From ce38988a3cf99edbde3f622cd4831be6283f92c3 Mon Sep 17 00:00:00 2001 From: "Sybren A. St?vel" Date: Sun, 19 Jun 2011 23:51:57 +0200 Subject: Split module into several files --- rsa/randnum.py | 38 ++++++++++++++++++++++++++++++++++++++ 1 file changed, 38 insertions(+) create mode 100644 rsa/randnum.py (limited to 'rsa/randnum.py') 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 + -- cgit v1.2.1