pkcs#1 padding, see RFC 3447 7.2.1

pkcs.py

import random
def random_bytes(size):
  return "".join(chr(random.randrange(1, 256)) for i in xrange(size))

def pkcs1_pad(text, size = 128):
  l = size - len(text) - 3
  if l >= 8: # see RFC3447 7.2.1
    padding = random_bytes(l)
    return '\x00\x02' + padding + '\x00' + text
  else:
    return text

# from http://kfalck.net/2011/03/07/decoding-pkcs1-padding-in-python
def pkcs1_unpad(text):
  if text and (text[0] == '\x02' or text[0:2] == '\x00\x02'):
    # Find end of padding marked by nul
    pos = text.find('\x00',1)
    if pos > 0:
      return text[pos+1:]
  return None