Hey, encryption is encryption.
I can't think of any good ideas, but maybe you can.
Also, feel free to modify/redistribute/repackage as you wish.

If anyone has any idea on how to make List to String conversion faster, please tell me how! It's currently the slowest part of the encryption/decryption process.

An encryption program I have decided to share with the world. (Loosely?)Based on the one-time pad.
This encryption is theoretically impossible to crack (IRL, it's just really really hard).
You can either use the program to generate your keys (DOES NOT USE RAND), create a program to rand-generate for you, or make your own keys with random.org or by hand (read readme for details).
Accepts up to a 998 dimension input (list or string). Strings can use alphanumeric characters and some symbols.

Yeah. If you really want to encrypt something on your calculator, here's your solution. I recommend 3000+ bytes free and a TI-83+ SE or better. You'll need more RAM if you're encrypting bigger stuff though.

Enjoy.

All right.

Taken from tibasicdev.wikidot.com/custominput
Advanced Editing Functionality

This routine adds several features that are not in the other versions. It allows for uppercase and lowercase text with switching in between them. It allows the user to move the cursor throughout the text and insert text and delete text where ever they would like. The user can also clear the current text and start over. Unfortunately, the code is a little hard to decipher, but we'll work through it. The main deficit of this program is that it is incompatible with the TI-83. This can be remedied, as explained below.

:"ABC  abc  DEFGHdefghIJKLMijklmNOPQRnopqrSTUVWstuvwXYZ(Theta)!xyz(Theta).  :?   :? →Str0
:"  →Str1   // 2 spaces in quotes
:DelVar M1→P
:Repeat K=105 and 2<length(Str1
:Text(0,0,sub(Str1,1,length(Str1)-P)+"|"+sub(Str1,1,length(Str1)-P+1,P)+"        // 5 spaces after quote
:Repeat Ans
:getKey→K:End
:P-(K=26 and Z>1)+(K=24 and Z<length(Str1)-1→P
:M xor K=31→M
:If K>40 and K<105 and K≠44 and K≠45
:sub(Str1,1,length(Str1)-P)+sub(Str0,K-40+5M,1)+sub(Str1,1,length(Str1)-P+1,P→Str1
:If K=23 and P<length(Str1)-1
:sub(Str1,1,length(Str1)-P-1)+sub(Str1,length(Str1)-P+1,P→Str1
:If K=45:Then
:"  →Str1   // 2 spaces in quotes
:1→P
:End
:End
:sub(Str1,2,length(Str1)-2→Str1
Okay so since I only wanted numbers, I changed the code up a bit.
"789          456          123      0" is now Str0.
Variable M (the ALPHA key) is not used.
getKey values changed to those of the numbers.
(If K>71 and K<103 and K!=75 and K!=81 and K!=85 and K!=91 and K!=95)
Substituted sub(Str0,K-40+5M,1) with sub(Str0,K-71,1)

Now, the problem is that all of these sub(Str1,1,length(Str1)-P+1,P commands have 4 arguments instead of three. This causes ERR:ARGUMENT and I have no idea how to solve it.