Split module into several files

1 files changed, 38 insertions, 0 deletions

diff --git a/rsa/randnum.py b/rsa/randnum.py
new file mode 100644
index 0000000..9bfaded
--- /dev/null
+++ b/rsa/randnum.py
@@ -0,0 +1,38 @@
+'''Functions for generating random numbers.'''
+
+import math
+import os
+import random
+
+import rsa.transform
+
+def read_random_int(nbits):
+    """Reads a random integer of approximately nbits bits rounded up to whole
+    bytes
+    """
+
+    nbytes = int(math.ceil(nbits/8.))
+    randomdata = os.urandom(nbytes)
+    return rsa.transform.bytes2int(randomdata)
+
+def randint(minvalue, maxvalue):
+    """Returns a random integer x with minvalue <= x <= maxvalue"""
+
+    # Safety - get a lot of random data even if the range is fairly
+    # small
+    min_nbits = 32
+
+    # The range of the random numbers we need to generate
+    range = (maxvalue - minvalue) + 1
+
+    # Which is this number of bytes
+    rangebytes = (rsa.transform.bit_size(range) + 7) / 8
+
+    # Convert to bits, but make sure it's always at least min_nbits*2
+    rangebits = max(rangebytes * 8, min_nbits * 2)
+    
+    # Take a random number of bits between min_nbits and rangebits
+    nbits = random.randint(min_nbits, rangebits)
+    
+    return (read_random_int(nbits) % range) + minvalue
+