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authorDeterminant <tederminant@gmail.com>2020-11-17 20:04:09 -0500
committerDeterminant <tederminant@gmail.com>2020-11-17 20:04:09 -0500
commitc4d90bf4ea0c5b7a016028ed994de19638d3113b (patch)
tree693279a91311155f565e90ecd2d93bf701d6d4e9 /frozen_deps/Cryptodome/Util/Counter.py
parent3bef51eec2299403467e621ae660cef3f9256ac8 (diff)
support saving as a keystore file
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+# -*- coding: ascii -*-
+#
+# Util/Counter.py : Fast counter for use with CTR-mode ciphers
+#
+# Written in 2008 by Dwayne C. Litzenberger <dlitz@dlitz.net>
+#
+# ===================================================================
+# 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.
+# ===================================================================
+
+def new(nbits, prefix=b"", suffix=b"", initial_value=1, little_endian=False, allow_wraparound=False):
+ """Create a stateful counter block function suitable for CTR encryption modes.
+
+ Each call to the function returns the next counter block.
+ Each counter block is made up by three parts:
+
+ +------+--------------+-------+
+ |prefix| counter value|postfix|
+ +------+--------------+-------+
+
+ The counter value is incremented by 1 at each call.
+
+ Args:
+ nbits (integer):
+ Length of the desired counter value, in bits. It must be a multiple of 8.
+ prefix (byte string):
+ The constant prefix of the counter block. By default, no prefix is
+ used.
+ suffix (byte string):
+ The constant postfix of the counter block. By default, no suffix is
+ used.
+ initial_value (integer):
+ The initial value of the counter. Default value is 1.
+ little_endian (boolean):
+ If ``True``, the counter number will be encoded in little endian format.
+ If ``False`` (default), in big endian format.
+ allow_wraparound (boolean):
+ This parameter is ignored.
+ Returns:
+ An object that can be passed with the :data:`counter` parameter to a CTR mode
+ cipher.
+
+ It must hold that *len(prefix) + nbits//8 + len(suffix)* matches the
+ block size of the underlying block cipher.
+ """
+
+ if (nbits % 8) != 0:
+ raise ValueError("'nbits' must be a multiple of 8")
+
+ # Ignore wraparound
+ return {"counter_len": nbits // 8,
+ "prefix": prefix,
+ "suffix": suffix,
+ "initial_value": initial_value,
+ "little_endian": little_endian
+ }