Gfrktyl

I had this idea not to long ago on creating a secure chat for people who need to be not meddled with when talking (like whistleblowers, hackers, etc) talking to one of my friends about it he said I could use the One Time Pad Cipher, so I decided to write my own in Python.

If you don't know what the one time pad is, in a nutshell it's a cipher that generates a key for you that is as long as the string you pass to it making it practically impossible to crack without the key itself.

My cipher uses sqlite to store a database into memory to keep the keys unique, once the program is exited, the database is destroyed (theoretically). I would like someone to poke as many holes in this as possible, I would like to see if the string is possible to be cracked and would also like someone to break the database if possible. Basically I want to know how secure this is. Please keep in mind, this is not a finished product but just a fundamental understanding to a larger project. So critique away and have fun with it, thank you!

The code:

import random

import string

import sqlite3





PUNC = string.punctuation

ALPHABET = string.ascii_letters





def initialize():

    """

    initialize the database into memory so that it can be wiped upon exit

    """

    connection = sqlite3.connect(":memory:", isolation_level=None, check_same_thread=False)

    cursor = connection.cursor()

    cursor.execute(

        "CREATE TABLE used_keys ("

        "id INTEGER PRIMARY KEY AUTOINCREMENT,"

        "key TEXT"

        ")"

    )

    return cursor





def create_key(_string, db_cursor):

    """

    create the key from a provided string

    """

    retval = ""

    set_string = ""

    used_keys = db_cursor.execute("SELECT key FROM used_keys")

    id_number = len(used_keys.fetchall()) + 1

    for c in _string:

        if c in PUNC:

            c = ""

        if c == " " or c.isspace():

            c = ""

        set_string += c

    key_length = len(set_string)

    acceptable_key_characters = string.ascii_letters

    for _ in range(key_length):

        retval += random.choice(acceptable_key_characters)

    if retval not in used_keys:

        db_cursor.execute("INSERT INTO used_keys(id, key) VALUES (?, ?)", (id_number, retval))

        return retval, set_string

    else:

        create_key(_string, db_cursor)





def encode_cipher(_string, key):

    """

    encode the string using a generated unique key

    """

    retval = ""

    for k, v in zip(_string, key):

        c_index = ALPHABET.index(k)

        key_index = ALPHABET.index(v)

        cipher_index = c_index + key_index

        try:

            retval += ALPHABET[cipher_index]

        except IndexError:

            cipher_index -= 26

            retval += ALPHABET[cipher_index]

    return retval





def decode_cipher(encoded, key):

    """

    decode the encoded string using the encoded string and the key used to cipher it

    """

    retval = ""

    for k, v in zip(encoded, key):

        c_index = ALPHABET.index(k)

        key_index = ALPHABET.index(v)

        decode = c_index - key_index

        try:

            retval += ALPHABET[decode]

        except IndexError:

            decode += 26

            retval += ALPHABET[decode]

    return retval





def main():

    """

    main messy function

    """

    exited = False

    choices = {"1": "show keys", "2": "create new key", "3": "decode a cipher", "4": "exit"}

    cursor = initialize()

    seperator = "-" * 35

    print("database initialized, what would you like to do:")

    try:

        while not exited:

            for item in sorted(choices.keys()):

                print("[{}] {}".format(item, choices[item]))

            choice = raw_input(">> ")

            if choice == "1":

                keys = cursor.execute("SELECT key FROM used_keys")

                print(seperator)

                for key in keys.fetchall():

                    print(key[0])

                print(seperator)

            elif choice == "2":

                phrase = raw_input("Enter your secret phrase: ")

                key, set_string = create_key(phrase, cursor)

                encoded = encode_cipher(set_string, key)

                print(seperator)

                print("encoded message: '{}'".format(encoded))

                print(seperator)

            elif choice == "3":

                encoded_cipher = raw_input("enter and encoded cipher: ")

                encode_key = raw_input("enter the cipher key: ")

                decoded = decode_cipher(encoded_cipher, encode_key)

                print(seperator)

                print("decoded message: '{}'".format(decoded))

                print(seperator)

            elif choice == "4":

                print("database destroyed")

                exited = True

    except KeyboardInterrupt:

        print("database has been destroyed")





if __name__ == "__main__":

    main()