Additive encryption toy script

encryption.py

import numpy as np
import matplotlib.pyplot as plt
import matplotlib.mlab as mlab

SHARED_KEY = "Michael".lower()

PLAIN_TEXT = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus accumsan neque id diam scelerisque et suscipit magna accumsan. Aenean suscipit lorem a sem semper non tincidunt nibh rhoncus. Morbi mattis sollicitudin dapibus. Aliquam erat volutpat. Proin leo ligula, tempor tincidunt faucibus eu, tempor in magna. Fusce ut odio leo, in volutpat lectus. Morbi in aliquet mi. Nam vitae neque vitae felis ultricies volutpat id ut dui. Morbi bibendum aliquam hendrerit. Proin vel libero sed nisl euismod cursus. Aliquam sagittis aliquam eleifend.".lower()

def encrypt(text, key):
    key_numeric = [ord(x) for x in key]
    text_numeric = [ord(x) for x in text]
    text_length = len(text_numeric)
    key_length = len(key_numeric)
    key_long = np.tile(key_numeric,(1,np.ceil(text_length/float(key_length) + 1))).squeeze()
    key_long = key_long[0:text_length]
    return [chr(x) for x in key_long + text_numeric]

def decrypt(text, key):
    key_numeric = [ord(x) for x in key]
    text_numeric = [ord(x) for x in text]
    text_length = len(text_numeric)
    key_length = len(key_numeric)
    key_long = np.tile(key_numeric,(1,np.ceil(text_length/float(key_length) + 1))).squeeze()
    key_long = key_long[0:text_length]
    return [chr(x) for x in text_numeric - key_long]

if __name__=='__main__':
    fig = plt.figure()
    fftfig = plt.figure()

    fftax = fftfig.add_subplot(211)
    ax = fig.add_subplot(211, xlim = (0,255))

    cyphertext = encrypt(PLAIN_TEXT, SHARED_KEY)
    print "".join(cyphertext)

    text_numeric = [ord(x) for x in PLAIN_TEXT]
    ax.hist(text_numeric, 256, normed=0, facecolor='green', alpha=0.75)
    fftax.plot(np.abs(np.fft.fft(text_numeric)))
    

    cypher = encrypt(PLAIN_TEXT, SHARED_KEY)
    cypher_numeric = [ord(x) for x in cypher]
    ax = fig.add_subplot(212, xlim=(0,255))
    fftax = fftfig.add_subplot(212)
    ax.hist(cypher_numeric, 256, normed=0, facecolor='green', alpha=0.75)
    fftax.plot(np.abs(np.fft.fft(cypher_numeric)))

    plt.show()