ActionScript 2.0 :: Parsing Input Into An Array Of Letters?

I would like to parse some User Input Text into individual letters (probably using an array so the letters can be used and changed easily). The goal is to create an encryption flash script, which will take in a user input sentence, and spit out a jumble of "random" letters with a 4-Digit code. The end-user then takes the jumble, puts it in to the box, punches in the 4-Digit Code, and decrypts the message. I understand there may be ActionCrypt and stuff, but I'd enjoy attempting this myself. I have all the other data I need (translating letters in an array into numbers, jumbling the numbers, turning those numbers into letters, and then allowing the end-user to enter those and reverse-engineer the original sentence).

All in all, I only need the code to parse input text (in this case, and for the easiest idea, lets say 10 letter maximum) into an array of individual letters per sector.To make this easy for me to understand, I'll give you some variables to work with, so if you post code, I understand what you mean with the variables:

input_txt = User Input Box
encrypt_btn = The button one will press, and thus make the (hopefully new) sentence be parsed into an array

So pretty much, I'm assuming the code will begin with the encrypt buttons AS:

"this.on(Release) = function()"

That's the way I imagine it at least... If any of you have an extremely advanced way, that's fine by me. Use all the variables you want, array names.... everything!