python2.7 and python2.6 compatability for bit-wise randrange

Author: pik

src/ecdsa/util.py

@@ -3,6 +3,7 @@
 import os
 import math
 import binascii
+import sys
 from hashlib import sha256
 from six import PY3, int2byte, b, next
 from . import der
@@ -16,12 +17,16 @@
 oid_ecPublicKey = (1, 2, 840, 10045, 2, 1)
 encoded_oid_ecPublicKey = der.encode_oid(*oid_ecPublicKey)
 
-
-def bit_length(num):
-    # http://docs.python.org/dev/library/stdtypes.html#int.bit_length
-    s = bin(num)  # binary representation:  bin(-37) --> '-0b100101'
-    s = s.lstrip('-0b')  # remove leading zeros and minus sign
-    return len(s)  # len('100101') --> 6
+if sys.version > '3': 
+    entropy_to_bits = lambda ent_256: ''.join(bin(x)[2:].zfill(8) for x in ent_256)
+else: 
+    entropy_to_bits = lambda ent_256: ''.join(bin(ord(x))[2:].zfill(8) for x in ent_256)
+if sys.version < '2.7':  #Can't add a method to a built-in type so we are stuck with this
+    bit_length = lambda x: len(bin(x)) - 2
+else: 
+    bit_length = lambda x: x.bit_length() or 1
+    
+        
 
 
 def orderlen(order):
@@ -41,11 +46,11 @@ def randrange(order, entropy=None):
     assert order > 1
     if entropy is None:
         entropy = os.urandom
-    upper_2 = (order-2).bit_length() or 1
+    upper_2 = bit_length(order-2)
     upper_256 = int(upper_2/8 + 1); 
-    while True:  #I don't think we need a counter with bit-wise randrange
+    while True:  #I don't think this needs a counter with bit-wise randrange
         ent_256 = entropy(upper_256) 
-        ent_2=''.join(bin(x)[2:].zfill(8) for x in ent_256)
+        ent_2=entropy_to_bits(ent_256)
         rand_num = int(ent_2[:upper_2], base=2) +1
         if 0 < rand_num < order: return rand_num
         else:continue