Question

So I wrote a little script in python that brings up a gui with 2 buttons and a text field. you type into the text area and click encrypt and the text all of a sudden looks crazy. coooooool.

but then when you hit decrypt, it doesn’t go back to the original. here is the code

from Tkinter import *
import ttk

root = Tk()
textArea = Text(root, state = "normal")

def encrypt():
    message = textArea.get('1.0', 'end')
    newMessage = ''
    lastChar = ''

    for c in message:
        if lastChar != '':
            newMessage += chr((ord(c) + ord(lastChar)) % 256)
            lastChar = chr((ord(c) + ord(lastChar)) % 256)
        else:
            newMessage += chr((ord(c) + 5) % 256)
            lastChar = chr((ord(c) + 5) % 256)

    textArea.delete('1.0', 'end')
    textArea.insert('end', newMessage)

def decrypt():
    message = textArea.get('1.0', 'end')
    newMessage = ''
    lastChar = ''

    for c in message:
        if lastChar != '':
            newMessage += chr((ord(c) - ord(lastChar)) % 256)
            lastChar = chr((ord(c) - ord(lastChar)) % 256)
        else:
            newMessage += chr((ord(c) - 5) % 256)
            lastChar = chr((ord(c) - 5) % 256)

    textArea.delete('1.0', 'end')
    textArea.insert('end', newMessage)

encrypt = ttk.Button(root, text = "Encrypt", command = encrypt)

encrypt.pack({"side": "top"})

decrypt = ttk.Button(root, text = "Decrypt", command = decrypt)

decrypt.pack({"side": "top"})

textArea.pack({"side": "bottom"});

mainloop()

the problem is that it doesn’t show the original text. It just seems to make it more cryptic. what is wrong here? Please help.

update:
a changed it so it just adds 5. and It works. So that tells me that it’s the part where I add last characters code value. There is still one problem: it adds a new line and this strange line character (not the pipe —> |).

now the code is fixed. thanks. here is the result:
WW1ueCVueCV1d2p5eX4laHR0cTMlWW1mc3AlfnR6JXh5ZmhwJXR7andrcXR8JWt0dyV5bWolZnN4fGp3Mw8=

after I made the decrypt so It doesn’t take away five, it worked. Thanks again.

Answer 1

You can’t put arbitrary bytes into a text area.

Your encryption algorithm is purely bytewise – it works on the numeric values of the characters. This isn’t going to work, even for ASCII, because byte 0 is an ASCII NUL – treated specially, and byte 127 (what ‘Z’, character 122, becomes when shifted up by five) is a DEL character: not what you want! Moving beyond ASCII, the real world’s UTF-8 has thousands of invalid byte sequences.

If you’re going to be using bytewise encryption like this, you can’t put the results into a text field – it’s binary data. If you want it to be able to go into a text field, you must make sure it’s valid text without control characters, NUL bytes, or invalid byte sequences.

One easy way of making the binary sanitary is to Base64-encode it on encryption, and have the first step of decryption be Base64 decoding.

Final note: you’re also encrypting the newline at the end of the text area. Probably not something you wish to do.