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Unified Diff: third_party/google-endpoints/rsa/randnum.py

Issue 2666783008: Add google-endpoints to third_party/. (Closed)
Patch Set: Created 3 years, 11 months ago
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Index: third_party/google-endpoints/rsa/randnum.py
diff --git a/third_party/google-endpoints/rsa/randnum.py b/third_party/google-endpoints/rsa/randnum.py
new file mode 100644
index 0000000000000000000000000000000000000000..3c788a570bf1a36c52776ed722a4ffd75260df78
--- /dev/null
+++ b/third_party/google-endpoints/rsa/randnum.py
@@ -0,0 +1,98 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright 2011 Sybren A. Stüvel <sybren@stuvel.eu>
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Functions for generating random numbers."""
+
+# Source inspired by code by Yesudeep Mangalapilly <yesudeep@gmail.com>
+
+import os
+
+from rsa import common, transform
+from rsa._compat import byte
+
+
+def read_random_bits(nbits):
+ """Reads 'nbits' random bits.
+
+ If nbits isn't a whole number of bytes, an extra byte will be appended with
+ only the lower bits set.
+ """
+
+ nbytes, rbits = divmod(nbits, 8)
+
+ # Get the random bytes
+ randomdata = os.urandom(nbytes)
+
+ # Add the remaining random bits
+ if rbits > 0:
+ randomvalue = ord(os.urandom(1))
+ randomvalue >>= (8 - rbits)
+ randomdata = byte(randomvalue) + randomdata
+
+ return randomdata
+
+
+def read_random_int(nbits):
+ """Reads a random integer of approximately nbits bits.
+ """
+
+ randomdata = read_random_bits(nbits)
+ value = transform.bytes2int(randomdata)
+
+ # Ensure that the number is large enough to just fill out the required
+ # number of bits.
+ value |= 1 << (nbits - 1)
+
+ return value
+
+
+def read_random_odd_int(nbits):
+ """Reads a random odd integer of approximately nbits bits.
+
+ >>> read_random_odd_int(512) & 1
+ 1
+ """
+
+ value = read_random_int(nbits)
+
+ # Make sure it's odd
+ return value | 1
+
+
+def randint(maxvalue):
+ """Returns a random integer x with 1 <= x <= maxvalue
+
+ May take a very long time in specific situations. If maxvalue needs N bits
+ to store, the closer maxvalue is to (2 ** N) - 1, the faster this function
+ is.
+ """
+
+ bit_size = common.bit_size(maxvalue)
+
+ tries = 0
+ while True:
+ value = read_random_int(bit_size)
+ if value <= maxvalue:
+ break
+
+ if tries and tries % 10 == 0:
+ # After a lot of tries to get the right number of bits but still
+ # smaller than maxvalue, decrease the number of bits by 1. That'll
+ # dramatically increase the chances to get a large enough number.
+ bit_size -= 1
+ tries += 1
+
+ return value
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