Basic python program for generating / decoding strings with a one-time-pad.

otp.py

#!/usr/bin/env python

import os
import string
import sys
import random

# =====================================================
CMIN=0x20
CMAX=0x7E
CDIFF = CMAX-CMIN
# =====================================================

def otp(source):
  key = ''
  out = ''
  with open('/dev/random') as f:
    for i in range(len(source)):
      assert ord(source[i]) >= CMIN and ord(source[i]) <= CMAX
      a = ord(source[i])-CMIN
      b = ord(f.read(1)) % CDIFF
      out += chr(CMIN + ((a+b)%CDIFF))
      key += chr(CMIN + b)
  return (key, out)

def decode(a,b):
  out = ''
  assert len(a) == len(b)
  for i in range(len(a)):
    out += chr(CMIN + ((ord(b[i])-CMIN)-(ord(a[i]) - CMIN)) % CDIFF)
  return out 

if __name__=='__main__':
  if len(sys.argv) != 2 or sys.argv[-1] not in ['-d','-e']:
    print "syntax: otp.py -[de]"
  elif sys.argv[-1] == '-d':
    s1 = raw_input("String #1: ").strip()
    s2 = raw_input("String #2: ").strip()
    print "========================================================"
    print "Decoded #1:", decode(s1,s2)
    print "Decoded #2:", decode(s2,s1)
    print "========================================================"
  elif sys.argv[-1] == '-e': 
    source = raw_input("String to encrypt: ").strip()
    res = otp(source)
    print "========================================================"
    print "Source:  ",source
    print "Decoded: ", decode(res[0], res[1])
    print "String1: ", res[0]
    print "String2: ", res[1]
    print "========================================================"