One-time pad

import random
import string
from sys import argv
#It's a global variable that we have to use, like a module
modulo = len(dict.fromkeys(string.printable, 0)) + 1
#We generate two pad keys for the two users
#They are generate in a random way in a range between 1 and the module
def genera(cantidad, largo):
    global modulo
    output1 = open('key1.txt','w')
    output2 = open('key2.txt','w')
    for i in range(cantidad):
        clave = ''
        for j in range(largo):
            clave += str(random.randrange(1, modulo)) + '.'
        print>>output1, '%s' % clave
        print>>output2, '%s' % clave
    output1.close()
    output2.close()
    return
#This function erase the key line that the user used to encrypt o decrypt
def borra(clave):
    Input = open(clave, 'r')
    keys = Input.readlines()
    Input.close()
    del keys[0]
    Output = open(clave, 'w')
    for k in keys:
        print >>Output, '%s' % k.strip()
    Output.close()
    return
#This function open 2 files, the pad key and the message to encrypt
#where we read the line that we have to read, then we create a dictionary
#and inside that we have a alphabet with a sequence, 1 by 1.
#after that I split the key by a point '.', then we initialize a
#boolean variable and string variable those we'll need forward.
#Now I iterate all the lines of the message until we get an empty line,
# inside of the for we cypher adding the value of the alphabet
#and the value of the pad key and we use the module of that product
# if we don't have enough keys, we fall in an exception and print a warning.
# Atfer all we erase the key line.

def cifra(mensaje, clave):
    global modulo
    Input = open(clave,'r')
    Mensaje = open(mensaje, 'r')
    llave = Input.readline()
    Input.close()
    alfabeto = dict.fromkeys(string.printable, 0)
    aux = 1
    for a in alfabeto:
        alfabeto[a] = aux
        aux+=1
    k = llave.split('.')
    ok = True
    cifrado = ''
    for l in Mensaje.readlines():
        l = l.strip()
        if len(l) > 0:
            for m in l:
                try:
                    cifrado += str(((alfabeto[m] + int(k.pop(0)))) % modulo) + '.'
                except:
                    print 'Mensaje demasiado largo.'
                    ok = False
                    break
    Mensaje.close()
    while len(k) > 0:
        cifrado += k.pop(0) + '.'
    Output = open('%s.cifrado' % mensaje,'w')
    print >>Output, cifrado
    Output.close()
    if ok:
        borra(clave)
    return
#We create a file called like the message plus '.original', then we open
#the pad key and read the line #that we need, we create an alphabet inside
#a dictionary and we put in this way " a[5] = 'a', a[7] = #'b' " then we
#read every line of message and we decrypt them find it in the dictionary
#using the letter of the message that is a number and the key value
#that is a key too, substracting #those and make a module of that
#we got our message, after all we erase the key line of the pad.
def decifra(mensaje, clave):
    global modulo
    Output = open('%s.original' % mensaje,'w')
    Input = open(clave,'r')
    Mensaje = open(mensaje, 'r')
    llave = Input.readline()
    alfabeto = dict.fromkeys(string.printable, 0)
    aux = 1
    reverso = dict()
    reverso[0] = ' '
    for a in alfabeto:
        reverso[aux] = a
        aux+=1
    k = llave.split('.')
    ok = True
    decifrado = ''
    for l in Mensaje.readlines():
        l = l.strip()
        for m in l.split('.'):
            if len(m) > 0:
                cl = int(k.pop(0))
                recuperado = reverso[((int(m) - cl) % modulo)]
                decifrado += recuperado
    print >>Output, decifrado
    Output.close()
    Mensaje.close()
    Input.close()
    borra(clave)
    return

def main():
    opcion = argv[1]
    if opcion == 'genera':
        genera(int(argv[2]), int(argv[3]))
    elif opcion == 'cifra':
        cifra(argv[2], argv[3])
    elif opcion == 'decifra':
        decifra(argv[2], argv[3])

main()