src/CryptoPlus/Util/util.py

   1 def number2string(i):
   2     """Convert a number to a string
   3
   4     Input: long or integer
   5     Output: string (big-endian)
   6     """
   7     s=hex(i)[2:].rstrip('L')
   8     if len(s) % 2:
   9         s = '0' + s
  10     return s.decode('hex')
  11
  12 def number2string_N(i, N):
  13     """Convert a number to a string of fixed size
  14
  15     i: long or integer
  16     N: length of string
  17     Output: string (big-endian)
  18     """
  19     s = '%0*x' % (N*2, i)
  20     return s.decode('hex')
  21
  22 def string2number(i):
  23     """ Convert a string to a number
  24
  25     Input: string (big-endian)
  26     Output: long or integer
  27     """
  28     return int(i.encode('hex'),16)
  29
  30 def xorstring(a,b):
  31     """XOR two strings of same length
  32
  33     For more complex cases, see CryptoPlus.Cipher.XOR"""
  34     assert len(a) == len(b)
  35     return number2string_N(string2number(a)^string2number(b), len(a))
  36
  37 class Counter(str):
  38     #found here: http://www.lag.net/pipermail/paramiko/2008-February.txt
  39     """Necessary for CTR chaining mode
  40
  41     Initializing a counter object (ctr = Counter('xxx'), gives a value to the counter object.
  42     Everytime the object is called ( ctr() ) it returns the current value and increments it by 1.
  43     Input/output is a raw string.
  44
  45     Counter value is big endian"""
  46     def __init__(self, initial_ctr):
  47         if not isinstance(initial_ctr, str):
  48             raise TypeError("nonce must be str")
  49         self.c = int(initial_ctr.encode('hex'), 16)
  50     def __call__(self):
  51         # This might be slow, but it works as a demonstration
  52         ctr = ("%032x" % (self.c,)).decode('hex')
  53         self.c += 1
  54         return ctr
  55