Small Keys (Implementation of One-Time Pads)

#! /usr/bin/env python

# One-Time Pad
# By: Magnie (http://scratch.mit.edu/users/Magnie)
# Copyright: GPLv3 (http://www.gnu.org/copyleft/gpl.html)
# I don't know why I bother adding this. I doubt my code will be used
# anyways, since it's probably not worth using. :P

import random

class OneTime(object):
    """
An attempt to make a one-time pad encryption system work with a key
smaller than the text.

It relies on a secure Pseudo-Random Generator (random.Random in this
case), and based on the seed/password/key given, it will generate a
"random" key, allowing the transferring of smaller, simpler (yet more
breakable), keys.

This follows the same caveats as the original One-Time Pad
protocol. For example, you can only use the key once (unless you send
a message/file of a different size than any others sent).
    """

    def __init__(self):
        """This sets up everything needed"""

        # This mostly just saves all the data in the class for later
        # retrieval.
        self.string = ""
        self.key = []
        self.seed = ""
        self.cipher = ""

    def generate_key(self):
        """
Based on the seed given, and the length of the file, the
final key will be different.
        """
        key = []
        seed = sum([ord(x) + len(self.string) for x in self.seed])
        generator = random.Random(seed) # Random number generator.
        for i in xrange(0, len(self.string) - 1):
            t1 = generator.random() # Generate random number
            t2 = int(str(t1)[2:5]) # Since it's going to be a decimal
                                   # take the three digits after the
                                   # decimal point.
            key.append(t2)

        self.key = [int(x) % 255 for x in key] # Removable.
        return self.key

    def encrypt(self):
        """Runs the original One-Time Pad encryption"""
        cipher = ""
        key = self.key
        n = 0
        for i in self.string:
            # Shift the letter and modulo it to keep it in correct
            # range to be put in binary format. Keeping the cipher
            # the same length as the original text.
            t1 = (ord(i) ^ key[n % len(key)]) % 255
            cipher += chr(t1)
            n += 1

        self.cipher = cipher
        return cipher

    def decrypt(self):
        """Runs the original One-Time Pad decryption"""
        plain = ""
        key = self.key
        n = 0
        for i in self.cipher:
            t1 = (ord(i) ^ key[n % len(key)]) % 255
            plain += chr(t1)
            n += 1

        self.plain = plain
        return plain

if __name__ == "__main__": # Just a list of tests.
    time = OneTime()
    time.seed = "testing12" # Original test - Set the seed
    time.string = "I am awesome." # Set the string
    print time.generate_key() # Generate key from seed
    print time.encrypt() # Encrypt the data
    print time.decrypt() # Decrypt the data

    time.seed = "testing13" # One bit difference in key
    print time.generate_key()
    print time.encrypt()
    print time.decrypt()

    time.seed = "testing12" # Different length of string.
    time.string = "I am awesome!!"
    print time.generate_key()
    print time.encrypt()
    print time.decrypt()

    time.seed = "testing12" # Same length, different letters.
    time.string = "I am awesome!"
    print time.generate_key()
    print time.encrypt()
    print time.decrypt()