slight update

env/lib/python3.12/site-packages/Crypto/Util/Counter.py

@@ -0,0 +1,79 @@
+# -*- 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.
+        Its length in bits must not exceed the argument ``nbits``.
+      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.
+        An ``OverflowError`` exception is always raised when the counter wraps
+        around to zero.
+    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")
+
+    iv_bl = initial_value.bit_length()
+    if iv_bl > nbits:
+        raise ValueError("Initial value takes %d bits but it is longer than "
+                         "the counter (%d bits)" %
+                         (iv_bl, nbits))
+
+    # Ignore wraparound
+    return {"counter_len": nbits // 8,
+            "prefix": prefix,
+            "suffix": suffix,
+            "initial_value": initial_value,
+            "little_endian": little_endian
+            }