===================================================================
+# 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.
+# ===================================================================
+"""DES symmetric cipher
+
+DES `(Data Encryption Standard)`__ is a symmetric block cipher standardized
+by NIST_ . It has a fixed data block size of 8 bytes.
+Its keys are 64 bits long, even though 8 bits were used for integrity (now they
+are ignored) and do not contribute to securty.
+
+DES is cryptographically secure, but its key length is too short by nowadays
+standards and it could be brute forced with some effort.
+
+DES should not be used for new designs. Use `AES`.
+
+As an example, encryption can be done as follows:
+
+    >>> from Crypto.Cipher import DES3
+    >>> from Crypto import Random
+    >>>
+    >>> key = b'Sixteen byte key'
+    >>> iv = Random.new().read(DES3.block_size)
+    >>> cipher = DES3.new(key, DES3.MODE_OFB, iv)
+    >>> plaintext = b'sona si latine loqueris '
+    >>> msg = iv + cipher.encrypt(plaintext)
+
+.. __: http://en.wikipedia.org/wiki/Data_Encryption_Standard
+.. _NIST: http://csrc.nist.gov/publications/fips/fips46-3/fips46-3.pdf
+
+:undocumented: __revision__, __package__
+"""
+
+__revision__ = "$Id$"
+
+from Crypto.Cipher import blockalgo
+from Crypto.Cipher import _DES
+
+class DESCipher(blockalgo.BlockAlgo):
+    """DES cipher object"""
+
+    def __init__(self, key, *args, **kwargs):
+        """Initialize a DES cipher object
+        
+        See also `new()` at the module level."""
+        blockalgo.BlockAlgo.__init__(self, _DES, key, *args, **kwargs)
+
+def new(key, *args, **kwargs):
+    """Create a new DES cipher
+
+    :Parameters:
+      key : byte string
+        The secret key to use in the symmetric cipher.
+        It must be 8 byte long. The parity bits will be ignored.
+    :Keywords:
+      mode : a *MODE_** constant
+        The chaining mode to use for encryption or decryption.
+        Default is `MODE_ECB`.
+      IV : byte string
+        The initialization vector to use for encryption or decryption.
+        
+        It is ignored for `MODE_ECB` and `MODE_CTR`.
+
+        For `MODE_OPENPGP`, IV must be `block_size` bytes long for encryption
+        and `block_size` +2 bytes for decryption (in the latter case, it is
+        actually the *encrypted* IV which was prefixed to the ciphertext).
+        It is mandatory.
+       
+        For all other modes, it must be `block_size` bytes longs. It is optional and
+        when not present it will be given a default value of all zeroes.
+      counter : callable
+        (*Only* `MODE_CTR`). A stateful function that returns the next
+        *counter block*, which is a byte string of `block_size` bytes.
+        For better performance, use `Crypto.Util.Counter`.
+      segment_size : integer
+        (*Only* `MODE_CFB`).The number of bits the plaintext and ciphertext
+        are segmented in.
+        It must be a multiple of 8. If 0 or not specified, it will be assumed to be 8.
+
+    :Return: an `DESCipher` object
+    """
+    return DESCipher(key, *args, **kwargs)
+
+#: Electronic Code Book (ECB). See `blockalgo.MODE_ECB`.
+MODE_ECB = 1
+#: Cipher-Block Chaining (CBC). See `blockalgo.MODE_CBC`.
+MODE_CBC = 2
+#: Cipher FeedBack (CFB). See `blockalgo.MODE_CFB`.
+MODE_CFB = 3
+#: This mode should not be used.
+MODE_PGP = 4
+#: Output FeedBack (OFB). See `blockalgo.MODE_OFB`.
+MODE_OFB = 5
+#: CounTer Mode (CTR). See `blockalgo.MODE_CTR`.
+MODE_CTR = 6
+#: OpenPGP Mode. See `blockalgo.MODE_OPENPGP`.
+MODE_OPENPGP = 7
+#: Size of a data block (in bytes)
+block_size = 8
+#: Size of a key (in bytes)
+key_size = 8