With no background in higher math or computer science, I could not quite grasp the value of modular math for simple OTP systems as described in other posts here.
I have an alphabet size of 40 characters, valued from 0 to 39. The pad uses alphabetics "A" through "Z", valued from 0 to 25. I am using modulo 40 math.
If my ciphertext for any given plaintext character is a single digit, I prepend a zero as a placeholder, this yields a consistent ciphertext of a pair of digits for any one character of plaintext.
This system is working just fine. But then I realized that I could skip the mod math entirely and the system works just as well and is easier and quicker for both parties in the exchange....as far as I can tell.
So: Why bother using the mod math at all if the encryption/decryption is working just fine without it?
And, from an attacker's point of view, if he realized the ciphertext digit pairing and therefore could see the highest pair value of 40 (in the case of using the mod math) or instead 64 (without the mod math), would one of those cases give him more advantage than the other?